Understanding the Science of Climate Change

Talking Points – Impacts to Arid Lands

Natural Resource Report NPS/NRPC/NRR—2010/209

National Park Service

U.S. Department of the Interior

Natural Resource Program Center
ON THE COVER

The view through Mesa Arch in Canyonlands National Park; NPS photo by Neil Herbert.
Understanding the Science of Climate Change

Talking Points – Impacts to Arid Lands

Natural Resource Report NPS/NRPC/NRR—2010/209

Rachel Loehman

Rocky Mountain Research Station

Fire Sciences Laboratory

5775 West US Hwy 10

Missoula, MT 59808-9361

With special thanks to the US Forest Service’s Rocky Mountain Research Station and contributions from (in alphabetical order): 

Michelle Bowie, Molly Cross, Mima Falk, Jennifer Getchell, Louise Hose, Ben Jefka, Caroline Jezierski, Kathy Jope, Frtitz Klasner, 

Kristin Legg, David Parsons, Dusty Perkins, David Peterson, Brant Porter, Kayla Sullivan, Kathy Tonnessen, and Leigh Welling. 

Layout and design: Sara Melena, Angie Richman, Caitlin Shenk, and Katherine Stehli.

June 2010

U.S. Department of the Interior

National Park Service

Natural Resource Program Center

Fort Collins, Colorado
The Natural Resource Publication series addresses natural resource topics of interest and applicability to a broad 

readership in the National Park Service and to others in the management of natural resources, including the scientific 

community, the public, and the NPS conservation and environmental constituencies. Manuscripts are peer-reviewed 

to ensure the information is scientifically credible, technically accurate, appropriately written for the intended audience, and is designed and published in a professional manner.

Natural Resource Reports are the designated medium for disseminating high priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain 

NPS policy considerations or address sensitive issues of management applicability. Examples of the diverse array 

of reports published in this series include vital signs monitoring plans; monitoring protocols; “how to” resource 

management papers; proceedings of resource management workshops or conferences; annual reports of resource 

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Views, statements, findings, conclusions, recommendations and data in this report are solely those of the author(s) 

and do not necessarily reflect views and policies of the U.S. Department of the Interior, National Park Service. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the 

National Park Service.

This report is available from the Natural Resource Publications Management website:

( http://www.nature.nps.gov/publications/NRPM )

Please cite this publication as:

Loehman, R. 2010. Understanding the science of climate change: talking points - impacts to Arid Lands. Natural Resource Report NPS/NRPC/NRR—2010/209. National Park Service, Fort Collins, Colorado.

NPS 999/103380, June 2010
Contents 

Introduction ............................................................................................................................................................1

Climate Change Impacts to Arid Lands ................................................................................................................... 2

Summary.........................................................................................................................................................................................2

List of Parks and Refuges .............................................................................................................................................................3

Sectors:

 Temperature............................................................................................................................................................................4

 The Water Cycle .....................................................................................................................................................................5

 Vegetation................................................................................................................................................................................8

 Wildlife ................................................................................................................................................................................... 11

 Disturbance............................................................................................................................................................................13

 Visitor Experience.................................................................................................................................................................15

 Cultural Resources............................................................................................................................................................... 16

No Regrets Actions .................................................................................................................................................17

Global Climate Change.......................................................................................................................................... 20

Sectors:

 Temperature and greenhouse gases...................................................................................................................................20

 Water, Snow, and Ice............................................................................................................................................................23

 Vegetation and Wildlife .......................................................................................................................................................25

 Disturbance...........................................................................................................................................................................28

References ........................................................................................................................................................... 29
National Park Service 1

Purpose

Climate change presents significant risks to our nation’s natural 

and cultural resources. Although climate change was once believed to be a future problem, there is now unequivocal scientific evidence that our planet’s climate system is warming (IPCC 

2007a). While many people understand that human emissions 

of greenhouse gases have contributed to recent observed climate changes, fewer are aware of the specific impacts these 

changes will bring. This document is part of a series of bioregional summaries that provide key scientific findings about 

climate change and impacts to protected areas. The information 

is intended to provide a basic understanding of the science of 

climate change, known and expected impacts to resources and 

visitor experience, and actions that can be taken to mitigate and 

adapt to change. The statements may be used to communicate 

with managers, frame interpretive programs, and answer general questions to the public and the media. They also provide 

helpful information to consider in developing sustainability 

strategies and long-term management plans. 

Audience

The Talking Points documents are primarily intended to provide 

park and refuge area managers and staff with accessible, up-todate information about climate change and climate change impacts to the resources they protect. 

Organizational Structure

Following the Introduction are three major sections of the document: a Regional Section that provides information on changes 

to the Arid Lands, a section outlining No Regrets Actions that 

can be taken now to mitigate and adapt to climate changes, and 

a general section on Global Climate Change. The Regional 

Section is organized around seven types of changes or impacts, 

while the Global Section is arranged around four topics.

Regional Section

•	 Temperature 

•	 The Water Cycle (including snow, ice, lake levels, sea levels 

and sea level rise, and ocean acidification)

•	 Vegetation (plant cover, species range shifts, and phenology)

•	 Wildlife (aquatic, marine, and terrestrial animals, range shifts, 

invasive species, migration, and phenology)

•	 Disturbance (including range shifts, plant cover, plant pests 

and pathogens, fire, flooding, and erosion)

•	 Visitor Experience

•	 Cultural Resources

Global Section

•	 Temperature and Greenhouse Gases

•	 Water, Snow, and Ice

•	 Vegetation and Wildlife

•	 Disturbance

Information contained in this document is derived from the 

published results of a range of scientific research including 

historical data, empirical (observed) evidence, and model projections (which may use observed or theoretical relationships). 

While all of the statements are informed by science, not all statements carry the same level of confidence or scientific certainty. 

Identifying uncertainty is an important part of science but can 

be a major source of confusion for decision makers and the 

public. In the strictest sense, all scientific results carry some 

level of uncertainty because the scientific method can only 

“prove” a hypothesis to be false. However, in a practical world, 

society routinely elects to make choices and select options for 

actions that carry an array of uncertain outcomes. 

The statements in this document have been organized to help 

managers and their staffs differentiate among current levels 

of uncertainty in climate change science. In doing so, the 

document aims to be consistent with the language and approach 

taken in the Fourth Assessment on Climate Change reports by 

the Intergovernmental Panel on Climate Change. However, this 

document discriminates among only three different levels of 

uncertainty and does not attempt to ascribe a specific probability to any particular level. These are qualitative rather than 

quantitative categories, ranked from greatest to least certainty, 

and are based on the following: 

•	 “What scientists know” are statements based on measurable 

data and historical records. These are statements for which 

scientists generally have high confidence and agreement 

because they are based on actual measurements and observations. Events under this category have already happened or 

are very likely to happen in the future.

•	 “What scientists think is likely” represents statements beyond 

simple facts; these are derived from some level of reasoning 

or critical thinking. They result from projected trends, well 

tested climate or ecosystem models, or empirically observed 

relationships (statistical comparisons using existing data). 

•	 “What scientists think is possible” are statements that use a 

higher degree of inference or deduction than the previous 

categories. These are based on research about processes that 

are less well understood, often involving dynamic interactions among climate and complex ecosystems. However, 

in some cases, these statements represent potential future 

conditions of greatest concern, because they may carry the 

greatest risk to protected area resources. 

I. Introduction 
2 Climate Change Talking Points NPS/FWS—2010

II. Climate Change Impacts to Arid Lands

The Arid Lands bioregion 

that is discussed in this section is shown in the map to 

the right. A list of parks and 

refuges for which this analysis is most useful is included 

on the next page. To help the 

reader navigate this section, 

each category is designated 

by color-coded tabs on the 

outside edge of the document.

Summary

Arid ecosystems are particularly sensitive to climate change and climate variability because organisms in these regions live 

near their physiological limits for water and temperature stress. Slight changes in temperature or precipitation regimes, or 

in magnitude and frequency of extreme climatic events, can significantly alter the composition, abundance, and distribution 

of species. Observed climate changes in the southwestern U.S. include increased seasonal and annual average temperatures, 

increased minimum temperatures, and decreases in the length of the frost-free period and number of frost days. In general 

the region has become more arid over the past few decades, with a significant decrease in regional snowpack and a broadscale shift in the timing of snowmelt runoff to earlier in the season. Projected climate changes include continued increases in 

temperature, potentially at rates faster than observed rates of change, and a large reduction in the volume and persistence of 

mountain snowpacks. Precipitation and flooding events are projected to become more extreme, even as drought conditions 

intensify. Observed and projected climate changes will likely alter plant species ranges; shift the geographic and elevational 

boundaries of the Great Basin, Mojave, Sonoran, and Chihuahuan deserts; cause major changes in vegetation composition and 

cover, increase rates of erosion and sediment transport to streams; result in increased tree mortality from synergistic associations between drought stress and insect outbreaks; increase the frequency, size, and duration of wildfires; and increase the 

probability of extinctions in plant and animal species.

