## April 17, 2009

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Acknow ledgments

EPA authors and contributors:
Benjam in DeAngelo, Jason Samenow, Jerem y Martinich, Doug G r ano, Di na Kruger, Marcus Sarofim , William Perk ins, Melissa Weitz, Leif Hockstad, W illiam Irving, Lisa Hanle, Dar rell Winner, David Chalm e rs, Chris Weaver, Susan Julius, Brooke Hemming, Sarah Garman, Rona Birnbaum , Paul Argy r opo ulos , Ann Wol v erton, Al McGartland, Alan Carlin, John Davidson, Ti m Benner, Carol Holm es, John Hannon, Jim Ketcham-Colwill, Andy Miller, Pamela Williams

Federal expe rt review ers Virginia Burkett, USGS; Phil DeCola; NASA (on detail to OSTP); William E m anuel, NASA; Anne Gra m bs ch, EPA; Jerry Hatfield, USDA; Anthony Janet os; DOE Pacific Northwest National Laborator y ; Linda Joy ce, USDA ForestService; Thomas Karl, NO AA; Michael McGe ehin, CDC; Gavin Sch m idt, NASA; Susa n Solom on, NOA A; Thomas Wilb anks, DOE Oak Ridge National Laboratory

Other contri butors:

Christine Teter, independe nt contractor for Stratus Consulting and Joel S m ith, Stratus Consulting, assisted with editing a nd form atting.



### ii

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Table of Contents
Executive Summary

.............................................................................................................. ES-1

I. Introduction

1. Introduction and Background

................................................................................................... .. 1
a. Scope and approach of this docum ent

....................................................................................... 1 b. Data and scientific findings considered by EPA

....................................................................... 3
c. Road m ap for this docum en t

...................................................................................................... 7

II. Greenhous e Gas Emis sions

2. Gre e nhouse Gas Emi ssio n s and Atmospheric Concentrations

................................................. 9
a. U.S. and global greenhouse gas em issions

................................................................................ 9 b. Historic & cu rrent global gr eenhouse gas concentrations

....................................................... 13

III. Global and U.S. Observed and Projected Effects from Elevated Gre enhouse Gas Concentrati ons

3. Direct Effect s of Elevated Gr eenhouse Gas Concen trations

.................................................... 17

4. Radiative Forcing and Ob served Cli m ate Change

................................................................... 19
a. Radiative forcing due to gr ee nhouse gases and other factors

.................................................. 19 b. Global changes in temp erature

................................................................................................ 22
c. U.S. changes in temp erature

.................................................................................................... 27 d. Global changes in precipitation

............................................................................................... 2 8
e. U.S. changes in precipitation

.................................................................................................. . 29 f. Global sea le vel rise

.......................................................................................................... ...... 30 g. U.S. sea le vel rise

............................................................................................................ ........ 31 h. Global ocean aci dification

..................................................................................................... .. 31 i. Global changes in phy s ical and biol ogic a l sy stems

................................................................ 31 j. U.S. changes in phy s ical and biol ogical sy stem s

.................................................................... 34 k. Global extrem e events

.......................................................................................................... ... 35 l. U.S. extrem e events

............................................................................................................ ..... 36

5. Attribution of Observed Climate Cha n ge to Anthropogenic Greenhouse Ga s Emis sions at the Global and Continental Scale

............................................................................................... 39
a. Attribution of observed climate ch ange to anthropoge nic em issions

...................................... 39 b. Attribution of observed changes in phy s i cal & biologi cal sy stem s

......................................... 43

6. Projected Fu ture Greenh o use Gas Co ncentrations and Climate Change

.............................. 45
a. Global e m issi on scenarios and associate d changes in concentrations and radiative forcing

... 45 b. Projected cha nges in global te mp erature, pr ecipitation patterns, sea l e vel rise, and ocean acidification

.................................................................................................................. ........... 52
c. Projected changes in U.S. temp erature, p r ecipitation patterns, sea l e vel rise

......................... 57 d. Cry o sphere (Snow and Ice) projections, fo cusing on North Am erica and the U.S

................. 60
e. Extrem e even ts projections, focusing on North Am erica and the U.S.

................................... 61 f. Abrupt clim ate change and high impact events

....................................................................... 63 g. Effects on/from stratospheric ozone

........................................................................................ 66



### iii

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

h. Land use and land cover change.........

............ ... ............ ... ............ ... ............ ....67

IV. U.S. Observed and Projected Human Health and Welfare Effects from Climate Change

7. Human Health

................................................................................................................... ........... 69
a. Temp erature effects

............................................................................................................ ..... 69 b. Extrem e even ts

................................................................................................................. ....... 71
c. Cli m ate- sensi tive di seases

..................................................................................................... .. 72 d. Aeroallergen s

.................................................................................................................. ......... 73

8. Air Quality

.................................................................................................................... ................ 75
a. Tropospheric ozone

............................................................................................................. .... 75 b. Particulat e matter

............................................................................................................ ........ 79
c. Health Effect s due to CO 2 - Induced Increases in Tropospheric O 3 and Particulate Matter...

.. 81

9. Food Produc tion and Agr i culture

.............................................................................................. 82
a. Crop y i elds and productivi t y

................................................................................................... 83 b. Irrigation requirem ents

........................................................................................................ .... 85
c. Cli m ate vari abilit y and ext r em e events

................................................................................... 85 d. Pests and weeds

................................................................................................................ ....... 86
e. Livestock

...................................................................................................................... ........... 87 f. Freshwater and m arine fisheries

.............................................................................................. 87

10. Forestry

....................................................................................................................... .................. 89
a. Forest produc tivit y

........................................................................................................... ...... 89 b. Wildfire and drought risk

...................................................................................................... .. 91
c. Forest co mposition

............................................................................................................. ..... 92 d. Insects and diseases

........................................................................................................... ...... 93

11. Water Re sources ................................................................................................................ .......... 94
a. Water supply

................................................................................................................... ........ 94 b. Water quality

.................................................................................................................. ......... 97
c. Extrem e even ts

................................................................................................................. ....... 98 d. Implications for water uses

.................................................................................................... .. 99

12. Sea Level Rise and Coastal Areas

............................................................................................. 10 0
a. Vulnerable ar eas

.............................................................................................................. ..... 100 b. Extrem e even ts

................................................................................................................. ..... 103

13. Energy, Infrastructure a nd Settlements

.................................................................................. 105
a. Heating and cooling requir e m e nts

......................................................................................... 105 b. Energy pr oduction

.............................................................................................................. ... 106
c. Infrastructure and settlem e nts

............................................................................................... 10 8

14. Ecosystems and Wildlife

........................................................................................................ .... 113
a. Ecosy s tems and species

......................................................................................................... 113 b. Ecosy s tem services

............................................................................................................. ... 120
c. Extrem e even ts

................................................................................................................. ..... 120 d. Implications for tribes

........................................................................................................ ... 120
e. Implications for touris m

... ............................................................................121



### iv

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

V. International Observe d and Projected Human Health and Welfare Effects from Climate Change

15. International Impacts

.......................................................................................................... ...... 123
a. National secu rity

.............................................................................................................. ...... 123 b. Overview of international i mp acts

........................................................................................ 125
References

..................................................................................................................... .......... 129 Appendix A on Adaptation

..................................................................................................... 14 0 Appendix B on Greenh ouse Gas Emissions from Section 202 Source Categories

......... 144 Appendix C on Direct Effects of Greenhouse Gases on Human Health

............................ 157



### v

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Executive Summar y

This docum ent provi des technical support for the endangerment analy s is concerning greenhouse gas (GHG) emissions that m a y be addressed under the Cl ean Air Act. This docum ent itself does not conve y any judgm e ntor conclusion regarding the question of whether GHGs may be reasonably a n ticipated to endanger public health or welfare, as this decision is u ltim at ely lef tto th e judgment of the Ad m i nistrator. The conclusions here an d the i n formation thr oug hout this d o c u m ent are primarily drawn from the assessment r e ports of the Intergovernmental P a nel on Cli m at e Change and the U.S. Cli m ate Change Science Program

. Observ ed Tre n ds in Green house Ga s E m issions and Concentrations

Gre e nhouse gases, once emitted, can remain in the atmospher e for decades to centurie s , meaning that 1) theirconcentrations become well-mixed t h roughout the global atmospher e re gardless of emis sion origin, and 2) their effect s on cli m ate are long las ting. The p r im ary long-l i ved GHGs directly em itted b y hum an activities include carbon dioxide (CO 2 ), methane ( CH 4 ), nitrous oxide (N 2 O), h y drofl uoroc arbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF 6 ). Green house gases have a war m i ng effect by trapping heat in the atm o sp here that would otherwise escape to spa ce. In 2006, U.S. GHG em issions were 7,054 teragrams 1 of CO 2 equ ivalent 2 (TgCO 2 eq). Th e dominant gas em itted is CO 2 , mostl y from fossil fuel co mbustion. Methane is the seco nd largest co mponent of U.S. em i ssio n s, followed by N 2 O, a nd the fluorinated gases (HFCs, PFC s, and SF 6 ). Electricity generation is the largest emitting secto r (34% of tot a l U.S. GHG em i ssions), f o llowed by transportation (28% ) and in dustr y (19% ).
Transportation sources u nder section 202 of the Cl ean Air Act (passenger cars, light duty trucks, other truck s and buses, motorcycles, and cooling) emit ted 1, 665 TgCO 2 eq in 2006, representing alm o st 24% of total U.S. GHG em issions.

U.S. transportation sources under sect ion 202 made up 4.3% of total global GHG emissi ons in 2005 , which, in addition to the U.S. as a whole, ranke d onl y behind to tal GHG emissions fro m China, Russia and India but ahead of Japan, Brazil, G e r m any and the r est of the world’ s countries. In 2005, total U.S. GHG em issions were responsible for 18% of glob al emissions, ranking onl y behind Chin a, which was responsible for 19% of gl obal GHG emi ssions.
The global atm o spheric CO 2 concent r ation has increased about 38% from pre-industrial levels t o 2009 , and al m o st all of the increase is due to anthropogenic em issions. The global atm o spheric concentration of CH 4 has increased by 149% since pre-industr ia l levels (through 2007); and the N 2 O concentration has increased 23% (thr ough 2007). T h e observed concentration increase in these gases can also be attrib uted primaril y to anthropogenic e m i s s ions. The industrial fluorinated gases, HFCs, PFC s, and SF 6 , have relatively low at m o spheri c concentrations but are increasing rapidly ; these gases are al m o s t entirely anth r opogenic i n o r igin.

Historic dat a show that current at mospheri c c o n centrations of the two most impor tant directly emitted, long-lived GHGs (CO 2 and CH 4 ) ar e well above the natura l range of atmospheri c

1 On e terag r am (Tg) = 1 m i llio n m e tric to n s

. 1 m e tr ic to n = 1 , 0 0 0 kg = 1

. 10 2 short ton s = 2 , 20 5 lb s. 2 Long-lived GHGs are com p ared an d s u m m e d t o geth e r o n a C O 2 eq u i v a len t b a sis b y mu ltip lyin g each gas b y its Global W a rm i n g Potential (GWPs), as estimated by IPCC. In accorda n ce w ith UNFCCC re portin g proc edures, the U.S

. qua nt i f i e s G H G em i ssi o n s usi n g t h e 10 0-y ear t i m e fra me v alu es for GWPs estab lish ed in t h e IPC C Second Assessm ent Report.



### ES-1

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

concentrations com pared to the las t650, 000 ye ars. Atm o spheric GHG concentrations have been increasing because anthropogenic em issions have been outpacing the rate at which GHGs are rem oved from the at mosphere by na tural processe s over timesc ales of decad es to centuries.

Observ ed Eff ects As sociated with Glob al Elevated Concentrations of GHGs

Current ambient air con centrations o f CO 2 and other GHGs remain well b e low publish e d exposure thresholds for any direct adverse health effects, su ch as respira tory or toxic effect s. The global average net ef fect of the increase in at mospheri c GHG conc entr ations, plus other human activities (e.g., land use change and aerosol em issi ons), on the global energy balance since 1750 has been one of warming. This total net heating effect, referred to as forcing, is estim ated to be +1.6 (+0.6 to +2.4) Watts per square meter (W/ m 2 ), with much of th e r a nge surroun ding th is estim ate due to uncertainties about the cooling and warming effects of aerosols. The co m b ined radiative fo rcing due to the cu mu lative (i.e., 1750 to 2005) i n crease in atm o spheric co ncentrations of CO 2 , CH 4 , and N 2 O is estimated to be +2.30 (+2. 07 to +2.5 3) W/m 2

. The rate of increase in positive radiative forcing due to these three GHGs during th e industrial era is very li kely t o have been unprecedented in m o re than 10,000 y ears. Warming of the cli m ate s y stem i s une quivocal, as is now evide n t from obs e rvations of increase s in global average air and ocean tempe r a tures, wide sprea d melti n g of snow and i ce, and r ising global average sea level. Globa l mean surfa ce te mp er atures have risen by 0.74°C (1.3o F ) (±0.18°C) over the last 100 y ears

. Ei ght of th e ten warm est y ears on rec o rd have occurred since 2 001. Glo b al mean surfac e temp erature was higher during the la st few decades of the 20th century than during an y co mp arable period during the preceding four centuries.

Most of the observed inc rease in global average tempe r ature s sinc e the mid-20th ce ntury is ver y likely due to the observed increas e in anthropogenic GHG concentr ations. Climate m odel si mu lations suggest natura l forcing alone (e.g., chan ges in solar irradiance) can not explain the observed
warm ing.

U.S. temper atures also warmed during the 20 th and int o th e 21 stcentury; temp er atures are no w approxim a tel y 0.7°C (1.3°F) war m er t h an at the star t of the 20th century , with an increased rat e of
war m ing over the past 30 y ears. Both the IPCC a nd CCSP reports attribute d recent North A m erica n war m ing to elevated GHG concentrations. In the C C SP (200 8g) report th e authors fi nd th at for North Am erica, “more than half of this warming [ f or th e period 195 1-20 06] is likely the result of h u man-caused greenhouse g as forcing of clim ate change.”

Obse rvations show that changes are occurring in the amount, intensity, frequency and type of precipitation. Over the contiguous U.S., total annual precipitati on increased by 6.5% from 1901-2006. It is likely that there have been increas es in the num b e r of heav y precipitation events within many land regions, even in those wh ere there has been a reduc tion in total precipitation am ount, consistent with a
war m ing cli m ate.

There is s tr o ng evidence that global sea level gr adually rose in the 20th century and is currently rising at an increased rat e . It is not clear whether the increasing rate of sea level rise is a reflection of short-term variabilit y or an increase in the longer-term trend. Nearly all of th e Atlantic Ocean shows sea level rise during the last 50 y ears with the rate of rise reaching a maxi mu m ( over 2 mm p e r y ear) in a band along the U.S. east co ast running e ast-northeast.



### ES-2

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Satellite data since 1978 s how that an nual av erage Arctic sea ice extent has shrunk by 2. 7 ± 0.6% per decade, with larger decre a s es in su mmer of 7.4 ± 2.4% per decade.
Widespr e ad changes in e x treme te mp eratures hav e been obse r v ed in the last 50 years across all world regions including the U.S. Cold da y s , cold nights, and fros t have become less frequen t , while hot day s , hot nig h ts, and heat waves have b eco m e m o re frequent.

Obse rvational evidence f r om all cont inents and mo st oceans shows that ma ny natural systems are being affecte d by regional climate ch ang es, particularly tempe r ature incr e a ses. Howe ver, clearly attributing specific r e gional changes in climate to em i ssions of greenhouse gases from human activities is difficult, especially for precipitation.

Ocean CO 2 uptake has lowered the average ocean pH (in creas e d acidity) le vel by approximately 0.1 since 1750. Consequences for m a rine ecosy ste m s may incl ude reduced calci fication by shell-form ing organisms, and in the l onge r term , the dissolution of carbonate sediments.

Obse rvations show that climate change is currentl y affecting U

. S. physical and biological systems i n significant ways. The consistency of these observed changes in phy sical and biological s y ste m s and the observed significant warming likely cannot be explaine d entirely due to n a tural variabilit y or other confoun ding non-clim ate factors Projections of Future Cli m ate Change with Con tinued Increas e s in Elevated GHG Conc e n trations

Most future scenarios t h at assume no explicitGHG mitigation actions (beyond those already enacted) pr oject increa sing global GHG e m i ssions over the centur y , with climbing GHG concentrations. Carbon dioxide is expected to rem a in the dom inant anthropoge nic GHG over the course of the 21 stc e ntur y

. The radiative for c ing associat ed with the non-CO 2 GHGs is still significant and increasing over ti m e

. Future war m ing over the course of the 21 st century, even under sc enarios of low emissi ons growth, is very likel y to be greater than ob served war m i n g over the past century

. According to cli m ate
m odel simu lations summarized by the IP CC, through about 2030, th e global warming rate is affected little by the choice of different future em i ssion scenarios. By the end of the century , projected average global
warm ing (co mp a red to av erage temp erature around 1990) varies significantly depending o n em issions scenario and cli m at e sensit ivity assump t ions, ranging from 1. 8 to 4.0°C (3.2 to 7.2° F), with an uncertainty range of 1.1 t o 6.4°C (2. 0 t o 11. 5°F).
All of the U.S. is very lik ely to warm during this century, and most areas of the U.S. ar e expected to
warm by more than the global aver age. The largest war m ing is projected to occur in winter over northern parts of Alaska. In western, central a nd eastern regi ons of North A m eric a, the projected
warm ing has less seasonal variation and is not as la rge, especi ally near the coast, consisten t with le s s war m ing over the oceans.
It is very lik ely that heat waves will become more intense, more frequ e nt, and longerlasting in a future war m climate, whe reas cold epi s od es are pr ojected to de crease significantly.

Increas e s in the a m ount of pre c ipitation are ver y likely in h igher latitudes, whil e de crease s ar e likely in most subtropic a l latitudes and the southweste r n U. S., continuing observed patterns. The mid-continental area is expected to experience dry ing during summer, indicating a greater risk of drou ght.



### ES-3

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Intensity of precipitation events is projected to in crease in the U.S. and other regions of the world. More intense precipitation is expected to increase t h e risk of flooding and result in greater runoff and erosion that has the potential for adverse water quality effects.
It is likely that hurricanes will become more i n tense , with stronger pe ak winds and m o re heav y precipitation associat ed wi th ongoi ng increases of tropi cal sea surf ace t e mp er at ures. Frequency changes in hurricanes are currently too uncer tain for confident projections.
By the end of the century, sea level is projected by IPCC to rise between 0.1 8 and 0.59 m e ters relative to around 1990 i n the absence of increased dynamic ice sheet loss. Recent rapid changes at the edges of the Greenland and West A n tarctic ice s h eets show a cceler ation of flow and thinning. While understanding of these i c e sheet proce sses is inco mplete, their in clusion in models would likely lead to increased s e a -level projections for the end of the 21st century

. Sea ice exten t is projected to shrink in the Arcti c under all IPC C emi ssion s cenarios. Projected Ris ks and Impacts Associated with Future Climate Chang e
Risk to socie ty, ecosyste m s, a nd ma ny natural Earth process es incr ease with increas es in both the rate and m a gnitude of c lim ate change. Climate warming may increase the possibility of large, abrupt regional or global clim atic events (e.g., di si ntegration of the Gr eenla nd Ice She et or collaps e of the West Antarctic I c e Sheet). The partial deglaciation of Greenland (and possibl y We st Antarctica) could be triggered by a sustained temperature in crease of 1 to 4o C above 1990 levels. Such war m ing would cause a 4 to 6 meter rise in s ea level, whic h would occur over a ti me period of centuries to millennia.
CCSP repor ts that climate change has the potential to accentu ate the disparities alread y evident in the Ame r ica n health care syste m s, as many of the expected health effects are likely to fall disproportionately on the poor, the el derly, the di sabled, and t he uninsur e d. IPCC rep o rts with very high confide n ce that climate ch ange imp acts on human health in U.S. cities will be co mpounded by populati on gr owth and an a g ing pop ulation.

Severe heat waves are p r ojected to i n tensify in magnitude and duration over the portions of the U.S. where t h ese events already occur , with potential increases in m o rtality and m o rbidity, especially
am ong the elderly , y o ung and frail.

The IPC C p r ojects redu ced human mortality fr om cold exposure throu g h 2100. I t i s n o t c l e a r whether reduced m o rtality fro m cold will be greater or less than increased heat-related m o rt ality in the U.S. due to cli m ate change.

I ncreas es in regional oz one pollution relative to oz one l e vels without climate change are expect ed due to higher temp eratu res and wea k er cir c ulation in U.S. and other world cities r e l a tive to air quality levels without clim ate change. Cli m ate ch ange is expec t ed to increase regional ozone pollutio n, with associat ed risks in respiratory infection, aggravation of asthma, a nd premature death. In addition to hum an health effects, tropospheric ozone has significan t adverse effects on crop y i elds, pasture and forest growth and species co mp o s ition. The directional effectof climate change on am bi ent particulate m a tter levels remains uncertain.

CCSP concl uded that, w ith increas e d CO 2 and te mperatur e , t h e life cycle of grain and oilseed c r ops will likely progress more rapidly. But, as tempera ture rises, these crops wil l increasingly begin to experience f a ilure, especially if climate variab ility increases and precipitation lessens or become s



### ES-4

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

more variab l e. Further m ore, the m a rketable y ield of m a ny horticultural crops – e.g., tom a toes, onions, fruits – is very likely to be m o r e sensitiv e to climate change than grain and oilseed crops.
Higher te mp eratures will very likely reduce live s t o ck production during the summer season, but these losses will very likely be partially offset by warmer t e mp eratures duri n g the winter season.

Cold-water fisheries will likely be negatively aff ected; warm-water fisheries will generally benefit; and the resu lts for cool-water fisheri es will be mi xe d, with gains in the northern and losses in the southern portions of ranges.

Climate cha n ge has very likely increased the si z e and number of forest fires, insec t outbreaks, and tree mortali ty in the interior west, t h e Southw est, and Alaska, and will continue to do so. An increased fre quenc y of disturbances l ike wildfire and insect o u tbreaks is at lea s t a s i mportant to ecosy ste m fu nction as inc re m ental cha nges in te mperature, pre c ipitation, atm o spheric C O 2 , nitrogen deposition, a nd ozone p o ll ution. IPCC estim ated that overall forest growth for North A m eri ca as a whole will likely inc rease m odestl y (10-20%) as a r esu lt of extended grow ing seasons and elevated C O 2 over th e next centur y , but with important spatial and temporal variation.

Coastal communiti es and habitats will be i n crea singly stressed by climate ch ange impact s interacting with development and pollution. Sea level is rising along mu ch of the U.S. coast, and the rate of change will increase in the futur e , exacerbatin g the impacts of progressive inundation, stor m

- surge floodin g , and shoreline erosion. St orm imp acts are like ly to be m o re severe, especially along the Gulf and Atlantic coas ts. Salt mars hes, other coastal habita ts, and dependent species ar e threatened by sea-leve l rise, fixed structures block ing landward m igration, a nd changes i n vegetation. Pop u lation growth and rising value of infrastructure in coastal areas incr eases vulnerability to climate variabilit y and futur e cli m at e change.

Climate cha n ge will likely further constrain already over-alloc a ted water reso urces in some sections of the U.S., increasing co mpetition among agricultu ral, municipal, industrial, and ecological uses. Although water m a nagement practices in the U.S. are generally advanced, part icularly in th e West, the reliance on past conditions as the basis for current a nd futu re pla nning will no longer be appropriate, as cli m at e change increasi ngl y creates conditions well outside of historical observ a tions. Rising temp eratures will dim inish snowpack and increase eva poration, a ffecting seasonal availability of water. In the Great Lakes and major river sy ste m s, lowe r l e vels ar e likely to exacerbate challenge s relating to water quality, navi gation, recreation, hydropower generati on, water t ransfers, an d bi-nati ona l relationships. Decreased water supply and lower wate r levels are likel y to exacerbate challenges relating to aquatic navigation i n th e U.S.
Higher wate r temp eratu res, incr ease d precipitation in tensity, and longer periods of low flows will exacerbate many forms of water pollution, potentially m a king attain m e nt of water quality goals m o re difficult. As waters beco me war m er, the aquatic lif e they now support will be replaced by other speci e s better adapted to warmer water. In the long te rm, warmer water and chan ging flow may result in deterioration of aquatic ecosy stem s.
Ocean acidi fication is projected to continue, re sulting in the reduc ed biological production of marine calcif iers, includin g corals.

Climate change is likely to affect both U.S. ener gy use and energy prod uction and physical and institutional infrastruct u res; and will likel y interact wit h and possibl y exacerbate ongoing environm ental change and environm ental pressures in settlements, particularly in Alaska where indigenous communities a re fa cing m a j o r environm e n tal and cultural i mpact s. The U.S. energy sector,



### ES-5

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

which relies heavily o n water for hy dropower and cooling capacity , m a y be adversely impacted b y changes to water supply a nd qualit y i n reservoirs an d other waterbodies. Water infrastructure, including drinking water and wastewater treat m entplants, and sewer and stormwat er managem e nt sy stems, will b e at greater ris k of flooding, sea level rise and storm s u rge, low flows, and other factors that could impair performance.

Disturbance s such as wi ldfires and i n sect outbr e a ks are incr easing in the U.S. and are likely t o intensify in a warmer fu ture with dr ier soils and longer grow ing seasons. Although recent cli m at e trends have increas ed vegetation growth, continuing increases in disturbances are likely to lim it c a rbon storage, facili tate invasive species, and disrupt ecosy ste m s e rvices.

Over th e 21st century, ch anges in climate will cause sp ecies to shift north and to high er el evation s and fundamentally rearrange U.S. ecosystems

. Differential capacities for range shifts and constraint s from development, habitat fragmentation, invasive species, and broken ecological connections will alter ecosy ste m str u cture, function, and servic es.
Within settl e m ents expe ri encing cli m ate change, c ertain parts of the population may be e s pecially vulnerable ; these include the poor, th e elderly , thos e alr eady in poor health, th e disabled, those living alone, those with li m ited r ights and power (such as recen t i mmig r ants with li mited English skills), and/or indigenous populations de pendent on one or a few resources. Thus, the potential impact s of clim at e change raise environm enta l justice issue s

. Climate cha n ge impacts in certain regions of the world may exacerbate problems that raise humanitarian, trade and national security issues f o r the U.S. The IPCC identifies the m o st vulnerable world regions as the Arcti c , because of the effe cts of high rates of projected war m ing on natural sy ste m s ; Africa, espe c i ally the sub-Saharan region, because of current low adaptive capacity as well as cli m at e change; sm al l islands, due to high exposure of popul ation and infr astructure to risk of sea-level rise and increased stor m surge; and Asian mega- d eltas, such a s the Ganges- Brah m a putra and the Zhujiang, due to large populati ons and h igh exposure to s ea level rise, st orm surge and river flo o d ing. Clim ate change has been described as a potential threat mu ltiplie r with regard to national security issues.



### ES-6

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 1
Introduction and Background
The purpose of this docu m ent is to provide scientif ic and technical inform ation for an endangerm ent analy s is regarding greenhouse gas (GHG) em issions from new motor vehicles and engines under section 202(a) of th e Clean Air Act. Section 2 0 2 (a)(1) of the Clean Air Act states that:

the Adm i nist rator shall by regulation prescr ibe (and from time to time revise)...st a ndards applicable to the e m is sion of any air pollutant from a n y class or cl asse s of new m o tor vehicle s

... , which in his j udgm ent cause, or contribute to, air pollution which may reasonably be anticipated to endanger public health or welfare.
Thus, absent so m e other st atutory provision, before EPA m a y issue st andards addressing emissions of an air pollutant fro m new m o tor vehicl es or new m o tor vehicl e engines under section 202(a), the Ad m inistrator mu st make a so-called “endangerm ent finding .” That finding is a two step test. First, the Ad m inistrator mu st decide if, in her ju dgm ent, ai r pollutio n m a y reasonably b e anticipated to endanger public health or welfare. Second, the Adm inistrator mu st decide whethe r, in her judgment, em issions of any air poll u tant fro m new m o tor veh icles or engines cause or contribute to this air pollution. If th e Ad m inistrator answers bot h questions i n the affir m at i v e, EPA shall issue standar d s under section 202(a).

This docum ent itself doe s not con v ey an y j udgm ent or concl u sion regardi ng the two steps of the endangerment finding, as th ese decision s are ulti m a t e ly left to the j udgm ent of the Ad m inistrator.
1(a) Scope and Approach of t his Document
The prim ary GHGs that are directly emitted by human activities in general are those report e d in EPA’s annual Inven tory of U.S. Greenhouse Gas Emissions an d Sin k s and inclu d e carbon di oxide (CO 2 ), methane ( CH 4 ), nitrous ox ide (N 2 O), h ydroflu orocarbons (HFCs), pe rfluorocarbons (PFCs) and sulfur hexafluoride (SF 6 ). The pri m ary effect of these gases is their influence on the cli m at e sy stem by trapping heat in the atm o sphere that would otherwise es cape to space. This heating effect (referred to as radiative forcing) is very likel y to be the cause of m o st of th e observed g lobal warm in g over the last 50 y ears. Global war m ing and clim a te change can , in turn, affe ct health, society and the environm ent. There als o are so me cases where these gases have o ther non-climate eff ects. F o r example, elevated concentrations of CO 2 can lea d to ocean acidification and stimulat e terrestri al plant growth, and CH 4 emissions can contribute to background levels of tropospheric ozone, a crit eria pollutant. These effects may in turn be influenced by clim ate ch ange in certain cases. Ca rbon dioxi de and other G HGs can also have direct health effects but at concentrations far in excess of cur rent or projec ted future ambient concentrations.

This document reviews a wide range o f observed an d projected vulnerabilities, risks and i m pacts due to the elevated l e vels of G H G s in the at m o sphere an d associat ed cli m at e chan ge. Any known or expect ed benefits of elevated at m o s pheric concentrations of GHG s or of cli m at e change are documented as w e ll (i.e., impacts can m ean eit h er positive or negative c onsequences). The extent to which observed climate change can be attributed to anthropoge nic GHG e m i ssi ons is as se ssed. The ter m“cli m ate c h ange” in this docum ent generally refers to clim ate c h ange induced by hum an activities, inc luding activities that e m i t GHGs. Future projections of cli m at e ch ange, based p r i m arily on future scenari o s of anthropogenic GHG
e m is sions, are shown for the global and national scale.

The focus of the vulnerability , risk and i mpact as ses s m ent is pri m arily withi n th e U.S. However, given the global nature of climate change, there is a brief review of potentia l international impacts. Greenhouse



### 1

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

gases, once emitted, become well m ix e d in the at mos phere, m e aning U.S. emissions can af fect not only the U.S. population and environm ent but other regions of the world as well; likewise, em issions in other countries can affect the U.S. Furthermore, impacts in other regio n s of th e wor ld m a y have consequences that transcend national boundaries and raise concerns for the U.S.

The tim e frame over which vulnerabil ities, risks and impact s are consider ed is consist e nt with the timefra me ov er which GH Gs, once e m i tted, have an effect on cli m ate, which i s decades to centuries for the primary GHG s of concern. Theref ore, in add ition to reviewing recent ob servations, this document generally considers the next several decades, the tim e period out to around 2100, and for certain i mpacts the time period be y o n d 2 1 0 0

. Adaptation to cli m ate change is a ke y focus area of the cli m ate change r esear ch co mmunity

. This docum ent, h o wever, does not focus on adaptation becau se adap tation is es se ntially a resp onse to any known and/ or perceived r isks due to climate cha nge. Likewise, mitigation measures to reduce GHGs, which could also reduce long-term risk s, are not addressed

. The purpose of this docum ent is t o review the effects of cli m ate ch ange and not t o assess any speculativ e polic y or societal response to climate ch ange. Adaptation will be m e n tioned to the extent that the i mpacts projections them selves contain som e em bedded assumptions about future adap tation. 3

3 A bri e f ove r v i e w of adap t a t i o n i s pr ovi ded i n A p pen d i x A

.



### 2

### Technical Support Docum e nt, U.S. Environm ental Protection Agency Box 1.1, Peer review, pu blication and appr oval processes for IPCC, CCSP and NRC reports

Int e rg ov ernmenta l Panel on C limat e C h ang e The Wo rl d M e t e or ol o g i cal Or ga ni zat i on ( WM O ) a nd t h e U n i t e d Nat i ons E nvi r o nm ent Pr o g ram m e (U NE P) estab lish e d t h e In tergo v e rn m e n t al Pan e l on Cli m a t e Ch an ge (IPCC) i n 198 8. It b a ses its assessm en t main ly o n p eer rev i ewed an d pu b lish e d scien tific/tech n i cal litera tu re. IPCC h a s estab lish e d ru les and pro c edu r es for p r od u ci n g its assessm en t rep o rts. Repo rt outlin es are ag reed to b y g o v e rn m e n t rep r esen tativ es in consu ltatio n with the IPCC bureau. Lead authors ar e nom i nated by gove rnm e nts and are selected by the res p ective IPC C Wo rk i n g G r o u p s o n t h e basi s of t h ei r sci e nt i f i c cre d ent i al s and wi th d u e co nsi d erat i on f o r br oa d g e og raphi c rep rese n t a t i on. For Wo rk i n g Gr ou p I t h ere were 15 2 c o o r di nat i n g l ead au t h ors , an d f o r

W o rki ng Gr o up II 48 coordinating lead aut h ors. Drafts pr ep ar ed by th e au tho r s ar e subj ect to t w o r oun ds of rev iew ; th e seco nd r oun d in clu d e s go v e rn m en t rev i ew. Fo r th e IPCC Wo rk in g Gro u p I repo rt , o v e r 30 ,0 00 written co mmen t s were su b m itted b y o v e r 6 5 0 ind i v i d u a l ex p e rts, go v e rn m e n t s an d in tern ation a l o r g a n i zation s . Fo r Work ing Gro u p I I there were 910 e xpe rt re vie w ers

. Re vie w E d itors fo r each c h ap ter are res p onsible for e n s u ring that all sub s t a nt i v e g o v er nm ent and expe rt re vi ew comments rece ive approp riate consideration. F o rtr an s p ar en c y , IP CC d o c u m en ts how ev er y co mmen t is addr e sse d. Each Summary for Policym akers is approv ed lin e-b y-l in e, an d th e unde rlying chapters are t h e n accepte d, by gove rnm e nt de legations in form al plenary sessions. Furthe r i n f o rm at i on ab out IPC C ’ s pri n ci pl es a n d pr o cedu r es ca n be fo u n d at : 0 H h tt p ://www.ip c c.ch /abo u t/pro cd.h tm

.
U.S . Cl i m ate Ch an ge Sci e n ce Pro g r a m Th e CCSP h as id en tified 21 syn t h esis and assessm en t p r odu ct s (SAPs) that ad d r ess th e h i gh est priorities for U.S. cl im at e change researc h , obse r vat i o n an d de ci si on- su p p o r t need s. As of J a nuary 1 6 th , 2 0 0 9 , al l 21 sy nthesi s an d
assessm ent pr o duct s ha d bee n com p l e t e d. D i ffere nt a g en ci es ha ve bee n d e si gnat e d t h e l ead fo r di ffe re nt S A Ps; EPA is th e d e sig n a ted lead for three o f th e six SAPs add r e ssing im pacts and adap tation. For eac h SAP, the r e is first a pro s p ect u s t h at pro v i d e s an ou tlin e, the propo sed au th ors and p r o c ess fo r co m p leti n g th e SAP; this go es t h r o u g h t w o st ages of ex pe rt , i n t e ra gency a n d p u b l i c re vi ew. A u t h or s pr od uce a fi r s t d r aft whi c h goe s t h r o ug h expe rt re vi ew; a secon d dra ft i s post e d f o r p ubl i c re vi ew

. The de signated lead age n cy en sures th at th e th ird d r aft
co m p lies with th e In fo rm ati o n Qu ality Act. Fin ally t h e SAP is su b m i tted to th e Natio n al Scien ce and Techn o l o g y C o un cil (NSTC ) , a Cab i n e t-level co un cil th at co or di nat e s s c i e nce an d t e c h nology re search across t h e Fe deral go ver n m e nt , fo r app r oval . Fu rt her i n f o rm a tion a b out the cl earance and re view proce d ures for t h e CCSP SAPs can be found at: 1H h ttp ://www.clim a t escien ce.gov /Lib rary /sap /sap -gu i d e lin es-clarificatio nau g20 07 .h tm

. Na ti on al Rese arch C o unci l of the U .S. N a ti on al Aca d e m y of Sci e nce s Th e Nation al Research Coun cil (NRC) is p art o f th e Natio n a l Acad em ies, wh ich also co m p rise the Nation a l Acad em y o f Scien ces, Nation al Acad em y o f Eng i n eering an d Institu te of Med i ci n e. They are p r i v ate, n onp ro fit in stitu tio n s that p r o v i d e science, tech no log y an d h ealth p o l icy ad v i ce un der a cong ressi on al ch arter. Th e NRC has bec o m e th e pri n ci pal o p e r at i ng a g ency of bot h th e Nat i onal Aca d emy of Sci e nc es an d th e Nat i o nal Academ y of E n gi nee r i n g i n p r ovi di n g ser v i ces t o t h e go ve rnm e nt , t h e pu bl i c and t h e sci e nt i f i c an d engi neeri n g co mmu n ities. Fed e ral ag en cies are th e p r i m ary fin a n c ial spo n s ors of t h e Acad em ies’ work

. Th e Acad em ie s p r ov id e ind e pen d e n t ad v ice; th e ex ter n al sp on so rs h a v e n o con tro l ov ert h e co nduct o f a st ud y o n ce th e state m en t o f task and b udg et ar e f i n a lized

. Th e N RC 2 001 stud y, C l i mat e C h an ge Sci e n ce: A n A n al ysi s of S o me Key Questions , or ig in ated fro m a W h ite H o u s e r e qu est

. Th e N RC 2 001 stud y, Glob a l Air Qu a lity: An Im

per a t i ve f o r

Lo ng -Ter m O b servat i o nal St r a t e gi es , w a s sup por ted b y EPA an d N A SA. Th e N RC 2004 st u d y , Air Qua lity Ma nag emen t in t h e Un ited S t a tes , w a s supp orted b y EPA

. Th e N RC 20 05 stu d y , R a di at i v e Forci n g of

C l i m at e C h an ge : Ex pa n d i n g t h e C o n cep t an d A d dressi ng U n cert a i n t i e s , was in respo n s e to a CCSP req u est, and s u pp ort e d by NO A A. Th e NR C 20 0 6 st udy , Su rf ace T e mpe r at ure Re con s t r uct i o ns f o r t h e L a st 2, 0 00 Ye ars , was re queste d by the Science Committee of the U.S. House of Represe n tatives. Each N RC repo rt is autho r e d b y i t s ow n c o m m i t t ee of e x pert s, re vi ewe d by o u t s i d e e x pert s, and ap p r o v e d by t h e G ove r n i n g B o ar d o f t

h e NR C

.

Uncertainties and confide n ce levels a ssociated wit h the scientific conclusions and findi ngs in this docum ent are reported, to the extent that such inform ation was provided in the original scientific report s upon which th is docum entis based.
1(b) Data and Scientific Findings Considered by EPA



### 3

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

This docume n t relies m o st heavily on existing, and in m o st c ase s very recent, synthesis reports of cli m ate change scien ce and potential impact s, which ha ve gone through th eir own peer-review processes includin g review by the U.S. Government. The information in this docum en t has been developed and prepared in a manner that is consistent with EPA' s Guidelines for Ensuring an d Maximizing the Quality, Objectivity, Utility and I n tegrity of Information Di sseminated by the Environmental Prot ection Agency

. In addition to its reliance on existing and prim aril y recent s y nthesis reports from the peer reviewed literature, it also underwent a technical review by 12 f e deral climate change expert s, internal EPA review, and interagency review.

These core referenc e (T able 1.1) docu m e nts incl ude the 2007 Fourth Assess ment Re port of the Intergovernmental Panel on Clim ate Change (IPCC), Synthesis and Assessment Products of the U.S. Clim ate Change Science Program (CCSP), National Research Council (NRC) reports und er the U.S. National Academ y of Sciences ( N AS), the EPA a nnual report on U.S. greenhouse gas em issio n inventories and the EPA a sses s m ent of the impa cts o f global chan ge on regio n al U.S. air qual ity.

Table 1.1, Co re refe ren c e s relied up on most heavily in this do cum ent.

Science bod y / author Short Title a nd Year of P ublication IPCC W o rking Grou p I: T he Phy s ica l Scienc e Basis (2007) IPCC Working Grou p II: Impacts, Ad aptatio n an d Vuln erab ilit y (20 07) IPCC Working Grou p III: Mitigation o f Climate Ch an ge (20 07) CCSP SAP 1.1: T e mperature T r ends in the Lo w e r A t mospher e (20 06) CCSP SAP 1.2: Past Climate Var i a b ilit ya nd C h a nge i n the Arc t ic and at Hi gh Latitudes (200 9) CCSP SAP 1.3: Re-analy s es of Histo rical Climat e Data (2008) CCSP SAP 2.1: Scen arios of GHG Emissions and A t mospher ic Co ncentrati ons (2 007) CCSP SAP 2.3: Aerosol Prop erties and the i r Impa cts on Climate
CCSP SAP 2.4: T r ends in Ozone- D epl eting S ubst ances (2 00 8)
CCSP SAP 3.1: Clima t e Chan ge Mo dels (2 008) CCSP SAP 3.2: Clima t e Projectio n s (200 8)
CCSP SAP 3.3: Weather an d Clim ate Ex trem es in a Cha ngi ng C li m ate (200 8)
CCSP SAP 3.4: Abrupt Climate C h a nge (2 00 8)
CCSP SAP 4.1: Coas tal Sensitiv it y t o Sea-L e ve l Ri se (2009)
CCSP SAP 4.2: T h reshol ds of Cha n g e in Ecos y s tem s (2009)
CCSP SAP 4.3: Agriculture, La nd R e sourc e s, Water Reso urces, and Bi odiv e rsit y(20 08)

CCSP SAP 4.5: Effects on Energ yPr oducti on a nd U s e (200 7) CCSP SAP 4.6: Anal yses of the Effects of Gl obal Cha nge on Hu man He alth (2 008)

CCSP SAP 4.7: Imp a cts of Clim ate Ch an ge and Varia b il it y on T r ansportation S y ste m s (200 8) NRC Climate C h a n g e Scienc e: Ana l y s is of Some Ke y Qu estions (200 1) NRC Radi ative Forci ng of Clim ate Cha nge (2 00 5) NRC Surface T e mperature R e con s tructions for the Last 2,0 00 Years (20 06) NRC Potentia l Impa cts of Climate Cha nge on U. S. T r ansportati on (20 08) EPA Impacts of Global C han ge o n Regi on al U.S. Air Qualit y ( 2 0 0 9 )

EPA Inventor yof U.S. Greenho use Gas Emission s and Sinks (2 008) ACIA 

### 4 Arctic Climate Impact Assess ment (200 4)

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

EPA is rely ing m o st heavil y on these sy nthesis reports because the y 1) are very recent and re present the current state of knowledge on clim ate change scien ce, vulnera bilities and potential impacts; 2) have
asse ssed nu merous individual studies in order to draw general conclusions about the state of science; 3 ) have been re viewed and f o rmally acce pted by , commi ssioned by, or in so m e cas es authored by , U.S. governm e nt agencies and individual governm e nt scien tists and provide EPA with assurances that this materi al has been well vetted by both the cli m ate change r esear ch co mmunity and by the U.S. governm e nt; and 4) i n m a ny cases, they reflect and conve y the c onsensus conclusions of e xpert authors. Box 1.1 describes the peerreview and publication approval proc esses of IPCC, CCSP and NRC reports. Peer review and transparency are key to each of these res ear ch organizations’ report developm en t process. In co mp liance with the U.S

. EPA’ s info r m ation quality guidelines, this document relies on inform ation t h at is objecti v e, technicall y sound and ve tted, and of high integrity. Box 1.2 describes the lexicon used by IPCC to co mmunicat e uncertainty a nd confide n ce levels a s sociated with the m o st important IPCC findings; this docum en t employ s th e sa me lexicon when referen c ing IPCC state m ents. The IPCC Fourth Assess ment Report (AR4) consists of three volumes: Working Group I a ddresses the phy s ical science of cli m at e change; W o rking Group II addresses i mpacts, vulnerabilities an d adaptation; and Working Group III addresses mitigation (i.e., em ission reduction) measures. These IPCC assessments are gener a lly global in scope but provide information at the countr y and regional level as well. The Working Gro up II vol um e contains ind i vi dual chapters devoted to the ke y climate change i mpact s ecto rs, which ar e also addre ssed in th is docum ent ( e .g., hum an health, agriculture, water resources, et c

. ), as well a s chapters devoted to ke y regions. This docum ent re lies heavily on the North Am erica chapter of the IPCC Working Group II r e port, tho ugh this chapter may not pr o v ide as mu ch regional detail within the U.S. as did the 2000 report , Climate Change Impacts on the United States: The Potential Consequences of Climate Variability and C hange (NAST, 200 0).
Throughout th is docum ent, when these various assessm ents ar e referred to in g e neral or as a whole, th e full reports are cited. Fo r example, a general refe rence to the CCSP report “Weather a nd Clim at e Extre m es in a Changing Cli m ate ” is c ited as “CCS P, 2008i” (tbe “i” differen tiates the rep o rt from other CCSP reports published that sa m e y ear). When specific findings or conclusions from these larger
asse ss ment re ports are refe renced, citati ons are given for the relevant individua l chapter or section. For
example, a finding fr om CCSP, 2008i c h apter 5 “Obser ved Changes in Weather and Climate” by Ku nkel et al. is cited as “Kunkel et al., 200 8.”



### 5

### Technical Support Docum e nt, U.S. Environm ental Protection Agency Box 1.2: Communi cation of Uncerta inty in the IPCC AR4 and U.S. CCSP SAPs
IPCC AR4 Uncertainty Tr eatme n t

A set o f term s to d e scrib e un certain ties in curren t kno wled ge is co mm o n to all p a rts of th e IPCC AR4 b a sed on th e Gui d ance N o te s for Lead Aut hor s of the IPC C Fourth Asse ssme n t Re port on A ddre ssi n g Unce rt ai nt i e s (h ttp ://www.ipcc.ch /activ ity/u n certain tygu idan ceno t e.p d f), p r od u c ed b y the IPCC i n Ju ly 2 005

. An y u s e of th ese term s in asso ciatio n with IPC C state m en ts in th is End a n g e rm en t d o c u m e n t carries th e sa m e m ean in g as orig in ally i n t e nde d i n t h e IPC C F o urt h Assessm ent R e po rt

.
Descri pt i o n of conf i d e n ce
On th e b asis of a co m p reh en s i v e read i n g of t h e literatu re and th ei r ex p e rt ju dg m e n t , au t h o r s h a v e assigned a co nfid en ce level to m a j o r state m en ts on th e b a sis o f th eir assessm en t o f cu rren t kn owledg e, as fo llows:
Very high c o nfidence At least 9 o u t o f 10 cha n ce of bei n g c o r r ect H igh co nf id ence A bou t 8 ou t o f 1 0 ch an ce M e di um confi d ence Ab o u t 5 o u t of 10 cha n ce Low co nf id en ce A bou t 2 ou t o f 1 0 ch an ce Very l o w confi d ence Less th an a 1 ou t of 10 ch an ce

Descri pt i o n of l i kel i hoo d

Lik elih ood refers to a p r ob abilistic assess m e n t of so m e well d e fi n e d ou tcome h a v ing o c cu rred or o c cu rrin g i n th e fu t u re, and m a y b e b a sed o n q u a n titativ e analysis o ran el i c itatio n of ex pert v i ews. When au tho r s ev al u a te th e l i k el i hoo d o f c e rt ai n out c o m e s, the ass o ciated m eanings are :
Virtu a lly certai n >9 9% p r o b a b ility o f o ccurrence Very lik ely 9 0 to 99 % p r ob ab ility Lik e ly 6 6 to 90 % p r ob ab ility Abou t as lik ely as n o t 3 3 to 66 % p r ob ab ility Un lik ely 1 0 to 33 % p r ob ab ility Very un lik ely 1 to 10 % prob ab ility Ex cep tio n a lly u n lik ely <1 % p r ob ab ility

U.S. CCSP SAP Uncer tainty Treatment

In m a n y o f its SAPs, th e U.S. CCSP u s es t h e sam e o rsim i la r term in o l og y to th e IPCC to d e scri b e co nfiden ce an d lik elih o o d

. Howev e r, th ere is so m e v ariab ility fro m rep o rt to repo rt, so read ers shou ld refer to th e i n d i v i d u a l SAPs for a fu ll accoun tin g of t h e resp ectiv e u n certain ty lan g u a g e

. I n t h i s d o cum e nt , whe n refe r e nci n g C C S P r e po rt s, EP A at t e m p t e d t o re fl ect t h e un de rl y i ng C C S P re p o rt s ’ t e rm i nol o g y f o r

com muni cat i ng u n cert a i n t y

.

In so m e ca se s, this docu m ent refer e nces other reports and studies in a ddition to the core references of IPCC, CCSP, NRC, and, for greenhous e gas emissions , EPA. These ref e rences are pri m aril y for m a jor reports and studies produced by U.S

. federal and st ate government agencies. This d o cument also referenc es dat a m a de avail a ble by other governm e nt ag encies, such a s NOA A and NASA.
EPA just rece ntly comp lete d and published an asses s m ent of the literature on the effect of cli m ate change on air quality (EPA, 2009). Therefore, because EPA eval uated th e literature it self in the preparation of that asses s m e n t, EPA does cite so m e individual studies it reviewed in its summar y of this topic in Section 8. Also, for Section 15a on the nation a l security i m plications of climate change, this document cites a num ber of analy ses and publications, from both insi de and outsi de the governm e nt, since IPCC and CCSP assessments have not explicitly addressed these issues.
EPA recognizes that scientific resear ch is ver y active in m a ny areas addressed in this docu m e nt (e.g. aerosol effe c t s on cli m ate , cli m ate f e e dbacks such as w a ter vap o r, and internal and external cli m at e forcing mech anis m s ) as w e ll as for some e m e rging i ssues ( e .g. ocean acidifi cation, and cli m ate change



### 6

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

effects on water quality ). EPA recognizes the potential i mportance of new scientific research, but, except as described above, studies that have n o t y e t been assessed by the sci entific community ar e not included in this document.
1(c) Roadmap for this Document

The re m a inde r of this document is struct ured as follows:

• Part II, Sect ion 2 describes source s of U.S. and global GHG e m i ssions. How anthropogenic GH G
e m is sions have contribute d to change s in globa l at m o spheric concentrations of GHGs is also described.

• Part III, Sec tions 3 – 6 describe the ef fects of eleva t ed concen trations of GHG s including a n y direct health and environm ental effect s; the heating or radiative forcing effects on the cli m at e s y stem ; observed climate change (e.g., changes in te mp erat ure, precipitation and sea level rise) forthe U.S. and for the globe; recent conclusions about the e x tent to whi c h observed cli m at e change can be attributed to the elevated levels of GHG concentra tions; and summariz e future projections of climat e change—driven prim arily by scenarios of anthropog enic GHG e m issions—fo r the remainder of this century

. • Part IV, Se ctions 7 – 14 review recent findin g s for the broad range of ob served and p r ojected vulnerabilitie s, risks and i mp acts for h u man health, society and th e environm ent within the U.S. due to climate ch ange. The specific s ectors and sy stem s i n clude:
o Hu m a n healt h (7)
o Air Quality ( 8 )
o Food Pr oduct i on and Agric u lture (9)
o Forestry (10)
o Water Re sources (11)
o Coastal Ar eas (12)
o Energy , Infra structure and Settlem e nts (13)
o Ecosy s tems and Wildlife ( 14)

• Part V, Section 15 briefly addresses s o me key inte rnational impacts that m a y occur due to climate change, with a view towar d s how som e of these i mpa cts m a y in turn affect the U

. S.
o International Impacts (15)



### 7

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Part II
Emissions and Elevated Concentrations of Greenhouse Ga ses

8

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 2

Greenhouse Gas Emissions and Concent r ations
This section first describes current U.S. and gl oba l anthropoge nic greenhouse gas (GHG) em issions. Future GHG em ission scenarios are described in Part III, Section 6, however, these scenarios prim arily focus on global e m issions , rather than detailing i ndividual U.S. s ources. This section then focuses on historic and current global GHG at mosp heric concentrations.
2(a) U.S. and glo bal greenhouse gas em issions

To track the national trend in GHG emi ssions and carbon rem oval s since 1990, EPA develops the official U.S. GHG inventory each y ear. In accordance with Article 4.1 of the U n ited Nations Fra m e w or k Conventio n on Clim ate Ch ange (UNFCCC), the Inventory of U.S. Greenhouse Gas Emissions and Sinks includes em issions and rem ovals of carbon dioxi de (CO 2 ), methane (C H 4 ), nitrous ox ide (N 2 O), h y drofl uoroc arbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF 6 ) resulting from anthropogeni c activities in the U.S.

Total em issi ons are presented in teragram s 4 (Tg) of CO 2 eq uivalent (TgCO 2 eq), consistent with Intergovernmental Panel on Clim ate Change (IPCC) inventor y guidelines. To determ ine the CO 2 equivalency of different GHG s, in order to su m an d co mp are di fferent G HGs , e m is sions of each g as ar e mu ltiplied by its global warm ing potential (G WP), a factor which relates it to CO 2 in its ab ilit y to trap heat in the at m o sphere over a certain timeframe. Bo x 2.1 pro v ide s m o re information about GWPs and th e GWP values used in this s ection of the r e port.

Bo x 2.1: Gl o b a l Wa rming Po t e nt ia ls used in this do cument

In acc o r da nce wi t h UNFC C C rep o r t i ng p r oc edu r es, t h e U. S. qua nt i f i e s G HG em i ssi ons usi n g t h e 1 0 0

- y ear t i m e fram e v alu es fo r GWPs estab lish e d in th e IPCC Sec ond Assessm ent Report (S AR ) (IPCC, 1 996 ). Th e GW P i nde x i s defi ne d as t h e cumu l a t i v e radi at i v e fo rci n g bet w ee n t h e p r ese n t and s o m e chose n l a t e r t i m e hori z o n ( 1 0 0 years) caused by a unit m a ss of gas em itte d now. All GWPs ar e expre ssed relative t o a re fere nce gas, C O 2 , wh ich is assigned a GWP = 1. Esti m a tio n o f th e GWPs requ i r es kn o w l e d g e of t h e fat e of t h e em it t e d gas and t h e radi at i v e fo rci n g due t o t h e a m ount rem a i n ing i n t h e at m o sphe re. T o est i m at e th e C O 2 e qui val e ncy of a n o n

- C O 2 GHG, the ap propriate GWP of that gas is mu ltiplied by the am ount of the gas em itted.

10 0

- ye ar GW Ps C O 2 1 C H 4 21 N 2 O 31 0 HFC s 14 0 t o 6, 30 0 ( d epen di n g o n t y pe of HFC ) PFC s 6, 50 0 t o 9, 20 0 (de p e ndi ng o n t y pe o f P F C ) S F 6 2 3 ,900

The GWP for CH 4 i n cl ude s th e di rect ef fec t s and th ose i n di rect effect s due t o t h e pr o duct i o n o f tr o pos p h eri c ozo n e a nd stra t o sp heri c wat e r vap o r. Thes e G W P val u es have bee n u p d at ed t w i c e , i n th e IPC C th i r d (T AR 2 001 ) and f ourth assessm en t rep o r t s ( A R 4 20 07)

.

4 1 t e rag ram (Tg) = 1 m i ll i on m e tri c t ons. 1 m e tri c t on = 1, 00 0 k g = 1. 1 0 2 sh ort t o n s = 2, 20 5 l b s.



### 9

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The national inventor y tot a ls used in th is report f o r

the U.S. (and other count ries) are gross em issions, which include GHG emissions fro m the electricity, i ndustrial, commercial, residential an d agriculture sectors. E m i ssions and sequestration occurring in the land-use, land-use change and forestry sector (e.g., forests, soil carbon etc.) are not inclu d ed in gr oss national total s , but are reported un der net em ission totals (source s and sinks), according to international pr actice. In t h e U.S., this sector is a si gnificant net sink, while in some developing co untrie s it is a significant net source of em issions.
Also excluded from emission totals in this report are bunker fuels (fuels used for internation a l transport). According to UNFCCC reporting gui delines, em issio n s from the consumption of these fuels should be reported separately , and not inclu d ed in natio na l e m ission totals, as ther e exists no agreed upon international formula for allocation between countries.

The m o st recent inventor y was published in 2 008 an d includes ann u al data for th e y ears 199 0-2006

.

U.S. Greenhouse Gas Emissions In 2006, U.S. GHG e m i ssi ons were 7,054.2 TgCO 2 eq (see Figure 2.1). 5 The dominant gas emitted is CO 2 , m o stly from fossil fuel com bustion (84.8% ) (EPA, 2008). Weig h ted b y GWP, CH 4 is the second largest
co mponent of em issions, followed b y N 2 O, and the high-GWP fluorinated gase s (HF C s, PF Cs, and SF 6 ). Electricity ge neration (237 7.8 TgCO 2 eq) is the largest em itting sector, followed by transportat ion (1969.5 TgCO 2 eq) and industr y (1 371. 5 TgCO 2 eq) (EPA, 2008) (Figure 2. 2). Agriculture and the co mmercial and residential sectors em it 533.6 T g CO 2 eq, 394 .6 T g CO 2 eq, and 34 4. 8 TgCO 2 eq, respectively (EPA, 2008). Rem ovals of carbon through land use, land-use chan ge and forestry activities are not included in Figure 2.2, but are significant; ne t sequestration is estim ated to be 883 .7 TgCO 2 eq in 2006, offsetting 12.5% of total em issio n s (EPA, 2008).

5 Per UNFCCC repo rting req u i rem e n t s, th e U.S. repo rts its an nu al em issio n s in g i g a g r am s (Gg ) with two sig n i fican t d ig its (h ttp ://un f ccc.in t/files/n a tio n a l

_ repo rt s/an n e x_ i_g hg_ inv e n t o r ies/ natio n a l_ i n v e n t o r ies_ su bm i ssi ons/ a p p l i cat i on/ x
- zi p

- co m p ressed/ usa

_ 20 0 7_c rf

_ 11ap r .zi p ). F o r eas e o f c o m muni cat i on of t h e fi n d i n gs, t h e Inve nt ory of U. S. Gree n h o u se Gas E m i ssi o n s a n d Si nks report presen ts to tal e m issio n s in Tg with on e si g n i fican t di gi t

.



### 10

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

U.S. emissions increased by 905.9 TgCO 2 eq, or 14.7% between 1990 and 2006 (see Figure 2.1) (EPA, 2008). Historically, changes in fossil fuel consumption have been the dominant factor affecting U.S. emission trends. The fundamental factors driving this trend include a generally growing domestic economy over the last 16 years, leading to overall growth in emissions from electricity generation (increase of 30.7%) and transportation activities (increase of 27.9%) (EPA, 2008). Over the same time period, i ndustrial, residential, and commercial emissions decreased by 6.0%, 0.6%, and 0.6% respectively, while emissions increased in the agriculture (5.3%) sector (Figure 2.2) (EPA, 2008).



### 11 Figure 2.1: T otal U.S. Gre e nhous e Ga s Emissions: 1990 -2 006

8,000

7,000

6,000

Eq. 5,000 Tg CO 2 4,000

3,000

2,000

1,000

0

Source: Inve ntor y of U.S. Greenh ous e Gas Emissions and Sinks: 199 0-2 0 06 (EPA, 200 8 ) . Ex clud es la n d

use cha n g e an d forestr y a nd i n ternati o n a l bu nker fuels. 6, 801 6, 760 6, 731 6, 494 6, 435 6, 343 6, 192 6, 106 6, 148 7, 054 7, 130 6, 998 6, 981 6, 921 6, 839 7, 033 7, 078

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 6

Figure 2.2: U.S. GHG Emissions Allocated to Ec onomic Sector.

0 50 0 1, 00 0 1, 50 0 2, 00 0 2, 50 0

199 0 1 991 19 92 199 3 1 994 19 95 199 6 1 997 19 98 199 9 2 000 20 01 200 2 2 003 2 004 20 05 200 6TgCO2Eq. T r a n s p o r ta ti o n

In d u s t r y

R e s i d ent ial A gr ic ult u r e Commercial

Source: Inve ntor y of U.S. Greenh ous e Ga s Emissions and Sinks: 199 0-2 0 06 (EPA, 200 8). All GHGs. Excludes l and us e, lan d

- u se cha n g e an d forestr y a nd intern ation a l b unker fue l s. E l ec t r ic i t y G en er at i on

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

U.S. Greenhouse Gas Emissions from Source Categories under Section 202(a) of the Clean Air Act

Source categories under Figure 2.3: T otal GHG Emissions for the Year 20 05 b y Country and for U.S. Section 202a Sour ce Cate gories

Section 202( a) of the Act include passenger vehicles, light- and he avy

- dut y trucks, buses, m o torcy c les, and the cooling s y ste m s designed for passenger co mfort, as wel l as auxiliary sy stems for refrigeration.

In 2006, section 202(a) source categories collectively
were the second largest GHG- em ittin g sector wit h in the U.S. (behind the electricity generating sect or),
em itting 1,665 TgCO 2 eq and representing 24 percentof total U.S. GHG e m i ssi ons. Between 199 0 and 200 6, t o tal 0 1, 0 00 2, 0 00 3, 0 00 4, 0 00 5, 0 00 6, 0 00 7, 0 00 8, 0 00

Ch

i n a U

.S

.A

. Wo

rl d

T

ra

n sp

o rt R

u ss

i a I nd

i a

U.

S .

Se

c t i o n

2 02

( a )

J

a p an

B

ra

z i l G

e rm

a n y Ca

n a da U. K

. Me

x i co In

d

o n e s i a Ir a nTgCO2eq.

Source: W R I Climate An al ysis and Indic a tors T ool. Availab l e at http://cait. w r i. org/

. Excl ud es lan d use, lan d -us e chan ge a nd fore str y , and i n tern ation a l b unker fuels. More rece nt emissions data are ava ila bl e for the U.S. and other in divi du al countri es, but 200 0 is the mo st recent y e ar for w h ic h data for all co untries and a ll gases ar e ava il abl e. Data accessed F ebr ua r y 20, 2 009.

GHG e m issi ons from passenger cars decreased 0.9 per cent, while e m issi ons from light-duty trucks increased 57 percent, largely due to the increased use of sport-utility ve hicles and other lig ht-duty trucks.
Globally i n 2005, section 202(a) source category GHG em i s sions represen ted 31 percent of global transport GH G e m i ssions and 4.3 percent of to tal global GHG e m i ssions (Figure 2.3). The global transport sector was 14 pe rcent of all global GHG emi ssions in 2005. If U.S. section 202(a) source category GH G em issions were ranked against tota l GHG emissi ons for entir e countries, U.S. section 202(a) em issions would ra nk behin d on ly Ch ina, the U.S. as a wh ole, Russia and India, an d would rank ahead of Japa n , Brazil, Ger m any and eve ry other country in the world.

Further detail on these em i ssions can be found in Appendix B of th i s docum ent.

Global Greenhouse Gas Emissions
Total global e m is sions are calculated by summ ing emi ssions of the six greenhouse gases, by country. The World Resources Institute co mp iles data fro m reco gnized national and international data sources in its Cli m ate Anal y s is Indicators Tool (CAIT). 6 Globally , total GHG emissions wer e 38,725.9 TgCO 2 eq in 2005 , the m o st recent y ear for which d a ta are available for all co untries and all GHGs (WRI, 2009). 7 This global t o tal for the y ear 2005 represents an increase of about 26% fr om the 1990 global GHG
em ission total of 30, 704. 9 TgCO 2 eq (WRI, 2009). Excluding land use, land- use change, and forestr y , U.S. em issio n s were 19% of the total y e ar 2005 globa l em issions, ( see Figure 2.3) (WRI, 2009).

6 Pri m ary dat as o u r ces refe re nc ed i n C A IT i n c l ude t h e U.S

. Depart m e nt of Ener gy ’s C a r b on Di oxi de In f o rm at i on Analysis Ce nter, t h e U.S. E n vironm ental Protection Age n cy , the Internati o nal E n ergy Agency and t h e National In stitu te for Pub lic Health and th e Env i ron m en t, an in tern at io n a lly reco gn i zed sou r ce of no n-CO 2 d a ta. 7 Source: W R I Clim a t e Analysis an d In di cat ors T ool

. Avai l abl e at http:/ / cait.wri.org/

.



### 12

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

2(b) Historic and current global greenhouse gas concentrations
Greenhouse gas concentrations in th e atm o sphere vary over ver y long tim e scales in response to natural influences su ch as geologic activity and te mp er ature ch ange assoc i ated with ice age cy cles, but ice core data show nearly consta nt concentrations of CO 2 , CH 4 and N 2 O over m o re than 10,0 00 y ears prior to the industrial revolutio n. However, since the industr ial revolution, anthropogen ic GHG emissions have resulted in substantial increases in the concentrations of GHGs i n the atm o sp here (IPCC, 2007d; NRC, 2001).

Carbon di oxide (CO 2 )

Carbon dioxi de concentrations have increased substantiall y from pre-industrial levels (Figure 2.4). The long-term trends in the CO 2 concentratio ns are as follows (NOAA, 2009c; F o rster et al., 200 7):

• The CO 2 concentration has increased about 38% from a pr e-industrial value of ab out 280 parts per million (ppm ) to 386 ppm (which is about 0. 039% of the atm o sphe re by vol um e) in 2008 8

. • The present at m o spheric concentration of CO 2 exc eeds by far the natural range over the last 650, 000 y ear s (180 to 30 0 ppm ) as determined from ice cores (Jansen et al., 200 7).

• The annual C O 2 concentration gr owth ra te 9 has been l a rger since 2000 ( 200 0-20 08 average: 2 .0 ppm pery ear), than ithas be en since the beginnin g of continuo us direct atmosp heric measurements (1960–2005 average: 1.4 ppm per y ear) although the re is y ear-to-y ear variabilit y.
Al m o st all o f the increas e in the CO 2 concentration durin g the Industria l Era is due to anthrop ogenic
em issions (Forster et al., 2007). Si nce the 19 80s, a bout half of th e anthrop o g e nic em issions have been taken up by the terrestrial biosphere and the oceans, but observations dem onst rate that thes e process e s cannot rem ove all of the extra flux due to hum an activ ities. About half of the anthropogeni c emissio n s have rem a ined in the atm o sphere (Forster et al., 2007 ).

8 Th e 200 8 v a l u e is pr eli m in ar y. 9 Th e esti m a ted u n c ertain ty in t h e Mau n a Lo a an nu al m ean growth rate is 0

. 1 1 pp m /yr.



### 13

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

M

e thane (CH 4 )

Methane co ncentrations have al s o risen substantially (Figure 2.4). The following trends in at m o spher ic methane have been o b served according to NOAA’ s report “State of the Clim ate in 2007” and IP CC (Horvitz, 200 8; Forster et al., 2007):

• The global atm o spheric concentration of methane has increased from a pre-industrial value of about 715 parts per billion (ppb) to 1732 p pb in th e early 1990 s, and was 1782 ppb i n 200 7 – a 14 9% in crease fro mpreindustrial lev e ls.

• The at m o sph e ric conc entration of m e th ane in 2007 exceeds by far the natural ran g e of the last 650,000 y ears (320 to 790 p p b ) as deter m ined from ic e core s (Jansen et al., 2007).

