Independent Scientific Advisory Board 

Climate Change Impacts on Columbia 

River Basin Fish and Wildlife 

May 11, 2007 

ISAB Climate Change Report 

ISAB 2007-2 
 

Independent Scientific Advisory Board

for the Northwest Power and Conservation Council, 

Columbia River Basin Indian Tribes, 

and National Marine Fisheries Service 

 851 SW 6th Avenue, Suite 1100

Portland, Oregon 97204

ISAB@nwcouncil.org

ISAB Members 

Robert Bilby, Ph.D., Ecologist at Weyerhaeuser Company. 

Susan Hanna, Ph.D., Professor of Agriculture and Resource Economics at Oregon State 

University. 

Michael Healey, Ph.D., Lead Scientist, CALFED Bay-Delta Program. 

Nancy Huntly, Ph.D., Professor of Wildlife Biology at Idaho State University. 

Stuart Hurlbert, Ph.D., Professor of Biology and Director, Center for Inland Waters at San 

Diego State University. 

Roland Lamberson, Ph.D., Professor of Mathematics and Director of Environmental Systems 

Graduate Program at Humboldt State University. 

Colin Levings, Ph.D., Scientist Emeritus and Sessional Researcher, Centre for Aquaculture and 

Environmental Research, Department of Fisheries and Oceans, Canada. 

David Montgomery, Ph.D., Professor of Geomorphology at the University of Washington. 

William Pearcy, Ph.D., Professor Emeritus of Oceanography at Oregon State University. 

Thomas P. Poe, M.S., Consulting Fisheries Scientist, formerly with the U.S. Geological Survey. 

Peter Smouse, Ph.D., Professor of Ecology, Evolution, and Natural Resources at Rutgers 

University. 

Ad Hoc Member 

Nathan Mantua, Ph.D., Associate Director of the Center for Science in the Earth System, 

Climate Impacts Group Principal, and Research Associate Professor, University of Washington 

 

Staff 

Erik Merrill, ISAB and ISRP Coordinator, Northwest Power and Conservation Council. 

Cover graphic adapted from the University of Washington Climate Impact Group’s graphic included as Figure 10 in

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 ISAB 2007-2 CLIMATE CHANGE REPORT

Climate Change Impacts on Columbia River Basin Fish and Wildlife 

EXECUTIVE SUMMARY ......................................................................................................................................III

IMPACTS OF CLIMATE CHANGE ON FISH AND WILDLIFE RESOURCES OF THE COLUMBIA BASIN ............................. III

INCLUDING CLIMATE CHANGE IN COLUMBIA BASIN PLANNING.............................................................................. VI

MITIGATING CLIMATE CHANGE EFFECTS ................................................................................................................ VI

INTRODUCTION .......................................................................................................................................................1

THE GREENHOUSE EFFECT AND HUMAN CAUSED GLOBAL WARMING..............................................2

THE GREENHOUSE EFFECT ........................................................................................................................................2

HUMAN CAUSED CHANGES IN ATMOSPHERIC COMPOSITION -- GREENHOUSE GASES AND AEROSOLS......................3

INDICATORS OF GLOBAL AND REGIONAL CLIMATE CHANGE...............................................................6

EXPECTED IMPACTS OF HUMAN-CAUSED INCREASES IN THE NATURAL GREENHOUSE 

EFFECT .......................................................................................................................................................................8

EXPECTED REGIONAL IMPACTS OF GLOBAL WARMING IN THE PACIFIC NORTHWEST............12

IMPACTS ON SNOW PACK, STREAM FLOW AND WATER TEMPERATURE ..................................................................15

CHANGES IN TERRESTRIAL ECOSYSTEMS ................................................................................................................17

What determines the response of terrestrial ecosystems to climate change?.....................................................17

The Predicted Patterns of Change in Terrestrial Ecosystems of the Columbia River Basin .............................22

EFFECTS ON TRIBUTARY HABITAT ..........................................................................................................................29

Egg Incubation and Fry Emergence ..................................................................................................................33

Spring/Summer Rearing.....................................................................................................................................34

Overwinter Survival ...........................................................................................................................................35

EFFECTS IN THE MAINSTEM.....................................................................................................................................36

Physical Effects..................................................................................................................................................36

Biological Effects – Juvenile Salmonids ............................................................................................................38

Biological Effects – Adult Salmonids.................................................................................................................43

Biological Effects – Other Species.....................................................................................................................45

EFFECTS IN THE ESTUARY .......................................................................................................................................47

Possible Changes in Oceanographic and Hydrological Conditions in the Estuary...........................................47

Biological Responses .........................................................................................................................................52

Effects on Estuarine Restoration Projects .........................................................................................................57

EFFECTS IN THE OCEAN ...........................................................................................................................................57

Climate Variability.............................................................................................................................................57

Biological Impacts .............................................................................................................................................63

Stratification ......................................................................................................................................................64

Wind-driven Upwelling ......................................................................................................................................66

Columbia River Salmon .....................................................................................................................................68

Pelagic Community ............................................................................................................................................69

Ocean Acidification............................................................................................................................................71

Summary of Ocean Impacts ...............................................................................................................................72

INTEGRATION OF POTENTIAL IMPACTS ON SALMONIDS ......................................................................73

INCORPORATING CLIMATE CHANGE INTO RESTORATION PLANNING ............................................76

MITIGATING CLIMATE CHANGE EFFECTS ..................................................................................................82

GENERAL STRATEGIES.............................................................................................................................................83

COMMUNITY RESPONSES TO CHANGING ENVIRONMENTAL CONDITIONS; A MITIGATION CAUTION........................84

POSSIBLE ACTIONS TO REDUCE CLIMATE CHANGE IMPACTS ..................................................................................85

MITIGATION OPTIONS FOR THE MAINSTEM, ESTUARY, AND PLUME........................................................................86

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MITIGATING EFFECTS OF CLIMATE CHANGE IN THE OCEAN....................................................................................90

THE ROLE OF THE NPCC IN ADDRESSING CLIMATE CHANGE IN THE COLUMBIA BASIN...........90

KEY FINDINGS........................................................................................................................................................91

RECOMMENDATIONS ..........................................................................................................................................95

REFERENCES ..........................................................................................................................................................98

APPENDIX A. GLOSSARY OF CLIMATE CHANGE TERMS.......................................................................123

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Climate Change Impacts on Columbia River Basin Fish and Wildlife 

Executive Summary 

Warming of the global climate is unequivocal. Evidence includes increases in global 

average air and ocean temperatures, widespread melting of snow and ice, and rising 

global mean sea level. Eleven of the last twelve years (1995 -2006) rank among the 12 

warmest years in the instrumental record of global surface temperature (since 1850). The 

linear warming trend over the last 50 years (0.13 +/- 0.03°C per decade) is nearly twice 

that for the last 100 years. The total global average temperature increase from 1850 – 

1899 to 2001 – 2005 is 0.76 +/- 0.19°C. 

Climate records show that the Pacific Northwest has warmed about 1.0 oC since 1900, or 

about 50% more than the global average warming over the same period. The warming 

rate for the Pacific Northwest over the next century is projected to be in the range of 0.1-

0.6 ̊ C/decade. Projected precipitation changes for the region are relatively modest and 

unlikely to be distinguishable from natural variability until late in the 21st century. Most 

models project long-term increases in winter precipitation and decreases in summer 

precipitation. The changes in temperature and precipitation will alter the snow pack, 

stream flow, and water quality in the Columbia Basin: 

• Warmer temperatures will result in more precipitation falling as rain rather than snow 

• Snow pack will diminish, and stream flow timing will be altered 

• Peak river flows will likely increase

• Water temperatures will continue to rise 

These changes will have a variety of impacts on aquatic and terrestrial habitats in the 

Columbia Basin. 

Impacts of Climate Change on Fish and Wildlife Resources of the Columbia

Basin 

Changes already have been observed in many species’ ranges, consistent with changes in 

climate. These range changes include poleward and elevationally upward movements of 

many insects, birds, trees, and forbs. Future climate change may lead to fragmentation of 

suitable habitats that may inhibit adjustment of plants and wildlife to climate change

through range shifts. 

Virtually all future climate scenarios predict increases in wild fire in western North 

America, including the Columbia Basin. Fire frequency and intensity have already 

increased in the past 50 years, and especially the past 15 years, in the shrub steppe and 

forested regions of the West. Drought and hot, dry weather already have led to an 

increase in outbreaks of insects in the Columbia Basin, especially mountain pine beetle, 

and insect outbreaks are likely to become more common and widespread. 

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Climate change in combination with expansion of human population will reduce and 

fragment wildlife habitats. Several community types and their associated wildlife 

populations are likely to decrease greatly in area, including alpine, subalpine spruce-fir, 

aspen, and sagebrush habitats. 

Changes in hydrology and temperature caused by changing climate have the potential to 

negatively impact aquatic ecosystems in the Columbia Basin, with salmonid fishes being 

especially sensitive. The intensity of the effects will vary spatially. However, climate 

change can generate ecological responses in virtually all the tributary systems of the 

Columbia Basin. Several projections of the potential impact of climate change on cool 

and cold water fishes have been completed. One of these analyses suggests that 

temperature increases alone will render 2% to 7% of current trout habitat in the Pacific 

Northwest unsuitable by 2030, 5%-20% by 2060, and 8% to 33% by 2090. Salmon 

habitat may be more severely affected, in part because these fishes can only occupy areas 

below barriers and are thus restricted to lower, hence warmer, elevations within the 

region. Salmon habitat loss would be most severe in Oregon and Idaho with potential 

losses exceeding 40% by 2090. Loss of salmon habitat in Washington would be less 

severe, with the worst case about 22% loss by 2090. These estimates do not consider the 

associated impact of changing hydrology. 

Climate change has the potential to affect most freshwater life history stages of trout and 

salmon. Increased frequency and severity of flood flows during winter can affect overwintering juvenile fish and incubating eggs in the streambed. Eggs of fall and winter 

spawning fish, including Chinook, coho, chum, and sockeye salmon and bull trout, may 

suffer higher levels of mortality when exposed to increased flood flows. Higher winter 

water temperatures also could accelerate embryo development and cause premature 

emergence of fry. Bull trout require very cold, headwater streams for spawning. 

Therefore, a warming climate may disproportionately impact this species. Recent 

projections of the loss of habitat suitable for bull trout in the Columbia Basin as a result 

of climate warming range from 22% to 92%. 

The construction of the hydrosystem has also altered mainstem hydrology and water 

temperature regimes. The changes in mainstem flows due to hydrosystem operations are 

substantially greater than the natural runoff changes, projected to be caused by climate 

warming in the 21st century. The changes caused by climate change will be similar to 

those changes already caused by operation of the hydrosystem. Currently, warming of 

water in the reservoirs begins earlier in the spring and persists longer into the fall than 

historically. Climate modeling of future water temperatures in the Columbia and Snake 

rivers predicts an increase of 1o

 C or greater by 2040, adding to the increases caused by 

the hydrosystem. 

Water temperature increases in the mainstem may impact Columbia River salmon in 

several ways. Increases in water temperature will accelerate the rate of egg development 

of fall Chinook, which spawn in the mainstem of the Snake and Columbia rivers, and 

lead to earlier emergence at a smaller average size than historically. Smaller sized fry are 

likely to have lower survival due to increased vulnerability to predators. Predation rates 

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also will increase due to elevated water temperatures. Potential impacts of increased 

water temperatures on adult salmon include delay in dam passage, failure to enter fish

ladders, increased fallback, and loss of energy reserves due to increased metabolic 

demand. Increases in mortality also may be caused by fish pathogens and parasites as 

these organisms often do not become injurious until their host becomes thermally 

stressed. 

Changes in freshwater flow into the Columbia River estuary caused by climate change 

will be less than those caused by the hydrosystem. Nonetheless, some changes in estuary 

habitats may occur. Sea level rise in conjunction with higher winter river flows could 

cause the degradation of estuary habitats created by sediment deposition from increased 

wave damage during storms. Numerous warm-adapted fish species, including several 

non-indigenous species, normally found in freshwater have been reported from the 

estuary and might expand their populations with the warmer water and seasonal 

expansion of freshwater habitats. The potential impacts on salmon are not understood. 

Climate change also may affect the trophic dynamics of the estuary due to upstream

extension of the salt wedge in spring-early summer caused by reduced river flows. The 

landward head of the salt wedge is characterized by a turbulent region known as the 

estuary turbidity maximum, an area with high concentrations of fish food organisms such 

as harpacticoid copepods. Changes in the upstream extension of the salt wedge will 

influence the location of this zone, but it is difficult to forecast the effect this change will 

have on juvenile salmon. 

Scientific evidence strongly suggests that global climate change is already altering 

marine ecosystems from the tropics to polar seas. Physical changes associated with 

warming include increases in ocean temperature, increased stratification of the water 

column, and changes in the intensity and timing of coastal upwelling. These changes will 

alter primary and secondary productivity, the structure of marine communities, and, in 

turn, the growth, productivity, survival, and migrations of salmonids. 

Earlier snowmelt and earlier, higher spring flows and warmer temperatures may cause 

spring Chinook and steelhead yearlings to smolt and emigrate to the estuary and ocean 

earlier in the spring. The early emigration coupled with a projected delay in the onset of 

coastal upwelling may cause the timing of ocean entry of juvenile salmonids to be 

suboptimal. The first few weeks in the ocean are thought to be critical to the survival of 

salmon off Oregon and Washington, so a growing mismatch between smolt migrations 

and coastal upwelling would likely have significant negative impacts on marine survival 

rates. 

Changing ocean temperatures may alter salmon behavior, distribution, and migrations, 

increasing the distance to migrations from their home streams to ocean feeding areas. 

Energetic demands are increased at warmer temperatures, requiring increased 

consumption of prey to maintain a given growth rate. In addition, food availability in the 

ocean may be altered by climate change. Increasing concentrations of CO2 in the oceans 

lowers pH, which reduces the availability of carbonate for shell-forming marine animals. 

Pteropods are expected to be especially impacted, and they can comprise up to 40% or 

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more of the diet of some salmon species. If salmon migrate farther to the north and/or 

food is less available, longer times may be required to reach maturity, delaying the usual 

times of adult migrations into coastal water and rivers. 

Including Climate Change in Columbia Basin Planning 

In many cases, impacts of climate change on fish at one life history stage contribute to 

increased mortality at later stages; the impacts of climate change can propagate 

cumulatively through the life of the fish. In addition, climate change will occur 

concurrently with other impacts in the Columbia Basin. Studies that have examined the 

simultaneous effects of more than a single stressor (e.g., climate and land use; climate, 

land use, and human population growth) generally conclude that the effects of more than 

a single stressor are not easily predictable, but may often be more severe than simple 

combination of the single-factor outcomes. Planners will need to consider all factors 

likely to impact habitats in the Columbia Basin in the future to develop effective 

restoration strategies and prioritize actions. 

Future impacts of climate change on fish and wildlife habitat in the Columbia Basin was 

poorly addressed in the subbasin planning process. The majority of plans acknowledged 

the general risk posed by global climate change but did not directly factor it into 

planning; about one quarter of the plans did not address climate change at all. Very few 

subbasin plans attempted to assess what future impact changes in climate might have on 

subbasin fish and wildlife populations and habitats and what effect these changes might 

have on the efficacy of proposed restoration measures. 

Inclusion of climate change in planning processes has been hampered by several factors. 

In some cases, the information on climate change is very technical, making it difficult for 

planners to interpret it in a manner relevant to their planning process. The nature of 

climate change predictions also can be problematic. These predictions have generally 

been reported at very coarse spatial scales, making them difficult to apply to planning at 

the watershed or subbasin scale. However, climate-change projections at a scale 

compatible with subbasin planning are becoming more available, making analysis of this 

issue in future subbasin plans more tractable. 

Mitigating Climate Change Effects 

Only global strategies for reducing the emission of greenhouse gases will completely 

address climate change impacts on all habitats in the Columbia Basin. Dealing with this 

issue will require unprecedented cooperation among public and private land stewards and 

even among nations. As we seek solutions to these larger issues, the identification and 

implementation of actions that may offset some of the negative effects of climate change 

in the Columbia Basin represent the only near-term, local option for dealing with climatechange effects. 

Climate change in conjunction with land-use changes has the potential to substantially

reduce diversity in the basin by making many areas unsuitable for the native species that 

currently occupy these sites. The role of biodiversity in protecting both contemporary 

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persistence and evolutionary potential of species is recognized in the Columbia River

Basin Fish and Wildlife Program and in many other guidelines for mitigating the 

damaging effects of climate change. Locations that are likely to be sensitive to climate 

change and have high ecological value are sites where establishing adequate protective 

measures, including reserve areas, will be a key component of any effort to address 

changing climate in the Columbia Basin. Efforts to protect biodiversity and to prevent 

critical areas are already supported by the Fish and Wildlife Program, but actions have 

not yet been targeted to address climate change concerns. 

In general, mitigating for changes in hydrology and temperature in tributaries that are 

caused by climate change will involve many of the same approaches that have been 

initiated in the basin to date. Any action that can help minimize water temperatures 

increases or augment stream flow during summer and autumn would contribute to this 

end. Specifically, protection of cold-water refugia for migrating salmon and restoration 

of riparian habitats in headwater reaches should have high priority. However, it is 

unlikely that there are any options to successfully deal with some of the projected 

changes. For example, there is little that can be done at a local scale to offset projected 

changes in elevation, accumulation, and melt timing of snowpack. 

Global warming impacts on the mainstem Columbia and Snake rivers, estuary, and plume 

must be considered in the context of hydrosystem management. Because the hydrology 

and salmon habitat of the mainstem and estuary have been extensively transformed, 

managed, and manipulated for decades, there is a range of alternatives for mitigating 

climate change impacts on in these habitats. To the extent that hydrosystem operations 

are flexible, there are opportunities to mitigate for some climate change impacts in the 

mainstem, estuary and plume, because projected changes in natural runoff, even under 

the most extreme warming scenarios for the late 21st century, are substantially smaller

than the changes caused by the development and operation of the hydrosystem in the late 

20th century. 

Possible actions that could be taken on the mainstem to address climate change impacts 

include: 

• Flow augmentation from cool/cold water storage reservoirs. If this strategy

requires addition storage capacity, careful consideration of the benefits and 

negative impacts of increasing the number of dams in the basin will be

required. 

• Use of removable surface weirs to reduce the time juvenile salmonids spend in 

the warm water of the dam forebays 

• Reduce water temperatures in the ladders with water drawn from lower, cooler 

strata in the water column of the dam forebays 

• Develop transportation strategies for initiating full transport of juvenile fall 

Chinook more focused on temperature criteria 

• Evaluate the possibility of transporting immigrating adults through the lower 

Snake River when water temperatures reach near lethal limits in the late 

summer 

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• Expand the predator control program to introduced piscivorous species such 

as smallmouth and largemouth bass, walleye, and channel catfish 

• Open backwater, slough, and other off-channel habitats along mainstem

reservoirs and the estuary to encourage increased flow through these areas to 

help reduce water temperature and provide cool-water refugia 

Climate change may delay the initiation of coastal upwelling in the spring, while earlier 

runoff and higher water temperatures may accelerate the emigration of smolts to the 

estuary and ocean. A mismatch between smolt migrations and coastal upwelling would 

likely have significant negative impacts on marine survival rates. Adjusting the timing of 

ocean entry by transportation or controlling the rate of downstream movement of in-river 

migrants could be evaluated as a possible option to ensure that ocean entry coincides with 

favorable ocean conditions. 

If the ocean environment becomes less productive, density-dependent interactions will 

intensify, resulting in increased competition in the ocean. This may result in lower 

growth and survival rates for wild salmon. Reduction in hatchery releases during poor 

ocean conditions may enhance survival of wild stocks, but more research on this topic is 

needed. 

Harvest managers need to adopt near- and long-term assessments that consider changing 

climate in setting annual quotas and harvest levels of fish from the Columbia Basin. For 

example, reduced harvest of stocks that are consistently below sustainable levels during 

poor phase ocean conditions could be allowed to recover their numbers and recolonize 

areas of freshwater habitat during favorable climatic phases. 

The Northwest Power and Conservation Council and the Fish and Wildlife Program are 

well suited to address the challenges that climate change will pose for the fish and 

wildlife resources of the Columbia Basin. The efficient production, distribution, and 

consumption of power, especially power generated without the release of greenhouse 

gases, can contribute to global efforts to reduce human impacts on the greenhouse effect. 

Incorporating climate change into future fish and wildlife recovery plans can help to 

ensure that all reasonable measures are taken to buffer the natural ecosystems of the 

Columbia Basin from the changes in temperature and hydrology expected over the 

coming decades. The educational mandate of the Council provides a mechanism for 

encouraging the residents of the basin to become engaged in the type of coordinated 

effort that will be required to ensure that the progress that has been made in restoring fish 

and wildlife populations to date continues into the future despite a changing climate. 

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Climate Change Impacts on Columbia River Basin Fish and Wildlife 

Introduction 

There is compelling scientific evidence that we are living in a time of rapid, world-wide 

climate change. A recent report from the International Panel on Climate Change (IPCC

2007) illustrates the broad consensus among the scientific community about changes to 

the global climate. Climate changes include temperature, winds, rainfall, snow, ocean 

currents, and the interactions among these. Alterations in climatically driven processes 

will impact aquatic and terrestrial habitats in the Columbia Basin and the marine 

environments used by anadromous fishes from the basin. The resultant changes in habitat 

distribution and quality will affect most of the fish and wildlife populations in the basin. 

The influence changing climate can have on the growth, survival, recruitment, and 

migration patterns of Columbia River salmon is amply demonstrated by the dramatic 

response of populations coast-wide to annual and decadal variations in climate and ocean 

conditions. Wild fire and severe insect outbreaks are both likely to increase in response 

to climate warming; both of these processes can fundamentally alter fish and wildlife 

habitats over large areas. Nonetheless, the impacts of climate change are rarely 

incorporated into natural resource planning in the Columbia Basin, despite the direction 

in the subbasin planning documentation that this issue be considered. Generally, the 

Council’s fish and wildlife program and the NOAA Fisheries recovery strategies do not 

consider the impacts of climate change and implicitly assume stable conditions. 

However, the changes in regional snow pack, stream flows, and temperature in the 

Columbia Basin that are projected by most climate models could have a profound impact 

on the success of restoration efforts and the status of Columbia River fish and wildlife 

populations. 

Some previous ISAB reports have touched on the subject of climate change. A section 

on climate and ocean change was included in the harvest report (ISAB 2005) and the 

tributary habitat report provided a brief discussion of climate change impacts on 

freshwater habitat (ISAB 2003). The treatment of this subject was superficial in these 

reports and a significant amount of recent scientific effort has been dedicated to better 

understanding the mechanics of climate change and the potential impacts. This report 

provides a much more thorough examination of the issue. 

In this report we review the basic physics of the natural greenhouse effect, the role of

past, present, and future human actions in altering the natural greenhouse effect, and how 

the resultant climate changes may affect the Columbia Basin. The potential impacts of 

these predicted climate changes on the aquatic ecosystems utilized by Columbia River 

salmon and other cool-water species and effects on the productivity of the salmon 

populations are explored, as are potential impacts on terrestrial ecosystems. Finally, we 

offer some suggestions as to how climate change might be incorporated into plans for 

ecosystem restoration and salmon recovery in the Columbia Basin and indicate some

possible mitigation measures. 

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Much of the vocabulary that has evolved around the climate change issue is specialized to 

this field. Therefore, a glossary has been provided (Appendix A) that defines many of 

the technical terms used in this report.

The Greenhouse Effect and Human Caused Global Warming 

The Greenhouse Effect 

The Greenhouse Effect is an essential, natural part of the Earth’s climate system that 

makes our planet remarkably hospitable for life as we know it. Earth’s atmosphere, 

where clouds are absent, is nearly transparent to the visible radiation (light) that carries 

the bulk of the energy coming from the sun. Clouds and bright surfaces, like snow cover, 

reflect about 30% of the total incoming energy from the sun back to space, a smaller 

fraction is absorbed by the atmosphere, and the rest is absorbed by the Earth’s surface. 

The absorbed solar radiation warms the Earth’s surface, and because the Earth’s surface 

is much cooler than the sun, its heat is radiated upward to the atmosphere at much longer 

infrared wavelengths. Because of trace gases in the atmosphere, such as water vapor,

carbon dioxide (CO2), methane, nitrous oxide, ozone, and a host of industrial chemicals, a 

substantial fraction of the infrared radiation from the Earth’s surface is absorbed and 

warms the atmosphere (Fig.1). The higher atmospheric temperatures lead to an increase 

in atmospheric emissions of infrared radiation both upward to space and downward back 

to the Earth’s surface where it is again absorbed, raising the Earth’s surface temperature, 

and re-emitting radiation back to the atmosphere. This trapped infrared energy warms 

both the atmosphere and the Earth’s surface substantially – surface temperatures without 

our natural Greenhouse Effect would be an icy 33 oC (60 oF) cooler than they are today. 

Because increased concentrations of greenhouse gases cause a reduction in the infrared 

radiation passing freely from the Earth’s surface through the atmosphere to space, this 

also causes increases in atmospheric and surface temperature until a net energy balance 

between incoming solar radiation and outgoing infrared radiation is achieved. Changing 

concentrations of aerosols in the atmosphere also cause a suite of changes in regional and 

global scale aspects of the Earth’s energy balance. Large changes in aerosol emissions in 

the past century are also important factors in recent patterns of global climate change. 

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Figure 1: The Earth’s annual energy budget in Watts per meter squared. 

Reproduced from Kiehl and Trenberth (1996) 

Human Caused Changes in Atmospheric Composition -- Greenhouse Gases 

and Aerosols 

Global warming refers to a globally averaged increase in the near-surface temperature of 

the Earth. Global warming has occurred in the distant past as the result of natural 

influences. Today, this term is commonly used as short-hand for Anthropogenic Global 

Warming, a phrase that refers to the observed and expected impacts of human-caused 

increases in the strength of the natural greenhouse effect (IPCC 2007). This current 

common usage of global warming applies to the remainder of this report. 

The intensity of the natural greenhouse effect has varied over geologic time, with very 

warm eras coinciding with periods of abundant atmospheric greenhouse gases and cool 

eras coinciding with periods of relatively low levels of greenhouse gases. During the 

most recent ice age, which ended about 12,000 years ago, atmospheric CO2 was slightly 

less than 200 parts per million by volume (ppm), while during the period from about 

10,000 years ago to the early 1700s CO2 concentrations were relatively stable at

~270ppm. 

In the 20th century human activities rapidly altered the composition of the atmosphere in 

ways that influence Earth’s energy balance. Atmospheric concentrations of man-made 

greenhouse gases like chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs) and 

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perfluorocarbons (PFCs), as well as sulfur hexafluoride (SF6) are all due to industrial 

development. Several of the important naturally occurring greenhouse gases (carbon 

dioxide (CO2), methane (CH4), and nitrous oxide (N2O) increased dramatically in the 20th

century, especially since ~1950 (Figure 2; IPCC 2007). Carbon-dioxide emissions from 

burning fossil fuels and converting forests into agricultural lands, account for the 

observed rise in atmospheric CO2 concentrations. Increased industrial activity and use of 

nitrogen fertilizer are key factors contributing to the observed rises in N2O. In contrast, 

causes for changing methane concentrations are not well understood, although livestock 

and certain types of agriculture are known to be large producers of methane. The growth 

in atmospheric methane concentrations began slowing in the 1980s, and methane 

concentrations were basically stable from 1999-2002 (Dluglokenky et al., 2003). Based 

on measurements obtained from deep ice cores from Antarctica, the current CO2 and CH4

concentrations are higher now than at any time in (at least) the past 650,000 years. 

Figure 2: Atmospheric concentrations 

of carbon dioxide, methane and nitrous 

oxide over the last 10,000 years (large 

panels) and since 1750 (inset panels). 

Measurements are shown from ice 

cores (symbols with different colors for 

different studies) and atmospheric 

samples (red lines). The corresponding 

radiative forcings are shown on the 

right hand axes of the large panels. 

Reproduced from the IPCC 2007 

Summary for Policymakers. 

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Key greenhouse gases emitted by human actions have long residence times in the 

atmosphere (Tab. 1). A molecule of CO2 can remain in the atmosphere from 5 to 200 

years. Synthetic greenhouse gases produced for industry have typical residence times of 

many centuries to millennia, while methane typically persists for about a decade (Tab. 1). 

Table 1: Residence times of greenhouse gases in the atmosphere (after IPCC 1990). 

Carbon Dioxide (CO2) 50-200 years (the range varies with sources 

and sinks and depends on the equilibration 

times between atmospheric CO2 and 

terrestrial and oceanic reserves) 

Methane (CH4) 12 years

Nitrous Oxides (N2O) 120 years

CFC-11 (a Chlorofluorocarbon) 50 years 

HCFC-22 (a Chlorofluorocarbon) 12 years 

Perfluorocarbon (CF4) 50,000 years

Aerosols, small airborne particles that influence the Earth’s energy balance, also changed 

dramatically in the 20th century. Natural sources for aerosols include sulfur dioxide from

volcanic eruptions, dust from desert areas, smoke from biomass burning, and salt from 

sea-spray. In the 20th century anthropogenic sources have contributed a growing portion 

of atmospheric aerosols; primarily smoke, soot, and sulfuric acid from burning fossil 

fuels and dust from intensive farming practices. For example, sulfuric acid deposition on 

Greenland ice rose dramatically with increased emissions from industrial activities in 

eastern North America from the 1950s until the 1990s. Sulphate deposition decreased in 

the 1990s as sulphate emissions were reduced to combat acid rain and other regional air 

quality problems in northeastern North America. Unlike greenhouse gases, aerosols have 

a short residence time in the atmosphere. This means that aerosols and their impacts on 

climate tend to be localized around source regions and they are unevenly distributed in 

space and time. 

The net impacts of aerosols on climate are complex and poorly understood. One direct 

effect of aerosols is to cool the local climate by reflecting incoming solar energy back to 

space. Increased aerosol concentrations also work to increase the number of water 

droplets in clouds, leading to smaller cloud droplets that reduce the rate at which water 

droplets fall out of clouds. A shift to smaller cloud droplets prolongs the lifetime of 

clouds so that they reflect more sunlight, thereby indirectly cooling local climate, and 

decreases the likelihood that droplets are large enough to fall to the ground before 

evaporating, thereby leading to decreased precipitation. Black soot offers yet another 

complication to aerosol impacts on climate. Black carbon in the atmosphere produced by 

burning biomass or fossil fuels can absorb sunlight and warm the atmosphere in ways that 

counter the direct and indirect aerosol cooling produced from increased reflection of 

sunlight.

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 ISAB 2007-2 CLIMATE CHANGE REPORT

Ozone (O3) is another important trace gas in the atmosphere whose concentrations have 

changed substantially in the 20th century. The seasonal development of an Antarctic 

“ozone-hole” was first documented in the mid-1970s, and is now understood to 

ultimately arise from emissions of man-made industrial gases known as 

chlorofluorocarbons. Stratospheric ozone is crucial for life at the Earth’s surface because 

it effectively filters out 95 to 99% of the harmful ultraviolet radiation that comes from the 

sun. Ozone is also an important greenhouse gas. While stratospheric ozone 

concentrations declined in the 20th century, ozone concentrations near ground level 

increased in smoggy areas as a consequence of hydrocarbon emissions from burning 

fossil fuels. This “bad” ozone caused in the formation of smog can damage lung tissue 

and plants, and serves to locally increase the greenhouse effect in polluted areas. On a 

global average the net effect of total ozone changes has been to slightly increase the 

greenhouse effect (see IPCC 2007). 

Indicators of Global and Regional Climate Change 

Warming of the climate system is unequivocal, as is now evident from observed increases 

in global average air and ocean temperatures, widespread melting of snow and ice, and 

rising global mean sea level (IPCC 2007). Globally averaged surface air temperature 

records indicate two periods of strong global-scale warming in the past century, the first 

taking place from 1910-1945 and the second beginning in the 1970s and continuing to 

present (Fig. 3). Global average surface temperatures were relatively stable from the late 

1800s through 1910, and cooled slightly from 1945 to the mid-1970s. Eleven of the last 

twelve years (1995 -2006) rank among the 12 warmest years in the instrumental record of 

global surface temperature (since 1850). The linear warming trend over the last 50 years 

(0.13 +/- 0.03°C per decade) is nearly twice that for the last 100 years. The total global 

average temperature increase from 1850 – 1899 to 2001 – 2005 is 0.76 +/- 0.19°C (IPCC 

2007). Urban heat island effects are real but local, and have a negligible influence (less 

than 0.006°C per decade over land and zero over the oceans) on these values. Analysis of 

various climate proxies for the Northern Hemisphere suggest that the rate of warming 

observed in the 20th century, as well as the magnitude of global temperatures from 1990 

to 2004, is unprecedented in the past 2000 years (Moberg et al. 2005). 

6
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 3: Globally averaged annual mean surface temperatures expressed as deviations from

the 1961-90 average. Annual averages are shown with the red bars, a smoothed indication of 

trend is shown by the heavy blue line. Figure obtained from the Hadley Center’s Climate 

Research Unit web-page: 

www.metoffice.com/research/hadleycentre/CR_data/Annual/HadCRUG.gif

The spatial pattern of 20th century warming was not uniform across the globe. The 

largest warming trends were in Alaska, western Canada, Russia, and the Antarctic 

Peninsula, with smaller warming trends over the global oceans and tropical land areas. 