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
National Park Service 3

U.S. National Park Service Units

•	 Amistad NRA

•	 Arches NP

•	 Aztec Ruins NM

•	 Bandelier NM

•	 Big Bend NP

•	 Black Canyon of the Gunnison NP

•	 Bryce Canyon NP

•	 Canyon de Chelly NM

•	 Canyonlands NP

•	 Capitol Reef NP

•	 Carlsbad Caverns NP

•	 Casa Grande Ruins NM

•	 Chaco Culture NHP

•	 Chamizal NME

•	 Chiricahua NM

•	 City of Rocks NR

•	 Colorado NM

•	 Coronado NME

•	 Death Valley NP

•	 Dinosaur NM

•	 El Malpais NM

•	 El Morro NM

•	 Escalante NM

•	 Fort Bowie NHS

•	 Fort Davis NHS

•	 Fossil Butte NM

•	 Gila Cliff Dwellings NM

•	 Glen Canyon NRA

•	 Golden Spike NHS

•	 Grand Canyon NP

•	 Great Basin NP

•	 Guadalupe Mountains NP

•	 Hagerman Fossil Beds NM

•	 Hohokam Pima NM

•	 Hovenweep NM

•	 Hubbell Trading Post NHS

•	Joshua Tree NP

•	 Lake Mead NRA

•	 Manzanar NHS

•	 Mesa Verde NP

•	 Minidoka NHS

•	 Mojave NPR

•	 Montezuma Castle NM

•	 Natural Bridges NM

•	 Navajo NM

•	 Organ Pipe Cactus NM

•	 Petrified Forest NP

•	 Petroglyph NM

•	 Pipe Spring NM

•	 Rainbow Bridge NM

•	 Saguaro NP

•	 Sunset Crater Volcano NM

•	Tonto NM

•	Tumacacori NHP

•	Tuzigoot NM

•	 Walnut Canyon NM

•	 White Sands NM

•	 Whitman Mission NHS

•	 Wupatki NM

•	 Yucca House NM

•	Zion NP

U.S. Fish & Wildlife Service Units

•	 Alamosa NWR

•	 Anaho Island NWR

•	 Ash Meadows NWR

•	 Baca NWR

•	 Bamforth NWR

•	 Bear Lake NWR

•	 Bear River MBR

•	 Big Boggy NWR

•	 Bill Williams River NWR

•	 Bitter Lake NWR

•	 Bosque del Apache NWR

•	 Browns Park NWR

•	 Buenos Aires NWR

•	 Cabeza Prieta NWR

•	 Camas NWR

•	 Cibola NWR

•	 Coachella Valley NWR

•	 Cokeville Meadows NWR

•	 Cold Springs NWR

•	 Colorado River WMA

•	 Columbia NWR

•	 Deer Flat NWR

•	 Desert NWR

•	 Desert NWR

•	 Fallon NWR

•	 Fish Springs NWR

•	 Hart Mountain NWR

•	 Havasu NWR

•	 Hutton Lake NWR

•	Imperial NWR

•	 Kofa NWR

•	 Leslie Canyon NWR

•	 Malheur NWR

•	 McKay Creek NWR

•	 McNary NWR

•	 Minidoka NWR

•	 Moapa Valley NWR

•	 Monte Vista NWR

•	 Mortenson Lake NWR

•	 Ouray NWR

•	 Oxford Slough WPA

•	 Pahranagat NWR

•	 Pathfinder NWR

•	 Ruby Lake NWR

•	 Saddle Mountain NWR

•	 San Andres NWR

•	 San Bernardino NWR

•	 Seedskadee NWR

•	 Sevilleta NWR

•	 Sheldon NWR

•	 Sonny Bono Salton Sea NWR

•	 Stillwater NWR

•	Toppenish NWR

•	Turnbull NWR

•	 Umatilla NWR 

MBR Migratory Bird Refuge

NHP National Historic Park

NHS National Historic Site

NM National Monument

NME National Memorial

NP National Park 

NPR National Preserve 

NR National Reserve

NRA National Recreation Area 

NWR National Wildlife Refuge 

WMA Wildlife Management Area

WPA Waterfowl Production Area

List of Parks and Refuges

Acronym Unit Type

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
4 Climate Change Talking Points NPS/FWS—2010

A. Temperature 

What scientists know....

•	 Winter and spring temperatures increased 

in western North America during the 20th 

century (Mote et al. 2005). The rate of 

change varied with location, but the central tendency is a warming of 1°C per 

century from 1916 to 2003 (Hamlet et al. 

2007).

•	 Regionally averaged spring and summer temperatures for 1987 to 2003 were 

0.87°C higher than those for 1970 to 1986, 

and spring and summer temperatures for 

1987 to 2003 were the warmest since the 

beginning of the record in 1895 (Westerling et al. 2006).

•	 A region-wide temperature increase of 0.3 

to 0.6oC has been observed in the Great 

Basin over the 20th century. Minimum 

temperatures increased more than maximum temperatures, variability in interannual temperatures declined, the probability of very warm years increased, and the 

probability of very cold years declined 

during this period (Wagner 2003, Chambers 2008). 

•	 An analysis of climate trends in the Sonoran Desert from 1960 to 2000 shows 

widespread winter and spring warming 

trends, a decrease in the frequency of 

freezing temperature days, a lengthening 

of the frost-free season, and increased 

minimum temperatures (Weiss and Overpeck 2005).

•	 Most areas in New Mexico have experienced temperature increases in recent 

decades. Warming has been greatest in 

the southwestern, central, and northern 

parts of the state, especially in the Jemez 

Mountains. In addition, most of New 

Mexico’s mid- to high-elevation forests 

and woodlands experienced consistently 

warmer and drier conditions or greater 

variability in temperature and precipitation from 1991 to 2005 (Enquist and Gori 

2008).

•	 A strong spring warming and an earlier 

spring onset (by 2 to 3 weeks during the 

past 50 years) has been documented in 

the western United States, based on temperature, snow cover, and phenological 

records (Groisman et al. 2004).

•	 The combined paleo-modern climate record (tree-ring data and modern instrumental records) of the southwest has at 

least three occurrences of multi-decadal 

variation (50 to 80 years) of alternating 

dry and wet periods. The amplitude of 

this variation (amount of change) has increased since the 1700s, and the current 

increase in temperatures is unprecedented 

in the last 400 years of climate history 

(Sheppard et al. 2002).

What scientists think is likely....

•	 Temperatures during the 21st century 

are very likely to increase throughout the 

southwest at a rate faster than that observed in past decades (Smith et al. 2001).

•	 Extreme cold temperatures are projected 

to increase faster than extreme warm temperatures during the 21st century (Kharin 

et al. 2007). 

•	 Temperatures in the Great Basin are expected to warm by 5 to 10oC during the 

21st century (Wagner 2003).

•	 Analysis of 19 climate models provides 

strong evidence for an imminent transition to a more arid climate in the southwestern U.S., due to increased air subsidTemperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

All the plants of the Sonoran 

Desert lay hidden under three 

inches of snow as seen through 

an Ocotillo plant. Events like 

this will become more rare as 

temperature increases due to 

climate change. NPS photo.
National Park Service 5

•	 Models identify southern California, 

northern Mexico, and western Texas as 

climate change ‘hotspots,’ areas that are 

predicted to be especially sensitive to 21st 

century anthropogenic (human caused) 

climate forcings (e.g. increased CO2 emissions) (Diffenbaugh et al. 2008).

B. THE WATER CYCLE

What scientists know....

•	 The current severe, multi-year drought 

in the western U.S. is the most extreme 

in 500 years, and has drastically reduced 

available water resources for people and 

wildlife (Cook et al. 2004, Glick 2006).

•	 The timing of snowmelt runoff has shifted 

to earlier in the snowmelt season for 84 

rivers in the western U.S. This shift has 

not been gradual, but appears to have occurred as a step change (significant difference in value) during the mid-1980’s, related to a regional increase in spring-summer 

temperatures (McCabe and Clark 2005).

•	 Daily observations from automated snowpack telemetry (SNOTEL) stations from 

within the drainage basin of the Great Salt 

Lake over the period from 1982 to 2007 

show a shift toward an earlier date of peak 

snow water equivalent (SWE) by around 

fifteen days and reductions in the amounts 

of peak SWE and April 1 SWE (Bedford 

2008).

•	 April 1 snow pack has on average decreased at most monitoring sites in the 

Great Basin since about 1950. Snowpack 

The Mojave Desert is an area 

that is likely to see large increases in temperature, which will 

decrease the available habitat 

for the Joshua Tree; FWS photo.

ence in the sub-tropics and intensified 

equatorial convection (Seager et al. 2007). 

•	 Rising temperatures are likely to shorten 

the snowpack season by delaying the autumnal change from rainfall to snow, and 

advancing spring snowmelt (Smith et al. 

2001).

What scientists think is possible....

•	 Model simulations predict that temperatures that are currently considered unusually high (e.g., 20-year return interval) will 

become very frequent in the desert southwest, occurring every couple of years, and 

unusually low temperatures will also become increasingly uncommon. As a result, 

winters will be warmer, leading to higher 

evapotranspiration and lower snowfall 

(Kharin et al. 2007).

•	 Two general circulation models project 

increases of 2.5 to 4.5oC and 5.0 to 8.0oC in 

seasonal temperatures in the Great Basin/

Rocky Mountain region by 2080 to 2100, 

based on the assumption of a doubling 

in the concentration of atmospheric CO2 

(Wagner 2003).

•	 Regional climate models predict that extreme temperature events (heat waves) 

may increase in frequency (increase of up 

to 100 days per year, or 560%), intensity, 

and duration (up to 15 days per event, or 

550%) by the end of the 21st century, 

mainly as the result of increased atmospheric concentration of greenhouse gases 

(Diffenbaugh et al. 2005).

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
6 Climate Change Talking Points NPS/FWS—2010

decline in the dry interior U.S. (including 

the Great Basin) has been among the largest observed, with the exception of central 

and southern Nevada (Baldwin et al. 2003).

•	 The onset of snow runoff in the Great 

Basin is currently 10–15 days earlier than 

50 years ago, with significant impacts on 

the downstream utilization of this water 

(Ryan et al. 2008).

•	 Water supply in the Colorado River basin 

is unsustainable under current environmental and management conditions due 

to a combination of currently scheduled 

depletions (loss of water from consumptive use), water losses due to evaporation/infiltration, and reductions in runoff 

due to climate change (Barnett and Pierce 

2008).

•	 Approximately 85% of the water used by 

humans in the Great Basin and Rocky 

Mountain region flows from spring melt 

of mountain snowpacks. Warmer wintertime temperatures and earlier melt dates 

will deplete this virtual reservoir, leaving 

much less available water for natural systems and human uses. Water resources in 

the region are totally allocated, with 80% 

of available water used for agriculture. 

Regional human populations and water 

needs are expected to double in the next 

40 years, taxing resources even further 

(Wagner 2003, Service 2004).

•	 The majority of the observed low-frequency changes in the hydrological cycle 

(river flow, temperature, and snow pack) 

over the western U.S. from 1950 to 1999 

are due to human-caused climate changes 

from greenhouse gases and aerosols (Barnett et al. 2008).

What scientists think is likely....

•	 There is broad consensus among climate 

models that the arid regions of the southwestern U.S. will become drier in the 21st 

century, and that a transition to a more 

arid climate is already underway. This 

forecast reverses earlier projections that 

the southwest might receive more rainfall 

as the climate warms (Lenart et al. 2007, 

Backlund et al. 2008).

•	 Projected future warming trends will significantly impact water resources, including a large reduction in the volume and 

persistence of mountain snowpacks, and 

a commensurate reduction in natural water storage. Current demands on water 

resources in many parts of the West will 

not be met under plausible future climate 

conditions, including water supplies for 

natural and anthropogenic systems (Barnett et al. 2004, Knowles et al. 2006).

•	 Warming in the western states is expected 

to increase the fraction of precipitation 

that falls as rain rather than snow and hasten the onset of snowmelt once snowpacks 

have formed. Snow deposition is sensitive 

to wintertime (November-March) warming trends, whereas snowmelt is sensitive to changes in springtime temperatures 

(Knowles et al. 2006). 

•	 Reduced snowpack and earlier runoff will 

mean less available water for summer irTemperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

Isolated summer monsoon 

thunderstorm at Guadalupe 

Mountains National Park (Top); 

Manzanita Spring, a wetland 

spring, provides essential habitat for plants and animals (Bottom); NPS photos.
National Park Service 7

•	 Early season spring runoff, a consequence 

of increased spring temperatures, is likely 

to increase risk of spring flooding, complicate seasonal water allocation schedules, 

and create difficulties in matching summer 

instream flow requirements (Smith et al. 

2001).

•	 Decreased late-season runoff will likely result in reduced water quality unless stronger pollution control measures are applied. 

Lower streamflows will concentrate pollutants in water bodies, and higher temperatures will decrease dissolved oxygen 

levels, with negative implications for fish 

and wildlife (Smith et al. 2001).