• Growth rates declined between the early 1990s and m i d-200 0s. Th e reasons for the decrea se in the at m o spheric CH 4 growth rate and the i mplications for future changes in its atm o spheric burde n are not w e llunderstood b u t are clearly related to the changes in t h e i m balanc e betwe e n CH 4 sources and s inks.

• The methane concentration grew 7 ppb between 200 6 and 200 7, the first y ear-toy ear increase since 1998. The reasons for the increase i n 2007 are not y e t known, but analy s is of carbon m onoxide m e asurements suggests it is not from biomass burning

. The observed increase in methane concentration is very likely due to anthropogeni c activities, predominantly agriculture a nd fossil fuel use, but relative contributi ons fro m different source types are not well determined (Forster et al., 200 7).
Nitrous Oxide (N 2 O)

The N 2 O concentration ha s increased 23% fro m its pre-industrial value of 262 ppb (Figure 2.4)to 321 pp b in 2 007 ( Horvitz, 200 8). The concentration has increased linearly b y about 0.8 p pb y r –1 over the past few decade s and is due prim aril y t o hum a n activities, particularly Figure 2.4: Atmosph e ric conce ntra t io ns of car bon dioxide, methane and ni trous oxide o v er the last 10,000 y ears

Source: IPCC ( 200 7d). Atmospher ic conce n t r ations of carbo n dio x id e, methane a nd nitrous o x ide o v er the last 10,00 0 years (l arge p a n e ls) a nd sinc e 17 50 (inset pa nels). Measur ements are sho w n fro m ice cores (s ymbols w i t h different col o rs for different studi es) and atmosph e ric sampl e s (red li nes). T he correspon din g rad i a t ive forcings (discuss ed in S e ction 2( e)) are sho w n o n the right ha nd axes of the lar ge pa ne ls.



### 14

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

agriculture and associated land use change (Forster et al., 2007). Ice core data show that the present at m o spheric concentration of N 2 O is hi gher than eve r measured in th e ice core r ecord of the past 650,000 y ears (Jansen et al., 2007).

Fluorinated Gases
Industrial fluorinated gases that serv e as substit utes for CFCs (chlorofluorocarbons) and HCFCs (h y d rochl o rof luorocarbons) , such as hy d r ofluorocarbo ns (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF 6 ), have relatively l o w atm o spheric concentr ations. Concent r ations of many of th ese gases have in creased by large factors (b etween 1.3 and 4.3) between 1998 and 2005. Their total radiative forcing in 20 05 was +0.017 [ ± 0.002 ] Wm -2 and is rapidly increasing by roughly 10% per y ear. Thes e gases ar e al most entirely a n thropogenic in origi n (For ster et al., 2007).
Ozone depleting substances cover ed by the Montreal Protocol

Chlorofluor ocarbons (CFCs) and hydrochlorofl u orocarbons ( H CFCs) are GHGs that are entirely anthropogeni c in origin. E m issions of these gases have decr eased due to t h eir phase-out under the Montreal Protocol, and the at m o spheric concentra tions of CFC-11 and CFC-113 are now decr easing due to natural re m oval processes (Forster et al., 2007). Ice core and in situ data confirm that industrial sources are th e cause of observed at m o spheric incr eases in CFCs and HCFCs (Forster et al., 2007).
Ozone (O 3 ) Tropospheric ozone is a short-lived greenhouse gas produ ced lar g ely b y chemical reactions of precursor species in the at m o sphere and with large spatial and temporal variabilit y

. Changes in tropospheric ozone also occur due to changes in transport o f ozone across the tropopause (Forster et al., 2007). Relative to the other gre e nhouse gases, there is less confidence in reproducing the changes in ozone associated with large changes in em issions or clim ate, and in th e simu lation of observed long-term trends in ozone concentrations over the 20th centur y (Fo r ster et al., 2007).
Aerosols (Sulfates, nitrates,organic a nd black carbon aerosols)

Aerosols are s m all, short-lived particles present in th e at m o sphere with widely vary ing size, concentration and chem ical co mposition, either directly em itte d or for m ed in seco ndary reactions from emitt ed
co mpounds. Aerosols are rem oved from the at m o sp here pri m aril y through cloud processing and wet deposition in precipitation, a m e chanis m that estab lishes average tro pospheric aerosol atm o sph e ric lifeti m es at a week or less ( CCSP, 2009a ). On a gl oba l basis, aerosol m a ss deriv es predo m inantl y from natural sources, m a inly sea salt and dust. However, a n thropogenic ( m an made) a e rosols, arising prim arily from a variet y of com bustion sources, can dom inate i n and downwind of highl y populated and industrialized regions, and in areas of intense agricultural burning ( CCSP, 2009a ). Aerosol optical density trends observed in th e satellite an d surface-ba sed data recor d s suggest that since the mid-1990s, the am ount of anthrop ogeni c aerosol has decreased over North Am erica and Euro pe, but has increased over parts of east and south Asia; on average, the at m o spheric co ncentration of low latitude sm oke particles has i n creas ed, consistent with changes in em i ssions (CCSP , 2009a). Ice core data from Greenland and Northern Hem isphere mid-latitudes show a ver y like l y rapid post-i ndustrial era increase in sulfate concentrations above the preindustrial b ackground, though in recent y ear s, sulfur dioxi d e em issions have decreased globall y an d i n m a ny regi o n s of the nor th ern hem isph e re. In general, the concentration, composition and distribu ti on of aerosol s in the paleo c lim a te record are not as well known as the long-li ved greenhou se gases (Jansen et al., 200 7).



### 15

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Part III
Global and U.S. Observed and Projected Effects from Elevated Greenhouse Gas Concentrations

16

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 3

Direct Effe cts of Elev ated Greenhouse Gas Concentrations

Carbon di oxi de and other GHGs can have direct effects that are independent of their radiativ e forcing on cli m at e (the pri m ary effect discussed throughout th is docum ent). Such effects ar e described below.
Effects on Human Health
Current and projected am bient greenhou se gas concentr ations rem a in well below published thr esholds for any direct adverse health effects, such as respirat or y or t oxic effects. The literature supporting this conclusion is described in Appendix C.

Carbon Dioxi d e Fertilization

Carbon dioxi de can have stimulatory or fertilizati on effect on plant growth

. There is debate and uncertainty about th e sensitivit y of crop y ields to th e direct effects of elevated CO 2 levels. However, the IPCC (East er ling et al., 2007) conclude d that elevate d CO 2 levels are expect ed to result in s m all beneficial impacts on crop yields. T h e IPCC confirm e d the gen e ral conclusions from its previous Thir d Assessmen t Report in 2001. Experimental resear ch on crop responses to elevated CO 2 through the FACE (Free Air CO 2 Enrichment) 10 experiments indicate that, at a m bie n t CO 2 concentrations of 5 50 p p m (approxim a te l y double the concentration from pre-industrial ti m e s) crop y ields increase under unstressed conditions by 10-25% for C3 crops, and b y 0-10% for C4 crops (medium confidence) 11 . Crop m odel simulations unde r elevated C O 2 are consistent with these ranges (high confidence) (Easterling et al., 200 7). Globally an d in the U.S., high temp eratures and ozone exposure, howev er, can significantl y li mit the direct stimulatory CO 2 response (see also Section 8 on Air Quality an d Section 9 on Food Pr oduc ti on and Agric u lture).

Elevated CO 2 has raised an issue about forage qualit y for livestock. Elevated CO 2 can increas e the carbon to nitrogen ra tio in forages and thus reduce the nutritional value of those grasses and thus a ffect ani m al weight and performance. The decline under elev ated CO 2 of C4 grasses, however, w h ich are less nutritious than C3 grasses, may comp en sate for the re duced protein. Yet the opposite is expected under associat ed temp erature inc rease s (Hatfi e l d et al., 2008).

At mu ch higher am bient CO 2 concentrations, such as tho se are as exposed to natural CO 2 outgassing due to volcanic activit y , the main characteristic of long-t e rm elevated CO 2 zones at the surface i s the lack of vegetation (I PCC, 2005). New CO 2 release s into vegetated area s cause noticea ble die-off. In those area s where significant impacts to vegetatio n have occurred, CO 2 makes up about 20–9 5% of the soil gas, whereas normal soil gas usually co ntains about 0. 2 –4% CO 2 . Carbon dio x id e concentrations above 5 % may be dang erous for vegetation and as concentrati ons approach 20%, CO 2 beco m e s phy t o toxic. Carbon dioxide can cause death of plants throu gh ‘root an ox ia’, together with low ox ygen concentration (IPCC, 2005).

As at m o spheric CO 2 increa ses, m o re CO 2 is absorbed at the surface of ocean s, es tuaries, strea m and lakes. Increases in the am ount of dissolved CO 2 and, f o r

som e species, bicarbonat e ions (HCO 3 - ) present in aquatic environm ents will lead to higher rates of phot osynthesis in submerged a quatic vegetation, sim ilar to the fertilization effects of CO 2 enrichment on m o st terrestrial plants, if oth e r lim iting factors do not

10 http://www. bnl.gov/face/ 11 C 3 a n d C 4 re f e r t o di f fere n t carb o n fi xat i o n pat h way s i n pl ant s du ri n g ph ot osy n t h esi s

. C 3 i s t h e m o st com m on pathway, a n d C3 crops (e.g., wheat, s o ybea ns a n d rice ) a r e mo r e r e sp on s i v e th an C4 cr op s su ch a s ma iz e

.



### 17

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

offset the po tential for enhanced prod uctivit y

. A stud y cited i n Nicholls et al. (200 7) in d icates algal growth may also respond positivel y to elevated dissolved inorganic carbon (DIC), though m a rine macroalga e do not appear to be lim ited by DIC levels . An increase i n epiphytic or suspended algae would decrea se light available to submerge d aquatic vegetation and also incr eas e the incidence of algal blooms that lower dissolved oxyge n available to fi sh and shell f ish (Nicholls et al., 200 7).
Ocean Acidification
According to the IPCC ( Fischlin et a l., 2007) elevated CO 2 c oncentrations are re sulting in ocean acidification which m a y a ffect marine ecosy ste m s ( m ediu m confidence). Thi s is dis c uss e d further in sections 4h, 6 b , and 1 4 a.



### 18

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Section 4 Radiative Forcing and Observed Climate Change
This section focuses pri m a rily on the more significant e ffects asso ciated with G HGs, which i s their heattrapping abil i ty (referred to as radiative forcing) th at results in climate change. Observed cli m ate change is reviewed, i n cluding cha nges in temp erature, preci pita tion, and sea level ri se, for the globe and the U.S. Observed changes in climate- sensitiv e phy s ical and biological sy stems are also addressed, as well as observed trends in extre m e events. Se c tions 7 to 15 provide m o r e specifi c inf o rmation on the sectoral i mplications of both the observed changes described he re and the projected changes described in Section 6.
4(a) Radiative forcing due to greenhouse gases and other factors

This section describes rad i ative forcing and the factor s that contribute to it. Radiative forcing is a
mea s ure of the change that a factor causes in a ltering the balance of inco ming (solar) and outgoing (infrared and reflect ed shortwave) ene rgy in the Earth-at m o sphere sy ste m , an d thus shows the relativ e i mportance o f different factors in terms of their c ontribution to climate change

. Positive forcing means the factor causes a w a r m in g effect and negative forcing m e ans the f actor cause s a cooling effect.
Radiative forcing values presented here for GHG s and other factors co me from the I P CC Fourth Assessment Report of Working Group I (2007). These r a diative forcing values ar e the r esult of global changes in atm o spheric concentrations of GHGs (s ee Section 2(c) above) and other factors, and are therefore not the result of U.S. transportation em i ssi ons in isolati on. All valu es are for the y ear 20 05 relative to pre-industrial times in 1750, represent globa l averages, and are expressed in wat t s per square meter 12 (W/m 2 ). IPCC (2007d) concluded that the understanding of an thropogenic war m ing an d cooling infl uences o n cli m at e has i mproved sinc e the TAR, l eading to very high confidence 13 that the global average net effect of hu man activities since 1750 has been one of wa rm ing, with a radiative fo rcing of +1.6 (+0.6 to +2.4) W/m 2

. Greenhouse gases have a positive forcing because they ab sorb a nd reradiate i n all directions outgoi ng, infrared radia tion that would otherwise directly escape into space. The co m b ined radiative forcing due to the cumu lativ e (i.e., 1750 to 2005) incre ase in at m o sp heric concentrations of CO 2 , CH 4 , and N 2 O is +2.30 W/m 2 (with an uncertainty range of +2.07 t o +2.53 W/m 2 ) (see Figure 4.1)

. This positi ve radiative forcing, like the observed accu mu lation of these gases in the at mosphere, is pri m arily anthr opogenic in origin. Further m ore, the I PCC (2007d) stated that th e rate of incr ease in positive radiative f o rcing due to these three GHGs during th e industrial era is “very likely to have been unprecedented in m o re than 10,000 y ears.”
The positive radiative forcing due to CO 2 is the largest (+1.66 ± 0.17 W/m 2 ) (Figure 4.1), and has increased by 20% fro m 1995 to 2005, th e largest ch ange for any decade in at least the l ast200 y ears. Methane is the second largest source of pos itive radia tive forcing ( + 0.48 ± 0.05 W/m 2 ). Nitro u s oxide has a positive radiative forcing of +0.16 (±0.02) W/m 2

.

12 W a tts p e r square m e ter is th e SI un it fo r radiativ e and o t h e r en erg y fl u x e s. 13 Acc o rding t o IPCC term inology, “ v ery high confide n ce” c o nveys a 9 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s.



### 19

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The other thr ee GHGs rep o rted b y the U.S. Invento ry

— HFCs, P F Cs and SF 6 —have a total radiative forcing in 20 05 of +0. 017 (± 0.002) W/m 2 (Forster et al., 2007).

Figure 4.1: G l obal a v erage radiativ e forcing (RF) estimates an d ranges in 2005 for anthr opoge n i c GHG emis sions and o t her fac t or s

Source: IPCC ( 200 7d). Globa l avera ge ra dia t ive forcing (RF ) estimates an d rang es in 2 0 05 for anthro p o gen ic carbo n dio x id e (CO2), methan e (CH4), nitro u s oxi de (N 2O) and ot h e r imp o rtant factors, together w i t h the t y pica l ge og raph ical e x te nt (spatia l scale) of the forci ng a nd the ass e sse d leve l of scien tific und erstan din g (LOSU). T he net anthrop og en ic radi ative forc ing a nd its ra n ge are a l so sh o w n. T hese requir e summing as ym metric uncerta i n t y estim a tes from the compo nent terms, an d cann ot be ob taine d b y s i mpl e add ition. Ad diti ona l forcing fac t ors not inclu d e d here ar e con s ider ed to hav e a ver y lo w L O SU. Volcanic aeros ols contri bute an add itio nal n a tural forc ing b u t are not inclu d e d in this figure du e to their e p iso d ic nature. T he range for li ne ar contrai l s does n o t inclu de oth e rpossib l e effec t s of aviation o n clou din e ss. The ozone-depleting substances cove red under the Montreal Protocol (chlorofluorocarbons (CFCs), h y drochl orofl uorocarbons (HCFCs), and chlorocarbons) are also strong GHGs and, as a group , contributed + 0 .32 (± 0.03) W/m 2 to an thropo genic r a diative forcing in 20 05. Their radiative forcing peaked in 2003 and is now beginning to decline (Forster et al., 2007). The radiative forcing due to th e destruction of stratospheri c ozone by these gas es i s esti m ated to be –0.05 ± 0.10 W/m 2 with a m e diu m level of scientific understanding (Solom on et al., 2 0 0 7 ).

In addition to the six m a in GHGs dir ectly em itted by hum an activities, and the gases co vered by the Montreal Protocol, there a r e additional anthropogeni c and natural factors that contribute t o both positive and negative forcing.



### 20

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

With regard to climate change, ozone affects th e radiative budget of the atm o sphere through its interaction with both shor twave and longwave radi ation (Forster et al. 2007). Troposp h eric ozon e changes due t o em issions of ozone -form ing chem icals, or precursor s (nitrogen o x ides, carbon m onoxide, and hydrocarbons i n cluding m e thane), contribute a po sitive forcing of +0.35 (+0.25 to +0.65) W/m 2

. As described in CCSP (2008d), robust model si mu lations project climate change will also i n crease th e radiative forcing from ozo n e by increasing stratosphe re-troposphere exchange a nd hence ozone near the tropopause where it is m o st important radiatively

. Unlike the GHGs mentioned above, tropospheric ozone is not as w e ll- m ixe d in the global at m o sphere becaus e its at m o spheric l ifeti m e is on the order of weeks to m o n ths (versus decades to centuries for the well-m i xed GHGs). Troposphe ric ozone is a criteria air pollutant under the U.S

. Clean Air Act.

Em issions of ozone precursors and oth e r substances also contribute to changes in levels of the reactive gas OH (the hy droxy l free radical). O H is a key ch e m ic al speci e s that influences the lif eti m es and thus radiative forcing values of CH 4 , HFCs, HCFCs and ozone; it also play s an imp o rtant role in the form ation of sulfate, nit rate and so m e organic aerosol species. (Forster et al. 2007).
Anthropogeni c em i ssions of aerosols co ntribute to bot h positive and negative radiative forcing. Aerosol s are non-gaseous substances other than wat e r or i ce that are susp ended in the at m o sphere, and are either solid particles or liquid droplets. Most aerosols, su ch as sulfate s (which are mainly the result of SO 2 e m is sions from fossil fuel burning), exert a negative fo rcing or cooling effect, as they reflec t and scatt e r incom ing solar radiation. Some aerosols, such as black carbon, cause a positiv e forcing b y absorbing incom ing solar radiation. IPCC (2007d) estimated thatthe net effect of all anthrop ogenic increases in aerosols (primarily sulfate, organic carbon, black carbon, nitrate and dust) prod uce a cooling effect, with a total direct radiative forcing of –0. 5 (– 0.9 to –0 .1) W/m 2 and an additional in direct cloud albedo (i.e., enhanced reflectivity ) 14 forcing of –0. 7 ( –1.8 t o – 0 .3) W/m 2

. These forcings are now better understoo d than at the ti me of the IP CC Third As sess ment Re port (2001), but nevertheless r e main t h e dom inant uncertainty i n radiative f o rcing (IPCC, 200 7d). T h e direct radiative forcing of the i ndiv idual aerosol species is l e s s certain than the total dire ct aerosol radi ative forcing. The estimat es are: sulpha te, -0.4 (+/- 0.2) Wm -2 ; fo ssil fuel organic carbon, - 0 .05 (+/-0. 05 )Wm -2 ; fossil fuel black carbon, +0. 2 (+/-0.15) Wm -2 ; biom ass burning, +0. 03(+/ -0.12) Wm -2 ; nitrate, -0.1( + /-0.1) Wm -2 ; and m i neral dust, - 0 .1(+/

- 0.2) Wm -2

. Including both fossil fuel a nd biom ass burning sources, the total bl ack carbon aerosol forcing is esti m at ed to be 0. 34 (0 .09 to .5 9) W/m 2

. In addition, black carbon can cau se another positive radiative forcing effect ( + 0.1 (0.0 to +0.2) W/ m 2 ) by decreasing the surface albedo of snow and ice with a low level of scientific understanding (Forster et al., 2007). A more recent estimate suggests a direct b lack carbon effect of 0.9 ( 0 .4 t o 1 .2) W/ m 2 , or m o re than half th at of CO 2 (Ramanathan and Carm ichael., 20 08). The spatial distribution of aerosol forcing is very diffe rent from that of the well- m ixe d GHGs, and they do not exert si mp l e co mp ensating or additive effects on cli m ate (CCSP, 2008d). The total forcin g associat ed with anthropogenic aerosols is less ce rtain than tha tfor GHGs, due to the indirect effects of aerosols, includin g clo ud form ation and albedo ch ange. The radiative forcing from increases in stratosphe ric water vapor due to oxidation of anthrop ogenic increase s in CH 4 is estimated to be +0.07 ± 0.05 W/m 2 (Solo m on et al., 2007). The le vel of scientific

14 In ad d ition to d i rectly reflectin g so la r rad i atio n, aero so ls cau s e an add itio nal, in d i rect n e gativ e fo rci n g effect b y enha nci n g cl o u d al be d o (a m e asure o f refl ect i v i t y or bri ght n e ss). T h i s occ u rs because aer osol s act as par t i c l e s ar oun d wh ich clo u d d r op lets can f o r m ; an increase in the num b er of ae ros o l pa rt i c l e s l eads t o a great e r num ber of
sm a ller clo u d d r op lets, wh ich leads to enh a n ced clou d albedo. Ae ros o ls also influe nce cloud lifetim e and p r eci p itatio n bu t no cen tral esti m a tes o f t

h ese in d i rect fo rc i n g effects are e stim a ted by IP CC. T h ese ae rosol indirect effect s rem a i n som e of th e bi gge st u n cert a i n t i e s of t h e cl i m at e fo rci n g/ fee dbac k p r oces se s (C C SP 2 0 09a ).



### 21

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

understanding is low because the contribution of CH 4 to th e correspondin g vert ical structure of the water vapor change near the trop opause is uncertain.
Changes in surface albedo due to hum a n-induced land c over changes exert a forcing of –0.2 (–0.4 t o 0.0) W/m 2

. Chan ges in solar irradiance since 1750 are estimated to cause a radiative forcing of +0.12 (+0.0 6 to +0.30) W/m 2

. This i s l ess than half of the esti m at e gi ven in IPCC’ s Third Assessment Report (2001), with a low level of scientific understanding (Sol om on et al., 2007). Uncertain ti es remain large because of the lack of direct observations and inco mp lete understanding of solar variability m e chanisms over long time scales. Empirical associations have been reported between solar- m odulated cosm ic ray i onization o f the atm o sphere and glo b al average low-level clouds cover but evidence for a sy stem atic indirect solar effect remain s am biguous. The lack of a proven phys ical mechanism and the pl ausibilit y of other causal factors m a ke the associatio n between galactic cos m i c ray -induced c h anges in aerosol and cloud form ation controversial (Solom on et al., 200 7).
Although wat e r vapor is the m o st abundant naturally occurring greenhouse gas, direct em issions of water vapor due to human activ ities make a negligible co ntribution to radiative forc ing (hence its absenc e in Figure 3.1). However, as temp eratures increase, tropospheric water vapor concentrations increase representing a key positive feedback (enhances war m i ng) but not a forcing of climate change (Solom on e t al., 2007). Feedbacks are defined as process es in the cli m ate syste m (su c h as a change in water vapor concentrations) that can either amplify or damp en the sy stem ’s initial res ponse to radiative forcing changes (NRC, 2003)

. 4(b) Global Changes in Tem p erature Multiple line s of evidence lead to the r obust conclus i on that th e climate sy stem is warming. The IPCC (2007d) stated in its Fourth Assessment Report:

“War m ing of the cli m at e sy stem i s unequivocal, as is now evident from obs ervations of increase s in global average air and ocea n te mp erature s , widespre ad m e lting of sn ow and ice, a nd rising global avera g e sea level.”

Air te mp er at ure is a mai n property of cli m at e and the m o st ea sily m e a s ure d , directly observable, and geographically consistent i ndicator of cli m ate change

. The extent to which ob served changes in global and continental te mp eratur e, and other cli m at e fa ctors, can be att ributed to anthropogenic e m issions of GHG s is addressed in Secti on 5.
Global Surface Temperatures

Surface temp erature is cal culated by pr ocessing data from thousands of worl d- wide observation sites on land and sea. Parts of the globe have no data, althou gh data coverage has i mpr ove d with time. The lon g

ter m mean temp eratures a re calculated by interpol a ting within areas with no measure men ts using the collected data available. Biases ma y exi s t in surface temp eratures due to changes in station exposure and instrumentation over land, or changes in measur e m e nt techniques by ships and buoy s in the ocean. It i s likely that these biases ar e largely random and therefor e cancel out over large regions such as the globe or tropics (Wigley et al., 2006). Likewise , urban heat island effects are real but local, and have not biased the large-scal e trends (Trenberth et al., 2007). The following trends in global surface te mp eratur e s have been observed, accor d ing to the IPCC (Trenberth et al., 200 7):



### 22

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Global mean surface te mperatures have risen by 0. 74°C ±0.18°C when esti m ated by a linear trend over the last 100 y ears (1 9 06–2 005) as shown b y the magenta line in Fi gure 4. 2 . The warm est y ears in the instrumental record of global surface temp eratures are 1998 and 2005, with 1998 rank ing first in one estim ate, but with 2 005 sli ghtl y h i gher in the o t her two estimates. 2002 t o 200 4 are the 3rd, 4th and 5th warmest y ears in the series since 1850. El even of the last 12 y ears (1995 to 20 0 6 ) – the exception being 19 96 – rank am ong the 12 warmest y ears on record since 1850. Temp eratures in 2006 were similar to the average of the past 5 y ears.

• The war m ing has not been steady , as shown in Figur e 4.2. Two periods of w a rm ing stand out: an increase of 0. 35°C occurred from the 1 910s to the 1 940s and the n a war m ing of about 0.55°C fro m the 1970s u p to the end of 2006

. The remainder of the past 150 y e ars has inclu d ed short periods of both cooli ng and warm ing. The rate of warm ing over the last 50 years is alm o st double that o v er the last 100 y ears (0.13°C ± 0.03°C vs. 0.07°C ± 0.02°C per decade).

Figure 4.2: Annual global mean tempe ratur es (bla c k dots ) w i th l i near fits to the data.

Source: Sol o m on et al., (200 7 )

. T he left hand a x is sho w s t e mper ature a n o mali es rel a tiv e to the 196 1 to 199 0 avera ge a nd th e right ha nd a x is sho w s estim a ted actu al te mperatur es, bo th in °C. Line ar trends are sh o w n f o r the last 25 ( y el l o w ) , 50 (ora ng e), 100 (mag e n t a) and 15 0 ye ars (red). T he smooth bl ue cu rve sho w s d e c ada l variati ons w i th the deca d a l 90 % error ran ge sho w n as a pa l e blu e ba nd a b out that lin e. T he total temp er ature incre a se from the per iod 185 0 to 1899 to the peri od 20 01 to 200 5 is 0.76° C ± 0.19°C (1.37 ° F ± 0.34°F )

.

• Land regions have war m e d at a fa ster r a te than the oceans. War m ing has occ u rred in both land and oceans and i n both sea surface temperature (SST) and nighttim e marine air temp erature over the oceans. Ho wever, for the globe as a whole, surface air t e mp er at ures over lan d have risen at about double the ocean rat e aft e r 1979 (m or e than 0.27° C per decade vs. 0.13°C per decade), with the greatest warming duri ng winter (Decem b e r to Februa ry ) and spring (March to Ma y ) in the Northern Hem i sphere. Recent war m i ng is strongl y evident at all latitudes in SSTs over each of the oceans.



### 23

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Average Ar ctic te mp eratur es increa sed at al m o st twi ce the global average rate i n the past 100 y ears. Arctic t e mp er atures have hi gh decadal variabilit y , and a war mperio d was also observed fro m 1 925 to 1945

.

• Between 190 1 and 2 005, warm ing is statistically significant over m o st of the world ’ s surface with the exception of an area south of Greenland and three smaller regions over the southeastern U.S. and parts of Boli via and the C ongo basin. T h e lack of sig n ificant warming at abou t 20% of th e locations, and the enhanced war m i ng in other places, is lik ely to be a result of changes in atmospheric circulation. Warm ing is strongest over the contin ental interiors of Asia and northwestern North A m eri ca and over some m id-latitude ocean regi ons of the Southern Hemisphere a s well as southeastern Brazil.

• Since 1979 , warm ing has been strongest over wester n North Am erica, northern Europe an d China in winter, Europe and north ern and eastern Asia in sp ring, Europe and North Africa in su mmer and northern North Americ a, G r eenland and eastern A s ia i n autum n

. Box 4.1: Updated Global Surface Tem perature Trends through 200 8
The global surface t e mp erature trend analy s is in IPCC (2007a) includes dat athrough 2005. Three additional y e ars of data have beco m e available since then (2006-2008). According t o N OAA’s 2008 State of the Climate Report (NOAA, 2009a):

• Eight of the t e n warmest years on record have occurred since 2001

.

• The y ear 200 8 tied with 2 001 as the eighth warmest y ear on record for the Earth. The com b ined global land and ocean s u rface te mpe rature fro m January -Dece m b er w as 0. 88 degree F (0.49 degree C) ab ove the 20th Century average of 57.0 degrees F (13.9 degrees C).

• Since 1880, th e annual com b ined global land and oc ean surface temp erature h as increased at a rate of 0.09 degree F (0.05 degree C) / decade. This rate ha s incr eased to 0.29 degree F (0. 16 degree C) / decade over the past 30 y ears. Data analy z ed b y NASA throug h 20 08 show sim ilar trends (NASA, 2009). It found 200 8 was the ninth
war m est y earin the period of instrum e n tal m e asure me nts, which extends back to 188 0. In b o th analy ses 1998 and 2 0 0 5 rem a in the two warmest y ears on reco rd.

Global Uppe r Air Temperatures

Te mp erature mea s ure m ents have al so been made ab ove the Earth' s surface over the past 50 to 60 y ears using radiosondes (balloon-bor ne instruments) an d for the past 28 y ears using satell ites. These measurements support the analy s is of trends and variabilit y in the tr oposphere (surface to 10-16 km ) and stratosphere ( 10-50 km above the earth' s surface).

The U.S. Climate Change Science Pro g ra m prepare d a report which asse ss ed te mp erature c h anges in the at m o sphere, differences in these changes at various le vels in the atm o sphere, and our understanding of the causes of these changes an d differences. It conclude d (Wigley et al., 2006): “...the m o st recent versions of all available data sets show that both the surface and troposp h ere have warmed , while the stratosphere has cooled. T h ese changes are in accord with our unders tanding of the eff ects o f radiative fo rcing agents and with the r esults fro m model simu lati ons.”



### 24

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The IPCC (Trenberth et al., 2007) re-affir m ed the m a jor conclusion s of this CCSP report findi ng:

• New analy ses of radiosondes and satellit e measure ments of lower- and m id-tropospheric temperature show war m in g rates that are si m ilar to those of the surface te mp erature recor d and are consistent within their r espective uncertainties.

• The satellite tropospheric temp erature r ecord is broa dl y consistent with surface temp eratur e trends. The range (d ue to differen t data sets) of globa l surfa ce warming since 1979 is 0.16°C to 0.1 8 °C per decade co mpared to 0.12°C to 0.19°C per d ecade for esti m ates of tropospheric temperatures measured by satellite.

• Lower-tropospheric temp eratures m e asured b y radi o s ondes have slightl y greater warm ing rates than those at the surface over the period 1958 to 2005. Th e radiosonde record is markedly less spatially
co mp lete than the surface record and increasing evid ence suggests that it is very likel y that a num ber of records have a cooling bias, especial ly in the tropics.
Lower stratospheric temp eratures have cooled since 1979. Estim ates fro m adjusted radiosondes, satellites and re-analy s es are in qualitative agreement, sugges ting a lower-stratospheric cooling of be tween 0.3°C and 0.6°C per decade since 1979.
The global upper air temp erature trend analy s is in IPCC (2007a) described ab ove includes data through 2005. Three additional years of da ta have beco me available since then (2006-2008). The addition of these three y e ars does not s ignificantl y a lter the above trends. For example, in NOAA (2009) the satellite tropospheric temp erature trend co mputed through 2 008 ranges from + 0.11°C to + 0.15°C per decade
co mp ared to the esti m at e of + 0.12°C to + 0.19°C per decade given in IPCC (2007a).



### 25Source: NR C (200 6b) Rec ons tructions of (No r thern Hem isp here av era ge o rglob al avera ge) surfa c e temperatur e variatio ns fr om six rese arch teams (in differ ent color shad es) alo ng w i t h the instru mental rec o rd of glob al av era ge surface tem peratur e (in black). Each curve illustrat e s a some w h at different histor y of temper atur e chan ges, w i th a rang e of unc ertainti es t hat tend to incr eas e back w a r d in t i me (as indic a ted b y th e shad in g). 

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Global S u rfa ce Temperatures Over the Last 2,00 0 Ye ars Figure 4.3: Recons truc tio ns of (Nor th ern Hemisp h e re av erage or global av era ge) sur f ac e tempera t ure v a r i ations fr om six resea rch teams Instrumental surface te mp erature records only began in th e late 19 th century , when a sufficiently large global network of measurements was in plac e to reliabl y co mpute global m ean te mp erature s

. To esti m at e te mp erature s further back in time, sci e n tists analy ze proxy evidence fro m sources such as tree rings , corals, ocea n and lake sedim ents, cave deposits, ice cor es, boreholes, glaciers, and docum entar y evidence. A longer te mp erature record can help place the 20 th century
warm ing into a historical context.

The National Rese arch Council cond ucted a study to describe and asses s the s t ate of scienti fic efforts to reconstruct surface te mperat ure records for the Earth over approxi mately the last 2,000 y ears and the i m p lications of these efforts for our under s tanding of global clim ate change. It found (NRC, 2006 b):

• Large-scale surface temp erature recon s tructions, as illustrated in Figure 4.3, y ield a generally consistent picture of temp erature trends duri ng the preceding m illennium , including relatively war m conditions centered around A.D. 10 00 (identified by some as the “Medieval Warm Period”) and a relatively col d period ( o r “Little Ice Age”) centered around 1700.

• It can be said with a high level of confidence that global mean su rface t e mp er a ture was higher during the last few decades of the 20th century than dur ing any comp arabl e period during the preceding four centuries. The observed war m ing in the instrum e n t al record shown in Fi gu re 4.2 sup p o r ts this conclusion.

• Less confidence can be pl aced in large- scale surfac e te mp erature r econstructions for the peri od from A.D. 900 to 1600. Presentl y available pr oxy evidence indicates that temp eratures at m a ny , but not all, indivi dual locations were higher during th e past 25 y e ars than during any period of co mp arable length since A.D. 900. The uncertainties a sso ciated with reconstructing hem ispheric m e an or global m e an temp eratures from these data incr ease substantially ba ckward in ti me through th is period and are not y e t full y quantified.



### 26

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Very little confidence can be assigned to statements concerning the hem i spheric mean or glo b al m e an surface t e mp erature prior to about A.D. 900 becau se of sparse data cover a ge and because the uncertainties associat ed wi th proxy data and the m e th ods used to a n aly ze and com b ine the ma re larger than duri ng m o re recent time periods.
Considering th is study and additional re search, the IP CC (2007d) c oncluded: “Paleocli m atic i n form ation supports the interpretation that the war m th of the last half century i s unusual in at leastthe previous 1,300 y ears.”
4(c) U.S. changes in temperat u res Like global mean te mp er atures, U.S. te mp erature s also war m ed during the 20 th and i n to th e 21 stcentury. According to NOAA (2009 b) and data fr om NOAA 15 :

• U.S. average annual temp eratures are now approxim a tely 1.2 5 °F (0 .69°C) warmer than at the start of the 20th century , with an increas ed rate of war m ing over the past 30 y ears. The rate of w a r m ing for the entire period of record (1895-2008) is 0.13 °F/decade while the rate of war m ing increased to 0.58°F/decade (0.32°C/decade) for the period from 1979-2008.

• 2005- 200 7 w e re exceptionally warm y e ars (am ong the top 10 warm est on record), while 2 008 was slightly warmer than average (the 39 th warm est y ear o n record), 0. 2 ° F (0.1°C) above the 20 th century (1901- 200 0) mean.

• The last ten 5- y ear period s (2004- 200 8 , 20 03-2 007, 2002- 200 6, 2 001-2 005, 2 0 00-20 04, 19 9 9 -200 3 , 1998- 200 2, 1 997-2 001, 19 96-20 00, and 1995- 199 9), were th e warmest 5-y ear periods (i.e. pentads) in the 114 y ears of national re cords, dem o n s trating the anom alous warm th of the last 15 y ears.

15 Data o b t ained fro m NOAA’s Natio n a l Clim a tic Data Cen t er. Data m a y b e d o wn lo ad ed fro m : h ttp ://www.epa.go v / clim atec h a ng e/anpr/d at a.h t m l ( s ee f ile: A nnu alU S Tem p

_ th r oug h 200 8.x ls)



### 27

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Regional data analy zed from NOAA’s National Climatic Data Center U.S. Historical Cli m ate Networ k 16 (USHCN), as illustrated in Figure 4.4, indicate war m ing has occurred throug hout m o st of the U.S., with all but three of the eleven climate r e gions showing an increas e of more than 1o F since 1901 through 2006 (NOAA, 2007). As shown in Fi g u re 4.4, the greatest te mp erature incre ase occurr ed in Alaska (3.3°F per centur y ) . The Southeast shows es sentia lly no trend over the entire period, but has warmed since 1979.
Including all of North America in its
asse ss ment of regional te mp erature s , the IPCC (Field et al., 2007) stated:

• For the per i od 1 955- 20 05, th e greatest wa r m ing occurred in Alaska and north-western Canada, with substantial warming in the continental interior and m odest
war m ing in the south-eastern U.S. and eastern C a nada.

• Spring and winter show the greatest chan ges in temp er ature and daily m i nimu m (night-tim e) temp eratures have warmed m o re than dail y maxi mu m (day tim e) te mp erature s

. Figure 4.4: Map of th e United Sta t es, depicting re gional U.S. tempera t ure tr end s for the period 1901 to 2 0 0 6

.

Red sh ad es in dicate w a rmin g over the peri o d and b l u e sha des indic a te co oli n g over the p e ri od.

4(d) Global changes in precip itation
A consequence of rising te mp erature i s increased ev apor ation, provided that a d equate surface m o isture i s available (e.g., over the oc eans and other m o ist surfac es). The ave rage at m o sph e ric wat e r va por content has increas ed since at leas t the 1980s over land a nd ocean as wel l as in the upper troposphere (IPCC , 2007d). When evaporation increases, m o r e wat e r vapor is available for precipitation producing weather sy stems lead ing to precipitation i n creases in some areas. Conversely , enhanced evaporation and evapotranspiration from w a r m ing ac cel erates land s u rface dry ing and increas e s the potential incidence and severity of droughts in other areas.

16 Dat a fo r m a p obt ai ne d fr om NO A A’s Nat i o nal C l im at i c Dat aC e nt er. D a t a m a y be d o w n l o a d ed f rom : h ttp ://www.epa.go v / clim atec h a ng e/anpr/d at a.h t m l (fi l e s ar e: C O N U S m ean t e m p anom al y 2.5 X 3. 5_t hr ou g h 2 006 .x ls an d AK -H I m ean tem p an o m aly_ t h rou gh 20 06 .x l s )



### 28

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Observations show that changes are occurring in the am ount, intensit y , frequency and t y pe of precipitation. According to the IPCC (Trenberth et al., 200 7):

• Long-term trends from 1900 to 200 5 h a ve been ob served in precipitation am ount o v er many large regions. Significantly increased pre c ipitation has b een observed in eastern part s of North and Sout h Am erica, northern Europe and northern and central A s ia. Dry ing has been obser ved in the Sahel, the Mediterranean, southern Africa and parts of southern Asia. Precipitation is hi ghl y variable spatially and temporally, and data ar e li m ited in some regions.

• More intense and l onger droughts have been obser ved over wi der areas since the 1970s, parti c ularly in the tropics and subtropics. Increa s e d dry i ng linked with higher te mp er atures and d ecre ased precipitation has contribut ed to changes in dr oug ht. The regions where drough ts have occurred see m to be deter m i n ed largely by changes in sea surface temp eratures (SSTs), especially in the tropics, through associated chang es in the at mospheric circ ulation and precipitation. Decr ea sed s nowpack and snow cov e r have also been linked to droug hts.

• It is likely that there have been increase s in the num be r of heavy precipitation events (e.g., 95th percentile) within m a ny la nd regions, even in those wher e ther e has been a reduction i n total precipitation
am ount, con s istent with a warming cli m at e and observed significant increasing am ounts of water vapor in the at m o sphere.

• Rising temp eratures hav e generally resulted in rain rather than snow in locations and seaso ns where clim atological average (1961 –19 90) te mp erature s were clos e to 0°C.
4(e) U.S. changes in precipitation

Data analy zed fro m N OAA’ s N a tional Cli m atic Data Center U.S. Historical Cli m ate Net w ork (USHCN) 17 show that over the co ntiguo us U.S., total an nual precipitation increased at an average r a te of 6.5% per century from 1901-2 006

. As shown in Figure 4.5, the greatest incr ea ses in precipitation were in the East North Central climate region (11. 2% per century ) a nd the S outh ( 10.5 % ). Precipitation in the Northe ast increas ed by Figure 4.5: Map of th e United Sta t es, depicting precipita tion trends for the contig uo us U.S. 1901 -200 6, Ha w a ii 19 05-2006 an d Ala ska 19 18-20 06.

Green sha des i ndic a te a trend to w a r d s w e tter conditi ons ov e rthe peri od, an d bro w n s h a des i ndi cate a trend to w a rds dr ye r co nditi ons. No data ar e av aila bl e for area s shade d in w h ite.

17 Data for m ap s ob tain ed fro m NOAA’s Nation al Cli m atic Data Cen t er. Data m a y b e do wn lo ad ed fro m : h ttp ://www.epa.go v / clim atec h a ng e/anpr/d at a.h t m l ( f iles are: CO NU S pr ecip ano m aly 2

. 5 X 3

. 5_ thr oug h 20 06 .x ls and A K

- H I p r eci p an o m aly_ th r oug h 200 6.x ls)



### 29

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

8.3%, in the Southeast by 1.9%, the Central U.S. by 8.1%, the West North Central by 1.9%, the Southwest b y 1.3% , the W est by 9.1% , and the North w est by 6. 0%

. Outside the contiguous U.S., Alaska experienced a p recipitation increas e of ab out 5.9% per century (since records began in 1918) and Hawaii ex perienced a decr ease of 7.2% per century (since records begin in 1905).
Despite the overall national trend towar d s wetter cond itions, a sev ere drought h as affected the southwest U.S. from 1999 thr ough 2008 (see Section 4(l)) whi c h is indicative of signific a nt variability in regi onal precipitation patterns over time and space.
4(f) Global sea level rise

There is strong evidence that global sea level gradu a lly rose in the 20th century and is currently risin g at an increased r a te, after a period of li ttle change between AD 0 and AD 1900 (IPCC, 2007a).
According to Bindoff et al. (2007), th ere is high c onfidence that the rate of sea level ri se increased between the mid-19 th and mid-20 th centuries. The a v erage rate of sea level ris e m e a s ured by tide gauges from 1961 to 2003 was 1.8 ± 0.5 mm per y ear (Bindoff etal., 2007). The global average rate of sea level rise measured by satellite altimetry dur ing 1993 t o 2003 was 3.1 ±0.7 mm per y ear (Bindoff et al., 2007). Coastal tide gauge mea s ure m ents confir m this observ a tion. It is unclear whetherthe faster rat e for 1993 to 2003 is a reflection of shor t-ter m variabi lit y or an incr ease in the longer-ter m trend (Bindoff e t al., 2007)

. The total 20 th century sea level rise is esti m ated to be 0.17 ± 0.05 m (Bindoff et al., 2007).
Two major process es lead to changes in global m e a n sea level on decadal and longer time scale s : i) therm a l expansion, and ii) the exchange of water be tween oceans and other re servoirs (glac iers and ic e caps, ice she e ts, and other land water reservoirs). It is believed that on average, over the period from 1961 to 2003, therm a l expansion contributed about one-quarter of th e obser ved sea level rise, while melting of land ice accounted for less th an half; the full magnitude of the observed sea level rise was no t satisfa ctorily explained by the available data sets (Bin doff et al., 2007). During this period, global ocean temp erature rose by 0. 10° C fro m the su rface to a dep th of 700 m , contributi ng an average of 0.4 ± 0.1 mm per y ear to s ea level rise (Bindoff et al., 200 7). T h e contributio n from ice was approximately 0.7 ± 0. 5 mm per y ear (Lemke et al., 200 7).

For recent years (1993-2003) f o r whi c h the obser ving s y stem is mu ch better, ther m a l expansion and melting of la nd ice each account for a bout half of th e observed sea level rise, although th ere is so m e uncertainty in the estimates. Ther m a l expansion co ntributed ab o u t 1. 6 ± 0.5 mm per y ear, reflecting a high rate of warm ing for the period relative to 19 61 t o 200 3 (Bind o ff et al., 200 7). The total contributi o n from melting ice to sea lev e l change betw een 1993 and 2003 range d from 1.2 ± 0.4 mm per y ear. The rat e increased over the 1993 to 2003 period primarily due to increasing losses f r o m m ountain glaciers and ice caps, fro m i n creasing sur face melt on the Greenla nd Ice Sheet and from f

a ster flow of parts of the Greenland and Antarctic Ice Sheets (Lemk e et al., 2007).

Ther m a l exp a nsion and exchanges of water bet w ee n oceans and other reserv o irs cause changes in the global mean as well as geographicall y non-uniform sea l e ve l change. Other f actors influence changes at the regional scale, including changes in ocean circula tion or atm o s pheric pressure, and geologic processes (Bindoff et al ., 2007). Satellite measurements (for th e period 1993-2003) pr ovi de unam b iguous evidence of regional variability of sea level chan ge (Bindoff et al., 2007). I n some regions, rates of ri se have been
as mu ch as several ti m e s the global m e an, while sea leve l is falling in other regi ons. According to IPCC (Bindoff et a l., 2007), the largest sea l e vel rise sinc e 1992 has t a ken place in the western Pacific and eastern India n Oceans, wh ile nearly all of the Atlan tic Oc ean sho w s s ea l e vel r ise during the past dec a de



### 30

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

with the rate of rise reaching a maximu m (over 2 mm y r –1 ) in a band runni ng east-northeast from the U.S. east coast. Sea level in the eastern Pacifi c a nd western Indian Oceans has been falling.
4(g) U.S. sea level rise

Sea level 18 has been rising 0.08-0. 12 in ches per y e ar (2.0-3.0 mm per y ear) along m o st o f the U.S. Atlantic and Gulf coasts. The rate of sea lev e l rise varies fro m about 0.3 6 inches per y ear (10 mm per y ear) along the Louisiana Coast (due t o land sinking), to a drop of a few inch es perdecad e in parts of Alaska (bec a u se land is rising). Records from the c o astof California indicate that sea levels have risen al m o st 18 cm during the past century (California Energ y Commission, 200 6). Accordin g to th e CCSP (2009 b), in th e m id-Atlan tic region from New Yorkto North Carolina, tide-gauge observations indicate that relative sea-level rise ( the com b inati on of global s ea-level rise a nd land subsidence) rates were higher than the global m e an and generally ranged between 2. 4 and 4.4 milli m e t e rs p e r y ear, or about 0.3 m e t e rs (1 foot) over th e twentieth century

. Rosenzweig et al. (2007) docum ent stu d ies that find 75% of the s horeline removed from the influence of spits, tidal inl e ts and engineering structures is erodi ng along the U.S. East Coastprobabl y due to sea level rise. They also cite studies reporting losses in coast a l wetlands observed in Louisiana, the mid-Atlantic region, and in parts of New England and New Yo rk, in spite of recent protective environm ental regulations.
4(h) Global ocean acidificatio n
Ocean water s can absorb large am ounts of CO 2 from t h e at m o spher e , because the gas is w eakl y acidic and the m ineral s dissolved in the ocean hav e over geologi c ti me c reat e d a slightly alkaline ocean, with surfac e pH ranging f r om 7.9 to 8.25. T h e amount of carbon contained i n the oceans has increased due to th e elevated at mospheric pressure of CO 2 from anthropogenic em issions (Den man et al., 20 07). IPCC esti m ates that the total inor ganic carbon content of the oceans incr eased by 118 ± 19 GtC between 1750 and 1994 and continues to increase (Bindoff et al., 2007)

. This absorptive cap acity of the oceans has resulted in at m o spheric C O 2 concentrations substantially lower than they other w ise would be. Since the beginning of the industrial revolution, sea surface p H has dropped by about 0.1 pH units, corresponding to a 30% increase in the co ncentration of hy drogen ions (Den man et al., 2007).

Ocean acidifi cation is caus i ng a seri e s of ca scading c h a nges to the che m i s try of ocean wate r, including a decrease in the saturation state of calcium carbonate. Marine calcifiers, such as corals, are dependent upon this m i neral to form shells, skeletons, and other protective structures. Reduced av ailability of calciu m carb onate can sl ow or even halt calcifica tion rates amongst these organisms (F ischlin et al., 2007). The availabilit y of carbonate is also i mporta n t because it controls the maxi mu m am o unt of CO 2 that the ocean is able to absorb (Bindoff et al. 2007, p. 406). More infor m ation regarding ocean acidification projections and impacts to m a rine ecos y s tems can be foun d in sections 6(b) and 1 4 (a), respectively

. It is i mportant to note that ocean acid ification is a direct consequence of foss il fuel CO 2 em issions, which are also the main driver of th e antici p ated clim ate change (Denman et al., 2007).
4(i) Global changes in physical and biological systems
Phy s ical and biological sy s te m s on all continents and in m o st ocea ns are alread y being affected by recent cli m at e chan ges, particula rly regional te mp erature increas es (ver y high confidence) (Ros enzweig. et al. , 2007). Climatic effects on hum an sy stem s, although m o re difficult to discern due to adapt a tion and non18 U.S. sea lev e l d a ta ob tain ed fro m th e Perm an en t Serv ice for Mean Sea Lev e l < h ttp ://www.p o l .ac.uk /psm s l/> o f th e Pr oud m a n O ceanog r aph ic Labo r a t o r y

.



### 31

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

cli m atic drive rs, are e m erging (m ediu m c onfidence) (Ro senzweig. etal., 2007). The majority of evidence
co m es fro m mid- and high latitudes in the Northe rn Hem isphere, while docu m entation of observed changes in tropical regions and the Southern He m i sp here is sparse (Rosenzweig

. et al., 2007). Hence, the findings presented in this se ction a pply generally to the globe but m o st directly to Europe and North Am eri ca (including the U.S.) where these observati ona l studies were conducted. The ext e nt to which observed changes discuss ed here c a n be attributed to anthropogenic GHG e m is sions is discussed in Section 5.
Cryosphere ( Snow and Ice)

Observations of the cry o sp here (the “fro zen” co mponentof the climate sy stem ) have revealed changes in
sea ice, gla c iers and snow cover, fr e ezing and th awing, and perm afrost. According to IPCC, the following ph y s ical changes have been observed:
Satellite data since 1978 show that annual average Arc tic sea ice extent has shrunk by 2. 7 ± 0.6 % per decade, with larger decr ea ses in su mme r of 7.4 ± 2. 4% per de cade

. The latest d a ta fro m NA SA indicate Arctic sea ice set a record low in Sep tem be r 2007, 38 percent below the 1979-20 07 average (NASA Goddard Space Flight Cen ter, 2007). The extent of t h e sea ice loss between 1979 and 2007 can be seen i n Figure 4.6. In Septem ber 2008, Arct ic sea ice re ached its second lowest extent on record (NASA Goddard Spa ce Flight Center, 2008). The size a nd speed of r ecent su mmer sea ice loss is highl y anomalous relative to the p r evious few thousands of y ears (Poly a k et al., 2009)

. 

### Figure 4.6 Arctic Sea Ice Co ncentrations Comparisons

1979 2007 These two images, constructed from sate llite data, compare arctic sea ice concentrations in September of 1979 and 2007 (Images courtesy of NASA).

• Antarctic sea ice extent sh ows no statist ically signi fic a nt average tr ends according to IPCC (2007d). However, the U.S. National and Snow and Ice Data Center stat es that Antarctic sea ice underwent a slight increase fro m 1979 t o 2007 (NSI DC, 2009).

• The average sea i c e thickness in the central Ar ctic has very likel y decreased by up to 1 m fro m 1987 to 1997, based upon subm arine-de rived data. Mode l-based recons tructions support th is, suggesting an arctic-wid e reduction of 0.6 t o 0. 9 m over the sam e period (Lemke et al., 200 7).

• Mountain gl aciers and snow cover have declined on average in both hemispheres. Northern hem isphere snow cover observed by satellite over the 1966 to 2005 period decreased in every m onth except Novem b er and Decem b er, with a stepwise drop of 5% in th e annual mean in the late 1980s. I n the Southern Hem i sphere, the few long records or pr oxies m o stly show either decreases or no changes in the past 4 0 y ears or m o re. The strong est m a ss lo sses of m ountain glaciers (per unit area) h a ve been



### 32

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

observed in Patagonia, Alaska and the northwester n U.S. and southwest Canada. Because of the corresponding large areas, the biggest contributi ons to sea level rise cam e fro m Alaska, the Arctic and the Asian high m ountains (Lemke et al., 2007).

• Freeze -up date for river a nd lake ice has occurred later at a ra te of 5.8 ± 1.6 da y s per century , averaged over available data for th e Nor thern Hem isp here spannin g the past 1 5 0 y ears. Breakup date has occurred earlier at a rate of 6.5 ± 1. 2 day s per centu r y (Lemke et al., 200 7).

• Temp eratures at the top of the permafrost lay e r ha ve generally increased since th e 1980s in the Arctic (by up to 3° C). The permafrost base has been thawing at a rate ranging up to 0.04 m per y ear in Alaska since 1992 an d 0.0 2 m per y ear on the Tibe tan Plateau since the 1960s. The m a ximum area covered by seasonally frozen ground has decreased by 7% in the Northern Hemisphere since 1900, with a decrease in spring o f up to 15% ( Lemke et al., 2007).

There ar e ad ditional effec t s relat e d to c h anges in th e cry o sphere. Melting of highl y reflective snow and ice reveals d a rker land an d ocean surfaces, creating a positive feedback that in creases absor p tion of the sun’ s heat and further war m s the planet

. Incre ase s in glacial melt and river runoff add m o re freshwat e r to the ocean, raising global sea level. Hydrosphere

The term “hydrosphere” refers to the co mponent o f the climate sy stem co mprising liqui d surface an d subterranean water, such as rive rs, lakes, and undergr ound water. Se veral chan ges in these f eatures have been observed, as summarized by th e IP CC (Rosenzweig et al., 2007):

• Docu m e nted trends in severe droughts and hea v y rains show that hy dr ological conditions are beco m ing m o re intense in so m e regions. Globall y , very dr y areas (Pal m e r Drought Severit y I ndex— PDSI—less than or equal t o -3.0) have m o re than do ubled since the 197 0s due to a com b ination of El Niño-Southern Oscillation events and surface war m in g. Very wet areas (PDSI greater than or equal to +3.0) declined b y abo u t 5% since th e 1970s, with precipitatio n as the m a jor contrib u ti ng factor during the early 1980s and te mp eratur e m o re i mpor tant thereafte r. The areas of increasing wetness include the Northern Hem i sphere hi gh l a titudes and equatorial regi ons.

• Cli m ate ch ange signals related to increasing runoff a nd strea m flow have been observed ove r the last century in m a ny regions, particularly i n basins fe d by glaciers, per m afrost, an d snowm e lt. Evidence includes increases in average runoff of Arctic rivers in Eurasia, which has been at least partly correlated wi th climate w a r m ing, and earlier spring snowmelt a nd increase in winter base flow in North A m eric a and Eurasia due to enhanced sea sona l snow melt as sociated with cli m at e war m ing.

• Freshwater l a kes and rivers are exper iencing increased wat e r te mp erature s and changes in water che m istry

. Surface and deep lake-water s are war m ing, with advances and le ngthening of periods of ther m a l stabil ity in som e c ases associ at ed with ph y s ical and chemical ch anges such as inc rease s in salinity and suspended solids, and a de creas e in nut rient content. Lake form ation and subsequent disappearanc e in permafrost have been reported in the Arctic.
Changes in river discharge as well as in drought s and heavy rains in so me regions indicate that hy drol ogical conditions have beco m e more intense but significant trends in floods and in evaporation and evapotranspiration have not been detected globall y

. Some local trends in reduced groundwat er and lak e levels have been repor ted, but studies ha ve been unable to separate t h e effects of variations in te mp eratur e and precipitation from the effects of human interven tions such as groundwater manage ment (Rosenzwei g et al., 2007)

.



### 33

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Biosphere
According to IPCC, terres trial ecosy stems and m arin e and freshw a ter sy ste m s show that recent war m ing is strongl y aff ecting natural biolo g ical systems (very h igh confi d ence) (Rosenzweig et al., 20 07 ):

• The overwhelm ing m a jority of studies of regiona l cli m ate eff ects on terr e s trial spe c ies reveal consistent res ponses to war m ing tr ends, including poleward and el eva tional range shifts of flora and fauna. Cha nges in ab u ndance of c e rtain sp ecie s , including lim ited evidence of a few loc a l disappearanc es, and changes in co mmunity co m position over the last few decades h a ve been attributed to c limate change

.

• Responses of terrestrial species to w ar m ing across t h e northern he m i sphere ar e well docu m ented by changes in the tim ing of growth stages, especially the earlier onset of spring events, m i grati on, and lengthening of the growi ng season. Changes in phenology (the tim ing of annual phenomena of ani m al and plant life) include clear temp erature-dri v en extension of the growing season by up to 2 weeks in the second half of the 20 th ce ntur y in m id- and high northern latitudes, m a inly due to an earlier spring, but partl y d u e also to a later autu m n

. Egg-la y in g dates have advanced in m a n y bir d species, and many small mammals have been found to come out of hibernatio n and to breed earlier in the spring now than the y did a few deca des ago.

• Many observed changes in phenology and distributi on of m a rine species have been associa ted with rising water te mp erature s , as well as other cli m at e-driven changes in salinity, oxy g en le vels, and circulation. For exa mple, plankton has m oved polew ard by 10° latitude over a period of 4 decades in the North Atlantic. While there is increasing evid ence for cli m ate change imp acts on c o ral reefs, discerning the i mpact s of cli m at e-relat e d stresse s from other stres ses ( e.g. over fishing and polluti on) is difficult. Warm ing of lakes and rivers is affecting abunda nce and productivit y , co mmunity
co mposition, phenolo g y , di stribution an d m igration of freshwater species (high confidence).
4(j) U.S. changes in physical and biological systems
Many of th e global chang es in phy sical and biolog i cal sy stem s mentioned in 4(h) broadl y appl y to the U.S. So m e U.S.-specific changes in these sy ste m s cited in IP CC’ s Fourth Ass ess mentReport ar e described in t h is subsectio n, as well as i n section 11(a) for phy sical sy ste m s r e la ted to wat e r r esources and section 14(a) related to biological sy ste m s. Of all the observed c h anges to phy s ical sy stems ass es sed by IPCC (Rosen zweig et al., 2007) for No rth America (tot aling 355 ), 94% of th em were consistent with changes one would expect with average warm ing. Sim ilar consistency was found between observed biolog ical sy s tem changes and warm ing for North America (see discussion belo w under bios phere ).

Furtherm ore, a CCSP (2008e) asses s m e n t reported that cli m ate ch anges are ver y likely alrea d y affecting U.S. waterresources, agri culture, land resources, a nd biodiversity as a result of cli m at e variability and change. It f o und, “The num b er a nd frequenc y of for est fires and insect outbreaks are increasing in th e interior West, the Southwest, and Alaska. Precip itation, streamflow, and strea m t e mp era tures are increasing in m o st of the continental U n ited States. The western United States is experienci ng reduced snowpack and earlier pea k s in spring runoff. The gr owth of m a ny crops and weeds is bein g stimulated. Migration of plant and animal speci es i s changing th e co mposition and structu r e of arid, po lar, aquatic, coastal, and other ecosy stems” (Backlund et al., 20 08 a)
Additional findings from this CCSP assessment al ong with results presented in IPCC’s Fourth Asse ss ment Report are described below.
Cryosphere ( Snow and Ice)



### 34

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

In North America, fro m 1 915 to 200 4, snow covere d area increased in Novem b er, Decem ber and January due to increases in preci pitation. However, snow c over decre ased during the latter half of the 20th century , especially during the spring over west ern No rth Am erica (Lemke et al., 20 07). Shi f ts towards earlier melt b y ab out eigh t day s since th e m id-1960s were also observed in north ern Alaska (Lemke et al., 2007). Consistent with these findings, Letten m ai er et al. (2008) note a trend toward reduced m ountain snowpack, and earlier spring snowmelt runoff peaks across mu ch of the western U.S.
The IPCC (Lemke et al., 2 007) cites a stud y docum enting glacier mass balance loss in the n o rthwest U.S. and Alaska, with losses especially rapid in Alaska aft e r the m id-1990s. Rosenzweig et al. (2007) refer to a study documenting evidence of present crustal uplift in response to recent glacier melting in Alaska.
Hydrosphere

Letten m ai er et al. (2008) docum ent i n creases in U. S. streamflow during the second half of the 20th century consistent with increase s in prec ipitation described in 4(e).
Rosenzweig et al. (2007) indicate surface water temper atures hav e warmed by 0.2 to 2°C in lakes and rivers in North Am erica since the 1960s. They also discuss eviden ce for an earlier occurren ce of spring peak river flows and an increas e in wi nter base flo w in basins with i mportant seasonal s now cover in North A m eric a. Biosphere
The IPCC (Rosenzweig et al., 2007) assessed a mu ltitude of studies that find ch anges in terrestrial ecosy stem s and m a rine and freshwater sy stems in North Am erica. Of 455 biolo g ical observations
asse ssed fro m these studies, 92% were co nsistent with the changes expected due to average wa r m ing.
Backlund et al. (200 8a) fin d :

• There has been a significant lengthening of th e growing season and increa se in net primary productivi t y (NPP) in the higher latitu d es of North Am erica. Over the last 19 y ears, gl o b al satellite data i ndicate an earlier onset of spring acr oss the temp erat e latitudes by 10 to 14 da y s

.

• In an analy s i s of 866 peer-reviewed p a pers e xploring the ecological consequences of cli m at e change, nearly 60 percent of the 1598 species studie d exhibi ted s h ifts in th eir distributio ns and/or phenolo g ies o v er the 20- an d 14 0- y ear time frame.

• Subtropical and tropical corals in shall o w wate r s ha ve already suffered major bleaching events that are clearl y driven by incr eas es in se a surface te mp eratures.
In addition, Ry an et al. (2008) note, “Clim a te chan ge has very l ikely i n creased the size and num ber of forest fires, insect outbreaks, and tree mortality in the interior west, the Southwe s t, and Alaska.”
4(k) Global extreme event s
Cli m ate is de fined not simply as averag e te mp eratur e and precipitation but also b y the t y pe , frequency and intensit y of extreme events. The IPCC documents observed changes in climate extre m e s related to te mp erature, precipitation, tropical c y clones, and sea le vel. The c h anges described apply ge nerally to all parts of the globe, inclu d ing the U.S., althoug h th ere are so m e regional an d local exceptions d u e to patterns of natural cli m ate variability

. Current obser vations are su mmarized here, projected trends are



### 35

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

covered in Section 6, and the sectoral i mpacts of these changes are covered a s relevant in Sections 7 to 15.
Temperature Widespread c h anges in extre m e t e mp er a t ures have be en observed in the last 50 y ears. Cold day s , cold nights, and fr ost have become less frequent, while hot day s , ho t nig h ts, and heat waves have beco m e m o re frequent (IPCC, 2007d). A widespread reduction in the num ber of frost day s in m id-latitude regions, an increase in the num ber of war m extre m es and a re duc tion in the num ber of daily cold extre m es ar e observed in 70 to 75% of the land regions where data ar e available

. The m o st marked change s ar e for cold (lowest 10%, based on 1961–1990) nights, which hav e beco me r a r e r over the 1951 to 2003 period. War m (highest 10% ) nights have beco m e m o re frequent.
Precipitation and Storms
It is likely that there have been increase s in the num ber of heavy precipitation events 19 within many la nd regions, even in those wh ere there has been a reduc tion in total precipitation am ount, consistent with a
warm ing climate and observed significant increasi ng am ounts of water vapor in the atm o sphere. Increas es have also been reported for rarer precipitation events (1 i n 50 y ear retu rn period), bu t onl y a few regions have sufficient data to asses s su ch tr ends reliably (Trenberth et al., 2007).

More intense and longer dr oughts have been observed over wider ar eas since the 1970s, partic ularly i n the tropics and subtropics (IPCC, 2007d). Increased dry i ng lin ked with higher temp eratures and decreased precipitation has contribut ed to changes in dro ught (I PCC, 2007 d).
The CCSP (2 008i) report on extrem e events, in its sec tion on tropical cy clones (i.e. tropical storm s and hurricanes), s t ates that ther e have been s p atially i nho m ogeneous increases in the power dissipation in dex , a m e asure of potential tropical cy clone d estructiveness, over the last few de ca des (Kunkel et al., 2008). However, there remain reliabilit y issu es with historical data. Kunkel et al. (2008) refer to a study that was not able to corroborate the presence of u p ward intensity trends over the last tw o decades in o cean basins other than th e North Atlantic. The report cautions th at quantif y i ng tropical cy clone variabilit y is lim ited,
so m e ti mes se riously , by a large suite of problem s wi th the historical re cord of tropical cy clone activity

. Correspondin g l y , there is n o clear trend in the annual num bers of tropical cy clo n es (IPCC, 2007d).
High Sea Level
Apart fro m non-climatic events such as tsunam i s, ex trem e sea levels o ccur mainl y in the form of storm surges genera ted by tropica l or extra-tropical cy clone s. There is e v idence for an increase in extre m e high sea level since 1975 based upon an analy s is of 99 th percentiles of hourl y sea level at 141 stations over the globe (Bind o f f et al., 200 7).
4(l) U.S. extreme events
Many of the global changes in extre m e events m e ntione d in 4(j) b r oadl y appl y to the U.S. Additionall y , the U.S. CCSP (2008i) p ublished a report that focused on changing clim ate extrem es in the U.S. and North Am erica. It conclud e d (Karl et al., 200 8 in CC SP, 200 8i):
Many extremes and their associated i mp acts ar e now changing. For exa mple, in recent decad es m o st of North America has been experiencing m o re unus ually h o t da ys and nights, fewer unusually col d

19 Heav y precip i tatio n even ts refer t o tho s e in t h e 9 5 th pe rcent i l e of preci pi t a t i on e v e n t s

.



### 36

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

day s and nig h ts, and fewer frost day s

. Heavy dow n pours have b eco m e more frequent and intense. Droughts are becom ing more severe in some regions, thoug h the r e are no clear trends for North A m eri ca as a whole. The power and frequency of A tlantic hurricanes have inc reased substa ntially in recent decades, though North Am erican mainland land-falling hurricanes do not appear to have increased over the past c e ntury

. Outside the tropi c s , stor m trac ks are shifting northward and the strongest storms ar e beco ming even stronger.
Many of thes e changes we re also ass ess ed in IPCC’ s Fourth Assessm ent Report and are described in th is subsection.
Temperature
The IPCC (T renberth et al ., 2007) cites North A m eri ca regional studies that all show patterns of changes in temp erature extrem es consistent with a general warm ing. Karl et al. (20 08) fin d th e num ber of heat waves (extended periods o f extremely h o t weather) h as been incr e asing over the past 50 y ears but note the heat waves of the 1930s remain the m o s t severe in the U.S. historical record.