Twentieth century surface temperatures cooled slightly in parts of the Antarctic, parts of 

the southern Ocean, and the North Atlantic Ocean just south and east of Greenland (IPCC 

2001). The warming trends were also greatest at nighttime, and in the wintertime. 

The cryosphere, the part of the Earth’s surface that is perennially frozen or below the 

freezing point, is a crucially important part of the Earth climate system. The most 

important influences on the cryosphere come from its interactions with the atmosphere, 

ocean, and land system. Feedbacks between the cryosphere and other components of the 

climate system can yield especially high regional, and even global, climate sensitivity. 

For example, ice-albedo (surface reflectivity) feedback in polar regions can lead to a high 

amplification of a small initial warming. Ice is highly reflective, so melting ice increases 

the amount of sunlight absorbed, which raises surface temperatures, melts more ice, and 

leads to a positive feedback of the initial warming. Similar sets of feedbacks exist with

7
 ISAB 2007-2 CLIMATE CHANGE REPORT

snow cover and sea ice, such that an initially small amount of melt can start a rapid 

process of additional melting and surface warming (NRC 1998). Changes in permafrost, 

snow and ice cover are also ecologically important. Snow and sea ice insulate the 

surfaces below them from what can be extremely cold atmospheric temperatures. 

Melting permafrost can alter moisture infiltration rates in ways that lead to large changes 

in soil moisture and vegetation cover. In summary, the cryosphere directly influences 

climate through its role in the surface energy balance, and indirectly through its 

ecological effects on biogeochemical cycles, photosynthesis in terrestrial and marine 

plants and the decay of organic matter. 

The Intergovernmental Panel on Climate Change (IPCC 2007) highlights the following 

cryosphere indicators of global climate change: 

• Mountain glaciers and snow cover have declined on average in both hemispheres. 

Widespread decreases in glaciers and ice caps have contributed to sea level rise 

(ice caps do not include contributions from the Greenland and Antarctic ice 

sheets). 

• New data since the IPCC’s Third Assessment Report (IPCC 2001) now show that 

losses from the ice sheets of Greenland and Antarctica have very likely 

contributed to sea level rise over 1993 to 2003. Flow speed has increased for 

some Greenland and Antarctic outlet glaciers, which drain ice from the interior of 

the ice sheets. The corresponding increased ice sheet mass loss has often followed 

thinning, reduction or loss of ice shelves or loss of floating glacier tongues. Such 

dynamical ice loss is sufficient to explain most of the Antarctic net mass loss and 

approximately half of the Greenland net mass loss. The remainder of the ice loss 

from Greenland has occurred because losses due to melting have exceeded 

accumulation due to snowfall. 

There were pronounced regional cryosphere changes in the latter half of the 20th century. 

Along the Antarctic Peninsula, the Wordie Ice Shelf and the Larsen Ice Shelf 

disintegrated in recent decades, dramatic indicators of a complex response to very strong 

regional warming trends of over 2.5°C since the 1950s. The Ward Hunt Ice Shelf, the 

Arctic’s largest ice shelf located on the north coast of Ellesmere Island in Canada's

Nunavut territory, fractured in September 2003 and released nearly all the freshwater 

from what was the Northern Hemisphere’s largest ice-shelf lake. 

Expected Impacts of Human-Caused Increases in the Natural 

Greenhouse Effect 

For the past few decades the international climate research community has been assessing 

the possible impacts of an intensified greenhouse effect on Earth’s climate. This research 

has relied on climate models that balance the incoming energy from the sun with the 

outgoing infrared energy emitted by the Earth. The most sophisticated approaches 

employ computer simulations for key aspects of the Earth’s climate system, including 

atmospheric winds and pressure patterns, clouds, ocean currents and temperatures, ice 

and snow cover, and the ecology (photosynthetic plants) and chemistry that controls 

8
 ISAB 2007-2 CLIMATE CHANGE REPORT

greenhouse gas concentrations in the atmosphere. At this extreme, the climate problem is 

a collection of very complicated problems that require the biggest and fastest computers 

on Earth. Teams of scientists work together to develop, operate, and diagnose the 

behavior of the most sophisticated computer models. At another extreme are energybalance models that aim to balance the incoming energy from the sun with the Earth’s 

outgoing infrared energy with very simplified physics. At both the very simple and very 

sophisticated extremes, every climate model in use today finds that increasing 

concentrations of greenhouse gases in the 21st century will intensify the greenhouse effect 

and warm the Earth’s surface and lower atmosphere. 

Uncertainty about future climate is due to two main factors. First, no one can know the 

exact quantities of CO2, methane, and other important greenhouse gases that will be 

emitted in the next century. Projecting future greenhouse gas emissions requires 

educated guesses about global economics, technology, and population. The second factor 

of uncertainty is our limited ability to understand exactly how sensitive the climate 

system is to a given change in greenhouse gas concentrations. There remain major 

challenges in simulating the behavior of clouds, the effects of aerosols, the carbon cycle, 

and how the ocean moves heat from its surface to deeper waters. Clouds, aerosols, the 

carbon cycle, and the way that oceans transport heat become crucially important for 

understanding how sensitive climate is to future changes in the greenhouse effect. 

The IPCC has coordinated a series of climate model experiments as part of the 

international effort to assess the future impacts of human-caused climate change. Since 

1988, the IPCC has issued major reports on global climate change science, impacts, and 

policy-responses about every five years (the fourth assessment report completed in 2007). 

Scientists involved in the IPCC assessments have explored the emissions uncertainties by 

examining a wide range of possible emissions futures. In order to gauge the uncertainties 

due to climate sensitivity to a given increase in greenhouse gases, scientists have 

examined the response of multiple models that have a range of climate sensitivities 

because they employ slightly different parameters for key physical processes. For the 

IPCC’s Fourth Assessment Report, published in 2007, the end result of their collection of 

emissions scenarios and model sensitivities suggests a range of ~1.1 to 6.4o C global 

average warming by 2100, with more warming at higher latitudes and less in the tropics, 

and more warming over land than over the oceans (IPCC 2007). 

At continental, regional, and ocean basin scales, numerous long-term changes in climate 

have been observed. These include changes in Arctic temperatures and ice, widespread 

changes in precipitation amounts, ocean salinity, wind patterns and aspects of extreme 

weather including droughts, heavy precipitation, heat waves and the intensity of tropical 

cyclones. Table SPM-2 (IPCC 2007) also provides a good summary of recent trends, 

assessment of human influence on the trend, and projections for extreme weather events 

for which there is an observed late 20th century trend. Key conclusions of the IPCC’s 

Fourth (IPCC 2007) and Third (IPCC 2001) Assessment Reports include: 

• Since the IPCC’s first report in 1990, assessed projections have suggested global 

averaged temperature increases between about 0.15 and 0.3°C per decade for 1990 to 

9
 ISAB 2007-2 CLIMATE CHANGE REPORT

2005. This can now be compared with observed values of about 0.2°C per decade, 

strengthening confidence in near-term projections. 

• Model experiments show that even if all radiative forcing agents are held constant at 

year 2000 levels, a further warming trend would occur in the next two decades at a 

rate of about 0.1°C per decade, due mainly to the slow response of the oceans. About 

twice as much warming (0.2°C per decade) would be expected if emissions are within 

the range of the emissions scenarios considered. Best-estimate projections from

models indicate that decadal-average warming over each inhabited continent by 2030 

is insensitive to the choice among emissions scenarios and is very likely to be at least 

twice as large as the corresponding model-estimated natural variability during the 

20th century. 

• Continued greenhouse gas emissions at or above current rates would cause further 

warming and induce many changes in the global climate system during the 21st 

century that would very likely be larger than those observed during the 20th century. 

• Advances in climate change modeling now enable best estimates and likely assessed 

uncertainty ranges to be given for projected warming for different emission scenarios. 

• Best estimates and likely ranges for globally average surface air warming for six 

emissions marker scenarios are provided by IPCC (2007). The best estimate for the 

low emissions scenario (B1) is 1.8°C (likely range is 1.1°C to 2.9°C), and the best 

estimate for the high emissions scenario (A1FI) is 4.0°C (likely range is 2.4°C to 

6.4°C) by the end of the century. Although these projections are broadly consistent 

with the span quoted in the IPCC’s Third Assessment Report (1.4 to 5.8°C), they are 

not directly comparable. The Fourth Assessment Report is more advanced as it 

provides best estimates and an assessed likelihood range for each of the marker 

scenarios. The new assessment of the likely ranges now relies on a larger number of 

climate models of increasing complexity and realism, as well as new information 

regarding the nature of feedbacks from the carbon cycle and constraints on climate 

response from observations. 

• Warming tends to reduce land and ocean uptake of atmospheric carbon dioxide, 

increasing the fraction of anthropogenic emissions that remains in the atmosphere. 

For the A2 emissions scenario, for example, the climate-carbon cycle feedback 

increases the corresponding global average warming at 2100 by more than 1°C. 

Assessed upper ranges for temperature projections are larger than in the IPCC’s Third 

Assessment Report mainly because the broader range of models now available 

suggests stronger climate-carbon cycle feedbacks. 

• Fourth Assessment Report model-based projections of global average sea level rise at 

the end of the 21st century (2090-2099) have a narrower range than in the Third 

Assessment Report mainly because of improved information about some uncertainties 

in the projected contributions. 

• Models used to date do not include uncertainties in climate-carbon cycle feedback nor 

do they include the full effects of changes in ice sheet flow, because a basis in 

published literature is lacking. The projections include a contribution due to increased 

ice flow from Greenland and Antarctica at the rates observed for 1993-2003, but these 

10
 ISAB 2007-2 CLIMATE CHANGE REPORT

flow rates could increase or decrease in the future. For example, if this contribution 

were to grow linearly with global average temperature change, the upper ranges of 

sea level rise for IPCC emissions scenarios would increase by 0.1 m to 0.2 m. Larger 

values cannot be excluded, but understanding of these effects is too limited to assess 

their likelihood or provide a best estimate or an upper bound for sea level rise. 

• Increasing atmospheric carbon dioxide concentrations leads to increasing 

acidification of the ocean. Projections based on IPCC emissions scenarios give 

reductions in average global surface ocean pH of between 0.14 and 0.35 units over 

the 21st century, adding to the present decrease of 0.1 units since pre-industrial times. 

• There is now higher confidence in projected patterns of warming and other regionalscale features, including changes in wind patterns, precipitation, and some aspects of 

extremes and of ice. 

• Projected warming in the 21st century shows scenario-independent geographical 

patterns similar to those observed over the past several decades. Warming is 

expected to be greatest over land and at most high northern latitudes, and least over 

the Southern Ocean and parts of the North Atlantic Ocean. 

• Snow cover is projected to contract. Widespread increases in thaw depth are 

projected over most permafrost regions. 

• Sea ice is projected to shrink in both the Arctic and Antarctic under all IPCC 

emissions scenarios. In some projections, Arctic late-summer sea ice disappears 

almost entirely by the latter part of the 21st century. 

• It is very likely that hot extremes, heat waves, and heavy precipitation events will 

continue to become more frequent. 

• Extra-tropical storm tracks are projected to move towards the poles, with consequent 

changes in wind, precipitation, and temperature patterns, continuing the broad pattern 

of observed trends over the last half-century. 

• Since the IPCC Third Assessment Report there is an improving understanding of 

projected patterns of precipitation. Increases in the amount of precipitation are very 

likely in high-latitudes, while decreases are likely in most subtropical land regions, 

continuing observed patterns in recent trends. 

• Based on current model simulations, it is very likely that the slow but important, heat 

transporting, north to south overturning circulation (also known as the meridional 

overturning circulation (MOC) in climate research jargon) of the Atlantic Ocean will 

slow down during the 21st century. The multi-model average reduction by 2100 is 

25% (range from zero to about 50%) for emission scenario A1B (assumes a balanced 

mix of future energy sources with increased efficiencies due to technology 

improvements; no single source of energy is overly dominant (IPCC 2001)). 

Temperatures in the Atlantic region are projected to increase despite such changes 

due to the much larger warming associated with projected increases of greenhouse 

gases. It is very unlikely that the MOC will undergo a large abrupt transition during 

the 21st century. Longer-term changes in the MOC cannot be assessed with 

confidence. 

11
 ISAB 2007-2 CLIMATE CHANGE REPORT

• Both past and future anthropogenic carbon dioxide emissions will continue to 

contribute to warming and sea level rise for more than a millennium, due to the 

timescales required for removal of this gas from the atmosphere. 

• Based on global model simulations and for a wide range of scenarios, global average 

water vapor concentration and precipitation are projected to increase during the 21st 

century. By the second half of the 21st century, it is likely that precipitation will have 

increased over northern mid- to high latitudes in winter. 

• The frequency of heavy precipitation events will very likely increase over most land 

areas, which is consistent with atmospheric warming and observed increases in 

atmospheric water vapor. 

• It is very likely that there will be warmer and more frequent hot days and nights over 

most land areas. 

• It is very likely that the frequency of warm spells and heat waves will increase over 

most land areas. 

• It is likely that the area affected by drought will increase. 

• It is very like that there will be higher minimum temperatures, fewer cold days and 

nights over nearly all land areas. 

• Confidence in projections of changes in the future frequency, amplitude, and spatial 

pattern of El Niño events in the tropical Pacific is tempered by some shortcomings in 

how well El Niño is simulated in complex models. Current projections show little 

change or a small increase in amplitude for El Niño events over the next 100 years. 

Expected Regional Impacts of Global Warming in the Pacific Northwest 

Climate records show that the Northwest (regionally averaged) has warmed about 1.0 oC 

since 1900, or about 50% more than the global average warming over the same period 

(Mote 2003a). Most glaciers in the region reached their recent maximum extent in the 

mid-1800s and since that time have been in rapid retreat. Recent studies indicate that the 

retreat of the past ~150 years has now brought many Northwest glaciers back to levels 

last seen ~6,000 years ago, a time near the end of a prolonged warm and dry period that is 

indicated by ancient pollen records and moraines (Walker and Pellatt, 2003). Regularly 

collected measurements indicate that Northwest springtime snow pack from the western 

Rockies to the coast, and from the central Sierras in California to southern British 

Columbia, declined substantially between 1950 and 1997 in part due to a reduction in 

precipitation and in part due to rising winter temperatures during this period (Mote et al. 

2003b; 2005b). 

These measurements indicate that for many individual recording sites decreases in this 

period were up to 60% in April 1st snow pack for the “warmest” locations in the 

Northwest -- areas including the lower elevations of the Cascades and the Olympic 

mountains in Washington. Over the period from 1948 to 2000 the timing of springtime 

12
 ISAB 2007-2 CLIMATE CHANGE REPORT

snow melt runoff came earlier in the vast majority of rivers in the Northwest, with 

advances in peak runoff timing of one to a few weeks depending on the basin (Stewart et 

al. 2005). Increases in regional winter and spring surface temperatures account for much 

of the documented runoff timing trend for western rivers. 

Taken together, a wealth of evidence paints a very consistent picture of a warming 

climate over the past 150 years for both the Pacific Northwest and the Earth as a whole. 

However, at the regional scale of the Pacific Northwest, substantial interannual and 

interdecadal variability in climate is caused by large-scale patterns of natural climate 

variability. Specifically, regional climate variations associated with the tropical El Niño 

Southern Oscillation (ENSO) and the extratropical Pacific Decadal Oscillation (PDO) 

had strong influences on Pacific Northwest climate in the past century, and PDO 

variability contributed substantially to Pacific Northwest precipitation and temperature 

trends in the 2nd half of the 20th century (Mantua et al. 1997; Mote et al. 2003a; Mote 

2006). 

Salathé et al. (in press) recently collected the output from 20 different global climate 

model simulations that were run as part of the IPCC’s Fourth Assessment Report. The 

relevant precipitation and surface temperature fields for the Pacific Northwest region

(here defined as the region between 124 ̊ and 111 ̊ west longitude, 42 ̊ and 49 ̊ north 

latitude, encompassing Washington, Oregon, Idaho, and western Montana) were 

extracted in order to generate a regional average time series. They examined output from

10 different models using, each using 2 different greenhouse gas and aerosol emissions 

scenarios, A2 and B1, which lie near the upper and lower limits of the full range of IPCC 

emissions scenarios considered in the IPCC’s latest assessment activities. The 

combination of 10 models each run under 2 different emissions scenarios provides a total 

of 20 different future climate scenarios. Based on an assessment of each model’s 

response to a specified change in greenhouse gas and aerosol concentrations, they note 

that the models used in their analysis are neither the most nor the least sensitive on the

global scale. 

Salathé et al’s analysis shows the projected warming rate for the next century to be in the 

range of 0.1-0.6 ̊ C/decade, with a 20-scenario average of 0.3 ̊ C/decade (Fig. 4). For 

comparison, the observed rate of warming in the 20th century was ~0.1 ̊C/decade. 

Because of long residence times for greenhouse gases and substantial inertia in energy 

systems (and emissions) there is relatively little spread between the high and low model 

estimates for regional warming over the next few decades. There is much greater spread 

between the high-end and low-end model estimates for regional (and global) warming by 

the 2nd half of the 21st century as future warming increasingly depends on future 

emissions. 

Projected precipitation changes are relatively modest and unlikely to be distinguishable 

from natural variability until late in the 21st century (Tab. 2). Most models project longterm trends with increases in winter precipitation and decreases in summer precipitation 

for the Pacific Northwest region. Notably, most models also generate substantial year-toyear and decade-to-decade fluctuations in regional precipitation that is comparable to 

13
 ISAB 2007-2 CLIMATE CHANGE REPORT

observed precipitation fluctuations in the 20th century. A summary of the range of model 

projections for temperature and precipitation for the 2020s, 2040s, and 2080s is provided 

in Table 2. 

Table 2: Summary of the range of 20 future climate scenarios for the Pacific Northwest 

examined by Salathé et al (in press). Note that “2020s” means the 2010-2040 

average minus the 1970-2000 average, similarly for the 2040s and 2080s. Thirty 

year averaging periods were chosen to help distinguish each model’s 

anthropogenic climate change signal from its internal decadal variations. 

2020s temperature Precipitation

Low 0.4 ̊ C -4% 

Average 1.1 ̊ C +2% 

High 1.8 ̊ C +6% 

2040s temperature Precipitation

Low 0.8 ̊ C -4% 

Average 1.6 ̊ C +2% 

High 2.6 ̊ C +9% 

2080s temperature Precipitation

Low 1.6 ̊ C -2% 

Average 3.1 ̊ C +6% 

High 4.9 ̊ C +18% 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 4: Projected changes in Pacific Northwest average annual temperature for the 21st 

century. This figure shows the range of warming projected for the Pacific Northwest from 20 

simulations of future climate by global climate models. The average of the 20 simulations is 

shown by the black line. The red shading encloses about 70% of the model results while the 

gold shading shows the lowest and highest values. Figure source: Climate Impacts Group, 

University of Washington.

Impacts on Snow Pack, Stream Flow and Water Temperature 

Quantitative assessments of the impacts of climate change on hydrology and water 

resources have been reported by researchers to link the output from global climate 

models used by the IPCC to physically-based hydrologic models for the Columbia River 

Basin (e.g. Hamlet and Lettenmaier 1999; Payne et al. 2004; Hamlet 2006). These and 

related studies have consistently identified the following types of climate change impacts 

on the snow pack, stream flow, and water quality in the Columbia Basin: 

• Warmer temperatures will result in more precipitation falling as rain rather 

than snow

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 ISAB 2007-2 CLIMATE CHANGE REPORT

The expectation that warmer air temperatures will result in a shift to more 

winter/spring rain and runoff, rather than snow that is stored until the spring/summer 

melt produces runoff, is among the most confident projections for global warming 

impacts on Pacific Northwest hydrology. It is important to note that the sensitivity to 

a given temperature change depends on how near or far each location’s mean winter 

temperature is to freezing. For locations at high elevations in the interior Columbia 

Basin, winter temperatures are typically far below freezing in winter, so one to a few 

degrees C of warming may not initiate a shift from snow to rain. In contrast, low 

elevation temperature in the Columbia Basin are typically much closer to freezing, so 

a small amount of warming in winter can cause these “transient snow zone” locations

to experience substantial shifts in accumulated rainfall versus snowfall in winter (Fig. 

5). 

• Snow pack will diminish, and the timing of stream flow will be altered 

For watersheds that historically develop a seasonal snow pack, warming air 

temperature in winter and spring will lead to more precipitation falling as rain rather 

than snow (see lower panels of Figure below). For affected watersheds, the reduction 

in the amount of water stored in snow pack will result in earlier exhaustion of the 

snow pack and lower flows in streams from June through September. The Pacific 

Northwest region’s typically low late-summer and early-fall stream flows are likely to 

be further reduced, while stream flows are likely to rise from December through 

April. Different watersheds will have different sensitivities to warming impacts on 

snowmelt hydrology. For example, a range of climate change impacts scenarios for 

natural runoff in the mainstem Columbia River at Grand Coulee and The Dalles for 

the 2040s shows only subtle changes in the shape of the monthly mean hydrograph 

for those locations, while the same climate change scenarios cause substantial losses 

of snow and snowmelt runoff for the Spokane and Yakima Rivers (see below). 

Analysis of historical and simulated snow pack records for the 20th century indicates 

that mid-elevation watersheds in the Pacific Northwest have demonstrated a high 

snow pack and runoff timing sensitivity to past fluctuations and trends in 

winter/spring temperatures (Mote et al. 2003 c; 2005b). These same watersheds will 

have the highest snow pack and runoff sensitivity to future temperature changes in the 

next few decades.

• Peak river flows will likely increase 

Because the intensity of precipitation events is expected to increase along with rising 

freezing levels, wet-season runoff and peak flows along many of the region’s rivers 

and large streams is expected to increase (Hamlet 2006). 

• Water temperatures will continue to rise 

Given the close correspondence between surface air temperature and surface water 

temperature for many streams, the latter is also projected to increase in many Pacific 

Northwest rivers, streams, and estuaries. The amount of warming will depend on the 

16
 ISAB 2007-2 CLIMATE CHANGE REPORT

hydrologic characteristics of each water body. For instance, streams with the least 

groundwater inflows will warm more than those having the most groundwater 

inflows. 

Figure 5: (upper panel) Winter 

precipitation sensitivity to 

warming and (lower panels) 

projected streamflow changes in 

the mainstem Columbia River at 

the Dalles and Grand Coulee, and 

for the Yakima and Spokane 

Rivers for a range of 2040s 

climate change scenarios (annual 

average temperature changes of 

+0.8 to +2.6C, annual 

precipitation changes of -4% to 

+9%). The hydrographs below 

the maps show simulated monthly 

naturalized streamflow. The 

black line represents simulated 

natural streamflow for typical 

hydrologic conditions under early 

20th century temperature; the 

gray line represents simulated 

natural streamflow for typical 

hydrologic conditions but late 

20th century temperature; the blue 

swath represents the range of 

projected streamflow for the 

2040s. Reproduced from Casola 

et al. (2005). 

Changes in Terrestrial Ecosystems

What determines the response of terrestrial ecosystems to climate change? 

The detailed responses to climate change of biological communities, such as sagebrush 

steppe or forest, and the wildlife they support, are uncertain because many causal factors 

are involved and much information on specific causal relationships is missing or 

imperfect. More research would improve prediction of change in biotic communities 

with climate change, but considerable uncertainty will remain. The predictions of

biological communities under unprecedented climatic and landscape conditions, and 

17
 ISAB 2007-2 CLIMATE CHANGE REPORT

under unprecedented rates of change in these conditions, must include uncertainty. The 

species composition and health of ecosystems is influenced not only by climate but also 

by interactions among species within communities, including interactions with non-native 

species that are new players in those communities and changes in interactions within a 

community as some species become locally extirpated or extinct and different sets of 

species are present. Additionally, landscape pattern and many ecosystem processes will 

be altered as climate, species, and human population and land use simultaneously change 

(e.g., Aber et al. 2001, Schmitz et al. 2003). Thus, although we can describe the ongoing 

and expected changes in climate and predict direct responses of some species to them, 

and we can define the factors that will be important in determining ecological responses 

and outcomes, considerable uncertainty of the final resulting communities will remain. 

The response of species to global climate change is mediated by several factors: 

Physiological suitability and migration rates 

Species have areas of occurrence (ranges) that are limited by suitable climatic conditions, 

especially temperature and moisture availability. Thus, as temperature and precipitation 

patterns change, species will disappear from parts of their former ranges that have 

become unsuitable for their existence, and they may appear in new areas where they were 

formerly absent. Whether or not the ranges move or expand depends on the ability of 

organisms to disperse or migrate to the areas that become suitable. Paleoecological data 

have been used to infer the rates at which populations migrated across the landscape in 

the past, changing range as climate changed and so persisting (e.g., Graham and Grimm 

1990, Jackson and Overpeck 2000). Migration rates for tree taxa during the Holocene 

were roughly 1000 m/yr (Pitelka and PMWG 1997). 

Recently, shifts have been observed in the ranges of many species that are in directions

predicted by climate change projections and that are correlated with changes in climate 

(Walther et al. 2002, Parmesan and Yohe 2003, Root et al. 2005, Parmesan 2006). These 

changes include poleward and elevationally upward movements of many insects, birds, 

trees, and forbs. It is expected that the ranges of species that are able to migrate rapidly 

enough to track climate changes will shift to new, suitable areas as climate changes. 

However, fragmentation of suitable areas may be a significant problem for some species. 

In Western North American, the area of future habitat that is suitable climatically for 

species is often small and disjunct, reflecting the heterogeneity of the Western landscape. 

Land use will reduce the available habitat that is both suitable climatically and available 

to plants and wildlife and will impede the ability of species to successfully disperse and 

shift ranges as climate changes. Western North America supports high habitat diversity, 

but the spatial extent of any habitat type may be relatively small, and patches may be 

separated from similar habitat by large distances. The relative isolation of habitat patches 

means natural dispersal may be a significant barrier to plants and wildlife adjusting to 

climate change through range shifts. 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

Biotic interactions within communities 

In addition to requiring suitable physical conditions of temperature and water to thrive, 

all species also are influenced by many ecological interactions including disease, 

predation, competition, and food resources. Because the magnitude of species’ range 

shifts is expected to be large, there will no doubt be changes in competitive interactions 

of species, which could affect the viability of some. Predicting future competitive 

interactions is especially difficult. Paleoecological evidence shows that species respond 

individualistically to climate change (Graham and Grimm 1990, Webb 1995, Jackson and 

Overpeck 2000), which means that the mix of species that interact in a location has 

changed with changing climate in the past and must be expected to continue to do so as 

climate changes in the future. Climate change also could eliminate an important predator 

and allow a species to expand its range. The interaction with humans due to our impacts 

on land use will no doubt be an especially important species interaction (Dale 1997). 

Additionally, the Columbia River Basin has many non-natives species, some invasive, 

and the interactions of these species with existing and shifting biological communities are 

only beginning to be understood. One example is cheatgrass (Bromus tectorum), which 

is invasive through much of the sagebrush steppe region and is a leading factor in 

degradation and conversion of the remaining shrubland habitat (Knick et al. 2003). 

Biotic interactions are often dependent on phenology, and directional changes in 

phenology (the seasonal timing of activities of organisms, such as bud break, spawning, 

birth, hibernation, emergence, migration, etc.), that are correlated with directional 

changes in climate have been observed worldwide in recent decades (e.g., Inouye et al. 

2000, Walther et al. 2002, Parmesan and Yohe 2003, Root et al. 2005, Parmesan 2006, 

Stenseth and Mysterud 2005). These changes include earlier arrival of migrant bird 

species, earlier emergence of hibernating animals, and earlier bud break and flowering of 

some plants. These changes provide evidence of the developing biological responses to 

climate change, and they also establish a set of previously unanticipated biological 

hazards of global climate change: mismatch or formerly coordinated phenology of plants 

and animals. Examples include migration timing that no longer corresponds well with 

the timing of growth of plants or animals that provide the food for the migrants (Stenseth 

and Mysterud 2002). An example is the case of the American robin, which was found to 

arrive at a high-elevation site in Colorado 14 days earlier on average than they did in 

1981 and for which the interval between arrival time and time at which bare ground was 

first observed had grown by 18 days (Inouye et al. 2000). This dilemma appears to result 

from differences in the rate of climate change at lower elevations, from which the robins 

migrate and where winter temperatures are warmer and snowmelt has advanced 

significantly, and that at higher elevations, where the combination of winter warming 

with higher snow pack has prevented an earlier spring. 

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Figure 6: A central concept when studying the relationship between climate, phenology 

and other life history traits is the match vs. mismatch of the climate-phenology response 

within different components of the ecological system. (A) The environmental cues 

triggering the onset of egg laying change in asynchrony to the environmental conditions 

prevailing when chicks are reared and when birds’ energetic demands are highest as 

shown for Great tit. (B) The differential climate change between summer and winter 

ranges may lead to problems in the transition for migratory birds, such as the American 

robin. (Figure from Stenseth and Mysterud 2002). 

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Because organisms cue on factors that are good indicators of past phenological 

relationships, but need not cue on the limiting factors themselves, changing temperature 

patterns may often lead to phenology mismatches between interdependent species with 

different cuing patterns and different climatic dependencies. Researchers and field 

biologists have voiced strong concerns that changing patterns of phenology and resulting 

phenology mismatches will result in breeding failures due to pollination failure, lack of 

appropriate food sources, and weather extremes such as early frosts, late freezes, or

unseasonal snowfalls. 

There are a number of reasons for concern that interactions involving natural enemies 

such as forest or rangeland pests will have increasingly strong effects as climate changes. 

It is well established that the life cycles and population dynamics of insects are highly 

responsive to patterns of temperature and moisture (Logan et al. 2003, Logan 2006, 

Williams and Leibhold 2002), and drought has been linked to many cases of insect 

outbreaks in both rangelands and forests (Barbosa and Schultz 1997). As climate 

changes and new areas become more and less suitable for particular species, the climatic 

overlaps of pest and host species will re-assort. Ranges of insects will change more 

rapidly than those of perennial host plants, and host plants at the edges of formerly 

suitable areas of their ranges will become more physiologically stressed. All of these 

changes are expected to raise the likelihood and intensity of outbreaks of insect pests. 

Insects can respond to patterns of climate change more rapidly than most plants. For 

instance, forest pest insects typically can respond to climate in a year, as opposed to their 

forest hosts, for which range changes would take decades or longer (Logan 2006). In 

agreement with this understanding, outbreaks of forest insects are occurring at 

unprecedented levels in western North America. Bark beetles are a striking example. 

Mountain pine beetles in the Sawtooth National Recreation Area, home to the headwaters 

of the Salmon River, which has historically been too cold for outbreaks, have been 

restricted to small thermally favorable areas, such as the west-facing side of a valley 

(Logan 2006). Beginning in the mid 1990s, these small localized populations began to 

increase and merge, forming an outbreak from 1995—2003. Similarly, an outbreak of 

mountain pine beetle in British Columbia, Canada, is both far north of observed 

outbreaks and unprecedented in size (10 million ha affected by summer 2005) (Carroll et 

al. 2003). Outbreak-caused loss of much of the tree cover from many watersheds in 

interior British Columbia has led to increasing concerns about the impact on hydrology 

and salmon habitat (Uunila et al. 2006). 

In the sagebrush and juniper habitat of the Columbia River Basin, similar problems of 

increasing insect outbreak are predicted. The most prominent outbreaking insects in 

these habitats are grasshoppers and Mormon crickets, but other important insects include 

several species of Lepidoptera (moths), Coleoptera (beetles) and Hemiptera (bugs) (Bentz 

et al. 2006, Welch 2005). An example is the sagebrush defoliator, Aroga websteri, a 

Lepidopteran, which occasionally defoliates sagebrush over huge areas. Outbreaks of 

Aroga appear to have become larger and more frequent in recent, warmer years. In both 

21
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forest and rangeland cases, warming temperatures can positively affect the insects 

directly, and moisture or other climatic stress can increase the susceptibility of plants to 

insects. 

Evolutionary responses 

It is also important to consider the nature and extent of evolutionary change in response 

to changing climate. The fact that rates of change in temperature are large compared with 

those observed or otherwise documented in the past means that our ability to anticipate

evolutionary responses is limited. However, there is evidence already of adaptive genetic 

change in some species resulting from changing climate. Species for which such 

evolutionary change is documented include mosquitoes, fruit flies, birds, and squirrels, 

all of which have populations for which long-term studies have established adaptive 

changes in phenology that correspond to changes in seasonal weather patterns such as 

earlier spring, longer growing season, and shifts in the time that is favorable for 

reproduction (Bradshaw and Holzapfel 2006). In the smallest of these species, 

mosquitoes, which have the shortest generation times, clear adaptive evolutionary change 

was seen over as little as 5 years, whereas for the larger and longer-lived squirrels and 

birds, changes were smaller and were apparent only over longer time periods, 10 years in 

red squirrels and more than 30 years in great tits. The great tits, despite adaptive changes 

in phenology, also had declining reproductive success, so it is unclear whether the rate of 

evolution in the population will be sufficient to track changing seasonal patterns of food 

or if the population will become locally or more broadly extinct. The relative rates of

environmental change and evolutionary adaptation will surely vary greatly among 

populations, but it appears that rates of climate change may outstrip the rates of adaptive 

change for many longer-lived species. 