•	 River and riparian ecosystems in arid 

lands are likely to be negatively impacted 

by decreased streamflows, increased water 

removal, and competition from nonnative 

species (Backlund et al. 2008).

•	 Changes in runoff patterns and river flows 

resulting from decreased precipitation 

and increasing seasonal temperatures may 

disrupt biological communities and sever 

ecological linkages. For example, as the 

result of earlier spring runoff aquatic species’ life histories (e.g. spawning) may be 

temporally out of synch with flow regimes 

in warming climates (Palmer et al. 2009).

What scientists think is possible....

•	 Future drought conditions are predicted 

to far exceed the severity of any drought in 

living memory, including the 1930’s “Dust 

Bowl’ period, and the immediate future in 

the southwest could look much like the 

peak drought years of 2000 to 2003 (Lenart et al. 2007, Seager et al. 2007, Schwinning et al. 2008). 

•	 Elevated aridity in the western U.S. occurs 

in response to climate warming, as demonstrated by drought-temperature patterns 

during the Medieval Warm Period in AD 

900 to 1300, and any trend toward warmer 

temperatures in the future could lead to a 

serious long-term increase in aridity over 

western North America (Cook et al. 2004).

•	 Model simulations predict that precipitation events that are currently considered 

extreme (20-year return interval) are exStella Lake and snowpack on 

Wheeler Peak in Great Basin 

National Park; NPS photo.

rigation needs, higher water temperatures, 

and increased conflict between agricultural users and those whose principal concern is sustaining fish populations. These 

effects will be especially profound in 

smaller, snowmelt-driven rivers (Barnett 

et al. 2004). 

•	 A water budget analysis shows that under 

current onditions there is a 10% chance 

that live storage (the reservoir space from 

which water can be evacuated by gravity) 

in Lakes Mead and Powell will be gone by 

about 2013, and a 50% chance that it will 

be gone by 2021 if no changes in water allocation from the Colorado River system 

are made. These projections are driven 

by climate changes, the effects of natural 

climate variability, and the current operating status of the reservoir system. There us 

a 50% chance that minimum power pool 

levels in both Lake Mead and Lake Powell 

could be reached under current conditions by 2017 (Barnett and Pierce 2008).

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
8 Climate Change Talking Points NPS/FWS—2010

pected to occur roughly twice as often as 

they currently do, consistent with general 

increases in rainstorm intensity (Kharin et 

al. 2007).

•	 Evaporation rates are expected to increase 

as a consequence of increasing temperatures, an effect that may increase the intensity of precipitation events and flooding. 

Changes in rainfall patterns may affect human systems (water storage, agricultural 

production, human mortality, seasonal energy demands) and ecosystem dynamics 

(plant communities, extinction, invasive 

species, and diseases) (Diffenbaugh et al. 

2005).

•	 Simulation models project that total water 

storage for the Colorado River basin will 

decrease by 36% for the period 2010-2039 

under a business-as-usual (no emissions 

reduction) scenario, resulting in a situation in which total system demand (water deliveries plus reservoir evaporation) 

will exceed (decreasing) reservoir inflows 

(Christensen et al. 2004).

•	 Multiple climate model projections suggest that groundwater recharge in the San 

Pedro Basin, a riparian river corridor in 

southeastern Arizona, will decrease by 

26% with 21st century climate changes, resulting in loss of some or all riparian habitat and associated species (Serrat-Capdevila et al. 2007).

C. VEGETATION

What scientists know....

•	 Arid ecosystems of the western U.S. are 

particularly sensitive to climate change 

and climate variability because organisms 

in the region live near their physiological 

limits for water and temperature stress. 

Slight changes in temperature or precipitation regimes, or in magnitude and frequency of extreme climatic events, can 

significantly alter the composition, abundance, and distribution of species (Archer 

and Predick 2008).

•	 An extreme drought accompanied by unusually high temperatures in the southwest 

in 2002 resulted in widespread mortality 

of dominant plants in multiple community 

types, including manzanita, quaking aspen, 

ponderosa pine, Fremont cottonwood, 

Engelmann spruce, white fir, Douglas-fir, 

and piñon pine. By 2003, 12,000 km2 of 

piñon and ponderosa pine had died across 

the region (Burkett et al. 2005, Gitlin et al. 

2006).

•	 Most of New Mexico’s mid- to high-elevation forests and woodlands experienced 

consistently warmer and drier conditions 

or greater variability in temperature and 

precipitation from 1991 to 2005. Should 

these trends continue, these habitats will 

experience increased vulnerability and 

susceptibility to ongoing climate changes 

(Enquist and Gori 2008).

•	 Recent drought, and in particular decreases in cool-season precipitation, has been 

linked with significant shrub mortality in 

parts of the Sonoran and Mojave deserts. 

Small, drought-deciduous shrubs such 

as Ambrosia deltoidea (triangle-leaf bursage) and Ambrosia dumosa (white bursage) experienced nearly 100% mortality, 

while larger, drought-enduring evergreen 

Larrea tridentata (creosote bush) showed 

somewhat lower mortality (McAuliffe and 

Hamerlynck 2010).

•	 The basic driver of recent tree mortality in 

the southwest has been climate-induced 

stress. Climate can act synergistically with 

insect outbreaks (e.g. bark beetles) to 

greatly amplify tree mortality, especially 

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

In 2002 pinon trees in the forest 

around Los Alamos New Mexico 

suffered a severe die off due to 

drought and pine beetle outbreak. Photos courtesy of Craig 

Allen, USGS.
National Park Service 9

under climatic conditions that promote 

large scale outbreaks through modification of insect life cycle dynamics (Allen 

2007).

•	 Extreme drought conditions in the southwest in 1996 and 2002 led to widespread 

mortality of piñon pines across northern 

Arizona, and a vegetation shift such that 

piñon-juniper woodlands are becoming 

dominated by juniper, a species that is 

typical of lower elevations and more arid 

conditions (Mueller et al. 2005).

•	 Forests in the western United States sequester 20 to 40% of U.S. carbon emissions from fossil fuels, an amount equal 

to about one-half of the carbon absorbed 

by terrestrial ecosystems in the conterminous U.S. Changes in forest productivity, 

structure, and composition will result in 

changes in the rate of carbon sequestration and amount of carbon stored as biomass (Pacala et al. 2001, Westerling et al. 

2006, Brown 2008).

•	 Widespread bleaching of desert moss in 

the northern Mojave Desert in the winter 

of 2002 and 2003 has been attributed to 

physiological stress resulting from lower 

than average rainfall during winter growing seasons and an extended period of 

drought in the region. Physiological stress 

reduces plant productivity, increases regeneration time, and reduces the overall 

health of biological crust communities, 

which perform valuable ecosystem functions such as nitrogen fixation, erosion 

control, and water retention (Barker et al. 

2005).

•	 Water availability greatly influences vegetation growth and composition in the 

Mojave Desert. For example, intense 

droughts (1989 to 1991 and the current 

drought) caused widespread mortality of 

chenopods and perennial grasses, and a 

wet period from 1976 to 1998 resulted in 

an increase in the size and cover of creosote bush (Hereford et al. 2006).

•	 Timing of precipitation is important for 

germination, establishment, and productivity of desert vegetation. Cool season 

precipitation is the most important and 

dependable source of rainfall for most 

vascular plants, although the extent and 

magnitude of warm-season rainfall is important for many species of cacti, yuccas, 

agaves, and leguminous trees (Hereford 

et al. 2006).

•	 Field experiments in a Sonoran Desert 

grassland demonstrated that changes in 

the timing and amount of precipitation 

can significantly impact soil carbon storage through effects on autotrophic (plant) 

and heterotrophic (soil microbe) respiration. Specific response depends on a number of ecological properties including soil 

texture, soil type, and spatial distribution 

of vegetation (Cable et al. 2008).

•	 Climate is the most important factor 

controlling saguaro populations in the 

Sonoran Desert. In particular, saguaros 

require adequate summer rainfall for establishment and survival, and maximum 

July temperatures appear to limit the number of young saguaros such that fewer are 

observed in areas characterized by higher 

temperatures (Drezner 2004).

Saguaro National Park is home 

to the iconic saguaro cactus 

which is a species that is likely 

to be strongly affected by climate change; NPS photo. 

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
10 Climate Change Talking Points NPS/FWS—2010

What scientists think is likely....

•	 Climate-induced vegetation mortality can 

occur much faster than regeneration, with 

profound ecological effects such as feedbacks to disturbance processes (e.g. wildfire and erosion, insect invasions), loss of 

sequestered carbon, changes in nutrient 

cycling, altered landscape composition 

and biodiversity, changes in hydrology, 

decreased wildlife habitat, and impacts to 

ecological services (Dale et al. 2001, Allen 

2007).

•	 Geographic boundaries of the southwestern deserts (e.g. Sonoran Desert) will likely 

expand to the north and east with a predicated decrease in the frequency of frost 

days, lengthening of the frost-free season, 

and increased minimum temperatures. In 

addition, climate changes will likely alter 

bioclimatic zones and shift distributions 

of arid land communities upward in elevation in response to warmer and drier conditions (Weiss and Overpeck 2005, Archer 

and Predick 2008).

•	 Increased fire activity in arid regions 

where ecosystems have not co-evolved 

with fire cycles will very likely result in the 

loss of iconic, charismatic megaflora such 

as saguaro cacti and Joshua trees (Backlund et al. 2008).

•	 Vegetation response to changing climate 

will depend on the factors that limit productivity at a particular site; for example, 

changes in growing season length may affect annual productivity, and increased nitrogen and CO2 inputs strongly influence 

forest productivity if other factors (water, 

temperature, radiation) are less limiting 

(Ryan et al. 2008).

•	 Extensive, recent piñon pine mortality in 

the southwest may represent a thresholdtype response to warming mean, maximum, minimum, and summer (June-July) 

temperatures. Ecological thresholds are 

points at which there are abrupt changes 

in ecosystem properties or processes in 

response to external conditions such as 

climate changes. Combined with fire and 

erosion, climate-induced forest die-back 

•	 The average elevation of plant species in 

the Santa Rosa mountains of southern 

California, including desert ceanothus, 

Muller oak, canyon live oak, Jeffrey pine, 

white fir, sugar sumac, creosote bush, and 

desert agave increased by an average of 65 

meters from 1977 to 2007, probably because of increased temperature and length 

of frost-free period, upward movement of 

the snowline, and occurrence of severe 

drought (Kelly and Goulden 2008).

•	 Field experiments show that semi-arid 

grasslands are capable of immediate and 

substantial responses to shifts in precipitation patterns that include changes in the 

magnitude (larger) and frequency (fewer) 

of rainfall events. Larger, less frequent 

rainfall events resulted in higher rates of 

aboveground net primary productivity 

over historical conditions, likely because 

of greater soil water content and deeper 

soil moisture penetration (Heisler-White 

et al. 2008).

Desert Agave plant at Saguaro 

National Park (Top); NPS photo. 

Yucca plant in the desert of New 

Mexico (Bottom); USFWS photo. 

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
National Park Service 11

may be causing permanent type-conversions in some southwestern ecosystems 

(CCSP: Fagre et al. 2009).