Extrem e cold has been decreasing. Tr enberth et al

. , 2007 cite a study finding intense war m ing of the lowest daily mini mu m te mp eratures o v er western and central North Ameri ca. Trenberth et al. (2007) caution the observed changes of the tails of the temp er ature distributions are often m o re co mplicated than a simp le shift of the entire distributio n would sugges t. Karl et al. (2008) note, “The last 10 y ears [ 1998­ 2007] have seen fewer sev ere cold sn aps than for an y other 10- y e ar period in th e historical record, which dates back to 1895.” Karl et al. al so indicate a decrease in frost day s and a leng thening of the frost-free season over the past century.
Precipitation and Storms
In the contig uous U.S., Trenberth et al. (2007) cite studies findin g statistically significant increases in heavy precipi tation (the heaviest 5 % ) and very heav y precipitation (the heaviest 1% ) of 1 4 and 20% , respectively

. Much of this increase oc curred during the last three d ecades of the 20th century and is m o s t apparent over the east ern parts of the co untry . There is also evide n ce fro m Eur ope and the U.S. that the relative increase in precipi tation extr e m es is largert h an the incre ase in mean precipitation (Trenberth et al., 200 7).

Letten m eir et al. (2008) fi nd, “With respect to dr ought, consistent with stre amflow and precipitation observations, m o st of the continental United Stat es experienced reductions in dr oug ht severity and duration over the 20th centur y . Howe ver, there is so m e indication of i n creased droug ht s e verity an d duration i n th e western and southwestern United States....”

Dim i nishing snow pack and subsequent reductions in soil m o isture appear to be factors in recent droug ht conditions in the western U.S. (Trenberth et al., 2007). This drought has also been attributed to changes in at m o spheri c cir c ulation associat ed wi th war m ing o f the w estern tropical Paci fic and India n oceans as well as mu lti decadal fluct u ations (Trenberth et al., 2007).
Karl et al. (2008) i ndicate a northward shift in the tr acks of strong low-pressure sy stems (al s o known as mid-latitude storm s and/or extratropical cy clones) in both the Nor th Atlantic and North Pacific over th e past fifty y e ars with increases in stor m intensity noted in the Pacific (data inconclu sive in the Atlantic). Correspondin g l y , the y also find northward shift in snow storm occurrence, which is also consistent with the war m ing te mp erature s a nd a decrease in snow cove r extent over the U.S.



### 37

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

IPCC (2007d) reports ther e is observat ional evidence fo r an incr ease in intense tropical cy clone (i.e. tropical storms and/or hurricanes) a c tivity in the N o rt h Atlantic (where cy clones develop that affect the U.S. East and Gulf Coasts) since about 1970, correlated with increases of tropical sea surface temp eratures. Sim ilarly , Kunkel et al. (2008) con c lude (for the North Atlantic): “There have been fluctuations in the num b erof tropical storms a nd hurricanes fro m decade to decad e, and data uncertainty is larger in the early part of the record comp ar ed to the satellite er a beginning in 1965. Even taking these factors into account, it i s likely that the annual num bers of tropical storms, hurricanes, and m a jo r hurricanes in the North Atlantic have increas ed over the past 100 y ears, a time in which Atlantic sea surface te mpe ratures also i n creas ed.”
High Sea Level
Studies of the longest records of extre m es in sea l e ve l are restr icted to a s m all num berof locations. Consistent with global changes, U.S.-based studi es docum ent i n creas es in e x tre m e s ea l e vel closely following the rise in mean sea level (Bin doff et al., 2007).



### 38

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 5

Attribution of Observed Climate Ch ange to Anthropogenic Greenhouse Gas Emissions at the Global and Continental S cale

This section addresse s the extent to w h ich observed clim at e change at the global and c ontinental or national scal e (desc ribed in Section 4) can be attri buted to glo bal anthropogenic e m i ssi ons of GHG s. Section 2 describes the share of the U.S. transportatio n sector to U.S. and global anthropogenic e m is sions of GHGs, and the resulta nt share of U.S. transportation e m issi ons to global increas es in at m o spheric concentrations of GHGs.
Evidence of the effect of anthropogen ic GHG emi ssions on the climate system , as well as climatesensitive sy stem s and sect ors, has incr eased over the last 15 y ears or so and even since the previous IPCC assessment published in 2001. The evi d ence in the recent IPCC Fourth Assessment Report (2007) is based on an aly ses of global- and continental-scal e te mp eratur e incre ase s, changes in o t her cli m ate variables and phy s ical and biological syste m s, and the radiative forcing caused by anthropogenic versus natural factors.
5(a) Attribution of observed climate chan ge to anthropogenic emis sions

Co mputer-based cli m at e m odel s are the primary tools used for simu l a ting the likel y patterns of response of the clim ate sy stem to d ifferent forcing m echanis ms (both natu ral and anth ropogenic). Confidence i n these m odel s co m e s fro m their foundation in accepted phy s ical principles and from thei r ability t o reproduce observed features of current climate and p ast cli m ate changes (IPCC, 2007a). F o r additional discussion on the strengths and lim it ations of m o dels , see S e c tion 6(b). Attribution studies evaluat e whether observed changes are consi s tent with quantitative r esponses to different forcings (from greenhouse gases, aerosols and natural forcings such as changes so lar intensity ) represented i n well-test ed
m odels, and are not consistent with alternative phy s ic ally plausible explanations.

Studies to de tect cli m ate c h ange and attribute its causes using patterns of observed temp e ra ture change show clear evidence of human influences on the cli m ate sy stem (Karl et al., 2 006). Discer nible human influences extend to additional aspects of cli m ate including ocean war m ing, continental-average te mp erature s , te mp erature extre m e s and wind patterns (Hegerl et al. , 2007).
Temperature

IPCC st atements on the li nkage between greenhouse gases and temp eratures have strengthened since it s early assessments (Solom o n et al., 2007). The IPCC’ s First Assessm ent Report in 1990 contained little observational evidence of a detectable anthropo geni c influence o n clim ate (IPCC, 1990). In its Second Assessment Report in 1995, it stated the balance of evidence suggests a discernible human influence on the cli m ate of the 20th centu r y (IPCC, 1996). The Th ird Assessment Report in 2001 concluded that m o st of the observed war m ing over the last 50 y ears is like ly to have been due to the increase i n greenhouse gas concentrations (IPCC, 2001b). The conclusion i n IPCC’ s 2007 Fourth Assessm ent Report (2007b) is the strongest y e t: Most of the observed increase in global average temperatures since the mid-20th century is ver y likely 20 due to t h e observed increase in anthropogenic greenhouse gas concentrations.

20 Acco rd ing t o IPCC term in o l o g y , “v ery lik el y” co nv eys a 90 to 99 % prob ab ility o f o ccurren ce. See B ox 1

. 3 on page 5 f o r

a ful l descri pt i o n of IPC C ’ s u n ce rt ai nt y t e rm s.



### 39

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The increased confidence in the greenhouse gas contributi on to the observed warm ing results fro m (Hegerl. et al. , 2007):

• an expanded and improved range of observations allowing attribution of warming to be m o re fully addressed jointly with othe r ch anges in the cli m ate syste m

• i mprovem e nt s in the simulation of many aspects of present mean cli m at e and its variability on seasonal to inter-decadal ti me s cale s

• m o r e detailed representatio ns of processes relat e d to aerosol and other forcings in m odels

• simu lations of 20th-centur y clim ate ch ange that u s e ma n y mo r e mo d e l s a n d mu c h mo r e c o mp l e t e anthropo geni c and natural forcings

• mu lti-m odel ensem b les th at increa se confidence in attribution r esults by pr oviding an improved representatio n of m odel uncertainty

Clim ate m o d e l simu lation s run by the I PCC, shown in Figure 5.1, suggest natural forcings alone cannot explain the observed war m ing (for the globe, the gl obal land and global ocean). The obser ved war m ing can onl y be r e produced with m odels that cont ain bo th natural and anthrop ogenic forcings.

Figure 5.1: Comparison o f observ e d global-sc ale c hange s in surfac e tempe r ature w i th results simu lated b y climate models u s ing natur a l and anthrop ogenic for c ings.

Source: IPCC ( 200 7d). Deca dal av erag es o f observatio n s are sho w n for the per iod 190 6 to 2005 (bl a ck line) plotted ag ainst the ce ntre of the deca d e and re lativ e to the corresp o ndi ng av erag e for 1901 –1 950. Lin e s are d a sh ed w h ere sp ati a l cover age is l e ss than 5 0 %. Blue sh ad ed b ands sh o w the 5–9 5% ra nge for 19 simul a tio n s from five climate mode ls u s ing o n l ythe n a tural forci ngs due to sol a r ac tivit y a nd volca noes. Re d shad ed b a n d s sho w the 5

– 9 5 % ran ge for 5 8 simul a tions fr om 14 clim ate mode ls usin g both nat ural a n d anthro p o gen i c forcings.
Additional evidence documented in the IPCC report s upports its statement linking war m ing to increasing concentrations of greenhou se gases (Heg erl et al., 200 7):

• War m ing of the cli m at e sy ste m ha s bee n detected in changes of surface and at mospheric te mperatures in the upper several hundred m e ter s of the ocean, a nd in contributions to sea level rise. Att r ibution studies have established a n thropogenic contributions to all of these changes.



### 40

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Analy ses of paleocli mate d a ta have incre ased confid ence in the role of external influences on cl i m ate. Coupled climate m odels u sed to predict future clim ate have been used to repro duce key features of past clim ates using b oun dary co nditi ons a nd radiative forcing for th ose periods.

The IPCC sta t es that it is very unlikely that the globa l pattern of warm ing observed during the past half century is du e to onl y kn own natural external caus es (solaracti v ity and volc a noes) since the war m ing occurred in both the atm o sphere and ocean and took place when natural external forcing factors would likel y have p r oduced cool ing (Hegerl et al., 2007)

. It also states greenhouse gas forcing alone would likel y have resulted in warm ing greater than observed if there had not been an offsetting cooling effect from aerosols and natural forcings dur ing the past half century (Hegerl et al. , 2007). Solom on et al. (2007) indica te the sum of solar and v o l canic forcing in the past half centur y wo uld li kel y hav e produced cooling, not warm ing. Figure 5.2: Comparison o f observ e d North Am eric an chang es in surfa ce temperature w i th results si mulated b y c limate models using Not onl y has an natur a l and anthr opoge n i c forcings. anthropo geni c signal been detected forthe surfa c e te mp erature s , but evidence has also accumu l a ted of an anthropo geni c influence throug h the vertical profile of the at m o sphere. Fingerprint s tudies 21 have identified gr eenhouse gas and sulfate a e rosol signals in observed surfac e te mp erature records, a stratospheric ozone depletion signal in
s tra tos phe ric te mp era t ures , and the com b ined effects of these forc ing agents in the vertical structure of at m o spheric te mp er ature changes (Kar l et al., 2006). However, an important inconsistency m a y hav e been identified in the Source: He gerl et al. (2007). Deca dal av er a ges of obs erva tions are sh o w n for the peri od 19 06 to 200 5 (black l i n e ) plotted a g a i nst the centre of the deca de and relativ e to the corresp ond in g a v erag e for 190 1–1 95 0. Lines are das he d w h ere tropics. In the tropics, m o st observational data sets spatia l covera g e is less than 5 0 %. Blue sh ad ed ba nds sh o wthe 5–9 5% ran ge for show m o re warm ing at the 19 simu latio n s from five climate mode ls usin g onl y the n a tur a l forcin gs du e to solar surface than in the activit y a nd vo l c ano es. Red s had ed b ands s h o w the 5

– 9 5 % rang e for 58 simulati ons fro m 14 climate m ode ls usin g bot h natura l an d a n throp o g enic f o rcin gs. troposphere, while alm o st all m odel simu lations have larger war m i ng aloft than at the surfa c e

. A possibl e explanation for this inconsistency is error in the observations, but the issue i s still under i nvestigation ( K arl et al., 2006).

21 Fi n g er pri n t st

udi es use ri go r ous st at i s t i cal m e thods t o c o m p are th e pat t erns o f o b ser v e d t e m p erature chan ges wi th
m odel expect at i ons an d det e r m i n e whet her or n o t si m i l a ri ti es co ul d ha ve occu rre d by c h ance. Li neartr end
com p ari s on s ar e l e ss p o w er ful th an fi nge rp ri nt anal y s es f o r study i n g cause

- ef fect rel a t i o n s hi ps , but ca n hi g h l i ght i m p o r tan t d i fferen ces and similarities b e tween m o d e ls an d ob serv ation s (as in Fi g u res 5

. 1 an d 5.2).



### 41

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The substantial anthropogenic contribution to surf ace t e mp er at ure increas es likely applies to every continent except Antarctica (which h as insufficient observational coverage to make an ass e s s m ent) since the m iddle of the 20 th centur y (Hegerl. et al., 2007 ). Figure 5. 2 indicates North Am erica’s observed te mp erature s over the las t century can only be re produced usi ng m odel simu lations containing b o th natural and anthrop ogenic forcings. In the CCSP (2008g) rep o rt “Reanaly s is of Historical Clim ate Data for Key Atm o spheric Features: I mplica tions for Attri bution of Causes of Obse rved Change ”, Dole et al. (2008) find th at for North Am erica “more than half of this warm ing [ f or the p e riod 19 51-2 006] is likely the result of h u man-caused greenhouse g as forcing of clim ate change.”

Difficulties rem a in in attri buting temp erature change s on s m aller than continental sc ales and over ti m e scale s of les s than 50 y e ars. Attribution at these scale s , with lim it ed exce ptions, has not y e t been established (Hegerl et al., 2007).

Temp erature extrem es have also likely been influe nced b y anthro pogenic forci ng. Man y in dicators of cli m at e extre m es, including the annual num bers of f r ost da y s , warm and cold day s , an d warm and cold nights, show changes that are consistent with warm in g (Hegerl et al., 2007). An anthropo genic influence has been detected in so me of these indices, and th ere is eviden ce that anthropogenic for c ing may ha ve substantially increased the risk of extr em ely wa r msu mm er conditions regionall y , such as the 2003 European he at wave (Hegerl et al., 2 007). Karl et al. (200 8) conclude the i n crease in h u man-induced
e m is sions of GHG s is esti m ated to hav e substantiall y increased the risk of a very hot y ear in the U.S., such as that experienced in 2006

. They add thatother aspects of observed increases in temp erature extre m e s , suc h as changes in war m nights and frostday s , have been linked to human influences.

Additional Cl imate Variabl es
There is evidence of anthropogenic infl uence in othe r parts of the climate sy stem

. The IPCC noted the following exa mpl es (H eger l et al., 2007):

• Trends over recent decades in the No rthern and Southern Annular Modes 22 , which correspond to sea level pressur e reductions over the pole s , are likely rela ted in part to hum an ac tivity , affecting storm tracks, winds and temp erature pattern s in both hemispheres. Models reproduce the sign of the Northern Annular Mode tr end, but the s i mu lated r esp onse is sm aller than observed. Models i n cluding both greenho use gas and stratospheric ozone chang es simu lat e a realistic trend in the Souther n Annular Mod e , leading to a detectable h u man influen ce on global s ea level pressure patterns.

It is m o re lik ely than not that an thropogenic influence has contributed to increa ses in the frequenc y of the
m o st intense tropical cy clo n es. Gutowski et al. (200 8), as cited in the CCSP (2008i) report , l ikewise find evidence suggesting a human contribution to recent hurricane a c tivity

. However, they caution that a confident assessment of human influence on hurrica n es will require further studies using m odel s and observations, with emphasis on disting u ishing natura l from hu man-induced cha nges in hurricane a c tivity through their influence on factors such as historical sea surface te mp eratures, win d shear, and at m o spheric vertical stabil ity.

• The latitudinal pattern of change in land preci pitation and observed increases i n heavy precipitation over the 20th century ap pear to be consist e nt with the anticipated response to anth ropogenic for c ing.

22 A n n u l a r m odes are p r efe rre d pat t e rns o f c h a nge i n at m o spheric circ ulation corres p onding to c h anges in t h e zonal l y av era g ed m i d-l a t i tude west erl y wi n d s . T h e No rthe r n An n u l a r M o de has a bi as t o th e No rth At l a nt i c an d has a larg e correlat i o n with t h e No rt h Atlan tic Oscillatio n (see fo o t n o t e 36 ). Th e Sou t h e rn An nu lar Mod e occu rs in t h e So ut he rn Hem i sph e re.



### 42

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Attributing c h anges in precipitation to anthropo genic forcing at continental or s m allersc ales is m o re challenging. Clark et al. (2 008) state that recent drought in the Southwest is consistent with projections of increasing subtropical aridity and recent trends in in creasing prec ipitation intensity are also consistent with projected trends. However, Clarket al. caution that there i s considerable natural variabilit y in the h y droclim ate in the South w est and conclude that: “The re is no clear evidence to date of hu man-induced global clim ate change on North Am erican precipitation am ounts.” Sim ilarly , K a rl et al. (200 8) find heavy precipitation events averag ed over North A m eri ca ha ve increas ed over the past 50 y ears at a rate higher than total precipitation increas ed, consistent with the observed increase s in at m o spheric water vapor, which have been associ ated with hum an -induced incr eases in greenhouse gases.
5(b) Attribution of observed changes in physical and biological systems
In addition to attributing the observed changes in a v erage global- and continental-scale te mp erature and other clim at e variables to anthropogenic GHG forc i ng, a sim ila r attribution can be made between anthropogenic GHG forci ng and observed changes in phy s ical sy stem s (e. g ., melting glaciers) and biological sy s te m s and spe c ies (e.g., geographic shift of species) w h ich are shown to change as a result o f recent war m i ng. This section includes the observed changes in phy s ic al and biological sy ste m s i n North Am e rica and in other parts of the world.
The IPCC (2007b) concluded that, “Observational evid ence from all continents and m o st oceans shows that many natural sy stems are being affect ed by regional climate changes, particularly te mp eratur e increases.” Furtherm ore, the IPCC states that, “A g lobal assessment of data since 1970 has shown it i s likel y that anthrop ogenic warm ing has had a discernible influ e nce on m a n y ph y s ical and biol ogical sy stems.” As detailed above in Section 5(a), recent wa r m ing of the last 50 y e ars is very likely the result of the accu mulation of anthropogenic GHGs in the atm o sphere.

Cli m ate vari abilit y and non-climate drivers (e.g., la nd-use change, habitat frag m entation) need to be considered in order to make r obust conclusions about the role of anthropogenic climate change in affecting biological and ph y s ical sy stems. IPCC (Rosenzweig et al. 2007) reviewed a num b e r of joint attribution studies that linked responses in some physical and biological sy stems directly to a n thropogenic cli m at e chan ge using climate, process, and statistical m odels. Th e conclusion of these studies is that “the consistency o f observed significant changes in phy s ical and biological sy ste m s and observed significant
war m ing acr oss the globe likely cannot be explained entirel y due to natu ral variability or other confoun ding non-clim ate factors (Rosen zweig et al. 2007).”
The ph y s ical sy stem s undergoing sig n ificant change include the cry o spher e (snow and ice sy stem s), hy drological sy stems, wat e r resources, coastal zones and the ocea ns . These effects (reporte d with high confidence by IPCC (Rosenzweig et al. 2007) incl ude ground i n stabilit y in m ountain and perm afrost regions, shorter travel seas on for vehicles over frozen roads in the Arctic, enlarge m ent and increase of glacial lakes in m ountain regions and destabiliza tion of m o raines d a mm ing these lakes, chan ges in Arcti c flora and fauna including the sea-ice biom e s and predators higher in th e fo od chain, li mitations on
m ountain sports in lower-elevation alpin e areas, and changes in ind igenous liveli hoods i n the Arctic.
Regarding bi ological sy ste m s, the IPCC (Rosenzweig et al. 2007) r e ports with very hi gh conf idence that the overwhelming majority of studies of regional c limate eff ect s on terrestrial species r e veal trends consistent with warm ing, in cluding p o leward and elevationa l range shifts of flora and fauna, the earlier onset of spring events, m igration, and le ngthening of the growing season, changes in abundance of certain species, incl uding lim ite d evidence of a few local disappearance s, and changes in community
co mposition.



### 43

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Hu m a n sy stem r esponses t o climate cha nge are m o re diffi cult to identify and isolate due to the larger role that non-climate factors p lay (e.g. , m a nagem e nt pr actices in agriculture and forestry , an d adaptation responses to protect hum an health against adverse cl i m atic conditions) (Rosenzweig et al., 2007).



### 44

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 6
Projected Future Gre e nhouse Gas Conc entrations and Climate Change
According to the IPCC (2 007d), “conti nued greenho use gas emissions at or above current rates would cause further war m ing and induce many changes in the global cli m ate sy ste m during the 21st century that would ver y likely 23 be large r than those observed during the 20th century .” This section descri b es future GHG e m i ssion scenarios, t h e associ ated changes in at m o s pheric co ncentrations and radiative forcing, and the resultant changes in temp erature, precipitation a nd sea level at global and U.S. scales. Scenarios are story lines regarding possible futures. These story lines ar e desig n ed to be internally consistent in their
assu mp tions regarding population a nd econom i c growth, implementation of pol icies, technol ogy change and adoptio n, and other factors that will influence em issions. Scen arios are not projections of the future, but are used to illustrate how the future m ight l ook if a given set of events occurred and policies i mple m ented. All future G HG e m is sion scena rios de scr ibed in this se ction assu me no new e xplicit GH G mitigation policies -- ne ither in th e U.S. nor in other countri es -- beyond those which were alread y enacted at th e ti m e the sc enarios wer e developed. Future risks and impa cts associat ed wi th the cli m at e change projections are addressed in Part IV for dom e s tic i mpacts an d Part V for international imp acts.
6(a) Global emiss ion scenarios and associated changes in concentrat ions and radiative forcing

Greenhouse Gas Emissions

As described in Section 4(a), a num b e r of different GHGs and other factors, including aerosols, cause radiative forcing changes and thus contribute to c limate change. This se ction discusse s th e range of published global reference (or baseline) future em i ssi on projections for which no explicit GHG m itigation policies beyond those currently enacted are as su m e d.

The IPCC’ s m o st rec e nt future cli m ate change projections fro m the Fourth A sses s m ent Re port (2007) (discussed in Section 6(b) below) ar e b ased on the GH G e m is s ion scenarios fro m the IP CC Special Report on E m ission Scenarios (IPCC, 2000). Bo x 6.1 pro v ides backgroun d i n form ation on the differen t SRES em issi on scenarios. The SRES developed a range of long-term (out to the y ear 2100) global reference scenarios for the m a jor GHGs directly em it ted by hum an activities and for some a e rosols. The IPCC SRES scenarios do not explicitl y account for i mplem entati on of th e Kyoto Prot ocol. Figure 6.1 presents the global IPCC SRES projections for the two m o st significant anthropogenic GHG s: CO 2 em issions primarily from the burni ng of fossil fuels, and CH 4 em issions.
Figure 6.1 O bserv e d, and Projected Global CO 2 a nd CH 4 Emissions for the IPCC SRES Scenarios

23 Acco rd ing t o IPCC term in o l o g y , “v ery lik el y” co nv eys a 90 to 99 % prob ab ility o f o ccurren ce. See B ox 1

. 3 on page 5 f o r

a ful l descri pt i o n of IPC C ’ s u n ce rt ai nt y t e rm s.



### 45

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Source: Mee h l et al. (2007). Projecte d fossil CO 2 and CH 4 emissio n s for six i llustrativ e S R ES non-m i tig a tion emissio n scen a rios. Historic a l emissi ons (b lack lin es) are sho w n for fossi l and i n d u strial CO 2 , and for CH 4 .

Box 6.1: I P CC Referen c e Cas e Emis s i on S cen arios from th e S p ecial Rep o rt on Emis s i on S cen arios

A1. The A1 story l ine and scenario family d e scr i bes a future wo rld of ver y r a pid economic gro w th, global pop ulation that peaks in mid-centur y and declines thereafter , and the rapi d introduction of new and more efficient technolog ies. Major underly i ng themes are conv ergen ce among reg i ons, capacity bu ilding andincr eased cultural an d social inter a ctions, with a substantial redu ction in region al differ e nc es in per cap ita inco me. The A1 scenario family d e velops into three groups that describe altern ative dire ctions of technological change in th e energ y s y stem. The three A1 group s are d i stinguish ed b y their techno logical emphasis: fossil intensive (A 1FI), non fossil energ y sources (A1T) , or a balan ce acr o ss all sources (A1B) (where balan ced is defined as not rely ing too h eavil y o n one particul ar energ y s our ce, o n the assump tion that sim ilar improvem e nt rates apply to all energ y suppl y and end use techn ologies).

A2. The A2 stor y l ine and scenar io family describes a v e r y he ter ogeneous world. The underly i ng theme is self r e lian ce and preservation of local iden tities. F e rtility p a tterns across regions co nverge v e r y slo w ly , which results in con tinuously incr eas ing population

. Eco nomic development is primar ily r e gionally orien t ed and per cap ita ec onomic growth and techno logical ch ange more fragmented and slower th an other story lin es.
B1. The B1 s t or yl ine and s cen ar io fam i l y d e s c ri bes a conv ergen t world with the sam e global po pulation , th at p e aks in m i dcentur y and declines th ereafter , as in the A1 sto r y l ine, but with rapid ch ange in economic structures toward a s e rvice and information eco nomy , with redu ctions in mater i al intensity and the introduction of clean and r e source effi cien t technolog ies. The emphasis is on glob al solu t i ons to econom i c , soc i al and en vironm ental sustainab ilit y, inc l u d ing improved equit y , but without addition al climate initiatives.

B2. The B2 s t or yl ine and s cen ar io fam i l y d e s c ri bes a world in which the emphasis is on loc a l solutions to e c o nom ic, soci al and environmen tal sustain a bility. It is a world with conti nuous ly in creasing global population , at a rate lower than A2, intermediate lev e ls of economic developmen t, and less rapid and more diverse technolog ical ch ange than in the B1 and A1
s t or y l ines

. W h il e th e s cen ario i s als o ori e ntedt o wards environ m ental pro t ec tio n and s o c i al eq uit y , it focus e s on loc a l and regional levels.

An illustrat i ve s cenar io was cho s en for each of the six s cen ario groups A1B, A1FI, A1T, A2, B1 and B2. All should be consideredequ a lly sound.

The SRES sc en arios do no t in cl ude add ition a l c lim ate ini tia tives , which m eans th at no scen arios are in cludedth at expli c it l y assume implementation of the United Nati ons Framework Convention on Clim ate Ch a nge or the emissions tar gets of th e Ky oto Protocol.

Box 6.2: CCSP (2007b) Reference Ca se Em ission Scenarios f r om Sy nt hesis a nd Assessme nt Product 2.1

The scenar ios in this report were deve loped u s ing three in teg r ated as s e s s m ent m odels (IAMs). Thes e m odel s integrat e socioeconomic and techno logical determinan ts of the emissions of GHGs with models of the na tu ral science of Earth s y stem response, in clud ing the atmosphere , o c eans, and terrestrial biosph er e. The thr ee I A Ms used are:

• The Integrated Global S y stems Model (IGSM) of the Ma ssachus etts Institute o f Techno log y ’s Joint Program on the Science and Policy of Global Change.
• The Model for Evalu a ting th e Regional and Global Eff ects (MERGE) of GHG re duction po licies develop e d jointl y a tStanfo r d Universit y andthe El ec tric Po wer Rese arch In stitute

.
• The MiniCAM Model of th e Joint Globa l Ch ange Re se arch Institute , a part nership betwe e n the Pa cifi c Northwest National Labor ator y and the Univer sity of Ma ry la nd. The MiniCAM mode l wa s a l so use d to genera te IP CC S R ES s cenar ios

. Each modeling g roup produceda referen c e scen ario under the a ssumption that no climate policies are imposed bey o nd curren t commitments, namely the 2008- 12 first period of the Ky oto Proto c ol and th e U.S. goal of reducing GHG e m issions per unit of its gross do m e stic product b y 18 % b y 2012. Th e resulting ref e re nce cas es are no t predic tions or best-judgm ent f o recasts but scenarios design ed to provid e clearly d e fined p o ints of depart u r e for stud ying the implic at ions of alte rnat ive s t abil iz ation goals. Th e modeling teams used model input assu mptions they considered meaningful and plausible

. The r e sultin g scenarios provide insights into how the world m i ght evolve without ad ditional efforts to constrain GH G em issions, gi ven various assumptions about princip a l dr ivers of these emissions su ch as population increase, econo mic growth, land and labor productivity gro w th, techno logical op tions, and r e source endowments.



### 46

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The main drivers of em issions are population, ec onom ic growth, technolo g i cal change, and land-use activities including deforestation. The detailed unde rly i ng assump tions (incl uding fi nal and prim ary energy by major fuel types) across al l scenarios, and across all m odeling teams that produced the scenarios, can be found i n IPCC (2000). The range of GHG em i ssi ons in the scenarios widen over time to reflect uncert a inties in the underl y i ng drivers. Sim i lar future GHG em i ssions can result from different socio-economic developments. The IPCC (2000) SR ES report did not assign probabi lities or likelihood to the sc enari o s, as itw as stated that th ere i s no singl e m o st likely, central, or b est-guess sc e n ario, either with respect to SRES scenarios or to th e underl y ing scenario literature. This is why IPC C (2000) has
reco mmended using a range of SRES scenarios with a variety of underl y ing assu mp tions for use in analy s is.
Despite the range in future e m is si on scenarios, the majority of all referenc e- case s cenario s project an increase of G HG e m is sions acros s the c e ntury , and show that CO 2 rem a ins the dom inant GHG over the course of the 21 st centur y . Total cumul a tive (1990 t o 21 00) CO 2 e m issions a c ross the SRES scenario s range from 2 ,826 gigaton n es of CO 2 (GtCO 2 ) (or 770 GtC) to approxim a tely 9,32 2 GtCO 2 (or 2,54 0 GtC). 24

Since the IP CC SRES (2000), new scenario s in the literature have emerged. The emission scenario range fro m the re cent literature is si milar to the range from the IP CC SRES. The IPCC (2007 c) reported that baseline annual em ission scenarios published since SRES are co mp arable in range to those presented in the SRES scenarios (25 to 135 GtCO2eq. per y ear in 2100). Studies since SRES used lower v a lues for so m e driv ers for emissi ons, notabl y pop u lation pro jections. However, f o r those studies incorporating these new populati o n proj ections, changes in other drivers, such
as econo m ic growth, resulted in little change in overall
em ission levels (IPCC, 200 7c).

For co mp arison, Figure 6. 2 provides gl obal projections of CO 2 emissions fro m the burning of fossil fuels and industrial sources fro m the three r e ference-case scenarios developed by th e U.S. Cli m ate Change Science Program (CCSP, 2007 b). Bo x 6.2 pr ovid es background inform ation on th e reference case scenarios developed by the CCSP. The CCSP scenari o s, because they were developed m o re recently than the IPCC SRES scenarios, do account for the implementa tion of the Ky ot o Protocol for participating countries, but no explicit GHG m itigation policies be yond th e K y ot o Protocol

. T h e em issions in 2100 are approxim a tely 8 8 GtCO 2 (24 GtC). This level of emissions is abo v e the post-SRES IPCC median of 60 GtCO 2 (16 GtC), but well within the 90 th percentile of the IPCC range.

24 1 Gig a t o nn e (Gt) = 1 b illio n metric to n s

. Figure 6.2: Projecte d Global Emissions of CO 2 fr om Fossil Fuels and Indus trial Sources a c ross CCSP Referen ce S cenarios

Source: CCSP (200 7b). Glob a l emissio n s of CO 2 from fossil fuel combustion and oth e r in du strial sourc e s, mainl y c e ment prod uction, i n c r ease ov er the centur y in a ll th ree refere nce s c enar ios. B y 2 100 em issio n s reach 2 2 .5 GtC/y r 24.0 GtC/y r.



### 47

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.3 ill ustrates reference case emission projections for CO 2 , CH 4 , N 2 O, a nd the fluorinated gase s in aggregate (H FCs, PFCs, a nd SF 6 or “F-gases” ). The e m is sions projections in Figure 6.3 are from the 21 st Study of Stanford Universi ty’s E n ergy Modeling F o ru m on mu ltigas m itigation as referenced by Fisher et al. (2007). Eighteen m odels participated in the EM F-21 stud y and the emission s ranges in Figure 6.3 are representativ e of the literature. The broad ranges of EMF-21 em issions p rojections in Figure 6.3, especially for N 2 O and the F-gases, illustrate the uncertainties in projecting these future em issi ons, which is generally c onsistent with the range fo und i n SRES. Modeling gro ups have dev e loped a mu lt iplicity of projections for the concentrati ons of aerosol species. Within the IPCC process, a ll the SR ES scenarios spec ified sulfate e m issions. The inclusion, magnitude and temporal evolutio n of other forcing agents such as nitrates and carbonaceous aerosols wer e left to the discretion of th e indivi dual m odeling groups. There are still large uncertainties associated with current inventories of BC and OC, the ad hoc scaling m e thods u sed to pro duce future emissions, and considerable variation am o ng estimates of the optical properties of carbonaceous aerosols. Given these uncertainties, future projections of forcin g b y BC and OC are quite dependent on the m odel an d em issions assu mp tions (Meehl et al., 2009). Sim ilarly, CCSP (2 008d) co nclu ded that one of the m o st important uncertainties in characte rizing the potential cli m ate i mp act of aeros ols is the projection of their future em i ssio n s.



### 48

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.3: EMF-21 a nd IPCC Global Emissions Projection s fo r CO 2 , CH 4 , N 2 O, and th e Fluorinate d Gase s

Source: CCSP (200 7b). Deve lopm ent of bas elin e emiss i on s in EMF

- 21 scenar ios dev el o ped b y a numb e r of diffe rent mode lin g teams (left) and a comparis on bet w e en EMF

- 21 an d SRES scenar ios (rig h t ).



### 49

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

For comp arison, Fig u re 6. 4 Figure 6.4 Projecte d Global CH 4 an d N 2 O Emissions acros s three provides the global CH 4 CCSP Refe r e nce Scen ar ios and N 2 O pro j ections fro m the three U.S. CCSP referenc e-ca s e s cenario s (CCSP, 2007 b).

Future Concentration and Radiative Forc ing Changes
Figure 6.5 sh ows the latest IPCC projec ted increas e s in at m o spheric CO 2 , CH 4 and N 2 O concentrations for the SRES scenarios, and Source: CCSP (200 7b). Glob al anthr op oge n i c emissio n s of CH 4 and N 2 O var y Figure 6.6 shows the associat ed ra diative forcing for these CO 2 scenarios. I n w i de l y amo ng the refere nce s c enar ios. T here is uncerta int y in year 20 00 C H 4 emissio n s, w i th MIT ’ s IGSM re ference sce nar io ascri b in g mo re of the emissi ons to huma n activit y and l e ss to nat ural so urces. Differenc es in scenar ios refle c t, to a larg e e x tent, di fferent assump tions ab out w h ether curre nt emissions rat e s w i ll b e general, reference reduc ed sig n ifi c antl yfor other reasons, fo r e x am pl e, w h eth e r hig her n a tur a l gas concentrations of CO 2 and prices w i ll stim ulate ca pture o f CH 4 for use as a fuel. other GHGs are projecte d to increase

. Concentrations of long-lived gases increase eve n for those scenarios wh ere annual emissions toward the end o f th e century are assu m e d to be lower than current annual em i ssi ons. The C C SP scenario s show a si m i lar picture of how atm o sph e ric concentr ations of the main GHGs and total radiat ive forcing ch ange over time.

Carbon diox i d e is projected to be the largest contribut or to t o tal radiative forcing in all peri ods and the radiative forcing associat ed with CO 2 is projected to be th e f astest growing. The radia tive forcing associat ed wi th the non-CO 2 GHGs is still significant and growing over tim e.



### 50

### 51 Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.5 Projecte d Global CO 2 , CH 4 and N 2 O Conc entrati ons for the IPCC SRES S cenarios

Source: Mee h l et al. (2007). P r ojecte d fossil CO 2 , CH 4 , and N 2 O concentrat i ons for si x il lus t rative SRES n on-mitigation emissio n scen a rios as pr odu ced b ya simp l e climate mo de l tuned to 1 9 atmosph e re-oc e an ge ner al circ ulati ons mod e l s (AOGCMs).

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.6 Projecte d Ra diativ e Forcing from CO 2 for th e IPCC SRES Scena rios

Source: Mee h l et al. (2007 ). Proje c ted radiative forci ng from CO 2 for six illust rati ve SRES nonmitigation em issi on sce nari o s a s pro d u c ed by a simpl e climate mo del tuned to 1 9 AOGCM s

. The lighter shad e d area s de pict the chang e in this un certa inty range, if carbon cycle feedba cks a r e assume d to be lowe r or hi g her than in th e medium set t ing.
6(b) Projected ch anges in global tempera ture, precipi tation patterns, sea level rise, and ocean acidification
Using the e m issions s c e n arios descri b ed in Section 6(a), computer m odels project future changes i n te mp erature, precipitation and sea level at global and regional scale s

. According to the IPCC (Meehl at al., 200 7):
“[C ] onfidence in m odels comes fro m th eir phy s ical basis, and their skill in representing observed cli m at e and past climate changes. Models have proven t o be extremely important tools for simu lating and understandin g clim ate, and there is considerable c onfidence that they are ab le to pro v ide credible quantitative esti m ates of future climat e change, particul arly at larger scal es. Models continue to have significant limitations, such as in their representat ion of clouds, which lea d to uncertainties in the magnitude and tim ing, as well as regional details, of pr edicted climate change. Nevertheles s , over several decades of m odel develo pment, they have consiste ntl y pr ovided a robust and unam b iguous picture of significant climate war m in g in response to increasing greenhouse gases. ” 25

Confidence decre ase s in c h anges projected by global m odels at s m allerspatial sc ales. M a ny importan t
s m all- scal e process es cann o t be represented explicitly in m odels, and so mu st be included in approxim at e form as they interact wit h larger-scale features (R andall et al., 2007). Som e of the m o st challenging aspects of understanding and projecti ng regional clim ate changes relate to possible changes in the circulation of the atm o sphere and oceans, and thei r patterns of variabilit y (C hristensen et al., 2007). Nonetheless, the IPCC (2007d) concluded that recent advances in regional-scal e m odeling lead to higher confidence in projected pat terns of warming and oth e r regional-sc ale feature s , including changes in wind patterns, precipitation and so m e a s pects of extre m es a nd of ice.
The CCSP (2008c) repor t “Clim a te Models: An Assess ment of Strengths and Lim itations” finds th at
m odel s “have been ste a dily improving over the past several de cad es”, “show many consistent features in their simu lations and pr oj ections for the futur e”, and “are able to simu late the recorded 20 th Centur y global m e an te mp erature i n a plausible way

. ” How e ve r, it cautions that proj ections of precipitation in

25 A nu m b er of cli m a t e m o d els are d ev el o p e d an d run at acade m ic in stitu tio n s and g o v e rnmen t sup p o r ted research lab o rato ries in th e U.S. and o t h e r coun tries. Th e IPCC h elps coo r d i n ate m o d eling efforts to facilitate com p ariso n s acros s m odel s , and sy nt hesi zes res u l t s p u b l i s hed by seve ral m odel i ng t eam s.



### 52

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

so m e c a s es r e m a in “proble m ati c” (e spe c ially at the re gional scale) and that “uncertainties in the cli m ati c effects of m a nmade aerosols (liquid an d solid partic les suspende d in the at m o sphere) const itute a m a jor stu m bling block” in certain m odeling experi m e nts. It adds “uncertainties relat e d to clouds increase the difficult y in si mu lating the cli m ati c eff ects of aerosols, since these aerosols are known to interact with clouds and p o tentially can change cloud ra diative prop erties and cloud cover.”
Global Temp erature

The latestIP CC a sse ss me nt uses a larg er nu m b er of si mu lations a v ailable fro m a broader r a nge of m odel s to project futu re clim ate relative to earlier assess men ts (IPCC, 2007d). All of th e simu lations perform ed by the IPCC project war m i ng, for the full range of em i ssions scenari o s.
For the next t w o decades, a war m ing of about 0.2°C (0 .36°F) per decade is projected for a range of SRES
em ission scenarios (IPCC, 200 7d). E v en if the con cen trations of all greenhou se gases and aerosols had been kept constant at y ear 2000 levels (see the “Y ear 2000 Const a nt Concentrations” scenario in Figure 6.8), a further war m ing of about 0.1°C (0.18°F) per decade would be expected because of the time it takes for the cli m ate sy stem , particularly the oceans, to r each equilibrium (with y ear 2000 greenhouse gas levels). Through about 2030, the warming rate is mo stly insensitive to choices between the A2, A1B, or B1 scenarios, and is consistent with that observed for the past few decades. Pos s ib le future variations in natural forcings (e.g., a large volcanic eruption) co ul d change these values so mewhat (Meehl et al., 2007). Large changes in e m issio n s of short-lived gases coul d also have a nea r-ter m eff ect on te mp erature s , especially on the regional scale (CCSP, 2008d).
According to IPCC (see F igure 6.8), by m id-centur y (2046–2065), the choice of scenario beco m es m o re important for the magnitu de of the projected warmi ng, with average values of 1.3°C (2.3°F), 1.8°C (3.2°F) and 1.7°C (3.1°F) from the m odel s for scen arios B1 (low e m issio n s growth), A1B ( m ediu m em issions growth) and A 2 (hig h em issions growth) , respectively (Meehl et al., 2007). About a third of that war m ing is project ed to be due to cli m at e chan ge that is alre ady comm itt e d (as shown in the “Y ear 2000 Constant Concentrations” scenari o ). B y the 2090-2099 period (relative to the 1980- 1999 range) , projected war m ing varies s i gnificantly by em is sions s cenario. The full suite of SRES sc enari o s (given below) provi des a warm in g range of 1. 8°C to 4.0°C (3.2 °F to 7.2° F) with an uncertainty ran g e of 1.1°C to 6.4°C (2.0°F to 11.5°F). The mu lti-m odel aver ag e war m ing and associated uncertainty ranges for the 2090- 2099 pe riod (relative to 1980-1999) for each sce nario, as illustrated in Figure 6.8 are:

Scenario Average Glo bal Warm ing by End of Uncertainty Range Century Rel a tive to ~1990 B1 1.8°C (3.2°F) 1.1°C to 2. 9° C (2.0°F to 5

. 2°F) A1T 2.4°C (4.3°F) 1.4°C to 3. 8° C (2.5°F to 5

. 7°F) B2 2.4°C (4.3°F) 1.4°C to 3. 8° C (2.5°F to 5

. 7°F) A1B 2.8°C (5.0°F) 1.7°C to 4. 4° C (3.1°F to 7

. 9°F) A2 3.4°C (6.1°F) 2.0°C to 5. 4° C (3.6°F to 9

. 7°F) A1FI +4.0°C (+7.2°F) 2.4°C to 6. 4° C (4.3°F to 1 1 .5°F)
The wide range of uncertainty in th ese esti m a t e s reflects th e different assu mp tions about f u ture concentrations of greenhou se gases and aerosols in th e various scenarios considered by th e IPCC and the differing climate sensitivities of the various climate m odels used in the simu lations (NRC, 2001a; Meehl et al., 2007)

.



### 53

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.8 M ulti-Model Av erages and Ass ess ed Ranges for Su rfac e Warmi ng

Source: IPCC ( 200 7d). Soli d l i nes ar e multi- mode l gl o b a l a v erag es of surface w a rmi ng (r elativ e to 198 0 – 199 9) for the scenar ios A2, A1B and B 1 , sho w n as co nti n u a tions of the 2 0 th centur y sim u lati ons. Sha d i ng den otes the ±1 standard d e vi ation ra ng e of indivi du al mo de l ann ual avera ges. T he orang e lin e is for the exper iment w h ere conc entrati ons w e r e hel d constant at yea r2000 va lu es. T he gre y bars at right ind i cate the best estimate ( s olid l i n e w i thi n each bar) a nd the lik e l y r ang e assessed for the si x SRES m a rker scen a rio s

. T he assessment of the best estimate and l i k e l y r a n ges in th e gre ybars i n cl udes the AOGCMs in the left part of the figure, a s w e ll as res u lt s from a hierar ch y of inde pe n dent mod e ls a nd obs ervati on al constra i nts.



### 54

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Box 6.3: Clim ate Sensitivity Th e sen s itiv ity of th e cli m ate syste m to a forcing is co mmo n ly ex pressed in term s o f the g lob al m ean te m p eratu r e change t h at woul d be expec t ed after a ti me sufficientl y long for both th e atm o sphere and ocean to com e to eq u ilibriu m with th e ch ang e in cli m ate fo rcin g (NRC, 20 01). Sin ce IPCC’s Th i r d Assessm en t Rep o rt (IPCC, 2 001 b), th e lev e ls o f scien ti f ic und erstan din g and con f i d en ce in qu antitativ e esti m a t e s of equ ilib ri u m cli m at e sen s itiv ity h a ve in creased substan tially (Meeh l et al. 2 007 ).

So lo m o n et al. (200 7) ind i cate th er e is increased c o nfi d ence of key pro ces ses that are im portant to clim a t e sen s itiv ity d u e to i m p r o v e d co m p ariso n s of m o d els to o n e ano t h e r and to ob serv ati o n s

. W ater vap o r ch ang es d o m in ate th e feed b a ck s affectin g cli m ate s e n s itiv ity an d are no w b etter u n d erst o o d

. Ob serv atio n al an d m o d el
ev id en ce suppo rt a co m b in ed w a ter v a por-lap se rate (th e rate at w h ich air te m p eratu r e d e creases with altitu d e ) feed bac k t h at cor r es po n d s t o abo u t a 50% am pl i f i cat i on of gl ob al m e an warm i ng. C l ou d fee dbac k s rem a i n t h e larg est sou r ce o f un certain ty.

Basin g t h eir assessm en t o n a co m b in atio n o f sev e ral indep e nd en t lin es o f ev iden ce, in clud ing o b s erv e d cli m at e chan ge a n d th e stren g th o f k n o w n fee d bac k s si mu l a t e d i n g e ne ral ci rc u l at i on m odel s , th e aut h o r s c o ncl u ded th at th e g l o b a l m ean eq u ilibrium war m in g fo r do ub ling CO 2 (a c once n trat i o n of ap pr o x i m at el y 540 p p m ), o r ‘equ ilib riu m cl i m ate sen s itiv it y’, v e ry lik ely g r eater t h an 1

. 5 ° C (2 .7 °F) and lik ely to lie i n th e ran g e 2 ° C to 4

. 5°C (3.6°F t o 8

. 1 ° F), with a m o st lik ely v a lu e of ab ou t 3 ° C (5 .4°F). For funda m ental physica l reas ons , as well as data li mitatio n s , th e IPCC states a cli m ate sen s itiv ity h i g h e r th an 4.5°C cann o t b e ru led o u t , bu t th at ag reemen t for th ese val u es wi t h o b s ervat i o ns a nd pr o x y dat ai s general l y wo rse com p ared to values in the 2-4.5°C ra nge (Meehl et al., 2 007 ).

IPCC Clima t e Sensit i v ity Pro b a b ilities

Less th an 1

. 5 ° C 1 0 % o rless pro b a b ility Less th an 2

. 0 ° C 5

- 17 % p r ob ab i lity 2 ° C t o 4

. 5 ° C 6 6 -9 0 % pro b a b ility Greater th an 4

. 5 ° C 5

- 17 % p r ob ab i lity



### 55

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Geographical patterns of projected war m ing show gr eatest temper ature increases over land (r oughl y twice the global a v erage temp erature increase) and at high northern latitudes, and less war m ing over the southern oceans and North Atlantic, c onsistent with observations (se e S ection 4b) during the latter part of the 20th century (Meehl et al., 2007).
Global Precipitation

Models simu late that global m ean precipitation in creases with global warming (Meehl et al., 2007 ). However, there are substantial spatial an d seasonal va riations. Increases in the am ount of precipitation are very likel y i n high latitudes, while d ecreases are likely in m o st subtropical land regions, continuing observed patterns in recent trends in observa tions. According t o Solom on et al. ( 2007):

• In the northe r n hem i sphere, a robust pattern of increased subpolar and decreased subtropical precipitation dom inates t h e projected precipitation pattern for the 21 stc e ntur y over North A m eri ca and Europe, while subtropical dry i ng is less evident over Asia.

• In the southern hem i sphere, there are few land ar eas in the zone of projected supolar m o istening during the 21 stcentur y , with the subtro pi cal dry i ng m o re prom inent.

• Projections of the precipitation over tro p ical land regions are m o re uncertain than those at highe r latitudes.

Global Sea Level Rise
By th e end of the centur y (2090- 2099), sea level is projected by I PCC (2007d) to rise between 0.18 and 0.59 m e ter s relative to the base perio d (1980- 1999) . These num b e rs r e present the lowest and highest projections o f the 5 to 95 % ranges for all SRES scen arios considered collecti v ely and include neither uncertainty i n carbon cy cle feedbacks no r rapid d y na mical changes in ice sheet flow. In all scenarios, th e average rat e of sea level ri se during the 21 stcentur y v e ry likel y exc eeds the 1961 to 200 3 average rate (1.8 ± 0.5 mm per y ear). Even if greenhouse gas concentrations were to be stabilized, sea level rise would continue for centuries due to the time scale s a ssoci ated with cli m ate proce s s es and feedb acks (IPCC, 2007d). T h er m a l expansi on of ocean water contributes 70 to 75% of the central esti m ate f o r the rise i n sea level for all scenarios (Meehl et al., 2007). Glaci ers, ice caps and the Greenland Ice Sheet are also projected to a dd to sea level. The IPCC projects a ra nge of sea level rise contributions from all glaciers , ice caps, an d ice sheet s between 0.04 m e ters to 0.23 m e t e rs, not includi ng the possibility of rapi d dy nam i c a l changes. The Antarctic ic e sheet is esti m at ed to be a negative contributor to sea level rise over the next century under the se as su mp tions (Meehl et al., 2007).

General Cir c ulation Mode ls indicate that the Antarc t ic Ice Sheet will receive i n creased snowfall without experiencing substantial su rface melting, thus gaini ng mas s and r e ducing sea lev e l rise a ccording to IPCC (Meehl et al., 2007). However, Meeh l et al. (2007) note further acceler ations in ice flow of the kind recently observed in so m e Greenland o u tlet glaciers a nd West A n tarctic ic e st rea m s could substantially increase the contributi on from the i ce sheets, a possib ilit y not reflected in the projections above. For
exa mple, if ice discharge from thes e processe s wer e to increase i n proportion to global ave rage surface temp erature change, it would add 0.1 to 0.2 m to the upper bound of sea level rise by 2090 t o 2099. Dy nam ical p rocesses rel a ted to ice flow not incl uded in curr ent m odels but suggested by recent observations could increase the vulnerab ility of the ice sheet s to war m ing, increasing future sea level rise.

In the CCSP (2008a) repor t on abrupt clim ate change, Cl ark et al. (2008) fin d , “Recent rapid changes at the edges of the Greenland and West An tarctic ic e she e ts show acceleration of fl ow and thinning, with the velocity of s o me glaci ers increasing m o r e than t w ofold.” They add, “Inclusion of these proces ses i n m odel s will li kely lead to s ea-level projections for th e end of the 21st century tha t substantially exceed the projections presented in the IPCC AR4 report.”



### 56

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The CCSP (2009b) sea level rise rep o rt notes, “It has been suggested by R a h m storf (2007) and othe r cli m at e scien tists that a global sea-leve l rise of 1 m (3 ft) is plau sible within this century if increased melting of ice sheets in G reenland and Antarctica is a dded to the factors included in the IPCC esti m ates

. Therefore, thoughtf u l precaution suggests that a global sea-level r ise of 1 m to the y ear 2100 should be considered for future plann ing and polic y discussions.”
The CCSP (2008c) report on the strengths and lim itations of m odels notes that m odels of glacial ice are “in their infa ncy ” and that “recent ev idence for rapid variations in this glacial outflow indicates that m o rerealistic glaci al m odels are needed to es timate the evol ution of future sea level. ”

Sea level rise during the 2 1 stcentur y is projected by IPCC to have substantial geographic variabilit y due to factors that influence changes at the regiona l scale, including changes in ocean circulation or at m o spheric pressure, and geologic process es (Me e hl et al., 2007). The patterns in different m odels ar e not generally si m ilar in detail, but have some co mm on features, including sma ller than average sea level rise in the Southern Ocean, largerthan average s ea level rise in the Arctic, and a narrow band of pronounced sea level rise s tretching across the southern Atlantic and Indian Oceans.
Global Ocean Acidification
The oceans have absorbed, and will cont inue to absor b , carbon di oxide em i ssions associ ated with anthropogenic activities. Surface ocea n pH has decr eased by 0.1 units due to oceanic absorp tion of CO 2 , and it is predi c ted to decrease by an ad dit ional 0.3- 0.4 units b y 210 0 (Fischlin et al., 20 07). T h i s projected rate of decline may lead to ocean pH leve ls within a few centuries that have not been observed for a few hundred m illion y ears (Den m a n et al., 2007)

. Acidification is affecting calciu m carb onate saturation in ocean water s , and is thereby reducing ca lcification rates of organisms who rely on the minerals for developm ent. Future acidification is projected to result in under-saturated ocean waters ( see Box 14.1 for inform ation on the effects of this under saturation). Polar and sub-polar surface waters and the Southern Ocean will be aragonite (a form of cal cium carbonate) under-saturated by 2100, and Arctic waters will be sim ilarly threatened (Fischlin et al ., 2007). According to a m odel experiment using a ‘business as usual’ em ission scenario (IPCC -IS92a), bio-calcificati on will be reduced by 2100, in particular within the Southern Ocean, an d by 205 0 for aragonite-producing orga nism s (Den man et al., 2007).
6(c) Projected ch anges in U.S. tempe r ature , precipitation patterns, and sea level rise
IPCC’s Fourth Assessment Report in cludes projections for changes in te mp er at ure, precipitation and sea level rise for North Am erica -- which can be genera lized for the U.S – as w e ll as so me U

. S. specific inform ation. These project ions are su mmariz e d in this section.

U.S. Temperatures According to the IPCC, a ll of North A m eri ca i s v e ry likel y to warm during this century as shown in Figures in 6.9 and 6.10, a nd warm m o r e than the global mean war m ing in m o st areas (Christ e nsen et al., 2007). F o r s cenario A1B (m oderate emissions growth), the largest warm ing thr ough 21 00 is projected to occur in wint er over north ern parts of Alaska, reac hing 7- 10°C ( 13-18°F) i n th e northernm ost parts as shown in Figure 6.10, due to the positive feedback fro m a short e r season of snow cover. In western, central and ea stern regions of North America, the pr ojected war m in g has less se a s onal variation and is not as large, espe c ially near the coast, consistent with less war m ing over the oceans. The average war m ing in the U.S. through 2100 is projected by nearly all th e m odels used in the IP CC assessment to exceed 2°C



### 57

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

(3.6°F) for all scenarios ( s e e Figure 6.9), with 5 out of 21 m odels pr ojecting average war m ing in excess of 4°C (7.2°F) f o r the A1B (mid-range) emissions scenario.
The CCSP (2008e) repor t “The Effects of Cli m at e Change on Agriculture, Land Resources, Wat e r Resources, a nd Biodiversity ” provides shorter-ter m te mp erature projections for the U.S. for the y ear 2030

. It projects a warming of approxi mately 1°C in the southeastern U.S., to m o re than 2°C in Alaska and north ern Canada, with other parts of North Am erica having interm ediate values (Backlund et al., 2008 b).

Figure 6.9: T e mpera t ure anomalies w i th respe c t to 1901 to 19 50 for four North Am eric an land regions

Source: Ch ristense n et al. (2007 ). Temp erat u r e an om alies with re spect to 190 1 to 1950 for four No rth A m eri c an la nd regio ns fo r 19 06 to 2005 (bl ack line) a nd as sim ulated (re d envelo pe ) by multi-mod el dataset (M MD) mo del s inco rpo r at in g kno w n forcin gs; and a s projecte d for 20 01 to 2100 by MMD mod e ls f o r the A1B scenari o (o ran g e envelop e). The ba rs at the end of the oran ge envel ope re presen t the range of proje c ted ch ange s for 20 9 1 to 2100 for the B1 scena rio (blu e), the A1B scen ario (oran ge) an d the A2 scena rio (re d). The bla c k line is da sh ed whe r e ob se rv ations a r e p r e s ent for le ss than 50% of the are a in the deca de con c erne d.



### 58

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.10 : Projecte d te mperatu re a nd preci pita tion change s ov er North America from the MM D- A1 B sim u lation s.

Source: Chr i stense n et al. (2 007). T op ro w : Annua l mea n , Decem ber-Ja n uar y-F ebr uar y, and Jun e -Ju l yAugust temp erature bet w e e n 198 0 to 199 9 a nd 20 80 to 20 9 9 , averag ed ov er 21 mod e ls. Bottom ro w : same as top, b u t for fractional chang e in pr e c ipitati on.

U.S. Precipitation A widespread increase in annual preci pitation is pr ojected by IPCC over m o st of the Nort h Am eri can continent exc e pt the south and south-w estern part of the U.S. and over Mexico largely consistent with trends in recent decades (as described i n Section 4) (Christensen et al., 2007). The largest i n creases are projected ove r northern North America ( i.e. Canada a nd Alaska) associated with a poleward shift in storm tracks wher e precipitation increases by the largest amount in autum n and by the largest fract ion in winter as shown in Figure 6.10. In western North A m eri ca, m odest c h anges in annual m e an precipitation are projected, but the m a jority of m odels indicate an in crease in winte r and a decrease in su mme r. Models show greaterconsensus o n winter incr ease s to th e north and on su mmerdec rease s to the south. These decrea ses are consistent with enhanced subsidence and flow of drie r air m a sse s i n the southw est U.S. and northern Mex ico. Accordingl y , som e models project dr y ing in th e southwest U.S., with m o re than 9 0 % of the m odels projecting dry i ng in north ern and par ticularly western Mexico. On the windward slopes of



### 59

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

the m ountains in the west, precipitation increases ar e likel y to be e nhanced due to orographic lifting 26

. I n the northeastern U.S., annual m ean preci pitation is very likely to inc rease.

U.S. Sea Level Rise

For North A m eric an coast s, e m issions s cenario A1B shows sea lev e l rise values close to the global m e an, with slightl y higher rates i n east ern Canada and we stern Alaska, and stronger positive anomalies in th e Arctic. The projected rate of sea level rise off the low-ly ing U.S. South Atlantic and Gulf c o asts is al so higher than the global average. V e rtic al land m o tion from geologic processe s m a y decrea s e (uplift) or increase ( s ubsidence) the relative sea l e vel rise at any site (Nicholls et al., 2007)

. Impact of Short-lived Species on U.S. Temperature and Precipitation
Modeling results suggest that changes in short-liv ed species (mainly sulfates and black carbon) m a y significantly influence 21 stcentury climate. A GF DL si mu l a tion of SRES s cenario A1B shows that changes in short lived species could be responsible for up to 40% of the continental U.S. su mmertime
war m ing projected to occur in this scenario by 2100 along with a st atistical ly significant decreas e in precipitation, m a inly due to a co m b ination of dom e s tic sulfat e e m issions r e ductions and increas es in Asian black carbon em issions (CCSP, 2008 d). Ho weve r, the CCSP stud y concludes that “we could no t find a consensus in this report on the duration, m a gn itude, or even sign (warm ing or coo ling) of the cli m at e change due to f u tu re levels of the shor t-lived gases and particles” d u e to uncertainties about different poll u tion co ntrol story li n es. 6(d) Cryosphere ( Snow and Ice) projection s , fo cusing on North America and the U.S.
Snow season length and snow depth are very likely to decrease in m o st of North America as illustrated in Figure 6.11, except in the northernm ostpart of Cana da where m a ximu m snow depth is likely to increase (Christensen et al., 2007). Widespread increas es in th aw depth are projected ove r m o st permafrost regions globall y (IPC C , 2007 d).

Letten m aier et al. (2008) find where shifts to ear lier snowm e lt peaks and reduced su mmer and fall lo w flows have already been de tected, continuing shifts i n this direction are very likel y. Meehl et al (2007) conclude that as the climate wa rms, glaciers will lose mass owing t o dom inance of
su mmer m e lti ng over winter precipitation increases, c ontributing to sea level ris e

.

26 Or o g rap h i c l i f t i ng i s defi ne d as t h e asce nt of ai r f r o m a lower elevation t o a highe r elevat ion a s it m oves over rising terrai n



### 60

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 6.11 Percen t Sno w Dep t h Ch a nges in Marc h

Source: Chr i stense n et al. (2 007). Perc ent sno w d epth ch ang es in Marc h (onl y calcul ated w h e r e climatol og ic al sno w am ou n t s exce ed 5mm of w a ter e quiv a le nt), as proj ected b y the Cana di an Regi on al Cl ima t e Model (C CR M), driven b ythe Can adi an Gen e ral Circ u l a tion Model (CGCM ) , for 2041 to 2 070 u n d e r SR ES A2 compar ed to 1 961 to 1 990. Sea ice is projected to shrink in both the Arcti c and the Anta rctic under all SRES scenar ios. In some projections, Arctic latesu mmer s ea i ce disappear s al m o st entirel y by the latter part of the 21 stcentury (IPCC, 2007 d). Taki n g into account recent late
su mmer se a ice loss , Pol y ak et al (2009) indicate that 

### the Arc t ic Ocean may become seasonally ice free as early as 2040.

6(e) Extreme e v ents, focusing on North America and the U.S.

Models suggest that hum an-induced cli m at e change is ex pected to alte r the prevalenc e and severit y of m a ny extre m e events such as heatwaves, col d waves, storms, floods, an d droughts. T h is section describes CCSP (2008i) and I PCC’ s projections for extrem e events f o cusing on North A m eri ca and the U. S. Sections 7-14 summari z e so me of the sectoral i m p acts of extre m e events for the U.S.
Temperature According to the IPCC, i t is very likely that h eat waves globally will become m o re intense, m o re frequent, and longer lasting in a f u ture war m cli m at e, whereas cold episodes ar e projected to decrease significantl y

. (Meehl, G.A. et al., 20 07)

. Meehl et al., 20 07 report on a stud y fi nding that th e pattern of future changes in heat waves, w ith great est intensity increas es overwestern Eur ope, the Mediterranean and the southeast and west ern U.S., is r e lated in part to circulatio n changes resulting from an increase in greenhouse gases.

The IPCC cites a num ber of studies tha tproject changes in temp erature extrem es in the U.S. (Christensen et al., 2007). One finds that the frequency and the m a gnitude of extrem e temp erature events changes dram atically under a high- end em ission scenario (S RES A2), wi th increases i n extrem e hot events an d decrea ses in extre m e co ld events. Another ex a m ines chan ges in temp erature extre m es in their si mu lations centered on C a lifornia and finds incr eases in extreme temp erat ure events, prolonged hot spells and inc reased diurnal te mp er ature range. A third finds increa ses in diurnal te mp er ature range in si x sub-regions of the western U.S. in summer.



### 61

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Karl et al. (2008) fi nd f o r

a m id-range scenario (A1 B ) of future GHG emissio n s, a da y so hot th at it is currently experienced only once every 20 y ears woul d occur every three years by the middle of th e century over mu ch of the continental U.S. and by th e end of the century , it would occur every other y ear or m o re.
Some i mplic ations for human health resulting from these projected changes in temp er ature extre m es ar e discussed in Section 7(b).
Precipitation and Storms
Intensity of precipitation events is projected to incr ease globally, p a rticularly in tropical and h igh latitude areas that ex perience incr ease s in m e a n precipitation (Meehl et al., 2007). Even in areas where mean precipitation decreases ( m ost subtropic a l and m id-latitude regions ), precipitation intensity is projected to increase but there would be longer periods between rainfall ev ents. Meehl et al. (2007) note that increases in heavy precipit a tion events ha ve been linked to increases in floodi ng. The IPCC projects a tendency for dry i ng in m id-continental areas during summer, indicating a greater ris k of droug hts in those regions (Meehl et al., 2007). Ex trem e drough t increases from 1% of present-day land area to 30% by the end of the centu ry in the A2 (high e m issions gr owth) scenario according to a study assessed in Meehl et al. ( 2007). Karl et al. (2008) i ndicate that for a m id-range em i ssion scenario (A1B), daily precipitation so heavy that it now occurs only once e v ery 20 y ears is project ed to occur approxim a tely every eight y ears b y th e end of th is century over mu ch of Eastern North A m eric a. Future projections in Gutowski et al. (2008) indicat e strong m id-latitude (or extratropical) storms will be
m o r e frequent though the overall num berof storm s ma y decrease.
Several regio n al studies in the IPCC pr oject changes in precipitation extrem es in parts of the U.S ranging from a de crea se in heavy precipitation in California to an increase during winte r in the north ern Rockies, Cascades and Sierra Nevada m ountain ranges (Christensen et al., 2 007). For the contigu ous U.S., a stud y in Christense n et al. (2007) finds widespread in crea ses in extre m e precipitation events under SRES A 2 (high em issio n s growth).
Based on a range of m odels, it is likely that tropical cy clones (tropical stor m s and hurricanes) will beco me m o r e intense, with stronge r peak winds and m o re heavy precipitation associated with ongoi ng increases of tropical sea surface t e mperatures (IP CC, 2007d)

. Karl et al. (2008) anal y ze m odel si mulations and find that for each 1o C (1.8o F ) increas e in tropical sea surf ace te mp erat ures, core rai n fall rates wi ll increase by 6-18% and the surface wind speeds of the strongest hurricanes will increase by about 1-8%

. Storm surge levels are likely to increas e due to projected sea lev e l rise, but note the degre e of projected increase has not been adequately studied.

Karl et al. (2008) in dicate projections in frequency changes in tropical cy clones are cu rrently to o uncertain for confident pr o jections. So me m odeling studies have projected a decrea se in the num ber o f tropical cy clones globally due to increased stability of the tropical at m o sphere in a warmer cli m ate, characterized b y fewer weak storm s and greater n u m b ers of in tense storm s (Meehl et al., 2 000). A
num ber of modeling studi es have also projected a g e neral tendency f o r m o re intense but fe wer storms outside the tropics, with a tendency towards m o re extr e m e wind events and higher ocean w a ves in sever a l regions assoc iated with these deepened c y clones (Mee hl et al., 2007).

Possible i mpl ications of ex tre m e precipi tation events in the U.S. for health are d escribed in C h apter 7, for food production and agri culture in Se ction 9, for water resour ces in Section 11, for coastal areas in Section 12, a nd for ecos y stem s and wildlife in Section 1 4

.



### 62

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

6(f) Abrupt Climate Change and High Imp a ct Events
CCSP (2008a), in its report on abrupt clim ate change, defines it as a “large-scal e change in the climate sy stem that t a kes plac e over a f e w d eca des or les s , persis ts (or is anticipated to persist) for a t least a f e w decades, and causes substa ntial disruptions in hum an a nd natural sy stems.” A b rupt clim ate changes are an i mportant consideration because, if triggered, they could occur so quickly and unexpectedly that hum an or natural sy stem s would have difficulty adap ting to them (NRC, 2002). Potential abrupt climate change i mplications in the U.S. are not discussed in t h e sections 7 through 14 (the U.S. se ctoral i mpa ct s ) because they cannot be predicted with confidence, par ticularly for specific r e gions. This secti on therefore focuses on the general risks of abrupt cli m ate change globally, with som e discu ssion of pote ntial regional i mplications where information is available.
According to the National Research Co uncil (2002): “Tec hnically , an abrupt climate change occurs when the climate s y stem is forc ed to cross some threshol d, triggering a transition to a new state at a rate deter m ined by the cli m ate sy stem it self and faster th a n the cause.” Crossing sy ste m ic thre sholds m a y lead to large and widespread c onsequences (Schneider et al., 2007). The triggers for abrupt climate chang e can be forces that are exter n al and/or int e rn al to the cli m ate sy stem including (NRC, 2002):

• changes in the Earth’ s orbit 27

• a brightenin g or dimm ing of the sun

• melting or surging ice sheets

• strengthening or weakening of ocean currents

• e m is sions of cli m at e-alteri ng gases and particles into the at m o sphere
More than one of these triggers can operate si mu lt an eousl y , sinc e all co mponents of the cli m ate sy stem are linked.
Scientific data show that abrupt changes in the cli m ate at the r e gional scale have occurred throughout history and are charact eris tic of the Earth’ s clim ate s y stem (NRC, 200 2). Dur ing the last gl acial period, abrupt regional war m ings (8 to 16°C within d ecades over Greenland) and coolings occurred repeatedly over the North Atlantic region (Jansen et al., 2007). These war m i ngs likel y ha d some large- scale effect s such as major shifts in tropical rainfall p a tterns and re distribution of heat within the cli m at e s y stem but it is unlikely that they were associated wit h larg e changes in global mean surfa ce te mp erature.