The Predicted Patterns of Change in Terrestrial Ecosystems of the Columbia 

River Basin 

Ecosystem Processes and Disturbance: Fire and Outbreaks of Natural Enemies

Fire is correlated strongly with climate, and virtually all future climate scenarios predict 

increases in fire in western North America, including the Columbia Basin. These 

predicted increases would extend the changes in fire frequency and intensity that 

characterize recent records. Wild-fires have been more frequent, larger, and more intense 

in the past 50, and especially the past 15, years in the shrub steppe and forested regions of 

the West. Westerling et al. (2006) found longer wildfire seasons and higher frequency 

and duration of wildfires in records of fires in western US forests since 1970. The largest 

increases were in the mid-elevation Northern Rockies and were strongly associated with 

increased spring and summer temperatures and an earlier spring snowmelt. 

Fires frequency, intensity, and the duration of fire season have increased in past decades 

in intermountain forest and sagebrush steppe (Fig. 7). These changes were associated 

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with temperature trends (McKenzie et al. 2004, Westerling et al. 2006). Generally, 

warmer and earlier springs correspond to years of higher fire hazards (Westerling et al. 

2006). 

Insect outbreaks are an even more significant source of mortality and disturbance in 

North American forests than is fire (Dale et al. 2001, Logan et al. 2003). Outbreaks of 

forest insects affect roughly 45 times as much area as does fire (Dale et al. 2001), and 

forest insects and pathogens are especially likely to change with climate. Insects are 

typically more mobile than their forest plant hosts, and they have more rapid growth rates 

and life cycles that will be more quickly responsive to climate warming. In recent years, 

hot, dry weather has led to an increase in forest insect outbreaks, and it is expected that

continued global warming will increase this trend, with insect outbreaks becoming more 

common and more widespread and with the ranges of insect pests shifting and in many 

cases expanding to invade new areas and new forest types (Logan et al. 2003). 

Figure 7. Increase in fire frequency in the Western United States, including interior 

regions of the Columbia River Basin. From Connelly et al. 2004 (Figure 7.6), as given at 

http://sagemap.wr.usgs.gov/FTP/images/fig7.6.jpg. 

Water Resources 

Hydrology is strongly linked to climate, and changes in climate are expected to alter 

hydrology and so affect availability of water to plants, fish and wildlife, and people. 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

Both changes in mean climate and changes in variability, especially size and frequency of 

extreme events, are of significance. Hurd et al. (1999) identified indicators of the 

vulnerability of water resources in the United States, grouped them to those that affected 

primarily (1) water supply, distribution, and consumptive uses or (2) stream use, water 

quality, and ecosystem support, and classified each into low, medium, and high 

vulnerability classes relative to all the 204 four-digit HUC watersheds of the continental 

United States. They then analyzed the vulnerability to climate change of the indicators 

separately and for the two aggregate categories. The watersheds most vulnerable to level 

of development, natural variability, and dryness ratio were clustered in the West (Hurd et 

al. 1999), and most of the interior Columbia Basin was characterized as moderately or 

highly vulnerable in these areas, given climate change. The Snake River Plain and 

southeast Oregon were also highly or moderately vulnerable to ground water depletion. 

The aggregate index of vulnerability to water supply, distribution, and consumptive use 

identified most of eastern Washington and Oregon and southern Idaho as at moderate 

vulnerability. 

The interior West was found to be of low vulnerability to flood risk in comparison with 

much of the more heavily-populated United States, but that was primarily because of 

lower population densities in the interior West. The risk would likely be evaluated as 

regionally high and would be expected to increase substantially with increasing 

population and development. The paper also found that the cold-water fisheries of the 

Rocky Mountain Regions were among the most vulnerable to impacts of warmer 

temperatures, with northern and eastern Idaho highly vulnerable, and most of the Oregon 

and Washington parts of the basin moderately vulnerable. The study concluded that the 

vulnerability of western watersheds that are currently water stressed by competing and 

rising water demands, which are likely to continue to rise, are of particular concern. 

Vegetation/Wildlife Habitat 

In the western United States, steep environmental gradients (for instance, in topography, 

elevation, and water availability) mean that there will be relatively few areas where a 

species’ potential range does not shift significantly under future climate scenarios (Shafer 

et al. 2001). The steep environmental gradients also mean that movement corridors, 

which would facilitate the migration of plants and animals to more suitable areas as 

climate changes, may be limited and should be given particular consideration in planning 

to mitigate for climate change. Many assessments of likely ecological responses to 

climate change conclude that several community types that are significant in the 

Columbia River Basin are likely to decrease greatly in area or disappear from the region. 

These include alpine habitats, subalpine spruce-fir forests, aspen stands, and sagebrush 

steppe (Hansen et al. 2001, Shafer et al. 2001). 

Many studies have combined simulations of future climates with information on the 

climate tolerances of plant species to examine the likely occurrence and range limits of 

important plant species that define Columbia Basin habitat types, such as sagebrush 

(Artemisia tridentata), the species that characterizes shrub-steppe vegetation of the 

intermountain West, aspen (Populus tremuloides.), and important forest tree species such 

24
 ISAB 2007-2 CLIMATE CHANGE REPORT

as subalpine fir (Abies lasiocarpa) and Douglas fir (Pseudotsuga menziesii). We review 

the most common predictions for major species of Columbia River Basin habitats below. 

Riparian areas and wetlands 

Riparian areas and wetlands are habitats where terrestrial and aquatic ecosystems are 

most closely linked. They are among the most diverse and dynamic habitats on the Earth, 

and are especially important sources of diversity in arid areas such as the interior 

Columbia River Basin (Naiman et al. 1993, Wissmar 2004). These habitats are critical to 

a broad range of wildlife. For instance, over 70% of the vertebrate species in some

regions have been reported to use riparian corridors in a significant way during their life 

cycle (Raedeke 1989 in Naiman et al 1993). In many areas, riparian and wetland habitats 

have been altered by increasing fire frequency and intensity associated with changing 

climate and by management actions following fires. The expected continuing increase in 

fire frequency in the Columbia Basin means that direct impacts of fire on the riparian 

zone may increase. Additionally, increasing fire frequency and intensity in forests 

increases the likelihood of habitat damage, with both direct effects of more extensive and 

intense fire and indirect effects due to post-fire management practices potentially of 

concern (Beschta et al. 2004, Wissmar 2004). 

The expected effects of climate change on riparian areas and wetlands are exacerbated by 

simultaneous changes in land use and human population. In the West overall, and in the 

Columbia River Basin, human population, land development, and private land ownership 

are concentrated disproportionately along waterways, thus introducing sources of conflict 

between human population and natural resources and biodiversity (Gude et al. 2006, 

Hansen et al. 2000, Hansen et al. 2002, Smith and Wachob 2006). The diversity of 

riparian vegetation is thought to be due to the high dynamism of the habitat, including 

intensity and frequency of floods, variation in soils and topography from natural river 

channel migrations, and disturbance originating from uplands. Decreased flow variation 

has resulted in failure of some dominant riparian tree species to establish, causing 

decrease in the diversity and productivity of the riparian corridor. Past influences of 

people, such as diking, damming, and irrigation, have in large part simplified riverine and 

riparian ecosystems (Naiman et al. 1993, Poff et al. 2007) and eliminated many wetland 

habitats (Sherwood et al. 1990), which would be expected to reduce the diversity of 

species dependent on these habitats. Climate change is likely to work in concert with 

these other factors to further compromise riparian habitats. 

Forests 

The Pacific Northwest hosts a complex suite of forests, including coastal temperate 

(dominated by Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), 

western red cedar (Thuja plicata), and Douglas fir (Psuedotsuga menziesii)), coastal 

subalpine (with mountain hemlock (Tsuga mertensiana) and Pacific silver fir (Abies 

amabilis)), interior montane (with western white pine (Pinus monticola) western red 

cedar, and western hemlock), interior subalpine (with Engelmann spruce (Picea 

engelmannii), subalpine fir, and lodgepole pine (Pinus contorta)), and mixed mesic 

25
 ISAB 2007-2 CLIMATE CHANGE REPORT

conifer (Ponderosa pine (Pinus ponderosa), Douglas fir, and western hemlock) forests 

(Noss et al. 2006). Predicted climate shifts over the next century, combined with known 

climate tolerances of the dominant species of these forests, lead to the expectation that 

there will be dramatic changes in the character of Pacific Northwest forestland (Fig. 8; 

Shafer et al. 2001, Hansen et al. 2001). Potential habitat for the subalpine species 

Engelmann spruce and mountain hemlock is expected to contract substantially in the 

western United States. In fact, alpine habitats, subalpine spruce-fir forests, and aspen are 

expected to be largely eliminated from the Western United States and displaced 

northward to Canada. The future distributions of some species, such as Douglas fir, are 

predicted to be considerably smaller in the region and also include areas significantly 

removed from the current distribution, which may pose problems for migration and range 

adjustments. In some areas, forest may expand, occupying sites currently supporting 

rangeland, as trees are increasingly favored by altered precipitation, enhanced water-use 

efficiency at elevated CO2 levels, and a lengthening of the growing season (Millar et al. 

2006). 

In addition to the predicted shifts of many species’ ranges northward with warming 

temperature, and the expected fragmentation of ranges of many species in the 

heterogeneous western topography, a number of species are predicted to shift in range 

from west of to east of the Cascades. Douglas fir, Pacific yew (Taxus brevifolia) and red 

alder (Alnus rubra) fall into this category. The potential habitats of dominant rainforest 

conifers (e.g., western hemlock, western red cedar) are expected to decrease west of the 

Cascades but expand into mountain ranges of the interior West. In contrast, Ponderosa 

pine, which is tolerant of relative warm and dry climate, is predicted to expand its range 

significantly and to occur west of the Cascades. 

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Figure 8. Comparison of observed distributions with future simulated distributions for Douglas fir 

(Pseudotsuga menziesii) and Ponderosa pine (Pinus ponderosa) using climate scenarios for 2090-

2099 generated by HADCM2, CGCM1, and CSIRO CGM (left three columns). “No change” 

indicates where the species is observed now and is simulated to occur under future climate 

conditions; “contraction” indicates where the species is observed at present but is simulated to be 

absent under future climate conditions; “extension” indicates where the species is not observed 

now but is simulated to be present under future climatic conditions. Agreement among the future 

distributions of each species as simulated by the 3 GCM scenarios is displayed as the number of 

model scenarios under which a species is predicted to be present or absent (right 2 columns). 

(Figure modified from Shafer et al. 2001). 

The increase in mean temperature of the coldest month (MTCO) along the Pacific 

Northwest coast drives the shift of potential ranges of species from west to east. Many 

Pacific Northwest tree species have a winter chilling requirement. Douglas fir, one of the 

major trees of Pacific Northwest forests, has a relatively long chilling period. Increase in 

MTCO thus means that a large disturbance, such as a stand-replacing fire, could be 

followed by low seedling establishment and major changes in species composition of 

27
 ISAB 2007-2 CLIMATE CHANGE REPORT

Douglas fir dominated forests. The absence of below-freezing temperature also could 

allow competitors currently excluded by low temperatures to establish in the region. In 

the west, the shift from below-freezing to above-freezing mean monthly temperature 

occurs for a region of the interior West that stretches from northern Arizona to southern 

Washington. 

These projected changes in suitable ranges of species are only initial predictions of where 

temperature and moisture conditions are expected to be suitable for growth. The final 

ranges will also be influenced by patterns of disturbance (e.g., fire and insect outbreaks), 

species interactions with native and non-native species, and landscape structure and the 

movement capabilities of the plant species, which will interact to determine the 

distribution and abundance of species in the future. 

Shrubland/rangeland 

Sagebrush steppe is the dominant low and mid-elevation vegetation of the interior 

Columbia Basin. This community type is predicted to change greatly in range and extent 

under future climatic conditions. Big sagebrush (Artemisia tridentata), the most 

widespread and characteristic shrub of the inner Columbia Basin, is expected to decline 

sharply throughout the region (e.g., Hansen and Dale 2001, Shafer et al. 2001). 

Sagebrush is found in regions where most precipitation falls in winter, and sagebrush has 

both ephemeral and perennial leaves that allow them to take advantage of this pattern

(Welch 2005). Although the range of big sagebrush remains very large, occurrence of 

big sagebrush is already sharply reduced from that of 100 years ago by the conversion of 

shrubland to agricultural uses, including rangeland, and by the high degree of 

fragmentation of remaining sagebrush habitat (Welch 2005, Knick et al. 2003). Millar et 

al. (2006) show that the interior shrublands/grass-lands also are likely to be impacted by 

expansion of woodlands (e.g. Ponderosa pine) or continental conifer forests (e.g., 

Douglas fir), due to increased precipitation, enhanced water-use efficiency for elevated 

CO2 and a lengthening of the growing season. The range of big sagebrush is predicted to 

shift to Canada, with shrubs now found in the southwestern United States replacing it 

throughout much of the Columbia Basin in the United States. (Hansen and Dale 2001, 

Shafer et al. 2001). 

Wildlife Species 

Prediction of effects of global warming is more complicated for wildlife, which depend 

not only on suitable conditions of temperature and moisture but also on the resulting 

vegetation for habitat and often for food. Thus, there is an additional layer of effects to 

be accounted. Paleoecological studies show clearly that the responses of both plants and 

wildlife to climate are species specific, so local assemblages of species are expected to be 

different in the future from what we know today (Graham and Grimm 1990, Jackson and 

Overpeck 2000). An additional concern comes from the many non-native species now

present in the Pacific Northwest or surrounding areas of North America. As these change 

their ranges in response to climate, novel predator-prey interactions and new sets of 

competing species will occur, with outcomes that we cannot anticipate (e.g., Schmitz et 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

al. 2003). The main lesson of the many studies of expected climate-caused changes in 

wildlife is that we must be prepared to accommodate major surprises (Root and 

Schneider 2002). Thus, a commonly recommended strategy for preparing to mitigate 

effects of climate change is to plan for a high degree of uncertainty rather than for a more 

narrow solution that might appear optimal today. 

The effects of changing climate on wildlife are expected to be strongly interactive with 

changes in habitat caused by changing land use. The expansion of population in the 

West, including expanding habitation that outstrips population growth through growing 

numbers of second homes, will result in decline in available habitat for most wildlife 

(excluding those that benefit directly from the kinds of environments that are created by 

people) and in increased fragmentation of remaining habitat. An example of the expected 

problems for wildlife that will accompany global warming and changing human 

population can be drawn from the sagebrush habitat of the inner Columbia Basin, which 

is highly fragmented, has increasingly high numbers of non-native plant species, and has 

had sharply increasing frequency, size, and intensity of fire in recent years. Many species 

of sagebrush birds and mammals are of concern to the Columbia River Basin Fish and 

Wildlife Program, including the greater sage grouse, Columbian sharp-tail grouse, pygmy 

rabbit, Brewer’s sparrow, sage sparrow, and sage thrasher, all of which have population 

declines and populations of concern in at least some Columbia River Basin states. The 

bird species of shrubland and grassland are declining more rapidly than any other group 

of species in North America (Knick et al. 2003). A survey of 61 species of birds and 

small mammals that are dependent on sagebrush habitat (43 upland species and 18 

riparian species) found that a majority of populations had either significantly declined or 

were not present in censuses of areas thought to be suitable habitat (Dobkin and Sauder 

2004). 

One important specific strategy to mitigate against damaging effects of climate change is 

the identification of locations likely to remain suitable for particular wildlife and 

retention of sufficiently large tracts of land within these regions to enable persistence of

these species. These protected areas also must be linked to enable seasonal movements 

and longer-distance, more permanent range shifts. Preservation of suitable vegetation that 

is naturally occurring under future climate conditions will require similar attention to 

protection of large areas that cover a range of linked climatic conditions (e.g., latitudinal 

and altitudinal variation to avoid unnecessary habitat fragmentation that would both 

increase local extirpation and decrease possibilities of migration of plants and animals to 

new ranges matched to future local climates). 

Effects on Tributary Habitat 

Changes in hydrology and temperature caused by changing climate both have the 

potential to negatively impact aquatic ecosystems in the Columbia basin with salmonid 

fishes being especially sensitive to projected changes. The intensity of the effects will 

29
 ISAB 2007-2 CLIMATE CHANGE REPORT

vary spatially. However, climate change does have the potential to generate ecological 

responses in virtually all the tributary systems of the Columbia Basin. 

The potential impacts of climate warming on stream habitat have been assessed (EPA 

1995; Eaton and Scheller 1996; Rahel et al. 1996; O’Neal 2002; Preston 2006). Several 

of these reports include information relevant to the Columbia Basin. Rahel et al (1996) 

projected losses of 7% to 76% of the trout habitat in the North Platte River drainage in 

Colorado as a result of warming. Although the North Platte River is outside the 

Columbia Basin, the conditions in this Rocky Mountain system are comparable to many 

of the tributaries of the Columbia in Idaho and Montana. 

O’Neal (2002) provides a detailed assessment of the potential impacts of climate 

warming on salmon and trout habitat in the contiguous 48 states of the United States and 

also provides specific projections for the Pacific Northwest. This analysis was conducted 

using the Canadian Climate Center CGCM2 model and an assumption of continued 

increase in atmospheric CO2 at a rate described in the A2 scenario (Nakicenovic et al. 

2000). This combination of model and emissions scenario produces a fairly high 

projection of climate warming with a 5o

C increase in average global temperature by 

2090. Those locations that experienced a projected average weekly maximum 

temperature that exceeded the upper thermal tolerance limit for a species were considered 

to be lost habitat. The results suggest a substantial decline in the habitats suitable for 

cold water fishes. For example, areas with thermal conditions suitable for trout would 

decrease by 15% to 40% by 2090 across the United States. In the Pacific Northwest 2% 

to 7% of current trout habitat would be unsuitable by 2030, 5%-20% by 2060 and 8% to 

33% by 2090. Salmon habitat may be more severely affected, in part because these 

fishes can only occupy areas below barriers and are thus restricted to lower, warmer 

elevations within the region. Salmon habitat loss would be most severe in Oregon and 

Idaho with potential losses exceeding 40% by 2090 (Fig. 9). Loss of salmon habitat in

Washington would be less severe; worst case of about 22% loss by 2090. These 

estimates do not consider the associated impact of changing hydrology. 

A recent analysis of the impact of climate warming on cold-water fish habitat applied a 

Monte-Carlo simulation to climate projections from multiple General Circulation Models 

and future greenhouse gas emission scenarios (Preston 2006). This approach was chosen 

to account for the uncertainty associated with future predictions of climate change. The 

median values for proportion of cold-water fish habitat lost in the Rocky Mountain region 

for the years 2025, 2050 and 2100 were 20%, 35% and 50%, respectively. Considerable 

variability was associated with these estimates (95% confidence intervals - 2025: 15% -

35%; 2050: 22%-58%; 2100: 20%-100%). Nonetheless, all combinations of models and 

greenhouse gas scenarios indicated a substantial loss of coldwater fish habitat in this 

region. 

Although there is considerable uncertainty about how severe or widespread the loss of 

cool-water fish habitat will be in the Columbia Basin, there is compelling and growing

evidence to indicate that significant changes in the quality and quantity of habitat suitable 

for salmon, trout, and cool-water species will occur. Sites most susceptible to effects 

30
 ISAB 2007-2 CLIMATE CHANGE REPORT

from higher summer water temperatures would include those locations that currently 

experience high summer air temperatures. Lower elevation areas, locations east of the 

Cascade Mountain crest and in the southern portions of the Columbia Basin would be 

expected to be most affected (Fig. 9). Changes in hydrology will most affect tributary 

habitats in those watersheds where snow levels are impacted. Watersheds that are just 

above the current snow line currently may experience a change from a snow melt 

dominated hydrologic regime to one that is driven primarily by rainfall or rain on 

transient snow pack. Even those watersheds that remain above the snow line will 

experience earlier snow-melt runoff. These changes in hydrology all may have 

associated impacts on salmon and trout productivity. 

Figure 9: Proportion of salmon habitat lost in the future in WA, OR and ID as a result of 

warming associated with climate change from O’Neal (2002). The projections represent 

output from the Canadian Climate Center CGCM2 model and an assumption of continued 

increase in atmospheric CO2 at a rate described in the A2 scenario (Nakicenovic et al. 

2000). This combination of model and emissions scenario produces a fairly high 

projection of climate warming with a 5oC increase in average global temperature by 

2090. 

Hydrologic changes to Columbia Basin streams will be driven primarily by reduction in 

snow pack as temperatures warm, and the snowline moves upward. The result of these 

changes will be higher frequency and intensity of flood flows; earlier occurrence of snow 

melt runoff and soil moisture recharge; reduced natural summer and early autumn flows; 

and an increase in the duration of the summer dry period with very low soil moisture 

(Hamlet 2006). Natural tributary flow regimes will be most altered in those watersheds 

at mid-elevations where higher freezing level causes a change from a snowmeltdominated to a rainfall-dominated flow regime (Hamlet 2006). 

There will be some watersheds that may not be subjected to large changes in flow regime, 

even in areas affected by elevated snow level. In areas with permeable geology, like 

volcanic fields, precipitation, either as snow or rain, enters into an extensive groundwater 

31
 ISAB 2007-2 CLIMATE CHANGE REPORT

reservoir. Water may be stored for years or decades and outflow from the aquifer is very 

stable, resulting in little seasonal change in flow. Watersheds such as the Deschutes and 

Metolius rivers in Oregon exhibit this type of hydrologic system. Flows in watersheds 

with these extensive groundwater systems will be modified much less by reduced 

snowpack as long as the total amount of precipitation does not decrease (O'Conner et al. 

2003; Jefferson et al. 2006). Such streams that are sourced from deeper groundwater 

reservoirs maintain much cooler summer temperatures than those supplied by shallow 

subsurface flows (Tague et al. in press). However, watersheds fed by these very large 

groundwater systems are relatively uncommon in the Columbia Basin. 

Increase in regional air temperatures and low stream flows will be the primary driver of

increased water temperatures. The most affected watersheds will be those that typically 

experience warmer summer temperatures (O’Neal 2002) including streams at lower 

elevations and those with channel conditions prone to heating (wide, shallow, lack of

riparian vegetation) (Crozier and Zabel 2006). Many of the most sensitive streams are 

located in eastern Washington and southern Idaho (Fig. 10). Crozier and Zabel (2006) 

reported that despite high elevation, stream temperatures in the Salmon River basin 

already exceed 13o

C and some streams have annual temperatures that are rising steadily 

about 1.2o

C per decade. Changes in water temperature also are linked to hydrologic 

changes. Lower summer and early autumn flows will make streams more responsive to 

increased air temperature and earlier snow melt will enable warming to begin earlier in 

the year. 

Figure 10: The warmest temperatures in the Columbia River basin are typically observed 

in August in the lower Columbia and Snake Basins. The monthly average August 

temperature maps shown below highlight those parts of the region that have experienced 

August mean temperatures greater than 20C for 1980-97, and for periods experiencing 

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+1.9C and +2.3C warming, temperature changes that are in the middle of projected 

temperature change scenarios for ~2050s and ~2060s. Note that only a few percent of the 

region had August mean temperatures greater than 20C in the 1980-97 period, but about 

20% of the region would have August temperature greater than 20C with 2.3C of 

warming. 

As discussed in the section in this report on potential effects on terrestrial ecosystems, 

climate change may increase the severity and frequency of both fires and insect 

infestations, which are likely to affect aquatic habitats as well. Removal of trees from

riparian areas by fire or insects will lead, at least temporarily, to an increase in solar 

radiation reaching the water and exacerbate the water temperature increase associated 

with climate warming (Beschta et al. 1987). Late summer flow may be increased by the 

loss of tree cover due to reduced transpiration (Ziemer and Lisle 1998). Higher summer

flows may offer some benefit to aquatic biota, provided that water temperatures are not 

limiting. However, it is not clear whether the increase in flow due to reduced 

transpiration would be sufficient to offset reduced flows related to earlier snowmelt 

runoff and any benefit would be of short duration, decreasing as vegetation reoccupied 

the watershed (Hicks et al. 1991). Reduction in tree cover also may lead to increased 

snow accumulation and earlier and more rapid melting (Harr 1986). These changes 

would further contribute to an earlier period of high flow in the basin. Sediment 

production and delivery to streams also may be increased as loss of vegetative cover can 

lead to increases in mass soil movements such as landslides and debris torrents (Benda et 

al. 1998). Some the of the highest quality aquatic habitat remaining in the Columbia

Basin is found in forested areas. Therefore, increased incidence of fire and insect 

outbreaks will disproportionately impact habitats of key importance to native fish and 

wildlife populations. 

The projected changes in thermal and hydrologic conditions have the potential to affect 

salmonid fishes during all their freshwater life history stages. These potential impacts are 

discussed below. 

Egg Incubation and Fry Emergence 

Increased frequency and severity of flood flows during winter can affect over wintering 

juvenile fish and eggs incubating in the streambed. Eggs of fall and winter spawning 

fish, including Chinook, coho, chum, and sockeye salmon and bull trout, may suffer 

higher levels of mortality when exposed to increased flood flows (Jager et al. 1997). 

Scouring of the streambed can dislodge the eggs (Schuett-Hames et al. 2000) and 

elevated sediment transport caused by high flow can increase sediment deposition in 

redds, suffocating eggs (Peterson and Quinn 1996). Spring spawning fish, such as 

steelhead and cutthroat trout, also may suffer increased egg mortality due to dewatering 

of redds caused by earlier snow melt runoff (Jager et al. 1997). Shifts in the timing and 

magnitude of natural runoff will likely introduce new selection pressures that may cause 

changes in the most productive timing or areas for spawning. 

33
 ISAB 2007-2 CLIMATE CHANGE REPORT

Warmer winter temperatures and the retreat of snow level to higher elevations may lead 

to earlier fry emergence for some populations (Healey 2006). Individual populations 

have spawning times and egg development rates that are matched to the environmental 

conditions of their spawning stream (Tallman 1986, Beacham and Murray 1990). Earlier 

emergence may expose the fry to increased mortality rates due to a lack of food or 

increased predation (Brannon 1987; Tallman and Healey 1994). Increased water 

temperature also may increase the metabolic rate of the developing embryos, causing 

them to divert energy from growth to metabolic maintenance. This process would result 

in smaller fry size at emergence (Beacham and Murray 1990). It is also possible in some

situations that elevated incubation temperatures could cause direct egg mortality or

increased susceptibility to disease (Healey 2006). 

Bull trout (Salvelinus confluentus) in the Columbia Basin require cold, headwater streams 

for spawning. Therefore, a warming climate may disproportionately impact this species. 

Recent projections of the loss of habitat suitable for bull trout in the Columbia Basin as a 

result of climate warming range from 22% to 92% (B. Reiman, USFS, pers. comm.). The 

areas most severely affected are at lower elevations. Reduction in bull trout spawning 

habitat also will further fragment existing populations and reduce the opportunity for 

genetic exchange, which may accelerate the decline of this species in the Columbia Basin 

beyond that predicted simply due to temperature change. 

Spring/Summer Rearing 

Reduction in spring and summer stream flow in watersheds where snow pack has been 

reduced and snow melt timing advanced may impact the quality of rearing habitat. 

Reduction in summer and early autumn flows will, at a minimum, reduce the area of

wetted stream channel, thereby reducing available habitat for rearing fish. In addition, 

susceptibility to predation may be increased due to shallower water or stranding of fish in 

isolated pools. Fall stream flow was found to be positively associated with survival in

some populations of Salmon River Chinook salmon populations (Crozier and Zabel 

2006). The populations sensitive to these flow changes tended to occupy cooler streams 

with narrow channels while survival of populations in wider, warmer streams was more 

closely related to summer temperature. 

Warmer water temperatures during summer can have a variety of effects. Salmonids may 

be excluded from reaches with temperatures that are already close to their upper thermal 

limit (O’Neal 2002). Even in systems where water temperatures do not exclude use by 

salmonids, metabolic rates will increase. In systems where food is limited, the increased 

energy required for metabolic maintenance will reduce growth rates leading to smaller 

size at the end of the summer (Marine and Cech 2004). Smaller fish typically suffer 

higher mortality rates during winter than larger fish (Quinn and Peterson 1996). Both 

native and non-native fishes may enjoy a competitive advantage over salmonids at 

elevated water temperatures. Brook trout (Salvelinus fontinalis) have been shown to be 

more efficient at obtaining food than cutthroat trout at 20o

C but the two species exhibited 

comparable ability to obtain food at 10o

C (DeStaso and Rahel 1994). Redside shiners 

(Richardsonius balteatus) have been shown to displace steelhead from preferred habitat 

locations at higher water temperatures (Reeves et al. 1987). Northern pikeminnow 

34
 ISAB 2007-2 CLIMATE CHANGE REPORT

(Ptychocheilus oregonensis) also prefer warmer temperatures than salmonids and may 

become more numerous in rearing areas of juvenile salmonids as stream temperatures 

increase (Petersen and Kitchell 2001). 

In some streams an increase in temperature may improve conditions for salmon and trout. 

In very cold streams, time of spawning and egg incubation may be delayed until well into 

summer resulting in small fry at the onset of winter and reduced survival (Harig and 

Fausch 2002). Increased spring and summer water temperatures caused by climate 

change could alleviate this problem to some extent by enabling earlier spawning and fry 

emergence and a longer growth period. Thus, fish would be larger at the end of summer 

provided adequate food is available. Winter mortality associated with anchor ice also 

might be reduced (Meisner at al. 1988). These types of positive effects would likely be 

limited to aquatic systems at the highest elevations in the Columbia Basin and would 

influence few stream occupied by anadromous species. However, Beckman et al. (1998) 

found that increased temperatures led to higher growth rates and earlier downstream

movements of yearling Chinook salmon, which may provide a survival advantage under 

some circumstances. 

Predation rates on juvenile salmon can be affected by elevated temperatures. If water 

temperature remains below 20o

C, increased activity by predators may be partially offset 

by increased activity of juvenile salmon, enabling them to better avoid predators. 

However, juvenile Chinook salmon have been shown to become less adept at avoiding 

predators at temperatures above 20o

C (Marine and Cech 2004). The consumption of prey 

by many piscivorous fishes continues to increase above 20o

C. Petersen and Kitchell 

(2001) used a bioenergetics model to assess the effect of temperature on predation by 

northern pikeminnow on juvenile salmon. They used temperature records from the 

Columbia River for the years 1933-1996. Their analysis suggested that during warmer 

years predation rates were 26% to 31% higher than during the coldest years. Predation 

rate during the single warmest year was predicted to be 68% to 96% greater than during 

the coldest years. Increases in predation on young salmon by other piscivorous fishes in 

the Columbia Basin also would be expected to increase if temperatures were elevated to 

stressful levels (Petersen and Kitchell 2001). 

Overwinter Survival 

Increased winter water temperatures may have both positive and negative impacts on 

fish. Higher winter temperatures may enable fish to feed more actively during the winter, 

potentially increasing growth rates if sufficient food is available. If food is in limited 

supply, the elevated metabolic demands created by elevated winter temperatures could 

reduce winter growth rates and contribute to reduced smolt size the following spring 

(Healey 2006). Higher winter temperatures also would increase the activity of predators, 

possibly increasing mortality due to this source (Petersen and Kitchell 2001). 

Climate change effects experienced by fish during the spring and summer also can affect 

their ability to survive through the winter. Generally, higher summer temperatures will 

reduce the growth rates of juvenile fish, reducing average size entering winter. Body size 

at the end of summer has been shown to be positively related to overwinter survival 

35
 ISAB 2007-2 CLIMATE CHANGE REPORT

(Quinn and Peterson 1996). As noted above, in certain circumstances higher water 

temperatures during spring and summer may accelerate growth, if sufficient food is 

available to offset the higher metabolic cost associated with elevated temperature. This 

effect is likely to occur most frequently in cold, high-elevation streams. 

Where the hydrologic regime changes from snow melt dominated to rain dominated, 

more frequent high flows could occur. These circumstances are likely to cause increased 

mortality if winter habitat that provides refuge from floods is not available. This type of 

habitat is often located on floodplains in the form of low-gradient tributaries or ponds 

(Peterson 1982). As floodplain habitat along many of the major rivers in the Columbia 

Basin has been modified or isolated from the channel, refuge habitat is likely to be very 

limited (Bottom et al. 2006). Therefore, the hydrologic changes during winter associated 

with climate change would be likely to elevate mortality. 

Effects in the Mainstem

Physical Effects 

Hydrosystem development on the mainstem Columbia and Snake rivers has altered these 

free-flowing rivers into a series of reservoirs, and along with other anthropogenic landuse and water-use practices has already altered seasonal water temperature regimes and 

flow patterns from historical conditions in the basin. With the completion and 

coordinated operation of the major Columbia Basin storage dams in the 1960s and 1970s, 

peak daily flows at The Dalles were substantially and systematically reduced, while flows 

from October through April have been substantially and systematically increased (Figure 

11; Naik and Jay (2005)). The net result of hydrosystem operations has been to reduce 

the historic peak flows in May, June, and July and to increase winter flows on a regular 

basis. Note that the changes in mainstem flows due to hydrosystem operations since at 

least the 1970s are substantially greater than the natural runoff changes projected to be 

caused by climate warming in the 21st century. 

36
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 11: (top) The observed daily 

average gauge flow at the Dalles, Oregon, 

from 1878-2004, in m3/s. (right) Average 

daily hydrographs at the Dalles for 1901-

1950 (in blue) and 1980-2003 (in red). 

Note that both figures show the major 

reduction in daily peak flows, primarily a 

consequence of hydrosystem development 

and operations, but also influenced by 

irrigation withdrawals and climate 

variations (Naik and Jay 2005). 