•	 High-elevation areas in New Mexico are 

potentially very vulnerable to climate 

changes, due to their large number of 

drought-sensitive species and evidence 

of susceptibility to recent warmer-drier 

conditions. Three areas that may be particularly vulnerable are the Sierra San Luis/

Peloncillo Mountains, the Jemez Mountains, and the Southern Sangre de Cristo 

Mountains (Enquist and Gori 2008).

•	 Drought-caused reductions in the number 

of piñon pines present in piñon-juniper 

woodlands are likely to be long-term, because piñons are slow-growing species 

and changes in stand dynamics and community interactions (e.g. maintenance of 

seed-dispersing birds) may prevent or delay a return to pre-drought stand conditions (Mueller et al. 2005).

What scientists think is possible....

•	 Significant portions of the current species 

range are projected to become climatically 

unfavorable for Joshua trees under climate 

change conditions. However, because elevated atmospheric CO2

 concentrations 

enhance the low-temperature tolerance 

of Joshua tree seedlings, anthropogenic 

increases in CO2 may allow for range expansion into regions with cooler climates 

than current range limits (Dole et al. 2003). 

•	 A comparison of satellite-derived land 

cover response to drought in the Great 

Basin suggests that valley ecosystems may 

be more resilient and montane ecosystems 

more susceptible to prolonged drought, 

including decreased growth and increased 

mortality, and increased susceptibility to 

invasion by exotic weeds (Bradley and 

Mustard 2008).

•	 Predictive modeling of the potential distribution of plant communities in Saguaro National Park East, Arizona, suggests 

that increasing temperatures will lead to 

upslope movement of communities and 

increase the area of desert scrub at the 

expense of montane conifer forests. Increased precipitation may mitigate some 

effects of temperature changes, depending 

on the timing and magnitude of rainfall 

events (Kupfer et al. 2005).

•	 Models suggest that populations of the 

federally endangered Arizona cliffrose in 

the central Arizona upper Sonoran Desert 

are slowly declining, and will be at greater 

risk of extinction with increased aridity. 

Favorable local site conditions (high soil 

moisture, low sand content, northern aspects) can mitigate extinction risk, suggesting important conservation strategies 

under climate change conditions (Maschinski et al. 2006).

•	 The potential ranges of arid plant species 

in the southwest are predicted to shift in 

response to increases in mean temperatures of the coldest month (the physiological parameter that commonly limits the 

range of North American tree species) 

Shifts include: big sagebrush - northward 

shift and contraction of current range; 

Joshua tree - fragmentation of current 

range and northward and eastward shift; 

saguaro - expansion and divergence of 

range, with new habitat west and east of 

current range; and creosote bush - expansion throughout the intermountain west 

into areas currently dominated by sagebrush (Shafer et al. 2001).

D. WILDLIFE

What scientists know....

•	 A consistent temperature-related shift has 

been observed across a broad range of 

plant and animal species (80% of species 

from 143 studies), including changes in 

species density, northward or poleward 

range shifts, changes in phenology, and 

shifts in genetic frequencies (Root et al. 

2003).

•	 A retrospective analysis of desert bighorn 

sheep population dynamics from 1941 to 

1976 on the San Andres National Wildlife 

Refuge, New Mexico indicates that belowaverage precipitation limited population 

size through regulation of forage and production and survival of lambs. When total 

annual precipitation was <28.2 cm, carrying capacity for desert bighorn sheep on 

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

Drought conditions are especially hard on Willow Flycatchers (Top); USFWS photo. YellowBellied Marmot making a living 

at 11,000 feet in Cedar Breaks 

National Monument. Marmots 

have already gone extinct in 

some ranges; NPS photo. 
12 Climate Change Talking Points NPS/FWS—2010

the refuge was zero (Bender and Weisenberger 2005).

•	 At least 26 populations of desert bighorn 

sheep have gone extinct from mountain 

ranges in the desert regions of California. 

These extinctions occurred in conjunction 

with a 20% decrease in precipitation and 

1oC increase in average temperature during the last half of the 20th century (Epps 

et al. 2004, Epps et al. 2006).

•	 A severe drought in central Arizona in 

2002 resulted in a reduced insect prey 

base and near total reproductive failure for 

the Southwestern Willow Flycatcher, an 

insectivorous Neotropical migratory bird 

that is restricted in its breeding sites to 

riparian habitats in the southwestern U.S. 

This suggests that events such as regional 

droughts that influence the overall abundance of insects may also be critical drivers of productivity for Willow Flycatchers 

(Durst et al. 2008). 

•	 Drought-related physiological stress has 

been observed to impair immune function 

in cavity-nesting Western Bluebirds, Ashthroated Flycatchers, and Violet-green 

Swallows in New Mexico. Specifically, 

decreases in adult weight, reduced clutch 

sizes, reduced nestling body mass, and 

lower overall survival were observed (Fair 

and Whitaker 2008).

•	 Water availability can be a limiting factor for egg production in desert tortoises, 

and dry and drought periods may result 

in reduced reproductive behavior, low 

feeding and activity levels, and increased 

adult mortality for both male and female 

tortoises (Henen et al. 1998, Longshore et 

al. 2003).

•	 Warming temperatures are raising lower 

elevations of habitable sites for pygmy rabbits in the Great Basin, while higher-elevation sites are being increasingly impacted 

by piñon-juniper encroachment. These 

changes have resulted in extirpations of 

pygmy rabbits at lower-elevation sites and 

a 157 meter increase in the elevation of 

occupied locations (Larrucea and Brussard 2008).

What scientists think is likely....

•	 Warmer temperatures are likely contributing to losses of pika populations in the 

Great Basin. Changes in population have 

occurred at a pace significantly more rapid 

than that suggested by paleontological records; for example, extirpations have occurred in three lower elevation areas since 

1956 (Beever et al. 2003, Grayson 2005).

•	 Marmots may have gone extinct in some 

Great Basin mountain ranges during the 

20th century, potentially as the result of 

climate changes that force montane vegetation zones further upslope and reduce 

habitat area (Floyd 2004).

•	 Restoration of population connectivity 

may be necessary to buffer the effects of 

climate change on desert bighorn sheep 

in southeastern California, particularly in 

low-elevation habitats within which populations have already experienced range 

contractions and extinctions as the result 

of decreased precipitation and increased 

temperatures (Epps et al. 2006).

•	 Drought-caused loss of piñon pines from 

piñon-juniper woodlands is likely to result 

in reductions in the numbers of avian seed 

dispersers, as birds abandon stands with 

reduced cone crops (Mueller et al. 2005).

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

Below average precipitation results in lower population for the 

Desert Bighorn Sheep, such as 

this one at Dinosaur National 

Monument; NPS photo.
National Park Service 13

•	 Climate change poses the greatest future 

threat to the persistence of the Colorado 

River cutthroat trout, because changes in 

temperature and precipitation will affect 

stream temperature, steam flows, the distribution of habitat areas, and decrease 

connectivity among populations (Young 

2008).

•	 Changes in minimum and mean temperatures and amount and timing of precipitation may increase prevalence of hantavirus, 

plague, and West Nile virus in wildlife 

populations through changes in phenological development, increased rates of reproduction and survival, altered geographic 

distributions, and expansion of favorable 

habitats of disease vector, host, and reservoir species (Patz et al. 2000, Epstein 2001, 

Field et al. 2007). 

What scientists think is possible....

•	 An analysis of potential climate change 

impacts on mammalian species in U.S. 

national parks indicates that on average 

about 8% of current mammalian species 

diversity may be lost. The greatest losses 

across all parks occurred in rodent species 

(44%), bats (22%), and carnivores (19%) 

(Burns et al. 2003). 

•	 Shifts in vegetation communities and increased wildfire frequencies, both resulting from temperature and precipitation 

changes, may exacerbate habitat loss and 

increase local extirpation for the Great 

Basin pygmy rabbit, a sagebrush obligate 

species (Larrucea and Brussard 2008).

•	 Big sagebrush habitats throughout the 

western U.S. could decrease in area by 

59% before the end of the 21st century, 

with devastating consequences for sage 

grouse, mule deer, pronghorn and other species that depend on these habitats 

(Glick 2006).

•	 Predicted future drought conditions in 

the southwest may impact trout by confining populations to smaller, upstream habitat with perennial flows, including some 

streams that are currently uninhabitable 

because of cold water temperatures. The 

overall effect may be a reduction in trout 

abundance and distribution, and an increase in susceptibility to small-population phenomena such as inbreeding and 

disturbance vulnerability (Young 2008).

E. DISTURBANCE

What scientists know....

•	 Drought and warm temperatures (1996 to 

2002) in combination with outbreaks of 

the Piñon Engraver bark beetles (2002 to 

2004) have resulted in widespread mortality of piñon pine at stand, landscape, and 

regional scales throughout the southwest, 

including about 2,500,000 acres of substantial piñon dieback across the region 

(Burkett et al. 2005, Allen 2007).

•	 The current insect outbreak among Ponderosa and piñon pines in the Pinaleño 

Mountains of southern Arizona is an order of magnitude larger (millions of acres 

affected) and more severe than an outbreak in 1957 (490,000 acres affected) that 

followed an extreme drought from 1955 

to 1957. Probable causes are increasingly 

warm maximum, winter, and annual average temperatures that stress trees and 

increase the length of the beetle breeding 

season and a drop in the number of frost 

days that decreases opportunities to kill 

off overwintering insect populations (Lenart et al. 2007).

•	 Soil dryness and air temperatures increased in the southwest over the 20th 

Fire rages through the Joshua 

Trees in July 2006 at Mojave 

National Preserve. Increased 

drought gives opportunities for 

invasive plants to invade, which 

then increase the fire cycle. NPS 

photo.

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience
14 Climate Change Talking Points NPS/FWS—2010

•	 Increased fire frequency and fire size in 

the Mojave Desert between 1980 and 2004 

has been linked to invasion of non-native 

grasses. Changes in fire history are especially evident in middle elevation shrublands dominated by creosotebush, Joshua 

tree, and/or blackbrush, where high rainfall years result in rapid and dense growth 

of non-native annual grasses (Brooks and 

Matchett 2006).

•	 Wetter conditions and increased periodicity of high rainfall events facilitate 

the spread of the invasive Sahara mustard throughout the Mojave and lower 

Sonoran deserts, at the expense of native 

plant populations. Drier conditions limit 

spread of Sahara mustard, but may have 

other negative consequences for native 

flora and fauna (Barrows et al. 2009). 

What scientists think is likely....

•	 Increases in frequency, size, and duration 

of wildfires in the western U.S. observed 

within the past three decades are attributed to a 78-day increase in the length of the 

wildfire season, increases in spring-summer temperatures of 0.87oC, and earlier 

spring snowmelt (Westerling et al. 2006). 

•	 Climate changes have very likely increased 

the size and number of forest fires, insect 

outbreaks, and tree mortality in the interior West and the Southwest, and will 

continue to do so as climate changes continue (Backlund et al. 2008).