The National Research Council concluded that anthr opogenic for c ing may inc r ease the risk of abrupt clim ate change (NRC, 2002):
“...greenhouse warm ing an d other human alterations of the Earth sy stem may increase the possibility of large, abrupt, and unwelco me regional or glo b al clima tic events. The abrupt c h anges of the past are no t full y ex plain e d y e t, and clim ate m odels typically underestim ate the size, speed, and ex tent of those changes. Hen ce, future abrupt changes cannot be pr edicted with confidence, and cli m ate surprises ar e to be expected.”
Changes in weather pattern s (so m eti m es referred to as weather r e gimes or natura l m odes) can result fro m abrupt changes that might occur spontaneousl y due to d y nam ical interactions in the atm o sphere-ice-ocean sy stem , or from the crossing of a th reshold from slow external forcing (as described above) ( M eehl et al.,

27 Acco rd i n g to th e Natio n a l R e search C o un cil (2 00 2), ch ang e s in th e Eart h ’ s o r b it o ccur to o slo w ly to b e p r i m e m overs o f a

b rupt c h a n g e bu t m i ght det e r m i n e t h e t i m ing o f e v e n t s

. A b ru pt cl im at e chan ges o f t h e pa st we r e esp ecially p r omin en t wh en orb ital proce sses were forcing th e clim a t e to ch ang e du ri n g th e coo ling i n to an d warm in g o u t of ice ag es ( N RC, 200 2)

.



### 63

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

2007). In a war m ing cli m ate, changes in the frequ ency and amplitudes of th ese patterns might not onl y evolve rapidl y, but also tri gger other pr ocesses that lead to abrupt cli m at e change (NRC, 2002). Examples of these patterns include the El N iño Southern Oscillation (ENSO) 28 and the North Atlantic Oscillation/Arctic Oscillati on (NAO/OA). 29

ENSO has important linkages to patterns of tropic a l sea surfac e te mp eratur es, which historically have been strongl y tied to dr oug ht, includ ing “m egadroughts” that likely occurred between 900-16 00 A.D. ove r large regions of the south w estern U.S. and Great Plains (Clark et al., 2008)

. The possibi lit y of severe drought as an abrupt change resulting from changes in sea surface temp er atures in a war m ing world is assessed by Clark et al. (2008). The y fi nd that under greenhouse war m ing scenarios, the cause of m odelprojected sub-tropical dry i ng is an overall widespread warm ing of the ocean an d atm o sphere, in contrast to the causes of historic droughts (lin ked specifically to sea surface temp erature). But they n o te m odels may not correctly represent the ENSO patterns of tr opical SST change that could create i mp act s on global h y droclim ate (e.g., droug ht ) in addition to those caused b y overall warm ing. Th e current model results do show dry i ng over the southwestern U.S ., potentiall y increasing the likelihood of severe and persisten t droug ht there in the future. Clark et al. (2008) n o te th is dry in g has already begu n (see also section 4k) but caution it is not clear if t h e present d ry i ng is outsi de the rang e of natural variability and linked to anthropogenic cause s.
Scientists hav e investigated the possibility of an ab rupt slowdown or shutdown of the Atlantic m e ridional overturning c irculation (MOC) trigge red by greenhouse gas forcing. The MO C transfers large quantities of heat to the North Atlantic and Eu rope so an abrupt change in the MOC could have important implications for the clim ate of this region (Meehl et al., 2007)

. However, according to Meehl et al. (2007), the pr obabilit y of an abrupt change in (or shut down of) the MOC is low: “I t is very unlikel y that the MOC will undergo a l a rge abrupt transition duri ng the 21st centur y

. Eve n further into the future, Clark et al. (2008) note “i t is unlikel y that the A tlantic MOC will collapse beyond the end of the 21st century because of global war m ing, alt hough the possi bility cannot be entirely excluded.” While m odels project a slowdown in th e MOC over the 21 stcentury and be y o nd, it is so gradual that the resulting decrease in heat transport to the North Atlantic and Europe woul d not be large enough to reverse th e war m ing that results fro m the increase i n GHGs ( C lark et al., 2008). Clark et al. (2008) do caution that while a collapse of the M O C is unlikely, the potential c onsequen ces of this event could be severe if it were to happen. Potential i mpacts include a southwar d shift of the tropical rainfall belts, a dditional sea level rise aro und th e North Atlantic, and disruptio ns t o m a rine ecosy stem s. The rapid di sintegration of the Green land Ice Sheet (G IS), wh ich would raise sea levels 7 meters, is another comm only discussed abrupt change. Clark et al. (2008) r e port that obs ervations dem onstr ate that it is extremel y likely that the Greenland Ice Sheet is losing m ass a nd that this loss has very likely been accel erating since the m id-1990s. I n the CCSP (2009b) report “Past Cli m ate Vari abilit y and C h ange in the Arctic and at High Latitudes”, Alley et al. (2009) fi nd a threshold for ice- sheet rem oval from sust ained
su mmertim e warm ing of 5°C, with a range of uncertain ties fro m 2° to 7°C. Meehl et al. (2007) in IPCC

28 ENSO descri bes th e fu ll range o f t

h e So u t hern Oscillatio n (see-saw o f at m o sp h eric m as s o r pressure between the Pacific and Indo-Australian areas) th at inc l udes both sea surface tem p erature (SST ) increases as well as SST decrease s w h e n com p ared t o a l ong-t e rm avera g e. It ha s som e t i m e s been use d by sci e nt i s t s t o rel a t e onl y t o t h e br oa der vi ew o f El Ni ñ o or t h e warm event s , t h e warm i ng of SSTs i n the c e ntral and east e rn e q uatorial Pacific. The acronym , ENSO, is com pose d of El Ni ño-Southe r n Oscillation, where El Ni ño is the oceanic com pone nt and the So uthe rn Osci l l at i on i s th e at m o spheri c c o mp o n e n t o f t

h e p h en om enon

. 29 Th e No rt h Atlan tic Oscillatio n (NAO) is t h e do m i n an t m o d e of win t er cli m ate v ariab ility in th e No rt h Atlan tic regi on ra ngi ng fr om central N o rt h Am eri ca to E u r o pe a n d mu ch in to Nort h e rn Asia

. The NAO is a large scale seesaw i n atm o spheric m a ss or press u re between the s ubtr opical h i g h an d th e p o l ar low. Si m ilarly, th e Arctic Oscillatio n (AO) refers to opp o s i n g atm o sp h e ric p r essure p a ttern s in no rt h e rn m i d d l e and h i gh latitu d e s. Th e NAO and A O ar e di f f ere n t way s o f descri bi n g th e sam e phen o m e no n.



### 64

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

suggest the comp lete melting of the GIS would onl y re quire sustained warm in g in the range of 1.9°C to 4.6°C (relative to the pre-industrial temperatures) but suggest it would take many hu ndre d s of y ears to
co mp lete.
A collapse of the West Antarctic Ic e Sheet (WAI S), which would raise seas 5-6 meter s , has been discussed as a low probabilit y , high imp act response to global warming (NRC, 2002; Meehl et al., 2007). The we akening or collapse of ic e shelv es, c a used by melting on the surface or b y m e lting at the bottom by
a war m er o c ean, m ight contribute to a potential destab ilization of the WAIS. R ecent satellite and in situ observations of ice streams behind disi ntegrating ice sh elves highlight som e rapid reactions of ice sheet sy stems (Lemk e et al., 2007). Clark et al. (2008) indicate that while ice is thickening ov er so m e higher elevation regions of Antarctica, s ubstan tial ice losses fro m West Anta rctica an d the Antarctic Peninsula are very like ly occurring and that Antarctica i s lo s ing ice on the whole. Ice sheet m o d e ls are only beginning to capture the small-scal e dy nam ical processes that involve co mp licated interacti ons with the glacier bed and the ocean at the peri m e ter of the ice sheet (Meehl et al., 2007). These processes are not represented in the m odels used by IPC C to pr oject sea level rise. These m o d e ls suggest Antarctica wil l gain m a ss due to increasing snowfall, (although recen t studies find no significant continent-wide trends in
snow accu mu lation over the past sever al decades; Lemk e et al., 2007), reducing sea level ri se. But it is possible that accel eration of ice discharge could beco m e do m i na nt, causing a net positive contribution. Given these comp eting fact ors, there is presently no c onsensus on th e long-term future of the WAIS or its contribution to sea level ris e (Meehl et al ., 2007).
Considering the Greenlan d and West Antarctic ice sheets to gether, Schneider et al. (2007) fi nd paleocli m a tic evidence suggests that Greenland and po ssibly the WAIS contributed to a sea-level rise of 4-6 m e t e rs d u ring the last interglacial, when polar te mp erature s were 3-5 degrees C war m er, and the global m e an was not notably warme r, than at presen t. Ac co rdingly, the y conclude with mediu m confidence that at l east p a rtial deglacia tion of the Greenland ice sheet, and possibly the WAIS, would
occur over a period of time ranging fr om centuries t o m illennia for a global aver age temp erature increase of 1-4 degrees Cel s ius (rel a tive to 1990-2000), causing a contribution to sea-level rise of 4- 6 m e ter s o r mo r e

. Another pote n tial abrupt change of concern assess ed by CCSP (2008a) is the catastrophic release of methane fro m cl athrate h ydrates in the se a floor a nd to a less erextent in per m afrost soils. Clark et al

. (2008) fi nd th e following:

• The size of the hy drate reservoir is unc ertain, perh aps by up to a factor of 10 making judgm e n ts about risk dif f icult to assess.

• Although the re are a number of suggestions in the li terature about the possibility of a dramatic abrupt releas e of methane to the at m o sphere, m odeling and isotopic fingerpr i nting of ice-core methane do n o t support su ch a releas e to the atm o sp here over the last 100,000 y ears or in the near future.
Clark et al (2008) conclu d e : “While the risk of catastrophic release o f m e thane to the atm o sphere in the ne xt century appe ars very unlikely , it is very likely that cli m at e change w ill acceler ate the pace of per s istent em i ssio n s fro m both hydrate sources and wetlands. Current m odels suggest that wetland em i s sions could double i n the next centu r y . However, since these m odel s do not realistically represent all the processes thought to be relevant to future n o rthern hig h

- latitude CH 4 e m is sions, mu ch larger (or s m aller) increase s cannot be di scounted. Acceleration of persistent release fro m h ydrate reserv o irs is likel y, but its magnitude is difficult to estimate.”



### 65

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

6(g) Effect s on/from Stratospheric Oz on e Substances that deplete str a tospheric ozone, which protects the Earth’ s surface from mu ch of the sun’ s biologically harm ful ultraviolet radi ation, are regulated under Title VI of the Clean Air Act. According to the World M e teorological Organization (2007), clim at e change that results fro m changing gre e nhouse gas concentrations will affect the evol ution of the oz one la y e r through changes in chem ical transport, atm o spheric co mposition, and temp erature. In tu rn, changes in the stratospheric ozone can have implications for the weather and climate of the tr oposphere. The coupled interactions between the changing cli m ate and ozone lay e r are comp lex and sc ientific understanding is incomp lete (WMO, 2007)

. Specific infor m ation on climate change effe cts on/fro m stratosp heric ozone in the U.S. has not been
asse ssed. Except where indicated, the fi ndings in this section apply generally to the globe with a focus on polar regions.
Effects of Elevated Greenh ouse Gas Concentrations on Stratosphe ric Ozone

The World Meteorological Organization ’ s (WMO) 200 6 Scient ific Assessment of Ozon e Depletion (2007) concl uded that future concentr ations of stratospheric ozone are sen sitive to future levels of the well- m ixed greenhouse gases. According to th e WMO (2007):

• Future increases of greenh ouse gas concentrations, pri m arily CO 2 , will contribute to the averag e cooling in th e stratosphere. Stratospheric cooli ng is expected to slow gas-phase ozone depletion reactions and increase ozon e.

• Enhanced methane em i s sion (from war m er and we tter soils) i s expected t o enhance ozone productio n in the lower stratosphere.

• An increase in nitrous oxide e m issions is exp ected to reduce ozone in the middle and high stratosphere.

Two-dimensi onal m odels that include coupling be tween all of t h ese well- m i xed greenhouse gases and temp erature project that ozone levels b e tween 60o S and 60o N will return to 1980 values up to 15 y ears earlier than in m odels that are uncouple d (Bodeker et al., 20 07). The impact of stratospheric cooling on ozone m ight be the opposi te in polar regions where cooling coul d cause incr eases in polar stratospheri c clouds, which, given enough halogens, w ould i n crease ozone loss (Bodeker et al., 2007).
Concentrations of stratosp heric ozone a re also sensiti ve to stratosp heric water v a por concentrations which may remain relatively cons tant or increase (Baldwin et al., 2007). Increase s in water vapor would cause increase s in hy drogen oxide (HO x ) radicals, affecting ozone lo ss pr ocesses (Baldwin et al., 2007). Several studies cited in Baldwin et al. (2007) sug g est increasing stratospheric water vapor would delay ozone la y e r recovery . Increase s in stratospheric wa ter vapor could also increas e spring-ti m e ozone depletion i n th e polar regi ons b y raisin g the temp erature threshold for the f o rmation of polar stratospheric clouds (WMO, 2007).
The possible effects of cli m ate change on stratospheri c ozone ar e further co mp licated by pos sible changes in climate dynam i cs. Clim ate change can affect temp eratures, upper level winds and storm pattern s which, in turn, impact planetary wa ves that affect the stratosphere (B aldwin et al., 2007)

. Changes in the forcing and p r opagation of planetary waves 30 in the polar winter are a m a jor source of uncertaint y fo r predicting futu re levels of Arctic ozone loss (Baldwin et al., 200 7).

30 A planeta r y wave is a large horiz ontal atm o spheric undulation t h at is ass o ciated with the pola r -front jet stream and separat e s col d , pol arai r fr om warm , tro p ical air.



### 66

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The CCSP (2008h) report “Trends in E m issions of Oz one-Depleting Substances, Ozone Lay e r Recover y , and Implications for Ultraviolet Radiation Exposure ” includes results fro m two-dim e nsional chem istry transport m odels and three-dim e nsional clim ate chem istry m odel s esti m ating th e recovery of the ozone lay e r un der a greenhouse g as scenario. It finds:

• From 60°N to 60°S, glo b a l ozone is expected to return to its 19 80 value up t o 15 y ears earlier than the halogen recovery date because of str a tos pheric cooling and changes in cir c ula tion associat ed wi th GHG emissions. Global ozone a bundances are expected to be 2 percentab ove the 198 0 valu es by 210 0 with values at mid-latitudes as mu ch as 5 percent higher.

• Model si mu lations show that the ozone am ount in the Antar c tic will reach the 1980 values 10 to 20 y ears earlier (i.e. fro m 2040 to 2 060 ) than the 2060 to 207 0 time frame of when the ozo n edepleting substances r each their 1980 levels in polar regions.

• Most cli m ate che m istry models show Arctic oz one values by 20 50 larger than the 198 0 v a lues, with the recovery date between 2020 an d 20 40.
Climate Change Effects from Stratosph eric Ozone
The WMO (2007) fo und c h anges to the temp erature and ci rculation of the stratosphere affect clim ate and weather in the troposphere. The dom inant troposp h eric response, simu lated in m odels and identified in analy ses of observations, comp ris es changes in the strength of m id-latitu de westerly winds. The mechanism for this respon se is not well-understood.
Modeling ex perim e nts (th a t simu late observed changes in stratospheric ozone a nd com b ined stratospheric ozone depletion and GHG increases) al so suggest that Antarcti c ozone depletion, through i ts eff ects on the lower stratospheric vortex, h as contributed to the observed surf ace cooling over interior Antarctica and warm ing of the Antarctic Penins ula, particularly i n su mm er (Baldwin et al., 2007). W h ile the ph y s ics of these effects are not well-understood, the simu lated pattern of war m ing and c ooling is a robust result
seen in m a ny different m odels, and well- supported by observational studies.
As the ozone lay e r recovers, troposphe ric changes thathave occurred as a result of ozone depletion are expected to reverse (B aldwin et al., 2007).
6(h) Land-Use and Land Cover Change
Changes in land surface (vegetation, soils, water) re sulting from h u man activities can significantly affect local cli m at e through shifts in radiation, cloudi ness, surface roughness, and surface temp eratur e.
Solom on et al. (2007) fin d th e impacts of land use cha nge on climate are expected to be locally sig n ificant in som e regions, but are small at the global scale in co mp arison with greenhouse war m ing. Sim ilarly , the release of h e at fro m anthropogenic energ y producti on can be significant over urban areas, but is not significant gl oball y (Sol o m on et al., 2007).
The CCSP report (2008e) on the effects of clim ate ch a nge on agric u lture, land r esources, wat e r resources, and biodivers ity in the U.S. concludes that global cli m ate change effe cts will be superi mposed on and
m odify those resulting fro m land use and land cover patterns in way s that are as of y e t uncertain.



### 67

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Part IV
U.S. Observed and Projected Human Health and Welfare Effects from Climate Change

68

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 7

Human He alth

War m t e mp er atures and ex tre m e we athe r already cause and contri bute to adverse hu m a n he a lth outcom e s through heat-related m o rta lity and m o rbidity , storm-related fatali ties and injuries, and disease. In the absence of ef fective adaptation, th ese effects ar e likely to increase with cli m at e change. De pending on progress in health care an d access, infrastructure, a nd technology , cli m ate chan ge could i n crease the risk of heat wave deaths, respiratory illness through exposu re to aeroallergens and ozone (discussed in Section 8), and certain diseases ( CCSP, 2008b; Confaloni eri et al, 2007). Studies in temp erate areas (which would includ e large portions of the U.S.) have shown that climate change is projected to bring so m e benefits, such as fewer d eaths fro m cold exposure. The balance of positive and negative health impacts as a result of cl i m ate change will vary from one locat ion to anothe r, and will al ter over ti me as cli m ate change contin ues (CCSP, 2008b).

In its Thir d Assessment Report (TAR), the IPCC produced a n u m b er of key findi ngs su mmarizing th e likely climate change health effects in N o rth America. These eff ect s, which were reaffir m ed in the IPC C Fourth Assessm ent Report (Field et al., 2007), includ e:

• Increas ed dea ths, injuries, infectious disease s, and stress-r e lated disorders and other adverse effects associat ed wi th social disruption and m igration from m o r e frequent extre m e w e ather.

• Increased frequenc y and s e verity of heat waves lead i ng to m o re ill ness and death, particularly am ong the y o u ng, el derly an d frai l.

• Expanded ra nges of vector-borne and tick-borne diseas es in N o rth America but with moderating influence b y public health measures and other factors.

The m o re recent CCSP (2008b) report o n hum an health st ated as one of its conclusions that, “The United States is cert a inly capable of adapting to the collect ive i mpacts of cli m at e cha nge. Howeve r, there will still be certai n individuals and locations where the ad aptive capacit y is less and these individuals and their
co mmunities will be disproportionall y i mp acted by c limate change.”

There are few studies which address the interactive e ffect s of mu ltiple cli m ate change imp acts or o f interactions between cli m a t e change he alth i mpact s and other kinds of local, regional, and global socioeconom ic changes (Field et al., 200 7). For example, climate change impacts on h u m a n health in ur ban areas will be co mpounded by aging infr astructure, mala dapted urban form and buildi ng stock, urban heat islands, air po llution, po pul ation growth and an aging populati on (F ield et al., 20 07).
Vulnerability is the su mmation of all the factors of ri sk and resilience that determine whether indivi duals experience ad verse health imp acts. Specific subpopu lations m a y experience heightened vul nerability for cli m at e-relat e d health effects. Climate change is very likely to accentuate the disparities already evident in the A m er ican health care sy stems as many of the expected health effects ar e likely to fall disproporti on ately o n the p oor, the elderl y, the disable d, and th e uni nsured (Ebi e t al., 200 8).

This section describes the literature on the impacts of clim at e change on hum an health in four areas: te mp erature effects, extre m e events, cl i m ate sensiti ve diseas es, and aeroaller g ens. The health i mpact s resulting from cli m ate ch ange effects o n air quality are discussed i n Section 8.
7(a) Temp eratur e Effect s



### 69

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

According to the IPCC (20 07d), it is ver y likel y 31 that there were w a r m er and few e r cold da y s and nights and war m e r and m o re fr e quent hot day s over m o st land areas d u ring the late 20 th century (see s ection 4(b)). It is virtually certain that these trends will continue during the 21 stcentury (see Section 6(b)). As a result of the projected warm ing, the IPCC projects increases in heat-rel a ted m o rtality and m o rbidit y globall y (IPCC, 200 7b). The projected warm ing is exp ected to result in fewer deaths due to reduce d exposure to th e cold. It i s not clear whether reduced m o rtality f rom cold will be greater or less than increased heat-related m o rt ality i n the U.S. due to clim ate change (Gam ble et al., 2008).

Increased he at exposure

Heatwaves are associated with m a rked short-term increases in mortalit y (Conf alonieri et al, 2007). Ho t te mp erature s have also been associated with increased m o rbidity . A study cite d in Field et al. (2007) indicates incr eased hospital ad m is s ions for cardiovas c ular dise ase and e m e rgency room visit s have be en docum ented in parts of North Am erica during heat events. The populatio ns m o st vulnerable to hot temp eratures are older adults, the chronically s ick, the very you ng, ci ty

- d wellers, those taking medications t h at disrupt ther m o regulati on, the menta lly ill , those lacking access to air conditioning, those working or pl ay in g o u tdo o r s , and the socially isolated (Ebi et al., 20 08; IPCC, 20 07b).
Ebi et al. (2008) report statistics fro m t h e Centers fo r Disease Control and Prevention (CDC, 2005a) tha t indicate exposure to excessive natural heat caused 4,78 0 deaths during th e period 19 79 to 2002 i n the U.S., and that an additional 1,203 deaths had hy pertherm ia reported as a contributing factor. They state these nu m b er s ar e underestimates of th e total m o rt al ity associated with heat wa ves because the person filling out the death certificate m a y not a lway s list heat as a cause.
Given projections for climate war m ing, heat-related m o rbidity and m o rtality are projected to increase globall y (incl uding in the U.S.) co mp ared to a futu re with no climate change (Confalonieri et al, 2007). Heat exposures vary wide ly, and current studies d o not quantif y the y ears of life lost d u e to high temp eratures. Esti m a t es o f heat-relat e d m o rtality a ttributable to cli m ate change are reduced but not eli m inated when assu mp ti ons about acclimatization and adaptation are included in m odels. Confalionieri et al. (2007) cite a series of studies that suggests po pulations in th e U.S. beca me less sensitive to hig h temp eratures over the period 1964 t o 1988, i n part, due to these factors. On the other hand, growing
num bers of older adults w ill increase the size of the populati on at risk because of a decreased abilit y t o ther m o -regulate is a normal part of the aging process (Confalonieri et al, 2007). In addition, according to a stud y in Co nfalonieri et al. (2007) , al m o st all the g r owth in pop ulation i n the next 5 0 y ear s is expected to occur in cities where te mp eratures t e nd to be hig h e r due to the urban heat island 32 effect inc reasing the total num ber of people at r isk of adverse health outc o mes fro m heat. In other words, non-cl im atic factors related to dem ographics will have a significan t infl uence on future heat-relat e d m o rtality

. Across North America, the populatio n over the age of 65 -- the seg ment of the p opulatio n m o st at-risk of dy ing from heat waves -- will increase slowly to 2010, and then grow dramatically as the Baby Boom ers age (Field et al., 2007). Severe heat wa ves are proje c ted to intensify in m a gnitude and duration over the portions of the U.S. whe re these eve n ts already occur (high confidence). The IPCC d o cuments the following U.S. regional sc enario projections of increa ses in he at and/or heat-rela ted effe cts ( C onfalonieri et al, 2007; Fi eld et al., 200 7):

31 Acco rd ing t o IPCC term in o l o g y , “v ery lik el y” co nv eys a 90 to 99 % prob ab ility o f o ccurren ce. See B ox 1

. 3 on page 5 f o r

a ful l descri pt i o n of IPC C ’ s u n ce rt ai nt y t e rm s. 32 A heat island refers to urba n air an d surface te m p eratures that are hi ghe r t h annear by rural areas. Ma ny U.S. cities and s u burbs ha ve air tem p eratures up t o 1 0 °F (5 .6 °C ) warmer th an th e surro und ing n a tural land co v e r.



### 70

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• By th e 2080s, in Los Ange les, the num b e r of heat wave day s (at or above 32o C or 90o F ) increases 4­ fold under the B1 em i ssio n s scenario (low growth) a nd 6-8-fold under A1FI e m issions scen ario (high growth). Annual num berof heat-relat e d deaths in Los Angeles increases fro m about 165 in th e 1990s to 319 to 1,182 for a range of e m issions scenarios.

• Chicago is pr ojected to ex perience 25% m o re fre quent heat waves annuall y b y the period spanning 2080- 2099 for a business-as-usual (A1B) em issions scenario.
Reduced cold exposure
Cold waves continue to pose health risks in norther n latitudes in te mp erature regions where very low temp eratures can be reached in a few hours and extend over l ong perio d s (Confalonieri et al, 2007). Accidental cold exposure occurs mainl y out doors, am ong socially depri v ed people (alcoholics, the hom el ess), w o rkers, and the elderly in te mp erat e an d co ld climat es but cold waves also af fect health in warmer climates (Confalonieri et al, 2 007). Livi ng in cold envi ronm ents in polar regions is associated with a range of chronic conditions in the non-indi ge nous populati on with acute risk fro m frostbite and h y potherm ia (Confalonieri et al, 200 7). In cou n tri es with pop ul ations well-adapted to col d conditi ons, cold waves can still cau se substantia l increases i n m o rtality if electricity or heating sy stem s f a il (Confalonieri et al, 2007)

. Ebi et al. ( 2 0 08) cite a stu d y reporti ng th at from 1979 to 200 2, an average of 68 9 reported deaths per y ear (range 417-1,021) in the U.S., totaling 16,555 over the period, were attributed to exposure to excessiv e cold temp er at ures. The IPCC projects reduced hum an mortality from co ld exposure through 2100 (C onfalonieri et al, 2007). It is not clear whether reduced m o rtal ity from cold will be grea ter or less than increased heat-related
m o rt ality in th e U.S. due to cli m ate ch ange. Pr ojections of cold-related de aths, and the potential for decreasing th eir num bers due to warmer winters, can be overestimated unless the y take int o account the effects of se a s on and influenza, which is not strongly associated w ith m onthly winter te mp e rature (Ebi et al., 200 8; Co nfalonieri et al, 200 7).
Aggregated changes in hea t and col d exposure The IPCC (2 007) does not explicitly assess studies since the TAR which analy ze ch anges in both heatand cold-related m o rtality in the U.S. i n the observed cli m ate or for different future cli m at e scenarios. However, a study cited in Confaloni eri et al. (2007) find existing m o rtality patterns in U.S. cities are relatively ins e nsitive to temp erature variabilit y

. In a future warming cli m ate, this study projects so me m o rt ality could be reduced with a winter-dom inan twarm ing and m o rtality i n crease with pronounced
su mmer war m ing. Given the paucity of recent literatu re on the s ubject and the challenges in esti m ating and projecting weather-r el ated m o rtalit y, IPCC conc ludes additional resear ch is needed to understand how the balance of heat-and cold-related deaths m i ght change gl oball y un der different climate scenarios (Confalonieri et al, 2007)

. 7(b) Extreme Eve n ts

In addition t o the direct effects of temp erature on heat and cold-related m o rtality , projected trends in cli m at e chan ge-related ex posures of importance to human healt h will increase the nu m b er of people (globall y , inc luding in the U.S.) suffering from di sease and injur y due to fl oods, storm s , droughts and fires (high confidence) (Confalonieri et al, 2007). Vulnerability to weather disaster s depends on the attributes of th e people at risk (including where the y live, age, inc o me, education, and disabilit y ) and on broader social and environmental fact ors (level of disaster preparedness, health sector responses, and environm ental degradation) (Ebi et al., 2 008).



### 71

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Floods a nd storms The IPCC projects a very likely increase in heavy precipitation event frequency over most areas as described in Sections 6(b and c). Increases in the fre quency of heavy precipitation events are as sociate d with increase d risk of deaths and injuries as well a s infectious, respiratory and skin dise ases (IPCC , 2007b). Floods are low-probabilit y, high-impact even ts that can overwhelm phy sical infrastructure, hum an resilience, and social organization (Confalonie ri et al, 2007)

. Flood health impacts include deaths, injuries, infectious diseases, intoxications and me ntal health problem s ( C onfalonieri et al, 2007)

. Floodi ng m a y also lead t o contam ination of waters with dangerous chem icals, heavy m e tals, or other hazardous su bstances, fro m storage orfro m chem i cals already in the environment (Confalonieri et al, 2007).
The IPCC (2 007d) also projects likely increases in in tense tropical cy clone activity as described i n Section 6(b). Increase s in tropical cy clone intensity ar e linked to increas es in the risk of deaths, injuries, water and foodbor ne diseases as well as post-trau matic stress disorders (IPCC, 2007b). Drowning by stor m surge, heightened by rising sea levels and m o re intense stor m s ( as proje c ted by IPCC), is the majo r killer in coastal storms wh ere there are large nu m b er s of deaths (Confalonieri et al, 2007). High-densit y populati ons i n low-l y in g c o astal regions such as the U.S. Gulf of Mexico experience a high health burden from weatherdisaster s, particularly among lower in co m e groups. In 2005, H u rricane Katr ina clai med over 1800 li ves in the vicinit y of th e low-ly ing U.S. Gulf Coast and lower inco me groups were disproporti on ately affected (Grau m ann et al., 200 5; Ni cholls et al., 2007; C onfal onieri et al., 2 007). Wh ile Katrina was a Category 3 hurricane an d its path was forecast well in advance, there was a secondary failure of the levee sy stem. This il lustr a tes that mu ltiple factors contribute to making a dis aster and that adaptation measures may not full y aver t adverse con se quences (E bi et al., 2008). Additional inform ation about U.S. vulnerabilit y to the potential f o r m o re inte n se tropical cyclones can be found in Sect ion 12(b).
Droughts

Areas affect ed by droughts are likel y to i n crease accor d ing t o IPCC (2007d) as noted in Section 6(e). The health imp act s associ ated with drought tend to m o s t affect s e m i- a rid and arid regions, poor area s and populati ons, and areas wit h hum an-induced water scarc ity ; henc e m a ny of these effects ar e likel y to be experienced in developin g countries and not directly in the U.S. Information about the effects of increasing drought on U.S. agriculture can be found i n section 9(c).
Wildfires
In some regi ons, changes in the m e an and variability of temp erature and precipitation are projected to increase the size and severity of fire events, including in parts of the U.S. (Easterling et al., 2007). Wildfires can increase ey e and respiratory illnesses and injuries, including burns and sm ok e inhalation (Ebi, et al., 2008). A study cited in Conf alonieri et al. (2007) indica tes large fires are also acco mp anied by an increas ed num ber of pa tients seeking e m erg e ncy services for in halation of sm oke and as h. The IPCC (Field et al., 2007) noted a num ber of observed chang es in U.S. wildfire size and frequency. Additional inform ation on the effects of forest fires can be found in Sections 8 ( b) and 1 0 (b).
7(c) Climate-s e ns itive diseases
The IPCC (2007b) notes th at many human diseases are sen sitive to weather. The incidence of airborne infectious diseas es ( e .g., coccidioidom y cosis) var ies s easonall y and annually, due partly to cli m ate variations such as drough t, which is projected to in crease in the southwestern U.S. (Field et al., 2007; Karl et al., 2008).



### 72

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Waterborne disease outbreaks are distin ctly seasonal (which suggests potential underl y ing environm ental or weather control), clustered in pa rticular wat e rsheds , and associat ed with heav y precipitation. The risk of infectious disease following flooding in high-i n come countries is generally low, although increases in respiratory and diarrheal di seases have b een reported after floods (Confalonieri et al, 2007). For example, after Hurric a n es Katrina a nd Rita in 2005, contam in ati on of watersupplies with fecal bacteri aled to many cases of diarrheal illness and som e deat hs (Ebi et al., 2008; CDC, 2005b; Confa lonieri et al, 2007).

Foodborne di seases show so m e r e latio nship with temp erature ( e

. g ., increased temp er atures have been associat ed with increased case s of Salm onellosis) ( C onfalonieri et al, 2007). Vibrio spp. in fections from shellfish consumption m a y also be influ e nced by te mperature (Confalonieri et al, 2007). F o r example, Confalonieri et al. (200 7) cited a stud y docum enting a 2 004 out break of V p a rahaemolyticus linked t o aty p ically high temp er ature s in Alaskan coastal w a ter s

. According to the CCSP (2 008b) report, there will likely be an increase in the spread of several food and water-borne pathogens among susceptib le populations depending on the path ogens’ survival, persistence, habitat range and transm ission u nder changing climate and enviro n m enta l conditions. While th e U.S. has successful programs to protect wat e r quality under the Safe Drinking Water Act and the Clean Water Act , so m e contamination pathw a y s and r oute s of exposure do n o t fall u nde r regulato r y program s (e.g., derm al absorption from floodwaters, swimmin g in lakes and ponds with elevated pathogen levels, etc.). The primary climate-relat e d factors that affect these pathogens include temp eratu r e, precipitation, extrem e weather even ts, and shifts in thei r ecological regimes. Consistent with our understandin g of clim ate change on human health, th e impact of climate on food and water-borne pathogens will seldom be the onl y factor de ter m ining the burden of huma n injuries, illness, and death (CCSP 2008b).
The sensitivity of m a ny zoonotic 33 diseases to cli m ate fluctuations is al so highlighted by the IPCC (Field et al., 2007). A study in Field et al. (2007) li nked above average temp eratures in the U.S. during th e su mmers of 2002- 2004 to the greatest transm issions of West Nile virus. Saint Louis encephalitis has a tendency to appear during hot, dr y La Nina y ears ac cording to a study cited in Field et al. (2007). Associations between te mperature and precipitation and tick-borne Ly m e disea se ar e also noted by IPCC (Field et al., 2007). A stud y cited i n Field et al. (2007) foun d that the north ern range li mit of Ixodes scapularis , the tick that carries Ly m e disease, could shif t north by 200 km by the 2020s and 1000 km by the 208 0s.
Although large portions of the U.S. may be at pote ntial risk for diseases such as m a l a ria b ased on the distribution of co mp etent disease ve ctors, locally acqui red cases have been virtually elim in ated, in part due to effecti v e publ ic health interventi ons, includin g vector and disease contr o l activities. (Ebi et al., 2008; Confal onieri et al, 2 007).

The IPCC concludes that hum an health risks fro m clim ate change will be stron g l y m odulated by changes in health care, infrastructure, technology, and accessib ilit y to health care (Field etal., 2007). T h e aging of the population and patterns of immigrat ion and/or emigration will also strongly infl uence risks (Field et al., 200 7).
7(d) Aeroallergen s
Cli m ate chan ge, including changes in CO 2 concentrations, could impact the production, distributio n, dispersion and allergenicity of aeroallergens and the growth and distribution of weeds, grass es and trees that produce them (McMichael. et al., 2001; Confal onieri et al., 2007). T h ese changes in aeroallergen s

33 A zo ono tic d i sease is an y i n fectio u s d i sease t h at is ab le to be tran sm itted fro m an an im al o r non hu m a n sp ecies to hum ans. The nat u ral rese rv o i r i s a no n hum an reser v oi r.



### 73

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

and subsequ e nt hum an exposures could affect th e prevalence and severity of allerg y sy mp tom s

. However, the scientific literature does not provide de finitive data or conclusions on how cli m ate change might impact aeroallergens and subsequently the preval ence of allergenic illnesses in the U.S. In addition, there are numerous other fa ctors that affe ct aeroall erge n levels and the prevalence of associat ed allergeni c illnesses, such as changes in land use, air polluti on, and adaptive r esponses, m a ny of which are difficult to
asse ss (Ebi et al., 2008).
It has generally been observed that the presence of elevated CO 2 concentrations and te mp erature s stimulates plants to increase photosynthesis, bio m ass, water use efficiency , and reproductive effort. Th e IPCC concluded that polle ns are likely to increase wi th elevated temp erature an d CO 2 (Field et al., 20 07)

. Laborator y studies cited by Field et al. (2007) stimul ated ragweed-pollen prod u c tion b y over 50% using a doubli ng of CO 2. A U.S.-based field study referenced by Fi eld et al. (2007) which used existing te mp erature/ CO 2 concentration differences be tween urban and rural areas as a prox y for climate change found that ragweed grew faster, flowered earlier, and produced sig n ificantly gre a ter aboveground biom ass and ragweed pollen at urba n locati ons than at rural locations.
The IPCC (C onfalonieri et al, 2007) noted that clima te change has caused an ea rlier onset of the spring pollen season in North America and that there is lim it ed evidence that the length of the pollen season has increased forsome spe c ie s. However, it is unclear whether the allergenic co ntent of thes e pollens has changed. Th e IPCC concluded that in troductions o f new invasive plant spe c ies with high allergenic pollen present importanthealth risks, noting that ragweed ( Ambrosia artemisiifolia ) is spreading in several parts of the world ( C onfalonieri et al, 2007).



### 74

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 8
Air Quality
Surface air concentrations of air pollutants are hi ghly sensitive to winds, temp erature, hum idity and precipitation (Den m a n et a l., 2007). Climate change can be expect ed to influence the concen tration and distribution of air pollutant s through a variety of dire ct and indirect processes, i n cluding th e m odification of biogenic emissions, the change of che m ic al rea c ti on rates, wash-out of po llu tants b y preci pitation, an d
m odification of weather patterns that influence pollut a nt buildup. In summarizi ng the impact of climate change on ozone and particulate matter (PM), the IP CC (Den man et al., 2007) states that “future clim ate change may cause significant air quality degradation by changing the dispersi on rate of pollutants, the chem ical environm ent for ozone and P M generation and the strength of em issions from the biosphere, fires and dust.”

This section describes ho w cli m ate change m a y alter a m bi ent c oncentrations of ozone and PM with associat ed i m pacts on publ ic health and welfar e in the U.S.
8(a) Tropospheric Oz one According to the IPCC (Denman et al., 2007), clim ate cha nge is ex pected to lead to increases in regional ozone polluti on in the U.S. and other countries. Oz o n e i mpact s on pubic health and welfare are described in EPA’s Air Quality C riteria Docu ment for Ozone (EPA, 2006). Breathing ozone at sufficient concentrations can reduce lung func tion, thereby aggravating asthma or other respiratory conditions. Ozone exposure at sufficient concentrations has been associated with increases in respiratory infection susceptibility, medicine use by asthm ati cs, emergency departm e nt visits and hospital ad m issi ons. Ozone exposure may contribute t o premature death, especi ally in susceptible populations. In contr ast to human health effects, which are associated with short-te rm exposures, the m o st significant ozone-induced plant effects (e.g., biom ass loss, y ield reducti ons) resu lt from the accumu lation of ozone exposures over the growing season, with diff erentially greater i mpact r esulting from exposures t o higher concentrations and/or lo nger durations.
Tropospheric ozone is both natura ll y occurring and, as the prim ary constituent of urban sm og, a secondary pollutant form ed through photochem ica l reactions involving nit r ogen oxi des (NOx) and volatile organic co mpounds (VOCs) in the presence o f s unlight. A s described below, cli m at e change can affect ozone b y m odify i n g (1) em ission s of precursor s, (2) at m o s pheric che m i s try , and (3) transport and
rem oval (Denman et al., 2007). Ther e is now consis tent evidence fro m mo dels and observations that 21st-century cli m at e change will worsen summerti m e surface ozo n e in polluted regions of North Am eri c a co mp ared to a future with no clim ate ch ange (Jacob and Win n er, 2 009).
The IPCC (Den m a n et al., 2007) states that, for all w o rl d regions, “cli m ate chan ge affects the sources of ozone precursors through ph y s ical response (lightni ng), bi olog ical response (soils, vegetation, and biom ass burn ing) and h u man response (energy gener a ti on, land us e, and agricu lture).” Nitrogen o x ides
em issions du e to lig htnin g are expected to i n cr ease in a warmer climate (Den m a n et al., 2 007). Additionall y , studies using general circ ulation m odels concur that in flux of ozone from the str a tosphere to the troposphe re could increase due to large-scale at m o spheric cir c ulation shifts (i.e., the Br ewer- D obson circulation) in response to clim ate warming (Denman et al., 2007). The sensitivity of m i crobial activity in soils to te mp erature also p o ints toward a substantial increas e in the nitric oxide emissions (Br a sseur et al., 2006). As described below, biogenic V O C em i ssi ons increase wit h increasing temp erature.



### 75

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Clim ate induced changes of biogenic VOC em issions alone may be region ally substanti a l and cause significant increas es in ozone concentr ations (Haugl ustaine et al., 200 5; Hogrefe et al., 2004; European Co mm ission, 2003). Sensitivit y simu lations for the 2050s, relative to the 1990s suggest under the A2 (high-end) cl i m ate scenari o that increased biogenic em issions alone add 1–3 parts per billion (ppb) to
su mmertim e average daily m a ximu m 8-hour ozone con centrations in the Midwest and along the eastern seaboard (Hogrefe et al., 2004). T h e IPCC (Meehl et al., 2 007 ) reports that bio g enic emissions are projected to increas e by between 27 and 59%, contri buting to a 30 to 50% inc rease in ozone formation over northern continental r e gions (for th e 2090-2 100 t i m e frame, relative to 199 0- 2000).
Consistent with this, for ne arly all simu lations in the EPA Interim Assessment (2009), clim ate change is associat ed with increases i n biogenic VOC e m i ssions over m o st o f the U.S., with especially pronounced increase s in the Southeast. These biogenic e m is sions increase s do not necessaril y correspond with ozone concentration increas es, however. The r e port suggests that the response of ozo n e to changes in biogenic
e m is sions depends on how isoprene che m istry is re pr esented in the m odels

— m odel s that recy cle isoprene nitrates back to NOx will tend to simu late significant O 3 concentration increases in regions with biogenic
em issions increases, while m odels that do not recy cle isoprene nitrates will tend to si mulate smal l changes, or even O 3 decreases.

Cli m ate chan ge impa cts on temp er ature could affect ozone chem istry significan tly (Denman et al., 20 07). A nu m b er of studies in the U.S. have shown that su mmer day time ozone concentrations correlate strongly with te mp era t ure. That is, ozone generally increases at higher te mp eratures. This correlation appears t o reflect contributions of co mp arable magnitude fro m (1) temp erature-dependent biogenic VOC em issions,
as m e ntioned above, (2) th er m a l deco mposition of peroxy acety l nitrate (PAN) , which acts as a reservoir for NOx, as described immedi ately below, and (3 ) associatio n of high te mp eratures with regional stagnation, also discussed below (Den man et al., 2007).

The EPA Interim Assessment (2009), however, reports that cons idering a sing le m e teorological variable, such as te mp erature, may not provide a sufficient ba si s for det e r m ining future oz one risks due to cli m at e change in every region. This is c onsist e nt with the potential for differe nt co mpeting effects in different regions. The m odeling studies found so m e r e gions of the country where si mulated increases in cloud cover, and hence decr eases in the amount of sunli ght reaching the surface, partially counteracted th e effects of wa r m ing temp e r atures on oz one concentra tions in these regions, to go along with the m a ny regions where the effects o f te mp erature and cl oud cover reinforced each other in producing O 3 increases.

Cli m ate chan ge is project ed to increas e surfa ce l a ye r ozone con centrations in both urban and polluted rural environ m ents due to deco mposition of PAN at higher temperatures (Sillm an and Samson, 1995; Liao and Seinfeld, 2006)

. War m ing enhances deco mposition of PAN, releasing NOx, an i mp o rtant ozone precursor (Stevenson et al., 2005). Mo del simu latio ns (using the high-end A2 em issions scenario) with higher temp eratures for th e y ear 2100 showed that enhanced PAN thermal de co mposition caused this species to decrease by up to 50% over source regions and ozone net production to increase ( H auglustaine et al., 2005)

. Atm o spheric circulation can be expected to change in a warm in g clim ate an d, thus, m odify p o llutant transport and rem oval. Th e CCSP (200 8b) reports th atstagnant air mass es rel a t e d to clim at e change are likel y to degr ade air quality i n som e densely populat ed areas. More frequent occu rrences of stagnant air events in ur ban or i n dustrial areas co uld enhance the intensit y of air pollution events, although the i mportance of these effects is not y e t well quantified ( D en m a n et al. , 2007). The IPCC (2007d) concluded that “extra-tr opical stor m tracks are p rojected to m ove poleward, with consequent changes in wind, precipitation, and temp erature patterns, continui ng th e broad pattern of observed trends over the last halfcentury .”



### 76

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The IPCC (Den m a n et al., 2007) cites a study for th e eastern U.S. which found an increase in the severit y and persistence of regional pollutio n episodes due to the reduced fre quency of ventilation by storms tracking across Canada. This study found that surf ace cy clone activit y decreased by approximately 10– 20% in a futu re si mu lation (for 2050, under the m i d-range IPCC A1B scenario), in gener a l agreement with a num be r of observational studies over the norther n m idlatitudes and North Americ a. N o rtheast U.S.
su mmer pollution episodes are project ed in this stud y to increase in severi t y and duration; pollutant concentrations in episodes increase 5-10% and episode dur ations increas e fro m 2 to 3-4 da y s

. Analy s is of historical data supports both the trend in decreasi ng frequency of ventilation and the increase in su mmer polluti on epis odes (Leibensperger et al., 2008).
Regarding th e role water vapor pla y s i n tro pospheri c ozone form ation, th e IP CC (Den m a n et al., 200 7) reports that simu lations for the 21st centu r y in dicate a decrease in the lifetim e of troposp h eric ozone due to increasing watervapor. The projected incre a s e in wate r vapor both decelerat es t h e che m i cal production a nd accelerates the chem ical destruction of ozone ( M eehl et al., 2007). Ove rall, the IPCC states that climate change is expected to decr ease background tr opospheric o z one due to higher water vapor and to increase regi onal and urban-scale ozone po llution due to higher te mp eratures a nd weaker air circulation (Den m a n et al., 2007; Confal onieri et al., 2 007).
For North America, the IPCC (Field et al., 2007) repor ts that su rface ozone concentration may increase with a warmer climate. For the continental U. S., the CCSP (2 008b) report states that the northern latitudes are likely to exper i ence the largest increases in average temp erat ures and th ey will also bear the brunt of increases in ground-level ozone and other airborne polluta nts. Modeling stu d ies discussed in EPA’s Interim Assessm ent (2009) show that simu lated climate change
causes increa ses in su mmerti m e O 3 concentrations over substantial re gions of the countr y , thoug h this was not uniform , and some areas sh owed little change or decreases. For those regions that showed cli m at e-induced increases, the increase in Maximu m Daily 8-hour Average O 3 concentration, a key m e tric for regulating U.S. air quality , was in the range of 2-8 ppb, averaged over the summe r season. The increase s w e r e substantiall y greater tha n this during the peak pollution episode s that tend to occur over a
num ber of day s each summer. While the results from the differ e nt research g roups agreed on the above points, th eir m odeling sy s tem s did not alway s simu la te the sa m e regional patte rns of clim at e-induced O 3 changes acro ss the U.S. C e rtain regions show greater agree m ent t h an others: for exa mple, t h ere is m o r e agreement on cli m at e-induced increases for the eastern half of the countr y than for the West. Parts of the Southeast also show strong disagreem ents acro ss the m odeling groups. Where cli m ate- change-induced increase s in ozone do occur, da m a ging effe cts on ec osy s tem s , agr iculture, and health are ex pected to b e especially pronounced, due to increases i n th e frequency of extreme polluti on eve n ts.

The EPA Interim Assessment (2009) suggests that cl im ate chan ge effects on ozone grow continuo usl y over tim e , with evidence for signi ficant increases emerging as early as the 2 020s. The EPA Interim Assessment (2009) and th e IPCC (Field et al., 2007; Wilbanks et al., 2007) cite a study whi c h evaluate s the effects of clim ate chan ge on regiona l ozone in 15 U.S. cities, f inding that average su mmerti m e daily 8-hour m a ximu m ozone concentrations could increase by 2.7 ppb in the 2020s and by 4.2 ppb i n the 2050s under th e A2 (high-e nd) scenario.

Studies reviewed in EPA’s Interim Assessment (200 9) and Jacob and Winner ( 2009) indicat e the largest increase s in o z one concent rations due to cli m ate cha nge occur during peak pollution events. Mickley et al. (2004) find that clim ate change projected to oc cur under the A1B (m id-range) scenario results in significant changes that oc cur at the hig h end of the pollutant con centration distributio n (episodes) in the Midwest and Northeast between 2000 a nd 2050 gi ven constant levels of cr i teria pollutant em i ssions. Using the A2 (high-end) emissions scen ario, Hogrefe et al. (2004) find that while regional climate change in the eastern U.S. causes t h e su mme r average daily maxi mu m 8-hour ozone concentrations to increase by



### 77

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

2.7, 4.2, and 5.0 p pb i n 2 0 20s, 20 50s, a nd 2 080s (c o mp a red to 19 90s), regiona l climate changes causes the fourth hi ghest summerti m e daily m a xi mu m 8-hour oz one concentrations to increase by 5.0, 6.4, and 8.2 p pb for th e 2020s, 2 0 50s, and 20 8 0 s, respectivel y (compared to 199 0s) (Hogrefe et al., 2004). T h e CCSP (2008b ) also reports clim ate chan ge is projected to have a much greater imp act on extrem e values and to shift the distributio n of ozone concentrations towards higher values, wit h larger relati ve increas es in future decades. In addit ion, simu latio ns reviewed in the EPA In teri m Assessment (2009) showed that, for parts of the countr y w ith a defined su mmertim e O 3 season, cli m ate change e xpanded its duration into the fall and spring. These findings raise particular health concerns.
The IPCC (Field et al., 2007) states that, “war m ing an d climate extr e m e s are like l y to increase respiratory illness, including exposur e to pollen and ozone.” And the IPCC further stat es th at “sever e heat waves, characte rized by stagnant, war mair mas ses and consecutive nights with high m i nimu m te mp e ratures wil l intensify in magnitude and duration ov er the portion s of the U.S. and Canada, where they already occur (high confi d ence) (Field et al., 2007).” F u rther, as de scribed in CCSP (2008 b), th ere is so me evidence that
co m b ined effects of heat st ress and air p o llution may be greater than si mp le additive effects and historical data show relationships bet w een m o rtalit y and temp er ature extre m e s

. Holding population, dose -response ch aracte ristics, a nd polluti on prevention me asures constant, ozonerelated deaths from cli m at e change in the New York City m e tropolitan area are projected to increase by approxim a tel y 4.5% from the 1990s to the 2050s (under the high-end IPCC A2 scenario) (Field et al., 2007). According to the IPCC (Field et al., 2007), th e “large potential populati on exposed to outdo or air polluti on, translates this small relative risk into a su bsta ntial attri butable health risk.” In New York City, health imp act s could be further exacerb a ted by clim a t e change interacting with urban heat island effect s (Field et al., 2007). For A2 scenario in the 2050s, Be ll et al. (2 007) report th at the projected effects of cli m at e chan ge on ozone in 50 eastern U.S. cities in creased the n u m b erof su mmer day s exceeding the 8­ hour U.S. EP A standard by 68%. On average acro ss the 50 cities, the summertim e daily 8-h maximu m increased 4.4 ppb. Elevated ozone levels correspond to approxim a tely a 0.11% to 0.27% increase in dail y total m o rtalit y. The largest ozone increas es ar e e s ti m a ted to occur in cities with present-day high polluti on. As noted in CCSP (2008b), the influence of clim ate ch ange on air qualit y will play out against a backdrop of ongoing regulatory control of bo th ozone and particulate matter (P M) that will shift the baseline concentrations of these two important pollutants. The range of plausible short-lived em issions projections is very large. For example, em ission projections used in CCSP (2008 d) and in the Fourth Assessment Report of the IPCC differ on whether black carbon partic le and nitrogen oxi des emissions tren ds continue to increase o r decrease. I mprovements in our abili ty t o project social, econ o m i c and technological developm ents affecting future e m issions are needed



### . However, most studies to date that have exa m ined potential future cli m ate change i mpacts on air quality isolate the cli m at e effectby holdi ng precursor air pollutant em issions constant over tim e.
The IPCC r e ports (Den man et al., 20 07) that “the cu rrent generation of trop os pheric ozone m odels is generally successful in de scribing the principal feat ures of the present-day global ozone distribution.” The IPCC (Den m a n et al., 2007) also states that “there are major discrepancies with observed lon g -term trends in ozone concentrations over the 20th century ” and “resolving these dis c repancies i s needed to establish confidence in the m odel s .”

In addition t o hum an health effects, elevated levels of tropospheric ozone have significant adverse effects on crop y ields in the U.S. and other world regions , pasture and forest growth and species composition (Easterling et al., 2007). Furtherm ore, the effects of air pollution on plant func tion may indi rectly affect carbon storage; recent research showed that troposph eric ozone resulted in significantly less enhancem en t



### 78

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

of carbon sequestration rates under elevated CO 2 , due to ne gative effects of ozone on biom ass productivi t y a nd changes in litter chem istry (Easterling et al., 2007).
8(b) Particulate Matter

Particulate matter (PM) i m pacts on public health and welfar e ar e d escribed in E P A’ s Air Qua lity Criteria Docu m e nt fo r Particulate Matter (EPA, 2004). Particul ate matter is a co mp lex mixture of an thropo genic , biogenic and natural m a te rials, suspended as aeros ol particles in the atm o sp here. When inhaled, the
sm all est of t h ese particles can reach the deepest r e gions of the lungs. Scienti f ic studies have found an association b e tween exposure to PM and significant health problem s, inclu d ing: aggravated asth m a; chronic bronc hitis; reduced lung function; irregular h eartbeat; heart attack; and prem ature death in people with heart orlung disease. Particle pollution also is the main cause of visibilit y impair ment in the nation ’ s cities and national parks.
The overall directional impact of climate change on PM levels in the U.S. remains uncertai n (National 

### Assessm ent, 2008), as t oo few data y e t exist for PM to draw firm conclusions about th e direction or magnitude of clim ate imp acts (CCSP, 200 8b). Howe ver, preliminary result s of m odeling anal y s es reported in the EPA Interi m Assessment (2009) ar e listed bel o w. These analy ses show a r a nge of increases and decreases in PM concen tr ations in different regions and for different co mponent chem ical species in the sa me region:

1. Precipitation is a m o re important prim ary m e teorological driver of PM than of O 3 , due to its role in rem oving PM fro m the atm o sphere (wet depos iti on). Precipitation, however, is particularly difficult to m odel and shows greater dis a gree ment ac ross si mu lati ons than other variables. 2. Aerosol chemical proces ses, espe c iall y those conc erning the for m ation of organic aerosols, ar e not full y u n d e rstood and th erefore not well charac terized in current regional ai r qualit y m odels. 3. Preli m inary si mu lation re sults suggest that, globally, PM generally decrease s as a result of si mu lated cli m ate ch ange, due to increased at m o spher ic hum idity a nd increased precipitation. 4. Regionally , s i mu lated 2050 clim at e cha nge produces both increases and decrea ses in PM (on the order of a few percent), depending on region. For the U.S., the largest si mulated increa se s a r e found in the Midwest and Northeast. 5. This PM resp onse refle c ts the co m b ined cli m at e change responses of the individual specie s th at make up PM (e.g., sulfate, nitrate, amm o nium , black carbon, organi c carbon, etc.). Depending on the region, th ese individual responses can be in comp eting directions. 6. Increas e in w ildfire frequency associated with a war m er cli m ate has the potential to increas e PM levels in certain regions.
Further, Jacob and Win n er (2009) summarize the current state of knowledge as:
“The response of PM to cl i m ate change is m o re co mp licated than that for ozone because of the diversity of PM comp onents, comp ensating effects, and genera l uncertai n t y in GCM projections of the future hy drol ogical cy cle. Observations show little useful correlation of PM with cli m ate vari ables to guide inferences of the effect of cli m at e change. Rising te mp erature is expected to have a m ild negative effec t on PM due to volatilization of sem i-volatile co mpone nts (nitr ate, organic), partly compensated by increasing sulfate producti on. Increasing stagnation s hould cause PM to i n crease. Precipitati on frequenc y , which largel y determ ines PM loss, is expected to i n creas e globally but to decre ase in so uthern North Am erica and southern Eur ope. PM is hi ghl y sensitiv e to m ixing depths but ther e is no consensus am ong m odel s on how these will respond to c limate chang e ... In creases in wildfires driv en by climate ch ange could signifi cantly i n crease PM concentrations be yond th e direct effect of changes in meteorological variables.”



### 79

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

PM and PM precursor emissions are affected by cl i m ate change throug h ph y s ical response (wind blown dust), bi ologi cal response (forest fi res and vegetati on t ype/distri bu tion) and hum an respo n se (energ y generation). Most natural aerosol sources are contro lled by clim at ic parameters like wind, moisture and te mp erature; thus, hum an induced climate change is expected to affect the natural aer osol burden. Biogenic organic material is both directly em itted into the atmosphere and produced by VOCs. All biogenic VOC emissions are highly sensitive to changes in temp erature, and are also highl y sensitive to cli m at e-induced changes i n plant species co mpositi on and biom ass distributions. Den m an et al. (2007) cite a study in which biogenic e m is sions rates are pr edicted to increase, on ave rage across w o rld regions , by 10% per 1°C increase in surface temp erature. The response of biogenic secondary or ganic carbon aerosol produ ction to a temp erature ch ange, however, could be considerably lower than the response of biogenic VOC e m i ssions since a e rosol y ields can decr e ase with increasing te mp erature ( D en m a n et al., 2007).

Particulate matter e m is s ions from fo rest fires ca n contribute to acute and chronic illnesses of th e respiratory s y stem , particul arly in chil dr en, incl udi ng pneum onia, upper respirator y diseases, asthma and chronic obstructive pulm onary diseases (WHO, 2002; Bowm an and Johnston, 2005; Moore et al., 2006; Confalonieri et al., 20 07). The IPCC (F ield et al., 20 07) reported with ver y hig h confidence that in North A m eri ca dist urbances like wildfire ar e i n creasing and are likely to intensify in a war m er future with drie r soils and longer growing seasons . F o rest fires w ith their ass ociated decre m ents to airquality and pulm onary effects are likel y to increase in frequenc y , severity , distribution, and duration in the Southeast, the Interm ountain West and the West co mp ared to a future with no clim ate change (CCSP, 2008b). Pollutants fro m forest fires can affect air qualit y for thousands of kilom e ters (Confalonieri et al., 2007). A study cited in Field et al. (2007) fo un d that, in the last three decades, the wild fire season in the western U.S. has incr eased by 78 day s , and burn durations of large fire s h a ve increa sed fro m 7.5 to 37.1 da y s , in response to a spring-summer warming of 0.87°C. It also found earlier spring snowmelt has led to longer growing seasons and drought, especially at higher elev ations, where the increas e in wildfire activity has been greatest. Analy s is by the State of California s uggests that la rge wildfires could become up to 55%
m o r e frequent in som e are as toward the end of the c e ntur y d u e to contin ued gl obal warm ing (California Clim ate Change Center, 2006).

PM chem istry is affected b y chan ges in temp erat ure brou ght about b y cli m ate change as follows. Temp erature is one of the m o st i mp o rtant meteo r ol ogical variables influencing air quality in urba n at m o spheres because itdirectly affects gas and heter ogeneous chemical rea c tion rates and gas-to-particl e partitioning. The net effectthat increased temp erature has on airborne particle c oncentrations is a bal a nce between incr eased production rates for secondary part ic ulate matter(increases particulate concentrations) and increased equilibrium vapor pressures for semi-v ol atile particulate co mpounds (decreases particulate concentrations). Increased temp eratures may either increase or decr ease the concentration of s e m i-volatile secondary reaction product s such as amm oniu m nitrate depending on am bient conditi ons.

Den m an et al ., 2007 note that there has been less work on the sensitivity of a e rosols to m e teorological conditions. It cites a st udy th at produces regional m odel si mu l a tions for Southern California on Septem ber 2 5 , 1996 proj ecting decreases in 24-hour average PM 2. 5 conce n trations with increasing te mp erature s for inland portions of the South Coast air basin, and projecting increase s for coastal regions. In CCSP (2008b), usin g th e NYCHP integrated m odel, PM 2. 5 concentrations are projected to increas e with clim ate change, with the effects differing b y co mponent species, with sulfates and primary PM increasing markedly and with organic and nitrated co mponents decreasing, mainly due to m ovement of these volatile species fro m the particulate to the gaseous phase.
The transport and rem oval of PM is highly sensitive to winds and precipitation. Rem oval of P M fro m t h e atm o sphere o ccurs mainly b y wet deposition (NAS, 2 005)

. S u lfate lifetim e, for example, is estim a ted to be reduced from 4.7 da y s to 4.0 da y s a s a result of i n creased wet deposition ( L iao and Sei n feld, 2006).



### 80

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Precipitation also aff ect s soil m o ist u re, with imp acts on dust source strength and on stomat a l opening/clos ure of plant l eaves, hence affecting bio g enic em issio n s (Den m a n et al., 200 7). Precipitation has generally increased o v er land north of 30° N over the period 190 0 to 2005 and it has beco me significantly wetter in eas tern parts of North Ame r ica (Trenberth et al., 2 0 07). However, m odel param e terizations of wet d e position are high l y uncertain and not full y realistic in th eir coupling to th e hy drol ogical cy cle (NAS, 2005). For m odel s to si mu l a te accur a tely the seasonally var y i ng pattern of precipitation, the y mu st correctly simu late a num be r of processes (e.g., evapotr a nspiration, condensation, transport) that are difficult to evaluate at a global scale (Randall et al., 2007).
In 1997 ( 62 FR 38680), EPA conclude d that particulate m a tter produces adverse effects on visibilit y , and that visibility impair ment is expe rienced (though not necessarily attribut ed to climate change) throughou t the U.S., in mu lti-st ate regions, urban areas, and rem o t e Federal Class I areas 34

. Visibilit y i mpairment depends strongl y on am bi ent relative h u m idity (NARSTO, 2004). Although surface specifi c hu m idit y globall y has generally i n creased aft e r 1976 i n close association with hi gher temp eratures o v er both land and ocean, observations suggest that r e lative hum i d ity has remained about th e sam e overall, from the surface throughout the tr oposphere (T renberth et al., 2007). Nevertheless, increases in PM due t o increases in wildfires induced by climat e ch ange m ight increase visibility impai r m e nt.
8(c) Health Effects due to CO 2 -Induced Increase s in Tr opospheric O 3 and Parti c ulate Matter

In addition t o the anal y ses described above of c limate chang e i mpacts o n air qualit y, one study specifically exa m ined the m o r e direct e ffect of CO 2 on air pollution m o rtality

. As described in the CCSP (2008 b) repo rt, using a coupled clim ate-air polluti on three-dimensional m o d e l, a stud y c o mp ared the health effects of pre-industrial vs. pres ent-day atm o spheric concentrations of CO 2 . The res u lts suggest that increasin g concentrations of CO 2 increas ed tropospheric ozone and PM 2. 5 , which increased m o rtality by about 1.1% per degree temp erature increase overth e baseline rate; the study esti m ated that about 40% of the increase was due to ozone and the rest to par ticulate m a tt er. The esti m ated m o rtality increase was higher in l o cations with poorer air quality.

34 The C l ean Ai r Act defi nes m a ndat o ry Fede r a l C l ass I ar eas as cert a i n n a t i onal parks ( o v e r 6, 00 0 ac res) , wi l d e r ness areas (over 5,000 acres ), national m e m o rial parks (over 5,000 acres), an d intern ation a l p ark s t h at were in ex isten ce as of A ugu st 7 , 19 77

.



### 81

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 9
Food Production and Agriculture
Food product ion and the agricultural sector within the U.S. are sensitive to short-term clim ate variability and long-term cli m at e change. This section addr esses how observed and projected cli m at e change m a y affect U.S. food prod uctio n and agriculture. Food pr oduc tion an d agriculture here include cro p yields and production, li vestock production (e.g ., milk and m e at), freshwater fisheries, and ke y climate-sensitiv e issues for this sector including drought risk and pests and weeds.
In addition to changes in average temp eratures and precipitation patterns, this section also addresses how U.S. food pr oduction and agriculture may be affected directly b y elevated CO 2 levels, as well as the frequency an d severity of extrem e events, such as droughts and st orms. Climate change-induced effects on tropospheric ozone levels and their i mpacts on ag riculture are discussed br iefly in Section 8 on Air Quality

. Vulnerability of the U.S. agricultural sector to cli m ate change i s a function of m a ny interacting factors including pre-existing climatic and soi l conditions, changes in p est co mp etiti on, water availability, and the sector’ s capacity to cope and adapt through m a na gem e nt practi ces, seed and cultivar technology, an d changes in econom ic co mp etition am ong regions.
The CCSP report o n U.S. agriculture (Backlund et a l., 2 008a) m a de the foll owing general conclusions fo r the U.S.:

• With increase d CO 2 and temp erature, th e life cy cle of grain and oilseed crops wi ll likely progress m o r e rapidly

. But, as temperature rises, these cr ops will increasin g ly begin to experience fail ure, especially if climate variabi lity increases and pr ecipitation lessens or becomes m o re variable.

• The m a rketable y ield of m a n y horticultu r a l crops – e.g ., tom a toes, onions, fruits – is very likel y to be m o r e sensi tive to clim at e change than grain and oilseed crops.

• Clim ate chan ge is likely to lead to a n o rthern m i gration of weeds. Many weeds respond m o re positively to increasing C O 2 than m o st cash crops, particularly C3 “invasive ” we eds 35 . Rece n t research al so suggests that glyphosate, the m o st wi dely used herbicide in the U.S., loses its effica cy on weeds grown at the increased CO 2 levels likely in the coming decades

.

• Disease pressure on crops and dom estic ani m als will likel y increase with earlier springs and warmer winters, which will allow p roliferati on and higher survival rates of pathogens and parasites. Regional variation in warming and changes in rainfall will also affect spati a l and te mporal distribution of disease.

• Projected increase s in te mperature and a lengthening of the growing season wi ll likely exte nd forage production into late fall and ea rly spring, thereby decreasing need for win ter se ason forage
reserve s. Ho wever, thes e benefits wil l very likel y be affe cted by regional variations in water availability

.

35 C 3 a n d C 4 re f e r t o di f fere n t carb o n fi xat i o n pat h way s i n pl ant s du ri n g ph ot osy n t h esi s

. C 3 i s t h e m o st com m on pathway, a n d C3 crops (e.g., wheat, s o ybea ns a n d rice ) a r e mo r e r e sp on s i v e th an C4 cr op s su ch a s ma iz e

.



### 82

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Clim ate change-induced shifts in plant sp ecies are alread y underway in rangel a nds. Establish m en t of perennial herbaceous species is reducing soil water availab ilit y earl y in the growing season. Shifts in plant productivity and type will likely also have significant imp a ct on livestock ope rations.