Management of the hydrosystem also causes substantial changes in stream flow at time 

scales shorter than one day. In the Hanford Reach section of the mainstem Columbia, 

daily fluctuations below Priest Rapids dam in the relatively low-flow months of summer 

and fall often have double the flow during daylight hours compared to flows at nighttime 

(Figure 12). 

Figure 12. USGS gauge flows in the mainstem Columbia River below Priest Rapids 

Dam, WA, from September 30 though October 30, 2006. Note that on most days daily 

flows range from lows of ~40,000 cfs to highs of ~160,000 cfs. Figure obtained from the 

USGS web-pages (http://waterdata.usgs.gov/wa/nwis/uv/?site_no=12472800). 

Long-term temperature series data were collected at Bonneville Dam (1938-1996) and 

Rock Island Dam (1933-1996) on the Columbia River (Fig. 13) to characterize how upper 

and lower mainstem river temperature change may have effected historical trends in 

predation rates on salmonids through a bioenergetic analysis (Petersen and Kitchell 

37
 ISAB 2007-2 CLIMATE CHANGE REPORT

2001). Trends as seen in Figure 13 indicate that water temperatures were relatively warm

in the 1930s, cooler in the late 1940s to 1950s, and gradually warmed from about 1960 to 

1996. If we were to plot temperatures from 1996 to the present we would see a definite 

trend in this increasing warming. 

Year

1930 1940 1950 1960 1970 1980 1990 2000

15

20

Average Julytemperature (oC) Dams

a )

b )

Figure 13. Average daily water temperature during July at Bonneville (O) and Rock 

Island (•) dams from 1933 to 1996. Also shown is the year of construction for dams on 

the lower Snake River (ν) and the Columbia River (τ; U.S. and Canadian dams). From 

Petersen and Kitchell (2001). 

The construction of the hydrosystem has also altered mainstem water temperature 

regimes. Currently, warming of water in the reservoirs begins earlier in the spring and 

persists longer into the fall than historically (Quinn and Adams, 1996). Climate 

modeling of future water temperatures in the Columbia and Snake rivers predicts an 

increase of 1o

 C or greater by 2040 (Hamlet and Lettenmaier 1999; Payne et al. 2004). 

The models also predicted an increase for winter precipitation of about 5% by 2040, with 

more falling as rain and less as snow, reducing winter snow accumulation, thus 

increasing winter to early spring flows and extending the low summer flow period to 

winter (Payne et al. 2004). The construction of the hydrosystem has also altered 

mainstem seasonal water temperature patterns. Currently, warming of water in the 

reservoirs begins earlier in the spring and persists longer into the fall than historically 

(Quinn and Adams, 1996). 

Biological Effects – Juvenile Salmonids 

Climate change effects will have the most significant impacts on the early life stages of

fall Chinook, which rear in mainstem habitats in the Hanford Reach of the Columbia 

River and in the lower Snake River above Lower Granite Dam (LGR). As the early life 

38
 ISAB 2007-2 CLIMATE CHANGE REPORT

stages of spring/summer Chinook salmon, coho salmon and steelhead are spent primarily 

in tributary habitats within the Columbia River Basin, impacts on those types/species 

from climate change will be most pronounced there, as indicated in the previous section 

of the report. 

Increased rate of embryonic development and earlier emergence 

Increases in water temperature during egg incubation will increase the rate of 

development and lead to an earlier hatch and emergence and most likely at a smaller 

average size than historically (Healey 2006). Smaller sized fry are likely to have lower 

survival due to increased vulnerability to predators (size selective predation and 

swimming performance) and increased maintenance metabolism leading to greater food 

demand, slower growth, and increased risk to predators due to added foraging time 

(Healey 2006). Earlier life stage timing may also lead to earlier smoltification and 

emigration timing, which may adversely affect optimal ocean entry. 

Contraction of juvenile fall Chinook summer rearing habitat due to temperature 

increases and decreased flow 

Water temperature was the most important variable effecting presence of subyearling fall 

Chinook in the shoreline habitats of the Hanford Reach, Columbia River (Tiffan et al. 

2006). These juvenile fall Chinook preferred shallow, relatively warmer water than 

occurs in the main channel waters of the Columbia River in this reach. However, climate 

change will likely increase water temperatures in shallow shoreline areas beyond their 

preferred temperature of 17o

 C (Sauter et al. 2001) and earlier in the season. At these 

higher temperatures, survival of wild subyearling generally decreases with increasing 

water temperatures (Connor et al. 2003). Juvenile fall Chinook will then likely move out 

of protected shallows earlier and potentially at a smaller size than normal for this risky 

transition. This may lead to a size-related increase in exposure and vulnerability (size 

related) to predators (Petersen and Kitchell 2001) (see below in predation section) and 

cause a decrease in growth rate if food resources are limited in less optimal habitat in 

down-river reaches. However, if the food base is equivalent or better in down-river 

habitats, growth rates would be increased with higher temperatures and potential negative 

effects could be compensated for. 

Alteration in timing of smolt migration 

Earlier snowmelt and earlier, higher spring flows and warmer temperatures may cause 

spring Chinook and steelhead yearlings to smolt and emigrate to the estuary and ocean 

earlier in the spring. This early emigration may cause these juveniles to arrive in the 

estuary and ocean either during favorable upwelling conditions, or prior to the period of

favorable ocean upwelling if upwelling is delayed (see section on upwelling). For spring 

Chinook, upwelling during April has been correlated with enhanced survival (Scheuerell 

and Williams 2005). Yearling migrants also may be exposed to increased predation risk

in the mainstem because of higher consumption rates by predators at the elevated spring 

water temperatures (see below in subsection on predation). 

39
 ISAB 2007-2 CLIMATE CHANGE REPORT

Increased water temperatures also may lead to faster growth rates, which may further 

contribute to earlier smoltification and emigration timing (Beckman et al. 1988). Smolt 

size is an important determinant of marine survival for some species, such as coho 

salmon (Bilton et al. 1982; Holtby et al. 1990). However, Henderson et al. (1992) found 

for pink salmon, O. gorbuscha, date of ocean entry timing, not size, was the primary 

determinant of survival, not size. Earlier outmigration may be advantageous for some 

stocks of in-river fish that now have poor survival due to delayed ocean entry (Snake 

River spring/summer Chinook), provided that upwelling and ocean conditions are 

favorable during entry. 

Another consequence of elevated spring water temperatures is that when water 

temperatures rise to above 13 0 C, gill ATPase (an indicator of migratory readiness) in 

yearling steelhead emigrants decline and these fish often stop downstream migration and 

residualize over winter (Zaugg and Wagner 1973). In addition to having consequences 

for survival and stock productivity, this behavior confounds PIT tag survival estimates 

because steelhead that hold-over are counted as mortalities. For example, during the 

2001 juvenile salmonid emigration, under extremely low flows and relatively high 

temperatures, survival of Snake River juvenile steelhead was only 4.2% from Lower 

Granite to Bonneville (Zabel et al. 2002). Zabel et al. (2002) indicated that the 

residualization of large numbers of steelhead juveniles below Lower Monumental Dam 

may have been a big cause for this low survival estimate. During the following spring 

migration only 0.15% of these 2001 PIT tagged fish were detected indicating that few 

survived predators or fisheries, and there were too few to substantially alter survival 

estimates for 2001. 

 

Temperature increases and decreasing flow in summer may also lead to earlier migration 

timing of both Columbia and Snake river populations of “ocean-type” fall Chinook. 

Thermal changes could be particularly damaging to the portion of the Snake River 

juvenile fall Chinook population that exhibits a “reservoir-type” life history Chinook. 

Research by Connor et al. (2002; 2003; 2005) has indicated that when water temperatures 

are warmer during the incubation period of fall Chinook eggs the timing of the various 

life history stages (emergence, parr, and smolt) occur earlier. Cool water flow 

augmentation from Dworshak Reservoir has led to lower water temperatures in the 

spawning areas for fall Chinook in the lower Snake River and may be an important factor 

in the development of the reservoir-type life history (Connor et al. 2003). Flow 

augmentation also maintains cooler summer and fall water temperatures, providing 

thermal refugia for the rearing reservoir-type Chinook. If water temperatures in the lower 

Snake River warm during spring, summer and fall sufficiently that the cannot be 

maintained at a level suitable for salmon by cold water releases from Dworshak 

Reservoir, the reservoir-type fall Chinook populations of the lower Snake River may be 

diminished or lost. 

Decreased flow owing to earlier snowmelt runoff may cause delay in migration of 

juvenile fall Chinook in the forebays of mainstem dams if summer spill is reduced. This 

could lead to higher predation rates in the forebay. It has also been shown that in low

flow periods in the summer there is some temperature stratification in the near dam

40
 ISAB 2007-2 CLIMATE CHANGE REPORT

forebay (Bennett et al. 1997). With warmer waters near the surface, juvenile salmonids 

may alter their vertical distribution by moving to deeper cooler waters and be less

efficiently passed through surface collection devices (e.g. removable spillway weirs 

(RSWs)). 

Changes in predation on juvenile salmonids 

If juvenile salmonids of all life history types emerge from spawning gravels earlier due to 

increased winter water temperatures, fry size may decline. Smaller fry are more 

vulnerable to predation by northern pikeminnow, which are generally size selective when 

feeding on juvenile salmonids (Poe et al. 1991). Also as indicated above, if juvenile 

salmonids of any life history type leave preferred rearing habitats too early this may 

reduce growth rates and result in increased vulnerability to predators. 

Predicted increases in water temperature in Columbia and Snake River reservoirs during 

the major smolt emigration will most likely increase consumption rates and growth rates 

of predators and hence predation related mortality. Summer emigrants, primarily 

subyearling fall Chinook, are particularly vulnerable. Juvenile salmonid consumption 

rates of the three major predators (northern pikeminnow, walleye, and smallmouth bass) 

in Columbia and lower Snake River reservoirs is highest in July concurrent with 

maximum availability and temperature (Vigg et al. 1991) and the maximum daily 

consumption of juvenile salmonids by northern pikeminnow increases exponentially as a 

function of temperature (Vigg and Burley 1991). Sublethal thermal stress is another 

factor known to increase vulnerability to predation (Coutant 1973; Yocum and Edsall 

1974). Thermally stressed fish may suffer elevated mortality when exposed to the 

additional physical stress associated with dam passage. The combined effects will likely 

increase the vulnerability of surviving fish to predators (Mesa et al. 1994; Mesa 1994). 

Another indication of how predation rates on juvenile salmonids emigrating through the 

Columbia River Basin may increase with projected climate change is revealed in a 

bioenergetics analysis by Petersen and Kitchell (2001). They examined climate regime 

shifts and corresponding water temperatures in the Columbia River from 1933-1996 to 

estimate how predation, primarily by northern pikeminnow, on juvenile salmonids may 

have varied. Three indices of climate, the Pacific Decadal Oscillation (Mantua et al. 

1997), the Pacific Northwest Index (Ebbesmeyer and Strickland 1995), and the Columbia 

Basin Index (Petersen and Kitchell 2001) were used to characterize historical climate 

conditions for the Columbia River Basin. All three indices were highly correlated and 

agreed that climate shifts occurred in 1946, 1958, 1969, and 1977. Summer water 

temperature varied as much as 2o

 C between different climate periods. Their results from 

the bioenergetics model indicated that predation on juvenile salmonids was estimated to 

be from 26% to 31% higher during warmer spring-summer periods (1933-1946, 1978-

1996) than during a much colder period (1947-1958) (Fig. 14). Their results also 

indicated that predation on salmonids by walleye and smallmouth bass would have varied 

in a very similar manner to that of pikeminnow. 

41
 ISAB 2007-2 CLIMATE CHANGE REPORT

-10

-5

0

5

10

Climate period

Percent change in cumulative 

salmonids consumed

 (relative to average)

-10

-5

0

5

10

1933-

1946

1947-

1958

1959-

1969

1970-

1977

1978 -

1996

a)

b)

Figure 14. Percent difference (relative to the overall average) in cumulative, per 

capita consumption of salmonids in the Columbia River by northern pikeminnow 

(black bars), smallmouth bass (white bars), and walleye (gray bars). Estimates were 

made using bioenergetics models and water temperature from Bonneville (a) and 

Rock Island (b) dams. (modified, with permission, from Petersen and Kitchell, 2001). 

Changes in smolt health (pathogens and parasites) 

Many fish pathogens and parasites are common in the environment and their salmon 

hosts but often don’t become injurious until their host becomes thermally stressed. One 

consequence from long-term chronic exposure of smolts to increased water temperatures 

42
 ISAB 2007-2 CLIMATE CHANGE REPORT

is an increase in the risk of high mortality in the forebays and collection systems of 

mainstem dams due to a bacterial gill disease, Cytophaga (formerly Flexibacter)

columnaris. This disease has the potential to kill very large numbers of smolts in a few 

days and has been documented as occurring at McNary and John Day dams by the smolt 

monitoring program (Martinson, Rick, et al. 1993 -1996 BPA Annual Reports). 

Another common pathogen known to infect wild and hatchery salmonids in the Columbia 

River Basin is Renibacterium salmoninarum commonly known as bacterial kidney 

disease (BKD) (Sanders et al. 1992). In a study examining BKD prevalence and severity 

in juvenile hatchery spring Chinook in the Columbia and Snake rivers (Maule et al. 1996) 

the results indicated that for juveniles emigrating from the Snake River hatcheries to the 

mainstem dams the severity of BKD increased significantly more than for infected 

Columbia River hatchery fish emigrating from the hatcheries to the mainstem dams. One 

of the conclusions from this study was that the temperatures experienced by fish 

emigrating in the Snake were considerably warmer than in the Columbia which may have 

caused the difference. Future increasing water temperatures may increase the frequency 

of occurrence and severity of BKD infections in salmonids throughout the Columbia 

River Basin. 

Biological Effects – Adult Salmonids 

Changes in immigration behavior, dam passage, and survival

Predicted future increases in water temperature are of particular concern for the return of

migrating adult spring, summer, fall Chinook, sockeye, and summer steelhead (many of 

them ESA listed ESUs) in the Columbia and Snake rivers. Average water temperatures 

in the summer currently often exceed 18o

 C in the lower mainstem Columbia River and 

may exceed 21o C in the lower Snake River (McCullough 1999). Water temperature is 

likely the most important variable affecting the migration behavior, physiology, and 

spawning success of adult Chinook salmon and steelhead (Groot and Margolis 1991), and 

there is a considerable body of literature dealing with the indirect and direct effects of 

temperature on adult salmonids. Richter and Kolmes (2005) reported the upper optimal 

temperature for adult salmonid migration to be 18o C. Marine (1992) suggested that an 

incipient upper lethal temperature limit for pre-spawn adult salmonids was 17o

 C to 20o C 

and McCullough et al. (2001) indicated that exposure of adult salmonids to constant 

temperatures of 21o C to 22o C for one week was lethal. 

The migrational timing and behavior of adult salmon and steelhead in the Columbia and 

Snake rivers has been linked to optimal or preferred water temperatures and immigration 

rates appear to increase up to about 16 o C and then decline as temperature goes higher 

(Salinger and Anderson 2006). Spring Chinook migrate through the Columbia and Snake 

rivers when water temperatures are near optimal and usually avoid thermal stress 

problems. However, when summer water temperatures are higher than average, fall 

Chinook and steelhead have been documented to stray into cooler water in Columbia

43
 ISAB 2007-2 CLIMATE CHANGE REPORT

River tributaries (Goniea et al. 2006, High et al. 2006). Fall Chinook and steelhead have 

also been found to delay entry into the Snake River (often several degrees warmer than 

the mainstem Columbia) until temperature conditions are suitable to continue migration 

(Perry et al. 2002). 

Some of the potential impacts from increased water temperatures on immigrating adult 

salmon passage at mainstem hydroelectric dams include delay in passage and failure to 

enter fish ladders due to higher temperatures in ladders (Caudill et al. 2006), increased

fallback (ref.), and loss of energy reserves because of increasing metabolic demand with 

increasing temperatures (Geist et al. 2003). Any or all of these factors may add to prespawn mortality or lack of spawning success. 

Since 1991, cold-water releases from Dworshak Reservoir have been made to reduce inriver water temperatures in summer for emigrating fall Chinook juveniles and fall 

Chinook and steelhead adult migrants. Clabough et al. (2006) found that tagged 

(temperature and depth acoustic tags) adult salmon and steelhead actively sought out and 

used these cooler waters, reducing the probability of thermal stress in the lower Snake 

River. In the future as water temperatures continue to become warmer and persist longer 

into fall, these delays may become more frequent and last longer unless cold water 

releases from Dworshak Reservoir can continue to moderate this warming. 

Changes in adult salmonid health (pathogens and parasites) 

Many fish pathogens and parasites commonly infect adult salmon but often don’t become

injurious until their host becomes thermally stressed. A classic example of this was the 

2002 Klamath River fish-kill, where over 33,000 adult salmon (primarily fall Chinook) 

died in the lower 36 miles of the river (California Department of Fish and Game 2003). 

The primary cause of this fish-kill was a combined outbreak of ich (the ciliated 

protozoan, Ichthyopthirius multifilis) and columnaris (the bacterial gill disease, 

Cytophaga (formerly Flexibacter columnare). However, other important factors which 

led to this outbreak were high water temperatures, atypically low river flows, and high 

fish densities which led to rapid transmission of disease. 

Another case where increasing water temperatures may have led to parasitic induced 

mortalities of adult salmon has been noted in Alaska. Increased pre-spawn mortality of 

adult Chinook salmon in the Yukon River, Alaska has been linked to infection by a 

protozoan parasite, Ichthyophonus spp. (Kocan et al. 2003) and rising average water 

temperatures in the last thirty years appear to be associated with the increase of the 

disease and the increased pre-spawn mortality. This parasite has now been found in 

herring in Puget Sound (Jim Winton, USGS, personal communication), and there is a 

high probability that if it is not already in the Columbia Basin, it will be soon.

The most likely locations where such health problems could occur for adult salmonids in 

the Columbia River Basin due to increasing water temperatures and high fish densities, 

would be in fish ladders at Columbia River Basin dams and in tributary spawning streams 

during low flow periods in the summer and fall. 

44
 ISAB 2007-2 CLIMATE CHANGE REPORT

Biological Effects – Other Species 

Changes in distribution and abundance of introduced and exotic species in 

mainstem reservoirs 

Introduced species (especially invasive exotic species) can have a distinct advantage in 

competing with native species because they escape a large percentage of the pathogens

and parasites from their native range and are slow to pick up new infections in their 

newly invaded range (Torchen and Mitchell 2004). There is convincing evidence that 

non-native fish species are continuing to increase in the Columbia Basin aquatic habitats 

and climate change is likely to further accelerate their expansion, often at the expense of 

native species. 

There is evidence that the resident fish assemblages in shallow nearshore habitats of 

Columbia River reservoirs are changing at a fairly rapid rate. In 1995, Barfoot et al. 

(2002) replicated an earlier 1984-85 study (Palmer et al. 1986) and found that relative 

fish species composition was very similar in 1984 and 1985, but was very different in 

1995. During 1984-85, four native taxa (chiselmouth, northern pikeminnow, suckers, and 

sand rollers) dominated the catch (90%) and introduced species comprised 1.3%. In 

1995, the same four native taxa comprised only 37.7% of the fish fauna and 33.9% were 

introduced taxa (primarily sunfishes and yellow perch), with the remaining 28% 

consisting of sculpin, peamouth, and several species of minnows. One of the primary 

explanations for this shift in composition was that the impoundments have created 

sloughs and backwater habitats where water exchange is very low and summer water 

temperatures are often several degrees warmer than the nearby main-channel habitats 

(Gadomski and Barfoot, 1998). These higher late summer temperatures have most likely 

caused native taxa to shift habitat use out of backwaters, while introduced warm-water 

taxa have moved into these habitats and remained there (Barfoot et al. 2002). With 

predicted increases in water temperatures, the expansion of introduced and exotic species 

into these backwater and shallow water habitats will most likely continue. 

Concurrent with these temperature increases in backwater and shallow water habitats of 

mainstem reservoirs, introduced warm-water and cool-water piscivorous fishes, such as 

centrarchids and percids are expanding their distribution and numbers (Poe et al. 1994). 

In some areas of the mainstem Columbia River smallmouth bass have been documented 

to prey selectively on wild fall Chinook subyearlings (Tabor et al. 1993). Any future 

increases in temperature will certainly favor further expansion of warm-water piscivores

like largemouth bass and channel catfish which are already present in mainstem

reservoirs (Poe et al. 1991). 

The rapid increase in the introduced American shad in the Columbia River coincides with 

the 1977 climatic regime shift in the north Pacific Ocean and the Pacific Northwest 

region (Beamish et al., 1999; Petersen and Kitchell, 2001; Petersen et al. 2003). It is 

known that shad spawn in a variety of habitats and the shad juveniles prefer rearing in 

warm water temperatures between 19o

C and 25oC (Ross et al. 1997). Larval and juvenile 

shad are suspected to have a potentially significant impact in reducing the abundance and 

45
 ISAB 2007-2 CLIMATE CHANGE REPORT

size of Daphnia spp. in two lower Columbia River reservoirs during summer (Haskell et 

al. 2006). This could have an impact of reducing the food resources for subyearling 

Chinook which prefer Daphnia spp. and rear in these reservoirs (Rondorf et al. 1990). 

Temperature increases and flow decreases in summer may also alter food web dynamics 

by causing zooplankton abundance, primarily cladocerans and copepods, to peak earlier 

in summer. This could reduce the availability of Daphnia, currently an important food 

source for emigrating subyearling fall Chinook, by enabling the juvenile shad to deplete 

this important food source prior to the entry of subyearling Chinook salmon into the 

mainstem reservoirs (Haskell et al. 2006). Future increases in water temperature will 

likely continue the expansion of shad in the Columbia River Basin. Research is needed 

to examine the potential interactions between larval, juvenile and adult shad and juvenile 

salmonids (Petersen et al. 2003). 

White Sturgeon and Pacific Lamprey 

While the thermal tolerance range of adult white sturgeon, Acipenser transmontanus, 

may be quite broad, several studies have documented some temperature requirements for 

spawning and egg incubation and survival. Spawning of the Columbia River white 

sturgeon typically occurs between 10o

 and 18o C with the peak spawning from 13o to 15o 

C (Parsley et al. 1993) usually in about June. Egg mortality increases when incubation 

reaches 18o C and total egg mortality occurs at 20o C (Wang et al. 1985). The Kootenai 

River white sturgeon also spawn in May or June; however, water temperatures are much 

cooler, about 8o

 to 9o C, and spawning ceases by 12o C (Paragamian et al. 1995). Eggs 

incubated at cooler than optimal temperatures develop normally but take longer to hatch 

(Wang et al. 1985). The other important factors that may be needed for successful white 

sturgeon recruitment is high water velocities that now occur primarily in tailrace areas

below hydroelectric dams in the Columbia River Basin (Parsley et al. 2002) and 

submergible riparian rearing habitat (Coutant 2004). Under future scenarios of warming 

water temperatures and reduced summer flows there is a likely possibility that the white 

sturgeon may be stimulated to spawn earlier than the May – June period. This may 

actually be advantageous for white sturgeon for both egg incubation/survival as well as 

flow/velocity requirements for successful recruitment. However, if white sturgeon do not 

spawn earlier due to warming water temperatures, the predicted lower summer flows will 

decrease or extinguish the already almost non-existent recruitment in the Columbia River 

Basin. 

Pacific lamprey, Lampretra tridentate, populations have declined significantly in the 

Columbia River Basin since the 1940s (Close et al. 1995). However, there has been very 

little research conducted to understand their life history, spawning and rearing habitat 

requirements, and factors limiting their production in the Columbia River Basin. In a 

laboratory study to determine the thermal requirements of early life stage lamprey 

(Meeuwig et al. 2005) with 22 o C determined to be the upper limit for successful survival 

of egg incubation and larval survival (though survival of larval lamprey was significantly 

less at 220 C than 3 lower temperatures ). 

46
 ISAB 2007-2 CLIMATE CHANGE REPORT

One recent lamprey passage study done by Vella et al. (1999 a and 1999b) has revealed 

that up to 80% of radio-tagged lampreys have failed to pass Bonneville Dam. The cause 

for this apparent passage failure has yet to be determined and potential reasons could be 

behavioral disorientation, swim performance limitations, physiological stress/exhaustion, 

depletion of energy reserves, thermal stress, or a combination of any of these factors. A 

study was recently conducted to estimate the oxygen consumption of lampreys swimming 

at several different speeds and three different temperatures (10, 15, and 20 o C) (Mesa and 

Bayer USGS unpublished data). Results indicated that lampreys had difficulty swimming 

at the higher water velocities and consumed greater rates of oxygen at the highest 

temperature. Future rising water temperatures may require lampreys to use higher 

reserves of energy and lead to exhaustion while attempting to pass hydroelectric dams, 

further pushing Pacific lamprey towards extinction in the Columbia River Basin. 

Effects in the Estuary 

The literature on effects of climate change on northeast Pacific estuarine habitat and 

ecosystems is limited - most of the papers on effects of climate change in estuaries focus 

on coastal plain estuaries on the Atlantic coasts of North America and Europe. Major 

estuary programs on the west coast such as the CALFED Delta Program have only 

recently started to focus on the problem (CALFED, 2003). We therefore found little data 

that relates specifically to the lower Columbia River and estuary. For example the major 

review paper by Scavia et al. (2002) does not mention the lower Columbia River and 

estuary. Further, the extensive literature on effects of climate change on salmonids has 

tended to focus on either freshwater or marine effects (see references elsewhere in this 

ISAB report). For this reason we had to make inferences about climate change effects 

from the existing general ecological and fisheries data on the lower Columbia River and 

estuary. 

In the both the vertical and horizontal plane, an estuary is a complex transitional zone

without sharp boundaries between freshwater and marine habitats. Any conclusions 

about possible climate change effects within an estuary must therefore also consider 

changes in the latter two habitats – freshwater effects propagate into the estuary from the 

river and marine effects from the ocean. An estuary may be highly stratified vertically, 

with freshwater on the surface and salt water near the bottom, and therefore changes in 

water properties and biota with depth also need be considered. 

Possible Changes in Oceanographic and Hydrological Conditions in the

Estuary 

Changes in Columbia River freshwater flow due to climate are expected to propagate 

through to the lower Columbia River and estuary but will less than those caused by 

construction of the hydrosystem (Fig. 11). Current long-range forecasts suggest there 

will be higher average Columbia River flows in winter and early spring flows and less

47
 ISAB 2007-2 CLIMATE CHANGE REPORT

snowmelt in summer in future years because of warmer temperatures, more precipitation 

as rain, and less snow storage. Late spring-autumn flows could be reduced and winter 

flows high but undependable (more floods). Reduced spring and summer flows could 

result in further attenuation of an already decreased flooding regime which has changed 

the amount of time specific elevations are submerged relative to natural conditions. (Fig. 

15). 

Figure 15. The incidence of flows above 18,000 m3s

-1 (the pre-1900 estimated bankfull 

flow level) and above 24,000 m3s

-1 (the present bankfull flow level). The present bankfull 

flow level has only been exceeded in four years since 1948 (Fig 28 from Bottom et al. 

2005). 

The best measure of total main stem freshwater input at the head of the estuary is the 

Columbia River flow at Beaver (river km 85), although there are some major rivers 

below this point (e.g., Grays River). At this location the pre dam (1892-1902) average 

estimated observed annual flow was 8300 m3

s

-1

 compared to 6960 m3s

-1 for the 1892-

1999 period (Bottom et al. 2005). It is extremely difficult to separate climate, flow 

regulation, and water-withdrawal effects on the freshwater flow into the lower Columbia 

River and estuary. However changes in flow or water quality upstream will be 

transported to the estuary. Thus, any warming in the tributaries and reservoirs may result 

in warming of the estuary. 

Temperatures in the estuary are significantly influenced by river and reservoir surface 

water because temperatures in the upper estuary and tidal freshwater are higher relative to 

reaches closer to the ocean. Only a few relatively long term data sets on temperature are 

available for the estuary and lower river. For example, in August 1981 mean surface 

temperature was about 14o

 C at river mile 5 compared to about 22o C at river mile 50 

(Fig. 16). Recent water temperature at Warrendale, Oregon (river mile 141) in the tidal 

freshwater part of the river showed numerous dates when surface temperature exceeded 

20o

 C (Fig 17). Temperatures in the estuary are also influenced by tidal entrainment of 

ocean water that is often cool during the summer upwelling periods. 

48
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 16. Mean temperatures and range measured at three mid-depth (6-9 m) stations at 

river mile 5, 15, and 50 in the Columbia River estuary, 1981. (Fig 3 from Bottom and 

Jones 1990). 

Figure 17. Median surface temperatures (middle line in box plot) at Warrendale (river 

mile 141) in the Columbia River based on measurements made between 1975 and 1992. 

The Washington State temperature standard is shown as a dashed line. Numbers beside 

boxes indicate number of observations (from Fuhrer et al. 1996). 

49
 ISAB 2007-2 CLIMATE CHANGE REPORT

Key habitats in the lower Columbia River and estuary for fall Chinook and chum salmon, 

such as wetland platforms, mud flats, and floodplains, are generated and maintained by 

sediments supplied from upriver tributaries (especially the Willamette River) and moved 

downstream in suspension. Suspended sediment increases downstream (e.g., 5 mg l-1 at 

Warrendale OR to 9 mg l-1 at Beaver OR (Fuhrer et al. 1996). Because some of the 

sediment load arises from re-suspension by bottom currents, decreases or increases in 

river flows from climate change could be influential. As well the effects of climate 

cycles, such as the PDO, are amplified in the sediment flow – increased river flow during 

cool wet La Niña years resulted in higher sediment loads from eastern subbasins (Bottom

et al. 2005). The distinct responses of sand transport (limited by transport capacity and, 

therefore, changes in flow) and fine sediment transport (limited by supply and, therefore, 

land use) suggest that other factors besides flow regulation, irrigation depletion and 

climate need to be considered with regard to sediment transport in the lower Columbia 

River and estuary. A combination of analysis of hindcasts and landscape modeling will 

be needed to fully understand the historical changes in sediment transport (Naik and Jay 

2005) but sediment input to the estuary has declined due to the altered hydrograph 

(Bottom et al. 2006) 

The distance that salt water moves upstream under the freshwater into the lower 

Columbia River and estuary is a complex function of tides and river flow. At present, 

during spring, when both tides and river flows are at their seasonal maxima, the salt 

wedge penetrates approximately 16 km into the estuary (Fig. 18). With reduced spring 

flows, this distance would be increased. Warming of the ocean at the mouth of the river 

could result in reduced strength of the salt wedge, since density differences between salt 

and freshwater are the main drivers for this phenomenon. Warmer ocean water might 

penetrate shorter distances upstream under the freshwater because it is less dense. 

50
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 18. Maximum (end of flood tide) and minimum (end of ebb tide) 

salinity intrusion distance in the Columbia River estuary, based on 1980 

bathymetric conditions (Fig 32 in Bottom et al. 2005 from Jay 1984) 

Assuming no future changes in management of the hydrosystem, decreased spring and 

summer flows owing to climate change could result in shallowing of some channels in 

the lower Columbia River and estuary, and this could imply increased dredging to keep 

navigational channels open (see ISAB 2000). Increased fall and winter flows could offset 

this effect but only in these seasons and dredging would still be required. 

Sea level rise and possible degradation of habitats created by sediment deposition owing 

to increased wave actions (storms) are also climate change impacts that could change 

estuarine ecosystems. The most recent estimates of sea level rise at the end of the 21st

century range between 0.18 and 0.59 m for the world ocean (IPCC 2007) – we found no 

estimates available for the northeast Pacific specifically. Sea level rise could be 

particularly important at the mouth of the river where the Columbia River littoral cell, 

generated by wave and current action, move sediments north and south and generates 

sandy beach habitats (Mitchell 2001). Data on effects of wind-generated wave action in 

the estuary proper are not available but wave cut terraces along the shoreline of the 

estuary could become more pronounced with increased storms and could affect the 

success of restoration projects using dredged sand (see below). 

51
 ISAB 2007-2 CLIMATE CHANGE REPORT

Hydraulic models have shown that water mass residency in the lower Columbia River 

and estuary was inversely correlated with stream flow but the relationship was complex 

(Sommerfield 1999 cited in Bottom et al. 2005). Decreased spring flow could result in 

increased residency time and the converse might be expected for increased winter flow. 

The flushing or residency time is an important descriptor of the behavior of water parcels 

in an estuary and is particularly important for distribution of food web materials and 

water quality since it determines how long particles are retained in the estuary (e.g., 

detritus important in the food web, trapping of pollutants). The models showed that 

residency in the lower estuary can vary from 10 to 60 h, depending on flow. Residence 

time for suspended particulate material for the north and south channels together suggests 

that sediment storage is short (less than 14 d) during the spring freshet—most of the 

suspended particulate material brought into the estuary is exported at the latest on the 

next spring tide (Faini et al 2001). However owing to channelization and changes in flow 

the embayments off the south channel are now more effective sediment traps, judging 

from changes in marsh vegetation at Russian Island in Cathlamet Bay (Bottom et al 2006) 

Biological Responses

In the following, we focus on responses by ocean-type Chinook salmon and their 

supporting ecosystem, given that this species is known to rely on estuarine conditions 

(Healey 1982; Bottom et al 2005). Where necessary, we extrapolate to other species, 

and, recognizing that all salmonids must transit the estuary as juveniles and returning 

adults, we also discuss other species of the salmon community.