•	 By 2070 the length of the fire season could 

be increased by two to three weeks in the 

northern Rockies, Great Basin, and Southwest as the result of increases in summer 

temperature and decreases in summer humidity (Barnett et al. 2004).

•	 Analysis of a twenty-year time series of 

satellite imagery for the Gila National Forest, New Mexico, suggests that burned 

area and severity of wildfires is related to 

the timing and intensity of rainfall events 

during the fire season, such that longer 

rain-free periods increase the likelihood 

that fires will burn as high-severity crown 

fires (Holden et al. 2007).

century, making the region more susceptible to forest fires (Groisman et al. 2004).

•	 There is strong synchrony between climate and wildfires in forested ecosystems 

of western North America; changes in 

temperature and precipitation will result 

in longer fire seasons and more frequent 

episodes of extreme fire weather (Ryan et 

al. 2008).

•	 The forested area burned in the western 

U.S. from 1987 to 2003 was more than six 

and a half times the area burned from 1970 

to 1986. Other observed trends include 

more frequent large wildfires (greater than 

400 ha in size), longer wildfire durations, 

and longer wildfire seasons (Westerling et 

al. 2006).

•	 A large area (approximately 120,000 km2) 

of California and western Nevada experienced a notable increase in the extent of 

forest stand-replacing (high severity) fire 

and increases in mean and maximum fire 

size and area burned annually between 

1984 and 2006. These changes in fire 

severity and activity are attributed to a 

regional increase in temperature and a 

long-term increase in annual precipitation 

(Miller et al. 2008).

•	 Climate change in arid lands will create 

physical conditions conducive to wildfire, 

and the proliferation of exotic grasses will 

provide fuel, resulting in a self-reinforcing 

increase in fire frequencies (Backlund et 

al. 2008).

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

Saguaro National Park’s iconic 

species, the saguaro cactus, is 

severely threatened by the invasion of buffelgrass; NPS photo.
National Park Service 15

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

•	 Large outbreaks of forest insects are likely 

influenced by observed increases in temperature because temperature controls life 

cycle development rates, influences synchronization of mass attacks required to 

overcome tree defenses, and determines 

winter mortality rates. Climate also affects 

insect populations indirectly through effects on hosts; for example, drought stress 

reduces the ability of a tree to mount a 

defense against insect attacks (Logan and 

Powell 2001, Ryan 2008).

•	 Climate change is likely to lead to a northern migration of weeds. Many weeds respond positively to increasing CO2, and 

recent research also suggests that glyphosate, the most widely used herbicide in the 

U.S., loses its efficacy on weeds grown at 

the increased CO2 levels likely in the coming decades (Backlund et al. 2008).

•	 Interactions between climate change and 

non-native invasive species may increase 

invasion risk to native ecosystems through 

expansion of habitat areas climatically 

suitable for invasion. Climate change may 

also create opportunities for ecosystem 

restoration on invaded lands that become 

climatically unsuitable for invasive species 

(Bradley 2009).

What scientists think is possible....

•	 Predicted trends in climate will reinforce 

the tendency toward longer fire seasons 

and accentuate conditions favorable to the 

occurrence of large, intense wildfires (e.g. 

increased storminess, higher fuel loads, 

drier conditions late in the season) (Lenihan et al. 2003, Whitlock et al. 2003, Westerling et al. 2006). 

•	 Changes in relative humidity, especially 

drying over much of the West, are projected to increase the number of days of 

high fire danger at least through the year 

2089, as compared to a 1975 to 1996 base 

period, under a business-as-usual emissions scenario. The regions most affected 

are the northern Rockies, Great Basin and 

the Southwest (Brown et al. 2004).

•	 Variable projections in the amount and 

timing of precipitation strongly influence 

prediction models for invasive species. 

For example, a bioclimatic envelope model indicates that decreased precipitation, 

particularly in the summer, may result in 

an expansion of suitable land area for invasive cheatgrass by up to 45%, elevating 

invasion risk in parts of Montana, Wyoming, Utah, and Colorado. Conversely, 

increased precipitation reduces suitable 

habitat by as much as 70%, decreasing 

invasion risk (Bradley 2009).

•	 Despite the uncertainty in future climate 

conditions, prediction models show consistent areas that maintain climate suitability for cheatgrass invasion, including parts 

of Nevada, the Snake River plain in Idaho, 

western Utah, and eastern Oregon. Under 

most future climate conditions, these areas will continue to be at risk of cheatgrass 

invasion (Bradley 2009).

F. VISITOR EXPERIENCE

•	 The tourism industry in the western U.S. 

is particularly sensitive to climate change 

because it is so strongly oriented towards 

outdoor activities. Climate changes will 

likely reduce the seasonal period for winter activities such as skiing, but may increase winter visitation for activities such 

as hiking and sight-seeing. The period for 

summer activities may increase because 

of an increase in the number of warm 

shoulder season days, but could also decrease due to increasing aridity and high 

temperatures in mid-summer (Smith et al. 

2001, Wagner 2003).

•	 Climate simulations for 2045 to 2055 suggest that warming, increased solar radiation, reduced rainfall frequency, increased 

stagnation occurrence, and reduced ventilation may negatively affect air quality in 

the western U.S., especially during the fall 

season (Leung and Gustafson 2005).

•	 Direct effects of projected climate changes 

on human health include increased incidence of heat stress and heat stroke, 

respiratory distress from pollutants released during wildfires, cardio-respiratory 

morbidity and mortality associated with 

ground-level ozone, and injury and death 

from floods, storms, fires, and droughts 

(Epstein 2001, Confalonieri et al. 2007). 
16 Climate Change Talking Points NPS/FWS—2010

Temperature Water Cycle Vegetation Wildlife Disturbance Visitor Experience

•	 Climate changes may favor zoonotic disease transmission to humans through 

altered distributions of pathogens and 

disease vectors, increased populations of 

reservoir or host species, and increased 

prevalence of diseases within host and 

reservoir populations. Diseases likely to 

increase in scope and/or incidence in the 

region include hantavirus pulmonary syndrome, plague, and West Nile virus (Epstein 2001, Confalonieri et al. 2007).

•	 Increasing water demands combined with 

decreasing supply are very likely to result 

in over-allocation of water resources for 

humans and ecosystems. Higher temperatures and growth of southwestern cities 

may result in additional demands for agricultural and home users, higher water 

prices, and water shortages (Lenart et al. 

2007).

•	 Increased summer temperatures will lead 

to increased utility expenditures in parks 

in the summer and, potentially, decreases 

in the winter.

•	 Potentially poorer visibility due to smoke 

from increased wildland fire activity will 

likely cause a negative impact on visitor 

experiences.

•	 Reduced runoff, particularly when combined with higher demands due to hotter 

and drier conditions, will very likely make 

allocation of water supplies a critical issue 

for the West. It is likely that instream uses 

such as hydropower and recreation will be 

among those most affected by a reduction 

in runoff (Smith et al. 2001).

G. CULTURAL RESOURCES

•	 Cultural resources such as pueblos, cliff 

dwellings, churches, and forts, already 

susceptible to damage from natural erosive forces, may be at additional risk from 

increased wildfires and extreme precipitation events likely to occur with climatic 

change. The following have been identified as resources in “immediate, imminent danger”: Grand Canyon National 

Park and Canyon de Chelly, Casa Grande, 

and Navajo national monuments (AZ); 

Bandelier, Gila Cliff Dwellings, and Fort 

Union national monuments and Chaco 

Culture National Historical Park (NM); 

Canyonlands and Zion national parks and 

Glen Canyon National Recreation Area 

(UT); Mesa Verde National Park and 

Colorado, Dinosaur, and Hovenweep national monuments(CO); Mojave National 

Preserve and Death Valley National Park 

(CA); Fort Laramie National Historic Site 

(WY); and Big Bend National Park and 

San Antonio Missions National Historical 

Park (TX) (Saunders et al. 2007).

•	 Increasing frequency and intensity of severe storms and floods may pose threats to 

historic structures, roads and trails, archeological sites, administrative facilities, and 

other park resources and infrastructure.

Hikers in Capitol Reef National 

Park; NPS photo.
National Park Service 17

III. No Regrets Actions: How Individuals, Parks, Refuges, and 

Their Partners Can Do Their Part

Individuals, businesses, and agencies release carbon dioxide (CO2), the principal greenhouse gas, through burning of fossil 

fuels for electricity, heating, transportation, food production, and other day-to-day activities. Increasing levels of atmospheric 

CO2 have measurably increased global average temperatures, and are projected to cause further changes in global climate, with 

severe implications for vegetation, wildlife, oceans, water resources, and human populations. Emissions reduction – limiting 

production of CO2 and other greenhouse gases - is an important step in addressing climate change. It is the responsibility of 

agencies and individuals to find ways to reduce greenhouse gas emissions and to educate about the causes and consequences 

of climate change, and ways in which we can reduce our impacts on natural resources. There are many simple actions that each 

of us can take to reduce our daily carbon emissions, some of which will even save money.

Agencies Can...

Improve sustainability and 

energy efficiency

•	 Use energy efficient products, such as 

ENERGY STAR® approved office equipment and light bulbs.

•	 Initiate an energy efficiency program to 

monitor energy use in buildings. Provide 

guidelines for reducing energy consumption. Conserve water.

•	 Convert to renewable energy sources 

such as solar or wind generated power.

•	 Specify “green” designs for construction 

of new or remodeled buildings.

•	 Include discussions of climate change in 

the park Environmental Management 

System. 

•	 Conduct an emmisions inventory and set 

goals for CO2 reduction.

•	 Provide alternative transportation options such as employee bicycles and shuttles for within-unit commuting. 

•	 Provide hybrid electric or propane-fueled 

vehicles for official use, and impose fuel 

standards for park vehicles. Reduce the 

number and/or size of park vehicles and 

boats to maximize efficiency.

•	 Provide a shuttle service or another form 

of alternate transportation for visitor and 

employee travel to and within the unit. 

•	 Provide incentives for use of alternative 

transportation methods.

•	 Use teleconferences and webinars or other 

forms of modern technology in place of 

travel to conferences and meetings.

Implement Management Actions

•	 Engage and enlist collaborator support 

(e.g., tribes, nearby agencies, private landholders) in climate change discussions, responses, adaptation and mitigation. 

•	 Develop strategies and identify priorities 

for managing uncertainty surrounding climate change effects in parks and refuges.

•	 Dedicate funds not only to sustainable 

actions but also to understanding the impacts to the natural and cultural resources.

•	 Build a strong partnership-based foundation for future conservation efforts.

•	 Identify strategic priorities for climate 

change efforts when working with partners.

•	 Incorporate anticipated climate change 

impacts, such as decreases in lake levels 

or changes in vegetation and wildlife, into 

management plans.

An interpretive brochure about 

climate change impacts to National Parks was created in 2006 

and was distributed widely. This 

brochure was updated in 2008.
18 Climate Change Talking Points NPS/FWS—2010

•	 Encourage climate change research and 

scientific study in park units and refuges. 

•	 Design long-term monitoring projects and 

management activities that do not rely 

solely on fossil fuel-based transportation 

and infrastructure.