• Higher temp eratures will v e ry likel y reduce liv estock production during the summer season, but these losses will very like l y be partially offset by war m ertemp er atures during the winter season. For rum inants, current managem e nt sy stem s genera lly do not pro v i de shelter to buffer the ad verse effects of changing clim ate; such protection is m o re frequentl y available for non- rum inants (e.g., swine and po ultr y )

. The IPCC (2007b) m a de the following general conclu sion about food pro duction and agri culture fo r North A m eric a:

• Moderate cli m ate change in the early decades of th e century is projected to increas e aggregate y ields of rainfed agriculture by 5-20%, but with i mportant variabilit y am o ng regions. Major challenges ar e projected fo r crops that a re nearthe w a r m end of their suitable ra nge or depend on highly utilize d water resou rces [high confidence]

. 36
9(a) Crop yields and productivity

• Observational evidence sh ows that, over the last cen tur y , aggregate y ields of major U.S. crops have been increasing (US DA, 2007; Fi eld et al., 20 07), with significant regional and temp oral variation. Multiple factors contribute to these long ter m trends, including seed technology, use of fertilizers, managem e nt practices, and cli m ate ch ange (e.g., lengthe ning of the growing season).
For projected cli m at e chan ge effect s, the IPCC su mmar y conclusion of net be neficial eff ect s in the early decades in the U.S. under m oder a te cli m ate change, w ith significant regional variation, is supported by a num ber of re cent ass ess ments for m o s t major crops, a nd is consistent with the previous IPCC Third Assessment (2001) conclu sion. 37 Moderate cli m ate c h ange for temp erate regi ons such as the U.S. is described as local increas es in te mp er ature of 1-3o C (~2-5o F), which m a y occur within the next few decades or past m id-century depending on scenario (see Section 6 for temp er ature projections). Increased average war m ing leads to an extende d growing s eason, especially f o r n o rthern regions of the U.S. Further warming, however, is projected to have increasingly ne gative impa ct s in all regions ( m eaning both temp erate, including th e U.S., and t r opical region s of the world ) (Easterling et al. 2007).

The CCSP re port on agriculture (Hatfie ld et al., 2008 ) provides fur ther crop-specific detail ab out o p timu m temp eratures in order t o assess the eff e cts of future cl i m ate change. Crops are characterized by an upper failure-point te mp erature at which pollination and grain-set process es fail. Considering these aspect s , Hatfield et al., (2008) detail the following optimum mean te mperatures forgrain yields of the m a jo r agronom ic crops: 18-2 2 o C for maize, 2 2 -24 o C for s o y b ean, 15 oC for wheat, 23-26 oC for ri ce, 25oC for sorghum , 25-26 oC for cott on, 2 0 -26 o C f o r peanut, 2 3

- 2 4 o C for dr y bean, and 22- 25 oC for t o mato.

36 Acc o r d i n g t o I P C C t e rm i nol ogy , “ h i g h c o n f i d ence” co n v ey s an 8 out of 10 c h ance of bei n g correct. Se e Box 1.3
on pa ge 5 f o r a f

u l l desc ri pt i o n of IPC C ’s un cert a i n t y t e rm s. 37 The Nort h America chap ter from th e I P CC Th ird A ssessm en t Repo r t ( Cohen et al. 20 07) co n c l u d e d : “Foo d p r od u c tion is proj ected to b e nefit fro m a warmer cli m ate, b u t th ere p r o b a bly will b e stro ng reg i o n a l effects, with
som e areas in North Am erica suffe ring si gni ficant los s of c o m p arat i v e ad vant a g e t o ot he r re gi o n s ( h i g h confide n ce).”



### 83

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Given the variable responses of differen t crops to te mp erature (and other climatic) changes, and the fact that different areas of the countr y specialize in diffe rent crops an d have differe nt regional clim ates, th e variable future climate change effects am ong regions and crops are important to consider. The southeastern U.S. may be m o re vulnerable to increas es in average te mp erature than m o r e northern regions due to pre-existing te mp eratur es thatare al ready relativel y high. Likewise, certa in crops that are currently near cli m at e thresholds (e.g., wine grap es in Califor nia) are likely to experie n ce decrea se s in y i elds, quality , or both, even under m oder a te cli m ate ch ange scenarios (Fie ld et al., 2007).

Without the benefit of CO 2 , the anticipated 1.2o C rise in te mp er ature over the next 30 y ears (a ba seline
assu mp tion assu m e d in the CCSP (Hat field et al., 2008) report) i s projected t o decrease maize, wheat , sorghum , and dr y bean yields b y 4.0, 6. 7, 9. 4, and 8. 6 percent, respectively , i n their m a jor productio n regions. For soybean, the 1.2o C temp er ature rise wil l increase y i eld 2.5 percent in the Midwest wher e temp eratures during Jul y , August, Sept em ber averag e 22.5o C, but will decrease y ield 3.5 percent in the South, where mean te mp e rature during July , August , and September averages 26.7o C. Like wise, in the South, th at same mean temperature will result in redu ced rice, cott on, and peanut y ields, whi c h will decrease 12.0, 5.7, and 5

. 4 percent, resp ectively (Hatfield et al., 2008). An ant icipated CO 2 increase fro m 380 to 44 0 pp m will increase maize and sorghum y ield b y onl y 1 p e rcent, whereas th e listed C3 crops will increase y i eld by 6.1 to 7.4 percent, except for cotton, which shows a 9. 2 percent increase (H at field et al., 2008). Changes in pr ecipitation patterns will play a large role in determ inin g the net impacts of cli m at e change at the national and sub-national scales, where uncertainties about precipitation changes rem a i n ver y large. The IPCC (Field et al., 2007) reviewed integrated as sess ment m o deling studie s exploring the interacting i mpacts of cl i m ate and econom ic f acto r s on agricu lture, waterresources, and biom e boundaries in th e U.S. and concluded that scenarios with decrea sed pre c ipitation create i mportant challenges, restricting the availability of water for irr igation and at the same ti me increasing water deman d for irrigated agriculture,
as well as urb a n and ecological uses. Th e critical i mp o rt ance of sp ecific agro-cl i m atic events, such as last frost, also intr oduces uncertainty in futur e projections (Field et al., 2007).
There is still uncertainty about the sensitivit y of crop y ields i n the U.S. and other world re gions t o the direct effe cts of elevated CO 2 levels. The IPCC (E asterling et a l., 2007) concluded that elevated CO 2 levels are ex pected to contribute to small benefici al i mpacts o n crop yields. The IPCC confirmed the general conclusions from its previ ous Third Assessment Report in 2001. E xperim e ntal research on crop responses to elevated C O 2 through th e FACE (Free Air CO 2 Enrich m e nt) 38 experim e nts indicate that, at
am bie n t CO 2 concentrations of 55 0 pp m (approximately d ouble the concentration from pre-industrial times), crop y ields i n crease under unstr essed conditions by 10- 25% for C3 crops, and b y 0- 10% for C4 crops (m ediu m confidence). Crop m odel simu lations under elevated CO 2 are consistent with these ranges (high confide n ce) (Easterli ng et al., 2007). High temp eratures, water and nutrie n t availabilit y, and ozone exposure, ho wever, can significantl y li mit the direct stimulatory C O 2 response.
Hatfield et al . (2008) provides further detail about indivi dual crop species r esponses to elevated CO 2 concentrations and the interactive effe ct s with other c limate chang e factors. Ov erall, the benefits of CO 2 rise over the next 30 y ears are projected to m o stly offset the negative effects of te mperature for m o st C 3 crops except rice and bean, while the C4 crop yields are reduced by rising temp erature becau se they have little response to the CO 2 r ise (Hatfi eld et al., 2008)

. Thus, according to Hatfield et al. (2008), the 30- y ear outloo k for U.S. crop prod uction is relatively neutra l. However, the outloo k for U.S. crop production o v e r the next 100 y ears would not be as optimistic, if te mperature continues to rise along with clim bing CO 2 concentrations, because the C3 response to rising CO 2 is reachin g a satu rating plateau, while the negative temp erature effects will beco m e progressively m o re severe (Hatfi el d et al., 2008)

.

38 http://www. bnl.gov/face/



### 84

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

There are co ntinual changes in the genetic resource s of crop var ieties and ho rticultural crops that will provide increases in y i eld due to increased re sista n ce to waterand pest stresse s. These need to be considered in any future assess ments of the climatic i mp acts; howe v er, the genetic m odifications have not altered the basic te mp er ature response or CO 2 response of the biological sy stem (Hatfield et a l., 2008).
Although hor ticultural crops (fruits, vege tables and nuts) account for m o re than 40 percent of total crop market value in th e U.S. ( 2002 Census of Agriculture ), there is relatively litt l e inform ation on th eir response to CO 2 , and few rel i able crop si mu l a tion m odels for use i n cli m ate cha nge asse ss me nts co mp ared to that which is available for m a jor grai n and oilseed crops (Hatfiel d et al., 2008) . The m a rket able y ield of many horticultural crops i s likely to be m o re sensiti ve to cli m at e change than grain and oilseed crops because even short-ter m , minor environmental stres ses c a n negatively affect vi sual and flavor quality (Hatfield et al ., 2008).
9(b) Irrigation re quirements

The impacts of climate ch ange on irri g a tion water re quirem e nts may be large (Easterling et al., 2 007). The IPCC co nsidered this to be a new, robust findi ng since the T h ird Assessment Report in 2001. T h e increase in irrigation dem a nd due to climate change i s expected in the m a jority of world regions including the U.S. due to decreased rainfall in certain regions a nd/or increas ed evaporation arising from incr eas ed temp eratures. Longer gr owing seasons may cont ribut e to th e increased ir rigation demands as well

. Hatfield et al. (2008) describe in the CCSP report studi es that examined changes in irrigation requires for the U.S. unde r cli m ate change scenarios. For corn, a st udy cited i n Hatfield et al. (2008) cal culated that by 2030 irrigation requirements will change from -1 (Lower Co lorado Basin) to +451 percent (Lower Mississippi B asin), becaus e of rainfall variation. Given the varia tion in the sizes and basel ine irrigation require m e nts of U.S. basins, a repres entative figure fo r the overall U.S. increase in irrigation require m e nts is 64 percent if stom atal effects are ignored, or 35 pe rcent if the y are included. Sim ilar calcu lations were made foralfalfa, for which overall irrigation require ments are predicted to increase 50 and 29 percent in the next 30 years in the cases of ignoring and includi ng stom at al effects, respectively. These increases ar e m o r e likely due to the decre ase in ra infall durin g the growing season and the reduction in soil water availability

. 9(c) Climate vari a bility and extreme events

Weather even ts are a major factor in annual crop y ield variation. T h e projected imp acts of climate change often consider changes in average temp erature and precipitation patte rns alone, while not reflecting the potential for altered variab ilit y in event s such as dr o ughts and floods. The pot ential for these events to change in fre quenc y and magnitude introduces a ke y uncer tainty regarding future projections of changes in agricultural and food pr oduction due to clim ate change

. On this issue, the IPCC (Easterling et al. 2007) drew the following conclusion: “Rece nt studies indicat e that c limate change sc enarios t h at include increased fr e quenc y of heat str ess, droughts and f loodin g even ts reduce crop y ields and livestock productivi t y beyond th e imp acts due to changes in m ean vari ables al one, creating the possibility for surprises. Cli m ate variability and change also m odify the risks of fires, and pest and pathoge n outbreaks, with negative consequences for food, fiber and forestry (hi gh con f idence).” The adverse effects on crop y ields due t o droug hts and other extreme events may o ffset the be neficial direc teffects of elevated CO 2 , m oder a te te mperature incre ases over the near ter m , an d longer growing seasons.
Drought eve n ts are already a frequent occurrence, esp ecially in the western U.S. Vul n erability to extended drought is, according to IPCC (Field et al., 2007), increasing across North Am eri ca as populati on growth and econom ic dev e lopment incr ease deman d s from agricultural, mu nicipal, and industrial uses, resulting i n frequent over-allocation of water resources. Though dr oughts occur m o r e



### 85

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

frequentl y and intensel y i n the western part of the U.S., the east is not immune fro m droughts and attendant reductions in water suppl y , ch anges in wa ter qualit y and ecosy stem function, an d c h allenges in allocation (Field et al., 2007).
Average annual precipitat ion is projected to decrease in the southwestern U.S. but increase over the rest of North America (Christ e nsen et al., 2007). So me studies project widesp read increases in extreme precipitation (Christensen et al., 2007) , with greater ri sks of not on ly floo ding from intense precipitation, but also droughts from greater temporal variability i n precipit a tion. Increased runoff due to intense precipitation on crop field s and anim al agriculture ope rations m a y result in an increased contributi on of sedi m ents, nutrients, pathogens, and pesticid es in surface waters ( K undzewicz et al., 2007).

One econo m i c consequence of excessiv e rainfall is dela y e d spring planting, which jeopardizes profits for farm ers paid a premiu m for early season producti on of high v a lue horticultural crops su ch as melon, sweet corn, and tom a toes (Hatfield et a l., 2008). Fie ld flooding during the growing season causes crop losses associ ated with anoxia, incr eases susceptibility t o root diseases, in cr eases soil co mp action (due t o use of heavy far mequipment on w e t soils), and causes m o r e runoff and leaching of nutrients and agricultural che m ical s into groundwater and surface w a ter (Hatfi eld et al., 2008).
9(d) Pests and we eds

Pests and w e eds can redu ce crop y i elds, cause eco nom ic los ses to far m er s, and require manage ment control options. How cli m ate chang e (elevated CO 2 , increas ed te mp eratu res, altered precipitation patterns, and changes in th e frequency a nd intensit y o f extre m e eve n ts) may affect the prevalence of pest s and weeds is an issue of concern for food pr oduction and th e agr icultural sect or. Recent war m ing trends in the U.S. have led to earlier insect sp ring activity a nd proliferation of som e species (E ast erling, et al., 2007).
The growth of m a ny crops and weeds is being st i mulated (Backlund et al., 2008a). Wee d s generally respond m o r e positively t o increasing CO 2 than m o st ca sh crops , particularly C3 invasive weeds; and while there are m a ny weed species th at h a ve the C4 photos y n thetic path way and therefore show a smaller response to at m o spheric C O 2 relative to C3 crops, in m o st agronom ic situations, crops are in co mp etition with both C3 and C4 weed s (Backlund et al.,, 2008a). The IPCC (Easterling et al., 2007) concl uded, with high confide n ce, that climate variabil ity and change m odify the risks of fires, and pest and pathogen outbreaks, with negative consequences for food, fibe r and forestry across all wo rld regions.

Cli m ate change is likel y to lead to a north ern m igra tio n of weeds (Backlund et al, 2008a). Recent research also suggests that glyphosate, the m o st widely used herbicide in th e U.S., loses its effica cy on weeds grown at the increas ed CO 2 levels likely in the com ing d ecades (Backlund et al., 2008a).
Disease pressure on crops and dom est ic ani m als w ill likely increase with ear lier springs and war m er winters, which will allow proliferation and higher su rvival rates of pathogens and parasites. Regional variation in warm ing and changes in rainfall will also affect th e spatial and temporal distribution of diseases (Backlund et al., 2008a).
Most studies, however, continue to investigate pest da m a ge a s a separate function of either elevated
am bie n t CO 2 concentrations or temp erat ure. Pests and weeds are additional factors that, for e x ample, are often om itted when projecting th e direct stimulatory effect of elevated CO 2 on crop y ields. Rese arch on the co m b ined effect s of el e v ated CO 2 an d cli m ate change on pests, w eeds and disease is still insufficient for U.S. and world agriculture (Easterli ng et al., 2007).



### 86

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

9(e) Livestock

Hatfield et al. (2008) describe how temp erature chang es and environmental str e sses can r esult in declines in phy s ical activity and an associ ated decline in ea ting and grazing activity (for rum inant s and other herbivores), or elicit a panting or shi v ering respons e, which increases m a intenance requirements of the ani m al and contributes to decreases in animal product ivit y

. Clim ate change has the po tential to infl uence livest ock productiv i ty in a num ber of way s

. Elevated CO 2 concentrations can affect f o rage quality ; thermal stres s can directly affect the health of livestock animals ; an increase in the frequency or m a gnitude of extrem e events c a n lead to li vestock loss; and cli m at e change m a y affect the spr ead of animal disease s. The IPCC has g e nerated a num b e r of new conclusions in this area comp ared to the Th ird Assessment Report in 2001. These conclusions (Easterling et al., 2007), along with those fro m the m o re recent CCSP report (Hatfield et al., 200 8) i n clude:

• Higher temp eratures will v e ry likel y reduce liv estock production during the summer season, but these losses will very like l y be partially offset by war m ertemp er atures during the winter season. For rum inants, current managem e nt sy stem s genera lly do not pro v i de shelter to buffer the ad verse effects of a changing climate; such protection is m o re frequen tly available for non-rum inants (e.g., swine and poultr y )

.

• Based on ex pected vegetation changes and known environm ent a l effects on forage protein, carbohy d rate, and fiber contents, both positive and negative changes in forage qualit y are possible
as a result of at m o spheric and cli m atic change. Elevated CO 2 can increase the carbon to nitr ogen ratio in forages and thus reduce th e nutritional value of those grasse s, which in turn affects ani m al weight and perform ance. Under elevated CO 2 , a de creas e of C4 grasse s and an increas e o f C3 grasses (depe nding upon the plant species that re mai n ) may occur which could potentially reduce or alter the n u tritional qua lit y of the forage gr as ses available to grazing livestock; however the exact effects on both types of grasses an d their nutritional quality still needs to be deter m ined.

• Increased climate variability (including extrem es in b o th heat and cold) and droughts may lead to livestock loss. The impact on anim al pr oductivit y du e to increased variabilit y in weather patt erns will likely be far greater th an effects associated with the average ch ange in climatic conditions

. 9(f) Freshwater and marine fisheries

Freshwater fisheries are sensitive to ch a nges in temp erature and water suppl y , which affect flows of rivers and strea m s, as well a s lake levels. Climate change can interact with other factors that affec tthe health of fish and productivity of fisheries (e.g ., habitat loss, land-use change).
The IPCC (F ield et al., 2007 and references ther ei n) reviewed a num b e r of North Am er ican studies showing how freshwater fi sh are sensiti ve to, or ar e being affected by , observed changes in climate:

• Cold- and cool-water fisheries, esp eciall y salm onids , have been declining as warm er/drier conditions reduce their habitat. The sea-run salmon stocks ar e in steep d ecline throug hout mu ch of North A m eri ca;

• Pacific s a l m o n have been appearing in A rctic rivers; 39

• Sal m onid species have bee n affected by war m ing in U.S. strea m s;

39 Ar ct i c i n cl u d e s l a rge re gi o n s of Al as ka, a n d t h e Al as ka n i n di ge no us p o pul at i on m a kes u p l a rgest i ndi ge no us p opu latio n of t h e A r ctic (see A C IA , 20 04 ).



### 87

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Success of ad ult spawning and survival of fry brook tr out is closel y linked to cold groundwater s eeps, which provi de preferred temp erat ure refuges for lake-dwelling pop ulatio ns. Rates of fish eg g developm ent and m o rtality increase with temp eratur e rise within species- speci fic tolerance ranges.
Regarding the i mpacts of future climate change , IPCC concluded, with hi gh confi d ence for North Am eri ca, that cold-water fi sheries will li kely be nega t ively affected; warm-water fisheries will generally benefit; and the results for cool-water fisheries will be m ixed, with gains in the northern and losses in th e southern port ions of ranges (Field et al., 2007). A number of specific imp acts b y fish species and regio n in North Am erica are projected (Field et al., 200 7 and references therein):

• Salm onids, which prefer cold water, are likely to experience the m o s tnegative impacts;

• Arctic freshwaters will likely be m o st affected , as they will experience the greatest warm ing;

• Many warm -water and co ol-water species will shift their ranges northward or t o higher altitudes;

• In the continental U.S., cold-water species will likel y disappear from all but the deeper lak es, coolwater speci es will be lost mainly from shallow lakes, and warm water species will thrive ex cept in the far south, where temp eratu res in shallo w lakes will exceed survival thresholds.

Clim ate variabilit y and change can also impact fish eries in coastal and estuarine waters, although nonclim atic factors, such as overfishi ng and habitat loss and degradatio n, are already responsible for reducing fish stocks (Nichols et al., 2007). Coral reefs, for exa mple, are vulnerable to a range of stre sses and fo r many reefs, ther m a l stress thresholds will be cro ssed, resulting in bleaching, with severe adver s e consequences for reef-based fisher ies ( N ichols et al. , 2007). Incr eased stor m i n tensity, temperature and salt water intrusion in coast al water bodies can al so ad versely impact coastal fisheries productio n.



### 88

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 10

Forestr y

This section addresse s how cli m at e change may affect forestry , including timber y i elds, wildfires and droug ht risk, forest co mposition, and pests in the U.S.

. The CCSP report addressing forestry a nd land resour ces (Ry a n et al., 2008) made the following general conclusions f o r the U.S.:

• Cli m ate chan ge has very likely increas ed the siz e a nd num ber o f forest fire s, insect outbreaks, and tree m o rtality in the interior west, the Southwest, a nd Alaska, and will continue to do so. An i n creased frequency of disturbance is at least as important to ecosy stem f

unction as incre m ental changes in te mp era t ure, precipitation, at m o spheric CO 2 , nitro g en depositi on, and ozo n e p o llutio n. Disturbances partially or c o mp let e ly change forest e c osy s tem stru cture and spe c ies co mposition, cause sh ort-ter m productivi t y and carbon st orage loss, allow better op por tunit ies for invasive alien species to beco me established, a nd command m o r e public and m a nage me nt attention a nd resources.

For North A m eric a, the IPCC (Field et al., 2007) concluded:



### • Overall forest growth in North Ameri ca will likely increase m odestly (10-20%) as a result of extended growing seasons and elevated CO 2 over the next centur y , but with i mportant spatial and temporal variation (m ediu m confidence). 40



### • Disturbances like wildfire and insect outbreaks ar e in creasing and are likely to intensify in a war m er future with drier soils and longer growing seasons (v ery high confidence). Although recent cli m at e trends have increas ed vegetation growth, conti nuing increases in disturbances are likely to lim it carbon storage, facilitate i nvasive species, and di srupt ecosy stem services. Over the 21st century , pressure for species to sh ift north and to higherelevations will fundam e ntal ly rearrange North A m eri can e c o sy stem s. D i fferential c a p acities for range shifts and constraint s fro m developm ent, habitat fragmentation, invasive speci es, and br oken ecological connections will alter ecosy s tem structure, function, and services.
10(a) Forest Prod uctivity
Forestry productivit y is known to be sensitiv e to changes in climate variables (e.g. te mp er ature, radiation, precipitation, water vaporpressure in the air, and wind speed), as thes e aff ect a nu m b erof phy s ical, che m ic al, and biological processe s in forest sy ste m s (Easterling, et al., 2007). However, as noted in a CCSP report addressing the forest secto r (Ry a n et al., 2008), it is difficult to separate the rol e of cli m at e from other potentially influencing factors, particular ly because thes e interactions vary by location.

For the U.S. as a whole, forest growth and pro ducti vi t y have been observed to change, in part due t o observed climate ch ange. Nitrogen de position and w a r m er t e mp er atures have very likely inc reased fores t growth where water is not lim iting (Ry a n et al., 2008). The IPCC (Field et al., 2007 and references therein) outli nes a nu m b er of studies dem onstrati ng the observed connection between ch anges in U.S. forest growth and changes in climate var iables:

40 Acc o rding t o IPCC term inology, “m edium c o nfide n ce” c onv eys a 5 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s.



### 89

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Forest growth appears to be slowly acceler ating (less than 1% per decade) i n regions where tree growth has historically bee n lim ited by lo w te mp eratu res and short growing seasons;

• The length of the vegetation growing season has in creas ed an a v erage of 2 day s per decade since 1950 in the c onterm inous U.S., with most of the incr ease r esulting from earlier spring war m ing;

• Growth is slowing in areas subject to drought;

• On dry south -facing slopes in Alaska, growth of white spruce ha s decr eas ed over the last90 y ears , due to increased drought stress;

• In sem i-arid forests of the south-western U.S., gr owth rates have decreased since 1895, co rrelated with drou ght from warming temp eratures;

• Mountain for ests are increasingly encro ached upon from adjacent lowlands, while simu ltan e ously losing hi gh al titude habitat s due to warming (Fischlin et al., 20 07)

. • In Colorado, aspen have advanced int o the m o re cold-tolerant s p ruce-fir forests over the past 100 y ears;

• A co m b ination of warmer temp eratures and insectinfestatio ns has resulted in econom ically significant losses of forest resource base to spruce bark beetle in Alaska.
Forest produ ctivit y gains may result th rough: (i) the direct stimulatory CO 2 fertilization effect (although the magnitude of this effect rem a ins uncertain over th e long term and can be c u rtailed b y other changing factors); (ii) war m ing in cold climates , given concom itant preci pitation increases to co mpensate for possibl y increasing wat e rvapor pressure deficits; a nd (iii) precipitation incr eases under water li mited conditions (Fischlin et al., 2007).

New studies suggest thatdirect C O 2 effects on tr ee growth may be lower than previously assu m e d (Easterling et al., 2007). Additionall y, the i n itial i n crease in gr owth increments may be lim ited by
co mp etition, disturbance, air pollutants (prim a rily tropospheric ozone), nutrient lim itations, ecological processes, an d other facto rs, and the r esponse is si te- and speci es-specific ( E asterling et al., 2007). Sim ilarly , Ry an et al. (2008) stated that , where nutrients are not lim iting, rising CO 2 increas es photos ynthesi s and wood production (with y o unger st ands respondi ng m o st strongl y ) , but th at on infertile soils the extra carbon from increased photos ynthesis will be quickl y respired.
The general findings from a nu m b er of recent sy ntheses using data fro m th e three A m er ican and one European CO 2 -enrichm ent FACE study sites show that No rth American forest s will absorb more CO 2 a nd might retain m o re carbon as atm o spheric CO 2 increases. The incr ease in th e rate of carbon sequestration will be highe st (m ostly in wood) on nutrient-rich soils with no water lim itation and will decrease with decreasing fertilit y and water suppl y . Se veral y e t unr e s olved questi ons prevent a definitive assessment of the effect of elevated CO 2 on other co mponents of the carbon cy cle in forest ecosy stem s (Ry a n et al., 2008).

As with cro p y ields, oz one pollution will m odify the effects of elevated CO 2 and an y changes in temp erature and precipitation, but thes e mu ltiple in te ractions ar e difficult to predict becau se they have been poorl y studied (Ry a n et al., 2008). Nitrogen de position also play s a role. Nitrogen deposition and
war m er te mperatures have very likely increased fo r est growth where w a teris not lim iti ng and will continue to do so in the near future. N itrogen depos ition has like ly increased forest growth rates over large areas, and interacts positivel y t o enhan ce the forest gro w th response to increasing CO 2 . These effects are ex pected to continue in th e fu ture as N deposition and ri sing CO 2 con tinue.
For the pr ojected temp erat ure increases over the nextfew decades, m o st studi es support the conclusion that a m odest warm ing of a few degrees Celsius will lead to greater tree grow th in the U.S. There are many causes for this enha nce m ent incl uding direct phy s iological CO 2 effects, a longer growing season, and potentially greater m in e ralization of soil nutrient s. Because dif ferent species may respond somewhat



### 90

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

differently to war m ing, the co mp etitive balance of species in for ests may change. Trees will probabl y beco m e estab lished in formerly colder habitats ( m ore northerly , higher altitude ) than at present (Ry a n et al., 200 8).

Productivit y gains in one area can occur simu ltaneous l y with pr oductivit y losses in other areas. For a widespread species like lodgepole pi ne, a 3 o C temp erat ure increase would i n crease growth in th e norther n part of its range, decrease growth in the m iddle, and decim a te southern forests (Field et al., 2007). Cli m ate change is expected to increase California tim b e r production by the 2020s because of stimulat ed growth in the standing forest. In the long run (u p to 2100), these productivity gains were offset by reductions in productive area for soft woods growth. Risks of lo sses fro m So uthern pine beetle likely depend on the seasonality of warm ing, with winter a nd spring w a r m ing leading to the greatest dam a g e (Easterling et al., 2007 and reference s therein).
According to studies reviewed b y IPCC (Field et al ., 2007), the eff ects of clim ate change, in th e absence of dram ati c increas es in disturbance, on the poten tial for commercial harvest in the 2040s ranged fro m mixed for a l o w em issions scenario to positive for a high em i ssions scenario. The tendency for North A m eri can producers to suffer losses incr ease s if cli m a t e change is a cco mp anied by increased disturbance, with si mu lated losses aver aging US$1- 2 billion/ y ear over the 21st century according to a 2005 study referenced in Field et al. (2007).

U.S. forestry , in addition t o experiencing direct cli m ate change effects, may be indirectly a ffected by changing for est productivity i n different regions of the world. Easterling et al. (2007) cite a study showing two cli m at e chan ge scenarios where North Am eri can for ests undergo m o r e diebackin general than forests in other regions of the world, and where certain North American forest y i elds increase but less so co mp ared to other regions. The implic ation is that forests in other parts of the world (including tropical forests with short e r rotations) could have a comp etitive advantage within the gl obal forestr y sector under a changing cl i m ate.

Cli m ate change will also substantiall y i mp act other non-tim ber goods and services, such as seeds, nuts, huntin g, resins, plants used in pharmaceutical and botan ical medici ne, and in the cos m etics in dustry ; these i mpacts will vary significantl y across world regions (Easterling et al., 2007).
10(b) Wildfire and Drought Risk

While in some cases a changing climate may have pos itive i mpacts on the pr oductivit y of fore st sy stems, changes in disturbance patterns are expected to have a substantial imp act on overall gains or losses. Mor e prevalent forest fire disturbances have recently b een observed in the U.S. and other w o rld regions (Fischlin, et al., 20 07). Wildfires and drou ghts, a m ong other extrem e events (e.g., h u rricanes) that can cause forest d a m a ge, pose t h e largest threats over ti me to forest ec osy s tem s

. Several lines of evidence suggest that l a rge, sta nd-re placing wildfires will likel y increase in frequency over the next several decades because of climate war m ing (Ry a n et al., 2008). General cli m ate war m ing encourages wildfires by extending the summer period that dries fuels, prom oting easier ignition and faster spread (Field et al., 2007)

. The IPCC (Fi e ld et al., 2007 and referen ces ther ein) noted a nu m b er of observed changes to U.S. wildfir e size and freq u ency , often associating these chang es with changes in average temp eratures:

• Since 1980, an average of about 22,0 0 0 km 2 /y ear (13,7 00 m i 2 /year) has burned in wildfires, alm o st twice the 1920-198 0 average of about 1 3 ,00 0 km 2 /y e a r (8,080 m i 2 /y ear);



### 91

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• The forested area burned i n the western U.S. from 19 87-20 03 is 6. 7 tim es the area burned fro m 1970­ 1986;

• Hu m a n vulnerability t o wildfires has increased, with a rising populati on in the wildland-urba n interface;

• In the lastthree de cades, t h e wildfire se ason in the w estern U.S. has incr eas ed by 78 da y s , and burn durations of fires greater than 1,000 ha (2, 470 acr es) have incr eased fro m 7.5 to 37.1 day s , i n response to a spring/summer warming o f 0.87°C (1. 4 °F);

• Earlier spring snowmelt has led to longer grow i ng seasons and drought, especially at higher elevations, where the increase in wild fire activity has been greatest;

• In the south- western U.S. , fire activity is corre lated with El Niño-Souther n Oscillation (ENSO) positive phases and higher Pal m er Drought Severit y Indices. 41 Major fire y ears tend to foll ow the switching from El Niño to La Niña conditions d u e to buil dup of material during wet y ears followed by desiccation duri ng a dr y y ear, whereas small fires are strongly associated directly with previous y ear drought. Further m o re, increa sed te mp er ature in the future will likely extend fire se asons throug hout th e western Un ited States, with m o re fires occurring earlier and later than is c u rrentl y typical, and will increase the total area burned in some regions.
Thoug h fires and extreme events are n o t well repre sented in m o dels, current clim ate m odeling studies suggest that increased temperatures and longer growi ng seasons will elevate fir e risk in connection with increased ari d ity

. Som e r esear ch identifies the possi bility of a 10% increase i n the seasonal severity of fire hazard over mu ch of the U.S. under cli m at e cha nge (Easterl ing, et al., 2007). For Arctic regions, forest fires are expect ed to increase in frequency and intensity (ACIA, 2004). In California, the risk o f increased wil d fires a s a re sult of cli m a t e change ha s been identi fied as a significant issue (California Energ y Commission, 200 6).
10(c) Forest Comp osition

Cli m ate chan ge and associ ated changes in disturbanc e re gi mes will cause shifts in the distributions of tree species and alter forest species co mp osition. With warm ing, forests will extend further north and to higher elevations. Over currently dry regions, in creased precip itation may allow forests to displac e grasslands an d savannas. Changes in forest co mposition in turn c a n alter the fr equencies, intensities, and i mpacts of disturbances su ch as fire, insect outbreaks, and disease.
In Alaska and neighboring Arctic regions, there is strong evi d ence of recent vegetation c o mposition change, as outlined by the IPCC (Anisi mov et al., 2007 and references therein):

• Aerial photog raphs show in creased shrub abundance in 70% of 20 0 l o cations;

• Along the Arctic to sub-Arctic boundar y , the tree-lin e has m oved about 6 m i (10 k m ) northwards and 2% of Alaska n tundra on the Seward Pen insula has b een displaced by forest in the past 50 y ears;

• The pattern of northward and upward tree-line ad vances is co mp arable wit h earlierHo locene changes;

• Analy ses of satellite i m ag es indicate th at the length of growing s eason is incr easing by 3 day s per decade in Ala s ka.
Likely rates of m igration northward and to higher el evations are unc ertain and depend not o n l y on climate change but also on f u tu re land-use patterns and habitat fragmentation, which can impede species

41 The Pal m er Dro u ght Seve ri t y In de x i s use d by NO A A a n d uses a fo rmul a t h at i n cl udes t e m p erat ur e a n d rai n fal l t o d eterm in e d r y n ess. It is m o st effectiv e in d et erm in in g lon g -term d r o ugh t. Po sitiv e PDSI in d i cates wet co nd itio ns, n e g a tiv e PDSI in d icates d r y co nd itio ns.



### 92

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

migration. Bioclimate m o deling based on outputs from five gener a l circulation m odel s suggests increases in tree species richness in the Nort hwest and decreases in the Southwest on long tim e scales ( m illennia). Over the next centur y , however, even positive long- term species richness m a y lead to short-term decreases because species that are in tolerant of local conditions may disappear relatively quickl y while migration of new species into the area may be quite slow (Field, et al., 2007; Currie 2001). The Arctic Cli m ate I mp act Ass ess ment (2004) a lso conclude d that vegetation zones are projected to m igrate northward, w ith forests encroaching on tundra and t undra encroaching on pol a r deserts. L i m itations in
am ount and qualit y of soils are likely to hinder these pol eward shifts. No experi ments have assessed the effect of chan ges in precipitation on for est tree species composition (Ry a n et al., 2008).
10(d) Insect s and Disease s

Insects and diseas es are a natural part o f forested ec osy s tem s and outbreaks often have co mplex cause s. The effects of insects and disease s can vary from defo liation and retarded growth , to tim be r damage, to
mas s ive forest diebacks. Insect lif e cycles can be a factor in pestoutbreaks; and insect lifecy cles are sensitive to cli m at e change. Many northern insects have a two-y ear life-cy cle, and war m er winter temp eratures allow a larger fraction of overwinteri ng larvae to s u rvive. Recentl y , spru ce budworm in Alaska has c o mp let e d its life cy cle in one y ear, rathe r than the pre v iousl y observed duratio n of two y ears (Field et al., 2007). Recent war m ing t r ends in the U. S. have led to earlier spring activit y of insects and proliferation of some species, such as the m ountain pine beetle (Easterling et al., 2007). During the 1990s, Alaska’s Kenai Peninsula experienced an outbreak of spruce bark beetle over 16,000 km 2 with 10­ 20% tree m o rtality (Anisim ov et al., 2007). Also f o llowing recent war m ing in Alaska, spruce budworm has reproduced farther north reaching problematic num b e rs ( A nisim ov et al., 2007). Climate change m a y indirectly affect insect outbreaks by affecting the over all health a nd productivity of trees. For example, susceptibility of trees to insects is increased when mu lti-y ear droughts degrade the trees’ ability to generate defensive chem icals (Field, et al., 2007). Warmer temp eratures have already enhanced th e opportunities for insect spread across th e landscape i n th e U.S. and other world regions (Easterling et al., 2007).
The IPCC (E asterling et al., 2007) stated that m odeling of future cli m ate ch ange i mpact s o n insect and pathogen out breaks remains lim ited. Nevertheless, the IPCC (Field et al., 2007) states with high confidence that, across No rth A m eric a, i mpacts of cl i m ate change on commer c ial forestry potential are likely to be sensitive to changes in disturbances fro m i n sects and diseases, as well as wildfires.
The CCSP report (Ry a n et al., 2008) states that the ranges of the m ountain pine beetle and southern pine beetle are projected to expand northward as a r esult of ave rage te mp era t ure increase s. Increase d probabilit y of spruce beetl e outbreak as well as incr ease in cli m ate suitability for m ountain pine beetle attack in high-elevation ec osy s te m s has also been pro jected in response to warming (R y a n et al., 200 8).

Cli m ate change can shift the current boundaries of in sects and pathogens and m odify tree phy s iology and tree defense. An increase in climate extre m es ma y also prom ot e plant diseas e and pest outbreaks (Easterling et al., 2007).



### 93

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 11

Water Resources

This section covers clim ate change effects on U.S. w a ter suppl y , water quality , extrem e events affecting water r esources, and wat e r uses. Information about observed trends as wel l as projected impacts i s provided

. The vulnerabilit y of freshwater resources in the U. S. to cli m at e change vari es fro m regi on to region. Although water m a nagement practices in the U.S. are generally advanced, part icularly in th e West, the reliance on past conditions as the basis for current a nd futu re pla nning will no longer be appropriate, as cli m at e chan ge increasing ly creates co nditions well outside of historical observations (Lettenmaieret al., 2008). Exa mpl es of large U.S. waterbodies where cl i m at e change raises a concern include the Great Lakes, Chesa peake Bay , Gulf of Mexi co, and the Colum b ia River Basin.

For North A m erica, IPCC (Field et al., 2007) co nclu ded:



### • Cli m ate change will constrain North Am erica’ s over-allocated water r e sources, increasing
co mp etition am ong agricultural, municipa l, industrial, and ecologi cal uses (ver y high confidence) 42

. Rising temp eratures will d i m inish snowpack and in crease evaporat ion, affecting seasonal availability of water. Higher dem a nd from econo m ic development, agriculture and pop ulatio n growth will further lim it surface and groundwater av ailability. In the Gr eat Lakes and m a jor river sy stem s, lower level s are likely t o exacerbate challenges relating to wat e r qualit y , navigation, re creation, hy dropower generation, water transfer s, and bi-natio n a l relationships.
11(a) Water Supply and Sn owpack
Surface W a ter and Snowpa ck

The semi-humid conditions of the eastern U.S. tran sition to drier conditions in the west that are interrupted b y the Rock y Mountains. The driest climates, howev er, exist in th e Interm ountain West and Southwest, beco m i ng m o r e hu m i d as one proceeds west and n o rth to m o re hum id conditions on the upslope areas of the Ca scade and coastal m ountain ranges, especially in the Pacific Northwest (Letten m aier et al., 2008)

. IPCC reviewed a nu m b er of studies showing trends in U.S. precipitation patte rns, surface water suppl y , and snowpack, and how cli m ate change may be contributing to som e of these tre nds (Field et al., 2007):



### • Annual precipitation has i n creased thro ugho ut m o st of North America.



### • Stream flow i n the east ern U.S. has incr eased 25% in the last 60 y ears, but has decreased by about 2% per decade in the central R o cky Mounta in region over the last century

. 

### • Since 1950, stream discharge in both the Colorado an d Colum b ia river basins has decreased.



### • In regions with winter snow, warming has shifte d the m a gnitude and tim i ng of h y drol ogic events. The fraction of annual precipitation falling as rain (rather than sn ow) increased at 74% of the weather stations studied in the western m ountain s of the U.S. f r om 1949-20 04.



### • Spring and summe r snow c over has also decrea sed in the U.S. West.

42 Acc o rding t o IPCC term inology, “ v ery high confide n ce” c o nveys a 9 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s.



### 94

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Break-up of river and lake ice across North Am eri ca advanced by 0.2 – 12.9 d a y s over the last 100 y ears. In the Arctic, precipitation has increased b y about 8% on average over the past century

. Much of the increase has f a llen as rain, with the largest increase s o ccurring in au tum n and winter. Later freeze -up and earlier break-up of ri ver and lake ice have co m b ined to reduce the ice se ason by one to three we eks in
so m e areas. Glaciers throughout No rth America are melting, and the par ticularly rapid retreat of Alaskan glaciers represents about h a lf of the estimated loss of glacial mass worldwide (ACIA, 2004). Permafrost play s a large role in the h ydrolog y of lakes and po nd s. The spatial pattern of lake disappearance strongl y suggests that per m afrost thawing is driving the change s. These changes to Arctic precipitation, ice extent, and glacial abundance will affect key regional bio-phy si cal sy stems, act as clima tic feedbacks (prim arily by changi ng s u rface albedo), and have socio-econom i c impacts (high confidence) (Anisi m ov et al., 2007).
In regions including the Colorado River, Colum b i a River, and Ogallala Aquifer, surface and/or groundwater resources ar e intensivel y used and subject to competition from agricultural, municipal , industrial, and ecological needs. This increases the potential vulnerability to future changes in tim ing and availability of water (Field et al., 2007)

. Projections for the western m ountains of the U.S. su gg est that warm ing, and changes in the form , tim ing , and am ount of precipitation will very likely (hi g h c onfidence) lead to earlier melting and significant reductions in snowpack by the m iddle of the 21st centur y (Lettenmaier et al., 2008; Field et al., 2007). In
m ountainous snowm e lt-dominated wate rsheds, projections suggest adva nces in the tim ing of snowmelt runoff, increases in winter and early spring flows (rais ing flooding potential), an d substantially decrease d
su mmer flows. Heavily

- u tilized water sy stem s of th e western U.S. that rel y on capturi ng snowm e lt runoff, such as the Colu mbia River sy stem , will be esp ecially vulnerable (Field et al., 2007). Reduced snowpack has been identified as a major concer n for the State of Calif ornia (California Energy Co mm ission, 2006).
Globally, cur rent water managem e nt practices are very li kel y to be inadequat e to reduce th e negativ e impacts of clim ate change on water suppl y reliabili ty, floo d risk , and aquatic ecosy stems (very hig h confidence) (Kundzewicz et al., 2007). Less reliable s upplies of water are likely to create challenges for managing ur ban water systems as well as for in du stri es that depend o n larg e volum es of water. U.S. water manag e rs currently anticipate local, regional, or state-wide water shortag es over the next ten y ears. Threats to reliable supply are co mp licated by hi gh p opulatio n gro w th rates in western states where man y resources are at or approaching full utilization. In Eastern Nort h A m eri ca, d a ily precipita tion so heavy that it now o ccurs only once every 20 years is projec ted to occur a pproxim a tely every eight y ears by the end of this centur y , un der a m i d-range em ission scenario (CCSP, 2008i). Pot e ntial increases in heavy precipitation, with expandi ng impervious surfaces, co uld increase urban flood risks and creat e additional design challenges and costs for stormw ater management (Field et al., 200 7). Th e IPCC (Field et al., 2007 and reference s therein) reviewed seve ral regional-le vel studies on cli m at e chan ge i mpacts to U.S. water management which showed:



### • In the Great Lakes – St. Lawrenc e Ba sin, m a ny , but not all, assess ments pr oject lower net basin supplies and lake wat e r lev e ls. Lowe r water level s ar e likely to influence many sectors, with mu ltiple, interacting imp acts ( IPC C: high confidence). A t m o sphere-la k e interactions contribute to the uncertainty in assessing these i mpact s though.



### • Urban watersuppl y s y stems in North Am erica ofte n draw wat e r fro m considerable distances, so clim ate impacts need not be local to affect cities. By the 2 020s, 41% of the w a ter suppl y to southern California is likel y to be vulnerable due to snow pack loss in the Sierra Nevadas and Colorado Rive r basin.



### 95

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• The New Yo rk area will likely experience greater wate r suppl y variabilit y

. Ne w York Cit y ’s sy stem can likely adapt to future changes, but the region’ s s m aller sy stems may be vulnerable, lea d ing to a need for enhanced regional water distribution plans.
In the Arctic, river dischar ge to the ocean has increa sed during the p ast fe w de cades, and pe ak flows in the spring are occurring earlier. These changes are pr ojected to accel erate wi th future climate change. Snow cover extent in Alaska is project ed to decreas e by 10-20% by the 2070s, with greatestdeclines in spring (ACIA, 200 4 and ref e rence therein).

The IPCC concluded with high confide n ce that unde r m o st cli m at e change scenarios, water resources in
sm all islands around th e gl obe are likely to be serious ly comp ro m i sed (Mimura et al., 20 07). Most sm all islands have a li m ited wat e r suppl y , and water reso urces in these islands are especially vulnerable to future changes and distrib u tion of rainfall. Reduc ed rainfall ty pically leads to decre ased surface wat e r suppl y and sl ower recharg e rates of the freshwater lens 43 , which can result in prolonged drou ght impacts. Many islands in the Caribbean (which in clude U.S. te r ritories of Puerto Rico and U.S. Virgin I s lands) are likely to experience incr e ased w a ter st ress as a r e s u lt of climat e change. U nder all SRES scenarios, reduced rainfall in su mmer is projected for the Ca ribbean, making it unlikel y that the dem a nd for water
resources wil l be m e t. Inc reased r a infal l in winter is unlikely to comp ens a te fo r these w a ter deficits due to lack of storage capacity (Mi mura et al. , 2007).

Groundwater
Groundwater sy stems generally respond m o re slowly t o clim at e change than surface wat e r sy stem s. Lim ited data on existin g supplies of gr oundwater makes it difficult to un derstand and m e asure clim ate effects. In general, groundwater levels correlate m o st strongly with preci pitation, b u t temp erature beco m e s m o re important for shallow aquifers, especia lly duri n g warm perio d s. In sem i -arid and arid areas, groundwater resou rces ar e particularly vul nerable becau se precipitati on and streamflow are concentrated over a few months, y ear-to-y ear variability is high, and d eep groundwater wells or reservoirs generally d o not exist (Ku ndzewicz et al., 20 07).

With clim ate change, availabilit y of gr oundwater is lik ely to be influenced by changes in withdrawals (reflecting development, dem a nd, and availability of other sources) and recharge (d eter m ined b y temp erature, tim ing, and am ount of precipitation, an d surface wat e r interactions) ( m ediu m confidence). In general, simu lated aquifer leve ls respond to chan ges in temp eratur e, precip itation, and the level of withdrawal. According to IPCC, base flows were f oundto decrease in scenarios that are drier or have higher pump i ng rates, and increase in w e tter sc enario s on average across world regions (Kundzewicz e t al., 2007).
Projections suggest that efforts to offset declin ing surface water availability by increasing groundwater withdrawals will be hamp ered by decreases in groundwater rechar ge in some wate r-stressed regions, such as the southwest US. Vulnerability in these ar eas is also often exacerbated by the rapid increase o f populati on an d water dem a nd (hi gh co nf idence) (Kundzewi cz et al., 20 07). Pro jections for th e Ogallala aquifer regio n suggest th at natural gr ou ndwater rechar ge decrea se s m o r e than 20% in all simulations with different climate m odels and futu re warm ing scenarios of 2.5 ° C or greater (Field et al., 2007 an d reference ther ein).

43 Freshwater len s is d e fin e d as a relativ ely th i n layer o f freshwater with in islan d aqu i fer sy ste m s th at flo a t s on an un de rl y i ng m a ss o f den s er se awat er. Num e ro us fact o r s c o n tro l th e sh ap e an d th ickn ess o f th e len s , i n clu d ing t h e rat e o f rechar g e fr om preci pi t a t i on, i s l a nd ge om etry , and ge ol o g i c feat ures suc h as t h e pe rm eabi l i t y of s o i l l a y e rs.



### 96

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

In addition, s ea level rise will extend areas of salini zation of groundwater and estuaries, resulting in a decrease in freshwater avai labilit y fo r humans and ecosy stems in coastal areas. For a discussion of these i mpacts, plea se se e Sectio n 12.
11(b) Water Quality

The IPCC concluded with high confi d ence that h i gher water te mp erature s , increas ed precipitation intensit y , and longer perio d s of low flows exacerba te many for m s of water polluti on and can impact ecosy stem s, hum an health, and water sy stem reliab ility and operating costs (Ku ndzewicz et al., 2007)

. A CCSP (2008e) report al so acknowledges that wat e r quality is sensitive to both increased water te mp erature s and changes in precipitation.

Pollutants of concern in th is case include sediment, nutrients, orga nic m a tter, p a thogens, pesticides, salt, and thermal polluti on (Kundzewicz et al., 200 7). IPCC (Kundzewicz et a l ., 2007) reviewed sever al studies discussing the impacts of cli m at e change on w a ter quality that showed:



### • In lakes and reservoirs, cli m ate change effects are pri m arily caused by water te mp erature va riations. These variati ons can be caused by clim ate change or indirectl y th r ough increases in therm a l pollution
as a result of higher demand for cooling water in the e n ergy sector. This affe cts, for the U.S. a nd all world regions , dissolved o x y gen regim e s, redox pote n tials 44 , lake stratification, mixing rates, and the developm ent of aquatic biota, as they all depend on water te mperat ure. Incre asi ng water t e mperatur e affects the self-purification capacity of rivers by red u cing the amount of dissolved ox ygen available for biodegrad ation.



### • Water polluti on problem s are exacerbated during low flow condi tions wher e small water quantities result in less dilution and greater concen trations of pollutants.



### • Heavy precipitation frequencies in the U.S. were at a m i nimu m in the 1920s and 1930s, and have increased thr ough th e 1990s (Field, et al., 2007). In creases in intense rain events resul t in the introducti on of m o re sediment, nutrients, pathoge ns , and toxics into water bodies from n on-poi nt sources but these events al s o provide the pul se flow needed for some ecosy ste m s.
North A m eri can si mu latio ns of future s u rface and bottom w a ter te mp eratures o f lakes, reser voirs, rivers, and estuaries consistently increas e, with su mmer surfa ce te mp er atures exceeding 30°C in m idwestern and southern lakes and re serv o irs. IPCC projects that warm ing is l i kely to exte nd and intensify summer ther m a l strati fication in surface w a ters, further contri buting to oxygen depletion (Field et al., 2007 and references therein).
Higher water temp erature and variations in runoff ar e likely to pr oduce adverse changes in water quality affecting human health, ecosy s tems , and water uses. Elevated surf ace water temp eratures will prom ot e algal bloom s and increase s in bacteria and fungi leve ls. Increase s in water temp erature ca n also m a k e so m e conta m inants, such a s a m m onia ( EPA, 1999), m o r e toxic for some specie s and foster the growth of microbial pathogens in sources of drinki ng water. War m er waters also transfer volatile and s e m i-volatile
co mpounds ( a mm onia, mercury , PCBs, dioxins, pesticides) fro m surface wat e r bodies to th e at m o sphere
m o re rapidly (Kundzewicz et al., 20 07). Althou gh th is transfer will improve water qualit y , th is m a y have implications for air qualit y

.

44 Redo x po ten ti a l is d e f i n e d as th e tend en cy of a ch em i cal species to ac qui re electrons a nd there f ore be re duce d

.



### 97

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Lowering of the water levels in rivers and lakes can lead to re-suspension of bott o m sediments and liberating compounds, with negative effects on wat e r supp lies (Field et al., 2007 and references ther ein). These i mpact s m a y lead to a bad odor a nd taste in ch lorinated drinking water and greater occurrence of toxins. More intense rainfall will lead t o increases in suspended solids (turbidity ) and pollutant levels i n water bodies due to soil erosion (Kundz ewicz et al., 2007). M o reover, even with enhanced phosph orus rem oval in wastewater treatm ent plants, algal growth in water bodies may incr ease with warm ing over the long term

. Increasing nutrient and sediment loads due to m o re intense runoff events will negatively affect water quality , requiring additional treatment to render it suitable for drinki ng water.

Cli m ate chan ge is likely t o make it more difficult to achieve exi s ting water q u alit y goals for sedi m ent (IPCC: high confidence) because hy drologic changes affect ma ny geom orphic proces ses including soil erosion, slope stability, c h annel erosion, and sedimen t transport (Field et al., 2007). IPCC reviewed a
num ber of region-specific studies on U.S. water quality and pr ojected that:



### • Changes in precipitation may increase nitrogen load s fro m river s in the Che s apeake and Delaw a r e Bay regio n s b y up t o 5 0 % b y 2 030 (Ku n d zewicz et al., 200 7 and ref e rence therein).



### • Decr eases in snowcover and increases in winter ra in on bare soil will likely lengthen the erosion
season and enhance erosi on intensity

. This will in crease the potential for sediment relat e d water qualit y impacts in agricultural areas without appro p r iate soil managem e nt techniques (Field et al., 2007 and reference therein). All studies on soil eros ion suggest that increased rainfall amounts and intensities will lead to greater rates of erosion, w ithin the U.S. and in other regions, unless protection
measures ar e taken (Kundzewicz et al., 2007). Soil management practices ( e .g., crop residue, no-till) in som e regions (e.g., the Cornbelt) may n o t pr ovi de sufficient erosion prot ection against future intense precipitation and associated runoff (Field et al., 2007).
11(c) Extreme Eve n ts

There are a n u m b er of climatic and non-clim atic drivers influencing flood and droug ht impacts. Whether risks are realized depends on several factors. Fl o ods can be caused by in tense and/or long-lasting precipitation events, rapid snowm e lt, dam failure, or reduced convey a nce due to ice jams or landslides. Flood m a gnitude and spatial extent depend on the in te nsity , v o lu me, and time of precipitation, and the antecedent conditions of ri vers and their drainage basi ns (e.g., presence of snow a nd ice, soil composition , level of hum an developm ent, existence of dikes, da ms, and reservoirs, etc.) (Kundzewicz et al. , 2007). Precipitation intensity will increase acro ss the U.S., but particularly at m id and high latitudes where mean precipitation also increases. This will affect the risk of flash floodi ng and urban flooding (Kundzewicz et al., 2007). S o me studies project widespread increases in extreme precipitation with greater risks of not onl y flooding from intense precipitation but also droughts from greater temporal v a riability in precipitation. In general, projected changes in pr ecipitation extre m es ar e larger than changes in m e a n precipitation (Field et al., 2 007).

The socio-econom ic impacts of droughts arise fro m th e interaction between clim ate, natural conditions, and hum an factors such a s changes in land use. In dry areas, excessive waterwithdrawals from surf ace and groundw ater sources can exacerbate the impact s of drought (Kundzewicz et al., 2007)

. Although droug ht has b een m o re frequent and i n t e nse in the wester n part of the U.S., the East is also vulnerable to droughts and attendant reductions in water supply, changes in water quality and ecosy stem fu nction, and challenges in allocation (Field et al., 2007).



### 98

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

In addition to the effects o n water supply, extrem e events, such as floods and dr oughts, will l ikely reduce water quality

. Increased erosion and runoff rates duri ng flood events will wash pollutants (e.g., organic matter, fertilizers, pesticides, heavy m e tals) fro m so ils into water bodies, with subsequent impacts to species and ecosy stem s. During dro ught events, th e lack of precipitation and subsequent low flow conditions will imp a ir water qualit y by r e ducing the am ountof water available to dilute pol lutants. These effects fro m floods and dr oughts will make it m o re di fficult to achieve pollutant discharge lim its and water quality goals (Kundzewicz et al., 2007).
11(d) Implications for Water U ses
There are many comp eting water uses in the U.S. th at will be adversely impacted by cli m ate change impacts to water supply and qualit y

. The IPCC revi ewed a num b e r of studies describing the impacts of cli m at e change on water uses in the U.S. which showed:



### • Decr eased water suppl y and lower water lev e ls are likely to exacerbat e challenges rel a ting to navigation in the U.S. (Fi e ld et al., 20 07). S o m e studies have f ound that lo w flow condi tions m a y restrict ship loading in shallow ports and harbor s (Kundzewicz et al., 200 7). However, navigational benefits fro m cli m at e cha nge exist as well. Fo r ex a mple, the n a vigation season for the North Sea Route is projected to increase fro m the current 20-30 da y s per y ear to 90-100 day s by 2080 (ACIA, 2004 and references therein ).



### • Clim ate change impacts to water supply and quality will affect agricultural pr actices, including th e increase of ir rigation demand in dry re gions and th e aggravation of non-point source water polluti on problem s in areas susceptible to intens e rainfall ev ents and flooding (Field et al., 2007)

. For m o r e inform ation on climate cha nge impact s t o agriculture, please s ee Se ction 9.



### • The U.S. en ergy sector, which relies heavily on water for generation (hy d ropower) and cooling capacity , will be adversely i mpacted by changes to water suppl y and qualit y i n reservoirs and other water bodies (Wilbanks et al., 2007)

. F o r m o re info rmation on cli m ate change impacts to the energy sector, please see Section 13.



### • Cli m ate-induced environmental ch an ges (e.g., loss of glaciers , reduced river discharge in some regions, reduced snow fall in winter) will affect park tourism , winter sport activities, inland water sports (e.g., fishing, rafting, boating), and other recreational uses dependent upon precipitation (Field et al., 20 07). While the N o rth Am erican tourism ind u stry acknow ledges the important i n flue nce of cli m at e, its imp acts have not been analy zed comp re hensively.



### • Ecological uses of water c ould be adversely impacted by clim ate c h ange. Temp erature increa ses and changed precipitation patt erns alte r flo w and flow tim ing. These ch anges will threaten aquatic ecosy stem s (Kundzewicz et. al., 2007 ). For m o re information, on clim ate change impacts on ecosy ste m s a nd wildlife, please see Se ct ion 14.



### 99

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 12

Sea Level Rise and Coastal Areas

This section of the document discus ses area s in th e U.S. vulnerable to sea l e vel ri se, as sociate d interactions with coastal developm ent, important co astal proces s es, observed and projected impa cts, and how cli m ate change effect s on extrem e events will i mp act coastal areas. Information on the observed and projected rates of sea level rise due to climate change can be found in Sec tions 4(g) and 6(c), respectively

. Inform ation on ocean acidification is discussed in Sec tions 4(l), 6(b), and 14(a).
The IPCC (Field et al., 2007) concluded the following when considering how climate change may affect sea level ris e and coastal ar eas in North A m eri ca:

• Coastal co mmunities and habitats will be increasingly stressed by cli m at e chan ge i mpacts in teracting with develop m ent and poll u tion (ver y hi gh confi d ence). 45 Sea level is rising along mu ch of the coast, and the rate o f change will increase in the future , exacerbating the imp acts of progressive inundation, storm

- surge floodin g , and shoreline erosion.

• Storm i m pac ts are likely to be m o re s e vere, e s peci ally along the Gulf and Atlantic coasts. Sal t marshe s, other coastal h abitats, and dependent species ar e t h reatened by sea-level ri se, fixed structures blocking landward m igration, and chang es in vegetation. Populatio n growth an d rising value of infrastructure in coastal areas i n creases vulnerability t o cli m ate variabil ity and futu re cli m ate change.
12(a) Vulnerable Areas
Interaction with Coastal Zone Development
Coastal popu lation growth in deltas, barrier islands, and estuaries has led to widespread conversion of natural coast al landscap es to agriculture and aqua culture as well as industri a l and residential uses. According to NOAA (Cr o ssett et al., 2007), approxi m a t e ly 153 m illion people (53% of the total populati on) li ved in th e 6 73 US coastal counties 46 in 2003. This represents an increase of 33 m illion people since 1980, and by 2008, the num b e r was projected to rise to 160 m illion. This popul ation growth, the rising value of coastal property , and the project ed increase s in storm inte nsity have increas ed the vulnerabilit y of coastal areas to clim ate variab ilit y and future climate change (IPCC, 2007b).

For sm all i s lands, the coast line is long relative to isla nd area. As a result, m a ny resources and ecosy stem services are t h reatened by a co m b ination of hum an pressures an d climate cha nge effects i n cluding sealevel rise, inc rease s in sea surface te mp erature, and p o ssible increa ses in extre m e w eather eve n ts (Mi mura et al., 2007)

. Although cli m ate change is impactin g coastal sy stem s, non-climate hu man impacts hav e been m o re dam a ging ov er the past centur y

. The major non-clim ate impacts for the U.S. and other world regions include drainage of coast al wetlands, resource ex traction 47 , deforestation, in troductions o f invasive species, shoreline protecti on, and the discharge of se wage, f e rt ilizers, and c ontam inants into coastal

45 Acc o rding t o IPCC term inology, “ v ery high confide n ce” c o nveys a 9 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s. 46 “Co a stal county” is g e n e r a lly d e f i n e d in NOA A r e p o r t s as a cou n t y in which at least 15 p e r c en t o f its t o tal lan d area is lo cated with in a co astal watersh e d. 47 Resou r ce ex tractio n activ ities in co astal areas in clud e sand/co ral m in in g , h ydro c arbon p r o d u c tion , and co mmercial
an d recreation a l fish ing

.



### 100

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

waters (Nich o lls et al., 2007). The cu mu lative effect of these non-climate, anthropog enic impacts increases the vulnerability of coastal sy stem s to cli m ate-related str e ssors.
Coastal Processe s
Cli m ate chan ge and sea-l e vel rise a ffect sedi m ent tr a n sport in complex way s

. Erosion and ecosy stem loss is affecting many parts of the US coastline, but it re mains unclear to what exte nt these losses result fr o m cli m at e chan ge instead of land loss a s sociated with relative sea- level rise due to subsidence and other hum an drivers (Nicholls et al., 200 7).

Coastal wetla nd loss is als o being observed in the U.S. where t h ese e c osy s tems are squee zed betwe e n natural and artificial landward bounda ries and risi ng sea levels, a process known as ‘coastal squeeze’ (Field et al., 2007). The d e gradation of coastal ecosy stem s, especially wetland s and coral reefs, can have serious impli cations for the well-being of societies dependent on the m for goods and services (Nicholls et al., 2007). For m o re information regarding clim at e c h ange impact s to coral reef s, see Se ction 14.
Engineering structures, su ch as bulkheads, dam s , le vees, and water diversions, lim it sedi m ent suppl y to coastal ar eas. Wetlands ar e especi ally th reatened by sea level ri se when insufficient am ounts of sedi m ent from upland watersheds ar e deposited on them

. If sea level rises slowly , the balance betwe e n sedimen t suppl y and m o rphol ogical adjust m e nt can be m a intai n ed if a salt marsh vertically accretes 48

, or a lago on infills, at the sam e rat e

. However, an acceler ation in the rate of sea-level ri se m a y mean that coastal marshes and wetlands can not keep up, particularly wh ere the su pply of sediment is li m it e d (e.g., whe re coastal floodplains are inundated after natural levees or artificial em b a nk m e nts are overtopped) (Nicholls et al., 2007)

. Although open coasts have been the focus of research on erosion a nd shore stabilization technology , sheltered coastal areas in the U.S. are also vulne rable and suffer secondar y effects from rising seas (NRC, 2006a). For example, barr ier island erosion in L oui s iana has increased the height of waves reaching the shorelines of coastal bays. This ha s enhanced er osion rates o f beache s , ti dal cre e ks, a nd adjacent wetlands. T h e i mpacts of acc elerat ed s ea-level ri se on gravel beaches have r e c e ived less att e ntion than sandy beaches; however th ese sy stem s are threat ened by sea-level r ise, even under high wetland accretion rates. The p e rsistence of gravel and cobble-boul der beaches will also be influenced by stor ms, tectonic events, and other factors that build and reshape th ese highly dynamic shorelines (Nicholls et a l., 2007).
Observed Changes
According to the IPCC, m o st of the world’ s sandy sh orelines retre a t e d during the past century a nd clim at e change induc ed sea-level r ise is one underly i ng caus e

. Over the past century i n the U.S., m o re than 50% of the original salt marsh habitat has been lost. In Mississippi and Texas, over half of the shorelines eroded at average rates of 2.6 t o 3

. 1 m /y r since the 1 970s, while 9 0 % of the L o uisiana shoreline eroded at a rate of 12.0 m/y r (Nicholl s et al., 2007 and references therein).

In the Great Lakes wher e sea level r i se is not a c oncern, both extremely hi gh and low water leve ls resulting from changes to the hydrol ogical cy cle ha ve been dam a ging and disruptive to shoreline
co mmunities (Nicholls et al., 2007). High lake wa ter levels in crease stor m surge floodi ng, accelerat e shoreline erosion, and da mage indus trial and co mmercial infrastructure located on the shor e. Conversely, low lake water levels can pose problems for navig a tion, expose intake/discharge pipes f o r electric a l utilities and municipal water treat ment plants, and cause unpleasant odors.

48 The term ‘vert i cal accretion’ is defi ned as t h e accumu latio n of se dim ents and ot her m ate rials in a wetland habitat th at resu lts in bu ild -up o f t

h e l a n d in a v e rtical d i rection

.



### 101

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

In the Arctic, coastal stability is affected by factor s common to all areas (i.e., sh oreline exposure, relative sea level ch ange, climate, and local geology ), and by factors specific to the high-latitudes (i.e., low temp eratures, ground ice, and sea ice) (Anisi m ov et al., 2007). Adverse imp acts have already been observed along Alaskan coasts and traditional know ledge poi nts to widespread coastal chan ge in Alaska. Rising te mp e ratures in Ala s ka are r e ducing the thickness and spati a l extent of sea ice. This cr eates mor e open water and allows for winds to generate strongerwaves, which increase sh oreline erosion. Sea level rise and thawing of coastal per m afrost exacerbat e th is problem

. Higher waves will create even greater potential for th is kind of er osion dam a ge (ACIA, 2004 ).
Projected Im pacts The U.S. coastline is long and diverse with a wide r a nge of coastal characteri s tics. Sea level rise changes the shape an d location of coastlines by m oving th em landward along low-l y i ng contours and exposing new areas to erosion (NRC, 2006a). Coasts subsidi ng d u e to natural or hu man-induced causes will experience la rger relative r i ses in s ea l e vel. In so m e locations, such as delta s a nd coastal cit ies (e.g., th e Mississippi delta and surroundi ng cities), this effect can be significant (Nicho lls et al., 2007). Rapid developm ent, including an additional 25 m illion people in the coastal U.S. over the next 25 y ears, will further reduce the resili ence of coast al areas to rising sea level s ( Field et al., 2007). Superimposed on the i mpacts of er osion and subsidence, the effects of rising sea level will exacerbate the loss of waterfron t propert y and increase vulnerability t o inundation hazards (Nicholls et al., 2007)

. If sea-level rise occurs over the next centur y at a rate consistent with the high er range of th e 2007 IPCC scenarios (i.e., 50-60 cm r ise in sea lev e l by 2100), it is about as likely as not that so m e b a rrier isl a nd coasts in the mid-Atlantic region will cross a geo m or phic threshold and experience significant changes. Such changes include m o re rapid landward m igrati on or barrier island seg mentation (Gutierrez et al., 2009).
Up to 21% of the remaining coastal wetlands in the U.S. m id-Atlantic region are potentially at risk of inundati on between 2000 a nd 2 100 (Field et al., 200 7 a nd reference therein). Rates of coastal wetland loss, in the Chesapeake B a y and elsew here, will incr ease with accelerated sea-l e vel rise, in part due to ‘coastal sque eze’ (IPCC: high confide n ce). It is vi rtually certain that thos e tidal wetla nds already experiencing submergence by sea-level rise and associated high rates of loss will continue to lose area in the future due to both accelerat ed rate s sea-l e vel ri se as well a s changes in other environmental and cli m at e drivers (Cahoon et al., 2009). Salt- marsh biodi versit y i s likely to decrease in north-eastern marshes through expansio n of non-nati ve species such as Spartina alterniflora

. The IPC C (Field et al

. , 2007) projects that m a ny U.S. salt m a r s hes in less d e veloped areas can potentially keep pace with sealevel rise through vertical accretion.