Temperature effects 

Temperature is widely recognized as a controlling factor for growth and survival in 

aquatic habitats and is also a key parameter related to climate change. There are few data 

that pertain directly to estuaries on this topic. However, numerous water quality criteria 

documents deal with this topic, and salmonids are usually listed as a sensitive group of 

organisms. 

Most of the physiological research on the temperature tolerance of salmonids has been 

done in freshwater or ocean conditions (see elsewhere in this report and Young et al. 

2006). The physiological implications for juvenile salmonids moving from a cold river to 

a warm upper estuary and then to a cool or possibly warmer ocean, as might be 

experienced with climate change, has not been researched. Returning adult salmonids are 

adapted to a different situation, experiencing cool temperatures in the coastal ocean, 

traveling through an often-warmer estuary and river, then to cooler spawning grounds. 

Climate change could modify this gradient in any of the above habitats. Returning 

salmon holding in estuaries while waiting for cool runoff conditions in their natal river 

can suffer stress and disease, as observed for sockeye in Alberni Inlet, BC (Johnson et al. 

1996) during a regional warming trend or the die off of thousands of salmon in the 

Klamath River in 2002 (California Department of Fish and Game 2003). 

52
 ISAB 2007-2 CLIMATE CHANGE REPORT

Both juvenile and adult salmon suffer direct lethal heat shock or sublethal effects if they

are subjected to temperatures above approximately 20o

 C, but it is very difficult to 

generalize for estuarine habitats because of the strong interaction with salinity (Clarke et 

al. 1981) and oxygen (Davis 1975; Marchand et al. 2002). Temperatures above 20o

 C can 

be achieved in certain estuaries where heated effluents (e.g., cooling water for power 

plants, Marchand et al. 2002). However, there are species specific differences in 

temperature tolerance (see below). Sublethal effects are also possible. Takami (1998) 

found that water temperatures > 16o

 C reduced the osmoregulatory ability of white 

spotted char, but low temperatures (< 4o C) did not. 

Temperature mediates numerous indirect effects on salmonids, especially at the juvenile 

stage. Temperature controls rate processes such as growth and metabolism and hence 

strongly influences the food demand in the estuary, as found for Chinook by MacFarlane 

and Norton (2002) in the Sacramento River estuary-San Francisco Bay area. However, 

as mentioned, salinity is a key interactive factor that is usually not considered in 

ecophysiological models. 

Knowledge of the extent to which the behavior of various Chinook populations in the 

estuary are genetically programmed, as opposed to environmentally responsive and 

plastic is poor. Perhaps the recent paper by Brannon et al. (2004) is relevant. They 

surmise that Chinook life history genetics are conditioned by temperature (i.e., life 

history types are arrayed on a temperature continuum). As well, as found by Crozier and 

Zabel (2006) in freshwater, the Chinook salmon response to climate change may be 

population specific. 

Alteration of fry and smolt arrival and residency in the estuary 

Rich (1920, cited in Bottom et al. 2005) found at least six specific life history patterns for 

wild Chinook in the pre-development lower Columbia River and estuary. These were 

variants of the broad life history categories commonly known as stream-type and oceantype (Healey 1991). Contemporary timing and relative abundance data indicate this has 

been narrowed to three patterns (Bottom et al 2005), with a possible fourth (reservoir 

type Chinook, see above) that is undocumented in the estuary (ISAB 2006). At present, 

fry and yearling fish peak in abundance in early April and fingerling catches peak in early 

July (Fig. 19). Hatchery smolts are now the dominant forms with complex but narrow

arrival times into the estuary. 

River flow is one of the dominant factors influencing arrival time and residency in the 

estuary, especially for hatchery smolts which tend to move through the estuary more 

quickly than wild fish (Bottom et al. 2005). Therefore it is likely that, in the absence of 

future changes in hydrosystem operations, changes in discharge owing to climate change 

will modify the above-mentioned patterns of estuary usage. 

53
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 19. Historical and contemporary early life histories for one broodyear of Chinook 

salmon in the Columbia River estuary. Historical timing and relative abundance (top 

panel) based on historical sampling throughout the lower estuary (Rich 1920). 

Contemporary timing and relative abundance (bottom panel) derived from Dawley et al. 

(1985) sampling at Jones Beach (river mile 46) (Fig 79 from Bottom et al 2005). 

Alteration in the fish community 

Water temperature increases in the estuary may favor the survival of non-salmonid fish 

species in the estuary, some of which may prey or compete with juvenile salmonids. 

Numerically, non-salmonids are more abundant than salmonids in the intertidal habitats 

54
 ISAB 2007-2 CLIMATE CHANGE REPORT

of the lower Columbia River and estuary (McCabe et al. 1983). Monaco et al. (1992) 

included the lower Columbia River and estuary in what they termed the “Northern 

Riverine Group” when classifying estuaries on the northwest coast based on fish species. 

This group was strongly associated with salmonids and cool water requirements. 

Abundant endemic species, such as staghorn sculpin (Leptocottus armatus), found in the 

estuary (McCabe et al. 1983; Bottom and Jones 1990) are not now known as major 

predators in the lower Columbia River and estuary on juvenile salmonids. This situation 

could change if warmer temperatures increased consumption rates of piscivores, as found 

by Footen and Tabor (2001) in Lake Washington in a study of endemic and nonindigenous fish predators and juvenile salmonids.1

 If cool water species like northern 

anchovy decline in the lower Columbia River and estuary, more predation could occur on 

juvenile salmonids by Caspian terns that nest in the estuary. 

Numerous warm adapted fish species, including several non-indigenous species normally 

found in freshwater (e.g., carp (Cyprinus carpio), yellow perch (Perca flavescens)) have 

also been reported from the estuary (e.g., McCabe et al. 1983; Weitkamp 1994) and 

might expand their populations if conditions allowed (e.g., warmer water, expansion of

freshwater habitats). Some of these species, and possibly those currently found further 

upriver (e.g., northern pike Esox lucius) could encroach into the lower Columbia River 

and estuary with higher flows. The ISAB (2000) noted that American shad (Alosa 

sapidissima) was by far the most abundant non-indigenous fish species in the lower 

Columbia River and estuary. The effects of climate change on the population dynamics 

of this species are not known. 

Effect of flooding on available rearing space 

The model developed by Bottom et al. (2005) showed that there was a correlation 

between stream flow and habitat availability for fish as preferred habitat is submerged for 

longer periods during higher flow. The relationships were more complex when depth 

criterion and combined depth-velocity criteria were used. Sea level rise owing to climate 

change would add to the complexity. According to model forecasts, reduced stream flow 

in spring would reduce habitat opportunity. Although not investigated with the model, 

the relationship implies that more habitat would be available for rearing in the estuary in 

fall and winter, for example, for reservoir-type Chinook moving seaward from the 

reservoirs. Sea level rise in the Columbia River due to climate change is expected to 

propagate upstream into the lower Columbia River and estuary, but will be substantially 

less than the May-June-July water level decreases caused by construction and operation 

of the hydrosystem. 

Possible changes in trophic dynamics, food webs, and connectivity 

Tidal flows and freshets are hydraulic forces that strongly influence primary production 

of vascular plants, benthic algae, and phytoplankton and also distribute the generated 

carbon to bacteria for heterotrophy, generating detritus and to the secondary consumers 

 

1 www.ci.seattle.wa.us/salmon/docs/workshop/footen.pdf (accessed Oct 17, 06).

55
 ISAB 2007-2 CLIMATE CHANGE REPORT

(invertebrates) which in turn are eaten by juvenile salmonids rearing in the estuary. 

However, this food web structure of the lower Columbia River and estuary has been 

altered by reservoir construction which altered production processes, modified flow, and 

changed seasonal patterns of flooding. 

Decreased flows in spring and summer could result in a reduction of upriver detritus 

source for the estuary, possibly moving the estuary closer to the historical situation. An 

important set of food web pathways leading to juvenile salmonids that feed in the estuary 

is thought to be dominated by heterotrophic processes involving detritus and bacteria 

originating from vascular plants and phytoplankton (Sherwood et al. 1990). Production 

of phytoplankton in the large lakes created by dams is now a major source of this detritus, 

relative to the pre-dam condition. 

As explained above, the salt wedge may penetrate further upriver in spring-early summer 

if these flows are reduced owing to climate change. The landward head of the salt wedge 

is characterized by a turbulent region known as the estuary turbidity maximum, an 

ecotone of high bacterial production by specific microbes (Crump et al. 1999) and 

concentrations of fish food organisms such as harpacticoid copepods (Simenstad et al. 

1994). Changes in the distribution of the salt wedge will influence the location of the 

estuary turbidity maximum, but it is difficult to forecast the ecological effects that might 

propagate to higher trophic levels such as juvenile salmon. 

The hydrosystem and diking have caused major changes in the flooding regime in the 

lower Columbia River and estuary, and climate change will modify it further. Overbank 

flooding from the spring freshet is widely recognized as a mechanism for distributing 

detritus from vascular plants in the horizontal plane of the estuary (e.g., sedges (Carex 

lyngbyei)) (Macdonald 1984). However, because of hydrosystem operations, modern 

flows required to generate the phenomena (24,000 m3

s

-1) are extremely rare now. 

Overbank flow is rare now even during cold wet PDO phases and was totally absent 

during the last PDO warm phase (1977-1995) (Bottom et al. 2005, Fig. 15). Depending 

on hydrosystem operations, increased winter freshets coupled with sea level rise could 

increase the occurrence of overbank flow in winter. However, overbank flow may 

become even less frequent during late spring and summer if climate change further 

reduces natural runoff at this time of year. Overbank flow is not expected to increase 

with higher discharge in autumn and if it did this would result in distribution of detritus at 

the wrong season for fish food invertebrates to utilize it for growth and reproduction. 

Changes in sediment supply from flows modified by climate change could modify the 

integrity of intertidal habitats in the lower Columbia River and estuary – these account 

for 40% of the area of the estuary (Wissmar and Simenstad 1998), especially as the 

sediment supply to the lower Columbia River and estuary has already been drastically 

reduced by the hydrosystem. Mud flats and tidal flat areas in the lower estuary are 

important detrital producers. For example, Baker Bay, Trestle Bay, Youngs Bay, and 

Cathlamet Bay produced 82% of the total benthic algal production in the estuary. Net 

annual primary production by emergent vascular plants in Youngs Bay was highest in the 

low marshes of the area (about 1000 gC m-2

y

-1) (Small et al. 1990). 

56
 ISAB 2007-2 CLIMATE CHANGE REPORT

Effects on Estuarine Restoration Projects 

Estuary restoration projects that have been planned and built with contemporary 

hydraulic and flow conditions in the lower Columbia River and estuary may need to be 

re-engineered if climate change reduces flow in spring and summer. Dike breaching 

projects, for example, may need to modify the elevation of ports for water inflow or 

control to account for heavier wave action, higher flows, and sea level rise. Culvert 

repositioning might also be required. Stronger wave action, however, could improve 

some problematic restoration projects such as dredged sand islands where bird predation 

on salmon smolts is severe (Collis et al. 2002). Bird nesting habitat might be scoured and 

reduced if flood currents become stronger in winter. 

Effects in the Ocean 

Scientific evidence strongly suggests that global climate change is already altering 

marine ecosystems from the tropics to polar seas (McPhee 1998; Levitus et al. 2000; 

Overland and Stabeno 2004; Whitney 2006a; and IPCC 2007). In the Pacific Northwest 

global climate changes are predicted to influence both freshwater and marine ecosystems. 

Changes in the ocean associated with warming will affect salmonids and their 

ecosystems, both directly and indirectly. Physical changes associated with warming 

include: increases in ocean temperature, increased stratification of the water column, and 

changes in the intensity and timing of coastal upwelling. These changes in climate 

forcing will alter both primary and secondary productivity and the structure of marine 

communities, and in turn, the growth, productivity, survival and migrations of salmonids. 

Eastern boundary currents along the west coast of North America are enriched by winddriven coastal upwelling and mixing processes resulting in productive ecosystems that 

support diverse marine life and major fisheries. These coastal systems are also inherently 

highly variable in both space and time, with changes occurring on scales of days and 

weeks, seasonally, interannually and interdecadally. Timing and intensity of upwelling 

varies greatly within and among years, El Niño-Southern Oscillation (ENSO) events 

occur on average every 2 to 7 years, and 20th century regimes in ocean climate and 

marine ecosystems, key aspects of which are reflected in the Pacific Decadal Oscillation 

(PDO), have lasted 20-30 years. On time scales of millennia, large natural variations in 

the productivity of salmon stocks have occurred over the past 3000 years in Alaska 

(Finney et al. 2000) and over 700 years in the Columbia River (Chatters et al. 1991, 

1995). These high and low frequencies of natural variability in physical forcing and 

ecosystems confound detection of long-term trends in ocean temperatures, ecosystem

properties, and other factors. 

Climate Variability 

Here we explore factors that are known to affect the climate of the Pacific Northwest. 

These include Aleutian Low variability, El Niño events, and PDO phases. These are all 

57
 ISAB 2007-2 CLIMATE CHANGE REPORT

possible analogs for future impacts of global warming in the North Pacific and Pacific 

Northwest. 

Climate conditions are clearly important in the fluctuations of abundances of salmon 

because climate is a key part of salmon habitat at every stage of their lives. In the past, 

studies have shown a strong correlation between multi-decadal climate cycles and trends 

in the population abundances of salmon, with responses varying across broad geographic 

ranges (Beamish and Bouillon 1993, Hare and Francis 1995, Mantua et al. 1997; Hare et 

al. 1999; Tolimieri and Levin 2004; Zabel et al. 2005; Mueter et al. 2002). Regional 

aspects of marine and freshwater habitat important for Pacific Northwest salmon are 

frequently influenced by ENSO events and phases of the PDO. A particularly important 

pathway for ENSO and PDO variations to impact Pacific Northwest salmon habitats is 

via their influence on the characteristics of the cool season Aleutian Low atmospheric 

pressure cell. 

Aleutian Low and Subtropical High pressure Cells 

Beginning about mid-October in each year a semi-permanent, low-pressure cell, 

commonly called the Aleutian Low2

, intensifies and migrates southeastward over the 

Aleutian Islands and Gulf of Alaska. Surface winds blow in a counterclockwise 

circulation around the Aleutian Low. Further south, winds blow in a clockwise 

circulation around a semi-permanent center of subtropical high pressure typically 

centered offshore southern California. Prominent cool-season climate changes over the 

North Pacific Ocean and western North America are associated with fluctuations in the 

strength and location of the atmosphere’s Aleutian Low pressure cell and associated 

position of the Pacific storm track (Fig. 20). The weak Aleutian Low circulation pattern 

typically brings a reduction in the poleward alongshore winds that tend to warm and 

stratify the coastal waters of the NE Pacific such that by the end of a weak Aleutian Low 

winter coastal ocean temperatures are cooler than average and the upper ocean is weakly 

stratified. In contrast, winters with an intense Aleutian Low have enhanced poleward 

winds along the Pacific coast, and this circulation pattern causes enhanced upwelling in

the center of the Alaskan Gyre, increased wind mixing of surface waters and onshore 

transport of offshore waters in Alaska such that by spring time coastal waters of the NE

Pacific are anomalously warm, surface mixed layers are anomalously deep. These 

atmospheric circulation patterns drive surface currents, with a strong low intensifying the 

Alaskan Current, and a weak low and strong subtropical high pressure cell intensifying 

the California Current (Fig. 20). 

 

2 Although the Aleutian Low dominates the winter (seasonally averaged) climate of the North 

Pacific, it is a statistical feature of the winter circulation in that its existence relies on the frequent 

development of eastward moving winter storms along a more-or-less regular path. The individual 

winter cyclones have a typical lifetime of one to a few days.

58
 ISAB 2007-2 CLIMATE CHANGE REPORT

Figure 20. PRESSURES and CURRENTS: From October through March the 

atmospheric sea level pressure field is dominated by low pressure and frequent winter 

storms (cyclones) over the North Pacific, giving rise to the climatological feature known 

as the Aleutian Low pressure cell. As indicated by the yellow curved arrows, the 

circulation around the Aleutian Low brings surface winds onshore and from the 

southwest into the Columbia River Basin and greater Pacific Northwest region. From 

April through September the Aleutian Low is substantially weaker and retreats 

northward, and the dominant feature in the Northeast Pacific is a subtropical high 

pressure cell that favors north-to-south alongshore winds along the west coast of the 

continental United States that cause coastal upwelling of cold nutrient waters into the 

California Current System. The West Wind drift carries subarctic waters into the coastal 

waters of the North Pacific, while copious freshwater runoff from the coast range of 

British Columbia and Alaska give rise to the Alaska Coastal Current. (Figure reproduced 

from the 2007 Sound Science report). 

The same Aleutian Low circulation changes that alter the upper ocean properties of the 

NE Pacific also have important impacts on precipitation, temperature, and snow packs in 

the Pacific Northwest region. Weak Aleutian Low winters typically have an active storm

track over the Pacific Northwest that bring relatively cold and frequent storms, heavy 

precipitation and plentiful snowfall on the west slopes of the mountains. In contrast, 

periods with a strong Aleutian Low typically bring a split storm track that diverts storms

to both the north and south of the Pacific Northwest region, which results in relatively 

warm and infrequent storms, and reduced precipitation and snowfall throughout the 

region. 

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These climatic changes over land then carry over into late spring and summer 

streamflows in what is typically a very strong seasonal snow melt pulse across the 

region’s major watersheds. Table 3 summarizes some of the key habitat changes 

associated with fluctuations in the intensity of the cool season Aleutian Low

3

. 

Table 3: Summary of the influence of Aleutian Low variations on regional aspects of 

Pacific Northwest salmon habitat. Note that strong Aleutian Low winters are favored 

during El Niño and warm phase PDO periods, while weak Aleutian Low winters are 

favored during La Niña and cool phase PDO periods.

Regional

Precipitation

Regional 

Temperature 

Regional snow 

pack and snow 

melt runoff

Coastal ocean water 

temperatures and 

stratification in 

winter and spring 

Weak Aleutian 

Low 

High Low High Low

Strong Aleutian 

Low 

Low High Low High 

El Niño/Southern Oscillation and Pacific Decadal Oscillation

Both ENSO and PDO are patterns of Pacific climate variability that include changes in 

sea and air temperatures, winds, and precipitation. ENSO is a natural part of climate that 

spontaneously arises from interactions between tropical trade winds and ocean surface 

temperatures and currents near the equator in the Pacific. Because of long-distance 

atmospheric and oceanic teleconnections, ENSO is a prominent source of cool season 

Aleutian Low and Pacific Northwest climate variability at year-to-year time scales. 

During El Niño events the Aleutian Low tends to be intense and shifts to the southeast, 

and these changes result in relatively dry and mild fall-winter periods in the Pacific 

Northwest region, along with warm upper ocean temperatures throughout the northeast 

Pacific Ocean and along the entire west coast of the Americas that persist from spring 

into summer. In contrast, the Aleutian Low tends to be weak and displaced to the 

northwest during La Niña events, and these changes result in relatively cool and stormy

fall-winter periods for the Pacific Northwest region, along with relatively cool upper 

ocean temperatures throughout the northeast Pacific Ocean and along the entire west 

coast of the Americas that persist from spring into summer (Mantua et al. 1997). 

 

3 At time scales shorter than a few months, prominent changes in the Aleutian Low and storm

track arise from instabilities contained within the chaotic flow of the atmosphere, and these 

processes lead to a fundamental limit in weather prediction of about 2 weeks. In practice, aspects 

of current weather forecasts have demonstrated skill at lead-times of up to 5 to 10 days in the best 

case scenarios. At interannual to interdecadal time scales there are two ocean-atmosphere climate 

processes especially prominent in Aleutian Low and Pacific Northwest climate variability: El 

Niño-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation.

60
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Some of the broad-scale effects of PDO phases are summarized in Table 4, showing how 

physical and biological indicators vary with cool and warm PDO conditions. 

Table 4. Summary of the manner in which the sign of the PDO influences broad–

scale and local physical ocean condition indicators as well as biological 

indicators.

Cool PDO Warm PDO

Broad–scale ocean indicators

Pacific Decadal Oscillation values negative positive

Multivariate ENSO Index values negative positive

Local physical indicators

Upwelling positive in winterspringnegative in winterspring

Physical spring transitiona may not be related to PDO

Sea surface temperatures cold warm

Continental shelf water type cold and salty warm and fresh

Local and regional biological indicators

Copepod species richness low high

Northern copepod biomass positive anomaly negative anomaly

Southern copepod biomass negative anomaly positive anomaly

Euphausiid egg abundance in shelf 

water

usually high usually low

Biological spring transition early late

Trawl surveys

Coho abundance high low

Chinook abundance high low

Coho survivalb high low

Developing indicators

Snake River Chinook SARsc high low

Forage fish abundances many few

Pacific hake abundances few many

(http://www.nwfsc.noaa.gov/research/divisions/fed/oeip/a-ecinhome.cfm)

 a (Logerwell et al. 2003)

 b (OPIH) Oregon Production Index, Hatchery

 c Smolt to adult returns (see Scheurell and Williams 2005)

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At time scales of one to a few decades, PDO impacts are manifest as ENSO-like changes 

in the spatial patterns of ocean temperatures and Pacific Northwest weather. Warm

phases of PDO are linked with El Niño-like climate anomalies, including periods having 

an intense cool season Aleutian Low. Likewise, cool phases of PDO are linked with La 

Niña like climate anomalies that include periods with a weak cool season Aleutian Low. 

The PDO was in its cool phase from about 1890 to 1925 and from 1945 to 1977. It was 

in its warm phase from 1925 to 1945 and from 1977 to at least the mid-to-late 1990's 

when there was a high frequency of warm ocean conditions in the coastal waters of 

northeast Pacific (Mantua et al. 1997; Minobe 1997). Coincident with a shift to a 

prevalence of tropical La Niña and cool phase PDO conditions, the California Current 

System (CCS) experienced a four-year period of cooler temperatures and increased coho 

and chinook production from 1999 through 2002. This cool productive era was followed 

by warmer and less productive period for west coast coho and chinook from 2003 

through 2005 before cooling again from 2006 to present. This variability highlights the 

fact that there is large year-to-year variability in the physical and ecological state of the 

California Current System, and only part of this variability is clearly related to larger 

scale ENSO and PDO-related climate changes. 

Differences in the temporal rhythms of ENSO and PDO are obvious: the lifetime of a 

typical ENSO event ranges from 6 to 18 months, and complete ENSO cycles typically 

have a 2 to 7 year period (Rasmussen and Carpenter 1982); by contrast, the energy in 

twentieth century PDO variations was concentrated at periods near 20 and 60 years, along 

with variations at periods less than a decade (Minobe 1999; Newman et al. 2003). 

Additional key differences between ENSO and PDO lie in the state of current scientific 

understanding and demonstrated predictability of the two phenomena. Scientists are 

reasonably agreed that ENSO exists because of strong air-sea interactions that take place 

in the tropical Pacific. These interactions give rise to a deterministic set of climate events 

that are inherently predictable at lead times of at least a few seasons, and possibly up to 

two years. While ENSO has been extensively studied and is now routinely predicted at 

more than a dozen centers around the world, the causes for PDO variations are not 

currently known. Newman et al. (2003) show that key characteristics of the 20th

Century’s PDO SST pattern can be explained as a consequence of ENSO-related forcing 

and a strong tendency for multi-year persistence in extratropical ocean temperatures. If 

PDO variability is largely determined by the evolution of ENSO and relatively simple 

mechanisms that favor persistence in ocean temperatures, then PDO predictability is 

inherently limited by the same factors that limit ENSO predictability to perhaps two years 

into the future. 

The relatively warm temperatures associated with the positive phase of the PDO and 

frequent tropical El Niño events during the1990-1998 period may represent a plausible 

scenario for the future since the predictions are for continued global warming (Meehl et 

al. 2001). A key caveat in this use of historic variability for analogs of future change is 

the prominent role that the persistently strong Aleutian Low pressure cell played in the 

warm era of 1990-1998. It is not clear that human-caused global warming will lead to 

62
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similar persistence in the strength and location of the cool-season Aleutian Low and 

warm season subtropical high pressure patterns (and wind field) over the North Pacific 

and North America, but it is clear that the large-scale and regional scale surface winds 

will play a prominent role in structuring ocean habitat. We return to a more detailed 

discussion of the impacts of global warming on coastal upwelling winds later in this 

section. 

Biological Impacts 

Climate variability is linked to changes in ocean ecosystems, with physical changes 

forcing changes in primary and secondary productivity, forage fishes and predators that 

interact at different time and space scales. First we discuss some of the known impacts of 

ENSO and PDO in the Pacific Northwest, then discuss how possible future changes in 

stratification and upwelling might impact our coastal ecosystem. 

The biological impacts of the 1982/82 and 1997/98 tropical El Niño events were 

particularly severe in the Pacific Northwest. Warm sea temperature, ineffective 

upwelling, and increased predation affected the distribution, survival and growth of many 

salmon stocks along the Pacific coast (Wooster and Flutharty 1985; Pearcy et al. 1985; 

Mantua et al. 1997). Five out of seven years in the late 1990s experienced El Niño-like 

events, as temperatures remained elevated (Trenberth and Hoar 1997). Perhaps El Niño 

events have been occurring more frequently than in the past (Rodbell et al. 1999), yet a 

recent review of climate models used in the IPCC assessments finds no consistent

changes in the simulated behavior of ENSO in a warmer future (Collins 2005). 

Shifts in the state of marine ecosystems, as reflected in the multi-decadal state of the 

PDO, are well documented in the Northeast Pacific Ocean (Table 4). From the 1920s to 

the 1990s a general inverse production pattern for Pacific salmon existed in the Pacific 

Northwest region vs. the northern subarctic Pacific (Francis and Hare 1994; Mantua et al. 

1997; Hare et al. 1999). Warm conditions in the Alaska region resulting from a strong 

Aleutian Low and Alaskan Current usually have resulted in higher than average salmon 

catches, but lower catches in the California Current region. The regime shifted from a 

negative or cool phase to a semi-stable warm or positive phase in 1976/77 (Mantua et al. 

1997). This warm phase, which included frequent tropical El Niño events, contributed to 

severe declines in the survival of Oregon coho salmon and lasted through the 

exceptionally strong 1997/98 El Niño event. During this period, large northern boreal 

and subarctic copepods decreased while smaller warm-water copepods dominated catches 

off in the California Current and off Canada (Mackas et al. 2001; Peterson and Schwing 

2003). In addition, the peak of abundance of the dominant copepod, Neocalanus 

plumchrus, occurred about two months earlier in the subarctic Pacific along the “Line-P” 

transect west of Vancouver Island (Mackas 1998). 

The PDO pattern shifted to its cool phase and the California Current intensified in the fall 

of 1998, and Pacific Northwest marine ecosystems returned to the more productive, cool 

state with increased productivity with predominance of large, lipid-rich, cold species of 

copepods. For the next four years (until the fall of 2002) salmon production in both 

63
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regions was generally high and coho and Chinook salmon stocks in the Pacific Northwest 

rebounded. Survival of coho and Chinook salmon entering the coastal ocean in 1999-

2001 improved substantially compared to the survivals of the preceding ten years. From

2003 to 2005 the PDO returned to a mostly positive, though variable state, and Pacific 

Northwest salmon production has shown signs of decline in concert with the return to 

warmer ocean conditions. On the other hand, La Niña-like conditions occurred during

the 2006-07 winter, indicating more favorable conditions for salmon in the region. 

In summary, if the regional impacts of global warming are expressed in El Niño-like or 

PDO-like ways, warmer waters due to global warming are likely to promote increased 

production of salmon in Alaskan waters, at least initially, provided primary and 

secondary production does not decline, while promoting decreased salmon production for 

salmon populations in the Pacific Northwest region (and throughout the California 

Current System). A key uncertainty here is how global warming will influence the 

characteristics of atmospheric surface pressure and wind fields over the North Pacific 

because of the prominent role that wind forcing plays in structuring the upper ocean. 

Stratification 

The density of water, which varies with salinity and temperature, affects stratification and 

mixing of surface waters. The thickness and stability of the surface mixed layer is a 

crucial factor in determining the effectiveness of nutrient inputs into the euphotic zone. 

Warm sea-surface temperatures and strong water column stratification impede wind 

mixing, which may reduce the availability of nutrients essential for the production of 

phytoplankton, the base of the ocean food web. On a global scale, upper ocean 

temperatures and increased stratification have already resulted in reduced net primary 

productivity since 1997. These trends are documented by Behrenfeld et al. (2006; Fig. 

21) who show that ocean productivity is closely related to the Multivariate ENSO index 

(MEI) and changes in ocean stratification. 

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Figure 21. Ocean productivity is closely coupled to climate variability. a: NPP 

anomalies in the permanently stratified oceans (grey symbols, left axis) are highly 

correlated (r2

=0.77) with the MEI of climate variability (red symbols, right axis). b: 

Changes in ocean stratification (red symbols, right axis) link climate variability to ocean 

biology and are well correlated (r2

=0.73) with NPP anomalies (grey symbols, left axis) in 

ocean regions with annual average surface temperatures over 15o

C. Stratification 

strength was assessed as the density differences between the surface and a depth of 200m.

Note that the MEI and stratification axes (right) increase from top to bottom. (Figure 

from Behrenfeld et al. 2006). 

In the subarctic Northeast Pacific, sea-surface temperatures show a warming trend and 

salinities a decreasing trend, over the last half-century (Fig. 22) and the stratification of 

the upper ocean has increased in the subarctic Pacific during recent decades (Freeland et 

al. 1997: Freeland 2006). Waters off British Columbia were warmer in 2004 and 2005 

than the previous 50 years (Whitney 2006a). These changes resulted in decreases in the 

density of a thin surface layer; increased stability and stratification; declines in the depth 

of winter mixed-layer depths; and decreased entrainment of nutrients in the euphotic 

zone. Reduced availability of nitrogen and iron has resulted in limited primary 

productivity that affects all levels of the food chain (Behrenfeld et al. 2006). 

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Figure 22: Observed global SST trend from 1950-2004 from NOAA’s Extended 

Reconstructed SST data. Figure produced by Todd Mitchell, University of Washington 

Joint Institute for the Study of the Atmosphere and Oceans (http://jisao.washington.edu). 

This trend of increased stratification also was the situation in the southern regions of the 

California Current where the abundance of zooplankton deceased by 80% between 1951 

and 1993. During this period surface temperatures increased, and increased stratification 

resulted in less effective injection of nutrients from upwelling (Roemmich and McGowan 

1995). However, zooplankton biomass recovered during the four-year cool phase of the 

PDO (1999-2002) and are at the long-term mean level (see Peterson et al. 2006). 

Increased stratification with lower nutrient availability may also have repercussions on 

the community composition of phytoplankton. Generally warmer nutrient-poor water 

favors small phytoplankters such as dinoflagellates, whereas cool, nutrient-rich water 

favors large diatoms which are the basis for a shorter food web for copepods, large 

herbivores, and salmonids. 

Wind-driven Upwelling 

Wind-driven upwelling and mixing of nutrient-rich water are major processes that fuel 

the ecosystem in the California Current and in the Gulf of Alaska. In the California 

Current, northerly winds during the spring and summer pump cold, nutrient rich waters

into the euphotic zone where primary production occurs (Barth et al. 2007). In the Gulf 

of Alaska, strong cyclonic (counter-clockwise) surface wind stress and tidal mixing 

pumps nutrients into the euphotic zone. These processes may change with global 

warming, affecting both ocean productivity and growth and survival of salmonids. Off 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

the Pacific Northwest, both the intensity and timing of upwelling in the spring have been 

related to salmon survival. Upwelling during April and May of the smolt migration year 

was correlated with the survival of Oregon Production Index Hatchery (OPIH) coho 

salmon (Nickelson 1986; Logerwell et al. 2003), and upwelling during April, September 

and October was related to the return of Snake River Spring Chinook salmon (Scheuerell 

and Williams 2005). 

Bakun (1990) hypothesized that increased greenhouse gas warming will lead to increased 

contrasts in land-sea temperatures and intensified coastal upwelling in the California 

Current. This theory has been supported by observations by Mendelssohn and Schwing 

(2002) and others. Snyder et al. (2003) used a regional climate model to show that winddriven upwelling in the California Current will intensify, with perhaps increased 

productivity, but with changes in the upwelling season. Diffenbaugh et al. (2004) 

predicted feedbacks with warming leading to sparser coastal vegetation, increased land 

temperatures and land-sea gradients of temperature, and thus more intense upwelling in 

the northern California Current but a later spring transition. A rapid 20th century increase 

in coastal upwelling off Northwest Africa was also attributed to land-sea gradients of 

temperature, which may continue as global warming increases (McGregor et al. 2007). 

In the northern California Current, the onset of the spring transition and coastal upwelling 

in 2005 was about five weeks later than average and effective upwelling of cold water did 

not occur until about seven weeks after this (Pierce et al. 2006; Kosro et al. 2006). Until 

late July 2005 surface waters were strongly stratified and anomalously warm, nutrient 

depleted, and incapable of supporting normal spring-summer primary production. 

Delayed onset of upwelling in the spring may reduce the effectiveness of enrichment of 

the euphotic waters by upwelling (Pennington and Chavez 2000). A late initiation of 

upwelling, as has occurred during 2005 and 2006, has the potential to miss the peak in 

ocean-entry timing of spring Chinook, coho, and steelhead from the Columbia River. 