•	 Incorporate products and services that address climate change in the development 

of all interpretive and management plans. 

•	 Take inventory of the facilities/boundaries/species within your park or refuge that 

may benefit from climate change mitigation or adaptation activities.

•	 Participate in gateway community sustainability efforts.

•	 Recognize the value of ecosystem services 

that an area can provide, and manage the 

area to sustain these services. Conservation is more cost-effective than restoration 

and helps maintain ecosystem integrity.

•	 Provide recycling options for solid waste 

and trash generated within the park.

Restore damaged landscapes

•	 Strategically focus restoration efforts, both 

in terms of the types of restoration undertaken and their national, regional, and 

local scale and focus, to help maximize 

resilience.

•	 Restore and conserve connectivity within 

habitats, protect and enhance instream 

flows for fish, and maintain and develop 

access corridors to climate change refugia. 

•	 Restoration efforts are important as a 

means for enhancing species’ ability to 

cope with stresses and adapt to climatic 

and environmental changes. Through restoration of natural areas, we can lessen climate change impacts on species and their 

habitats. These efforts will help preserve 

biodiversity, natural resources, and recreational opportunities.

•	 Address climate change impacts to cultural 

resources by taking actions to document, 

preserve, and recover them. 

Educate staff and the public

•	 Post climate change information in easily accessible locations such as on bulletin 

boards and websites.

•	 Provide training for park and refuge employees and partners on effects of climate 

change on resources, and on dissemination of climate change knowledge to the 

public.

•	 Support the development of region, park, 

or refuge-specific interpretive products on 

the impacts of climate change. 

•	 Incorporate climate change research and 

information in interpretive and education 

outreach programming.

•	 Distribute up-to-date interpretive products (e.g., the National Park Service-wide 

Climate Change in National Parks brochure).

•	 Develop climate change presentations for 

local civic organizations, user and partner 

conferences, national meetings, etc.

•	 Incorporate climate change questions and 

answers into Junior Ranger programs.

•	 Help visitors make the connection between reducing greenhouse gas emissions 

and resource stewardship.

•	 Encourage visitors to use public or nonmotorized transportation to and around 

parks.

Park Service employees install 

solar panels at San Francisco 

Maritime National Historical 

Park (Top); At the National Mall, 

Park Service employees use 

clean-energy transportation to 

lead tours; NPS photos. 
National Park Service 19

The Climate Friendly Parks 

Program is a joint partnership 

between the U.S. Environmental Protection Agency and the 

National Park Service. Climate 

Friendly Parks from around the 

country are leading the way in 

the effort to protect our parks’ 

natural and cultural resources 

and ensure their preservation 

for future generations; NPS image. 

•	 Encourage visitors to reduce their carbon 

footprint in their daily lives and as part of 

their tourism experience.

Individuals can...

•	 In the park or refuge park their car and 

walk or bike. Use shuttles where available. 

Recycle and use refillable water bottles. 

Stay on marked trails to help further ecosystem restoration efforts.

•	 At home, walk, carpool, bike or use public transportation if possible. A full bus 

equates to 40 fewer cars on the road. 

When driving, use a fuel-efficient vehicle.

•	 Do not let cars idle - letting a car idle for 

just 20 seconds burns more gasoline than 

turning it off and on again.

•	 Replace incandescent bulbs in the five 

most frequently used light fixtures in the 

home with bulbs that have the ENERGY 

STAR® rating. If every household in the 

U.S. takes this one simple action we will 

prevent greenhouse gas emissions equivalent to the emissions from nearly 10 million cars, in addition to saving money on 

energy costs.

Reduce, Reuse, Recycle, Refuse

•	 Use products made from recycled paper, 

plastics and aluminum - these use 55-95% 

less energy than products made from 

scratch. 

•	 Purchase a travel coffee mug and a reusable water bottle to reduce use of disposable products (Starbucks uses more than 1 

billion paper cups a year). 

•	 Carry reusable bags instead of using paper 

or plastic bags. 

•	 Recycle drink containers, paper, newspapers, electronics, and other materials. Bring recyclables home for proper 

disposal when recycle bins are not available. Rather than taking old furniture and 

clothes to the dump, consider “recycling” 

them at a thrift store. 

•	 Keep an energy efficient home. Purchase 

ENERGY STAR® appliances, properly 

insulate windows, doors and attics, and 

lower the thermostat in the winter and 

raise it in the summer (even 1-2 degrees 

makes a big difference). Switch to green 

power generated from renewable energy 

sources such as wind, solar, or geothermal.

•	 Buy local goods and services that minimize 

emissions associated with transportation.

•	 Encourage others to participate in the actions listed above.

•	 Conserve water.

For more information on how you can reduce carbon emissions and engage in climatefriendly activities, check out these websites:

EPA- What you can do: http://www.epa.gov/

climatechange/wycd/index.html

NPS- Do Your Part! Program: http://www.

nps.gov/climatefriendlyparks/doyourpart.

html

US Forest Service Climate Change Program: 

http://www.fs.fed.us/climatechange/

United States Global Change Research Program: http://www.globalchange.gov/

U.S. Fish and Wildlife Service Climate change: 

http://www.fws.gov/home/climatechange/

“Humankind has not 

woven the web of life. 

We are but one thread 

within it. Whatever we 

do to the web, we do 

to ourselves. All things 

are bound together. 

All things connect.”

 —Chief Seattle
20 Climate Change Talking Points NPS/FWS—2010

IV. Global Climate Change

The IPCC is a scientific intergovernmental, international body established by the World Meteorological Organization (WMO) 

and by the United Nations Environment Programme (UNEP). The information the IPCC provides in its reports is based on 

scientific evidence and reflects existing consensus viewpoints within the scientific community. The comprehensiveness of the 

scientific content is achieved through contributions from experts in all regions of the world and all relevant disciplines including, where appropriately documented, industry literature and traditional practices, and a two stage review process by experts 

and governments.

Definition of climate change: The IPCC defines climate change as a change in the state of the climate that can be identified (e.g. 

using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, 

typically decades or longer. All statements in this section are synthesized from the IPCC report unless otherwise noted.

A. Temperature and 

Greenhouse Gases

What scientists know...

•	 Warming of the Earth’s climate system is 

unequivocal, as evidenced from increased 

air and ocean temperatures, widespread 

melting of snow and ice, and rising global 

average sea level (Figure 1).

•	 In the last 100 years, global average surface 

temperature has risen about 0.74°C over 

the previous 100-year period, and the rate 

of warming has doubled from the previous 

century. Eleven of the 12 warmest years in 

the instrumental record of global surface 

temperature since 1850 have occurred 

since 1995 (Figure 1).

•	 Although most regions over the globe have 

experienced warming, there are regional 

variations: land regions have warmed faster than oceans and high northern latitudes 

have warmed faster than the tropics. Average Arctic temperatures have increased 

at almost twice the global rate in the past 

100 years, primarily because loss of snow 

and ice results in a positive feedback via 

increased absorption of sunlight by ocean 

waters (Figure 2).

•	 Over the past 50 years widespread changes 

in extreme temperatures have been observed, including a decrease in cold days 

and nights and an increase in the frequency of hot days, hot nights, and heat waves.

•	 Winter temperatures are increasing more 

rapidly than summer temperatures, particularly in the northern hemisphere, and 

Figure 1. Observed changes in (a) global average surface temperature; (b) 

global average sea level from tide gauge (blue) and satellite (red) data and (c) 

Northern Hemisphere snow cover for March-April. All differences are relative 

to corresponding averages for the period 1961-1990. Smoothed curves represent decadal averaged values while circles show yearly values. The shaded 

areas are the uncertainty intervals estimated from a comprehensive analysis of 

known uncertainties (a and b) and from the time series (c) (IPCC 2007a).
National Park Service 21

there has been an increase in the length 

of the frost-free period in mid- and highlatitude regions of both hemispheres.

•	 Climate change is caused by alterations in 

the energy balance within the atmosphere 

and at the Earth’s surface. Factors that 

affect Earth’s energy balance are the atmospheric concentrations of greenhouse 

gases and aerosols, land surface properties, 

and solar radiation. 

•	 Global atmospheric concentrations of 

greenhouse gases have increased significantly since 1750 as the result of human 

activities. The principal greenhouse gases 

are carbon dioxide (CO2), primarily from 

fossil fuel use and land-use change; methane (CH4) and nitrous oxide (N2O), primarily from agriculture; and halocarbons 

(a group of gases containing fluorine, chlorine or bromine), principally engineered 

chemicals that do not occur naturally.

•	 Direct measurements of gases trapped in 

ice cores demonstrate that current CO2 

and CH4 concentrations far exceed the 

natural range over the last 650,000 years 

and have increased markedly (35% and 

148% respectively), since the beginning of 

the industrial era in 1750.

•	 Both past and future anthropogenic CO2 

emissions will continue to contribute to 

warming and sea level rise for more than 

a millennium, due to the time scales required for the removal of the gas from the 

atmosphere. 

Figure 2. Comparison of observed continental- and globalscale changes in surface temperature with results simulated 

by climate models using either 

natural or both natural and anthropogenic forcings. Decadal 

averages of observations are 

shown for the period 1906-2005 

(black line) plotted against the 

centre of the decade and relative to the corresponding average for the period 1901-1950. 

Lines are dashed where spatial 

coverage is less than 50%. Blue 

shaded bands show the 5 to 

95% range for 19 simulations 

from five climate models using 

only the natural forcings due 

to solar activity and volcanoes. 

Red shaded bands show the 5 

to 95% range for 58 simulations 

from 14 climate models using 

both natural and anthropogenic 

forcings (IPCC 2007a).
22 Climate Change Talking Points NPS/FWS—2010

•	 Warming temperatures reduce oceanic uptake of atmospheric CO2, increasing the 

fraction of anthropogenic emissions remaining in the atmosphere. This positive 

carbon cycle feedback results in increasingly greater accumulation of atmospheric 

CO2 and subsequently greater warming 

trends than would otherwise be present in 

the absence of a feedback relationship.

•	 There is very high confidence that the 

global average net effect of human activities since 1750 has been one of warming.

•	 Scientific evidence shows that major and 

widespread climate changes have occurred with startling speed. For example, 

roughly half the north Atlantic warming 

during the last 20,000 years was achieved 

in only a decade, and it was accompanied 

by significant climatic changes across most 

of the globe (NRC 2008).

What scientists think is likely...

•	 Anthropogenic warming over the last 

three decades has likely had a discernible 

influence at the global scale on observed 

changes in many physical and biological 

systems. 

•	 Average temperatures in the Northern 

Hemisphere during the second half of the 

20th century were very likely higher than 

during any other 50-year period in the last 

500 years and likely the highest in at least 

the past 1300 years. 

•	 Most of the warming that has occurred 

since the mid-20th century is very likely 

due to increases in anthropogenic greenhouse gas concentrations. Furthermore, 

it is extremely likely that global changes 

observed in the past 50 years can only be 

explained with external (anthropogenic) 

forcings (influences) (Figure 2). 