Cli m ate change is likely to have a strong impact on saltwat er intrusion into coastal sources of groun dwater in the U.S. and other wor ld regions. S ea-level rise and hig h r a tes of water withdrawal prom ote the i n trusion of saline water into the ground water supplies, which adversely affects water quality

. Reduced groundwater recharge associated wi th decreases in preci pitation and increased evapotranspiration 49 will ex acerbate sea l e vel rise effects on sa linization rates (Kundzewicz et al., 2007)

. This effect c ould impose enorm ous co sts on water tr eat ment infrastructure (i.e ., costs asso ciated with relocating infrastructure or buildi ng desalinization capacity ), especially in densely populated coast al
areas. Saltwater intrusion is also proje c ted to o ccur in freshwater bodies along the coast. Estuarine and

49 Evap otranspiration is defi ne d as the t o tal am ount of e v ap oration from surface water bodi es (e. g

. , lakes, ri vers , reservo i rs), so i l , and p l an t tran sp i r atio n. In t h is co n t ex t, warm er te m p eratu r es b r ou gh t o n b y cli m ate ch an g e will dri v e great er l e vel s of e v apot r a ns pi rat i o n

.



### 102

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

mangrove ecosy s tem s can withstand a range of saliniti es on a short ter m basi s; however, they are unlikely to survive per m anent exp o sure to high salinity envir onm ents. Saltwater intrusion into freshwater rivers has already been linked with the decline of bald c ypr ess forest s in Louisiana and cabbage palm fore sts in Florida. Given that these ecosy ste m s p rovide a vari ety of ecos y ste m s e rvices and goods (e.g., spawning habitat for fish, pollutant filtrati on, sedi m ent control, storm surge attenuation), the loss of these areas could be sign ificant (Kundzewicz et al., 2007).
The vulnerable nature of coastal indigenous commu n iti es to cli m ate change ari ses fro m theirgeographical location, reliance on the local environment for aspects of everyda y life such as diet and econom y , and the current state of social, cultural, econom i c , and politic al change taking place in th ese regions (Anisi m ov et al., 2007). Sea ice extent i n the Arctic Ocean i s exp ected to continue to decr ease and may even disappear entirely during summer m onths in th e co m ing de cades. This reduction of sea ice incre ases extre m e coastal erosi on in Arctic Alaska, due to the incr eased exposure of the coastline to strong wave action (CCSP, 2008i). These eff ects, along with sea level rise, will accelerate the al ready hi gh c o astal erosio n rates in per m afrost-rich ar eas of Al aska’ s coastline, th ereby forcing the issue of relocation for threatened settlements. It has been estimated that relocating th e village of Ki valina, AK to a nearby site would cost US$54 m illion (Anisim ov et al., 2007)

.
For s m all isl a nds, some s tudies suggest that sea-lev e l rise could reduce island size, particu larly in the Pacific, rai s i ng concerns for Hawaii a nd other U.S. territories ( M i mura et al ., 2007). In so m e c a s es, accel erated coastal erosio n may lead t o island aban donm ent, as has been docum ented in the Chesapeake Bay

. Island infrastructure tends to predom inat e in co astal locations. In the Caribbean and Pa cific Islands,
m o re than 50% of the population lives within 1.5 k mof the shore. International airports, roads, capital cities, and other ty pes of infrastructure are ty pical ly sited along the coasts of these islands as well. Therefore, the socio-economic well-being of island co mmunities will be threatened by inundat ion, sto r m surge, erosion, and other coastal haz a rds resulting from cli m ate c h ange (high c onfidence) (Mi mura et al. , 2007).
12(b) Extreme Eve n ts Although i n creases in mean sea l e vel over the 21 st century and beyond will i nundate unpr otected, lowly ing areas, t h e m o st deva stating i mpac ts are likely to be associ a ted with stor m surge ( N ic holls et al., 2007). For e x ample, the Mary land Ge ological Surv ey estimated that m o re than 20 acres of the State’ s land was lost on the western shore of Chesapeake Bay in the w a ke of Tropical Storm Is a b el, causing approxim a tely $8 4,00 0,0 0 0 in dam a ges to shorelin e structures (NRC, 2006a an d references therein).
Superimpose d on accelera ted sea level rise, stor m i n tensity, wave height, and stor m surge projections suggest m o re severe coast al floodi ng a nd erosion hazards (Ni c holls et al., 2007). Highe r sea level provides an e levated base f o r storm surges to build upon and dim inishes the rate at which low-ly ing areas drain, thereby increasing the risk of fl ooding from ra instor m s ( CCSP, 2009b). In New York City and Long Island, flooding from a co m b inat ion of sea lev e l rise and st orm surge co uld be several m e ter s deep (Field et al., 2007). Pr ojections suggest that the retu rn period of a 100- y ear fl o od event in th is area m ight be reduced to 19-68 y ear s, on average, b y the 205 0 s , and to 4-6 0 y ears b y th e 2080s (Wilbanks et al., 2007; and ref e rences therein).

Additionall y , some major urban centers in the U.S. ar e situated in low-l y ing fl ood p lains. For example, areas of N e w Orleans and its vicinity are 1.5-3 m e ters below sea lev e l. Considering the rate of subsidence and using a mid-range estim ate of 480 millim e ters sea-level rise by 2100, it is projected that this region could be 2.5 t o 4.0 m e ters or m o re below mean sea level by 2 100 (Field et al., 2007). In th i s scenario, a storm surge from a Catego ry 3 h u rricane (estimated at 3 to 4 m e ters without waves) could be six to seven meter s above areas that wer e heavily populated in 2 004 (Field et al., 2007 and ref e rences therei n).



### 103

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The IPCC discusse s a num b e r of othe r extre m e ev ent scenarios and observations with implications for coastal ar eas of the US (See also section 6(f) for a dis c ussion of abrupt changes and sea level rise):

• Very large s ea-level rise s that would result fro m widespread d e glaciation of Gre e nland and West Antarctic ice sheets imply major changes in coastlines and ecosy st em s, and inundation of low-ly ing areas, with greatest eff e cts in river deltas. Rel o cating populations, econom ic activity, and infrastructure would be cos tly and challenging (IPCC, 200 7b).

• Under El Niño con d itio n s , high water levels co m b ined with ch anges in win ter storm s along th e Pacific coast have produced severe coastal flooding a nd storm imp acts. In San Francisco, 140 y ears of tide-gauge data suggest an increase in sever e winter storm s since 1950 an d some studies hav e detected ac ce lerated coast a l erosion (Field et al., 2007).

• Recent winters with les s i ce in the Gr eat Lake s an d Gulf of St. Lawrenc e h a ve increa sed coastal exposure to d a m a ge fro m winter storm s (Field et al., 2007).

• Recent s e ver e tropical and extra-tropica l stor m s de monstrate that North A m eri can urban ce nters with
assu med high adaptive capacity rem a in vulnerabl e to extre m e events (Field et al., 2007).

De mand for waterfront pr operty and bu ilding land in the U.S. co ntinues to grow, increasin g the value of propert y at ri sk. Of the $19 trilli on value of all in s u red residential and commercial property in th e U S states exposed to North Atlantic hurricanes, $7. 2 trillion (41%) is located in coastal counties 50

. According to a study referenced in Field et al. (200 7), this economic value includes 79% of the property in Flori d a, 6 3 % of pro p erty in New York, and 61 % of the property in Connecticut. The devastating effects of hurricanes Ivan in 2004 and Katrina, Rit aand Wilma in 2005 ill ustrate the vulnerability of North A m eri can infrastruc ture and urban sy stems tha t were not designed or not m a intained to adequate safety margins. When prot ective sy stems fail, i mpact s can be widespread and multi-dim e nsio nal (Field et al., 200 7).

50 “Co a stal county” is g e n e r a lly d e f i n e d in NOA A r e p o r t s as a cou n t y in which at least 15 p e r c en t o f its t o tal lan d area is lo cated with in a co astal watersh e d.



### 104

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 13
Energ y , Infrastructure and Settlements
According to IPCC (Wilbanks et al., 2007), “[ i ] ndustr ies, settlements and hum an society ar e accusto m ed to variabilit y in environm ental conditi ons, and in m a ny way s the y have b ecome resilient to it when it is a part of their norm a l experience. Enviro nmental chang es that are m o r e extre m e or persiste nt than that experience, h o wever, can lead to vulnerabilities, esp ecially if the changes are not foreseen and/or if capacities for adaptation are li m ited.”

Cli m ate change is likely 51 to affect U.S. energy use and energ y p r oduction; ph y s ical infrastructures ; institutional i n frastructures; and will likely interact with and possibly exacerbate ongoing e nvironm ental change and environm ental pressures in settlements ( W ilbanks et al., 2007), particularly in Alaska where indigeno us communities are facing m a jor environm ental and cultural impacts on their hist o r ic lifesty les (ACIA, 2004). The research evidence is relatively cl ear that climate war m in g will m ean reductions in total U.S. heating requirements and in creas es in to t a l cooling requirements f o r buildings. These change s will vary by region and by season, but they will a ffect household and business energy costs and thei r dem a nds on energy suppl y institut ions. In general, th e changes i mply increased demands for electricity , which suppli es virtually all cooling energy services but onl y some heating services. Other effect s on energy consumption are le ss cle a r (CCS P, 2007a).
13(a) Heating and Cooling Requirements

With clim at e warm ing, less heating is re quired for in dustrial, commercial, and residential buildings in the U.S., but m o r e cooling is required, with changes vary ing by region and by season. Net energ y demand at a national scale will be infl uenced by th e structure of the energy s uppl y. T h e main source of energy f o r cooling is electricity , while coal, oil, gas, biom a ss, and electricity are used for space heati ng. Regions with substant ial requirem e nts for both cooling and he ating coul d fi nd that net an nual electricity dem a nd s increase whil e de mands f o r other heat ing energy sour ces declin e. Criti cal f actors for the U.S. ar e the relative effici ency of space cooling in su mmer co mp ared to space heating in winter, and the relative distribution of populations in colder northern or warmer southern regions. Seasonal variati on in total dem a nd is also important. In so m e cases, due to in frastructure lim i tations, peak dem a nd could go be y o n d the maxi mu m capacity of the electricity trans m is sion sy stem (Wilb anks et al., 2007).

Recent North A m eri can st udies generally confirm ea rlie r work showing a smal l net change (increas e or decrease, depending on methods, scenarios, and loc a ti on) in net dem a nd for energy in buil dings but a significant increas e in demand for electricity fo r space cooling, with further increase s caused by additional m a rket penetration of air conditi onin g ( h igh co nfide n ce) (Field et al., 20 07). Generally speaking, the net effects of clim ate change in the U. S. on to tal energ y dem a nd are projected to am ount to between perh aps a 5% incr ease and decr ease in de m a nd per 1o C in war m ing in buildings. Existing studies do not agree on whether there would be a net increa se or decrease in energ y c onsumption with changed cli m at e becau se a variety of methodologies have been used (CCSP, 2007a).
In California, if te mp erat ures rise acc ording to a hi gh scenario range (8-10.5oF; ~4.5-5.6o C ), annual electricity demand for air conditioni ng could increa se by as mu ch as 20% by the end of the century (assu m ing population rem a ins unchange d and lim ited i mplem entati on of efficiency m e asures) (California

51 Acco rd ing t o IPCC term in o l o g y , “lik ely” con v e ys a 6 6 to 90 % p r ob ab ility of o ccurren ce. See B o x 1

. 3 on p a g e 5 for a fu ll d e scrip tio n of IPCC’s un certain ty term s.



### 105

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Energ y Commission, 2006) 52

. In Alaska, there will be savings on heating costs: m odeling has predicted a 15% decline in the dem a n d for heatin g energy i n the pop ulated parts of the Arctic and sub-Arctic and up to one m onth decrease in the duration of a period when heating is n eeded (Anisim ov et al., 2007).
Overall, both net delivere d energy and net pri m ary energy consumption incre ase or decr ea se only a few percent with a 1oC or 2 o C warm ing; however, there is a robust result that, in th e absence o f an energy efficiency policy directed at spac e co oling, clim at e change wo uld cause a significant increas e in the dem a nd for electricity in th e U.S., which would req u ire the build ing of addi tio nal electricity generation capacity (and probabl y transm ission facilities) wo rth many billi ons of dollars (C CSP, 2007a).
Bey o nd the general ch anges described above, general temp er ature increases can m e an changes in energy
consumption in ke y cli m ate- sensitiv e sectors of th e econom y, such as t ransportation, construction, agriculture, and others. Furtherm ore, there may be in creases in energ y used to suppl y other resources fo r cli m at e-sensit i ve processe s , such as pu mp ing w a ter fo r irrigated agriculture a nd municipal uses ( C ENR , 2008).
13(b) Energy Production

Clim ate change could affect U.S. energy prod uctio n and suppl y (a) if extreme weather events beco me m o re intense, (b) where regions depend ent on water supplies for hydrop ower and/or thermal power plant cooling face reductions or increases in watersupplies, (c) where changed condi tions affectf acility siting decisions, and (d) where climatic conditions change (positivel y or ne gatively ) f o r biom ass, wind power, or solar energy prod uction (Wilbanks et al., 200 7; CCSP 200 7a).
Significant u n certainty ex ists about the potential im pacts of climate change on energ y pro duction an d distribution, in part because the tim ing and m a gnitude of clim at e impa cts are uncertain. Nonetheless, every existing source of energy i n the U.S. has so me vulnerabilit y to clim at e variability

. Renewable energy sourc es tend to be m o re sens iti ve to cli m at e variables; b u t fossil ener gy production can also be adversely effected by air a nd water te mperatures, an d the ther m o e lectric cooling process thatis criti cal to maintaining high electrica l generation efficiencie s a lso applies to nuclear ener gy . In addition, extreme weather even ts have adver se ef fect s on energy produc tion, distri bution , and fuel transportation (CCSP, 2007a).

Fossil and N u clear Energy

Cli m ate change i mpacts o n U.S. electri city generation at fossil and nuclear power plants ar e likely to be si m ilar. The m o st direct climate i mp a cts are related to power plant cooling and water availabilit y

. As currently des igned, power plants require significan t am ounts of water, and they are vul nerable to fluctuations in water supply. Regional scale chang es would likely m ean that some area s would see significant increases in water av ailability while other regions would see significant decreases. In those
areas seeing a decline, the impact on power plant ava ilability or even siting of new capacity could be significant. Plant designs are flexible and new technol ogies for water reuse, heat rejection , and use of alternative w a ter sources a re being developed; but, at present, so m e impa ct—sig nificant on a local level— can be forese en (CCSP, 2007a).
Renewable Energy

52 Tem p erat ure p r o j ect i o ns fo r th e St at e of C a l i f or ni a ar e bas e d on I PC C gl obal em i ssi on scenari o s as di scusse d i n Section 6(a).



### 106

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Because renewable energy depends directly on am bien t natural resources such as hydrological resources, wind patterns and intensit y, and solar radiation, it is l ikely to be more sensitive to climate variabilit y than fossil or nuclear energy s y ste m s that rely on geologi c a l stores. Renewable energ y s y stems in the U.S. are also vulnerable to damage from extr eme weather even ts (CCSP, 2007a).
Hy dr opower generation is sensitive to the am ount, tim i ng, and geographical pattern of precipitation as well as temp erature (rain or snow, tim ing of m e lting )

. Reduced stream flows are expected to jeopardize h y dro power productio n in some areas of the U.S., whereas greater stream flows, dependi ng o n thei r tim ing, m igh t be beneficial (Wilbanks et al., 2007)

. In California, where h ydrop ower now co mp rises about 15% of in-state energy prod uction, dim inished snow melt flow ing through dam s will decrease the potential for h y dro power productio n b y u p to 30% if temp eratures rise to the mediu m warming range by the end of the century (5.5-8o F (~3.1-4.4o C) increas e in California) and precipitation decreases by 10 to 20%

. However, future pre c ipitation pr o jections are qu ite uncertain so it is possi ble that preci pitation m a y increase and expand hydropower generation (California Energy Commis s ion, 2006).

North Am eri can wind and solar resources are about as likely as not to i n crease ( m ediu m confidence). Studies to date project wind resources that are either unchanged by climate cha nge, or reduced by 0-40%. Future changes in cloudiness could slightly i n crease t h e potential for solar energ y i n North America south of 60°N, but one study projected that in creased cloudiness will likely decrease t h e output of photovoltaics by 0-20% (Field et al., 2007).
Bioenergy potential is cl i m ate-sensiti ve through direct i mpact s on crop growth and availabilit y of irrigation water. War m i ng and precipitation incr ease s are expected to allow the bioe nergy crop switchgrass, for instance, to comp ete effectively with traditional crops in the central U.S (Field et al., 2007). Renewable energy production i s highl y susceptib le to l o calized and regional changes in the resource base. As a result, the greater uncertainti es on regional i mp acts under current climate change
m odeling pose a significant challenge in evaluating me diu m to lo ng-term impacts on renewable energy productio n (C CSP, 2007a).
Energy Suppl y and Transm ission

Extre m e we a t her events can threat en coastal energ y infrastructures and electricity trans m ission and distributio n infrastructures in the U.S. and other world regions (Wilbanks et al., 2007). Hurricanes in particular can have severe imp acts on energy infrastru cture. In 2004, hurricane Iv an destroy e d seven Gulf of Mexico oi l drilling plat forms and damaged 102 pi pelines, while hurricanes Katrina and Rita in 2005 destroy e d m o re than 100 p l atform s and dam a ged 558 pipelines (CCSP, 2007a). Thou gh it is not p o ssible to attribute the occurrence of any singular hurrica ne to clim ate change, projec tions of climate change suggest that extre m e we at her events ar e very likely to beco m e more intense. If so, then the i mpa cts o f Katrina may be a possible indicator of the kinds of i mpacts that could manife st as a r esult of cli m ate change (CCSP, 200 7a).

In addition t o the direct effects on operating facilities themselves, U.S. networks for transport, electri c transm ission, and delivery would be susceptible to cha nges due to cli m at e change in stream flow, annual and sea sonal precipitation patterns, s torm severit y, and even te mp er ature increas es (e .g., pipelines handling supe rcritical fluids m a y be imp acted by greater heat loads) (CCSP, 200 7a).

U.S. rail tran sportation lines, which transport approxim ately 2/3 of the coal to the nation’ s power plants (CCSP, 2007 a), often closely foll ow riverbeds. More severe rainstorm s can l ead to floodi ng of rivers which then can wash out or degrade the nearby ro adbeds. Flood ing m a y also disrupt the operation o f inland waterway s, the second-m o st important method of transporting coal. With utilities carry i ng smaller stockpiles and projections showing a g r owing reliance on coal for a m a jority of the nation’ s electricity



### 107

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

productio n, an y significant disruption to the transpor tation network has serious implications for the overall reliabilit y of th e gri d as a whole. (CCSP, 2007a)

In the Arctic , soil subsidence caus e d by the melting of permafr o st is a risk to gas and oil pipelines, electrical transm ission towers, and natural gas pr ocessing plants (Wilbanks et al., 2007). Along th e Beaufort Sea in Alaska, cl i m ate i m pact s on oil and g as development in the region are likely to result in both financia l benefits and costs in the future. Fo r e x ample, offshore oil explor ation and pro duction are likel y to benefit fro m less extensive and thinner sea i ce, although equipm ent wi ll have to be designed to withstand increased wave f o rces and ice m ovement (ACIA, 2004).
13(c) Infrastructure and Settlements

Clim ate chan ge vulnerabil ities of industry, settlement and society are mainly related to extreme weather events rather than to gradual cli m ate ch ange. Th e si gnificance of gradual cli m ate ch ange, e. g., increase s in the mean te mp erature, lies mainly in changes in the intensity and frequency of extre m e events, although gradual changes can also b e associated with thresholds be y o n d which imp acts beco me significant, such as in the capacities of infrastructures (Field et al., 2007). Such clim ate-related thresholds for hum an settlem e nts in the U.S. are currently not wel l understoo d ( Wilbanks et al., 20 08).

Extre m e w eat her events could threaten U.S. coastal e n ergy infrastructure and electricity transmission and distribution infrastructures

. Moreover, soil subsidence c a used by the m e lting of per m afro st i n the Arctic region is a ri sk to gas and oil pipelines , and electrical transm ission t o wers. Vulnerabilities of i ndustr y , infrastructures, settlement s and societ y to clim ate ch ange are generally greater in certain high-risk locations, par ticularly coastal and riveri ne areas, and areas whose econom ies are closely li nked with cli m at e-sensit ive resources, such as agricultural and fo rest product i ndustries, water dem a nds and tourism; these vulnerabilities tend to be localized but are often large and growing (high confidence) (Wilbanks et al., 200 7). Additionall y , infrastructures are often c onnected, meaning that a n impact on one can also affect others. For examp le, an interruption in energy supply can increase h eat stre ss forvulnerable populati ons ( Wilbanks et al., 20 08). A few studies have projected increasing vulnerability of U.S. infrastructure to extrem e weath e r relat e d to cli m at e war m ing unless adaptation is effective (high confidenc e ). Exa mple s include the New York Metropolitan Region, the m id-Atlanti c Region, an d the urban transportation network of the Bosto n metropolitan area (Wilban ks et al., 2007). In Alaska, ex amples where infrast ructure is projected to be at

“ m oderate to high hazard” in the m id -21 stcentury include Shish m aref, No me, Barrow, the D a lton Highway , an d the Alaska Railroad (Field et al., 2007)

. Where extrem e weather events beco m e more intense and/o r m o re frequent with climate change, the econom ic and social costs of those events will increase (hig h confidence) (Wilbanks et al., 2007).

Buildin gs an d Constructio n

In som e Ar c tic areas, interactions between cli m ate war m ing and inadequate engineering are causing problem s. T h e weight of buildi ngs on perm afrost i s an i mportantfactor; while m a ny heavy , mu lti-stor y buildi ngs of northern Russia have suffered structural failures, the lighter-weight buil d ing s of North Am erica hav e had fewer such problem s as per m afros t has w a r m ed. Conti nuo us repair and maintenance is also required for building on permafros t, a le sson le a r ne d because many of the buildings that failed were not pro p erl y maintained. The problems now being experienced in Russia may be expected to occur elsewher e in the Arctic if buildings are not desi gne d and m a inta ined to accommodate fut u re war m in g (ACIA, 2004 ).



### 108

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The cost of rehabilitating co mmunity i n frastructure dam a ged by th awing permafrost could be significant. Even buildings designed specifically for per m afrost environm ents m a y be subject to severe damage if design criteri a ar e exc eed ed. The i m pervious nature of ice-rich perm afrost has been relied on for contam inant holding fa cilities, and thawing such areas could result in severe contam ination of hy drol ogical resources and large cleanup costs, even for relatively sm all spills ( A nisi m ov et al., 2007).
The construction season in the northern U.S. likely will lengthen with war m in g. In per m af rost areas in Alaska, incre asing depth of the “active lay e r” or loss of permafro st can lead to substantial decre ase s in soil strength. Constructi on m e thods are likely to require changes in areas currently underlain by per m afrost, p o tentially increasing c onst r uction and maintenance cost (h igh confidence) (Field et al., 2007).
Transportatio n In a 2008 report entitled, “Potential I mp acts of Cl i m ate Change on U.S. Tr ansportation,” the National Research Council (NRC) issued the follo wing findi ng:
Cli m ate chan ge will affect transportation prim arily through increases in several ty pes of weather and clim ate extremes, such as very hot da y s ; intense precipitation even ts; intense hu rricanes; drought; and rising sea levels, coupled with storm surges and land subsidence. The impacts will vary by m ode of transportation and region o f the countr y , but th e y w ill be widespread and costl y in b o th human and
econom ic terms and will requi re significant changes in the planning, design, construction, operation, and m a intenance of transportation s y stems (NRC, 2008).

NRC state s t h at transportation infrastructure wa s d esigned for typical weath e r patterns, r e flecting loca l cli m at e and i n corporating assu mp tions about a reasonabl e range of temp eratures and precipit a tion levels (NRC, 2008)

. An increase in the frequency , intens ity, or d u rati on of heat spells in the U.S. and other world regions could cause railroad track s to buckle, and affect roa d s through soft ening and tr affic-related rutting. Warmer or less snow y winters will likel y reduce delay s , improve gr ound and air transportation reliability , and decrease t h e need for winter road maintenance. More intense winter storms could, however, increase risk fo r traveler s a f e ty and require increa sed snow re m o val. Continuation of the declining fog trend in at least so m e parts of North America should benefit transport (Field et al., 2007).

War m ing wil l likely affect infrastructure for surfac e transport at high northern latitudes, such as Alaska

. Per m afrost degradation reduces surfa ce bearing capa c ity and pote n tially trigge rs landslides. While t h e season for transport by barge is likely to be extended, the season for ice roads w ill likely be comp ressed. Other types of roads are likely to incur costly improvem e nts i n design and construction (Field et al., 2007).

Sim i larly , N RC found the following:

Potentiall y , th e greatest i mp act of cli m ate change for North America’s transp ortation sy ste m s will be flooding of coastal roads, railway s, transit sy st em s, and runway s because of global rising sea levels, coupled with stor m surges and exacerbat e d in som e lo cations by land subsidence (NRC, 2008)

. Because of war m ing, the num b er of days per y ear in which travel on the tundra is allowed under Alaska Depart ment of Natural Resources standards has dropp ed from over 200 t o about 100 i n the pa st 30 y ears, resulting in a 50% reducti on i n da y s th at oil and gas exploratio n and extraction can occur ( A CIA, 2004). Forestry is an other industr y th at requires frozen grou nd and rivers. Higher temperatures mean thinner ice on rivers and a longer peri od d u ring wh ich the gro u n d is thawed. This leads to a shortened p e riod duri ng



### 109

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

which tim ber can be moved from f o rests to sa wm ills, and increasing problem s associated with transporting wood (ACIA, 200 4). Lakes and river ice have historically provided m a jo r, winter transportation r outes and co nnections to
s m all e r settl e m ents in the Arctic. R e ductions in ice thickness will reduce the l o ad-bearing capacity , and shortening of the ice-seaso n will shorten period of acc ess. Wher e an open-water network is viable, it will be sensible to increa se r e li ance on w a te r transport. In land locked locations, co nstruction of all-weather roads may be the only via b le option, w ith implicatio ns for significantly increased costs. Similar issue s will impact the use of sea ice roads pri m arily used t o access offshore facilities (Anisi m ov et al., 2007). Loss of su mmer sea ice will bring an increasingly na vigable Northwest Passag e. Incr eased marin e navigation and longer su mmers will i m prove conditi ons for tourism and tr avel associat ed wi th research (Anisi m ov et al., 2007). Along with r ising water temp eratures, however, increased shipping will also
mu ltiply the r isk of m a rine pests and poll u tion (Anisi m ov et al., 2007).
Negative imp acts on transportation very likel y will incl ude coastal and riverine flooding and landslides. Although off set to so m e d e gree by fewer ice threats to navigation , reduced water depth in the Great Lak e s would lead to “light loadi n g” and adver se econo m ic i mp acts (Field et al., 2007).
Of all the possible impacts on transportation, the greatest in terms of cost is that of floodin g

. The costs o f delay s and lost trips woul d be relativel y sm all co mp ar ed with damage to the infrastructure and to other propert y (Wil banks et al., 2 007).

The central Gulf Coast i s particularly vulnerable to cli m ate variabilit y and change because of the frequency with which hurricanes strike, because mu c h of its land is sinking rela tive to m ean sea level, and because mu c h of its natural protection—in the formof barrierislands and wetlands—h as been lost. While difficult to quantif y, the loss of natural storm buffers will likel y intensi fy m a ny climate i mpacts, particularly i n relation to s torm damage (CCSP, 2008 f).

Since mu ch of the land in the Gulf Coast is sinking , this area is facing mu ch higher increase s in relative sea level ri se (the co m b ination of local land surface m ove ment an d change in mean s ea lev e l) than m o st other parts of the U.S. coa s t. Th e CCSP report found that relative sea leve l ris e in the study area is very likely to increase by at least 0.3 m (1 ft) across the r e gion and possibly as mu ch as 2 m (6 to 7 ft) in some parts of the stud y area over the next 50 to 100 y ears. Th e analy s is of even a mid d le range of p o tential sea level rise of 0

. 3 to 0.9 m (2 to 4 ft) indicates that a vast portion of th e Gulf Coast fro m Housto n to Mobile may be inundated in the future. Th e projected rate of relative sea le ve l rise for the region during the next 50 to 100 years is consi s tent with historical trends, region-specific analy ses, and the IPCC Fourth Asses sment Report (2007) findings, which assu m e no m a jor c h anges in ic e-sheet dy na mics (C CSP, 2008f).
Twenty -seven percent of the major roads, 9 percent of the rail li nes, and 72 percent of the ports in the region are at or below 122 cm (4 ft) in elevation, althoug h portio ns of the infrastructure are guarded b y protective structures such as levees and dikes. Thes e protective structures could m itigat e so me i mp acts, but considerable land area is still at risk to perm anent flooding from rising tides, sinking land, and erosion during storm s

. Furtherm ore, the crucial connectivit y of the intermodal s y ste m in the area m e ans that the services of the network can be threatened even if small seg m e nts are inundated (CCSP, 2008f).
A great deal of the Gulf Coast study area’ s infrastru cture is subject to temporary flooding associated with stor m surge. More than half (64 percent of inters tates; 57 percent of arterials) of the area’ s m a jo r highwa y s, alm o st half of the rail miles, 29 airports, and virtuall y all of the ports are subject to flooding based on the study of a 5.5- and 7.0-m (18- and 23-ft) storm surge (CCSP, 2008f ).



### 110

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Aviation ma y also be affected. Incre ases in preci pitation and the frequency of severe w eather events could negati vely affect aviation. Higher temp erat ures aff ect a i rcraft perfor m ance and i n creas e the necessary runway lengths. Some of these risks ar e ex pected to be offset by improvements in technology and inform ation s y stems (CENR, 2008)

. Settlements
According to IPCC (2007b), “The m o st vulnerable i ndustries, s e ttlements and societies are generally those in coastal and river flood plains, those who se econom ies are closely linke d with climate-sensitive resources, an d those in areas prone to extre m e weat he r events, e s pecially where rapid urbanization is occurring (hi gh confidenc e ). Poor c o mmunities can be especially vulner able, in part icular those concentrated in high-risk areas. They tend to ha ve m o re li m it e d adaptive capacities, and are m o re dependent on clim ate-sensitive r esources such as local water and food sup p lies (high co nfiden ce)”.

Effects of cli m ate change on hum an s e t tle m e nts in the U.S. are ve r y likely to vary considerably according to location-specific vulnerabilities, with the m o st v u lnerable areas likely to include: Alaska, flood-risk coastal zones and river basins, arid areas with asso ciated water scarcity and areas wher e the econom i c base is cli m at e sensitive (CCSP, 2007a).

In Alaska and elsewhere in the Arctic, indigeno us communities are facing major econom ic and cultural i mpacts. Ma ny indigenous peoples depend on huntin g polar bear, walrus, seal s, and caribou, and herding reindeer, fishing and gathe r ing, n o t o n l y for foo d an d to sup port th e local econom y , but also as the basis for cultural and social identity

. Changes in speci es’ ranges and ava ilability , a ccess to these speci es, a perceived reduction i n weather predictabilit y , and t r avel safety i n changing i ce and weather conditions present serio us challenges to human health and food security , and possibl y even the survival of so m e cultures (ACIA, 2004).

Co mmunities in risk-prone U.S. regions have reason to be part icularly concerned about any potential increase in s e vere weathe r events. The co m b ined ef fects of seve re stor ms an d sea-level ri se in coa s ta l areas or incre ased risks of fire in drier arid areas are exa mples of how climate change may increas e the magnitude of challenges already facing risk-prone c o mmunities. Vulnerabilities m a y be especially great for rapidly -growing a nd/or larger m e tro politan areas, where the potential magnitude of both i mpacts and coping requir e m e nts are likely t o be very large. On the other hand, such regions have greater opportu nity to put m o re adaptable infrastructure in place and m a ke decisions that lim it vulnerability (CCSP, 2007a).

Cli m ate cha nge has the potential not only to a ff ect U.S. c o mmunities directly but also throug h underm ining their economic bases. In particular, some regional econom i es ar e dependent on sectors highly sensitive to change s in climate: agriculture, fo restry , water resources, or tourism

. Cli m ate change can add to stress on social and political structures by increasing managem e nt an d budget requirem ents for public services such as public health care, disaster ri sk reduction, and even public safety

. As sources of stress grow and com b ine, the resilience of social and political structures are expect ed to suffer, especially in locales with relativel y lim it ed social and political capital (CCSP, 2007a). Additionall y , as noted i n Wilbanks et al. (2008) , “ H u m an settlements are the foci for m a n y econom ic, social, and governm e ntal processes, an d historical experience has shown that catastrophes i n cities can have significant econom ic, financial, and political effects mu ch m o re broadl y

. ”
Within settlements experiencing clim ate change, ce rtain parts of the popul a tion may be especially vulnerable. These include the poor, the elderly , tho se already in poor health, the disabled, those living alone, those with li m ited r ights and power (such as recen t i mmig r ants with li mited English skills), and/or indigenous populations de pendent on one or a few resources. Environm ental j u stice issues are clearly



### 111

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

raised through exa mples s u ch as war m er te mp er atures in urban areas having a m o re dire c t i mpact o n those without air-conditioning (Wilbanks et al., 2008)

. Finally , grow th and devel opm ent is ge nerally m oving toward areas m o r e likely to be vulnerable to the effects of climate change. For ex ample, approxim a tely half of th e U.S. population, 160 m i llion people, will live in one of 673 coastal counties by 2008. C o ast al residents – particular ly those on gently -sloping coasts – should be concern e d about sea level rise in th e longer term, especially if these areas are subject t o severe stor ms and storm s u rges and/or if their regions are showi ng gradual la nd subsidenc e . Area s that have been classified as highly vulnerable to cli m at e change (based on m e asures of phy s ical vulnerability and adaptive capacity ) include countie s lying along the east and west coasts and Great Lakes, with mediu m vulnerability counties m o stly inland in the southeast, southwest, and northeast (CCSP , 2007a).



### 112

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 14
Ecosy s tems and Wildlife

This section of the docum ent covers: 1) ecosy stem a nd species-l e vel i mpacts due to clim at e change and elevated C O 2 levels, 2) i m plications for ecosy ste m s e rvices, 3) h o w cli m at e c h ange effects on extre m e event frequency and intensity m a y impa c t ecosy stems, and 4) impact s to tourism a nd recreation.

For North A m eric a, the IPCC (Field et al., 2007; Fis c hlin et al., 2007 53 ) conclud e d:

• Disturbances such a s wildfire and ins ect outbreak s are increasi ng and are li kely to intensify in a
war m er future with drier s o ils and longer growing seasons (very h igh confidenc e )

. 54 Although recent cli m at e trends have increased vege tation growth, continuing increase s in disturbances are likely to lim it carbon storage, facilitate invasive species, and disrupt ecosy stem ser vices. Overthe 21st century , cha nges in cli m ate will cause species to shift north and to higher elevations and fundam e ntally rearrange North Am erican ecosy stem s. Differential capaciti es for range shifts and constraints from develop m ent, habitat frag m en tation, in vasive species, an d broken ec ological connections will alter eco sy stem struct ure, function, and services.
14(a) Ecosystem s and Species
Ecosy s tems, plants, and animals are sensitive to climat e variabili ty and always have been. Three clearl y observable c onnections between cli m a t e and terr est rial ecosy ste m s are the s e asonal ti m i ng of life-cy cle events (referr ed to as phenology ) , responses of plant growth or primar y production, and the biogeographic distribution of species (s ee Figure 14.1).

IPCC review ed a num be r of studies describing observations of cli m ate change effect s on plant species: (Field, et al., 2007 and references therein ):



### • Between 1981 and 2000, global dail y sat ellite data in dicate earlier onset of spring “greenness” by 10­ 14 da y s , parti c ularly across temp erate latitudes of the Northern Hemisphere. Field studies co nducted in the sam e ar eas confir m t h ese sat ellite observations.
o Leaves ar e expanding earlier (e.g., apple and grape plants--2 da y s /decade at 72 sites in Northeastern U.S.).
o Flowering plants are blooming earlier (e.g., lilac - 1.8 da y s /decade earlier fro m 1959-1993, a t 800 sites across North Am erica, hone y s uckle -- 3.8 da y s /de cade earlier in the western U.S.).



### • The tim ing of autum n leaf senes cen ce 55 across the continental US, which is controlle d by a
co m b ination of temp erature, photo p erio d a nd water deficits, shows weaker trend s

.
IPCC also discussed sever a l studies showing how North Am eri can ani m al s are responding to clim at e change, with effects on phenolog y, m ig r ation, reprod uction, dorm a ncy , and ge ographic range (Field, et al., 200 7 and references therein):

53 Fisch lin et al., 20 07 citation refers to C h apte r 4, “Ec o syste m s, Their Prope rties, Goods, and Se rvices” i n IPCC’s 20 0 7 F o urt h A ssessm ent R e port , Work i n g G r o u p I I

. 54 Acc o rding t o IPCC term inology, “ v ery high confide n ce” c o nveys a 9 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s. 55 The term ‘senescence’ is defined a s the last stage of l eaf d e vel o pm ent th at i n cl ude s c h an ges i n pi gm ent expressi on, cel l death, an d eventual leaf drop.



### 113

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Warm er springs have led to earlier nesting for 28 m igrating bird sp ecies on the East coast of the U.S. and to earlier egg la y ing f o r Mexican jays and tree swallows.



### • Several frog species now i n itiate breeding calls 10-13 da y s earlier than a century ago in th e Upstate New York re gion.



### • In lowland California, 16 of 23 butterfl y species advan ced the dat e of first spring flights an average 24 da y s o v er 31 y ears.



### • Reduced wat e r depth, relat e d to recent war m ing, in Oregon lakes has increased exposure of toad eggs to UV-B, leading t o increased m o rtality from a fungal parasite.



### • The Edith’ s c h eckerspot butterfly has beco m e locall y extinct i n th e southern, l o w elevation portion of its western North American range, b u t has exten d ed its range 90 km north and 12 0 m hig h er in elevation.
Changes in phenology vary between species, and the life-cy cles of plants, pre y anim al s, and predators may shift ou t of sy nc, causing species to beco m e decoupled from their resource requirements. Fo r example, the decline of long-distance migratory bir d s in the United States may originate in m istim ing of breeding and food abun dance due to differences in phe nolo g ical shifts in response to climate change (Scott et al., 2 008).
Many North A m eri can spe c ies, like the Edith’ s checker spot butterfly, have shifted their ranges, ty picall y to the north o r to higher elevations (Field, et al., 2007 ). Migrating to higher elev ations with more suitable te mp erature s can be an eff ective str a teg y for species if habitat connectivit y 56 exists and other biotic a n d abiotic condi tions are appropriate. However, many organism s cannot shift their ranges fast enough to keep up with the current p ace of cli m at e change (Fisch lin et al., 2007). In addition, species that require higher-elevation habitat (e.g., alpine pik as), or ass emblages for which no substrate may exist at higher latitudes (e.g., coral reefs), often have nowhere to m i gr ate (Fischlin et al., 2007). Cold- and cool-water fisheries, e s pecially sal m o nids, have been declining as warmer/drier conditions reduce their habitat (Field et al., 2007)

. The direct eff ects of elev ated CO 2 conce n trations and cli m at e chan ge to marine ecosy ste m s i n clude ocean
war m ing, increased ther mal stratification, reduced upw elling, sea level rise, i n creased wav e height and frequency , l o ss of sea ice, and decreases in the pH and carbonate ion concentration of the sur f ace oceans (see Box 14.1). With lower pH, aragonite (calciu mcar bonate) that is used by m a ny orga nism s to m a k e their shells or skeletons will decline or become unde r-saturated, affecting coral reefs and other m a rine calcifiers (e.g., pteropo ds-m arine snails). Additi onal co mpoundi ng effects, such as higher seawater te mp erature s leading to bleaching events, or higher seaw ater te mp erature s and nutrients leading to increased riskof diseases in m arine biota will m a ke t h ese ecosy stems even m o r e vul nerable to changes in ocean chemistry along the U.S. and other world regi ons (Fischlin, et al., 2007). Subtropical and tropical coral reef s in shallow wat e rs have alr e ady suffered major bleach ing events that are clearly driven by increase s in sea surfa ce t e mp erature s (Janetos et a l ., 2008). The effects of various other stressors, particularly h u man impacts such as overfishing, p o lluti on, and the in troduction of invasive species, appear to be exacer bating the ther m a l stres s e s on reef sy ste m s and, at least on a local scal e, e x ceeding the thresholds be yond which coral is replaced b y other or ganism s (Nicholls, et al., 2 007).
In the Bering Sea along the Alaskan coast, rising air a nd sea water temp eratures h a ve caused reductions in sea-ice cover and prim ary productivi t y i n benthic ecosy stems 57 (Anisim ov et al., 2007). A ch ange from Arctic to sub-Arctic conditions is happening with a northward m ovement of the pelagi c-dom inated

56 C o nnect i v i t y i s de fi ne d as t h e de gree t o w h i c h a ha b itat is p h y sically lin ked with o t h e r su itab l e areas for a particulars p ecies. 57 B e nthi c i s de fi ned as t h e deep est en vi ro nm ent of a wat e r bo dy w h i c h u s ual l y i n cl udes th e seabe d or l ake fl o o r.



### 114

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

marine ecosy stem thatwas previousl y confined to the Southeaster n Bering Sea (Anisi m ov, et al., 2007)

. Cli m ate- relat e d impa cts observed in the Bering Sea in clude significant reductions in seabird and m a rin e mammal populations, incr eases in pelagic fish, occurren ces of previousl y rare algal bloom s, abnorm a lly high water temp eratures, and sm aller salm on runs in coastal rivers (ACIA, 2004). Plants an d anim als in polar regions are also vulnerable to attacks fro m pe sts and paras ites that develop faster and are m o r e prolific in warm er and m o ister c onditions (Anisim ov, et al., 2007). See Box 14.1 for m o re information on potential climate change i m pacts to polar bears.
Ecosyste m Le vel Projectio ns
For terrestri a l ecosy ste m s acros s all world regions, the IPCC concluded th at substantial changes in structure and functionin g o f terrestrial ecosy s tems ar e very likely to occur with a global wa r m ing greater than 2 to 3° C above pre-industrial lev e ls (high con f idence) (Fischlin, et al., 2007). I n North America, disturbances like wildfire and insect outbreaks are inc reasi ng and are likely to intensify in a war m er futur e with drier soils and lon g er growing se asons (very high co nfide n ce) (Field, et al., 200 7). Figure 1 4

. 1 shows the ob served NPP trend in North Am erica between 1981 an d 19 88.



### 115

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Figure 14.1: North Ameri can Observ a t ions (Field et al., 2007)

Observed tren ds in some b i o p h y sic a l an d socio- econ omic indic a tors. Backgrou nd: cha nge i n an nua l mean temperatur e from 195 5 to 20 05. Insets: (a) trend i n April 1 SW E across w e stern North A m erica from 19 25­ 200 2, w i t h a li n ear fit from 195 0-20 02, (b) Spr i ng b ud-b u rst d a tes for trembli ng asp en i n Ed monton si nce 190 0, (c) anom al y in 5- ye ar m ean ar ea b u rne d ann ua ll y in w ildfires i n Ca na da sinc e 19 30, plus o b serve d mean summ er air temper ature anoma l y , w e ig hted for fire ar e a s, relative to 1 920- 199 9, (d) relativ e sea l e vel rise from 185 0- 200 0 for Churc h ill, MB, Pointe -au-Pèr e , QB, Ne w York, NY, and Galvest o n , T X , (e) hurricane ener g y (P DI), econom ic dama ges, and death s from Atl antic hurrica nes si nc e 190 0, and, (f) trend North America n NPP (Net Primar y Productiv i t y ) from 198 1 to 19 98. T he ten studi es up on w h i c h the data of this figure is b a se d are summariz e d and refer enc ed in F i e l d et al . (2007).

At high latitudes, sever al m odel s project longer growing seasons and increased net primary productivit y (NPP) as a result of forest expansion int o tundra ecosy stem s. In th e m id latitud es, simulated changes in NPP are variable, depending on whe ther there is su fficient enhancem ent of precipitation to offset increased eva potranspiration in a war m er cli m ate. By the end of the 21st century , ecosy s t e m s in the northeast and southeast U.S. are projected to beco me carbon sources, while the western U.S. rem a ins a carbon sink ( Field, et al., 2 007).

The areal ex tent of drought-lim ited e c o sy stem s is projected to increase 11% per o C warming in the continental U.S. Clim ate change and direct human land-use press ures are both likely to ha ve adverse i mpacts on desert ecosy ste m s and speci es. Increa ses in plant productivity resulti ng from the direct effect s of rising at m o spheric CO 2 concentrations m a y partially offset these adver se effe cts. In California, temp erature i n creases greater than 2° C may lead to th e conversion of shrubland into desert and grassland



### 116

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

ecosy stem s and evergreen conifer forests into m ixed deciduous forests (Fischlin, et al., 2007). Clim ate
m odel s suggest a w a r m er , drier future cli m ate for the Prairie Po thole Region, which would result in a reduction in, or elim inatio n of, wetlands that pr ovide waterfowl breeding habi tat (CCSP, 2009d). These types of regional impacts are indicative of the kinds o f changes tha t can be expe cted acros s la rge parts of the countr y

. The sea-i ce b iome accounts for a large proporti on of pr imary production in polar wat e rs an d supports a substantial food web. In th e Northern Hem i sphere, projections of ocean biological response to climat e war m ing by 2050 show contraction of the highl y pr oduc tive m a r g inal sea ice biom e by 42% (Fischlin, et al., 2007). I n the Bering Sea, pri m ary productivit y in surface wat e rs is projected to i n crease, the ranges of
so m e cold-water species will shift north, and ice- dwelling speci es will experience habitat loss (ACIA, 2004).
Species Lev e l Projections

After reviewi ng studies on the projected impact s of cli m ate change on species, IPCC concluded that on a global scale (Fischlin et al., 2007 and reference s therei n):



### • Projected i m pacts on biodiversity are significan t and of ke y relevance, si nce global losses in biodiversit y a r e irreversible (very hig h co nfidence).



### • Endem i c spe c ies 58 richness is highest where regional pal aeocli m atic changes have been subtle, providi ng cir c u m stantial evidence of their vulner abilit y to projected climate change (mediu m confidence). With gl obal average temperature ch anges of 2°C above pre-i ndustrial lev e ls m a ny terrestrial, fr e s hwater, and marine specie s (particularl y endem i cs a c ross the globe) are at a f a r greater risk of extinct ion than in the geol ogical past ( m ediu m confidence).



### • Approxim a tely 20% to 30 % of species (global uncertainty ran g e fro m 10% to 40% , b u t vary i ng am ong regional biota from as low as 1% to as high as 80%) will be at increasingly hi gh risk of extinction b y 2100

. In North America, cli m ate change impacts on inland aquatic ecosystems will range from the direct effect s of increased te mp erature and CO 2 c oncentration to indirect effect s as s o ciated with alterations in hy drological sy stems resul ting from cha nges to precip itation regi mes and melting glaciers and snow pack (Fischlin et al., 2007). Fo r m a ny fresh water animals, such as amphibians, m ig r ation to breeding po nds and the production of eggs is intimatel y tied to te mperature and m o i s ture avai labilit y

. As ynchronous tim ing of breeding cy cles and pond dr y i ng due to the lack of precip itation can lead to reproductive failure. Differential r esponses among species in arrival or persis tence i n ponds will likel y lead t o changes in
co mmunity c o mposition and nutrient fl ow in pon ds (Fi schlin et al., 200 7). M a ny warm -water and coolwater (freshwater) fish species will shifttheir ranges nor thward and to higher al titudes. In th e continental U.S., cold-water species wi ll likel y disappear fro m all but the deeper lakes, cool-water species will be lost mainly from shallow lak es, and warm water spec ies will thrive except i n the far south, where temp eratures in shallow lakes will ex ceed survival thresholds (Field etal., 2007). See also section 9(f) for a discussion of climate ch ange impa cts to freshwater and m a rine fish pop ulation s

. Bioclim a te modeling based on outp u t f r om five gen e ra l circulati on m odels ( G CMs) suggests that on the long (m illennial) ti m e scale there may be decreases o f bird and m a mmal species richness in war m er, low elevation areas, but increases in cold high elevation z ones, and increases of r e ptile species richness in al l
areas. Over the next century , howe ver, even positive long-term sp ecies richness m a y lead to short term decreases because species that are in tolerant of local conditions may disappear relatively quickl y while

58 Endem i c species are unique t o thei r location or re g ion and ar e n o t f oun d an ywh e r e else on Ear th

.



### 117

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

migration of new species into the area may be quite slow (Field et al., 2007; Currie, 2001)

. Changes in plant species co mposition in response to cli m ate ch ange can increase ecosy stem vulnerability to other disturbances, including fire and biologic a l invasion. There are other possible, and even probable, imp acts and changes i n biodiversit y -related relationships (e.g., disruption of th e interactions between pollinators, such as bees, and flowering plants), for which we do not y e t have a substantial observational databas e (Janetos et al. , 2008).

On small oceanic islands with cloud forests or high elevation eco sy stems, such as the Hawaiian Islands, extre m e elevation gradients exist, ranging from n ear ly tropical to alpine environm ents

. In these ecosy stem s, anthropogeni c cli m ate change, land- u se changes, and bi ologi cal invasions will work sy nergistically to dri v e several species (e.g., ende m ic birds) to exti nction (Mimura et al., 2007 ).
According to IPCC, cli m at e change (ver y high confid ence) and oce a n acidificati on (see Box 14.1) due to the direct eff ects of eleva t ed CO 2 concentrations (mediu m confiden ce) will i mpair a wid e range of plankton ic and other m a rin e organism s that use aragonite to make their shells or skeletons (Fis chlin et al., 2007). Avera g e pH for the ocean surface is projected to decrease by up to 0.3-0. 4 units by 2100 (Fischlin et al., 2007). These i mp acts could r esult in poten tiall y severe ecological changes to tropical and coldwater marine ecosy stems where car bonate-based phy t oplankt on and corals are the foundation for th e trophic s y stem (Schneider et al., 2 007). The IPCC c oncluded th at it is ver y lik ely th at a pr o jected future sea surf ace t e mp erature increase of 1 to 3°C will resu lt in m o re frequent bleaching events and widespread
m o rt ality , if there is not therm a l adaptation or acc limatization by corals an d their algal sy m b ionts (Nicholls et al., 2007). T h e ability of c o ral reef eco sy stem s to wit h stand the impacts of cli m ate change will depend to a large degr ee on the extent of degrad ation from other anthropoge nic pressures (Nicholls et al., 2007).

Box 14.1: Ocean Acidification Effects on Marine Calcifiers

El evat ed at m o sphe ri c c once n t r at i ons o f gree nh o u se gases im pact the health of m a rine calcifiers by cha n ging the phy si cal a n d c h em i cal prope r t i e s of t h e ocea ns. C a l c i f i e rs pl ay im port a nt rol e s i n m a ri ne ecosy st em s by ser v i n g as t h e ba se of f o o d c h ai ns , pr o v i di ng s ubst r at e, an d hel p i n g t o re gulate bioge o chem ical cycl es (Fisc h lin et al., 2007).

Ocean acidific ation lowe rs the satu ration of calcium carbonate (CaCO 3 ) in sea water, m a kin g it m o re di fficult fo r marine calcifiers to build shel ls and s k eletons (Fisc h lin et al ., 2007). T h e IPCC (De n m a n et al., 2007) m a de the following state m ents rega rding ocean acidifi cation:

• The bi ol ogi cal pr o duct i o n of c o ral s , as wel l a s cal ci fy i ng p h o t o pl an kt o n a n d z o o p l a n k t o n wi t h i n t h e wat e r col u m n , m a y be i nhi bi t e d or s l owe d do w n as a res u l t o f oce a n aci di fi cat i on;

• Cold-water corals are lik ely to sho w larg e redu ctio ns in g e ograph i c rang e t h is cen tury.

• The di ss ol ut i o n of C a C O 3 at the ocean fl oor will be e nha nc ed, m a ki ng it difficult for bent hic calcifiers t o devel o p p r ot ect i v e structure s ;

• Aci d i f i cat i o n c a n i n fl ue nce t h e m a ri ne fo od web at hi ghe r t r o p h i c l e vel s

. The im pacts of elevated CO 2 co n c en tration s o n o cean ic ch emistry will lik ely b e greater at h i gh er latitu d e s (Fisch lin et al., 2007). Polar a n d s u b-polar s u rface wa ters and t h e So uthe rn Ocea n ar e projecte d t o be ar agonite (a form of CaCO 3 ) u n d e r-satu rated b y 210 0, an d Arctic waters will b e si m ilarl y th reaten ed (Den m a n et al., 200 7). Th ese i m p acts will li k e ly th reaten eco s ystem d y n a mics in th ese areas wh ere m arin e calcifiers play d o m in an t ro les in th e f ood web and i n carbon cyclin g ( F isch lin et al., 200 7)

. The o v eral l rea c t i on of m a ri ne bi ol ogi cal car b o n cy cl i n g a n d ec osy s t e m s to a warm and hi g h -C O 2 world is no t yet well unde rstood. In a d dition, the res p onse of m a rine biota t o ocean acidi fi cation is not yet clear, bot h for the phy si ol o g y o f i ndi vi d u al o r ga ni sm s and fo r e c osy s t e m funct i oni n g a s a w h ol e ( D e n m a n et al ., 2 0 0 7 )

.
For the Arctic, IPCC (Anisi m ov et al., 2007 and references therein ) concluded th at:



### 118

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

• Decreases in the abundance of key s tone species 59 are expected to be the pri m ary factor in ca using ecological ca scades 60 and other changes to ecological d y nam ics.



### • Arctic anim als are likely to be m o st v u lnerable to warm ing-induced dry i ng of sm all water bodies; changes in sn ow cover and freeze- thaw cy cles that affect access to food (e.g., polar bear dep e ndence on sea ice for seal hunti ng – see Box 14.2) and protection f rom predator s (e.g., snow rabbit
ca m ouflage i n snow); cha nges that affect the tim ing of behavior (e.g., m i gration and repro duction) ; and influx of new co mp etit ors, predators, parasites, an d diseases.



### • In the past, s ub-arctic spe c ies have be e n unable to li ve at higher latitudes because of harsh conditi ons. Cli m ate chan ge induced war m ing wil l increas e th e rate atwh ich sub-arcti c spe c ies are able to establish. So me non-native species, such as the North Am erican mi nk, will beco m e invasiv e , while other species that have already coloniz e d some Arct ic areas ar e likely to expand into other regions. The spread of non-native, invasive plants will likel y have adverse impacts o n native plant species. For example, experimental war m ing and nutrient addition has shown that native m o sses an d lichens beco m e less abundant when non- native plant biom ass increases.



### • Bird m igratio n routes and tim ing are likely to chan ge as the availability of suitable habita t in th e Arctic decr ea ses.



### • Loss of sea ice will i mpact species, such as harp seals, which are dependent on it for survival.



### • Cli m ate w a r m ing is likel y to increase the incidence of pests, par asites, and diseas es such a s mu skox lung worm and abom asal nem a todes of reindeer.

B o x 1 4

. 2 : P o l a r bear s ( a d a p t ed fr om B o x 4 .3 i n Fi schl i n , et al ., 2 0 0 7 ) There ar e an es tim a ted 20,00 0 t o 25, 0 00 p o l ar bears ( Ursu s ma ritimu s ) wo rld w ide, m o stly inha biting the annual sea ic e ove r t h e c onti n ental s h elves and inte r-isla n d arc h ipela g os of the circ um polar Arctic. Polar bears are s p ecialized pre d at o r s th at hu nt i ce- bree di ng seal s a n d ar e th ere f ore de pe nde n t on se a ice for s u rvi v al. After emergi ng i n spring fr om a 5 t o 7 m ont h fast i n nu rsi n g de ns, f e m a l e s req u i re i m m e di at e no uri s hm ent and t hus de pe nd o n cl ose pr o x i m i t y betwee n land a nd sea ice be fore the sea ice breaks up. Con tinuous access t o sea ice allows bear s to hunt throughout the year, but in areas whe r e the sea ice m elts c o m p letely each summer, th ey are force d to s p end se veral m onths in tundra fasting on stored fat rese rve s un til freeze-up (Fischlin , et al., 2007).

The t w o Al ask a n p o p u l a t i o ns (C h ukc hi Sea- ~ 2 , 0 0 0 i n di vi d u al s i n 1 9 9 3 , S out her n B eau f o rt Seas - ~ 1 , 5 0 0 i ndi vi d u al s i n 2 006 ) are vu ln erab le to larg e-scale dram atic seasonal fluctuations in ice m ovem e nts because of the ass o ciated decrease s in a b undance a n d access to prey and i n creases in the ene r get i c cost s of hunting (FWS, 2007). T h e IPC C p r oj ects th at with a w a r m in g o f 2.8°C ab ov e pr e- i n du str ial te m p eratures a n d ass o ciated dec lines i n sea ice, pola r bears will face a high risk of extinc tion. Othe r ice-de pe nde nt spe c ie s (e.g., walruses – for rest; s m all whales – for protection from predat ors ) face sim i lar cons eque nces, not only in t h e Arctic b u t also in th e An tarctic (Fisch lin , et al., 200 7).

In 20 0 5 , t h e Wo rl d C onse r vat i on U n i o n’s (I UC N ) Pol a r B ear Speci al i s t Gr ou p c onc l ude d t h at t h e IUC N R e d L i st cl assi fi cat i on f o r p o l a r bear s sh oul d be u p g ra de d f r o m Least Co ncer n to V u l n er abl e base d on th e l i kel i h o o d o f a n o v e rall d eclin e in th e size o f th e to tal po pulatio n of m o re th an 30 % with in t h e n e x t 35 to 50 years (Fischlin, et al., 2 007 ). I n May 2 008 , t h e U.S. Fish and W i l d life Serv ice listed th e po lar b ear as a threate n ed s p ecies unde r th e End a ng ered Species Act. Th i s d ecision was b a sed on scien tific ev id en ce sh owing th at sea ice lo ss th reaten s, an d will lik ely co n tinu e to thr eaten, p o larb e ar h ab itat ( F W S , 2008 )

.

59 K e yston e sp ecies is d e f i n e d as a sp ecies th at h a s a d i spr opor tio n a te ef f ect o n its env i ro nmen t r e lativ e to its abundance or t o tal biom ass. Typically, ecos y ste m s experie n ce dram atic c h anges with the rem oval of s u ch a s p ecies. 60 Ecol ogical cas cades ar e defi ned as seque n tial chains of ec ol ogical e ffects, includ i n g st ar va t i on a n d deat h, begi nni ng at th e b o t t o m l e vel s o f th e f o o d c h ai n an d a s cen d i ng t o hi g h er l e vel s , i n cl u d i n g apex p r e d at or s.



### 119

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

14(b) Ecosyste m S ervices
Ecosy s tems provide m a n y g oods and services that ar e of vital importance fo r biosphere function and provide the basis forthe d e livery of tangible benef its to humans. These s e rvice s include: ma intenance of biodiversit y , nutrient regul ation, shoreli n e protectio n , food an d h abitat provisi oning , sediment control, carbon sequestration, regulation of the water cy cle and water quality, protectio n of hum an h ealth, and the production of raw materi al s (Fischlin et al., 2007). Cl i m ate chan ge is projected to have an increasing effect on the provisioning of ecosy ste m servic es i n the U.S. Increasing te mp eratures a nd shifting precipitation patterns, along with the direct effects o f elevated CO 2 concentra tions, sea l e vel rise, and changes in cli m atic variab ility , will affect the quan tity and quality of these services. By the end of the 21 stcentury , cli m at e chan ge and its i m pacts may be th e dom inan t driver of bi odiversit y los s and changes in ecosy stem services globally (Millenni u m Ec osy s tem Assessment-Synthesis, 2005).
Many U.S. ecosy stem s and the services they provide a r e already thr eatened by natural and anthropogenic non-clim at e stressors. Cli m ate-r e lated effects on ecosy s tem s ser vices will amplify the effects of nonclim ate stressors. Multiple U.S. indus tri es, such as tim b er, fisheries, tr avel, tourism , and agriculture that
are already threatened co uld face sub s tantially gre a ter i mp acts with concurrent effe cts on financial markets (Ry a n et al., 20 08; Field et al., 2 007).
14(c) Extreme Eve n ts
Many sign ifi cant impacts of clim ate change on U.S. ecosy stems and wildlife m a y emerge through changes in the intensit y and the frequency of ext r e m e weathe r events. Extre m e event s , such as hurricanes, can cause m a ss m o rtality i n wildlife populati ons and contribute significantly to alterations in species distribution and ab undance follo wing the disturba nce. For example, the aftermath of a hurrican e can caus e coa s tal forest to die from storm surge-indu ced salt deposition, or wil d life m a y find it difficult t o find food , th us lowering the chance of survival. Droughts pla y an important role in forest d y nam ics a s well, causing pulses of tree m o rtality in the North American woodlands. Grea ter intensity and frequenc y of extre m e e v ents m a y al ter disturbance r e gi m e s i n North A m erican coasta l ecosy ste m s leading t o changes in d iversity an d ecosy stem functionin g (Fi e ld et al., 2 007; Fischlin et al., 2 007 ). Species inhabiting sal t m arshes, mangroves, and coral reefs ar e lik ely to be particularly vulnerable to these effect s (Fischlin et al., 2007). Higher temp eratures, increa sed drought, and m o re intense thunderstor m s will very likel y increase erosion and prom ote invasion of exotic grass species in arid lands (Ry a n et al., 2008).
14(d) Implications for Tribes
North American indigenous communities whose hea lth, economic well-being, and cultural traditions depend upon the natural environm ent will likely be a ffected by th e degradation of ecosy stem goods and services asso ciated with climate ch ang e (Field et al., 2007). Am ong the m o st cli m ate-sensitive North Am erican communities are those of i n d igenous pop u lati ons depen d ent o n o n e o r a few natur a l resources. About 1.2 m illion ( 60%) of U.S. tribal mem b ers live on or near re servations, and m a ny pursue lifesty les with a m ix of traditional subsistence activiti es and wage labor (Field et al., 20 07)

. In Alaska and elsewhere in the Arctic, indigeno us communities are facing major econom ic and cultural i mpacts. Ma ny indigenous peoples depend on huntin g polar bear, walrus, seal s, and caribou, and herding reindeer, fishing and gathe r ing, n o t o n l y for foo d an d to sup port th e local econom y , but also as the basis for cultural and social identit y

. These li velihoods are already being threatened by mu ltiple cl i m ate-r e lated factors, including reduced or displaced populati ons of m a rine mammals, cari bou, seabirds, and other wildlife, loss es of fore st r esources due to insect da mage, and re duced/thinner sea ic e, ma king hunting
m o re difficult and dangero us (ACIA, 2004).



### 120

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

14(e) Implications for Tourism

The U.S. ranks am ong th e top ten nat ions for inte r n ational touri s m receipts (US $112 b ill ion), havi ng dom estic tourism and outd oor recreation m a rkets that ar e several tim es larger than m o st other countries. Nature-based tourism is a major ma rket seg ment in North Am erica, with over 900 m illion visitor-day s in national/provincial/state parks in 2001. Clim ate v a riability affects many s e g m ents of this growing
econom ic sector. For exa mple, wildfires in Colorado ( 200 2) caused tens of m illions of d o llars in tourism losses by reducing visitation and destroy i ng infrastructur e. Si m ila r econo m ic lo sses during that sa me y ear were c a used by drought-affected wat e r levels in rivers and reservoirs in the western U.S. and parts of the Great Lakes. The ten-da y closure and clean-up fo llo wing Hurricane Georges (Septem b er 1 998) resulted in tourism revenue losses of approxi mately US $32 m illion in the Florida Key s . While the North Am erican tourism industry acknowledg es the important influence of climate, its impacts have not been analy zed comprehensively (Field et al., 2007 and references therein)

.



### 121

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Part V International Observed and Projected Human Health and Welfare Effects from Climate Change

122

### Technical Support Docum e nt, U.S. Environm ental Protection Agency



## Section 15

Internatio nal Impact s The prim ary focus of this docum ent i s on the observe d and potential future impacts associated with elevated GH G concentrat ions and ass ociated cli m at e change within the U.S. However, EPA has considered the global nature of cli m ate c h ange in at le ast two way s for purposes of this docum ent.
First, GH Gs, once e m itt ed, re main in the at m o sphere for decade s to centuries, and thus become, for al l practical purposes, unifor m ly m ixed in the at m o spher e , meaning that U.S. e m is s ions have cli m atic effe cts not onl y in th e U.S. b u t i n all parts of the world. Likewise, GHG em issions from other countries can influence the cli m at e of the U.S., and therefore affe ct human health, society a nd the natura l environm en t within the U.S. All observed and potent ial future clim ate change imp acts within th e U.S. reviewed in this docum ent co nsider cli m at e change driven by gl obal anthropogenic GHG e m is s i ons. Second, despite widely di scussed metr ics such as global average temp eratu re, cli m ate change will manifest itself ver y differentl y i n different parts of the world, where regional cha nges in temp eratures and precipitation patterns, for example, can deviate signi ficantly from changes in the global average. This regional variation in climate change, coupled with th e fact that countries are in very different positions with respect t o their vulnerabilit y and adaptive capacit y , means that the i mpacts of cli m at e ch ange will be experienced very differently in different parts of the world. In g e neral, the relatively po or nations m a y experience th e m o stsevere i mpacts, d u e to their heavier reliance on cli m ate-sensitive s ect ors such as agriculture and tourism , an d due to their lack of resources for increasing resilien ce and adaptive capacity to clim ate ch ange (see Parry et al ., 2007). In addition to the fact th at U.S. GHG em issions may contri bute to these imp acts (s ee Sec tion 2 for a co mp arison of U.S. total and transportation em i s s ions to other countries’ emissions), cli m ate change imp acts in cer tain regions of the world may exacerbate problems that raise humanitarian an d nati onal security issues for the U.S.
15(a) National Security

A nu m b er of analy ses an d publications, both inside and outside the government, have focused on the potential U.S. national security implicati ons of clim at e change.
A public repo rt prepared fo r the Department of Defe nse (Schwart z and Randall, 2003) exam i n ed what the effects on U

. S. national security m ig h t be from an abrupt climate change scenario. 61 The authors concluded th at the resultant clim atic conditi ons co ul d lead t o r esource constraints and p o tentiall y destabilize the global geo-political environment, with resultant national security concerns for the U.S.

The Arctic Clim ate Imp act Assessment (2004) r a ised security issues, stating that as Arctic sea ice declines, hist orically closed sea pass ages will open, thus raising questions regarding sove reignt y over shipping rout es and ocean resources. In IPCC (Ani si m ov, 2007) , a study shows projections suggesting that by 2050, the Northern Sea Route will have 125 da y s per y ear with less than 75% sea-ice cover, which represents favorable conditions for navigation by ice-strengthened cargo ships. This may have implications for trade and t ourism as well.