Delayed upwelling may not be as important for ocean-type Chinook since they enter the 

ocean over an extended period later in the year and migrate closer to shore than streamtype Chinook or coho salmon. Both the intensity of coastal upwelling and the date of 

spring transition are correlated with the survival of OPI coho salmon. Hence, changes in 

either the intensity or the timing of coastal upwelling may significantly impact the ability 

of the coastal ocean ecosystem to support high growth and survival of salmon exiting 

their natal streams and rivers, and these changes will likely have different impacts on 

different stocks and different life history types. 

Both upwelling and intrusion of subarctic waters affect the oxygen content in Pacific 

Northwest waters. During the past several decades declining oxygen levels have been 

reported in the subarctic Pacific (Emerson et al. 2004; Whitney 2006b), resulting in 

shoaling of the hypoxic layer from about 400m in the 1950s to about 250m in 2005. This 

low oxygen water may contribute to the hypoxic conditions that have occurred off the 

Oregon and Washington coasts during the summer in recent years. 

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In 2002, anomalously strong southward transports of cold and fresh, low oxygen and 

nutrient waters from the subarctic Pacific into the coastal zone of Oregon (Freeland et al. 

2003) provided conditions favorable for phytoplankton blooms. The phytoplankton 

production greatly exceeded the capacity of the grazing community to consume the 

phytoplankton. Much of the excess phytoplankton biomass sank to bottom waters on the 

shelf and slope, where through bacterial action, it decomposed. This regeneration 

process reduced oxygen concentrations of the already low concentration waters even 

further, so much so that in 2002 and 2006, the lack of oxygen caused high mortality of 

crabs, benthic invertebrates, and benthic fishes. Near-bottom hypoxia has occurred on 

selected sections of the Oregon coast in all summers since 2002 but was most widespread 

in 2006, when most regions of the northern Oregon and Washington shelves showed 

severe hypoxia. However, the biological impacts of these hypoxic conditions are 

confined to a narrow band along the seafloor of the inner continental shelf during the 

upwelling season and are not in near-surface waters inhabited by pelagic fishes and 

salmonids (Grantham et al. 2004). During 2004 and 2005, upwelling was delayed but 

was intense later in the year. During 2006, the hottest year in U.S. history when July 

temperatures recorded from terrestrial Oregon stations were four degrees warmer than the 

20th century average, upwelling was unusually strong. These limited data suggest, as 

predicted by Bakun (1990) and Snyder et al. (2003), a possible linkage between global 

warming, coastal upwelling and, indirectly, the occurrence of hypoxic waters. 

Columbia River Salmon 

Many other factors that interact with climatic physical forcing, upwelling and 

stratification influence the ocean survival and migration patterns of salmonids from the 

Columbia River basin. The effects of climate on productivity, prey resources and 

predation of salmon will depend on the species, evolutionary significant unit (ESU), 

distribution and life history. For example, different ESUs of west coast Chinook salmon 

responded differently to the regime shifts in 1996-97 and 1989-90, with the Snake River 

spring-summer ESU exhibiting the largest decline (Tolimieri and Levin 2004). Mueter et 

al. (2002) reported that regional sea-surface temperatures, within several hundred 

kilometers of a stock’s ocean entry point, is a better predictor of survival rates than largescale climate anomalies such as the PDO, indicating that regional conditions early in 

ocean life are one of the factors linked to subsequent survival.

Based on projections by the Northwest Power and Conservation Council (2005), natural 

flows at the Dalles will be higher during the winter and early spring and lower during the 

summer through early fall. Flows for 2040 are predicted to be lower than historic flows 

during May and June, the months of peak smolt migration for many stocks of salmonids. 

Increased temperatures in rearing habitats of salmonids in fresh water, may result in 

faster growth, and early downstream migrations and ocean entry of smolts (Beckman et 

al. 1998), if rearing temperatures are not excessive and food is not limited. With earlier 

peak flows in the Columbia and the projected delay in the onset timing of coastal 

upwelling (Snyder et al. 2003), the timing of ocean entry of juvenile salmonids may not 

be optimal. The first few weeks in the ocean are thought to be critical to the survival of 

68
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salmon off Oregon and Washington (Fisher and Pearcy 1988; Pearcy 1992), so a growing 

mismatch between smolt migrations and coastal upwelling would likely have significant 

negative impacts on marine survival rates. 

Changing ocean temperatures may alter the behavior, distribution and migrations of 

salmon, increasing the distance to migrations from their home streams to ocean feeding 

areas. Pacific salmon are known to have thermal preferences (Manzer et al. 1965) which 

may change with season. Welch et al. (1998) suggested that warming of the Pacific 

Ocean associated with a doubling of CO2 would push the range of sockeye salmon into 

surface waters of the Bering Sea or farther north. During the 1997 El Niño, Kaeriyama et 

al. (1998) and Grebmeier et al. (2006) observed that the distribution of several species of 

salmon were more concentrated in the Bering Sea, leading to intra- and inter-specific 

competition. However, salmon are not always confined to surface waters. Chinook 

salmon are known to adjust their vertical distribution in the water column to maintain a 

range of preferred temperatures (Hinke et al. 2005). Other species make excursions into 

cool deepwater below the thermocline (Myers et al. 1996), so warm surface waters may 

not be as limiting as once suspected. 

Energetic demands are increased at warmer temperatures, requiring increased 

consumption of prey to maintain a given growth rate. Growth rates of salmon in the 

ocean will therefore be affected by sea temperatures and the amount of food available. 

Hatchery fish may compete with wild fish, decreasing the amount of food available. If 

salmon migrate farther to the north and/or food is less available, longer times may be 

required to reach maturity, delaying the usual times of adult migrations into coastal water 

and rivers. With increased energetic demands, density-dependent competition for food, 

both interspecific and intraspecific, will likely intensify among maturing salmon on the 

high seas affecting both growth and survival (Pearcy et al. 1999; Ruggerone et al. 2003; 

Kaeriyama et al. 2004). 

Pelagic Community 

Ecosystem production and structure respond to changes in ocean regimes. Between 1998 

and 2002, after an intense 1997 El Niño and a prolonged La Niña (summer 1998-2002), 

species composition of pelagic nekton shifted from a community dominated by southern 

predatory species (mackerels and hake) to one dominated by northern species (smelts, 

squid and salmonids (Emmett and Brodeur 2000; Brodeur et al. 2005). Hake, a migratory 

species from the south is potentially a predator on small juvenile salmonids. They were 

exceptionally abundant in 1998 during the El Niño, declined during the following cool 

years (1999-2002) and then increased in 2003 (Fig. 23) During El Niño events and warm

PDO cycles, when coastal upwelling is relaxed and the countercurrent is intensified, the 

latitudinal distribution of pelagic fauna, including predatory fishes, moves north and for 

some species into the nearshore waters typically occupied by coho and Chinook salmon 

in the California Current (Pearcy et al. 1985; Lluch-Belda et al. 2005). The spring 

transition and upwelling were delayed in both 2004 and 2005. This was associated with 

elevated sea-surface temperatures, stable water column conditions, low productivity and 

69
 ISAB 2007-2 CLIMATE CHANGE REPORT

low abundances of forage fishes (Brodeur et al. 2006). In these same years, the voracious 

Humboldt squid (Dosidicus gigas), a large subtropical species, has been observed far 

north along the west coast, even into Alaska. This species has the potential to eat large 

quantities of fish (Ehrhardt 1991; Brodeur et al. 2006; Field et al. Ms). 

Fisher and Pearcy (1988) and Pearcy (1992) postulated that predation on juvenile 

salmonids during early ocean life is a critical factor to their survival. During weak 

upwelling and warm water conditions, juvenile salmonids, their predators and their prey 

are concentrated near shore where predation may be intense, especially since warm water 

predators, such as hake, migrate into northern waters during warm ocean conditions. 

Presence of alternative prey to juvenile salmonids is thought to be an important buffer to 

predation. Holtby et al. (1990) reported that predation on juvenile coho salmon was less 

intense when herring of about the same size were abundant. Emmett et al. (2006) 

reported the forage fish abundance off the mouth of the Columbia River was low 

following the 1997/98 ENSO, but increased catches, especially of northern anchovy and 

whitebait smelt, occurred during cool years with early spring transitions and strong 

upwelling of 2001 and 2003 (Fig. 23). These trends were correlated with the marine 

survival of OPI coho salmon. Forage fishes are often about the same size as juvenile 

salmonids, and are thought to buffer predation on juvenile salmonids in the area. If ocean 

temperatures increase, cool-water forage species that are alternative prey may decrease, 

increasing predation on juvenile salmonids. 

Seabirds and marine mammals that prey on fishes are also likely be affected by global 

warming. Caspian terns nesting along the Columbia River may switch to feed more 

intensely on juvenile salmonids if anchovy and other cool-water forage fishes decline. 

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Figure 23. Anomalies in forage–fish and Pacific whiting (hake) abundance, 1996 to

2006. From Emmett et al. (2006). 

Ocean Acidification 

Evidence is accumulating that carbonate equilibrium of the oceans is changing in 

response to increasing atmospheric concentrations of CO2 (Kleypas et al. 2006). 

Increasing concentrations of CO2 dissolved in the oceans lowers the pH and decreases the 

availability of carbonate ions and lowers the saturation state of major shell-forming 

carbonates in marine animals. This will lead to decreased calcification rates and 

increased carbonate dissolution, affecting the population dynamics of pelagic 

communities and abundances and distributions of major calcareous organisms such as 

coccolithophores, formanifera, and pteropods. Pteropods (pelagic mollusks) that produce 

71
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CaCO3 in aragonite form will be more strongly affected than coccolithopores and 

forminifera which produce the calcite form. 

Pteropods are important prey for salmonids in the subarctic Pacific, sometimes 

comprising up to 40% or more of the diet of some species (Andrievskaya 1958). 

Pteropods, primarily Limacina and Clio, are important food for maturing pink, chum, 

sockeye and coho salmon and steelhead in the northeastern Pacific (LeBrasseur 1966, 

Allen and Aron 1958). Limacina is also prey for juvenile coho salmon in coastal waters 

off Oregon and Washington (Peterson et al. 1982; Brodeur and Pearcy 1990). The effects 

of decreased abundance of pteropods on salmonids and pelagic food webs are unknown 

and would depend on the animals that replaced them in the ecosystem. 

 

Summary of Ocean Impacts 

Global climate change in the Pacific Northwest is predicted to result in changes in coastal 

ecosystems and salmon production that may be similar or potentially even more severe 

than those experienced during past periods of strong El Niño events and warm phases of 

the PDO, with warmer upper ocean temperatures, increased stratification and decreased 

productivity along the coast. However, a lack of certainty in future wind and weather 

patterns yields large uncertainties for future changes in the characteristics of salmon 

habitat in the northeast Pacific Ocean. For example, if upwelling winds remain 

unchanged from those of the past century, coastal upwelling may become less effective at 

pumping cold, nutrient-rich to the upper ocean because of increased stability in the upper 

ocean caused by surface warming. Or, as some modeling studies and hypotheses suggest, 

upwelling winds may become more intense, and perhaps the timing for the upwelling 

season will change because of timing shifts in upwelling wind patterns. With warmer 

ocean temperatures we can expect shifts in the size and species composition of 

zooplankton to smaller lipid-replete zooplankton instead of large, lipid-rich, cool-water 

species. Because of food chain effects and warm ocean waters, forage fishes will decline 

and warm-water predators will increase. With less productive coastal waters and 

modifications in timing of ocean entry, early ocean survival rates for Columbia River 

salmon will likely decline, and as observed in past periods of poor ocean conditions, 

declines in adult return rates may be exacerbated by large releases of hatchery fish (Levin 

et al. 2001). 

It is unknown whether the predicted rapid rate of change of new selective forces induced 

by climate change on salmonids will allow natural selection to produce evolutionary 

responses that will ameliorate impacts and retain the viability of populations. Such 

changes have occurred. In less than a century, ocean-type Chinook introduced to New 

Zealand colonized rivers and evolved significant differences in heritable traits (Quinn et 

al. 2001; Quinn 2005). The advanced spawning times of hatchery reared salmon is 

another example of evolutionary change, in this case from artificial selection. In any 

event, the future will depend on adequate freshwater spawning and rearing habitats, the 

chain of habitats in the life histories of anadromous salmonids, and maintenance of 

populations with diverse life histories and phenotypic and genetic variability to provide 

resilience to future changes.

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Integration of Potential Impacts on Salmonids 

The impacts of climate change on salmon vary among species and with life history stages 

but have the potential of impacting virtually every species and life history type of 

anadromous salmonid in the basin (Tab. 5). Resident cold-water fishes also may be 

affected (O’Neal 2002). Changes in freshwater ecosystems will impact most 

dramatically those species that have extended periods of freshwater rearing, but even 

species with abbreviated freshwater rearing (e.g., chum salmon), may be impacted by 

higher water temperatures during egg incubation and changes in winter and early spring 

flows. Impacts of climate change on flow and temperature in the mainstem will impact 

all species and life history types as will changes in the estuary and the ocean. Climate 

change has the potential to fundamentally alter the capacity of the Columbia River Basin 

to produce salmon. It is possible that certain life history types, or even species, may be 

extirpated from the system if changes are severe enough. 

Table 5. Potential impacts of influence of climate warming on salmon life cycle stages. 

Modified from Healey (2006). 

Life Stage High Temperature Effects 

Egg 1) Increased maintenance metabolism will lead to smaller fry. 

2) Lower disease resistance may lead to lower survival. 

3) Changed thermal regime during incubation may lead to lower 

survival. 

4) Faster embryonic development will lead to earlier hatching. 

5) Increased mortality due to more frequent flood flows as snow level 

rises. 

Spring, Summer 

Rearing 

1) Faster yolk utilization may lead to early emergence. 

2) Smaller fry are expected to have lower survival rates. 

3) Higher maintenance metabolism will lead to greater food demand. 

4) Growth rates will be slower if food is limiting or if temperature 

increases exceed optimal levels or growth could be enhanced food is 

available and temperatures do not reach stressful levels. 

5) Predation risk will increase if temperatures exceed optimal levels. 

Overwinter Rearing 1) Smaller size at start of winter is expected to result in lower winter 

survival. 

2) Increased mortality due to more frequent flood flows as snow level 

rises. 

3) Warmer winter would lead to higher metabolic demands, which may 

also contribute to lower winter survival if food limiting, or higher winter 

survival if growth and size are enhanced. 

4) Warmer winters may increase predator activity/hunger, which can 

also contribute to lower winter survival. 

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Smolts 1) Smaller fry entering the winter may lead to smaller potential smolts, 

which would have a lower survival rate or larger juveniles could have 

higher survival rates. 

2) Smaller fry at end of first summer may cause delay of smolting by 

one year 

3) Faster growth and warmer temperatures could lead to earlier 

smolting, which may affect marine survival, either positively or 

negatively. 

Estuary and Coastal 1) Changes in smolt timing into the estuary because river flow shifts 

may lead to a match/mismatch with estuarine/nearshore productivity, 

which would likely cause altered survival/growth. 

2) Increases in predator populations (e.g., hake, mackerel) and prey 

populations (e.g., changed timing of Neocalanus dynamics) may cause 

increased predation risk/reduced food available, which could contribute 

to reduced growth and survival during first summer. 

3) Higher coastal water temperatures will lead to greater maintenance 

metabolism, which would cause greater food demand and possibly 

slower growth/lower survival. 

4) Decreases in abundances of cool-water forage fishes could increase 

predation on juvenile salmonids by fishes, birds, and marine mammals. 

5) A warm, stratified ocean with ineffective upwelling could reduced 

ocean productivity and growth and survival of juvenile salmonids during 

first summer. 

6) Higher coastal water temperatures will lead to greater maintenance 

metabolism, which would cause greater food demand and possibly 

slower growth/lower survival. 

Open Ocean 1) Warmer North Pacific is expected to reduce thermal habitat for 

salmon in North Pacific. This may cause changes in ocean salmon 

distributions, greater density in remaining habitat/greater competition 

for food, which may contribute to slower growth. 

2) A sufficient decline in growth could lead to delayed maturation, 

increasing marine mortality. 

Returning Adults 1) Reduced quality of marine habitats may lead to fewer and smaller 

adults with lower energy reserves returning to the Columbia. Increased 

pre-spawning mortality may result. 

2) Lower discharge during upstream migration coupled with higher 

average temperatures could cause greater energy cost during migration, 

leading to higher pre-spawning mortality. 

3) Increased temperatures during migration and spawning may lead to a 

greater risk of disease outbreak, which would contribute to a greater risk 

of pre-spawning mortality. 

4) Smaller adults will produce fewer, smaller eggs with shorter 

development times, produce smaller fry, and lead to mis-timed

emergence (as detailed in previous life cycle stages above). 

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In many cases, impacts on the fish at one life history stage due to climate change 

contribute to increased mortality at later stages (Fig. 24). For example, reduced growth 

rates due to higher metabolic costs and altered trophic dynamics in freshwater can reduce 

the growth rate of rearing salmon. The resulting smaller smolts have reduced survival at 

later life history stages (Koenings et al. 1993). Reduced adult size due to lower food 

availability and higher metabolic rate in the ocean (Pearcy et al. 1999) may cause an 

increase in marine mortality and a decrease in body size of returning fish (Cox et al. 

1997). Smaller adult fish often suffer increased pre-spawn mortality (Rand et al. 2006) 

and those that do spawn deposit fewer eggs than would larger fish. Thus, the impacts of 

climate change can propagate cumulatively through the life of the fish and ultimately 

impact the productivity of future generations. 

Figure 24. Illustration of the points in the salmon life history where climate change may 

have an effect. The effects of climate change on salmon cannot be fully understood if 

impacts on only one stage of their life history are examined; a full appreciation requires 

examination of the cumulative impacts of all factors that influence salmon during thei

cycle. In addition, climate change effects cannot be assessed in isolation from the impacts

other factors influencing habitat or of harvest and hatchery practices (Figure from Ma

presentation to the ISAB, October 2006). 

r life

of

ntua

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Incorporating Climate Change into Restoration Planning 

The increasing certainty that climate in the Columbia Basin will change over the coming 

decades suggest that inclusion of climate change in fish and wildlife planning will be

critical if these plans are to succeed. Inclusion of climate change in planning has been 

hampered by several factors. In some cases the information on climate change is very 

technical, making it difficult for planners to interpret the information in a manner relevant 

to their planning process. The nature of climate change prediction results also can be

problematic. These predictions have generally been reported at very coarse spatial scales 

making it difficult to apply them at the watershed or subbasin scale (Jones et al. 1998). 

However, climate-change projections at a scale compatible with subbasin planning are 

becoming more available, making analysis of this issue in future subbasin plans more 

tractable. 

Climate change will occur concurrently with other impacts on fish and wildlife habitat 

and populations in the Columbia Basin. The recent declines in some fish and wildlife 

species, and in plant species that constitute their habitat, have been attributed primarily to 

habitat fragmentation, overexploitation, and global warming (Parmesan and Yohe 2003; 

Chapin et al. 2006; Mora et al. 2007). Studies that have examined the simultaneous 

effects of more than a single stressor (e.g., climate and land use; climate, land use, and 

human population) generally conclude that the effects of more than a single stressor are 

not easily predictable but may often be more severe than simple combination of the 

single-factor outcomes. Recently, Mora et al. (2007) used laboratory microcosms to 

simulate the simultaneous ecological effects of exploitation (harvest), habitat 

fragmentation (a common result of population increase and human land use), and climate 

change and concluded that declines in the sizes of populations could be up to 50 times 

faster when all three factors were simultaneously present. This result, if typical for other 

species and natural landscapes, implies higher risk of extinction for listed stocks (or other 

species) that experience land use and resource use impacts simultaneously with climate 

change impacts. 

The forthcoming ISAB report on human population increase and its potential impact on 

ecosystems in the Columbia Basin will indicate another stressor of fish and wildlife 

populations in the Columbia Basin whose impact is increasing through time. In areas 

where human population will increase over the next several decades, fish and wildlife 

will have to contend with both effects of a warming climate and more intensive land use. 

Some of the impacts may be additive or synergistic. For example, hydrological impacts 

caused by climate warming will be compounded by the flow changes caused by 

development in urbanizing areas. It will be critical for planners to consider both climate 

change impacts and changes in land use for fish and wildlife restoration efforts in the 

Columbia Basin to succeed. 

Battin et al.’s (2007) recent study of climate change and Chinook restoration scenarios

for the Snohomish River Basin offers a promising model for incorporating climate 

change into other watershed-scale restoration efforts. They used a series of linked 

models of climate, land cover, hydrology, and salmon population dynamics to investigate 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

the impacts of climate change on the effectiveness of proposed habitat restoration efforts 

designed to recover depleted Chinook salmon populations in the Snohomish Basin. This 

study found large, negative impacts on freshwater salmon productivity due to climate 

change, primarily due to increases in peak flows during egg incubation, with lesser but 

additional negative impacts due to reduced late summer and early fall spawning flows 

and increased summer stream temperatures. The modeling suggested that restoration 

actions and habitat protection can help to mitigate the negative effects of climate change, 

but that the habitat deterioration associated with changes in streamflows will make 

salmon recovery targets in the Snohomish Basin hard to meet. The study was able to 

identify portions of the Snohomish Basin where climate change effects were likely to be 

most pronounced, and the suggested strategy for restoration was to focus on those areas 

where increases in winter streamflow, and the associated impact on incubation survival, 

would be less severe. 

To date, however, future impacts on fish and wildlife habitat in the Columbia Basin have 

been addressed in relatively few planning efforts. In 2005, the Northwest Power and 

Conservation Council completed one of the largest locally-led watershed planning efforts 

in the United States, producing separate plans for 58 tributary watersheds or mainstem 

segments of the Columbia River4

. The plans guide the implementation of the Council’s 

Columbia River Basin Fish and Wildlife Program, which directs more than $140 million 

per year of Bonneville electricity revenues to protect, mitigate, and enhance fish and 

wildlife affected by hydropower dams. The subbasin plans primarily provide this 

guidance by identification of priority restoration and protection strategies for habitat and 

fish and wildlife populations and were not intended to regulate land use. 

Development of subbasin plans was guided by a subbasin planning template that 

described the various elements needed to provide contextual information for selection 

and prioritization of habitat restoration actions. One of these elements was to identify 

trends in macroclimate and human occupation and use that may affect hydrological or 

ecological processes in the subbasin over the long term (50 years into the future and 

beyond). Thus, climate change, or macroclimate trend, was explicitly identified as a 

component of the planning process. The ISAB and Independent Scientific Review Panel 

(ISRP) reviewed these plans (ISRP&ISAB 2004-135

). One consideration of the reviews 

was whether potential impacts from climate change or human population growth were 

considered. Generally, most plans simply recognized that climate change is possible and 

that human populations are likely to increase. For over 65% of the subbasin plans, the 

ISAB/ISRP considered the coverage of these issues to be insufficient and considered this 

deficiency to be a major omission for a forward-looking planning initiative. 

Instead of forward-looking, the ISAB/ISRP found that most of the subbasin plans largely 

documented the history of land conversion, resource consumption, demand for water, and 

changes in fish and wildlife resources. The focus of the plans was to address the 

 

4 See the Council’s Web site for a complete description of the subbasin planning process, ISAB 

and ISRP review, and the adopted plans: www.nwcouncil.org/fw/subbasinplanning/Default.htm. 5

 ISRP and ISAB 2004-13. Scientific Review of Subbasin Plans for the Columbia River Basin

Fish and Wildlife Program: www.nwcouncil.org/library/isrp/isrpisab2004-13.htm.

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problems caused by human activities over the past 50-100 years but very few attempted 

to assess what future impact changes in climate or human population might have on 

subbasin resources and what effect these changes might have on the efficacy of proposed 

restoration measures. The ISAB/ISRP noted that this approach was like driving down the 

road looking in the rearview mirror while accelerating. The ISAB/ISRP emphasized that 

evaluating alternate scenarios for the future is the essence of planning and is crucial to 

defining realistic restoration opportunities for the future. 

In addition, a survey of the plans was conducted for this ISAB climate change review. 

This survey confirmed that the majority of plans acknowledged the general risk posed by 

global climate change but did not directly factor it into planning; about one quarter of the 

plans did not address climate change at all. The survey revealed various levels of 

integration of climate change into the plans. Some included general discussions that 

climate change was a global threat that could derail habitat restoration actions at the local 

level. Others, notably those from Oregon, discussed the prediction of climate models that 

the Pacific Northwest will become warmer and wetter over the next half century, with an 

increase in winter precipitation and warmer, drier summers, concluding that such changes 

could lead to enormous, and mostly negative, impacts on the region’s water resources, 

ecosystems, and plant and animal species’ distributions (see Oregon Technical Outreach 

and Assistance Team (TOAST) 2004). Many of these plans also discussed the 

confounding effects of localized climate trends and ocean cycles. The Okanogan and 

Flathead subbasin plans noted contemporary evidence of climate change at the local 

level, such as changes in lake ecology and receding glaciers. The Deschutes Plan noted 

that much of the biological diversity within species is expressed at the margins of the 

habitats for each species and so recommended the importance of maintaining marginal 

habitats to maintain this diversity. The plan’s rationale was that “individuals able to 

persist in these habitats provide a source of strength for the species should these marginal 

habitats become more widespread with climate change or normal variation.” 

Unfortunately, the plans that included a more quantitative discussion of climate change 

dealt with this issue only in the assessment portion of the plan and the findings were not 

incorporated into project planning. An exception to this general pattern was the 

Fifteenmile Subbasin Plan, which recommended consideration of construction of offchannel reservoirs to mitigate for loss of water storage in snowpack. By mentioning this 

proposal here, the ISAB does not mean to endorse this strategy. Clearly many potential 

negative impacts on fish and wildlife resources could be associated with reservoir 

construction. However, this example represented perhaps the only instance in the 

subbasin planning process where a restoration strategy was proposed specifically to 

address habitat impacts related to climate change. 

The results of the ISAB/ISRP review of the subbasin plans were echoed in a recent 

assessment of watershed planning in Washington (Whitely Binder 2006). This study 

found a wide disparity in the extent to which climate change had been considered. This 

evaluation interviewed 11 of 15 Watershed Planning Leads representing 33 of the 43 

Washington Resource Inventory Areas (WRIAs) participating in the Watershed Planning 

Program and found that climate change was discussed in 15 of the 33 WRIAs covered in 

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the study. Most of these treatments were superficial, including only a sentence or two in 

the plan to indicate that this phenomenon was occurring. Two of the plans did contain 

brief technical treatments of climate change impacts for their planning areas. 

This report identified factors that can influence the integration of climate change 

information in watershed planning activities. (Whitely Binder 2006). Six factors were 

identified: 

• Watershed Planning Lead familiarity with climate impacts 

Watershed planning groups participating in Washington State’s Watershed Planning 

Program received guidance on the planning process from Department of Ecology 

Watershed Planning Leads. The familiarity of the Planning Lead (or any other 

individual serving in an advisory capacity) with climate change impacts can help 

bring climate impacts into the watershed planning process. 

• Interest and knowledge of planning unit members 

Planning unit members initiated discussion of climate impacts in 73% of the WRIAs 

where climate impacts had been discussed, and in these cases there was strong 

support among a few planning unit members. 

• Leadership 

Leadership can affect the overall success of watershed partnerships. Leadership may 

also influence if and how climate change is addressed in the planning effort, although 

opinions varied on the extent to which strong leadership helped or hindered 

discussions on climate change. 

• Trust among team members: 

Trust can plan an important role in determining whether “new” issues like climate 

change are included in a watershed planning process. Trust creates a process that 

allows viewpoints to be shared and new information to be sought and developed. 

• Willingness to accept new ideas/information 

Information that appears to challenge long-term experience, or “genetic knowledge,” 

can create a barrier to including climate change in a watershed planning effort by 

hindering development of a shared problem among participants. 

• Strategic gain 

The likelihood that climate change is addressed in planning efforts may increase 

when climate change impacts are seen as supporting other planning objectives. For 

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example, existing projections for increased drought risk may be used strategically to 

support proposals for new reservoir construction. 

This study also provided some suggestions for future actions that would encourage 

inclusion of climate change impacts in future planning (Whitely Binder 2006). 

• Commitment to updating plans 

Regular updating of plans, as envisioned in the subbasin planning process, provides 

the opportunity for these plans to evolve thorough time and incorporate new issues, 

like climate change, as they arise. 

• Continuation of the planning team 

Continuation of the watershed planning teams increases the probability that the 

knowledge, experience, and personal relationships (i.e., trust) developed through the 

planning process are maintained. 

• Requirement by funding organization to include climate change in plans 

The format and content of the plans was largely dictated by the requirements outlined 

in the planning documentation from the funding agency. A clear mandate to consider 

climate change likely would encourage a more thorough evaluation of this issue. 

• Dedicated funding for inclusion of climate change in plans 

Many of the teams would have required some funding to access the necessary 

expertise to address the technical aspects of climate change. Lack of dedicated 

funding to address climate change likely made it difficult for planning teams to 

include climate change in their planning efforts. 

• Availability of hydrologic modeling tools 

Hydrologic modeling tools create opportunities for planning units to consider how 

climate change impacts on snowpack and streamflow may affect various watershed 

management objectives. Adding a climate change assessment capability to new or 

existing models could enhance efforts to address climate change in watershed 

planning provided that the effort was cost effective and not too technically difficult. 

• Availability of technical support/information 

Planning Leads identified several types of information or other support that could 

help planning units more effectively integrate climate change into the watershed 

planning process. These included developing information for different types of 

audiences; providing more detailed, locally-scaled climate change scenarios; 

providing technical reports from peer-reviewed journals, research groups, and other 

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credible sources; developing case studies showing how climate information can be 

integrated into a plan; providing technical support to planning units; and, finally, 

providing information on the impacts of climate change on groundwater supplies. 

This evaluation clearly indicated that climate change is not yet an important consideration 

in natural resource planning in Washington. The likelihood that these plans will meet 

their objectives may be compromised if climate change is not addressed, especially in

cases where the resources of focus are sensitive to its potential effects. 

For future natural resource planning efforts, a variety of ways are possible to incorporate 

climate change considerations. Most of the subbasin plans that addressed climate change 

did so by inputting predicted changes in flow and water temperature to the EDT model. 

Although the EDT model is considered a “steady-state” model (Mobrand et al. 1997), 

this approach does provide one method of generating estimates of possible effects of 

climate change on salmon populations. In addition, Jones et al. (1998) proposed a 

method they termed an “integrated impact assessment” that coupled climate change 

projection results with an assessment of how these changes might impact salmon at each 

stage of their life history. This seems to be a reasonable approach to assessing impacts of 

climate change on salmon in the Columbia Basin, and similar approaches could be 

developed for other fish and wildlife resources in the basin. The accuracy and specificity 

of these approaches will improve as projections of changes in temperature and hydrologic 

conditions driven by climate change are generated at spatial scales more relevant to fish 

and wildlife planning. Additional improvements could be attained by addressing some of 

the impediments and opportunities identified in Whitely Binder (2006). 

Snover et al (2003) describe an online climate change streamflow scenario tool

(www.cses.washington.edu/cig/fpt/ccstreamflowtool/sft.shtml) that is designed to support 

simple and inexpensive evaluation of a water resource system’s vulnerability to climate 

change in the Columbia Basin. The streamflow scenarios can be directly incorporated 

into existing planning methods (such as critical period analysis) in place of the historic 

streamflow record. 

The scenarios are currently available at 16 locations in the Columbia River basin (Fig. 

25). For each location, there is a 40 year monthly time-step streamflow scenario for the 

2020s and for the 2040s as well as simulated historical streamflow for water years 1950-

1989. These flow records represent what historical observed (naturalized) flows would 

be if the average climate of the Pacific Northwest (PNW) changed as projected by global 

climate models. 

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Figure 25: Map of the Columbia Basin indicating locations for which Snover et al. (2003) 

provide monthly time step climate change impacts on simulated natural streamflow for 

1950-89, the decade of the 2020s, and the decade of the 2040s. Figure reproduced from

www.cses.washington.edu/cig/fpt/ccstreamflowtool/sftscenarios.shtml. 

Mitigating Climate Change Effects 

Only global strategies for reducing the emission of greenhouse gases will completely 

address climate change impacts on all habitats in the Columbia Basin, and even if

effective measures were put in place today, changes in the climate would still occur over 

the next several decades due to previous emissions of greenhouse gases (Tab. 1). Dealing 

with this issue will require unprecedented cooperation among public and private land

stewards and even among nations (Hansen et al. 2001, and many others). As we improve 

our understanding of climate change (and its interaction with other processes such as 

population and land use change), uncertainty of future conditions, especially biological 

conditions, will remain, and policymakers and managers should incorporate the 

uncertainty in future outcomes into their decision making (Root and Schneider 1993, 

Hansen et al. 2001, and many others). As we seek solutions to these larger issues, the 

identification and implementation of actions that may offset some of the negative effects 

of climate change in the Columbia Basin represent the only near-term, local option for 

mitigating effects of climate-change. 

Below, we provide some general recommendations of the types of actions that might be 

employed to help address the likely impacts of climate change in the Columbia Basin. 

However, the specific actions and the locations where they should be deployed must be 

determined through careful analysis of the regional, or subbasin, sensitivities to climate 

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change. The crucial need to incorporate careful and thorough assessment of climate 

change in basin planning activities cannot be overstressed. 