•	 There is much evidence and scientific consensus that greenhouse gas emissions will 

continue to grow under current climate 

change mitigation policies and development practices. For the next two decades 

a warming of about 0.2oC per decade is 

projected for a range of emissions scenarios; afterwards, temperature projections 

increasingly depend on specific emissions 

scenarios (Table 1). 

•	 It is very likely that continued greenhouse 

gas emissions at or above the current rate 

will cause further warming and result in 

changes in the global climate system that 

will be larger than those observed during 

the 20th century.

•	 It is very likely that hot extremes, heat 

waves and heavy precipitation events will 

become more frequent. As with current 

trends, warming is expected to be greatest 

over land and at most high northern latitudes, and least over the Southern Ocean 

(near Antarctica) and the northern North 

Atlantic Ocean.

What scientists think is possible...

•	 Global temperatures are projected to increase in the future, and the magnitude of 

temperature change depends on specific 

emissions scenarios, and ranges from a 

1.1oC to 6.4oC increase by 2100 (Table 1). 

Table 1. Projected global average surface warming at the 

end of the 21st century, adapted 

from (IPCC 2007b).

Notes: a) Temperatures are 

assessed best estimates and 

likely uncertainty ranges 

from a hierarchy of models of 

varying complexity as well as 

observational constraints. b) 

Temperature changes are expressed as the difference from 

the period 1980-1999. To express the change relative to the 

period 1850-1899 add 0.5°C. c) 

Year 2000 constant composition 

is derived from AtmosphereOcean General Circulation Models (AOGCMs) only. 

Temperature Change (°C at 2090 – 2099 relative to 

1980 – 1999)a,b

Emissions Scenario Best Estimate Likely Range

Constant Year 2000 

Concentrationsa 0.6 0.3 – 0.9

B1 Scenario 1.8 1.1 – 2.9

B2 Scenario 2.4 1.4 – 3.8

A1B Scenario 2.8 1.7 – 4.4

A2 Scenario 3.4 2.0 – 5.4

A1F1 Scenario 4.0 2.4 – 6.4
National Park Service 23

Figure 3. Sea ice concentrations 

(the amount of ice in a given 

area) simulated by the GFDL 

CM2.1 global coupled climate 

model averaged over August, 

September and October (the 

months when Arctic sea ice concentrations generally are at a 

minimum). Three years (1885, 

1985 & 2085) are shown to illustrate the model-simulated 

trend. A dramatic reduction of 

summertime sea ice is projected, 

with the rate of decrease being 

greatest during the 21st century 

portion. The colors range from 

dark blue (ice free) to white 

(100% sea ice covered); Image 

courtesy of NOAA GFDL.

•	 Anthropogenic warming could lead to 

changes in the global system that are 

abrupt and irreversible, depending on the 

rate and magnitude of climate change.

•	 Roughly 20-30% of species around the 

globe could become extinct if global average temperatures increase by 2 to 3oC over 

pre-industrial levels.

B. Water, Snow, and Ice

What scientists know...

•	 Many natural systems are already being affected by increased temperatures, particularly those related to snow, ice, and frozen 

ground. Examples are decreases in snow 

and ice extent, especially of mountain glaciers; enlargement and increased numbers 

of glacial lakes; decreased permafrost extent; increasing ground instability in permafrost regions and rock avalanches in 

mountain regions; and thinner sea ice and 

shorter freezing seasons of lake and river 

ice (Figure 3).

•	 Annual average Arctic sea ice extent hasshrunk by 2.7% per decade since 1978, and 

the summer ice extent has decreased by 

7.4% per decade. Sea ice extent during the 

2007 melt season plummeted to the lowest 

levels since satellite measurements began 

in 1979, and at the end of the melt season 

September 2007 sea ice was 39% below 

the long-term (1979-2000) average (NSIDC 

2008)(Figure 4).

•	 Global average sea level rose at an average 

rate of 1.8 mm per year from 1961 to 2003 

and at an average rate of 3.1 mm per year 

from 1993 to 2003. Increases in sea level 

since 1993 are the result of the following 

contributions: thermal expansion, 57%; 

melting glaciers and ice caps, 28%, melting 

polar ice sheets, 15%. 

•	 The CO2 content of the oceans increased 

by 118 ± 19 Gt (1 Gt = 109 tons) between 

A.D. 1750 (the end of the pre-industrial 

period) and 1994 as the result of uptake 

of anthropogenic CO2 emissions from the 

atmosphere, and continues to increase 

by about 2 Gt each year (Sabine et al. 

2004; Hoegh-Guldberg et al. 2007). This 

Figure 4. Arctic sea ice in September 2007 (blue line) is far below the previous low 

record year of 2005 (dashed line), and was 39% below where we would expect to be 

in an average year (solid gray line). Average September sea ice extent from 1979 to 

2000 was 7.04 million square kilometers. The climatological minimum from 1979 to 

2000 was 6.74 million square kilometers (NSIDC 2008).
24 Climate Change Talking Points NPS/FWS—2010

increase in oceanic CO2 has resulted in 

a 30% increase in acidity (a decrease in 

surface ocean pH by an average of 0.1 

units), with observed and potential severe 

negative consequences for marine organisms and coral reef formations (Orr et al. 

2005: McNeil and Matear 2007; Riebesell 

et al. 2009).

•	 Oceans are noisier due to ocean acidification reducing the ability of seawater 

to absorb low frequency sounds (noise 

from ship traffic and military activities). 

Low-frequency sound absorption has decreased over 10% in both the Pacific and 

Atlantic over the past 200 years. An assumed additional pH drop of 0.3 (due 

to anthropogenic CO2 emissions) accompanied with warming will lead to sound 

absorption below 1 kHz being reduced by 

almost half of current values (Hester et. al. 

2008).

•	 Even if greenhouse gas concentrations are 

stabilized at current levels thermal expansion of ocean waters (and resulting sea 

level rise) will continue for many centuries, 

due to the time required to transport heat 

into the deep ocean.

•	 Observations since 1961 show that the 

average global ocean temperature has increased to depths of at least 3000 meters, 

and that the ocean has been taking up 

over 80% of the heat added to the climate 

system.

•	 Hydrologic effects of climate change include increased runoff and earlier spring 

peak discharge in many glacier- and snowfed rivers, and warming of lakes and rivers. 

•	 Runoff is projected to increase by 10 to 

40% by mid-century at higher latitudes 

and in some wet tropical areas, and to decrease by 10 to 30% over some dry regions 

at mid-latitudes and dry tropics. Areas in 

which runoff is projected to decline face a 

reduction in the value of the services provided by water resources. 

•	 Precipitation increased significantly from 

1900 to 2005 in eastern parts of North 

and South America, northern Europe, and 

northern and central Asia. Conversely, 

precipitation declined in the Sahel, the 

Mediterranean, southern Africa, and parts 

of southern Asia (Figure 5).

What scientists think is likely....

•	 Widespread mass losses from glaciers and 

reductions in snow cover are projected 

to accelerate throughout the 21st century, 

reducing water availability and changing 

seasonality of flow patterns.

•	 Model projections include contraction of 

snow cover area, widespread increases 

in depth to frost in permafrost areas, and 

Arctic and Antarctic sea ice shrinkage.

•	 The incidence of extreme high sea level 

has likely increased at a broad range of 

sites worldwide since 1975. 

•	 Based on current model simulations it is 

very likely that the meridional overturning 

circulation (MOC) of the Atlantic Ocean 

will slow down during the 21st century; 

nevertheless regional temperatures are 

predicted to increase. Large-scale and 

persistent changes in the MOC may result 

in changes in marine ecosystem producFigure 5. Relative changes in 

precipitation (in percent) for 

the period 2090-2099, relative 

to 1980-1999. Values are multimodel averages based on the 

SRES A1B scenario for December 

to February (left) and June to 

August (right). White areas are 

where less than 66% of the 

models agree in the sign of the 

change and stippled areas are 

where more than 90% of the 

models agree in the sign of the 

change (IPCC 2007a).

December to February June to August
National Park Service 25

tivity, fisheries, ocean CO2 uptake, and 

terrestrial vegetation.

•	 Globally the area affected by drought has 

likely increased since the 1970s and the 

frequency of extreme precipitation events 

has increased over most areas.

•	 Future tropical cyclones (typhoons and 

hurricanes) are likely to become more 

intense, with larger peak wind speeds and 

increased heavy precipitation. Extra-tropical storm tracks are projected to move 

poleward, with consequent shifts in wind, 

precipitation, and temperature patterns.

•	 Increases in the amount of precipitation 

are very likely in high latitudes and decreases are likely in most subtropical land 

regions, continuing observed patterns 

(Figure 5).

•	 Increases in the frequency of heavy precipitation events in the coming century are 

very likely, resulting in potential damage 

to crops and property, soil erosion, surface and groundwater contamination, and 

increased risk of human death and injury.

What scientists think is possible...

•	 Arctic late-summer sea ice may disappear 

almost entirely by the end of the 21st century (Figure 3).

•	 Current global model studies project that 

the Antarctic ice sheet will remain too cold 

for widespread surface melting and gain 

mass due to increased snowfall. However, 

net loss of ice mass could occur if dynamical ice discharge dominates the ice sheet 

mass balance.

•	 Model-based projections of global average sea level rise at the end of the 21st 

century range from 0.18 to 0.59 meters, 

depending on specific emissions scenarios 

(Table 2). These projections may actually 

underestimate future sea level rise because 

they do not include potential feedbacks or 

full effects of changes in ice sheet flow. 

•	 Partial loss of ice sheets and/or the thermal 

expansion of seawater over very long time 

scales could result in meters of sea level 

rise, major changes in coastlines and inundation of low-lying areas, with greatest 

effects in river deltas and low-lying islands.

C. Vegetation and Wildlife

What scientists know...

•	 Temperature increases have affected Arctic and Antarctic ecosystems and predator 

species at high levels of the food web.

•	 Changes in water temperature, salinity, 

oxygen levels, circulation, and ice cover 

in marine and freshwater ecosystems have 

resulted in shifts in ranges and changes 

in algal, plankton, and fish abundance in 

high-latitude oceans; increases in algal and 

zooplankton abundance in high-latitude 

and high-altitude lakes; and range shifts 

and earlier fish migrations in rivers. 

•	 High-latitude (cooler) ocean waters are 

currently acidified enough to start dissolving pteropods; open water marine snails 

Table 2. Projected global average sea level rise at the end of 

the 21st century, adapted from 

IPCC 2007b.

Notes: a) Temperatures are assessed best estimates and likely 

uncertainty ranges from a hierarchy of models of varying complexity as well as observational 

constraints.

Emissions Scenario

Sea level rise 

(m at 2090 – 2099 relative to 1980 – 1999)

Model-based range (excluding future rapid 

dynamical changes in ice flow)

Constant Year 2000 

Concentrationsa 0.3 – 0.9

B1 Scenario 1.1 – 2.9

B2 Scenario 1.4 – 3.8

A1B Scenario 1.7 – 4.4

A2 Scenario 2.0 – 5.4

A1F1 Scenario 2.4 – 6.4
26 Climate Change Talking Points NPS/FWS—2010

which are one of the primary food sources 

of young salmon and mackerel (Fabry et al. 