61 Th e abr u p t cli m ate ch ang e used f o rt h e study w a s t h e u n likely, b u t p l au sible, co llap s e of t

h e th er m o h a line circu l atio n in t h e Atlan tic, mo d e led after an ev en t th at o c cu rr ed 8,200 year s ag o.



### 123

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

The Center for Naval Analy ses (CNA) Corporation, a non-pr ofit national securit y anal y s is institution, issued a repo rt entitled National Security and the Th reat of Climate Change ( 2007), in wh ich a dozen retired gener a ls and ad m i rals were briefed by cl i m ate ch ange s c ientists and business lead ers over th e course of m a n y m onths and then tasked with pr ovidi ng their own views and reco mmendations about the linkage between cli m ate change and national secu r ity over the next 30 to 40 y ears. Am ong their conclusions was that cli m ate change acts as a “t hreat mu ltiplier” for instabilit y in some of the m o st volatile regions of the worl d. “Projected cli m ate ch ange will seriously exacerbat e alr eady mar g inal living standards in many Asian, African, and Middle East ern nations, causing widespread political instabilit y and the likelihood of failed states,” said the authors. Regarding th e potential impact of climate change on military s y stems, infrastru cture and ope rations, the report stated that cli m ate change will stress the U.S. military by affecting weap ons sy stem s and platform s, bases, and military operations. A U.S. Navy (2001) study was cit e d which stat es that an ice-free Arctic will require an increased sc ope for naval operations. Given these concerns, one of the reco mmendations of the CNA (2 007) report was for the Depart m e nt o f Defense to conduct an assessment of the imp act on U.S. m ilit ar y i n stallations worldwide of rising sea levels, extre m e w eather e v ents, and other possible clim ate ch ange imp acts over t h e next 30 to 40 y ears. The U.S. Congress has expressed national security c oncerns due to climate cha nge by reque sting that the defense and intelligence communities exam ine these li nkages. H.R. 4986, passed in Januar y 2008, requires the Depart ment of Defense to consider the effect of cli m ate change on its facilities, capabilities and m issions. Specifi c dir ectives in the bill include that future national securit y strategies and nationa l defense str a t e gies mu st i n clude guida nce for m ilit ary planners to assess the risks of projected cli m ate change on current and futu re ar m e d forces m i ssions , as well as update defense plans based upon these assessments ( H .R. 4986, 2008).

In June 2008 testim ony before the Hou se, Dr. Tho m as Fingar, Deput y Director of National Intelligence for Analy s is, laid out a national intelligence state m ent on the U.S. national security implications fro m cli m at e chan ge projected out to 2030. Using a broad definition for national security , 62 the a sses s m ent found that:
“[G]lobal climate change will ha ve wide-ranging implications for U.S. nationa l security interests over the next 20 y ears...We judge tha t the m o st significant imp act for the United States will b e indirect and result fro m climate-driven effects on many other countries and their potential to seriously affect U.S. national security interests. We asse ss that c limate chang e alone is unlikely to trigger state failure in any state out to 2030, but th e impacts will worsen existing proble m s— such as pove rty, social tensions, envir onm ental degradation, i n effectual leadership, and weak political insti tutions. Climate change could th reaten dom estic stab ilit y in som e states, potentiall y contributing to intra- or, less likely , interstate confl ict, particularly over acces s to increasingly
scarc e wat e r r esources.” (Fi ngar, 2008)
Building on th at work, the National Intelligen ce Co uncil in Novem b er 2008, in its publication Global Trends 2025: A Transformed W o rld , discussed cli m at e change imp acts pr o m ine n tly

. The report posed a scenario named “October Surprise,” wh ich discussed the econom i c and sociopolitical ram ifi cations of an extrem e flooding event li nk ed to glo b al climate change in New York City in 2 020 (NIC, 2008).

62 Th is d e fin ition co nsid ered i f th e effects wou l d d i rectly imp act th e U.S. ho m elan d , a U.S. eco n o m ic p artn er, o r a U.S. ally. Additio n a lly, th e po ten tial fo r human itarian d i saster wa s foc u se d on as well as if an effect would res u lt in deg r a d i n g or e nha nci n g a n el em ent of nat i o nal p o w er

. Fo r m o re i n f o rm ati on, see Fi n g ar , 2 0 0 8

.



### 124

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

15(b) Overview of International Impacts
The IPCC Working Grou p II volume of the Fourth A sse ss ment Report revie w s the potential i mpa cts in different regions of the wo rld. The IPC C (Parry et al., 20 07) ident ifies as the most vulnerabl e regions:

• The Arctic, because of high rates of projected war m in g on natural sy stem s;

• Africa, espe c ially the sub-Saharan regi on, becau se of current low adaptive c a pacity as w e ll a s cli m at e change;

• Sm all islands, due to hig h exposure of populati on an d infrastructu re to risk of s ea-level rise and increased stor m surge;

• Asian mega deltas, such as the Ganges-Brah m a putra and the Zhuj iang, due to l a rge populati o n s and high exposure to sea level rise, stor m surge and river floodi ng.
Table 15.1 summari zes th e vulnerabilities and projected i mpact s for different regions of the world, as identified by IPCC (2007b). And the paragraphs th at follow provide som e additional de tail for ke y sectoral i m pa cts that have rec e ived att e ntion by the res earch community

. There is curre ntly a lack o f inform ation about how the se potential i mp acts in oth e r regions of the world m a y influence i n ternational trade and m ig r ation pattern s, which in tu rn could raise concerns for the U.S.
On a global b asis, according to IP CC, “projected climate change-relate d exposures are likely to affect the health status of m illions of people, parti c ularly th ose with low adaptive capacit y ,” through s e veral factors including “the increased frequency of c a rdio-respir ator y diseases due to higher concentrations of ground level ozone related to climate change (IPCC, 2007b). ” More specifically , “cities that currently experience heat wave s a r e expected to be further ch allenged by a n increased n u m b er, intens ity and duration of heat waves during the course of the century , with potential for adverse health i mpacts. ”
Mosquito-borne diseases which are se nsitive to climate change, such as dengue and m a l ar i a are of great importance g loball y

. Stu d ies cited in Confalonieri et al. (2007 ) have reporte d associations between spatial, temp oral, or spat iotemporal patterns dengue and climate, although these are not entirel y consistent. Sim il a rly , the spatial distribution, in te nsity of transm ission, and seasonality of m a l a ria i s observed to be influenced b y clim ate in sub-Saharan Africa (Co n falonieri et al., 2007) . In other world regions (e.g., South America, continent a l regions of the Russian Federation) there is no clear evidence that malaria has been affected by cli m ate change (Confalonieri et al., 2007 ). Changes in reportin g, surveillance, disease contr o l m e asures, populati on chang es and other factors such as land use change mu st to be taken into account when attemp ting to attr ibute changes in hum an di seases to climate change (Confalonieri et al., 200 7).
Food pr oduct ion is expected to be mu ch m o re vulnerable to climate change in po orer regions o f the world
co mp ared to food pr oducti on in the U.S. and othe r high, norther n latitude regions. The IP CC (2007b) stated with medium confidence 63 that, at lower latitudes, especi ally seasonally dry and tropic a l regions, crop producti vit y is projected to decrease for even small local temp erature in creases (1-2°C; ~2-3.5 ° F), which would increase ri sk of hunger. Further m ore, increases in the frequency of droughts and floods are projected to a ffect local production negatively , especia lly in subsistence sectors at low latitudes. Drought conditions, flooding, and pest outbreaks are so m e o f th e current stressors to food securit y that m a y be influenced by future clim at e change. Sub-Saharan A frica is current ly highly vul nerable to food insecurity (Easterling et al., 2007). A study cited by Easterlin g et al. (2007 ) projected increases in carbon storage on croplands globall y un der clim ate change up t o 2100 , but fo und th at ozo n e damage to crops coul d significantly offset these gains.

63 Acc o rding t o IPCC term inology, “m edium c o nfide n ce” c onv eys a 5 out of 10 cha n ce of being c o rrect. See Box 1. 3 on pa ge 5 f o r

a f u l l de scri pt i o n o f IPC C ’ s u n cert a i n t y t e rm s.



### 125

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Regarding global forest production , the IPCC (Easter ling et al., 2007) concluded that forestry pr oductio n is esti m ated t o change m o destly with cli m ate change in the short a nd m e diu m term (medium confidence). The projected change in gl obal forest pr oducts output ranges from a m odest increase to a slight decrease, with significant variations regionall y

. There is projected to be a producti on shift from low latitude regions in th e short-term , to high latitu d e regions in the long-ter m

. Projected changes in the frequency and severity of extre m e cl i m ate events have signifi cant consequences for fores try production in addition to impacts of projected mean climate (h igh confiden c e ) (Easterling et al., 2007). Climate variabilit y and change also m odify the ri sks of fires, and pest and pathogen out breaks, with negative consequences fo r forestry (high confidence) (Easterling et al., 2007).

The IPCC made the follo wing conclus ions when cons idering how cli m ate c h ange m a y affect wat e r resources a c r o ss all world regions:



### • The i mpact s of cli m ate ch ange on fres h water sy ste m s and their manage ment are mainly due to the observed and projected increases in temp eratur e, sea level, and precipitation variabilit y (v ery hi gh confidence) (Kundzewicz et al., 2007)

. 

### • All regions show an overall net negative i mpact of cl i m ate change on water res ources and freshwat e r ecosy ste m s ( h igh confide n ce). Areas in which runo ff is projected to decline are likely to face a reduction in the value of the service s provided by water r esources (very high confidence). Th e beneficial i m pacts of increased annual runoff i n othe r areas will be temp er ed by negative effects due to increased precipitation variabilit y and seasonal r unoff shifts on water supply, water qual ity, and flood risk ( h i gh confi d ence) (Kundzewicz et al., 2007 ).



### • Clim ate change affects the function an d operation of existing water infrastruct ure as well as water manage mentpractice s

. Adverse eff e cts of cli m at e change on freshwat e r sy stems aggravate the impacts of other stresses, such as popu lation gr owth , changing econom ic ac tivity, land use change, and urbanization. Globally, water demand will grow in the com ing decad es, pri m arily due to populati on gr owth and inc r eased affluence; regionally , large changes in irrigation water demand as a result of climate change s are likely

. Current wa ter m a nage me nt practices are very likely to be inadequate to reduce negative impacts of climate change on water suppl y re liabilit y , fl ood risk, health, energy, and aquatic ecosy stems ( v ery high confidence) (Kundzewicz et al. , 2007).



### • In polar regions, components of the terrestrial cry o sphere and h y drol og y ar e increasingly bei n g affect ed by c limate chang e

. Changes to cryospheric processes 64 are also m odify ing seasonal runoff (very high co nfidence) (Anisim ov et al., 2007).
The IPCC (Nicholls et al., 2007) ide n tified that c o asts are experiencing the adverse consequences of hazards relat e d to clim at e and sea level (very high c onfidence). The y are highly vulnerable to extre m e events, such as stor ms which impose s ubstantial cost s on coasta l societies. Through the 20th century, global rise of sea level contributed t o i n creased co astal inundation, erosion, a nd ecosy stem losses, but with considerable local and regional vari ation due to o ther factors (Nicholls et al., 200 7).
The IPCC (Fi schlin et al., 2007) recently m a de the f o llowing conclusions when considering how cli m at e change m a y affect ecosy ste m s a c ross all world regions :



### • During the course of this century the resilience of many ecosy st em s is likely to be exceed ed by an unprecedented com b ination of changes in clim at e and in other global change dr ivers (especially land use, polluti on , and overexploitation), if greenhouse g as em issions and other c h anges conti nue at or above current rates (high c onfidence). The elevated CO 2 levels and associated climatic cha nges will

64 Cryos p heric proces ses ar e de fine d to include the a n nual freezing a n d m e lting of snow c ove r, ice sheets , lake a n d river ice, perm afrost, a n d sea ice.



### 126

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

alter ecosy s tem structure, reduce biodiversit y , p e rturb functioning of most ecosy stems, and
co mp ro m ise t h e services th ey currently provide (high confidence). Present and future land us e change and associat e d landscape f rag m e ntation are very likely to impede s p ecies’ m igra tions and geographic range shifts in response to chang es in climate (very high confidence).

• Ecosy s tems and species are very likel y to show a wide range of vulnerabilitie s to cli m ate change, depending o n the extent to which climate change alters conditions that could cross critical , ecosy ste m -sp ecific thresho l ds (very high confidence)

. The m o st v u lnerable ecosy stems include coral reefs, the sea ice biome and other high latitude ecosystems (e.g. b o real forests), m ountain ecosy stems and Mediterranean-cli mat e ecosy ste m s 65 (high confidence). Least vulnerable ecosy stems include savannas and species–poor deserts, but this assessment is especiall y subj ect to uncertainty rel a ting to the CO 2 fertilization effect and disturbance regi mes su ch as fire (low confidence).

Table 15.1 : Examples of ke y regional impacts as i d entifie d b y IPCC (2 007b ) *

Afric a • Ne w stu d ie s confi r m tha t Africa is o ne of the m o st vulne r abl e co ntinent s to climate variability an d cha nge b e c au se of mu ltiple stre sse s and lo w a daptive ca pa city. Some adaptatio n to curre n t climat e variability is taki ng pl ace; however, thi s may be i n sufficient fo r future changes in c limate.

• By 2020, be tween 75 mi llion an d 25 0 million p e ople a r e p r oj ected to be exposed to increa sed wa ter st re ss du e to climate cha nge. If co upled with i n cre ased dem and, thi s will adversely affect livelihood s and ex a c e r bate wate r-rel a ted pro b lem s

. • Agricultural p r odu ction, i n cluding acce ss to f ood, in m any countri es and re gion s i s p r oje c ted to be severe ly compro mi sed by clim ate variability and cha nge . The area suitabl e for agri c ultu re, th e length of g r owin g sea s on s a nd yi eld p o tential, pa rticula r ly alo ng the ma rgin s of semi -a rid and a r id are a s , are expe ct ed to d ecrea se. Thi s woul d furthe r a dversely affect food se cu rity and exa c e r b a te mal nutriti on in the con t inent. In so me cou n trie s, yields fro m rain -fed ag riculture could b e redu ce d by up to 50% by 2020.

Asia • Glaci er m elt in the Him ala yas is proj ect ed to in cre ase flooding, a nd ro ck avala nch es fro m destabilized slopes, and to affe ct water resour ces within the next two to three decades. This will be followed by decreased ri ver flows as the gl aciers recede.

• Fre s h w ater a v ailability in Central, South, East and South-Ea st Asia, parti cula rly in larg e river b asi ns, i s p r oje c ted t o de crea se d ue to climate cha nge which, along with popul atio n gro w th an d i ncrea sing de mand a r i s ing from hi g her stand ard s o f living, coul d adversely affect more th an a billion p eople by the 2050 s.

• Coa s tal are a s , e s pe cially heavily-po pul ated m ega d e lta region s i n South, E a st and SouthEast Asi a, wil l be at greate s t ri sk d ue to incr ea sed flo oding from th e sea and, i n some me ga deltas, floodi ng from the ri vers.

• It is proje c ted that crop yiel ds could in crease up to 2 0 % in East a nd South-E a st Asia while they could de cre a se up to 30% in Ce ntral and S outh Asia by the m id-21 st century. The risk of hunge r is p r oje c ted to re main very hig h in several d e veloping co untrie s

. • Endemi c mo rbidity and m o rtality due t o diarrh ea di sea s e prim ari l y associ ated with flood s and d r ou ghts are expe cte d to rise in East, South and South

- E a st Asia due to proje c ted cha nge s in the hydrol ogi cal cy cle a s sociate d with global warmi ng. Incre ase s in co astal water tem perature would exace r bate t he abu nda nce and/or toxi city of cholera in South As ia.

65 Mediterra nea n clim ate ecosyste m s f eature s u btropical clim a t e with dry s u mmers. Des p ite the nam e, these ecosystem s exist in the US al ong t h e c o as t s of centr al an d s out her n C a l i f or ni a.



### 127

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Latin America • By mid-ce ntu r y, incre a ses in temperature a nd a s sociate d de creases in soil water a r e proje c ted to l ead to gradu al repl aceme n t of tr opical fore st by sava nna in e a ste r n Amazo n ia. Semi-a rid ve getation will t end to be re placed by ari d-lan d veget ation. The r e is a risk of signifi cant bi odiversity loss throug h sp ecie s extincti on in many area s of tro p ical Latin America.

• In drie r area s, climate ch ange i s expe cted to lea d to salini z atio n and d esert ification of agri c ultu ral l and. Pro d u c tivity of some impo rtant cro ps is proj ected to de cre ase an d livestock p r o ductivity to declin e, with a d vers e con s e quen ce s for f ood se curity. In temperate zon es soybe an yields a r e proje c ted to i ncrea se.

• Sea-level rise is proje c ted t o ca use incre a se d ri sk of floodin g in lo w-lying a r ea s. Increa se s in sea surfa c e temperature due to clim ate ch a nge a r e proje c ted to have adverse effect s o n Meso ame r ica n coral re efs, and cau s e sh ifts in the loca tion of south-east Pa cific fish sto c ks.

• Cha nge s in pre c ipitation pattern s and the disap pe aran c e of gl acie rs a r e p r oje c ted to signifi cantly affect wate r availability fo r hum an consumption, agri c ultu re and e nergy gene ration.

Polar Region s • For huma n communitie s i n the Arctic, impact s , pa rti c ula r ly tho s e re sulting f r o m ch angi ng sno w and i c e conditio ns, are proj ecte d to be mixed. Detriment al impact s would incl ude those o n infra s tru c ture and traditional in d igeno us ways of life.

• Beneficial im pact s would i nclu de red uced he ating costs an d mo re naviga ble northe r n se a route s

.

Small Islands • Small isl and s, wheth e r lo cated in the tropics o r h i ghe rla titu d e s , ha ve ch ar ac te ris t ics w h ic h make them esp eci ally vu lnera ble to the e ffe cts of climate cha nge, sea - lev e l ri se and extreme even ts.

• Deteri oration in coa s tal condition s, for ex ample through erosi o n of be ache s and coral blea ching, i s expected to affect local resou r ces, e. g., fisherie s, and redu ce t he value of these d e stin a t ions for tou r i s m.

• Sea-level ri se is exp ecte d to exacerbate inund ation, st orm su rge, e r osio n an d oth er coa s tal hazards, thus threateni ng vita l infrastructure, settlements and facilities that support the livelihood of islan d com m u n ities.

• Climate chan ge is proje c ted by mid-century to red uce water re sou r ces in many smal l islan d s, e.g., in the Cari bb ean a nd Pa ci fic, to the poi nt whe r e th e y beco m e in sufficient to meet dema nd during lo w-ra infall perio ds.

* W i th the exc e ption of some v e r y h i g h confi d ence stateme n t s for small isla nds , all oth e r IPCC conc lusi o n s w i t h i n the table ar e of eit her hi gh or me dium co nfide n c e

.



### 128

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Reference s

A C IA (20 04) I m

p a ct s of a W a rmi n g Arct i c : Ar ctic Clima t e Impa ct Assessmen t

. Cam b r id g e U n iv er sity P r ess.

A d g e r , N

. et al. ( 200 7) Tech n ica l Su mma ry. Clima te Ch ang e 200 7: Impa cts, Ada p t

a tio n an d Vu ln erab ility

. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A. Alley, R.B., Brig h a m

- Grett e , J., Miller, G.H., Po ly ak , L, and Wh ite, J.W.C. (200 9) Key Fin d i n g s and R ecom m e ndat i ons . In Past Clima te Va riab ility a n d C

h ang e in th e Arctic an d a t High La t itu d e s . A report b y th e U.S. Clim ate Change Program and Su bcom m i t t ee on Gl o b al C h an ge R e sear ch . U. S. Ge ol ogi cal S u r v ey , R e st on, VA ,p p. 4 2 1 – 43 0.

Ani s i m ov, O

. A. et al . ( 2 0 0 7 ) P o l a r R e gi ons . I n : Climate Ch an g e 2 0 0 7 : Imp a c ts, Ada p t

a tio n and Vu ln era b ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.

Back lun d , P., A. Janeto s, D.S. Sch i m e l, J. Hatfield , M.G. Ryan, S.R. Archer, and D. L e tten m aier (2008a ) Exec utive Sum m ary. In: The ef f

ect s of c l i m at e c h a n g e on a g ri c u l t u re, l a nd res ourc e s , w a t e r res o u rces, an d bi odi v e rsi t y i n th e Un ited S t ates. A R e po rt by t h e U.S . C l im at e C h ange Sci e nce P r o g r am and t h e S u bcom m i t t ee on Gl o b al Ch ang e Research . W a sh ingto n , D C., USA, 36 2 pp
Backlund, P ., D. Schim e l, A. Janet o s, J. Hat f ield, M. G. R y an, S.R

. A r che r , a n d D. Let t e nm ai er (20 0 8 b ) I n tr o duct i o n. In: The effects of climate change on ag ricult ure, land res o urces, w a ter res ources, a n d bi odi versi t y i n t h e U n i t e d St

at es. A Report by t h e U.S. Clim a t e Change Science Pr o g r am and th e S u bcom m i t t ee on Gl o b al C h an g e Resear ch. W a sh ing ton , D C., U S A , 36 2 pp

Bald w i n, M. et al. ( 200 7) Climat e-Ozone connections , Chap ter 5 in S cien t ific Assessmen t o

f

Ozon e Dep l etio n : 20 06
, Global Oz one Research and M oni t o ri n g P r oject —R e p ort No . 50 , 57 2 p p

. , Ge ne va, Swi t zerl a n d

.
B e l l , M .L, R . Gol dbe r g , C

. Ho gr efe, P.L. Ki n n ey , K . K n owl t o n, B

. Ly n n , J. R o se nt hal , C . R o se nzwei g , a nd J . Pat z

. (200 7) Clim a t e ch an g e , am b i en t o z o n e , and h ealth in 5 0 U.S. cities. Clim. C h ang e , DO I 10 .1 007 /s10 584 -00 6­ 9 166 -7

. Bindoff, N.L. et al. (2007) Observations: Oceanic Clim at e Change a n d Sea Level. In: C l i m at e C h an ge 2 0 0 7 : T h e Physi c al Sci e nce Basi s. C ont ri but i o n of Worki n g Gr ou

p I t o t h e Fourt h Asse ssme n t Repo rt of t

h e In terg o v ernmen ta l Pan e l on Clima te Ch ang e [S ol om on, S., D

. Qi n, M

. M a nni n g , Z

. C h en , M

. M a r qui s , K.B

. Av eryt, M.Ti gn or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited King do m and New Yo rk , NY , US A.

B ode ker et al . (2 0 0 7 ) The oz one l a y e r i n t h e 21st cent u ry , C h apt e r 6 i n S c ien tific Assessmen t o f

Ozon e Dep l etio n: 2 006
, G lob al O z on e Resear ch an d Mon ito r i n g Proj ect—R ep or t N o

. 5 0 , 57 2pp ., G e n e v a , Sw itzer lan d

. Boko, M. et al . (2007) Africa. In: Clima te Cha n g e 20 07: Impa cts, Adap ta tion an d Vuln erab ility. Con tribu tio n o f Wo rking Group II to th e Fo urth Assessmen t Rep o r t o f

th e In terg o v ernmen ta l Pan e l on Clima t e Ch ang e [ M.L. Parry , O. F. C a nzi a ni , J .P. Pal u t i k o f , P.J. va n der Li n d en a n d C .E. Ha ns on (eds .)] . C a m b ri d g e U n i v e r si t y Press, Ca m b r i d g e , Un ited K i ng do m and N e w Yor k, NY , USA.
Brasseur, G.P., et al (2006) Im p act of Climate Change on the Fu tu re C h e m i cal C o m posi t i on of th e G lob al Trop osp h e r e , Jo ur nal of C l i mat e , 19 , XX -X X.



### 129

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Cahoon, D.R ., D.J. Ree d , A

. S

. Kol k er , M.M. Brinson, J.C. St ev enson , S. Rig g s , R. Christian , E. Reyes, C. Vo ss, and D. Kun z (200 9) Co astal W e tlan d Su stain a b i lity. In : Co a s t a l S e n s itivity t o S e a
- Level Rise: A Fo cu s on th e Mid

Atla n tic Reg i on

. A report by th e U.S. Climate Ch an g e Scie nce P r o g r am and t h e S ubc om m i t t ee on Gl o b al Ch ang e Research

. W a sh i n g t on D

. C., USA, 32 0 pp

. C a l i f or ni a C l i m at e C h ange C e nt er ( 2 00 6) S cena r i o s o f

C lima t e Cha n g e in Ca lifo rn i a : An Overview . CEC- 50 0-2 005

­ 1 86- SF.

C a l i f or ni a En ergy C o m m i ssi on (2 0 0 6 ) O u r C h a ngi ng C l im at e: Assessi ng t h e R i s k s t o C a l i f or n i a. [Acce ssed 0 8 .08

. 07 : h ttp :/ /w ww .en e rg y.ca.go v / 2 006 publicatio n s /CEC- 5 00- 200 6- 077 /CEC- 5 0 0 -2 006- 077 .PD F ]
CCSP (2009a) Atmospheric Aeros o l Pr ope rties an d I m

pa cts on Climate, A Rep o r t by th e U

. S

. Clim a te C h ang e Sci e nce Pr o g r a m an d t h e S u b co m m i t t ee on Gl o bal C

h a n g e Researc h . [ M ian C h i n , R a l ph A. Kah n , a nd St e p hen E. Sc h w art z (e ds. ) ] . Nat i onal Aer o naut i c s a n d S p ace Ad m i n istr a tio n, W a sh ing ton , D

. C ., U S A , 13 9 pp

. CCSP (2 009 b) Coast a l Se nsi tivity to Sea-Level Rise : A F o cus on t h e Mi d-Atlantic Re gion . A rep o rt by the U. S. C l im at e C h ange Sci e nce Pr og ram and th e Subc om m i t t ee on Gl obal C h ange R e se arch . [Jam es G. Ti tu s (Coo rd in ating Lead Au t h or), K. Eric And e rso n , Don a ld R. Cah oon , Dean B. Gesch , Steph en K. Gill, Ben j am in T. Gu tierrez, E. Ro b e rt Th i e ler, an d S. Jeffress W illiam s (Lead Au t h ors)], U.S. En v i ron m en tal Pro t ection Age n cy, Was h ington D.C ., U SA, 320 pp.
CCSP (2009c) Pa st Clima t e Va riab ility a n d Ch ang e in th e Arctic a n d a t High La titu d e

. A repo rt b y th e U.S. Clim ate Ch ang e Pro g ram an d Sub c o mmit t ee o n Gl o b al Ch ang e Res earch [Alley, R.B., B r igh am

- Grette, J., Miller, G.H., Poly ak, L. , a n d White, J. W.C. (c oo rd i n at i n g l ead aut h o r s ) . U.S . Geol ogi cal Sur v ey, Reston , VA 46 1 pp

. CCSP (2 009 d) Thres h ol ds of C l i m at e C h an g e i n Ec osyst e m s . A re p o rt by t h e U.S . C l i m ate C h a nge Sci e nce P r og ram and the Subc ommittee on Global C h a nge Research [Fagre, D. B., C.W. C h arles, C.D. Al len , C. Birk elan d, F.S. C h api n I II , P

. M

. G ro ffm an, G.R

. G unt e n s p erge n, A

. K

. Kn app , A. D. M c Gui r e, P.J. M u l hollan d , D .P.C . Peters , D. D. R oby , a n d Geo r ge S u gi hara]

. U. S. Ge ol o g i cal Su r v e y , R e st on , VA , 1 5 6 p p

. C C SP, ( 2 00 8a ) Abr u pt

C l i mate C h an ge . A re port by the U.S. Clim ate Change Scie nce Program and the Su bcom m i t t ee on Gl obal C h a nge R e searc h [ C l a rk, P. U., A

. J. Weave r (co o r di nat i n g l ead aut h ors ) , E. B r oo k, E.R

. C o o k , T. L. Del w orth , a n d K . St e ffe n ( c hapt e rl ead auth or s) ]. U

. S. Geo l og ical Su rvey, Resto n , VA , 45 9 pp

. CCSP (2 008 b) An al yses of t

h e ef f

ect s of gl ob al ch a nge o n h u m a n heal t h a n d w e l f

a re an d h u m a n syst e m s . A Report by the U.S. Cli m ate Change Science Progra m and the S ubcommittee on Global Cha n ge Researc h

. [Ga m ble, J.L. (ed .), K .L. Ebi , F. G. Sus s m a n, T.J. W i l b a n ks, (A ut ho rs)]

. U. S. E n vi ro nm ent a l Prot ect i o n Age n cy , Was h i ngt o n , DC, US A.

C C SP, ( 2 00 8c ) : C l i m at e Mo de l s : A n Asse ss ment of St ren g t h s an d Li mi t a t i ons

. A Re port by the U.S. Cli m ate Change Sci e nce P r og ra m and th e S u b c om m i t t ee on Gl o b al C h a n ge R e sear ch [ B aderD

. C. , C. Cov e y, W

. J. G u tow s k i Jr ., I.M. Held, K.E. Kun k el, R.L. Miller, R.T. Tok m ak ia n and M.H. Zh ang (Au t h o rs)]. Departm e n t o f En erg y , Office of Biol ogical and E n vi r onm ent a l R e search , Washi ngt on , D.C ., U S A , 1 2 4 p p

. CCSP (2008d): C l i m at e Proj ect i ons Ba sed on E m i ssi o n s Scen ari o s f o r Lo ng -Li v e d a n d S hort

- Li ved Ra di at i vel y Active Gases and Aer o s o ls. A Report by the U.S. Clim ate Change Scienc e Program and the Subc ommittee on Glob al Ch an ge Research H. Lev y II, D.T. Sh ind e ll, A. Gillilan d , M.D. Schwarzkop f, L.W. Horo wi tz (ed s .). Depart m e nt of C o m m e rce, Washi n gt o n , DC , US A, 1 0 0 pp

. CCSP ( 2008 e) Th e Effects o f Clim a t e Ch ange o n Ag ricu ltu re, Land Reso urces, Wa ter Reso u rces, a n d Bi o d i versity in th e Un ited S tates

. A R e p o rt by t h e U.S . C l im at e C h ange Sci e nce Pr o g r a m and t h e S u bcom m i t t ee on Gl o b al C h an ge R e sear ch . P. B a c k l u nd , A . Ja net o s , D. Schi m e l et al

. U.S. De part m e nt of A g ri c u l t u re, Wa shi n gt o n , D C ., U S A , 362 pp

. CCSP (2 008 f) Imp a cts o f

Clima t e C h ang e an d Va ri a b ility o n Tra n s po rta t io n S y stems and In

frastru c ture: Gu lf Coa s t S tud y, Ph ase I. A Report by the U.S. Climate Change Scie nce Pr o g r a m and th e S ubc om m i t t ee on Gl o b al



### 130

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Ch ang e Research [Savon is, M. J., V. R. Bu rk ett, and J.R. Po tter (ed s .) ]

. Depa rt m e nt of T ran spo rt a t i o n , W a sh ing t on , DC, U S A , 445 pp

. CCSP (2 008 g) Rea nal ysi s of Hi st ori c al C l i m at e D a t a f o r K ey At mo sp her i c Feat ure s : I m

pl i c at i o ns f o r

At t r i but i o n of C

auses of O b s e rved C h a n g e

. A R e po rt by t h e U. S. C l i m at e C h an ge Sci e nc e Pr o g ram and t h e S ubc om m itt ee on Gl o b al C h a n ge R e searc h [R a n dal l D o l e , M a rt i n H o e r l i n g , a n d Si e g f r i e d Sc hu be rt (e ds. ) ]

. Nat i onal Ocea ni c an d Atm o sp h eric Ad m i n i stratio n , Natio n al Clim a tic Data Cen t er, Ash e v ille, NC, 156 p p

. CCSP, (20 08h ): Tren ds i n E m i ssi ons of Oz on e-De pl et i n g S u b st a n ces, O z o n e Laye r Rec o v e ry, an d Im pl i c at i o n s f o r Ultra v io let Rad ia tion Expo sure . A Report by th e U.S. Climate Ch an g e Science Progra m and the Subcommittee
on Gl obal C h a nge R e searc h

. [R avi s han k ara , A.R

. , M .J

. Ku ry l o , a n d C

. A. En ni s (e ds. )]

. Depa rt m e nt of Co mmerce, NOAA’s Natio nal Cli m a tic Data Cen t er, Ash e v ille, NC, 240 p p

. CCSP (2008i ) Weat h er a nd C l i m at e Ext r emes i n a C h an gi n g C l i m at e. Regi o n s of Fo cus: N o rt h A m eri c a, H a w a i i , Ca ribb ean , a n d U.S

. Pa cific Isla nd s. A R e po rt by t h e U.S. C l i m at e C h an ge Sci e nce Pr o g ram and t h e Su bcom m i t t ee on Gl o b al C h a nge R e sear ch

. [Th o m a s R. Karl, Gerald A. Meeh l, Ch rist op h e r D. Miller, Su san J. Hasso l , Ann e M. W ap l e, an d W illia m L. Mu rray (ed s .)]. Dep artm e n t o f Commerce, NOAA’s Nati onal Clim a tic Data Center , Was h ington, D

. C., US A, 164 pp.
CCSP (2007a): Effects o f Clima te C h a n g e on En erg y Produ ctio n and Use in th e Un ited S ta tes. A Repor t b y t h e U

. S. Clim a t e Change Science Program and the subcomm i ttee on Global c h ange Researc h . T homas J. W ilba n ks,, Vatsal Bh att, Dan i el E. Bilello , Stan ley R. Bu ll, Jam e s Ek man n , Willia m C. Horak, Y. Jo e Hu ang , Mark D. Levi ne , M i cha e l J. Sal e , Da vi d K. Schm al zer, a n d M i chael J. Sc ot t )

. De part m e nt of E n er gy , Of fi ce o f B i ol ogi cal & E nvi ro nm ent a l R e search , Was h i n gt o n , DC

. , US A, 1 6 0 p p

. CCSP (2 007 b) Sce nari o s of Gree nh o u se G a s E m i ssi o n s an d At mo sp he ri c Conce n t r at i ons ( P art A) an d Revi ew of Inte grate d Sce nari o Devel opment and Application (Par t B) . A Report by the U.S. Climate Change Science Prog ram an d th e S u b c o m m ittee on G l ob a l Ch ang e Research [Clarke , L

. , J. Edm o nds, J. Jac oby, H. Pitcher, J. Reilly, R. Ric h els, E. Parso n , V. Burk ett, K. Fish er-Vand en, D. Keith , L. Mearn s , H. Pitch e r, C. Rosen z weig, M

. W e bst e r ( A ut ho rs)]

. De part m e nt of E n er gy , Of fi ce of B i ol o g i cal & En vi r o nm ent a l R e search, Was h i n gt o n , D C ., U S A , 260 pp

. CCSP ( 200 6) Temp era t u r e Trend s in th e Lower Atmo sph e re: S t ep s fo r Und e rstand ing and Reco n c iling Differen ces

. A Rep o rt by t h e C l i m at e C h a nge Sci e nce Pr ogr a m a n d t

h e Su bc om mi t t ee on Gl o b a l C

h an ge Rese arc h . Thom as R. Karl, Su san J. Hasso l, Chri sto p h er D. Miller, and W illiam L. Mu rray (ed s .), Wash ingto n , DC

. CDC (2 005 a) Heat-related mo rtality – Arizo n a , 199 3-2 002 , an d Un ited States, 19 79 -20 0 2

. MM WR

–Morb i d ity & Mo rtality W e ek ly Repo rt, 54 (2 5), 628 -6 30

. CDC (20 05b ) Vibrio illn esses after Hurrican e Katr in a: mu ltip le states, Augu st– S ep tem b er (2 00 5) MMWR–Mor b. Mortal. Wkly. Rep

. , 54 , 92 8- 9 31

. Christense n, J.H. et al. (2007) Reg i o n a l Climate Proj ection s . In : C l i m at e C h an ge 2 0 0 7 : The P hysi c al Sci e nce Ba si s. Cont ri b u t i o n o f

Worki n g Gro up I t o t h e F o urt h A ssess me nt Rep o rt of t

h e Int e r g overn m ent a l

Pa nel on C l i m at e Ch ang e [So l om o n , S., D. Qin , M. Man n i ng , Z. Ch en , M

. Ma rqu i s, K.B. Av eryt, M. Tig n o r and H.L. Miller (eds .)] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.
Clark, P.U., A.J. Weave r , E. Br oo k, E.R. C o ok , T.L. D e lwo r th , and K

. Stef f e n ( 200 8) E xecutive Summary . In : Abr upt C l i m ate C h an ge

. A R e po rt by t h e U. S. C l i m at e C h ange Sci e nce P r og ram and t h e Su bcom m i t t ee on Glo b al Cha n ge Researc h

. U. S

. Ge olo g ical S u r v ey, Rest on, VA , pp. 7–18.

CN A Corp oratio n (2 007 ) N a t i o n a l Se curi t y an d t h e T h reat of C l i mat e C han ge , Alex and r ia, Virg in ia. h ttp ://secu rityan d c lim ate.cn a.o r g /

Co h e n , S., K. Miller et al. (2 0 01) No rt h America. In : Clima te C h ang e 20 01: Impa cts, Ada p t

a tio n and Vu ln era b ility. Cont ri b u t i o n o f

Worki ng Gro up I I t o t h e T h i r d Assess ment Report of t

h e Int e r gove r n m e n t a l

Pa nel o n C l i m at e



### 131

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Ch ang e [J .J. M c C a rt hy et al . (e ds. ) ] . C a m b ri d g e U n i v ersi ty Press, C a m b ri dge, U n i t e d K i ng dom and N e w Yo rk , NY , US A.
Confalonieri, U. et al. (2 0 07) Hu m an Health

. In : Clima te Ch an g e 2 007 : Imp a c ts, Ada p t

a tio n a n d Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.

Cro ssett, K.M., T.J. Cu llito n, P.C. W iley, and T.R. Goo d s peed (2 004 ). Po pu la tion Trend s Alon g th e C o a s t a l Un ited S ta tes: 198 0-20 08

. NOAA pu b lication , Silver Sp ri n g , M D

. C ubasc h et al

. ( 2 0 0 1 ) Pr o j e c t i ons of F u tu re C l im at e C h ange

. In: C l i m at e C h ange 20 0 1 : T h e Sci e nt i f i c B a si s. C ontri but i o n o f Work i ng Gr o up I t o th e T h i rd Asses s m e nt R e po rt o f th e Int e rg o v er nm ent a l Panel on C l im at e Ch ang e [H ough ton , J.T., Y. D i ng , D.J. Gr i g g s , M. No gu er , P.J. v a n d e rLin d e n , X

. D a i, K

. Mask ell an d C.A

. Joh n s o n (e ds .)] . C a m b ri dge U n i v e rsi t y Press , U n i t e d Ki n g d o m and New Y o rk , N Y, US A.

C u r r i e , D. J. ( 2 00 1 ) Pr o j ect ed effect s o f cl i m at e chan ge o n pat t e rns of ve rt ebrat e a nd tr ee speci es i n t h e cont e r m i nous United States. Ecosyste ms , 4 : 2 16- 225

.
Denm an, K.L. , et al . ( 2 0 0 7 ) C o u p l i n gs B e t w een C h a nge s i n t h e C l i m at e Sy st em and B i oge ochem i stry . In: Clima te Ch ang e 200 7: Th e Physica l Scien ce Ba sis. Co n tribu tion of Wo rking G r ou

p I to th e Fou r th Assessm e n t Repo rt of

t

h e Int e r gov ernm ent a l

Pan e l on C l i m at e C h a n g e [S ol o m on, S., D. Qi n, M . M a n n i n g , Z. C h en , M . M a rq ui s, K.B. Av eryt, M.Tig nor an d H.L. Miller (ed s .)]. Cam b ridg e Un i v ersity Press, Cam b rid g e , Un ited Ki n gdo m an d N e w Yo rk , NY, USA.

Do le, R., M. Ho erling , and S. Schub ert (20 08) Executive summary . In: Reanalysis of Hist orical Climate Data for Key At m o sphe ri c Feat ures: I m pli cat i ons fo r At tr i b ut i on o f C a uses o f O b ser v e d C h an g e . A R e po rt by t h e U.S. C l im at e C h an ge Sci e nce P r og ram and t h e Su bcom m i tt ee o n Gl o b a l C h ang e Research [Ran dall Dole, Martin Hoe r l i n g, an d Si egf r i e d Sc h u b ert (e ds. ) ] . Na t i onal Ocea ni c and At m o sphe ri c Adm i ni strat i on, Nat i o nal C l im at i c Data Cen t er, Ash e v ille, NC, pp . 1– 4

Easter lin g, W

. et al. ( 200 7) Foo d , Fibr e and Fo r e st Pro ducts. I n : Clima te Ch ang e 2007 : I m

pa cts, Ada p t

a tio n and Vu ln erab ility. Co n t ribu tion of Wo rking Gro u p II to t h e Fou r th Assessmen t Repo rt of th e In terg o v ern m en t a l Pa nel o n C l i m at e C h an ge [ (e d s. )] . C a m b ri dge U n i v e rsi t y Press, C a m b ri dge , U n i t e d Ki ng d o m and Ne w Y o rk , NY , US A.

Eb i, K.L., J. B a lb u s , P.L. Ki nn ey, E. Lipp , D. Mills, M.S. O’Neill, and M. W ilso n , 2 0 0 8 : Effects o f Glob al Ch ang e on H u m a n Heal t h . I n : Ana l yses o f

th e effects o f

g l oba l ch ang e on h u m a n h e a lth and welfa re and h u ma n systems

. A R e po rt by t h e U

. S. C l i m at e C h ange Sci e nce Program and t h e Subc ommittee on Global Change R e search . [ G a m bl e, J.L. (e d. ), K.L . E b i , F. G. S u ssm an, T .J. Wi l b a nks , (A ut h o r s ) ] . U.S . E nvi r onm ent a l Prot ect i o n A g e n cy , Was h i n gt on , DC , US A, p. 2 -1 t o 2- 7 8

.
EI A (2 006 ) An nu al En erg y O u tlook 200 6, w ith Pr oj ecti o n s to 2 030

. D O E /EIA -0 383 (20 06 )

. E n er gy I n f

o r

m at i on Administration , W a shi ngt on , D.C

.
Eu rop ean C o mmissio n ( 200 3) Ozon e-clima te in tera ctio ns . In: Air polluti on researc h re po rt [Isak se n, I.S. A. (ed s .)]

. R e po rt 8 1 , E U R 2 0 6 2 3 , L u xe m bour g. Field, C.B. et al. (200 7) North Am erica. In: Clima te Ch an g e 20 07: Impa cts, Ada p t

a tio n an d Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.



### 132

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Fin g ar, T. (2 00 8) “Nation a l In tellig en ce Assessm en t on th e Natio n a l Security Imp licatio n s of Glob al Cli m at e Ch ang e to 20 30 .” Testi m o n y b e fore th e Hou s e Perm an en t Select Co mmi ttee o n In telligen ce and Ho u s e Select C o m m i tt ee on Ener gy In de pe nde nce a n d Gl obal Wa rm i ng, Ju ne 2 5 , 2 0 0 8

. Fish and W i l d life Service (FWS) (2008) En dan g e red a n d Th rea t en ed Wild life a n d Plan ts; Dete rmina tion o f Th rea t en ed S t a t u s f o r th e Po la r Bea r ( Ursu s ma ritimu s ) Th rou gho u t Its Ran g e

. 50 C F R Part 17 , R IN 1 0 1 8

­ A V 19 , FW S- R 7

- E S-20 08 -003 8.

Fish an d W ild life Service (F WS ) (2 0 0 7 ) 12 -Mon th Petitio n Fi n d i n g a n d Propo sed Ru le to List th e Po la r Bear (Ursu s ma ritimu s ) a s Th rea ten ed Th rough It s Rang e

. 50 C F R Par t 17 , R I N 1 018 -A V19

.
Fish er, B. et al. (2 007 ) Issues related to m i t i g atio n i n th e l o ng term co n t ex t. In : Clim a te Ch ang e 200 7: Mitig a tio n. Cont ri b u t i o n o f

Worki n g G ro u p I I I t o t h e F ourt h Assess m e nt Re po rt of t

h e Int e r g overn m ent a l

P anel o n C l i m at e Ch ang e [B . M e t z , O.R

. Davi dso n , P.R . B o sch, R

. Dave , L.A . M e y e r ( e ds. ) ] . C a m b ridge U n i v er si t y Press, Ca m b r i d g e , Un ited K i ng do m and N e w Yor k, NY , USA.

Fisch lin , A. et al. ( 200 7) Eco s ystem s , th eirProp er ties, Go od s, an d Serv ices. In : C l i m at e C h a nge 20 07 : Im p a ct s, Ada p t

a tio n and Vu ln era b ility. Co n t ri b u tion o f

Wo rking Group II to th e Fou r th Assessmen t Report o f

th e In terg o v ernmen ta l Pan e l on Clima te Ch an ge [M .L. Par r y , O.F . C a nzi a ni , J.P. Pal u t i ko f, P.J. va n de r Li nde n an d C.E. Han s o n ( e ds. ) ] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.

Fo rster, P. et al. (2 007 ) Chang es in Atm o sph e ric Con s tituen ts and in Rad i ativ e Forcing

. In : Clim a te Ch ang e 20 07 : Th e Physica l S c ien ce Ba sis. Co n t ribu tion o f

Wo rki n g Group I to t h e Fo urth Assessmen t Report o f

th e In terg o v ernmen ta l Pan e l on Clima te Ch ang e [S ol om on, S., D

. Qi n, M

. M a nni n g , Z

. C h en , M

. M a r qui s , K.B

. Av eryt, M.Ti gn or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited King do m and New Yo rk , NY , US A.

Gam b le, J.L., K.L

. Ebi, F. G. Sussm an, T.J. W i l b anks , C. Reid, J.V. Thomas, C.P. W ea v er, M. Harris, and R. Freed, 2008: E x ecuti ve Summ ary. In : Analyses of the effects of global cha nge on hum an health and welfare a nd hum an sy st em s. A R e po rt b y t h e U.S . C l i m at e C h ange Sci e nce P r o g r a m and t h e S ubc om m i t t ee on Gl o b a l C h an ge R e sear ch. [ G am bl e, J.L. (e d. ), K .L. Ebi , F. G. S u ss m a n, T.J. W i l b ank s , ( A ut ho rs )] . U.S . En vi r o nm ent a l Prot ect i o n A g e n cy , Was h i n gt on , DC , US A, p. 1

– 1 1

. Grau m a nn, A. , T

. H o ust o n, J. Law ri m ore, D. L e vi nso n , N. L o t t , S. M c C o w n , S. St e phe ns an d D. Wue rt z , 2 0 0 5 : Hu rri ca ne Katr i n a - a cl im at ol ogi cal per p ect i v e. Oct o be r 2 0 0 5 , up dat e d Au g u st 20 0 6

. Tech ni cal R e port 2 0 0 5

­ 01

. 2 8 p. NO A A Natio nal Clim ate Data Center, availa ble a t: http://www. ncdc .n oaa. g ov /oa/rep o rts/tec h

- r ep o r t2 005 01 z.pd f
Gutierrez, B.T., S. J. W illiams, a n d E. R. Thieler (2009) Ocean C o asts. In: Coastal Se nsitivity to Sea-Level Rise: A Foc u s on t h e Mi d- At l ant i c Regi on

. A r e po rt by t h e U. S. C l i m ate C h a nge Sci e nce P r og ram an d t h e Su bcom m i t t ee on Gl obal C h a nge R e searc h

. Was h i n gt o n D. C ., U S A , 32 0 pp

.
Gut o ws ki, W.J ., G .C. Heg e rl, G.J

. H o llan d , T.R. Kn utso n, L.O

. M ear ns, R.J. Sto u ffe r, P.J. We bster, M

. F. Weh n e r , F. W. Z w i e rs ( 2 0 0 8 ) C auses of O b ser v e d C h an ges i n E x tr em es and Pr o j ect i ons of F u tu re C h a n ges. I n : Weather

an d C l i m at e E x t r emes i n a C h a n g i n g C l i m a t e. Regi on s of Foc u s: N o rt h Ameri c a , Haw a i i , C a ri b b ea n, a n d U. S. Pa cific Islan d s . T.R. Karl, G.A. Meeh l, C.D. Miller, S.J. Ha sso l, A.M. W ap l e, and W.L. M u rray (ed s .). A Rep o rt b y th e U.S. Clim a t e Ch ang e Scien ce Progr am and the Subcommittee on Global Cha n ge Research , Was h ington, D C

.
H a t f i e l d , J

. , K

. B o o t e , P

. F a y , L

. H ah n , C

. I z a u rr a l d e , B

. A

. K i m b a l l , T

. M a d e r , J

. M o r g a n , D

. O r t , W

. P o l l e y , A

. Tho m so n , and D

. W o lf e (200 8) Ag r icu lt u r e. In : The effects of climate change on agr iculture, l a nd resources,
wa ter reso u r ces, and b i od iversity in th e Un ited S t a t es. A R e po rt by t h e U .S. C l i m at e C h ange Sci e nce Pro g r am and t h e Su bc o m m i t t ee on Gl obal C h a nge R e search

. Was h i ngt on , DC ., U S A, 3 6 2 pp

.



### 133

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Hau g l u st ai ne D. A., et al

. ( 2 00 5 ) F u t u re tr op os ph eri c oz o n e simu lated with a clim a t e

- ch em istry-b i osp h ere m o d el, G e ophys. Res. Lett. , 32 , L2 480 7, d o i:10

. 10 29 /20 05G L0 2403 1.
Hege rl , G.C

. e t al . (2 00 7 ) U n derst a ndi ng an d At tri but i n g C l im at e C h ang e . I n : Clim a te Ch ang e 200 7: Th e Physica l Sci e nce B a si s. Cont ri but i o n of Wor k i n g G rou p I t o t h e Fo urt h A ssess ment Re p o rt o

f

t

h e I n t e rg ov ernm ent a l Pa nel o n C l i m at e C h a nge [S ol om on, S., D

. Qi n, M

. M a nni ng , Z

. C h e n , M

. M a r qui s , K

. B

. A v ery t , M

. Ti gn o r a n d H.L. Miller (eds.)]. Cam b ridge Un iv ersity Press, Cam b rid g e, Un ited Kingd o m an d New York , NY, USA. Hogrefe C.B

. e t al. (2004) Si mu la ting cha n ges in re gional air pollution over th e easte rn United States due to cha n ges i n gl obal a n d r e gi o n al cl i m at e an d em i ssi ons, J. Geophys. R es ., 10 9 : D2 230 1.
Horvitz, A ed., (2008) Gl obal Clim ate, in State of the Climate in 2007. Levi ns o n , D. H ., a n d J. H. La wrim ore e d s., Bu lletin o f t

h e American Meteo ro l o g i ca l S o ci ety , 89 : S3 7- S61

.
H

. R. 498 6 ( P L 1 1 0

- 18 1, Jan

. 28 , 2 008 )

. A v ailab l e f r om Thom as ( L i b r ar y o f Congr ess) h ttp ://th omas.lo c .gov ; accessed 2/23/ 0 9.

IPC C ( 2 00 7a) C l im at e C h an g e 2 0 0 7 : T h e P h y s i cal Sci e nc e B a si s. C o ntri but i o n o f Wo rk i n g Gr ou p I t o t h e F o u rt h Assessm ent R e po rt o f t

h e I n t e rg ove rnm e nt al Panel on C l i m at e C h ange [ S ol om on, S. , D. Qi n , M . M a nni ng , Z

. Ch en, M. Marq u i s, K.B. Averyt, M.Ti gno r and H.L. Miller (ed s .)]. Cam b ri d g e Un i v ersity Press, C a m b ridg e, U n ited K i n gdom an d N e w Y o r k , NY , USA.
IPCC ( 2 0 0 7 b ) Sum m ary for Policym akers

. In: Clima te Ch ang e 20 07: Imp a c ts, Adap ta tion and Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.

I P CC (2 007 c) Su mm ar y f o r Po licy m ak ers. In : C l i mat e C h a nge 2 0 0 7 : Mi t i gat i o n. C o nt ri but i o n of Wor k i ng Gr ou

p I II t o t h e F ourt h Assessme n t Re port of t

h e I n t e rgo vern m e n t a l

Pa nel o n C l i m at e C h an ge [ B . M e t z , O.R

. Davi ds on , P

. R

. B o s c h , R

. D a v e , L

. A

. M e y e r( e d s

. ) ]

. C a m b r i d g e U n i v e r s i t y P r e s s , C a m b r i d g e , U n i t e d K i n g d o m a n d N e w Yo rk , NY , US A.

IPCC ( 2 00 7 d ) Sum m ary for Policym akers. In: C l i m at e C h an ge 2 0 0 7 : T h e Phy s i c al Sci e nce B a si s. Co nt ri b u t i o n of Worki n g Gr o u

p I t o t h e Fo urt h Asses s me nt Rep o rt of t

h e Int e r gove r nme n t a l

P anel on C l i m at e C h a n g e [So l o m o n , S., D. Qin, M. M an n i n g , Z. Chen , M. Marq u i s, K.B. Av ery t , M.Tign or an d H.L. Miller (ed s .)]. Ca m b r id g e Univ er sity Pr ess, Ca m b r id g e , Un ited K ing do m and N e w Yor k, NY , USA.

I P CC (20 0 1 a ) Su mm ar y f o r Po licym ak er s. In Clima te Ch ang e 2001 : Impa cts, Adap ta tion a n d Vu ln erab ility. Cont ri b u t i o n o f

Worki ng Gro up I I t o t h e T h i r d Assess ment Report of t

h e Int e r gove r n m e n t a l

Pa nel o n C l i m at e Ch ang e [J .J. M c C a rt hy et al . (e ds. ) ] . C a m b ri d g e U n i v ersi ty Press, C a m b ri dge, U n i t e d K i ng dom and N e w Yo rk , NY , US A.
IPCC ( 2 0 0 1 b ) Sum m ary for Policym akers. In

. Clima t e Cha n g e 2 001 : The S c ien tific Basis. Con t rib u t i o n o f

Wo rking Group I to th e Th ird Assessmen t Repo rt o f

th e In tergo vern m en ta l Pan e l on Clima t e C h ang e [J.T . Houghton et al . (e ds. ) ] . C a m b ri dge Uni v e r si t y Press , C a m b ri dge, U n i t e d Ki n g d o m and New Y o rk , NY , US A.

I P CC (2 000 ) Speci al Rep o rt o n E m i s s i ons Sce nari o s. A S p eci al Rep o rt of Worki n g Gr o up II I of t h e In terg o v ernmen ta l Pa n e l on Clima te Chan g e [N. Naki cenovic et al. (eds .)]. Cam b ri dge Unive r sity Press, Ca m b r i d g e , Un ited K i ng do m and N e w Yor k, NY , USA.
IPCC ( 1 9 9 6 ) Clim a te Ch ang e 199 5: Th e S c ien ce o f

Clima t e C h ang e . Int e r g ove r n m e nt al Panel on C l im at e C h ang e , J.T. H o ug ht o n , L.G. M e i r a Fi l ho, B

. A. C a l l a nde r, N. Harr i s , A. Kat t e n b e rg , an d K. M a skel l , eds. C a m b ri dge Uni v ersity P r e ss. Cam b ridge , U. K.



### 134

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

I P CC Techn o l o g y and Eco nomic A ssess m e n t Pan e l (2 005) I P CC/TEAP Sp ecial Rep o r t o n Saf e -gu a rdin g th e O z on e Layer and the Global Clim ate Syste m : Issues Related to Hy dr o f l u or ocarb o n s an d Pe rf l u o r ocarb o n s. Prepar e d by W o rk i n g G r o u p I an d I II of t h e IPC C , a nd t h e TEA P. Edi t e d by B

. M e t z , L. Kui j pers , S. S o l o m o n , S. O. An de rsen , O. Davi ds on , J. Pons , D. de Jag e r, T. Kest i n , M . M a nni n g , and L. A. M e y e rs, 4 8 8 p p ., C a m b ri dge Uni v ersity P r e ss, Cam b ride, U. K., an d Ne w Y o rk , N Y , US A.

Jaco b, D.J ., a n d D. A. Win n e r ( 2 0 0 9 ) Ef f ect of clim ate change on ai r qual ity , Atmos p her i c Environment ., 43: 5 1

- 6 3.

Janet o s , A., L. Ha nse n , D. I n ouy e, B .P

. Kel l y , L. M e y e rs o n , B . Pet e rso n , an d R

. S h aw ( 2 0 0 8 ) B i odi ver s i t y . In: T he ef

f

ect s of cli m a t e chan ge o n a g ri cul t u re , l a n d reso urces , w a t e r reso urces, an d bi o d i versi t y i n t h e Uni t e d St at es

. A Report by t h e U.S. Clim a t e Change Sci ence Progr am and the Subc ommittee on Gl obal C h a nge Research. Was h i n gt o n , D C ., U S A , 36 2 pp

.
Janse n , E ., J

. Ove r peck, K

. R. Briffa , J. -C . D uplessy, F. Joo s , V. Masso n -Delm o tte, D. Olago , B. Otto -Bliesn er, W.R. Peltier, S. Rah m sto r f, R. Ram esh , D. Rayn aud , D. Rin d , O. So lomin a , R. Villalb a an d D. Zh an g (2 007 ) Pa la eo clima te . In: Clim ate Change 2007: The Ph y s i cal Sci e nce B a si s. C ont ri b u t i on of Wo rk i n g G r o u p I t o t h e Fo urt h Asse ss m e nt R e port of t h e I n t e rg o v er nm ent a l Panel o n C l im ate C h an ge [ S o l om on, S., D. Qi n, M

. Man n i n g , Z. C h en, M. Marq uis, K.B. Av ery t , M. Tig n o r an d H.L. Miller (ed s .)]. Ca m b ridg e Un iv ersity Press, Ca m b r i d g e , Un ited K i ng do m and N e w Yor k, NY , USA.
Karl, T.R. , G. A. M e e h l, T

. C. Peters on , K.E

. Ku n k el, W. J. Gut o ws ki, Jr. , D.R. Easterlin g (2 0 0 8 ) Exec utive Summary in W eat her and Clim ate Extremes in a C h a n gi n g C l i m at e. R e gi o n s of F o c u s: N o rt h Am eri ca, Hawai i , Carib b e an , and U.S. Pacific Islan d s . T. R

. Karl, G.A. Meeh l, C.D. Miller, S.J. Hasso l, A.M

. W a p l e, and W.L. M u rr ay (e ds. )

. A R e po rt by t h e U. S. C l i m at e C h an ge Sci e nc e Pr o g ram and t h e S ubc om m itt ee on Gl obal C h an ge Research, Was h ington, DC.
Kundzewicz, Z.W. et al. ( 200 7) Fr eshw ater Reso ur ces a n d T h ei r M a na g e m e nt . In: Clim a te C h ang e 2 007 : I m

pa cts, Ada p t

a tio n and Vu ln era b ility. Co n t ri b u tion o f

Wo rking Group II to th e Fou r th Assessmen t Report o f

th e In terg o v ernmen ta l Pan e l on Clima te Ch an ge [M .L. Par r y , O.F . C a nzi a ni , J.P. Pal u t i ko f, P.J. va n de r Li nde n an d C.E. Han s o n ( e ds. ) ] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.
Kunkel, K

. E., P.D. Bromirski, H

. E. Brooks , T. C a vazos, A

. V. Dou g las, D

. R. Easter li ng, K.A. Eman uel, P.Ya. Grois m an, G.J. Holland, T.R. Knutson, J.P. Kossin, P. D. Komar, D. H. Le vinson , R.L. Smith (200 8) Observed Ch anges in Weather and Clim ate Extr em e s in Wea ther and Climate Extrem es in a Changing Climate. Reg i on s of Fo cus: North America , Haw aii, Caribbean, and U.S. Pacific Isla nds . T

. R. K arl, G

. A

. M eeh l, C. D

. M ill er, S

. J

. H as s o l, A

. M

. W ap le, andW

. L. M u rra y ( eds .). A Report b y th e U.S

. Clim at e Ch ange S c ien ce P r ogram and the Subcommittee on Global Ch ange Research , Washington, DC.

Leib en sp erg e r, E. M., L. J. M i ck ley, D. J. Jaco b (20 0 8 ) Sensitiv ity o f U. S. air qu ality to mid

- latitu d e cycl o n e f r e q u e n c y an d i m p licatio n s of 19 80- 200 6 climate ch ang e , A t m o s. Ch em . Ph ys., 8 : 707 5-7 086

.
Lem k e, K. et al . (20 0 7 ) O b s e rvat i o ns: C h a nge s i n Sn ow , Ice and Fr oze n Gr o u n d . I n : Clim a te Ch ang e 20 07 : Th e Physi c al Sci e nce Basi s. C ont ri but i o n of Worki n g Gr ou

p I t o t h e Fourt h Asse ssme n t Repo rt of t

h e In terg o v ernmen ta l Pan e l on Clima te Ch ang e [S ol om on, S., D

. Qi n, M

. M a nni n g , Z

. C h en , M

. M a r qui s , K.B

. Av eryt, M.Ti gn or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited King do m and New Yo rk , NY , US A.

Lettenm aier, D ., D

. Major, L. Pof f , a nd S. Ru nn ing (20 08) W a terResour ces. In : The e ffects of climate change on

a g r icu ltu re, lan d reso urces, wa ter reso urces, a n d b iod iversity . A R e po rt by t h e U. S. C l im at e C h ange Sci e nce Pro g r am and t h e s u bcom m i t t ee o n Gl o b al c h an ge R e sear c h

. Was h i n gt o n , DC ., U S A , 36 2 pp

. Liao , C. and Sein feld (2 006 ) Ro le of clim a t e ch an g e in g l ob al p r e d i c t i ons of f

u t u re tr o p o s ph eri c ozo n e and aer os ol s , J. Ge o phy s. Re s ., 1 1 1 , D12 304 , do i:1 0.102 9 / 2 005 JD00 685 2.
McMichael et al. (2001)

. Hum a n Health. I n : Clima te Ch ang e 2 001 : Impa cts, Adap ta tion a n d Vu ln erab ility. Cont ri b u t i o n o f

Worki ng Gro up I I t o t h e T h i r d Assess ment Report of t

h e Int e r gove r n m e n t a l

Pa nel o n C l i m at e



### 135

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Ch ang e [ M.L. Parry, O.F. Canz iani, J

. P. Palutik o f, P.J. van de r Linde n an d C.E. Han s on (eds. ) ]

. Ca m b r id g e Univ er sity Pr ess, Ca m b r id g e , Un ited K ing do m and N e w Yor k, NY , USA.
Meehl, G.A. e t al. (2007) Glo b a l Cli m ate Proj ection s . In: C l i m at e C h a nge 2 0 0 7 : T h e Physi c al Sci e nce B a si s. Cont ri b u t i o n o f

Worki n g Gro up I t o t h e F o urt h A ssess me nt Rep o rt of t

h e Int e r g overn m ent a l

Pa nel on C l i m at e Ch ang e [So l om o n , S., D. Qin , M. Man n i ng , Z. Ch en , M

. Marqu i s, K.B. Av eryt, M.Tig n o r and H.L. Miller (eds .)] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.

M i ckl e y , L.J., D.J. Jac o b, B

. D. Fi el d, a nd D. R i nd ( 2 0 0 4 ) Effect s o f f

u t u re cl i m at e change on re gi o n a l ai r pol l u t i o n episodes i n the United States. G e ophys. Res. Lett. , 30 , 186 2, do i:1 0.102 9 / 20 03G L0 179 33

. Millen n i u m E co s ystem Assessm en t (2 0 0 5 ) Ec osyst e m s an d Hu m a n Wel l

- bei n g : Synt hesi s . I s l a nd P r ess , Was h ington, D C

.
M i mu ra, N. e t al. (2 00 7 ) Sm all Islands. In: Clima te Ch ang e 200 7: Impa cts, Ada p t

a tio n and Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [ ( e d s. ) ]

. Cam b rid g e Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.

N A R STO (2 00 4) P a rticul ate Matter As se ssme n t for Policy Makers: A NARSTO A ssessme n t . P. McMu rr y , M. She phe r d , a n d J. Vi c k ery , ed s . C a m b ri dge U n i v e rsi t y Press , C a m b ri dge, E ngl a n d

. ISB N 0 52 1 8 4 2 8 7 5.

NAST (200 0) Cli m a t e Ch ange Im p acts on t h e Un ited Stat es : Th e Po ten tial Co n s equ e n c es of Clim ate Variab ility an d Ch ang e.
National Ae ronautical and Space Adm i nistration (NASA) Godda rd Sp ac e Flight Center (2008) 2008 Arctic Sea Ice fr om AM SR-E

. h ttp ://sv s .g sfc.n a sa.gov /v is/a0 000 00 /a0035 00 /a003 556 / . Accesse d M a rc h 4, 2 0 0 9

. National Ae ronautical and Space Adm i nistration (NASA) Godda rd Sp ac e Flight Center (2007) 2007 Arctic Sea Ice fr om AM SR-E

. h ttp ://sv s .g sfc.n a sa.gov /v is/a0 000 00 /a0034 00 /a003 464 /in d e x

. h tm l . A ccessed Mar c h 4 , 20 09

. National Aeronautical and Space Ad ministration (NASA) (2009) GISS Surfa ce Te m p erature Analysis. http://data.giss .nas a.gov/ gistem p/2008/ . A c cessed Mar c h 4, 20 09

. Natio n al In tellig en ce Coun cil (NIC ) (200 8) Gl o bal Tre n d s 20 25 : A Tra n s f

o rme d Wo rl d

. Office of the Director of Natio n a l In telli g e n c e, Wash ing t on DC, 12 0 p p

.
Nat i onal Oce a ni c an d At m o spheri c Ad m i ni strat i on ( N O A A ) ( 2 0 0 9 a) Clim a te o f 200 8 - An nua l Rep o r t. h ttp ://www.n cd c.n o a a.gov /o a/cli m a t e/research /20 0 8 / ann / g l o b al.h t m l A ccessed Mar c h 4, 2 009

.
Nat i onal Ocea ni c an d At m o sphe ri c A d m i nistrat i on (N OA A) (2 0 0 9 b ) 2 0 08 A n nu al C l i m at e Revi ew - U. S. Su m m ary

. h ttp ://www.n cd c.n o a a.gov /o a/cli m a t e/research /20 0 8 / ann / u s -su m m a ry.h t m l Accesse d M ar c h 4, 2 0 0 9

.
Nat i onal Ocea ni c a n d At m o sph e ri c Adm i ni strat i on (N O A A ) (2 0 09c ) Tren ds i n At m o sp heri c C a r

b on Di oxi d e
- Ma un a L o a. h ttp ://www.esrl.n o a a.gov /g m d/ccg g /trend s / Accessed Mar c h 4 , 200 9.

Nat i onal Ocea ni c an d At m o sph e ri c A d m i ni strat i on (N O A A ) ( 2 0 0 7 )

. U.S. Histo r ical Clim ate Netwo r k Data. h ttp ://www.n cd c.n o a a.gov /o a/cli m a t e/research /u sh cn /u sh cn .h tml

Natio n a l Research Coun cil (NRC) (2 008 ) Pot e nt i a l I

m

pa ct s of C l i m at e C h a nge on U .S. T r a n s p o r t a t i o n . Nati o n al Academ y Pres s, Washi ngt on, DC.