General Strategies 

The scientific foundation of the Fish and Wildlife Program is well-suited to support 

strategies to mitigate for climate change (NPPC 2000). The role of biodiversity in 

protecting both contemporary persistence of species and evolutionary potential is 

recognized in the Fish and Wildlife Program and in many other guidelines for mitigating 

the damaging effects of climate change. A good example of the value of biodiversity in 

promoting persistence, evolutionary potential, and various ecosystem functions comes 

from the literature on Pacific salmon (Hilborn et al. 2003). The sockeye salmon fishery 

of Bristol Bay is famously productive. Population-scale variability in responses of the 

salmon to environmental conditions appears to be responsible for maintaining this 

productivity, as different stocks contribute disproportionately to the spawning complex of 

fishes in years of different conditions. Ecological theory supports the interpretation that 

presence of diverse stocks in diverse sites is responsible for the robustness of the Bristol 

Bay fishery to changing conditions (Chesson and Huntly 1997). 

Identification of locations that are likely to be sensitive to climate change and 

establishment of adequate protective measures, including reserve areas, may be the most 

effective strategy for maintaining diversity in the face of changing climate in the 

Columbia Basin (Hansen et al. 2001, Shafer et al. 2001, Halpin 1997). Habitat protection 

and acquisition efforts are already supported by the FWP, but actions have not yet been 

targeted to address climate change concerns. 

There are several frequently recommended and generally accepted guidelines for 

selection of reserves or protected areas that are specifically intended to preserve

biodiversity in the face of changing climate (summarized in Halpin 1997). These 

include: 

• Select redundant reserves. 

• Select reserves that provide habitat diversity (as large as possible, with as 

much elevational and latitudinal variation as possible, as much

topographic heterogeneity as possible, with major vegetation transitions at 

the cores to avoid movement of a vegetation perimeter outside of the 

reserve). 

• Manage for buffer zone flexibility. Reserves should be surrounded by 

managed buffer zones that maximize management options under future 

climate and land-use conditions. Flexible zoning should be established 

around reserves to allow for land-use modifications and land trades in the 

future. 

• Manage for landscape connectivity. Consider proximity of reserves to 

other reserves and to unprotected compatible habitat, as well as corridors 

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to enable movement, recolonization of habitats, and genetic exchange 

among populations. 

• Manage for habitat maintenance, allowing natural disturbances as possible 

and avoiding as many exogenous stresses (e.g., pollution, non-native 

species, etc.) as possible. 

In addition, a specific guideline for the Columbia River Basin fishes would be: 

• Reserves or strongholds for salmonids and cool-water species will be most 

effective if they include productive populations with diverse life histories 

and large phenotypic and genetic diversity to provide resilience and 

evolutionary potential to adapt to climate change. 

These recommendations are compatible with the scientific foundation and guidelines of 

the 2000 FWP, though the current guideline to “Build from strength” requires some

modification to take into account the relationships of current and anticipated future 

strongholds. Halpin (1997) points out an additional concern in applying these guidelines: 

one must decide whether the goal is to protect the current mix of species over time or 

provide an arena for protecting changing species diversity. 

Additionally, the interplay of human population and land uses with climate change must 

be considered carefully. The leading cause of habitat loss and species loss or range 

contraction has been people and their activities (e.g., Laliberte and Rippel 2004, Knick et 

al. 2003, Dale 1997) and effective planning to mitigate effects of climate change on fish 

and wildlife must include consideration of and coordination with planning for the 

population and activities of people. 

Community Responses to Changing Environmental Conditions; a Mitigation 

Caution 

Because species differ in their climatic tolerances and optima, as well as in their 

physiological, behavioral, and evolutionary responses to changing climate, the results of 

climate change at the community level are difficult to predict. The paleoecological 

record makes clear that the species assemblages of past climatic conditions have been 

unique, with combinations of coexisting species, both plant and animal, unlike those 

observed today. These records suggest that the communities of the future will have 

different species combinations than now and will be glued together by species 

interactions that we do not understand and cannot predict with precision. Consequently, 

strategies to mitigate climate change will not likely be effective if planned at too narrow a 

scale, whether for single species, single areas, or single habitat types or species 

assemblages. Managing to accommodate uncertainty requires broader tolerance for error 

in predicting the expected and so requires broader and more inclusive strategies for 

protection of species, habitats, and ecosystems. 

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Possible Actions to Reduce Climate Change Impacts 

Mitigation Options for Tributary Habitat 

As climate and streams warm, tributary habitats will become increasingly important 

because they usually provide the cool waters for salmonids and other cool-water species 

in a watershed. Three actions that could contribute to mitigation of climate change 

impacts on tributary habitat are provided below; however, to be most effective these 

actions should be implemented in an integrated manner. A set of considerations relevant 

to the integration of mitigation actions was provided by Naiman et al. (1993): (1) plan 

from a broad perspective, rather than from the ecologically incomplete perspective of

restoration of isolated components such as fish, vegetation, or restoration of particular 

stream sections; (2) maintain hydrological connectivity and variability of riparian 

corridors from the headwaters to the sea; and (3) recognize the environment as a 

legitimate consumer of water, and strive to achieve a balance between immediate human 

water needs and long-term environmental and human requirements for water instream 

and in the riparian corridor. 

In general, mitigating for climate-induced changes in hydrology and temperature in

tributaries will involve many of the same approaches that have been initiated in the basin 

to date. Any action that can help minimize increased water temperatures or increase 

stream flow during summer and autumn would contribute to this end. However, it is 

unlikely that there are any options to successfully deal with some of the projected 

changes. For example, there is little that can be done at a local scale that will offset 

projected changes in snow pack elevation, accumulation, and melt timing. 

Temperature increases in some tributaries may be minimized by implementing measures 

to retain shade along stream channels and augment summer flow. Adequate protection or 

restoration of riparian buffers along streams is the most effective method of providing 

summer shade. This action will be most effective in headwater tributaries where shading 

is crucial for maintaining cool water temperatures. Expanding efforts to protect riparian 

areas from grazing, logging, development, or other activities that could impact riparian 

vegetation will help reduce water temperature increases. It will be especially important 

to ensure that this type of protection is afforded to potential thermal refugia. Removing 

barriers to fish passage into thermal refugia also should be a high priority. The possible 

effect of increased fire and insect damage on riparian vegetation due to warming climate 

was discussed earlier in this report and could reduce the effectiveness of this strategy. 

Nonetheless, implementing measures to ensure adequate levels of shade will be one of

the most effective approaches to limiting temperature increases. 

Managing water withdrawals to maintain as high a summer flow as possible could help 

alleviate both elevated temperatures and low stream flows during summer and autumn. 

This is very important in areas where decreased snowpack will result in lower and 

warmer stream flows in the summer. There are a variety of strategies being employed in 

the Columbia Basin to address stream flow issues. Buying or leasing of water rights and 

dedicating this flow to the stream has used more frequently in the basin over the last 

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decade. Increased efficiency of diversions and irrigation systems complement this 

approach. However, this approach typically does not permanently increase water flow, 

and actions implemented now may not persist long enough to mitigate for climate 

warming. In addition, water enhancement efforts tend to be implemented at locations 

where there are willing water rights holders, and these locations may not be the most 

critical for the fish or wildlife species of interest. Effectively using this strategy to offset 

impacts from climate change may require targeting the implementation of flow 

enhancement at sites that will provide the greatest benefit. 

Protecting and restoring wetlands, floodplains, or other landscape features that store 

water also will provide some mitigation for declining summer flow as the climate warms. 

Watersheds with extensive groundwater reservoirs will be among the most resistant to the 

impacts of climate change, due to the relatively constant release of cool water from the 

aquifers that feed the channel networks (Jefferson et al. 2006). Protecting these 

groundwater systems, and restoring them where possible, may provide refugia for coolwater species, like salmon, during periods of warm temperatures and low flows. 

Identification and protection of such thermal refugia may be one of the most effective 

strategies available to mitigate for climate change impacts on salmon and trout. Such 

locations are utilized by large numbers of fish or by stocks, some that are critically 

imperiled. These cool-water refugia include many tributaries along the mainstem

Columbia where migrating adult salmon and steelhead fish congregate, especially during 

warm years. These areas need protection as sanctuaries for migrating salmonids, and 

they might be considered for purchase or conservation easements to ensure that they are 

buffered from human impacts. 

These techniques will be most effective if they are focused on locations where they will 

be of greatest benefit to the fish and wildlife species of most concern. If the predicted 

changes occur, the distribution of fish and wildlife populations in the basin will change

and many currently suitable habitats will not be so in the future, regardless of actions 

taken at the local level. Therefore, subbasin plans should consider the potential influence 

of future climate change when identifying and prioritizing restoration projects. 

Mitigation Options for the Mainstem, Estuary, and Plume 

Impacts of global warming in the mainstem, estuary and plume must be considered in the 

context of hydrosystem management. Because the hydrology and salmon habitat of the 

mainstem and estuary have been extensively transformed, managed and manipulated for 

decades, there is a range of alternatives for mitigating climate change impacts on 

Columbia Basin salmon in these habitats. Past changes in hydrosystem infrastructure and 

operations have already caused enormous changes in the timing, magnitude, and 

variability in mainstem and lower Columbia River hydrology at seasonal to hourly time

scales. To the extent that hydrosystem operations are flexible, there are opportunities to 

mitigate for some climate change impacts in the estuary and plume because projected 

changes in natural runoff, even under the most extreme warming scenarios for the late 

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21st century, are substantially smaller than the changes caused by the development and 

operation of the hydrosystem in the late 20th century. 

Miles et al. (2000) and Payne et al. (2004) have examined climate change impacts on 

multiple water resource objectives in the Columbia Basin, and both studies identified an 

unequal distribution of climate change impacts on hydropower generation, recreation, 

irrigation, instream flow targets, and flood control (Fig. 26; from Miles et al. 2000). 

Payne et al. (2004) evaluated the potential effects of climate change on the hydrology and 

water resources of the Columbia River Basin by driving hydrologic and water resources 

models with changing temperature and precipitation scenarios produced in a global 

climate model under a “business as usual” greenhouse gas emissions scenario. They note 

that some of the projected climate change impacts can be mitigated by alternative 

mainstem hydrosystem operations, there are trade-off between firm hydropower 

production and instream flow targets for salmon, and there were some impacts that would 

not be mitigated by the altered operations they evaluated: 

“From the perspective of water resource operations, the projected hydrologic 

changes would have the greatest effect from spring to autumn, when the reservoir 

system refills and is intended to maintain storage until the winter reservoir 

drawdown for flood control and hydropower production. Increasing winter 

inflows associated with seasonality shifts would necessitate the continuation of 

present flood control policies despite the decreased ability of the system to 

replenish current evacuations in the spring. Lower summer streamflows would 

exacerbate the reduced reservoir refill by increasing drafts for instream flow 

targets. The lower resulting storage at the end of summer would reduce the ability 

of the system to meet present firm power production (hydropower ‘safe yield’) 

targets during the winter, before reservoir storage begins to be restored by winter 

precipitation. Hydropower revenues were predicted to be relatively unaffected, 

however, because annual streamflow volume changes were generally small, and 

fall and early winter generation reductions would be compensated by increases in 

late winter and spring. 

The starkest result of this study is an evolving tradeoff between reservoir releases 

to maintain instream flows for fish and hydropower production. In order to 

maintain performance of the reservoir system with respect to instream flow 

targets developed under the NMFS Biological Opinion associated with ESA 

listing of Columbia River salmonids, substantial (10–20%, depending on the 

future time period) reductions in firm hydropower would be required. Even with 

these reductions in firm power, late summer minimum flows would still be lower 

than at present.” (Payne et al. 2004). 

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Figure 26. Columbia River Basin reliability by sector for current and future climate under 

a fixed management policy regime that optimizes flood control and firm hydropower 

production. The chart shows the simulated reliability of meeting reservoir operation 

targets estimated using two different climate models (one with a wetter future, the other a 

dryer future) for the current climate, the 2020s, and the 2040s. Reliability is calculated as 

the percentage of years that a system target is met. The dark bars represent the control 

model run, or current climate. It is clear that targets for simulated instream flow, 

agriculture, and recreation are met less than 100% of the time given the current climate 

conditions. With the exception of the 2020 projections from the wet models, the 

projections show losses of reliability in the future for most of the system targets. Figure 

based on data from Miles et al. (2000). Reproduced from Casola et al. 2005. 

Some actions may be possible at mainstem hydroelectric dams in the Columbia and 

Snake Rivers to help offset projected climate change effects in the mainstem reservoirs 

and the estuary (i.e., increased water temperatures and reduced river flows during 

summer and fall). A number of measures are currently used to mitigate for hydroelectric 

development in the Columbia River Basin and improve juvenile and adult salmonid 

passage and survival. Below are described several mitigation options that may be 

considered in the future to help address changes associated with climate change. 

Flow augmentation - Flow augmentation from cool/cold water storage reservoirs to 

reduce water temperatures or create cool water refugia in mainstem reservoirs and the 

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estuary may be an effective strategy to reduce impacts from elevated water temperatures. 

As reducing water temperature is the goal of this strategy, simply increasing flow may 

not achieve the desired effect. Water sufficiently cool to impact downstream thermal 

conditions must be released. Effective implementation of this strategy may require 

increasing the number of storage reservoirs for additional cool/cold water flow. Careful 

consideration of the benefits and negative impacts of increasing the number of storage 

facilities in the basin will be required. Such consideration should occur in the near future 

if storage capacity is to be increased in time to address impacts of climate change. 

Juvenile fish passage- The use of removable surface weirs (RSWs) has proven to be an 

efficient spillway passage device passing a large number of fish in a relatively small 

volume of water. Another benefit of RSWs is reducing the time juvenile salmonids 

spend in the forebay, which will reduce exposure to the warmer surface water 

temperatures and predators that concentrate there. Juvenile fall Chinook, which move

past the dams during summer and fall when water temperatures are high and flows low 

will especially benefit from the RSWs. 

Adult fish passage –There have been recent observations in the summer of adult 

salmonids delaying dam passage at very high water temperatures. Increasing water 

temperatures due to climate change may exacerbate this problem. One mitigation option 

is to reduce water temperatures in the ladders with water drawn from lower cooler strata 

in the water column of the forebay using large current mixers or exit outflows designed to 

extract cooler water from lower strata. Covering the ladders to provide shade may also 

have some effect on water temperature. Cooling water temperatures at ladder exit 

locations may help encourage fish to enter the ladders. 

Transportation – The juvenile fish transportation program run by the U.S. Army Corps of 

Engineers could develop strategies more focused on temperature criteria for initiating full 

transport of juvenile fall Chinook. The possibility of transporting immigrating adults 

through the lower Snake River when water temperatures reach near-lethal limits in the 

late summer should also be explored. 

Reservoir and estuary predation – As indicated above, increases in water temperatures

will likely increase predation on juvenile salmonids in mainstem reservoirs and the 

estuary. One mitigation measure would be an addition of programs by the states to 

liberalize harvest of introduced piscivorous species such as smallmouth bass, walleye, 

and channel catfish. 

Habitat restoration –Removal of dikes to open backwater, slough and other off-channel 

habitats along mainstem reservoirs and the estuary can increase flow through these areas 

and may encourage increased hyporheic flow. Increasing the proportion of flow that is 

transported below the surface of the river bed or riparian area can substantially cool the 

water and has been shown to be an important mechanism for the formation of cool water 

refugia. 

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Mitigating Effects of Climate Change in the Ocean 

If the ocean environment becomes less productive, density dependence will be 

intensified, resulting in increased competition among species and stocks in the ocean.

This may result in lower growth and survival rates for wild salmon in the ocean. 

Reduction in the hatchery releases during poor ocean conditions may enhance survival of 

wild stocks, but more research on this topic is needed. 

If climate change causes changes in the timing of the spring transition and initiation of 

coastal upwelling is delayed, as some predict, transportation or inriver passage of 

juveniles could be controlled so that ocean entry coincides with favorable ocean 

conditions. 

As recommended in the recent ISAB “Report on Harvest Management of Columbia 

Basin Salmon and Steelhead” (ISAB 2005), harvest management needs a new strategy to 

adapt to climate changes -- to anticipate and incorporate changes such as PDO and ENSO 

cycles and global warming in pre-season abundance forecasts and in-season estimates of 

returning run sizes. Climate change affects identification of the critical needs for (1) 

maximizing survival of ESA-listed populations, (2) protecting and enhancing important 

habitats, and (3) managing other factors in the salmon life cycles. During favorable 

climatic phases “stocks that are below sustainable levels in the poor phase should be 

allowed to recover their numbers and recolonize or expand areas of freshwater 

production.” Harvest managers need to adopt near- and long-term assessments that 

consider changing climate in setting annual quotas and harvest levels for fish from the 

Columbia Basin. 

Harvest of salmon in the ocean differentially affects wild and hatchery stocks. Stock 

identification at sea is already used and could provide a mechanism to determine if stocks 

are segregated in time or space so that fisheries could target only hatchery stocks or 

robust wild stocks. Harvest also could be further modified to favor wild populations or 

ESA-listed ESUs, especially when ocean conditions are not favorable. Harvest 

management strategies that would achieve this goal include 1) reducing overall harvest 

levels to help improve survival of wild adults and 2) reducing the allowable levels of take 

on wild fish in mixed hatchery-wild fisheries. 

The Role of the NPCC in Addressing Climate Change in the Columbia 

Basin 

The roles played by the Northwest Power and Conservation Council enable this 

organization to be an influential force in forging the strategy by which climate change 

impacts will be addressed in both the Columbia Basin and the Pacific Northwest in 

general. The Council’s responsibilities for regional power planning and implementing a 

fish and wildlife program place the Council in a position to influence both the human 

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factors that are driving climate change and the management of the natural resources that 

will be impacted by these changes. The three primary tasks of the Council are: 

1. Develop a 20-year electric power plan that will guarantee adequate and 

reliable energy at the lowest economic and environmental cost to the 

Northwest 

2. Develop a program to protect and rebuild fish and wildlife populations 

affected by hydropower development in the Columbia River Basin 

3. Educate and involve the public in the Council’s decision-making processes. 

All of these tasks relate to how the region will deal with climate change. The efficient 

production, distribution, and consumption of power, especially power generated without 

the release of greenhouse gases, can contribute to global efforts to reduce human impacts 

on the greenhouse effect and thus reduce human-caused global change over the long 

term. Incorporating climate change into future fish and wildlife recovery plans can help 

to ensure that all reasonable measures are taken to buffer the natural ecosystems of the 

Columbia Basin from the changes in temperature and hydrology expected over the 

coming decades. The educational mandate of the Council provides a mechanism for 

encouraging the residents of the basin to become engaged in the coordinated effort that 

will be required to ensure that the progress that has been made in restoring fish and 

wildlife populations continues into the future, despite a changing climate. 

Key Findings 

• Climate records show that the Northwest has warmed about 1.0 oC since 1900, or 

about 50% more than the global average warming over the same period (Mote 

2003a). The warming rate for the Pacific Northwest over the next century is 

projected to be in the range of 0.1-0.6 ̊ C/decade. Projected precipitation changes 

for the region are relatively modest. Most models project long-term increases in 

winter precipitation and decreases in summer precipitation. The changes in 

temperature and precipitation will have impacts on the snow pack, stream flow, 

and water quality in the Columbia Basin. 

• Virtually all future climate scenarios predict increases in wildfire in western 

North America. Fire frequency and intensity have already increased, with more 

frequent, larger, and more intense fires in the past 50, and especially the past 15, 

years in the shrub steppe and forested regions of the West, including the 

Columbia Basin. 

• It is expected that global warming will cause insect outbreaks to become more 

common and widespread. Drought and hot, dry weather have already led to an 

increase in insect outbreaks in the Columbia Basin, especially outbreaks of 

mountain pine beetle. 

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• Several community types in the Columbia River Basin are likely to decrease 

greatly in area or disappear regionally, including alpine habitats, subalpine 

spruce-fir forests, aspen, and sagebrush. Shifts in the distributions of forest tree 

species will be complex, depending on altered temperature and water availability, 

summer maximum and winter minimum temperatures, and changing frequencies 

of fire and insect outbreaks. 

• Predicting the effects of global warming on wildlife is complicated because 

wildlife will be impacted by changing conditions of temperature and moisture and 

also by the resulting shifts in vegetation, which they depend on for habitat and 

food. However, populations relying on habitat types that are likely to decrease 

will decline. For example, the bird species of shrubland and grassland are 

declining more rapidly than any other avian species group in North America. 

This habitat type is expected to become increasingly rare as the climate changes 

over the next century. 

• An analysis of the effects of temperature increases associated with climate change 

suggests that 2% to 7% of current trout habitat in the Pacific Northwest will be 

unsuitable for these fishes by 2030, 5%-20% by 2060 and 8% to 33% by 2090. 

Salmon habitat may be more severely affected, in part because these fishes can 

only occupy areas below barriers and are thus restricted to lower elevations within 

the region. Predicted loss of salmon habitat would be most severe in Oregon and 

Idaho with potential losses exceeding 40% by 2090. Loss of salmon habitat in 

Washington would be less severe, about 22% loss by 2090. 

• Lower-elevation tributaries, streams east of the Cascade Mountain crest and in the 

southern portions of the Columbia Basin would be expected to be most affected 

by temperature changes due to climate change. 

• Watersheds that are just above the current snow line will experience a change 

from a snow-melt dominated hydrologic regime to one that is driven primarily by 

winter rainfall or rain on transient snow pack. Even those watersheds which 

remain above the snow line will experience earlier snow-melt runoff. 

• Increased frequency and severity of flood flows during winter can affect overwintering juvenile fish and incubating eggs in the streambed. Eggs of fall- and 

winter-spawning fish, including Chinook, coho, chum, and sockeye salmon and 

bull trout, may suffer higher levels of mortality when exposed to increased flood 

flows. Higher winter water temperatures also could accelerate embryo 

development and cause premature emergence of fry. 

• Bull trout require cold, headwater streams for spawning. Therefore, a warming 

climate may disproportionately impact this species. Recent projections predict 

22% to 92%.loss of habitat suitable for bull trout in the Columbia Basin as a result 

of climate warming. 

• Warmer water temperatures may exclude salmonids from reaches with 

temperatures that are already close to their upper thermal limit. Even where water 

temperatures do not exclude use by salmonids, metabolic rates will increase, 

leading to reduced growth rates where food is limited and smaller size at the end 

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of the summer. Smaller fish typically suffer higher mortality rates during winter 

than do larger fish. 

• Higher winter temperatures may enable fish to feed more actively, increasing 

growth rates if sufficient food is available. If food is limited, the elevated 

metabolic demands created by elevated winter temperatures could reduce winter 

growth rates and contribute to reduced smolt size the following spring. Larger 

smolts have higher marine survival. 

• The changes in mainstem flows due to hydrosystem operations are substantially 

greater than the natural runoff changes projected to be caused by climate warming 

in the 21st century. Current predictions suggest climate change will produce 

higher flows in winter and early spring due to an increase in the proportion of 

precipitation falling as rain and less snow storage. Late spring to autumn flows 

could be reduced. 

• The increased water temperatures in the mainstem caused by development of the 

hydropower system will be exacerbated by climate change. Climate modeling of 

future water temperatures in the Columbia and Snake rivers predicts an increase 

of 1o C or greater by 2040, adding to the increases caused by the hydrosystem.

• Fall Chinook spawn in the mainstem of the Snake and Columbia rivers. Increases 

in water temperature will accelerate the rate of egg development and lead to 

earlier emergence, most likely at a smaller average size than historically. 

Smaller-sized fry are likely to have lower survival due to increased vulnerability 

to predators. 

• Predation on salmonids will likely be increased by elevated water temperatures. 

Northern pikeminnow generally select smaller fish when feeding on juvenile 

salmonids. Warmer temperatures may reduce the size of smolts. Elevated water 

temperatures also will increase consumption rates and growth rates of predators. 

• Potential impacts of increased water temperatures on adult salmon include delay 

in dam passage, failure to enter fish ladders, increased fallback, and loss of energy 

reserves due to increased metabolic demand. Increases in mortality also may be 

caused by fish pathogens and parasites as these organisms often do not become

injurious until their host is thermally stressed. 

• Sea level rise in conjunction with higher winter river flows could cause the 

degradation of estuary habitats created by sediment deposition owing to increased 

wave damage during storms. 

• Numerous warm-water adapted fish, including several non-indigenous species, 

normally found in freshwater may expand their populations with the warmer 

water and seasonal expansion of freshwater habitats. The potential impacts on 

salmon are not understood. 

• Climate change may affect the trophic dynamics of the estuary due to upstream

extension of the salt wedge in spring early summer due to reduced river flows. 

The landward head of the salt wedge is characterized by a turbulent region known 

as the estuary turbidity maximum, an area with high concentrations of fish-food 

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organisms such as harpacticoid copepods. Changes in the distribution of the salt 

wedge will influence the location of this zone, but it is difficult to forecast the 

effect this change will have on juvenile salmon. 

• Earlier snowmelt and earlier, higher spring flows and warmer temperatures may 

cause spring Chinook and steelhead yearlings to smolt and emigrate to the estuary 

and ocean earlier in the spring. Earlier emigration coupled with the projected 

delay in the onset timing of coastal upwelling may cause juveniles to arrive in the 

estuary and ocean prior to the onset of favorable conditions. The first few weeks 

in the ocean are thought to be critical to the survival of salmon off Oregon and 

Washington; thus, a growing mismatch between smolt migrations and coastal 

upwelling would likely have significant negative impacts on marine survival 

rates. 

• Global climate change in the Pacific Northwest is predicted to result in changes in 

coastal ecosystems and salmon production that may be similar to those 

experienced during past periods of strong El Niño events and warm phases of the 

PDO, with warmer upper ocean temperatures, increased stratification and

decreased productivity along the coast. However, a lack of certainty in future 

wind and weather patterns yields large uncertainties for future changes in the 

characteristics of salmon habitat in the northeast Pacific Ocean. 

• Evidence is accumulating that carbonate equilibrium of the oceans is changing in 

response to increasing atmospheric concentrations of CO2. Increasing 

concentrations of CO2 dissolved in the oceans lowers the pH and decreases the 

availability of carbonate ions and lowers the saturation state of major shellforming carbonates in marine animals. Pteropods are expected to be especially 

impacted, and they can comprise up to 40% or more of the diet of some salmon 

species. 

• Changing ocean temperatures may alter the behavior, distribution and migrations 

of salmon, increasing the distance from their home streams to ocean feeding 

areas. Energetic demands are increased at warmer temperatures, requiring 

increased consumption of prey to maintain a given growth rate. If salmon migrate 

farther to the north and/or food is less available, longer times may be required to 

reach maturity, delaying the usual times of adult migrations into coastal water and 

rivers. 

• In many cases, impacts of climate change on a fish at one life history stage 

contribute to increased mortality at later stages. The impacts of climate change 

can propagate cumulatively through the life of the fish. 

• Climate change will occur concurrently with other impacts in the Columbia Basin. 

Studies of the simultaneous effects of more than a single stressor (e.g., climate 

and land use; climate, land use, and human population growth) generally conclude 

that the effects of more than a single stressor are not easily predictable, but may 

often be more severe than a simple combination of the single-factor outcomes. 

• Future impacts of climate change on fish and wildlife habitat in the Columbia 

Basin were poorly addressed in the subbasin planning process. The majority of 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

plans acknowledged the general risk posed by global climate change but did not 

directly factor it into planning; about one quarter of the plans did not address 

climate change at all. Very few subbasin plans attempted to assess what future 

impact changes in climate might have on subbasin resources and what effect these 

changes might have on the efficacy of restoration measures. 

• Inclusion of climate change in planning has been difficult because the information 

on climate change is very technical, making it difficult for planners to interpret 

the information in a manner relevant to planning, and climate projections have 

generally been reported at very coarse spatial scales, making them difficult to 

apply at the watershed or subbasin scale. Climate-change projections at a scale 

compatible with subbasin planning are becoming more available, making analysis 

of this issue in future subbasin plans more tractable. 

Recommendations 

• Assessing potential climate change impacts in each subbasin and developing a 

strategy to address these concerns should be a requirement in subbasin plan 

updates. Providing technical assistance to planners in addressing climate change 

may help ensure that this issue is addressed thoroughly and consistently in the 

subbasin plans. 

• Tools and climate change projections that will aid planners in assessing subbasin 

impacts of climate change are becoming more available. Of particular interest for 

the Columbia Basin is an online climate change streamflow scenario tool that is 

designed to evaluate vulnerability to climate change for watersheds in the 

Columbia Basin (www.cses.washington.edu/cig/fpt/ccstreamflowtool/sft.shtml). 

Models like this one can be used by planners to identify sensitivities to climate 

change and develop restoration activities to address these issues. 

• Although actions that will reverse the process of global climate change cannot be 

effectively implemented at the scale of the Columbia Basin (these must be global 

in scale), there are actions that may be beneficial in mitigating some of the 

impacts of climate change in the basin. 

• Locations that are likely to be sensitive to climate change and have high 

ecological value would be appropriate places to establish reserves through 

purchase of land or conservation easements. Landscape-scale considerations will 

be critical in choice of reserve sites, as habitat fragmentation and changes of 

habitat will influence the ability of such reserves to support particular biota in the 

future. These types of efforts are already supported by the Fish and Wildlife 

Program, but actions have not yet been targeted to address climate change 

concerns. 

• Actions that minimize water temperature increases or augment stream flow during 

summer and autumn would contribute to the mitigation of some climate-induced 

changes in hydrology and temperature in tributaries. However, there are no 

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 ISAB 2007-2 CLIMATE CHANGE REPORT

options for addressing some of the projected changes. For example, there is little 

that can be done at a local scale that will offset projected changes in snow pack 

elevation, accumulation and melt timing. 

• Possible actions that could be taken on the mainstem to address climate change 

impacts include: 

o Flow augmentation from cool/cold water storage reservoirs to reduce water 

temperatures or create cool water refugia in mainstem reservoirs and the 

estuary. Effective implementation of this strategy may require increasing the 

number of storage reservoirs. Careful consideration of the benefits and 

negative impacts of increasing the number of storage facilities in the basin 

will be required. Such consideration should occur in the near future if storage 

capacity is to be increased in time to address climate change impacts. 

o Use of removable surface weirs to reduce the time juvenile salmonids spend in 

the warm water of the forebay. 

o Reduction of water temperatures in the ladders with water drawn from lower, 

cooler strata in the water column of the forebay. 

o Development of transportation strategies more focused on temperature criteria 

for initiating full transport of juvenile fall Chinook. 

o Evaluation of the possibility of transporting immigrating adults through the 

lower Snake River when water temperatures reach near lethal limits in the late 

summer. 

o Liberalization of harvest of introduced piscivorous species such as 

smallmouth bass, walleye, and channel catfish. 

o Opening of backwater, slough, and other off-channel habitats along mainstem

reservoirs and the estuary to encourage an increase in flow through these areas 

to help reduce water temperature. 

• Flow augmentation from cool/cold water storage reservoirs may be an effective 

strategy to reduce impacts from elevated water temperatures. 

• There are opportunities to mitigate for some climate change impacts in the estuary 

and plume with changes to hydrosystem operations. Possible actions would 

include reducing the frequency and magnitude of winter flows, extending the 

period of spring runoff later in the year and increasing late summer and autumn

flows. 

• If the ocean environment becomes less productive, density-dependent interactions 

will be intensified. This may result in lower growth and survival rates for wild 

salmon in the ocean. If this occurs, reduction in hatchery releases during poor 

ocean conditions may enhance survival of wild stocks, but more research on this 

topic is needed. 

• If climate change alters the timing of the spring transition and initiation of coastal 

upwelling is delayed, as some predict, transportation or inriver passage of 

96
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juveniles might be controlled so that ocean entry coincides with favorable ocean 

conditions. 

• Harvest management should develop a strategy to adapt to climate changes -- to 

anticipate and incorporate changes such as PDO and ENSO cycles and global 

warming in pre-season abundance forecasts and in-season estimates of returning 

run sizes. 

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Tech. Rep. RMRS-GTR-144. Fort Collins, CO: U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Forest Station. 210 p. 

Welch, D.W., Y. Ishida, and K. Nagasawa. 1998. Thermal limits and ocean migration of 

sockeye salmon (Oncorhynchus nerka): long-term consequences of global 

warming. Can. J. Fish. Aquat. Sci. 55:937-948. 

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Westerling, A. L., H. G. Hidalgo, D. R. Cayan, and T. W. Swetnam. 2006. Warming and 

earlier spring increase Western U.S. forest wildfire activity. Science 313:940-943. 

Whitely Binder, L. C. 2006. Climate change and watershed planning in Washington 

State. Journal of the American Water Resources Association 42(4):915-926. 

Whitney, F. 2006a. Decreased nutrient drawdown in the surface ocean. In: State of the 

Pacific Ocean 2005. Fisheries and Oceans of Canada Ocean Status Report 

2006/001, p. 25. 

Whitney, F. 2006b. Declining oxygen in the ocean interior, an update. In: State of the 

Pacific Ocean. Fisheries and Oceans of Canada, Ocean Status Report 2006/001, 

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Williams, D. W. and A. M. Leibhold. 2002. Agricultural and Forest Entomology 4:87-99. 

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Wissmar, R. C. and C. A. Simenstad. 1998. Variability of estuarine and riverine ecosystem

productivity for supporting Pacific salmon. Chapter 6. Pages 253-301 in G. R. McMurray

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the Pacific Northwest Coastal Ecosystems Regional Study Workshop, August 13-14,

1996, Troutdale, Oregon. NOAA Coastal Ocean Program, Decision Analysis Series No. 