2008, Feely et al. 2008). In lower latitude 

(warmer) waters, by the end of this century Humboldt squid’s metabolic rate will 

be reduced by 31% and activity levels by 

45% due to reduced pH, leading to squid 

retreating at night to shallower waters to 

feed and replenish oxygen levels (Rosa 

and Seibel 2008). 

•	 A meta-analysis of climate change effects 

on range boundaries in Northern Hemisphere species of birds, butterflies, and 

alpine herbs shows an average shift of 6.1 

kilometers per decade northward (or 6.1 

meters per decade upward), and a mean 

shift toward earlier onset of spring events 

(frog breeding, bird nesting, first flowering, 

tree budburst, and arrival of migrant butterflies and birds) of 2.3 days per decade 

(Parmesan and Yohe 2003).

•	 Poleward range shifts of individual species 

and expansions of warm-adapted communities have been documented on all continents and in most of the major oceans of 

the world (Parmesan 2006).

•	 Satellite observations since 1980 indicate 

a trend in many regions toward earlier 

greening of vegetation in the spring linked 

to longer thermal growing seasons resulting from recent warming.

•	 Over the past 50 years humans have 

changed ecosystems more rapidly and extensively than in any previous period of 

human history, primarily as the result of 

growing demands for food, fresh water, 

timber, fiber, and fuel. This has resulted in 

a substantial and largely irreversible loss of 

Earth’s biodiversity 

•	 Although the relationships have not been 

quantified, it is known that loss of intact ecosystems results in a reduction in 

ecosystem services (clean water, carbon 

sequestration, waste decomposition, crop 

pollination, etc.).

What scientists think is likely...

•	 The resilience of many ecosystems is likely 

to be exceeded this century by an unprecedented combination of climate change, 

associated disturbance (flooding, drought, 

wildfire, insects, ocean acidification) and 

other global change drivers (land use 

change, pollution, habitat fragmentation, 

invasive species, resource over-exploitation) (Figure 6). 

•	 Exceedance of ecosystem resilience may 

be characterized by threshold-type responses such as extinctions, disruption of 

ecological interactions, and major changes 

in ecosystem structure and disturbance 

regimes.

•	 Net carbon uptake by terrestrial ecosystems is likely to peak before mid-century 

and then weaken or reverse, amplifying 

climate changes. By 2100 the terrestrial 

biosphere is likely to become a carbon 

source.

•	 Increases in global average temperature 

above 1.5 to 2.5°C and concurrent atmospheric CO2 concentrations are projected 

to result in major changes in ecosystem 

structure and function, species’ ecological interactions, and species’ geographical 

ranges. Negative consequences are projected for species biodiversity and ecosystem goods and services.

•	 Model projections for increased atmospheric CO2 concentration and global 

temperatures significantly exceed values 

for at least the past 420,000 years, the 

period during which more extant marine 

organisms evolved. Under expected 21st

century conditions it is likely that global 

warming and ocean acidification will compromise carbonate accretion, resulting in 

less diverse reef communities and failure 

of some existing carbonate reef structures. 

Climate changes will likely exacerbate local stresses from declining water quality and overexploitation of key species 

(Hoegh-Guldberg et al. 2007).

•	 Ecosystems likely to be significantly impacted by changing climatic conditions 

include:

i. Terrestrial – tundra, boreal forest, and 

mountain regions (sensitivity to warming); Mediterranean-type ecosystems 

and tropical rainforests (decreased 

rainfall)
National Park Service 27

Figure 6. Examples of impacts associated with projected global average surface warming. Upper panel: Illustrative examples of global 

impacts projected for climate changes (and sea level and atmospheric CO2 where relevant) associated with different amounts of increase 

in global average surface temperature in the 21st century. The black lines link impacts; broken-line arrows indicate impacts continuing with 

increasing temperature. Entries are placed so that the left-hand side of text indicates the approximate level of warming that is associated 

with the onset of a given impact. Quantitative entries for water scarcity and flooding represent the additional impacts of climate change 

relative to the conditions projected across the range of SRES scenarios A1FI, A2, B1 and B2. Adaptation to climate change is not included 

in these estimations. Confidence levels for all statements are high. Lower panel: Dots and bars indicate the best estimate and likely ranges 

of warming assessed for the six SRES marker scenarios for 2090-2099 relative to 1980-1999 (IPCC 2007a).
28 Climate Change Talking Points NPS/FWS—2010

ii. Coastal – mangroves and salt marshes 

(multiple stresses) 

iii. Marine – coral reefs (multiple stresses); 

sea-ice biomes (sensitivity to warming)

What scientists think is possible...

•	 Approximately 20% to 30% of plant and 

animal species assessed to date are at increased risk of extinction with increases in 

global average temperature in excess of 1.5 

to 2.5°C.

•	 Endemic species may be more vulnerable 

to climate changes, and therefore at higher 

risk for extinction, because they may have 

evolved in locations where paleo-climatic 

conditions have been stable.

•	 Although there is great uncertainty about 

how forests will respond to changing 

climate and increasing levels of atmospheric CO2, the factors that are most 

typically predicted to influence forests 

are increased fire, increased drought, and 

greater vulnerability to insects and disease 

(Brown 2008).

•	 If atmospheric CO2 levels reach 450 ppm 

(projected to occur by 2030–2040 at the 

current emissions rates), reefs may experience rapid and terminal decline worldwide from multiple climate change-related 

direct and indirect effects including mass 

bleaching, ocean acidification, damage to 

shallow reef communities,reduction of 

biodiversity, and extinctions. (Veron et al. 

2009). At atmospheric CO2 levels of 560 

ppmv, calcification of tropical corals is expected to decline by 30%, and loss of coral 

structure in areas of high erosion may 

outpace coral growth. With unabated CO2 

emissions, 70% of the presently known 

reef locations (including cold-water corals) will be in corrosive waters by the end 

of this century (Riebesell, et al. 2009).

D. Disturbance

What scientists know...

•	 Climate change currently contributes to 

the global burden of disease and premature death through exposure to extreme 

events and changes in water and air quality, food quality and quantity, ecosystems, 

agriculture, and economy (Parry et al. 

2007).

•	 The most vulnerable industries, settlements, and societies are generally those 

in coastal and river flood plains, those 

whose economies are closely linked with 

climate-sensitive resources, and those in 

areas prone to extreme weather events. 

•	 By 2080-2090 millions more people than 

today are projected to experience flooding 

due to sea level rise, especially those in the 

low-lying megadeltas of Asia and Africa 

and on small islands.

•	 Climate change affects the function and 

operation of existing water infrastructure 

and water management practices, aggravating the impacts of population growth, 

changing economic activity, land-use 

change, and urbanization.

What scientists think is likely...

•	 Up to 20% of the world’s population will 

live in areas where river flood potential 

could increase by 2080-2090, with major 

consequences for human health, physical 

infrastructure, water quality, and resource 

availability.

•	 The health status of millions of people is 

projected to be affected by climate change, 

through increases in malnutrition; increased deaths, disease, and injury due to 

extreme weather events; increased burden 

of diarrheal diseases; increased cardiorespiratory disease due to higher concentrations of ground-level ozone in urban 

areas; and altered spatial distribution of 

vector-borne diseases.

•	 Risk of hunger is projected to increase at 

lower latitudes, especially in seasonally 

dry and tropical regions.

What scientists think is possible...

•	 Although many diseases are projected to 

increase in scope and incidence as the 

result of climate changes, lack of appropriate longitudinal data on climate changerelated health impacts precludes definitive 

assessment.
National Park Service 29

V. References

Allen, C. D. 2007. Interactions across spatial scales among forest dieback, fire, and erosion in 

northern New Mexico landscapes. Ecosystems 10:797-808.

Archer, S. R. and K. I. Predick. 2008. Climate change and ecosystems of the southwestern United 

States. Rangelands 30:23-28.

Backlund, P., A. Janetos, D.S. Schimel, J. Hatfield, M.G. Ryan, S.R. Archer, and D. Lettenmaier, 

2008. Executive Summary. In: The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. A Report by the U.S. 

Climate Change Science Program and the Subcommittee on Global Change Research. 

Washing¬ton, DC., USA, 362 pp.

Baldwin, C. K., F. H. Wagner, and U. Lall. 2003. Water resources. Pp. 79-112 In F. H. Wagner (ed.). 

Rocky Mountain/Great Basin Regional Climate-Change Assessment. Report for the U.S. 

Global Change Research Program. Utah State University, Logan,UT: IV + 240 pp.

Barker, D. H., L. R. Stark, J. F. Zimpfer, N. D. McLetchie, and S. D. Smith. 2005. Evidence of 

drought-induced stress on biotic crust moss in the Mojave Desert. Plant, Cell & Environment 28:939-947.

Barnett, T., R. Malone, W. Pennell, D. Stammer, B. Semtner, and W. Washington. 2004. The 

effects of climate change on water resources in the west: Introduction and overview. 

Climatic Change 62:1-11.

Barnett, T. P. and D. W. Pierce. 2008. When will Lake Mead go dry? Water Resources Research 

44:W03201.

Barnett, T. P., D. W. Pierce, H. G. Hidalgo, C. Bonfils, B. D. Santer, T. Das, G. Bala, A. W. Wood, 

T. Nozawa, and A. A. Mirin. 2008. Human-induced changes in the hydrology of the 

western United States. Science 319:1080.

Barrows, C. W., E. B. Allen, M. L. Brooks, and M. F. Allen. 2009. Effects of an invasive plant on 

a desert sand dune landscape. Biological Invasions 11:673-686.

Bedford, D. 2008. Changing properties of snowpack in the Great Salt Lake basin, western United 

States, from a 26-year SNOTEL record. The Professional Geographer 60:374-386.

Beever, E. A., P. F. Brussard, and J. Berger. 2003. Patterns of apparent extirpation among isolated 

population of pikas (Ochotona princeps) in the Great Basin. Journal of Mammalogy 

84:37-54.

Bender, L. C. and M. E. Weisenberger. 2005. Precipitation, density, and population dynamics of 

desert bighorn sheep on San Andres National Wildlife Refuge, New Mexico. Wildlife 

Society Bulletin 33:956-964.

Bradley, B. A. 2009. Regional analysis of the impacts of climate change on cheatgrass invasion 

shows potential risk and opportunity. Global Change Biology 15:196-208.

Bradley, B. A. and J. F. Mustard. 2008. Comparison of phenology trends by land cover class: a 

case study in the Great Basin, USA. Global Change Biology 14:334-346.
30 Climate Change Talking Points NPS/FWS—2010

Brooks, M. L. and J. R. Matchett. 2006. Spatial and temporal patterns of wildfires in the Mojave 

Desert, 1980–2004. Journal of Arid Environments 67:148-164.

Brown, R. 2008. The implications of climate change for conservation, restoration, and management of National Forest lands. National Forest Restoration Collaborative.

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