Natio n a l Research Coun cil (NRC) (2 006 a) Mi t i gat i ng S h o re Er osi o n A l on g S h el t e red Coast s , Nation al Acad em y Press, Washi n gton, DC.

Natio n al Research Coun cil (NRC) (20 06b ) S u rf ace Te mp er at ure Rec o n s t r uct i o n s For t h e Last 2, 00 0 Ye ars . Nat i onal Academy Pres s, Washi ngt on, DC.



### 136

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Natio n a l Research C o un cil (2 005 ) R a di at i ve Forci n g of C l i m at e C h a n g e: Ex p a n d i n g t h e Conce p t

a nd A d dressi ng Unce rtainties, Committee on Radiative Forcing E ffects on Cl im ate, Climate Research Committee, ISBN: 0­ 3 09- 546 88 -5

. Natio n a l Research Coun cil (NRC) (2 004 ) Air Qua lity Ma nag emen t in th e Un ited S t a t es . National Academ y Press, Was h ington, D C

. Natio n a l Research C o un cil (NRC) (2 003 ) Un derst an di n g C l i m at e C h a nge Fee d bac k s

. Nation al Acad em y Press, Was h ington, D C

. Natio n a l Research C o un cil (NRC) (20 02) Abr upt C l i m at e C h a n g e, Ine v i t abl e S u r p ri s e s . National Academy Press, Was h ington, D C

. Natio n a l Research C o un cil (NRC) (20 01) C l i m at e C h an ge Sci e nce: An An al ysi s of S o me K ey Q u es t i ons . Nation al Academy Pres s, Washi ngt on, DC.

Natio n a l Research C o un cil (NRC) (200 1) Glob a l Air Qua lity: An Imp e ra tive fo r Lon g -Term Ob serva tiona l St rat e gi es . National Academ y Press , Was h ington, DC.

Nat i onal Sci e n ce an d Tec h nol ogy C o unci l ( 2 00 8 ) S c ien tific Assessmen t o f

t

h e Effects o f

Glo b a l Chan g e o n th e Uni t e d St at es

. A R e po rt o f t

h e C o m m i t t ee on E n vi ro nm ent an d Nat u ral R e so urces , Was h i n gt o n , DC

.
Nat i onal Sn ow an d I ce Dat aC e nt er (NS I DC ) (2 0 0 9 ) C r y o s phe ri c C l im at e In di cat o r s, http://nsidc.org/sotc/sea_ice.ht ml Accessed March 4, 2009.
Nicholls, R.J. et al. (2007) Coasta l Syste m s an d Low-lying Areas. In : C l i m at e C h a n g e 20 07 : Im p a ct s, Ad apt at i o n
an d V u l n er abi l i t y . Cont ri but i on of Worki n g Gro u p II t o t h e Fourt h Assess ment Re port of t

h e Int e rg over nme n t a l Pa nel o n C l i m at e C h an ge [ M .L. Pa rry , O

. F. C a nzi a ni , J

. P. Pal u t i k of, P.J. va n de r L i nde n a nd C

. E

. Ha ns on (eds .)] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A. Parry, M.L. et al. (200 7) T echnical Sum m ary. Clima te Cha n g e 20 07: Imp a c ts, Ada p t

a tio n and Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e, M.L. Parry , O.F . C a nzi a ni , J .P. P a l u t i k o f , P. J. van der Li n d e n an d C .E . H a ns on , Eds ., C a m b ri d g e Uni v ersity P r e ss, Cam b ridge , UK, 23-78. Polyak, L ., Andre w s, J

. T., B r igham

- Grette, J., Da rby, D. , Dyke, A. , Funder , S., H o lland, M., Je nnings, A. , Sa velle, J., Serreze, M

. , Wolff, E., 2009: Hist ory of Sea Ice in t h e Arctic. In Past C l i m a t e Variability and C h ange in t h e Arct i c an d at Hi g h Lat i t udes . A re po rt by t h e U.S . C l im at e C h ange P r og ram and Su bcom m i t t ee on Gl oba l Ch ang e Research

. U

. S. G e o l og ical Surv ey, Resto n , VA , pp

. 35 8 – 420

.
R a m a nat h an V. an d C a rm ichael , G. ( 2 00 8) Gl obal a nd regional climate change s due to black c a rbon. Na tu re Geos cience , 1 : 2 21– 227

. Randall, D

. A ., R.A. Wood, S. Bony, R. Co lm an, T. Fichef et, J. Fyfe, V. Kattsov, A. Pit m an, J. Shukla , J. Srini v asan, R.J. St o u f f e r , A

. Su m i an d K.E. Taylor ( 2007 ) Clima te Mod e ls and Th eir Eva lua tion

. In: Clim ate Change 2007: Th e Ph ysical Scien ce Basis. Con tr i bu tion of W o r k i n g G r o up I t o the Four th A ssessm en t Rep o r t of th e Int e r g ove r n m e nt al Pan e l o n C l im at e C h an g e [S ol om on, S ., D. Qi n , M

. M a nni ng , Z. C h en , M

. M a r q ui s, K.B

. Av eryt, M.Ti gn or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited King do m and New Yo rk , NY , US A.
Ribeiro et al. (2007) T r ans por t an d its In frastru c ture. In : Clima t e Cha n g e 2 007 : Mitiga tio n. Con t ribu tio n o f

Wo rki n g Gro u p II I t o t h e Fourt h Asses s ment Re port of t

h e Int e r gov ernm ent a l

Pan e l on C l i m at e C h a n g e [B. Metz, O.R. Davi ds on , P.R

. B o sc h, R

. Da v e , L. A. M e y e r (ed s .)]

. C a m b ri dge U n i v e rsi t y Press, C a m b ri dge, U n i t e d K i ng dom and Ne w Y o rk , N Y, US A.



### 137

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Ro sen z w eig, C., et al. ( 2007 ) A ssessm en t o f o b serv ed ch ang es and respo n s es i n n a tu r al and m an ag ed syste m s. C l i mat e C h a n g e 20 07 : I mp a ct s, Ad apt at i on an d V u l n er abi l i t y . Cont ri but i on of Worki n g Gro u p II to t h e Fourt h Assessmen t Rep o rt o f

th e In tergo vern m enta l Pa n e l on Clima t e Ch ang e , M.L. Parry, O.F. Canzi a ni, J.P. Pal u t i k o f , P.J

. van de r Li nde n an d C .E

. Han s on , E d s. , Cam b r i dg e U n i v er sity Pr ess, Cam b r i d g e , UK , 79- 13 1.
Ryan, M., S

. Arc h er , R. Bir d sey, C. Dahm , L. Heath, J

. H i ck e, D. Ho llin g e r , T. Hu x m an , G. Okin , R. O r en , J. R a nde rs on , an d W. Schl esi n ger ( 2 0 0 8 ) Lan d R e so urce s. I n : The effects of climate cha nge o n a g ri cul t ure, l a nd resources, wate r res ource s, and biodiversit y

. A Report by th e U.S. Climate Ch ange Sci e nce Pr og ra m and t h e Su bcom m i t t ee on Gl obal C h a nge R e searc h

. Was h i n gt o n , D C ., U S A , 36 2 pp
Schneide r, S.H. et al. (2007) Assessing key vulnerabilities and the risk fr om climate change. Climate Change 2007: Imp a cts, Ad ap t a tio n an d Vu ln erab ility. Co n t rib u tion o f

Workin g Gro u p II to th e Fou r th Assessmen t Rep o r t o f th e In tergo vern m en ta l Pan e l o n Clima te C h a n g e , M.L. Parry, O.F. Canzi a ni, J. P. Palu tik of , P.J. van der Lind en an d C.E. H a n s o n , Ed s., Cam b r i dg e U n i v er sity Pr ess, Cam b r i d g e , UK , 779 -8 10

. Schwartz, P. and D. Randall (2003) “ A n Abrupt Clim ate Ch ange Sce n ari o and Its Im pl icatio n s for Un ited States Nat i onal Sec u r i t y .” Pre p are d fo r t h e De part m e nt of De fen s e by t h e Gl o b a l B u si ness Ne t w o r k

. Scott, J.M ., B

. Griffith, R.S. Adam cik, D.M. As he, B. Czech, R.L

. Fischm an, P. G onzalez, J.J

. L a wler, A.D. McG u ir e, and A

. Pi d gor n a , 20 08 : Nation a l W i l d life Refu ges. In : Prelimin a r y review o f

a dap ta tion optio n s fo r climate-se nsitive ecosystems and res o urces. A R e po rt by t h e U.S . C l im at e C h ange Sc i e nce Pr og ram and t h e Su bcom m i t t ee on Gl o b al C h a nge R e sear ch [ J ul i u s, S.H ., J. M

. W e st (e ds. ) , J.S. B aro n, B . Gri ffi t h , L .A

. Joy ce, P. Kareiv a, B.D. Keller, M.A. Palm er, C.H. Peterson , a n d J

. M

. Scot t ( A utho rs)]

. U. S. E n vi r onm ent a l Prot ect i on A g en cy, W a shin g ton , D C , USA , pp . 5- 1 to 5

- 10 0.

Si l l m a n, S., an d P. J. Sam s on (19 9 5 ) Im pact of t e m p erat u r e on o x i d a n t p hot ochem i stry i n ur ba n, p o l l u t e d ru ral and
rem o te en v i ronmen ts, J. Ge op hys. Res ., 1 00 : 1 1,497 –11 ,5 08.

Solom on, S. , D. Qin , M

. M a nni ng , R.B. Al ley , T. Ber n tse n , N. L. Bin d o f f , Z

. C h en , A. Chidthais o n g , J.M

. Gre g ory , G.C

. H e ge rl , M . Hei m ann, B . Hewi t s o n , B .J. H o ski n s, F. Jo os, J. J o uz el , V. Kat t s o v , U. L ohm ann, T. M a t s un o, M. Mo lin a, N. Nicho lls, J. Ov erp eck, G. Rag a, V. Ra maswam y, J. Ren , M. R u sticucci, R. So m erv ille, T.F. Stocke r, P

. Whetton , R.A

. Wo o d an d D. Wratt (2 0 0 7 ) Tech nical Su m m a ry . In: C l i mat e C h an ge 20 07 : T h e Physi c al Sci e nce Basi s. C ont ri but i o n of Worki n g Gr ou

p I t o t h e Fourt h Asse ssme n t Repo rt of t

h e In terg o v ernmen ta l Pan e l on Clima te Ch ang e [S ol om on, S., D

. Qi n, M

. M a nni n g , Z

. C h en , M

. M a r qui s , K.B

. Av eryt, M. Tign or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited Ki n gdo m an d New Yo rk , NY , US A.

Stev enson , D.S., et al. (20 05) Im p acts of cl i m ate ch an g e an d v ariab ility on trop o s ph eric o z on e and i t s p r ecursors. Far a day Disc uss. , 13 0, d o i:10.10 39 /b41 741 2g

.
Trenbe rth, K.E

. et al. (2007 ) Observations: Surface a n d Atm o spheric Clim a t e Change. In: Clima te Ch ang e 2 007 : Th e Physica l S c ien ce Ba sis. Co n t ribu tion o f

Wo rki n g Group I to t h e Fo urth Assessmen t Report o f

th e In terg o v ernmen ta l Pan e l on Clima te Ch ang e [S ol om on, S., D

. Qi n, M

. M a nni n g , Z

. C h en , M

. M a r qui s , K.B

. Av eryt, M.Ti gn or and H.L. Miller (ed s .)]. Ca m b rid g e Univ ersity Press, Ca m b rid g e , Un ited King do m and New Yo rk , NY , US A.

US DA ( 2 0 0 7 ) C rop Pr od uct i o n Hi stori c al T

r ack Rec o r d

s , Natio n a l Ag ricu ltu ral Statistic s Serv ice (NASS): h ttp ://u sd a.m a n n lib.corn e ll.ed u / u s d a /c u r rent/h trcp /h t r cp-04

- 27 -2 007 .p df.

U.S

. EP A ( 2 00 9) Assessmen t o f

th e Imp a c ts o f

Globa l Chan g e on Reg i ona l U.S

. Air Qua lity: A S y n t h e sis o f

Clima t e Change Impac t s on Gr ound-Level Oz one

. An I n t e ri m R e po rt of t h e U.S. EP A G l obal C h a nge R e search Pro g r am

. U. S . E nvi r o nm ent a l Pr ot ect i on A g ency , W a shi n gt o n , DC , EP A / 60 0/ R

- 0 7 / 0 9 4

.
U

. S. EPA (200 8) I n ve nt ory of U. S. Gree n h o u se G a s E m i ssi o n s a n d Si nks : 1 9 90 – 20 0 6 . EPA- 43 0- R-08 -0 05 , Was h ington, D C

.



### 138

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

U.S

. EP A ( 2 0 0 6 ) Air Qua lity Criteria fo r Ozo n e and Rela ted Pho to c h e mica l Oxi d an ts , E P A 6 0 0/ R -0 5/ 0 04a F , Februa ry.
U.S

. EP A ( 2 0 0 4 ) Air Qua lity Criteria fo r Particu l a t e Ma tter , EP A/ 6 0 0 /P

- 99/ 00 2aF , Oct obe r.

U.S

. EP A ( 1 9 9 9 ) 1 9 9 9U p date of A m bi ent W a t e r Qu ai t y C r i t e ri a f o r A m m oni a , EPA

- 8 22- R-9 9

- 014

.
U

. S. N a v y ( 200 1) N a va l Op era tion s in an Ice-Free Arctic: S y mpo s ium , Office of Na va l Research, Na val Ice Center, April 17 -18

. Victor Cruz, R

. et al. (2007) Asia. In: Clima te Ch ang e 200 7: Impa cts, Ad ap ta tion a n d Vu ln erab ility. Co n tribu tion of

Worki ng G rou p II t o t h e Fou r t h Asse s s ment Re p o rt of t

h e I n t e rg o vern m ent a l

Pa nel o n C l i m ate C h a n g e [(e ds. )] . C a m b ri dge U n i v e rsi t y Press, C a m b ri dge, U n i t e d K i ng dom and N e w Yo rk , NY , US A.

W i gley, T

. M.L ., V. Ram a swam y, J.R. Christy, J.R. La nza n t e , C

. A. M e ar s, B .D. Sant e r , C

. K. Fol l a n d , 2 0 06: Exec ut i v e S u m m a ry i n Tem p erat ure Tre n ds i n t h e L o we r At m o sphere: St e p s fo r Un de rst a ndi ng an d Reco n ciling Differen ces. T. R

. Karl, S. J. Hasso l, C. D. Miller, an d W. L. Mu rray, ed ito rs. A Repo rt b y th e Clim a t e Change Science Program and the Subcomm i tt ee on Global C h ange Researc h , Washington, DC.

W i l b an ks , T. J., P. Ki rs he n, D. Q u at tr oc hi , P. R o m e ro-Lan ka o, C . R o senz w e i g , M

. R u t h , W. Sol e c k i , a n d J. Tarr (200 8) Effects o f Gl o b al C h an g e on Hu m an Settle m en t s. In : A nal yses of t

h e Ef f

ect s of G l ob al C

h a nge on H

u ma n H e a lth an d Welfa re an d Hum a n S y stem s. A R e p o r t by th e U .S. C l im at e C h ange Sci e nce P r og ra m and t h e S ubc om m itt ee on Gl obal C h an ge R e sear ch. W a shi ngt o n , DC , US A, p p

. 3

- 1 – 3

- 3 1

.
W i l b ank s , T. et al. (2 007 ) In du stry, Settlemen t an d So ci ety. In : Clim a te Ch an g e 20 07 : I m

pa cts, Ad ap ta tion a n d Vu ln erab ility. Co n t ribu tion of Wo rking Gro u p II to t h e Fou r th Assessmen t Repo rt of th e In terg o v ern m en t a l Pa nel o n C l i m at e C h an ge [ M .L. Pa rry , O

. F. C a nzi a ni , J

. P. Pal u t i k of, P.J. va n de r L i nde n a nd C

. E

. Ha ns on (eds .)] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.

WM O ( Wo rl d M e t e orol ogi cal Or ga ni zat i o n ) (2 0 0 7 ) S c ien tific Assessmen t o f

Ozon e Dep l etio n : 200 6, Gl obal Oz one R e search an d M oni t o ri n g P r oject —R e p ort No . 50 , 57 2 p p

. , Ge ne va, Swi t zerl a n d

. WRI (2 0 0 9 ) C l i m at e An al y s i s In di cato rs To ol ( C AIT) Versi o n 6.0 . Available at h ttp ://cait.wri.org / . Accesse d Febr u ar y 20 , 20 09

.



### 139

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Appendix A: Brief Overvie w of Adaptation
Adaptation to cli m ate ch ange is the adjustment in the behavior or nature of a sy stem to the effects of cli m at e chan ge. In the process of developing i n formation to support the Ad m inistrator’ s decision regarding whether el evated co m b ined greenhouse gas (GHG) co ncentrations e ndanger public health or welfare, various questio ns were raised about th e rele vance of adaptation. As noted in the Introd uction, this docum en t does not focus on adapta tion because it (like GHG mitigation) is essentially a response t o any kn own a nd/or perceived risks due to clim ate change. Althoug h adapt a tion was no t considered explicitl y in the document, it does note where the underl y i ng references already take into account certain
assu mp tions about adaptat ion when pr ojecting futu re risks and i mpacts due to clim at e change. This appendix pro v ides a brief review of the stat e of knowl e dge pertaining to adaptati on. What is Adaptation?
As defined in the Intergove rnmental Panel on Clim at e Change (IPCC) Fourth Assessment Rep o rt (2007),
Adaptation to cli m ate change takes place throug h adj u st m e nts to reduce vulnerabilit y or enhance resilience in r esponse to observed or expected ch anges in clim at e an d associated extrem e weath e r events. Adaptation occurs in ph y s ical, e c ological an d hum an sy stems. It involv es changes in social and environm ental process es, perceptions of cli m at e ri sk, practices and functions to reduce potential dam a ges or to realise new opportunities.
Adaptations vary according to the sy stem in which t h ey occur, who undertake s them , the cl i m atic sti muli that prompts them , and their tim ing, functions, form s a nd effects. Adaptation can be of two br oad t y pes:

• Reactive or autonom ous adaptation is th e process by which species and ecosystems respond t o changed conditions. An example is the north ward m igration of a speci es in re sponse to increasing temp erature.

• Anticipatory adaptation is planned and implemen ted before imp acts of cl i m ate change are observed. A n example is the constructi on of di kes in response to (and to prepare for) expected sea level ris e

. Summary of the Scientific Literature o n Adaptation

1. There is experience with a dapting to weather, climat e variability and the current and projected impacts of climate change.

o There is a lo ng record of practice s to adapt to the i mpact s of weather as w e ll as natural cli m at e variability

. These practices include pr oactive steps like water storage and crop and livelihood di versification, as well as reactiv e or e x -post steps like e m erg e ncy response, disaster re covery and m igra tion. 66

o The IPCC (2007) states – with very hig h confidence 67 – that “Adapt ation to cli m a te change i s already taking place, but on a lim ited ba sis.” 68

66 A dge r et al

. ( 2 00 7 ) , p. 7 2 0 67 A set o f term s to d escri b e u n certain ties in cu rren t kn ow ledg e w a s u s ed thr oug hou t I P CC ’ s Fou r th Assessm en t Rep o rt. On the b a sis of a com p reh e n s iv e read ing o f th e literatu re and t h eir exp e rt ju dgmen t, IPCC auth ors assi g n e d a confi d ence level to m a jor st ate m ents on the basis of th eir assessm en t o f cu rren t kn owled g e , as fo llo ws:



### 140

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

o A wide array of adaptation options is available, ranging from purely technolo g i cal (i.e., sea walls), through behavioral changes (i.e. , altere d food and recreational choices), to managerial (e.g. altered far m practi ces), and to polic y (e.g. plan ni ng regulatio n s ). 69

o Some programs have developed strategic plan s for respondin g to clim ate change. A n exa mple of s u ch a plan is EPA’ s National W a ter Program Strategy: Response to Clima te Change (EP A , 2008).

2. Although adaptation options are known, ava ilable and used in some pl aces, ther e are significant barriers to their adopti o n.

o The IPCC st ates with ver y high confidence that “th e re are substantial li m its and barriers t o adaptation.” These include for m idable environm en tal, econom i c , informational, social, attitudinal and behavioral barriers to t h e i mpl ementation of adaptation that are not fully understood. 70 The IPCC also states that there are significant knowledge gaps for adaptation as well as imp e dim e nts to flows of knowledge and inf o rm ation relevant to adaptation decisions. 71

3. Current s c ie ntific information does not provide sufficient information to as sess how eff ectiv e currentand f uture adaptat ion options will be at redu cing vulnera bility to the i m pacts of climate change. The fact that a c o untry has a high capacity to a dapt to c limate change does not mean that its actions will be effective at redu c ing vulnerability.

o While m a ny technologies and adaptation stra tegies are known and developed in so m e countries, the available scientific literature does not i ndicate how effective various options are at full y reduc ing risks, par ticularly at h i gher levels of warm ing and re lated i mpacts, and fo r vulnerable gr oups. 72

o High adaptive capacity does not necessarily translat e into actions that reduce vulnerability

. For example, despite a high capacity t o adapt to heat stress through relativel y inexpensiv e adaptations, residents in urban areas in so m e parts of the world, including European cities, continue to experience high levels of m o rt ality

. 73 To m ini m ize the risks of heat str e s s dom estically , EPA (200 6) has worked collaborativ ely with oth e r governm e nt agencies to provide guidance to municipalities on steps they can take to reduce heat-rel a ted m o rbidit y and m o rtality

. 74

Very high c o nfidence At least 9 o u t o f 10 cha n ce of bei n g c o r r ect H igh co nf id ence A bou t 8 ou t o f 1 0 ch an ce M e di um confi d ence Ab o u t 5 o u t of 10 cha n ce Low co nf id en ce A bou t 2 ou t o f 1 0 ch an ce Very l o w confi d ence Less th an a 1 ou t of 10 ch an ce

68 Adge r et al. (2007), p. 720 69 ib id 70 ib id 71 A dge r et al

. ( 2 00 7 ) , p. 7 1 9 72 ib id 73 ib id 74 E x c e s s i v e H e at E v en ts Gu id eb ook (2 006 )



### 141

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

o Further resea rch is needed to m onitor progress on adaptation, and to assess the direct as well as ancillary effects of adap tation m e asures. 75

4. For any country – even one with high adaptive ca pacity -- it is particularly difficult to reduce vulnerability for all seg ments of the populati on. The most vulnerable and difficult to reach popula tions are the elderly, children and the poor.

o The IPCC st ates with very high confidence that “ a daptive cap acity is uneven across an d within societies.” There are individuals and gr oups w ithin all societies that have insufficien t capacity to adapt to clim at e change. 76

5. More adaptation will be required to redu ce vulnerability to climate chang e . 77 Additional adapt ation c a n potentiall y reduce, but is never exp ected to completely elimin ate vulnerability to current and future climate change.

o According to the IPCC, “adaptation alone is not e xpected to c ope with all the projected effects of climate change, and especially not ove r th e long term as m o st imp a cts increase in magnitude.” 78

6. A portfolio of adaptation and mitigation measures can dimi nish the risks associated with climate change.

o Even the m o st stringent m i tigation effort s cannot avoi d further impacts of climate change in the next few decades, whi c h makes ada p tation essential, particularly in addressing near-ter m i mpacts. Un mitigated climate ch ange would, in the long term , be likel y to exceed the capacity of natural, m a nag e d and hum a n sy stem s to adapt. 79

75 A dge r et al

. ( 2 00 7 ) p. 7 37 76 A dge r et al

. ( 2 00 7 ) , p. 7 1 9 77 Adge r et al. (2007), p. 719 78 I P CC ( 200 7) , p

. 19 79 I P CC ( 200 7) , p

. 20



### 142

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Refe renc es f o r Adaptation Appendix

Ad ge r, W.N ., S. A g ra wala, M .M .Q. M i rza , C. Con d e, K. O’ Brien , J. Pu l h in , R. Pu lwarty , B

. Sm i t and K. Takaha shi , ( 200 7) Asses s m ent of a d apt at i o n pr act i ces , o p t i o ns, c o ns t r ai nt s an d c a paci t y . C l i m ate C h a n g e 20 0 7 : Im p a ct s, Ada p t

a tio n and Vu ln era b ility. Co n t ri b u tion o f

Wo rking Group II to th e Fou r th Assessmen t Report o f

th e I n terg o v ernm en ta l Pan e l on Clim a te Ch ange , M .L. Par ry , O.F . C a nzi a ni , J.P. Pal u t i k o f, P.J. van der Li nde n an d C.E. H a nson , Ed s., Cam b r i dg e U n i v er sity Pr ess, Cam b r i dg e, UK , 71 7-74 3.

Excessi ve Hea t Event s G u i d e b o o k . R e p o rt f

r om th e Uni t e d St at es Envi r o nm ent a l Prot ect i on A g ency

. 5 2 pa ges. J une 2 006 . EPA 4 30- B-0 6

- 005

. IPCC ( 2 0 0 7 ) Sum m ary for Policym akers

. In: Clima te Ch an ge 2007 : Impa cts, Ad ap ta tion a nd Vu ln erab ility. Cont ri b u t i o n o f

Worki n g Gr o up II t o t h e F o urt h Asse ssme n t Repo rt o f

the In terg o vernmen t a l Pan e l on Clima t e Ch ang e [M

. L

. Par r y , O .F. C a nzi a ni , J .P. P a l u t i k o f , P .J. v a n der Li n d en and C .E. Ha ns on (e ds. ) ] . C a m b ri dge Uni v ersity P r e ss, Cam b ridge , U n ited Kin g d o m and New Y o rk , N Y , US A.

U.S

. EP A ( 2 0 0 8 ) N a t i o nal W a t e r Pr o g ra m St rat e gy: Resp ons e t o C l i m ate C h an ge. O ffi ce o f Water. E PA 8 0 0

- R0 800 1, Sep t emb e r.



### 143

### Technical Support Document - Appendix B
Greenhouse Gas Emissions from Section 202(a ) Source Categories
This Annex provides greenhouse gas (GHG) e m issi ons inform ation fro mClean Air Act section 202(a) source categories. It in cludes an overview of the resp ective source cate gories with a description of how the e m issions data from the I n ventory of U.S. Greenhouse Gas Emissions and Sinks m a p to these source categories. Then, re levant em issions data are presented and
comparisons are m a de between U.S. GHG e m iss i ons from se ction 202(a) source categories and dom estic an d global emissions d ata. To inf o rm the Adm i nistra tor’s asse ssm ent, the f o llowing types of comparisons for both the collective a nd individual em issions of GHGs from section 202(a) source categories are provided:

• as a share of total global aggregate em issions of the six GHGs;

• as a share of total U.S. aggreg ate emissions of the six GHGs; and

• as a share of the total global tran sportation em issions of the six GHGs.
In addition, for each individual GHG, the follo wing comparisons were also calculated:

• as a share of total U.S. section 202(a) GHG e m is sions;

• as a share of U.S. e m i ssions of that individual GHG, including comparisons to the
m a gnitude of e m issions of that GHG from non-transport related source categories;

• as a share of global em issions of that individual GHG;

• as a share of global tr ansport GHG em issions; and

• as a share of all global G HG e m issions.
(A) Overv iew of sectio n 202(a) so urce catego ries

To inform the Adm i nistrator’s cause or c ontribute finding, EPA analyzed historical GHG
em issions data for m o tor vehicles and m o tor ve hicle engines in the Un ited States from 1990 to 2006 (the most recen t y ear for which official EPA estim ates are availab l e). The m o tor vehicles and m otor vehicle engines addressed include:

• Passenger c ars

• Light-duty trucks

• Motorcyc les

• Buses

• Medium /heavy-duty trucks

• Cooling (a ll transpo r ta tio n sources )

The source of the em issions data is the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2006 (USEPA #430-R-08-002). The U.S. Inventory is organized around the source classification schem e put forth by the Intergov ernm ental Panel on Clim ate Change, in which
em issions from m o tor vehicles and m o tor vehicl e engines are reported within tw o different sectors: E nergy, and Industrial Processes. Table TSD-B.1 describes the correspondence between section 202(a) GHG e m ission source categories and IPCC source categories:

144

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Table TSD-B.1 – Source categories included under section 202(a) section 202(a) Source Category IPCC Sector IPCC Source Category Greenhouse Gases
Passenger C a rs Energy 1A3b (i) Cars CO 2 

### , CH 4 

### , N 2 

### O Light-Duty Trucks Energy 1A3b (ii) L i ght-duty trucks CO 2 

### , CH 4 

### , N 2 

### O Motorcycles Energy 1A3b (iv) Motorcycles CO 2 

### , CH 4 

### , N 2 

### O Buses Energy 1A3b (iii) Heavy-duty truck s and buses CO 2 

### , CH 4 

### , N 2 

### O

Medium /Heavy-Duty Trucks Energy 1A3b (iii) Heavy-duty truck s and buses CO 2 

### , CH 4 

### , N 2 

### O
Cooling (all transpo r ta tio n sources) Industrial Processes 2F1 Refrigeration and Air Conditioning Equipm ent Hydrofluorocarbons (HFCs)

Greenhouse gas em issions from avi ation, pipelines, railways, and m a rine transport are included in the IPCC Energy Sector under 1A 3 but are not included within section 202(a).
(B) Greenhouse gas emissions from s ection 202(a) source categories
(1) Total, com b ined GHG e m issions from section 202(a) source categories

145Table TSD-B.2 presents historical emissions of all GHGs (CO2, CH4, N2O, and HFCs) from section202(a) source categories from1990-2006, in carbon dioxide equivalent units (Tg CO2e).80Passenger cars (39.1 percent), light-duty trucks (31.7 percent), andmedium/heavy-duty trucks (24.2 percent) emitted the largest shares of GHG emissions in 2006, followed by cooling (all transportationsources) (4.2 percent), buses (0.7 percent) and motorcycles (0.1 percent).From1990 to 2006, GHG emissions fromsection 202(a)source categories grew by 35.2 percent due, in part, to increaseddemand for travel and the stagnation of fuel efficiency across the U.S.vehicle fleet. Since the 1970s, thenumber of highway vehicles registered in the United States has increased faster than the overallpopulation, according tothe FederalHighway Administration (FHWA).81Likewise, the number of miles driven (up 40.6 percent from1990 to 2006) and the gallons of gasoline consumed each year inthe United States have increasedsteadily since the 1980s, accordingto the FHWA and Energy Information Administration, respectively.82These increases inmotor vehicle usage are the result of aconfluence of factors including population growth, economic growth, urban sprawl,low fuel prices, and increasing popularity ofsportutility vehicles and other light-duty trucks that tend tohave lower fuel efficiency.Table TSD-B.2 – Total greenhouse gas emissions by section 202(a) source category (Tg CO2e)Section202(a) Sources199019952000200120022003200420052006PassengerCars656.9633.9670.3673.1686.5664.4660.7Light-DutyTrucks336.2428.6489.5492.7502.6536.2556.9Motorcycles1.81.81.91.71.71.71.8Buses8.39.110.910.09.710.514.7Medium/Heavy-DutyTrucks228.8272.4342.9342.0356.2352.6365.4Cooling(alltrans. Sources)0.018.652.657.261.164.467.8677.3516.31.611.8393.269.7651.2528.21.912.1402.569.5Total1231.91364.41568.11576.81617.91629.71667.41670.01665.4Between 1990 and 2006, GHG emissions frompassenger cars decreased 0.9percent, though there was somegrowth in GHGemissions from2000 to 2002, and again from2004 to 2005.Emissionsfromlight-duty trucks increased 57.1 percent from1990-2006,largely due to the increased use of sport-utility vehicles and other light-duty trucks.Meanwhile,GHG emissions fromheavy-dutytrucks increased 75.9 percent, reflecting the increased volumeoftotal freight movement and an increasing share transported bytrucks.In 1990 there were no hydrofluorocarbons (HFCs) used in vehicle cooling systems.HFCswere gradually introduced into motor80ATg is one teragram, oronemillionmetrictons.81FHWA(1996through2008) HighwayStatistics.FederalHighwayAdministration, U.S. DepartmentofTransportation, Washington, DC.ReportFHWA-PL-96-023-annual. Available online at<http://www.fhwa.dot.gov/policy/ohpi/hss/hsspubs.htm>.82DOE(1993 through 2008)TransportationEnergyData Book.Office ofTransportationTechnologies, CenterforTransportation Analysis, EnergyDivision,Oak RidgeNational Laboratory. ORNL-5198.146Technical Support Document, U.S.Environmental Protection Agencyvehicle air conditioning and refrigerating systems during the 1990s as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons(HCFCs) started to phase out of productionas required under the Montreal ProtocolandTitle VI of the Clean Air Act.Table TSD-B.3 presents GHG emissions fromsection 202(a) source categories alongside total U.S. emissions.The table also presentsemissions fromthe electricity generation and industrial sectors for comparison.In 1990, section 202(a) source categories emitted 20.0percent of total U.S. emissions, behind the electricity generation sector (30.2 percent) and the industrial sector (23.8 percent).By2006, section 202(a) source categories collectively were the second largest sector with23.6 percent of total U.S. emissions, due bothto growth in vehicle emissions anda decline in emissions from industry.Table TSD-B.3 – Sectoral comparison tototal USgreenhouse gas emissions (Tg CO2e)U.S.Emissions199019952000200120022003200420052006Section 202(a) GHGemissions1231.91364.41568.11576.81617.91629.7Share of U.S. (%)20.0%21.0%22.3%22.8%23.2%23.3%Electricity Sectoremissions1859.11989.72328.92290.92300.42329.4Share of U.S. (%)30.2%30.6%33.1%33.1%33.0%33.3%Industrial Sectoremissions1460.31478.01432.91384.31384.91375.5Share of U.S. (%)23.8%22.8%20.4%20.0%19.8%19.7%1667.423.6%2363.433.4%1388.919.6%1670.023.4%2430.034.1%1354.319.0%1665.423.6%2377.833.7%1371.519.4%Total USGHG emissions6148.36494.07032.66921.36981.26998.27078.07129.97054.2Table TSD-B.4 compares total GHG emissions fromsection 202(a) source categories to allU.S. GHG emissions, global GHGemissions fromthe transport sector (as defined by IPCC), andtotal global greenhouse gas emissions fromall source categories,for theyear 2005.83Section 202(a) GHG emissions are a significantly larger share of global transport greenhouse gas emissions (28.3percent) than the corresponding share of all U.S. GHG emissions tothe global total (18.4 percent), reflecting the relative size of thetransport sector in the U.S. compared to the global average.Section 202(a) GHG emissions were4.3 percent oftotal global emissionsin 2005.The global transport sector was 15.3percent of all global emissions in 2005.83The year2005 is the most recent yearforwhichcomprehensivegreenhouse gas emissionsdata are available for all gases, all countries, and all sources. Globalestimates are ‘gross’ emissions estimates anddo not include removalsofgreenhouse gasemissionsfromtheatmospherebyterrestrialsinks(i.e.,forestsandotherbiomass).Global data come fromtheWorldResourcesInstitute’s ClimateAnalysis Indicators Tool, whichcontains national datasubmittedbyParties totheUNFCCC, and other independent andpeer-revieweddatasets (e.g., International EnergyAgency).147Technical Support Document, U.S.Environmental Protection AgencyTable TSD-B.4 – Comparison to global greenhouse gas emissions (Tg CO2e)2005Sec 202(a) ShareAllU.S. GHGemissions7,13023.4%GlobaltransportGHGemissions5,90928.3%AllglobalGHG emissions38,7264.3%(2)Individual GHG emissions fromsection 202(a) source categoriesTable TSD-B.5 presents total GHG emissions fromsection 202(a) source categories by gas, in CO2equivalent units.In 2006, CO2madeup the largest share of emissions (93.9percent), followed by HFCs (4.2 percent), N2O (1.8 percent) and CH4(0.1 percent).Since 1990, the share of HFCs has increased (fromzero in 1990), whereas the shareof the other gases have correspondinglydecreased.Methane and N2O emissions have decreased inabsolute terms since 1990.Table TSD-B.5 - Greenhouse gas emissions from section 202(a) source categories by gas (Tg CO2e)Section 202(a)Sources199019952000200120022003200420052006CO21187.31291.91463.81470.51512.01524.21561.41565.61564.6Share of Sec 202(a)GHGsCH496.4%4.294.7%3.893.4%2.993.3%2.893.5%2.493.5%2.293.6%2.193.8%1.993.9%1.8Share of Sec 202(a)GHGsN2O0.34%40.40.28%50.10.18%48.80.18%46.40.15%42.30.14%38.90.13%36.10.12%32.70.11%29.5Share of Sec 202(a)GHGsHFCs3.3%0.03.7%18.63.1%52.62.9%57.22.6%61.12.4%64.42.2%67.82.0%69.71.8%69.5Share of Sec 202(a)GHGs0.0%1.4%3.4%3.6%3.8%4.0%4.1%4.2%4.2%Total GHGs1231.91364.41568.11576.81617.91629.71667.41670.01665.4(a)Carbon dioxide emissions fromsection 202(a) source categoriesCarbon dioxide is emitted frommotor vehicles andmotor vehicle engines during the fossil fuelcombustion process.Duringcombustion, the carbon(C) storedin the fuelsis oxidizedand emitted as CO2and smaller amounts ofother carbon compounds,including CH4, carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs).These other C-containing nonCO2gases are emitted as by-products of incomplete fuel combustion, but are,for the most part, eventually oxidized to CO2in theatmosphere.148Technical Support Document, U.S.Environmental Protection AgencyAs the dominant GHG emitted frommotor vehicles and motorvehicle engines (93.9 percent oftotal emissions in 2006), CO2emissiontrends in Table TSD-B.6 mirror those of the GHG emissions total.Carbon dioxide emissionsgrew by 31.8 percent between 1990 and2006.Most of this growth occurred as a result of increased CO2emissions fromlight-duty trucks(60.5 percent) and medium/heavyduty trucks (76.1 percent).Emissions frompassenger cars did not grow over the sametime period.Table TSD-B.6 – CO2emissions by section 202(a) source category (Tg CO2)Sec.202(a) Source Categories199019952000200120022003200420052006PassengerCars628.8604.9643.5647.9662.6642.1640.0658.4634.5Light-DutyTrucks320.7405.0466.0470.3483.2518.8540.8501.9514.9Motorcycles1.71.81.81.71.71.61.71.61.9Buses8.39.010.910.09.610.514.711.812.1Medium/Heavy-DutyTrucks227.8271.2341.5340.6354.8351.2364.1391.9401.3Cooling(alltrans. Sources)N/AN/AN/AN/AN/AN/AN/AN/AN/ATotal1187.31291.91463.81470.51512.01524.21561.41565.61564.6Table TSD-B.7 presents CO2emissions fromsection 202(a) source categories alongside total U.S. CO2emissions.The table alsopresents emissions fromthe electricity generation and industrial sectors for comparison.In 1990, section 202(a) source categoriesemitted 23.4percent of total U.S. CO2emissions, behind the electricity generation sector (36.1 percent), and ahead of the industrialsector (18.7 percent).By 2006, emissions fromsection 202(a) source categoriesincreased to 26.2 percent of total U.S. CO2emissions.Table TSD-B.7 - Sectoral comparison to total U.S. CO2emissions (Tg CO2)U.S.CO2Emissions199019952000200120022003200420052006Section202(a) CO2emissions1187.31291.91463.81470.51512.0Share of U.S. CO2(%)23.4%23.9%24.6%25.2%25.6%Electricity Sector CO21829.71964.62310.82273.02283.0Share of U.S. CO2(%)36.1%36.4%38.9%38.9%38.6%Industrial Sector CO2947.5977.3967.3943.2943.0Share of U.S. CO2(%)18.7%18.1%16.3%16.1%16.0%1524.225.6%2313.238.9%948.415.9%1561.425.9%2346.238.9%974.716.1%1565.625.8%2412.339.7%965.315.9%1564.626.2%2360.339.4%984.116.4%Total U.S. CO2emissions5068.55394.25939.75846.25908.65952.76038.26074.35983.1Table TSD-B.8 compares total CO2emissions fromsection 202(a) source categories to total U.S. emissions, global GHG emissionsfromthe transport sector (as defined by IPCC), and total globalGHG emissions from all source categories, for the year 2005.Section149Technical Support Document, U.S.Environmental Protection Agency202(a) CO2emissions are a significantly larger share ofglobal transport greenhouse gas emissions (26.5percent) than thecorresponding share of all U.S. CO2emissions to the global total (22.0 percent), reflecting the relativesize of the transport sector inthe U.S. compared to the global average. Section 202(a) CO2emissions were 4.0 percent of total global greenhouse gas emissions in2005.Table TSD-B.8 – Comparison to U.S. and global greenhouse gas emissions (Tg CO2e)GlobalEmissions2005Sec 202(a)CO2ShareAllUSGHGemissionsAllglobalCO2 emissionsGlobaltransportGHGemissionsAllglobalGHG emissions7,13027,5265,90938,72622.0%5.7%26.5%4.0%(b)Methane emissions fromsection 202(a) source categoriesMethane emissions frommotor vehicles are a function of the CH4and hydrocarbon content of the motor fuel, the amount ofhydrocarbons passing uncombusted through the engine, and any post-combustion control of hydrocarbon emissions (such as catalyticconverters).Table TSD-B.9 shows the trend in CH4emissions fromsection 202(a) source categories since 1990, presented in carbon dioxideequivalents.The combustion of gasoline inpassenger cars and light-duty trucks wasresponsible for the majority (90.8 percent) of theCH4emittedfromsection 202(a) source categories.From1990 to 2006, CH4emissions decreased by 57.6 percent.Table TSD-B.9 – CH4emissions by section 202(a) source category (Tg CO2e)202(a)Sources199019952000200120022003200420052006PassengerCars2.62.11.61.51.4Light-DutyTrucks1.41.41.11.10.9Motorcycles0.00.00.00.00.0Buses0.00.00.00.00.0Medium/Heavy-DutyTrucks0.20.20.10.10.1Cooling(alltrans. Sources)N/AN/AN/AN/AN/A1.30.80.00.00.1N/A1.20.70.00.00.1N/A1.10.70.00.00.1N/A1.00.70.00.00.1N/ATotal4.23.82.92.82.42.22.11.91.8150Technical Support Document, U.S.Environmental Protection AgencyTable TSD-B.10 presents CH4emissions fromsection 202(a) source categories alongside total U.S. CH4emissions.The table alsopresents CH4emissions fromlandfills and natural gas systems for comparison.In 2006, section 202(a) source categories emitted 0.3percent of total U.S. CH4emissions; landfills (22.6 percent) andnatural gas systems (18.4percent) representeda significantly largershare.Overall, total U.S. CH4emissions decreased by 8.4 percent (50.8 Tg CO2e) from1990 to 2006, in part due to efforts to reduceemissions at individual sources such as landfills and coal mines.Table TSD-B.10 - Sectoral comparison to total U.S. CH4emissions (Tg CO2e)U.S.CH4Emissions199019952000200120022003200420052006Section202(a) CH4emissions4.23.82.92.82.4Share of U.S. CH4(%)0.70%0.64%0.50%0.50%0.43%Landfill CH4emissions149.6144.0120.8117.6120.1Share of U.S. CH4(%)24.7%24.1%21.0%21.0%21.3%Natural Gas CH4emissions124.7128.1126.5125.3124.9Share of U.S. CH4(%)20.6%21.4%22.0%22.4%22.2%2.20.40%125.622.5%123.322.1%2.10.38%122.622.5%114.020.9%1.90.36%123.722.9%102.519.0%1.80.32%125.722.6%102.418.4%Total U.S. CH4emissions606.1598.9574.3558.8563.5559.4545.6539.7555.3Table TSD-B.11 compares total CH4emissions fromsection 202(a) source categories to U.S. GHG emissions, global GHG emissionsfromthe transport sector (as defined by IPCC), and to totalglobal GHG emissions fromall source categories, for the year 2005.Section 202(a) CH4emissions are a significantly smaller share of U.S., global transport, and globalemissions in comparison to section202(a) CO2emissions.Table TSD-B.11 – Comparison to US and global greenhouse gas emissions (Tg CO2e)GlobalEmissions2005Sec 202(a)CH4ShareAllU.S. GHGemissionsAllglobalCH4 emissionsGlobaltransportGHGemissionsAllglobalGHG emissions7,1306,4085,90938,7260.03%0.03%0.03%0.005%(c)Nitrous oxide emissions fromsection 202(a) source categoriesNitrous oxide (N2O) is a product of the reaction that occurs betweennitrogen and oxygen during fuel combustion. Nitrous oxideemissions frommotor vehicles andmotor vehicle enginesare closelyrelated to fuel characteristics, air-fuel mixes, combustion151Technical Support Document, U.S.Environmental Protection Agencytemperatures, and the use of pollution control equipment.For example, some types of catalyticconverters installed to reducemotorvehicle NOX, CO, and hydrocarbon emissions canpromote the formation of N2O.Table TSD-B.12 shows the trend in N2O emissions fromsection 202(a) source categories since 1990, presented in carbon dioxideequivalents.Section202(a) emissions of N2O decreased by 26.9 percent from1990 to 2006.Earlier generation control technologiesinitially resulted in higher N2O emissions, causing a 24.2 percent increase in N2O emissions frommotorvehicles between 1990 and1995. Improvements in later-generation emission control technologieshave reduced N2O output,resultingina 41.1 percent decreasein N2O emissions from1995 to 2006. Overall, N2O emissions were predominantly from gasoline-fueled passenger cars (53.0 percent)and light-duty trucks (42.8 percent) in 2006.Table TSD-B.12 – N2O emissions by section 202(a) source category (Tg CO2e)202(a)Sources199019952000200120022003200420052006PassengerCars25.426.925.223.822.5Light-DutyTrucks14.122.122.421.318.5Motorcycles0.00.00.00.00.0Buses0.00.00.00.00.0Medium/Heavy-DutyTrucks0.81.01.21.21.3Cooling(alltrans. Sources)N/aN/AN/AN/AN/A21.016.60.00.01.3N/A19.515.30.00.01.3N/A17.813.70.00.01.2N/A15.612.70.00.01.1N/ATotal40.450.148.846.442.338.936.132.729.5Table TSD-B.13 presents N2O emissions from section 202(a) source categories alongside total U.S. N2O emissions.The table alsopresents N2O emissions from agricultural soil management, and nitric acid production, for comparison.In 2006, section 202(a) sourcecategoriesemitted 8.0 percent of total U.S. N2O emissions, making it the second largest source category.Byfar the largest sourcecategory in the U.S. is agricultural soil management, representing 72.0 percent of total N2O emissions in 2006. The third largestsource in 2006 was nitric acid production (4.3 percent).152Technical Support Document, U.S.Environmental Protection AgencyTable TSD-B.13 - Sectoral comparison to total U.S. N2O emissions (Tg CO2e)US N2OEmissions199019952000200120022003200420052006Section202(a) N2O emissionsShareofU.S.N2O(%)Agricultural Soil N2O emissionsShareofU.S.N2O(%)Nitric AcidN2O emissionsShareofU.S.N2O(%)40.410.5%269.470.3%17.04.4%50.112.7%264.866.9%18.94.8%48.812.7%262.167.9%18.64.8%46.411.8%277.070.5%15.13.8%42.311.3%262.069.7%16.44.3%38.910.9%247.369.4%15.44.3%36.110.2%246.969.8%15.24.3%32.78.8%265.271.7%15.84.3%29.58.0%265.072.0%15.64.3%Total U.S. N2Oemissions383.4395.6385.9392.9376.1356.6353.5370.1367.9Table TSD-B.14 compares total N2O emissions fromsection 202(a) source categories to U.S. GHG emissions, global GHG emissionsfromthe transport sector (as defined by IPCC), total global N2O emissions, and to total global GHG emissions fromall sourcecategories, for the year 2005.Section 202(a) N2O emissions are just under 0.55 percent ofglobal transport emissions and 0.08 percentof all global GHG emissions.Table TSD-B.14 – Comparison to U.S. and global greenhouse gas emissions (Tg CO2e)2005Sec 202(a) N2O ShareAllU.S. GHGemissions7,1300.46%AllglobalN2O emissions3,2860.99%GlobaltransportGHGemissions5,9090.55%AllglobalGHG emissions38,7260.08%(d)HFC emissions fromsection 202(a) source categoriesHFCs (a term which encompasses a group of eleven related compounds) are progressively replacing CFCs and HCFCs in section202(a) cooling and refrigeration systems as they are being phasedout under the Montreal Protocoland Title VI of the Clean AirAct.84For example, HFC-134a has becomea replacement for CFC-12 inmobile air conditioning systems.A number ofHFC blends,containing multiple compounds, have also been introduced.The emissions pathway can be complex, with HFCs being emitted to theatmosphere during charging of cooling and refrigeration systems, during operation, and during decommissioning/disposal.842006IPCCGuidelines, Volume3,Chapter 7.Page 43.153Technical Support Document, U.S.Environmental Protection AgencyTable TSD-B.15 shows the trend in HFC emissions fromsection 202(a) source categories since 1990, presented in carbon dioxideequivalents.The estimates are presented asthe total ofall section202(a) sourcecategoriestogetherdueto the fact that theU.S.Inventorydoes not disaggregate data by vehiclemode.HFCs were not used in motorvehicles in 1990, but by 2006 emissions hadincreased to 69.5 Tg CO2e.From1995 to 2006, HFC emission fromsection 202(a) source categories increased by 274%.Table TSD-B.15 – HFC emissions by section 202(a) source category (Tg CO2e)202 HFCSources199019952000200120022003200420052006Cooling&refrigeratedtransport0.00018.652.657.261.164.467.869.769.5Table TSD-B.16 presents HFC emissions fromsection 202(a) sourcecategories alongside total U.S.HFC emissions.The table alsopresents HFC emissions from HCFC-22 production, and all other end-use applications of substitutes for ozone depletingsubstances(ODS substitutes), for comparison.In 2006, section 202(a) source categories emitted 55.8 percent of total U.S. HFC emissions,making it the largest source category.Other applications of ODSsubstitutes (including foamblowing, fire protection, aerosolpropellants, solvents, and other applications) accounted for 41.2 percent.HCFC-22 chemical production results inby-product releasesof HFC-23, which accounted for 99 percent of HFC emissionsin 1990, but declined by 2006 and now represents 11.0 percent.Table TSD-B.16 - Sectoral comparison to total USHFC emissions (Tg CO2e)U.S. HFC Emissions199019952000200120022003200420052006Section 202(a) HFCemissionsShareofUSHFC(%)HCFC-22 ProductionShareofUSHFC(%)Other ODSSubstitutesShareofUSHFC(%)0.00.0%36.498.6%0.51.4%18.630.0%33.053.4%10.316.6%52.652.5%28.628.6%18.918.9%57.258.4%19.720.2%21.021.4%61.157.5%21.119.9%24.122.7%64.461.7%12.311.8%27.726.6%67.858.2%17.214.8%31.527.0%69.757.4%15.813.0%35.929.5%69.555.8%13.811.1%41.233.1%TotalU.S.HFCemissions36.961.8100.197.9106.3104.5116.6121.4124.5Table TSD-B.17 compares total HFC emissions fromsection 202(a)source categories to U.S. GHG emissions, global GHG emissionsfromthe transport sector (as defined by IPCC), to total globalHFC emissions, and to total global GHG emissions from all sourcecategories, for the year 2005.Section 202(a) HFC emissions are just over 1 percentof global transport emissions and 0.18 percent ofall global GHG emissions, but actually makeup 18.3 percent of global HFC emissions.154Technical Support Document, U.S.Environmental Protection AgencyTable TSD-B.17 – Comparison to US and global greenhouse gas emissions (Tg CO2e)2005Sec 202(a) HFCShareAllU.S. GHGemissions7,1300.98%AllglobalHFCemissions38118.3%GlobaltransportGHGemissions5,9091.18%AllglobalGHG emissions38,7260.18%(e)PFC and SF6emissionsPerfluorocarbons (PFCs) are not emitted frommotor vehicles ormotor vehicle enginesin the U.S.The main sources of PFCemissions in the U.S. are aluminumsmelting and semiconductor manufacturing.Similarly, sulfur hexafluoride (SF6) is not emitted frommotor vehicles or motor vehicle engines in the U.S., although use of SF6fortire inflation has been reported in other countries.85The main sourcesof SF6emissions in the U.S. are electrical transmission anddistribution systems, and primary magnesiumsmelting.852006IPCC Guidelines, Volume3,Chapter 8.155

### References for Appendix B

U

. S. EPA (200 8) I n ve nt ory of U. S. Gree n h o u se G a s E m i ssi o n s a n d Si nks : 1 9 90 – 20 0 6 . EPA- 43 0- R-08 -0 05 , Was h ington, D C

. WRI ( 2 00 9 ) C l i m at e An al ysi s In di cat o rs Tool ( C AIT) Versi o n 6. 0 . Available at http ://cait.wri.o r g /

. Accesse d Febr u ar y 20 , 20 09

.



### 156

### Appendix C: Direct Eff ects of Ambient GHG Concen trations on Human Health
Greenhouse gases, at both current and projected atm o s pheric concentrations, are not expected to pose exposure risks on hum an respiratory s y stem s (i.e. br eathing/inhalation). T h e literature supporti ng this conclusion is described below.

Carbon diox ide (CO 2 )
The direct effects of high CO 2 concentrations on hu man health were assessed in the EPA (2 000) repor t, Carbon Diox ide as a Fire Suppressant: Examining t h e Risks , and have also been reviewed by the IPCC (2005) S p ecial Report on Carbon Dioxide Capture and Storage

. At concentrations above about 2% , CO 2 has a strong effect on respiratory p h y siolog y an d at concentrations above 7–10% , it can cause unconsciousness and death (IPCC, 2005). Exposure studies ha ve not revealed any adverse health effect of chronic expo sure to concentrations below 1% . At concentrations greater th an 17 perce n t, loss of controlled and purposeful activity , unconsciousness, convulsions, co m a , and death occur wit h in 1 m i nut e of initial inhalation of CO 2 (OSHA, 1989; CCOHS, 199 0; Dalgaard et al., 1972; CAT A MA, 1953; Lam b ertsen, 1971). But C O 2 is a phy s i o logicall y active gas and i s a norm a l component of blood gases (EPA, 2000). Acute CO 2 exposure of up t o 1 percent and 1.5 percent b y volum e is tolerated quite
co m f ortably ( EPA, 2000 b).

The a m bient concentration of CO 2 in th e at m o sphere is presentl y about 0.039 percent by vol ume (or 386 ppm ). Proje c ted increa se s in CO 2 concentrations from anthropo ge nic em issions range from 41 to 158 percent above 2005 levels (o f about 380ppm ) or 535 to 983 parts pe r m illion (ppm) by 2100 ( Meehl et al., 2007) (see Section 5). Such increases would result in at m o spheric CO 2 concentrations of 0.05 4 to 0.09 8 percent by vo lume in 210 0, which is well below publis hed thresholds for adverse health effects

. Methane (CH 4 )

Methane is fl a mmable or e xplosive at concentrations of 5% to 15 % by v olum e (50,00 0 to 1 50,0 00 p pm ) of air (NIOSH, 1994; NR C, 2000). A t high eno u g h concentrations, CH 4 is also a simp le asphyxiant, capable of di splacing eno ugh ox ygen to cause death b y suffocation. Thresh old lim it values are not specified because the lim iting factor is the ava ilabl e ox y g en (NRC, 2000)

. Atm o spheres with o x y gen concentrations below 19.5 percent c a n have advers e p h y s iological effects, and a t m o spheres w ith less than 16 percent oxygen can become life threatening (MS HA, 2007). Methane displaces oxygen to 18% in air when present at 14% (140,000 ppm ).
When oxyge n is readily available, CH 4 has little toxic effect (NRC, 2000). In assessi ng em ergency exposure limits for CH 4 , the NRC (2000) determ ine d that an exposure lim it that presents a n explosion hazard cannot be reco mme nded, even if it is well below a concentr ation that would produce toxicit y

. As such, it recommended an exposure lim it of 5000 ppm for m e than e (NRC, 2000). The National Institute for Occupational Health Safety (N IOSH, 1994) established a threshold lim it v a lue (TLV) for m e thane at 1,00 0 ppm

. The current at m o spheric c oncentration of CH 4 is 1. 78 ppm

. The projected CH 4 concentration in 2 100 ranges fro m 1.46 ppm to 3.39 ppm by 2100 , well below any reco mmended ex posure lim its (Meehl et al., 2007). Nitrous Oxi d e (N 2 O)
Nitrous oxide is an asphy x iant at high concentrati ons. At lower co ncentrations, exposure cau ses central
nervous s y stem , cardiovascular, hepatic (pertaining to the li v e r), hem a topoietic (pertaining t o the



### 157

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

formation of blood or bl ood cells), and reproducti ve effects in hum ans (Hathaway et al., 1991) . At a concentration of 50 t o 67 p e rcent (500,0 00 to 670, 00 0 ppm ) nitrous oxide is us ed to ind u ce anesthesia in hum ans (Ro m , 1992).
NIOSH has established a reco mmended exposure limit (R EL) fo r nitrous oxi de of 25 pp m as a timeweighted average (TWA) for the duration of the e xposure (NIOSH, 1992). The Am erican Co nference of Governmental Industrial Hygienists (ACGIH) has assigned nitrous oxide a TLV of 50 ppm as a TWA for a normal 8-hour workda y and a 40-h our workweek (ACGIH, 199 4).
The NIOSH lim it is based on the risk of reproductiv e sy stem effects an d decreases in audiovisu al performance (NIOSH, 19 92). The ACGIH li mit is b ased on the risk of r e productive, hematological (related to the study of th e nature, funct ion, and diseases of the blood and of bl ood-form ing organs), and
nervous s y stem effects (ACGIH 1994)
The current atm o spheric concentration of nitrous oxide is 0.3 2 ppm

. Th e projected nitrous oxi de concentration in 2100 rang es fro m 0.36 to 0.46 ppm in 2100 , well below any ex posure lim its (Meehl et al., 200 7). Fluorinated Gases ( H FC s, PFCs, SF 6 )
Most fluorina ted gases em i tted from ant h ropogenic activities are r e leased in very sm all quant ities relativ e to established thresholds for adverse health outcomes fro m exposure. The health effects of exposure to one illustrative HFC gas, one illustrative HCFC g as and SF 6 are given in the context of their current at m o spheric concentration. Chlorofluorocarbons are not included in this discu ssion given their phaseout under the Mo ntreal Protocol. The NRC (1996) recommended a 1-hr em ergency e xposure gui dance level (EEGL) of 4, 000 ppm for HFC-134a. This reco mmendation was based on a no- observed- adverse-eff e ct level of 40,000 ppm in cardiac-sensitization tests of m a le beagles (NRC, 1996). It reco mmended 24-hr EEGL of 1,0 00 ppm based on the fetotoxicit y effects ( s light retardation of skeletal ossification) observed in rats exposed to HFC-134a. Finall y , it recommended a 90-da y CEGL of 900 ppm based on a 2- year chronic toxicit y study conducted in male rats ex posed to HF C-134a at dif f erent concentrations for 6 hours/da y , 5 da y s /week. The atm o spheric concentration of HF C 134a in 2 003 was in th e range of 26 to 31 parts per trillion according to I PCC/TEAP ( 2005), m a ny orders of m a g n itude below EEGLs.
For HCFC-1 23, the end p o ints of phar m acological or adverse eff ects considered for establi shing an EEGL
are c a rdiac s e nsitization, anesthesia or CNS-rel a ted e ffects, malignant h y pertherm ia, and hepatotoxicit y

. According to the NRC (1 996), concentration requir e d to produce cardiac sen sitization in 50% of the anim als) for HCFC-123 was determined in dog studi es to be 1.9% (19,000 ppm) for a 5-m in u te exposure. The NRC reco mmended that 1,900 p p m (19,000 ppm divided b y an uncertainty factor of 10 for interspecies v a riability ) should be consi d ered the huma n no-observed-effect lev e l for a 1-m in exposure to HCFC-123 on the basis of the dog cardi ac-sen sitizati on m odel. T h e concentration of HCFC-123 i n 1996 was 0.03 parts per trillion according to IPCC/TEAP (2005) , many orders of m a gnitude below the established ef fect level.

Sulfur hexafl uoride (SF 6 ) is a relatively non-toxic gas but an asphy xiant at high concentrations. The NIOSH, 1997) recommen d ed exposure lim it is 1,00 0 ppm

. The SF 6 co ncentration in 20 03 was around 5 parts per trillion according to IPCC/TEAP (2005), m a ny orders of magnitude below the expos ure lim it.



### 158

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

Refe renc es f o r Appendix C

A C GI H ( 199 4) 199 4- 199 5 Thres h ol d l i m i t val u es f o r

c h emi c al su bst ance s a n d p h y si cal a g ent s an d bi ol o g i c al exposure indice s. Cincinnati, OH: Am erican Confe r ence of Go v e rn m e n tal In du str ial H ygien ists.

CA TA MA (1953) Aviation Toxicology-

- an Introduc tion to th e Subject and a Handboo k of Data

. Co mmit t e e o n Av ia t i o n T o xic o lo g y , Ae r o Me d i c a l As s o c i a t io n

. T h e Bla k is t o n Co .: N e w Y o r k
, N Y . p p

. 6-9, 31-3 9
, 52-55, 74- 79, 110- 115.

Dal g aard , J.B

. , G. De nc ker, B . Fal l e nt i n , P. Hanse n , B . Kaem pe, J. St eensb er ger , W i l h ar dt , P. (19 7 2 ) Fat a l poi s o ni n g a n d ot he r heal t h ha zards co n n ect e d wi t h i n d u stri al fi shi n g. Br. J. Ind. Me d . 29: 3 07- 316

. Hatha w ay GJ, Proct o r N H , Hu g h es JP, and Fisch m an ML ( 199 1) Pr oc t or a nd H ug he s ' c he mi c al ha zar ds of t

he
w o rkpl ace

. 3r d ed . N e w Yo rk , NY : V a n No str a nd Reinho ld

. IPC C ( 2 00 5) S p eci al Re p o rt on C a r

b on Di ox i d e C a

pt ure a n d Stor age

. A Sp ecial Repo r t o f W o r k i n g Gr oup II I of th e Int e r g ove r n m e nt al Panel o n C l im at e C h an ge.

I P CC Techn o l o g y and Eco nomic A ssess m e n t Pan e l (2 005) I P CC/TEAP Sp ecial Rep o r t o n Saf e -gu a rdin g th e O z on e Layer and the Global Clim ate Syste m : Issues Related to Hy dr o f l u or ocarb o n s an d Pe rf l u o r ocarb o n s. Prepar e d by W o rk i n g G r o u p I an d I II of t h e IPC C , a nd t h e TEA P. Edi t e d by B

. M e t z , L. Kui j pers , S. S o l o m o n , S. O. An de rsen , O. Davi ds on , J. Pons , D. de Jag e r, T. Kest i n , M . M a nni n g , and L. A. M e y e rs, 4 8 8 p p ., C a m b ri dge Uni v ersity P r e ss, Cam b ride, U. K., an d Ne w Y o rk , N Y , US A.

Lam b ertsen , C

. J. (197 1) “Therap e u tic Gases—Ox yg en , C arbon Di o x i d e , and Heliu m

. ” Drill’s Ph armaco lo g y in Med i cin e. C h ap ter 55 , Ed . By J.R. DiPalm a. McGraw-Hill Bo ok C o .: New York, NY.
Meehl, G.A. e t al. (2007) Glo b a l Cli m ate Proj ection s . In: C l i m at e C h a nge 2 0 0 7 : T h e Physi c al Sci e nce B a si s. Cont ri b u t i o n o f

Worki n g Gro up I t o t h e F o urt h A ssess me nt Rep o rt of t

h e Int e r g overn m ent a l

Pa nel on C l i m at e Ch ang e [So l om o n , S., D. Qin , M. Man n i ng , Z. Ch en , M

. Marqu i s, K.B. Av eryt, M.Tig n o r and H.L. Miller (eds .)] . Cam b ridge U n ive r sity Press , Cam b ridge , United Ki ng d o m and Ne w Yo rk , NY , US A.

Min e Safety an d H ealt h A d min istr a tio n (MSH A) (2 007) The Danger of Ox yge n Def i ciency in Undergr o und C oal Mines

. De par t m e nt of La bo r Pr og ram I n f o rm at i on B u l l e t i n N O

. P0 7- 0 5

. I n t e r n et si t e l o cat ed at h ttp ://www.m sh a.g o v / reg s /com p l ian /PIB/200 7 / p i b0 7-0 5 .asp

NIOSH (1997) NI OSH Pocke t Guide t o Che m ical H azards. U.S. De partment of Health a nd Hum a n Services, Publi c Health Se rvice , Centers for Disease Co n t ro l an d Prev en tio n, W a sh ing ton , D.C. NIOSH Pu b lication no . 9 7 -1 40 ; N T IS n o

. PB

- 9 7 177 604 . In te rnet site located at h ttp ://www.cd c.g o v /n i o s h /n p g /npg d05 76 .h tml
NIOSH (1 994 ) In tern ation al Ch em ica l Safety Card s - Meth ane. U.S . De part m e nt of H eal t h and Hum a n Ser v i ces, Pub lic Health Serv ice, Cen t ers fo r Di sease Control and Prevention, Was h ingt on, D.C. Internet site located at h ttp ://www.cdc.go v / n io s h /ip csn e n g / n e ng0 291 .h tml

NI OS H ( 1 99 2 ) R ecom m endat i ons fo r occ upat i o nal sa fet y and heal t h : C o m p endi um of p o l i c y do cum e nt s and state m en ts. Cin cinn ati, OH: U.S. Dep a rtm e n t of Health a n d Hum a n Servi ces, Public He alth Service, C e nters for Disease C o n trol, Nation al In st itu te for Occupatio n al Safety an d Health (NIOSH ) Pub licatio n No . 92 -100

.
N a tio n a l Resear ch Coun cil ( N RC) ( 200 0) Emerge ncy a nd C ont i n u ous Expos ure Li mi t s f o r Sel e c t ed Ai rbo r ne Cont ami na nt s , Vol u m e 1. Nat i onal Academy Press , Was h ington, D.C

. Natio n a l Research C o un cil (NRC) (19 96) Tox i city o f Al tern ativ es t o Ch lorofluo ro carbons: HFC-134a and HCFC12 3. Nat i o nal Academ y Pres s, Washi ngt on , D.C

.



### 159

### Technical Support Docum e nt, U.S. Environm ental Protection Agency

OS HA (1 9 8 9 ) C a rb o n Di oxi d e, In d u st ri al Exp o su re a n d Cont r o l Tech n o l o gi es f o r O S HA Re gul at ed Ha zar d

ous Su bst ances , V o lum e I of II, Su bstance A - I. Occ u pationa l Safety and Health Ad m i n i st ratio n. W ash ing t on , DC : U

. S. D e p ar t m e n t of Labo r. M a r c h.

Ro m , W N ( 199 2) E n vi r o n m e n t a l

an d occ u p a t i o n a l medi ci ne

. 2n d ed. B o sto n , MA: Littl e, Bro w n and Co m p an y.
U.S

. EP A ( 2 0 0 0 a) Ca rbo n D i o x id e a s a Fire Su pp ressan t: Exam in ing t h e Risks , EPA 430

- R

- 0 0

- 00 2, M a y.

U

. S. EPA (2 00 0b) C a r

b o n Di oxi d e as a Fi re Su p

p ress ant : Exa m i n i n g t h e Ri sks, A ppe n d i x

B – O vervi ew of Acu t e Hea lth Effects , EPA 430

- R

- 0 0

- 00 2, May.



### 160