11. NOAA Coastal Ocean Office, Silver Spring, MD. 342 pp.

Wooster, W.S. and D.L. Fluharty. 1985. El Niño North. 312 p. Washington Sea Grant 

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Andrea; Healey, Michael C.; English, Karl K, 2006. Physiological and energetic 

correlates of en route mortality for abnormally early migrating adult sockeye 

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between climate variability and density dependence in the population viability of 

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Snake and Columbia River dams and reservoirs, 2001. Prepared for the U.S. 

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APPENDIX A. Glossary of Climate Change Terms 

This glossary was adapted from California’s Climate Change Portal glossary 

(www.climatechange.ca.gov/glossary/index.html) which combined information from 

numerous sources:

• (EPA) = United States Environmental Protection Agency 

http://yosemite.epa.gov/oar/globalwarming.nsf/content/glossary.html - (see also 

www.globalwarming.org/article.php?uid=123)

• (IPCC) =Intergovernmental Panel on Climate Change www.ipcc.ch/pub/syrgloss.pdf

(Australia) = Green House Office of the Commonwealth of Australia (Australia) 

• (CAN) = - Climate Action Network - 

www.climatenetwork.org/pages/canglossary.html 

• (BBC) = http://news.bbc.co.uk/1/hi/sci/tech/1015162.stm - BBC News / Science & 

Technology / Climate Change Glossary, 10 November, 2000 

• (CalSpace) = http://calspace.ucsd.edu/virtualmuseum/Glossary_Climate/ 

• (Exploratorium) = www.exploratorium.edu/climate/glossary/

The glossary also includes terms from: 

• (NOAA Paleo) NOAA’s National Climatic Data Center (paleo perspective glossary) 

www.ncdc.noaa.gov/paleo/abrupt/glossary.html 

• (Pew) the Pew Center www.pewclimate.org/global-warming-basics/full_glossary/. 

• (Wikipedia): wikipedia.org/wiki/Glossary_of_climate_change 

• As well as terms defined by the ISAB. 

Many terms pertaining to international and governmental agreements are not included in 

the ISAB glossary but can be found in California’s glossary. 

Abrupt climate change. Transition of the climate system into a different state (of temperature, 

rainfall, and other aspects) on a time scale that is faster than the responsible forcing (mechanistic); 

change of the climate system that is faster than the adaptation time of social and/or ecosystems

(impacts). (NOAA Paleo)

Absorption lines. Any portion of the electromagnetic spectrum (including visible light) that is 

trapped by free atoms or molecules in the path of the radiation, thus reducing their transmission. In 

the climate context, this is important for the greenhouse effect since water vapor, carbon dioxide 

and methane absorb certain wavelengths of infrared radiation. (Calspace)

Absorption of Radiation. The uptake of radiation by a solid body, liquid or gas. The absorbed 

energy may be transferred or re-emitted. (EPA)

Aerosols. Particles of matter, solid or liquid, larger than a molecule but small enough to remain 

suspended in the atmosphere. Natural sources include salt particles from sea spray and clay 

particles as a result of weathering of rocks, both of which are carried upward by the wind. 

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Aerosols can also originate as a result of human activities and in this case are often considered 

pollutants. See also Sulfate Aerosols. (EPA)

Afforestation. The Revised 1996 Intergovernmental Panel on Climate Change (IPCC) Inventory 

Guidelines defines afforestation as the planting of new forests on land which historically been 

covered by forest. (Australia)

Albedo. The ratio of reflected to incident light; albedo can be expressed as either a percentage or a 

fraction of 1. Snow covered areas have a high albedo (up to about 0.9 or 90%) due to their white 

color, while vegetation has a low albedo (generally about 0.1 or 10%) due to the dark color and 

light absorbed for photosynthesis. Clouds have an intermediate albedo and are the most important 

contributor to the Earth's albedo. The Earth's aggregate albedo is approximately 0.3. (EPA)

Aleutian Low. The Aleutian Low is a statistical feature of the winter circulation that dominates 

the winter climate of the North Pacific. Its existence relies on the frequent development of 

eastward moving winter storms along a more-or-less regular path. While the individual winter 

cyclones have a typical lifetime of one to a few days, the Aleutian Low pressure cell is prominent 

from October through March, the months of frequent winter storm development over the North 

Pacific and Aleutian Islands region. Variations in the location and intensity of the Aleutian Low 

contribute to large variations in Pacific Northwest climate and ocean conditions in the Northeast 

Pacific. (ISAB) 

Anthropogenic. Derived from human activities. (EPA)

Atmosphere. The mixture of gases surrounding the Earth. The Earth's atmosphere consists of 

about 79.1% nitrogen (by volume), 20.9% oxygen, 0.036% carbon dioxide and trace amounts of 

other gases. The atmosphere can be divided into a number of layers according to its mixing or 

chemical characteristics, generally determined by its thermal properties (temperature). The layer 

nearest the Earth is the troposphere, which reaches up to an altitude of about 8 km (about 5 miles) 

in the polar regions and up to 17 km (nearly 11 miles) above the equator. The stratosphere, which 

reaches to an altitude of about 50km (31 miles) lies atop the troposphere. The mesosphere which 

extends up to 80-90 km is atop the stratosphere, and finally, the thermosphere, or ionosphere, 

gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of 

gases between layers. (EPA)

Baseline Emissions. The emissions that would occur without policy intervention (in a business-asusual scenario). Baseline estimates are needed to determine the effectiveness of emissions 

reduction programs (often called mitigation strategies). (EPA)

Benthic Foraminifera. Single-celled animals that live near the sediment water interface and have 

calcium carbonate skeletons. The skeletons of benthic foraminifers are often preserved in ocean 

sediments, providing a rich fossil record of the environmental conditions of the water. (NOAA 

Paleo)

Biodiversity. The variety of organisms found within a specified geographic region. (Pew)

Biogeochemical Cycle. The chemical interactions that take place among the atmosphere, 

biosphere, hydrosphere, and geosphere. (EPA)

Biomass Energy. Energy produced by combusting renewable biomass materials such as wood. 

The carbon dioxide emitted from burning biomass will not increase total atmospheric carbon 

dioxide if this consumption is done on a sustainable basis (i.e., if in a given period of time, 

regrowth of biomass takes up as much carbon dioxide as is released from biomass combustion). 

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Biomass energy is often suggested as a replacement for fossil fuel combustion which has large 

greenhouse gas emissions. (EPA)

Biomass. Organic nonfossil material of biological origin. For example, trees and plants are 

biomass. (EPA)

Biosphere. The region on land, in the oceans, and in the atmosphere inhabited by living 

organisms. (EPA)

Black Carbon Aerosols. Particles of carbon in the atmosphere produced by inefficient 

combustion of fossil fuels or biomass. Black carbon aerosols absorb light from the sun, shading 

and cooling the Earth's surface, but contribute to significant warming of the atmosphere (see 

"radiative forcing"). (Pew)

Calcium carbonate (CaCO3). A molecule consisting of calcium, carbon and oxygen that is 

secreted by corals, forming their skeleton; it also secreted by mollusks (clams, oysters, etc.), 

forming their protective shells. (NOAA Paleo)

Carbon Cycle. The global scale exchange of carbon among its reservoirs, namely the atmosphere, 

oceans, vegetation, soils, and geologic deposits and minerals. This involves components in food 

chains, in the atmosphere as carbon dioxide, in the hydrosphere and in the geosphere. (EPA)

Carbon dating. A dating method that uses the disintegration of the 14C atom to determine the age 

of sample containing carbon. 14C is produced in the atmosphere by cosmic ray bombardment, and 

has a half-life of 5570 years, making it useful for dating samples in the range of 0-40,000 years. 

(NOAA Paleo)

Carbon Dioxide (CO2). The greenhouse gas whose concentration is being most affected directly 

by human activities. CO2 also serves as the reference to compare all other greenhouse gases (see 

carbon dioxide equivalents). The major source of CO2 emissions is fossil fuel combustion. CO2 

emissions are also a product of forest clearing, biomass burning, and non-energy production 

processes such as cement production. Atmospheric concentrations of CO2 have been increasing at 

a rate of about 0.5% per year and are now about 30% above preindustrial levels. (EPA)

Carbon Sequestration. The uptake and storage of carbon. Trees and plants, for example, absorb 

carbon dioxide, release the oxygen and store the carbon. Fossil fuels were at one time biomass and 

continue to store the carbon until burned. (EPA)

Carbon Sinks. Carbon reservoirs and conditions that take in and store more carbon (carbon 

sequestration) than they release. Carbon sinks can serve to partially offset greenhouse gas 

emissions. Forests and oceans are common carbon sinks. (EPA)

Carbonaceous Aerosol(s). Aerosol(s) (q.v.) containing carbon. (IPCC)

Columbia Basin Index (CBI). Developed by Petersen and Kitchell (2001), the CBI is an index 

specific to the Columbia River based on unregulated flows (1938-1999) to describe historical 

climate changes within the Basin. (ISAB)

Chlorofluorocarbons and Related Compounds. This family of anthropogenic compounds 

includes chlorofluorcarbons (CFCs), bromofluorcarbons (halons), methyl chloroform, carbon 

tetrachloride, methyl bromide, and hydrochlorofluorcarbons (HCFCs). These compounds have 

been shown to deplete stratospheric ozone, and therefore are typically referred to as ozone 

depleting substances. The most ozone-depleting of these compounds are being phased out under 

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the Montreal Protocol. (EPA)

Chronology. A general term for the age-depth relationship in ice, sediment, or another deposit. 

Ages are usually measured for discrete samples, and the ages of intermediate samples is 

interpolated between samples with measured ages. (NOAA Paleo)

Climate Change (also referred to as “global climate change”). The term “climate change” is 

sometimes used to refer to all forms of climatic inconsistency, but because the Earth's climate is 

never static, the term is more properly used to imply a significant change from one climatic 

condition to another. In some cases, climate change' has been used synonymously with the term, 

“global warming”; scientists however, tend to use the term in the wider sense to also include 

natural changes in climate. See also Enhanced Greenhouse Effect. (EPA)

Climate Feedback. An atmospheric, oceanic, terrestrial, or other process that is activated by the 

direct climate change induced by changes in radiative forcing. Climate feedbacks may increase 

(positive feedback) or diminish (negative feedback) the magnitude of the direct climate change. 

(EPA)

Climate Lag. The delay that occurs in climate change as a result of some factor that changes only 

very slowly. For example, the effects of releasing more carbon dioxide into the atmosphere may 

not be known for some time because a large fraction is dissolved in the ocean and only released to 

the atmosphere many years later. (EPA)

Climate Model. A quantitative way of representing the interactions of the atmosphere, oceans, 

land surface, and ice. Models can range from relatively simple to quite comprehensive. Also see 

General Circulation Model. (EPA)

Climate Modeling. The simulation of the climate using computer-based models. Also see General 

Circulation Model. (EPA)

Climate Sensitivity. The equilibrium response of the climate to a change in radiative forcing; for 

example, a doubling of the carbon dioxide concentration. (EPA)

Climate System (or Earth System). The atmosphere, the oceans, the biosphere, the cryosphere, 

and the geosphere, together make up the climate system. (EPA)

Climate Variability. Refers to changes in patterns, such as precipitation patterns, in the weather 

and climate. (Pew)

Climate. The average weather (usually taken over a 30-year time period) for a particular region 

and time period. Climate is not the same as weather, but rather, it is the average pattern of weather 

for a particular region. Weather describes the short-term state of the atmosphere. Climatic 

elements include precipitation, temperature, humidity, sunshine, wind velocity, phenomena such 

as fog, frost, and hail storms, and other measures of the weather. (EPA)

Climatic feedback mechanisms. A feedback is an enhancement (positive feedback) or a damping 

(negative feedback) of an initial change, in this case in the climate system. For example, when less 

energy reaches the earth, temperature decreases and the area covered by snow increases. The 

albedo of the planet decreases, reflecting more energy towards the atmosphere. Consequently less 

energy is available at the surface, and temperature further decreases. The whole "cycle" from the 

initial cooling to the further cooling is a feedback. It is a positive feedback in this example. 

(NOAA Paleo)

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Cloud Condensation Nuclei. Airborne particles that serve as an initial site for the condensation of

liquid water and which can lead to the formation of cloud droplets. (IPCC)

CO2 Fertilization. Te enhancement of plant growth as a result of elevated atmospheric CO2 

concentrations. (IPCC)

Cryosphere. The part of the Earth’s surface that is perennially frozen or below the freezing point. 

(CA)

Deforestation. Those practices or processes that result in the change of forested lands to nonforest uses. This is often cited as one of the major causes of the enhanced greenhouse effect for 

two reasons: 1) the burning or decomposition of the wood releases carbon dioxide; and 2) trees 

that once removed carbon dioxide from the atmosphere in the process of photosynthesis are no 

longer present and contributing to carbon storage. (EPA)

Dendrochronology. A science based on the exact calendar dating of annual growth rings in wood. 

(NOAA Paleo)

Dendroclimatology. A subfield of dendrochronology, which investigates the climatic effect on 

tree growth, and uses dated tree rings to reconstruct and study past and present climate. (NOAA 

Paleo)

Desertification. The progressive destruction or degradation of existing vegetative cover to form

desert. This can occur due to overgrazing, deforestation, drought, and the burning of extensive 

areas. Once formed, deserts can only support a sparse range of vegetation. Climatic effects 

associated with this phenomenon include increased albedo, reduced atmospheric humidity, and 

greater atmospheric dust (aerosol) loading. (EPA)

Diatom. Single celled phytoplankton that produce silica skeletons. Diatoms are one of the most 

abundant, widely distributed primary producers in the ocean. Different species of diatoms living in 

ocean and lakes have affinities for different environmental conditions such as alkalinity, available 

nutrients, salinity and acidity. (NOAA Paleo)

Diurnal cycle. Mean solar day occurring as Earth rotates from east to west on its axis. (NOAA 

Paleo)

Diurnal Temperature Range. The difference between maximum and minimum temperature over

a period of 24 hours. (IPCC)

Ecosystem. Relationships between and among living organisms and their non-living environment. 

(NOAA Paleo)

El Niño. A climatic phenomenon occurring irregularly, but generally every 3 to 5 years. El Niños 

often first become evident during the Christmas season (El Niño means Christ child) in the surface 

oceans of the eastern tropical Pacific Ocean. The phenomenon involves seasonal changes in the 

direction of the tropical winds over the Pacific and abnormally warm surface ocean temperatures. 

The changes in the tropics are most intense in the Pacific region, these changes can disrupt 

weather patterns throughout the tropics and can extend to higher latitudes, especially in Central 

and North America. The relationship between these events and global weather patterns are 

currently the subject of much research in order to enhance prediction of seasonal to interannual 

fluctuations in the climate. (EPA)

Emissions. The release of a substance (usually a gas when referring to the subject of climate 

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change) into the atmosphere. (EPA)

Enhanced Greenhouse Effect. The natural greenhouse effect has been enhanced by 

anthropogenic emissions of greenhouse gases. Increased concentrations of carbon dioxide, 

methane, and nitrous oxide, CFCs, HFCs, PFCs, SF6, NF3, and other photochemically important 

gases caused by human activities such as fossil fuel consumption and adding waste to landfills, 

trap more infra-red radiation, thereby exerting a warming influence on the climate. See Climate 

Change and Global Warming. (EPA)

ENSO. An acronym for El Niño Southern Oscillation (NOAA Paleo)

Equilibrium Response. The steady state response of the climate system (or a climate model) To 

an imposed radiative forcing. (IPCC)

Equivalent CO2. The concentration of CO2 that would cause the same amount of radiative 

forcing as a given mixture of CO2 and other greenhouse gasses. (IPCC)

Euphotic Zone. That portion of the water column receiving sufficient light to support 

photosynthesis. (ISAB)

Evapotranspiration. The sum of evaporation and plant transpiration. Potential evapotranspiration 

is the amount of water that could be evaporated or transpired at a given temperature and humidity, 

if there was plenty of water available. Actual evapotranspiration can not be any greater than 

precipitation and will usually be less because some water will run off in rivers and flow to the 

oceans. If potential evapotranspiration is greater than actual precipitation, then soils are extremely 

dry during at least a major part of the year. (EPA)

Evolutionary change. Either phenotypic or genetic changes that occur in an organism from

generation to generation through the exchange of genes. (NOAA Paleo)

Feedback Mechanisms. A mechanism that connects one aspect of a system to another. The 

connection can be either amplifying (positive feedback) or moderating (negative feedback). See 

also Climate Feedback. (EPA)

Fluorocarbons. Carbon-fluorine compounds that often contain other elements such as hydrogen, 

chlorine, or bromine. Common fluorocarbons include chlorofluorocarbons and related compounds 

(also know as ozone depleting substances), hydrofluorocarbons (HFCs), and perfluorcarbons 

(PFCs).

Flux. Shifts or flows of carbon over time from one pool to another (e.g. from the atmosphere to 

the forest). (Australia)

Forcing Mechanism. A process that alters the energy balance of the climate system, i.e. changes 

the relative balance between incoming solar radiation and outgoing infrared radiation from Earth. 

Such mechanisms include changes in solar irradiance, volcanic eruptions, and enhancement of the 

natural greenhouse effect by emission of carbon dioxide. See also Radiative Forcing. (EPA)

Fossil air. A sample of air that preserves the composition of the environment at the time it was 

deposited. Bubbles found in ice cores are one example of fossil air that records the atmospheric 

composition of the atmosphere at the time the ice was formed. (NOAA Paleo)

Fossil Fuel Combustion. Burning of coal, oil (including gasoline), or natural gas. This burning, 

usually to generate energy, releases carbon dioxide, as well as combustion by products that can 

include unburned hydrocarbons, methane, and carbon monoxide. Carbon monoxide, methane, and 

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many of the unburned hydrocarbons slowly oxidize into carbon dioxide in the atmosphere. 

Common sources of fossil fuel combustion include cars and electric utilities. (EPA)

Fossil Fuel. A general term for combustible geologic deposits of carbon in reduced (organic) form 

and of biological origin, including coal, oil, natural gas, oil shales, and tar sands. A major concern 

is that they emit carbon dioxide into the atmosphere when burnt, thus significantly contributing to 

the enhanced greenhouse effect. (EPA)

General Circulation Model (GCM). A global, three-dimensional computer model of the climate 

system which can be used to simulate human-induced climate change. GCMs are highly complex 

and they represent the effects of such factors as reflective and absorptive properties of atmospheric 

water vapor, greenhouse gas concentrations, clouds, annual and daily solar heating, ocean 

temperatures and ice boundaries. The most recent GCMs include global representations of the 

atmosphere, oceans, and land surface. (EPA)

Geologic time scale. Relative time scale based on stratigraphic position and correlation, and many 

different types of chronologic evidence. Geologic time is broken down into eons, eras, periods and 

epochs. (NOAA Paleo)

Geosphere. The soils, sediments, and rock layers of Earth’s crust, both continental and beneath 

the ocean floors. (EPA)

Global Warming Potential (GWP). The index used to translate the level of emissions of various 

gases into a common measure in order to compare the relative radiative forcing of different gases 

without directly calculating the changes in atmospheric concentrations. GWPs are calculated as the 

ratio of the radiative forcing that would result from the emissions of one kilogram of a greenhouse 

gas to that from emission of one kilogram of carbon dioxide over a period of time (usually 100 

years). Gases involved in complex atmospheric chemical processes have not been assigned GWPs 

due to complications that arise. Greenhouse gases are expressed in terms of Carbon Dioxide 

Equivalent. The International Panel on Climate Change (IPCC) has presented these GWPs and 

regularly updates them in new assessments. (CA)

Global Warming. An increase in the near surface temperature of the Earth. Global warming has 

occurred in the distant past as the result of natural influences, but the term is most often used to 

refer to the warming predicted to occur as a result of increased emissions of greenhouse gases. 

Scientists generally agree that the Earth's surface has warmed by about 1 degree Fahrenheit in the 

past 140 years. The Intergovernmental Panel on Climate Change (IPCC) recently concluded that 

increased concentrations of greenhouse gases are causing an increase in the Earth's surface 

temperature and that increased concentrations of sulfate aerosols have led to relative cooling in 

some regions, generally over and downwind of heavily industrialized areas. Also see Climate 

Change and Enhanced Greenhouse Effect. (EPA)

Greenhouse Effect. The effect produced as greenhouse gases allow incoming solar radiation to 

pass through the Earth's atmosphere, but prevent most of the outgoing infra-red radiation from the

surface and lower atmosphere from escaping into outer space. This process occurs naturally and 

has kept the Earth's temperature about 59 degrees F warmer than it would otherwise be. Current 

life on Earth could not be sustained without the natural greenhouse effect. (EPA)

Greenhouse Gas (GHG). Any gas that absorbs infra-red radiation in the atmosphere. Greenhouse 

gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), 

halogenated fluorocarbons (HCFCs) , ozone (O3), perfluorinated carbons (PFCs), and 

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hydrofluorocarbons (HFCs). (EPA)

Half-life. The time required for half the nuclei in a sample of a specific isotopic species to 

undergo radioactive decay. (NOAA Paleo)

Heterotrophic. Capable of deriving energy for life processes only from the decomposition of 

organic compounds, and incapable of using inorganic compounds as sole sources of energy or for 

organic synthesis. In the estuary, the term refers to energy provided by bacteria associated with 

decaying organic material. (ISAB)

HGWP (High Global Warming Potential). Some industrially produced gases such as sulfur 

hexafluoride (SF6), perfluorocarbons (PFCs), and hydrofluorocarbons (HFCs) have extremely 

high GWPs. Emissions of these gases have a much greater effect on global warming than an 

equal emission (by weight) of the naturally occurring gases. Most of these gases have GWPs of 

1,300 - 23,900 times that of CO2. These GWPs can be compared to the GWPs of CO2, CH4, and 

N2O which are presently estimated to be 1, 23 and 296, respectively. (Pew)

Hydrocarbons. Substances containing only hydrogen and carbon. Fossil fuels are made up of 

hydrocarbons. Some hydrocarbon compounds are major air pollutants. (EPA)

Hydrofluorocarbons (HFCs). These chemicals (along with perfluorocarbons) were introduced as 

alternatives to ozone depleting substances in serving many industrial, commercial, and personal 

needs. HFCs are emitted as by-products of industrial processes and are also used in manufacturing. 

They do not significantly deplete the stratospheric ozone layer, but they are powerful greenhouse 

gases with global warming potentials ranging from 140 (HFC-152a) to 12,100 (HFC-23). (EPA)

Hydrosphere. The part of the Earth composed of water including clouds, oceans, seas, ice caps, 

glaciers, lakes, rivers, underground water supplies, and atmospheric water vapor. (EPA)

Ice Age. Period during which polar ice extends to much lower latitudes than normal. (NOAA 

Paleo)

Infra-red Radiation. The heat energy that is emitted from all solids, liquids, and gases. In the 

context of the greenhouse issue, the term refers to the heat energy emitted by the Earth's surface 

and its atmosphere. Greenhouse gases strongly absorb this radiation in the Earth's atmosphere, and 

reradiate some back towards the surface, creating the greenhouse effect. (EPA)

Insolation. Amount of solar radiation received on a given body or in a given area. (NOAA Paleo)

Instrumental record. data measured using instruments, such as thermometers and rain gauges. 

(NOAA Paleo)

Integrated Assessment. A method of analysis that combines results and models from the 

physical, biological, economic and social sciences, and the interactions between these components, 

in a consistent framework, to project the consequences of climate change and the policy responses 

to it. (IPCC)

Interglacial. A time interval between glacial periods characterized by lack of glacial ice in midlatitudes, such as modern Holocene climate. (NOAA Paleo)

Intergovernmental Panel on Climate Change. The IPCC was established jointly by the United 

Nations Environment Programme and the World Meteorological Organization in 1988. The 

purpose of the IPCC is to assess information in the scientific and technical literature related to all 

significant components of the issue of climate change. The IPCC draws upon hundreds of the 

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world's expert scientists as authors and thousands as expert reviewers. Leading experts on climate 

change and environmental, social, and economic sciences from some 60 nations have helped the 

IPCC to prepare periodic assessments of the scientific underpinnings for understanding global 

climate change and its consequences. With its capacity for reporting on climate change, its 

consequences, and the viability of adaptation and mitigation measures, the IPCC is also looked to

as the official advisory body to the world's governments on the state of the science of the climate 

change issue. For example, the IPCC organized the development of internationally accepted 

methods for conducting national greenhouse gas emission inventories. (IPCC)

Isotope. A form of a specific element that has the same number of protons, but differs in the 

number of neutrons; forms of the same element that have different mass numbers. (NOAA Paleo)

Lifetime (Atmospheric). The lifetime of a greenhouse gas refers to the approximate amount of 

time it would take for the anthropogenic increment to an atmospheric pollutant concentration to 

return to its natural level (assuming emissions cease) as a result of either being converted to 

another chemical compound or being taken out of the atmosphere via a sink. This time depends on 

the pollutant's sources and sinks as well as its reactivity. The lifetime of a pollutant is often 

considered in conjunction with the mixing of pollutants in the atmosphere; a long lifetime will 

allow the pollutant to mix throughout the atmosphere. Average lifetimes can vary from about a 

week (sulfate aerosols) to more than a century (CFCs, carbon dioxide). (CA)

Littoral cell. Coasts are divided into natural compartments called littoral cells. Each cell contains 

a complete cycle of sedimentation including sources, transport paths, and sinks. The presence of 

sand on any particular beach depends on the transport of sand within the cell. When structures 

such as training walls at the mouth of the Columbia River interfere with sand transport, beaches 

will erode. (ISAB) 

Littoral zone. Area of shore between mean high water and mean low water. (NOAA Paleo)

Marine Biosphere. A collective term for all living marine organisms. (IPCC)

Mauna Loa Record. The record of measurement of atmospheric CO2 concentrations taken at 

Mauna Loa Observatory, Mauna Loa, Hawaii, since March 1958. This record shows the 

continuing increase in average annual atmospheric CO2 concentrations. (Pew)

Meltwater plume. Body of fresh water derived from the melting of glacial ice that floats in large 

bodies of salt water. (NOAA Paleo)

Methane (CH4). A hydrocarbon that is a greenhouse gas with a global warming potential most 

recently estimated at 24.5. Methane is produced through anaerobic (without oxygen) 

decomposition of waste in landfills, animal digestion, decomposition of animal wastes, production

and distribution of natural gas and oil, coal production , and incomplete fossil fuel combustion. 

The atmospheric concentration of methane has been shown to be increasing at a rate of about 0.6% 

per year and the concentration of about 1.7 parts per million by volume (ppmv) is more than twice 

its preindustrial value. However, the rate of increase of methane in the atmosphere may be 

stabilizing. (EPA)

Natural climate record. A record of climatic events found by examining the natural environment 

(tree rings, coral growth bands, layers of ice in glaciers). (NOAA Paleo)

Negative Feedback. A process that results in a reduction in the response of a system to an 

external influence. For example, increased plant productivity in response to global warming 

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would be a negative feedback on warming, because the additional growth would act as a sink for 

CO2, reducing the atmospheric CO2 concentration. (Pew)

Nitrogen Oxides (NOx). Gases consisting of one molecule of nitrogen and varying numbers of 

oxygen molecules. Nitrogen oxides are produced in the emissions of vehicle exhausts and from

power stations. In the atmosphere, nitrogen oxides can contribute to formation of photochemical 

ozone (smog), can impair visibility, and have health consequences; they are thus considered 

pollutants. (EPA)

Nitrous Oxide (N2O). A powerful greenhouse gas with a global warming potential of 320. Major 

sources of nitrous oxide include soil cultivation practices, especially the use of commercial and 

organic fertilizers, fossil fuel combustion, nitric acid production, and biomass burning. (EPA)

Ocean Acidification. Increasing concentrations of CO2 dissolved in the oceans lowers the pH and 

decreases the availability of carbonate ions and lowers the saturation state of major shell-forming 

carbonates in marine animals. (ISAB)

Osmoregulatory. Refers to the process of osmoregulation, the physiological process which 

maintains a balance of water and ions (particulary sodium and potassium) in a fishes blood.

Oxygen isotope ratio (d18O). An expression for the ratio of the 18O to 16O atoms in a sample 

relative to a standard, defined as:D18O= (18O/16Osample. 18O/16Ostandard)/ 18O/16Ostandard 

(NOAA Paleo)

Oxygen isotopes. Oxygen atoms having the same atomic number (protons) but different mass 

numbers (and different numbers of neutrons). The two stable isotopes of oxygen are 16O and 18O. 

(NOAA Paleo)

Ozone (O3). Ozone consists of three atoms of oxygen bonded together in contrast to normal 

atmospheric oxygen which consists of two atoms of oxygen. Ozone is an important greenhouse 

gas found in both the stratosphere (about 90% of the total atmospheric loading) and the 

troposphere (about 10%). Ozone has other effects beyond acting as a greenhouse gas. In the 

stratosphere, ozone provides a protective layer shielding the Earth from ultraviolet radiation and 

subsequent harmful health effect on humans and the environment. In the troposphere, oxygen 

molecules in ozone combine with other chemicals and gases (oxidization) to cause smog. (EPA)

Pacific Decadal Oscillation (PDO). A pattern of Pacific climate variability that shifts phases on a 

multi-decadal time scale, usually about 20 to 30 years. The PDO is detected as warm or cool 

surface waters in the Pacific Ocean, north of 20° N. During a "warm", or "positive", phase, the 

west Pacific becomes cool and part of the eastern ocean warms; during a "cool" or "negative" 

phase, the opposite pattern occurs. (Wikipedia)

Pacific Northwest Index (PNI). Developed by Ebbesmeyer and Strickland (1995), PDI is a 

terrestrial climate index useful for studying climate effects on salmon productivity trends. It is a 

composite index that characterizes Pacific Northwest climate patterns in both coastal waters and 

freshwater habitats. In addition, it is a century-long record. A composite climate index is an 

effective measurement because many environmental parameters in the Northwest are statistically 

related to one another; consequently, they may be combined to furnish a broad-scale 

understanding of the state of the Pacific Northwest environment. The PNI uses three parameters: 

1) air temperature at Olga in the San Juan Islands, averaged annually from daily data; 2) total 

precipitation at Cedar Lake in the Cascade Mountains; and 3) snowpack depth at Paradise on 

Mount Rainier on March 15 of each year. For each parameter, annual values are normalized by 

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subtracting the annual value from the average of all years and dividing by the standard deviation. 

The sign of the normalized temperature is reversed because low temperature corresponds with 

high precipitation and snow. Finally, the three variables are averaged yearly giving a relative 

indicator of the variations in climate. Years with positive values of the PNI are warmer and drier 

than average and those with negative values are cooler and wetter than average. (ISAB)

Paleoclimate. Past or ancient climates. (NOAA Paleo)

Parameterize (Parameterization). In climate modeling, this term refers to the technique of 

representing processes that cannot be explicitly resolved at the resolution of the model (sub-grid 

scale processes) by the relationships between the area-averaged effect of such sub-gird scale 

processes and the larger scale flow. (IPCC)

Particulates. Tiny pieces of solid or liquid matter, such as soot, dust, fumes, or mist. (EPA)

Perfluorocarbons (PFCs). A group of human-made chemicals composed of carbon and fluorine 

only: CF4 and C2F6. These chemicals, specifically CF4 and C2F6, (along with 

hydrofluorocarbons) were introduced as alternatives to the ozone depleting substances. In addition, 

they are emitted as by-products of industrial processes and are also used in manufacturing. PFCs 

do not harm the stratospheric ozone layer, but they are powerful greenhouse gases: CF4 has a 

global warming potential (GWP) of 6,300 and C2F6 has a GWP of 12,500. (EPA)

Photosynthesis. The process by which green plants use light to synthesize organic compounds 

from carbon dioxide and water. In the process oxygen and water are released. Increased levels of 

carbon dioxide can increase net photosynthesis in some plants. Plants create a very important 

reservoir for carbon dioxide. (EPA)

Plankton. Small or microscopic organisms, including algae and protozoan that float or drift in 

great numbers in fresh or salt water, especially at or near the surface, and serve as food for fish and 

other larger organisms. (NOAA Paleo)

Planktonic Foraminifera. Marine zooplankton that passively float or weakly swim, and have 

calcium carbonate skeletons that are present in large numbers on the surface of the ocean. The 

skeletons of planktonic foraminifers are preserved in large numbers in deep-sea sediments, 

providing a rich fossil record of the environmental conditions of the upper ocean. The size of the 

shells is typically from 50 to 100 microns. (NOAA Paleo)

Pollen. Pollen grains that are made up of microspores containing a mature or immature male 

gametophyte. (NOAA Paleo)

Positive Feedback. A process that results in an amplification of the response of a system to an 

external influence. For example, increased atmospheric water vapor in response to global 

warming would be a positive feedback on warming, because water vapor is a GHG. (Pew)

Quaternary period. The second period of the Cenozoic era containing the Pleistocene epoch and 

the Holocene epoch and dating from 1.8 million years to the present. (NOAA Paleo)

Radiation. Energy emitted in the form of electromagnetic waves. Radiation has differing 

characteristics depending upon the wavelength. Because the radiation from the Sun is relatively 

energetic, it has a short wavelength (ultra-violet, visible, and near infra-red) while energy reradiated from the Earth's surface and the atmosphere has a longer wavelength (infra-red radiation)

because the Earth is cooler than the Sun. (EPA)

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Radiative Damping. An imposed positive radiative forcing (q.v.) on the Earth-atmosphere system 

(e.g., through the addition of greenhouse gases) that represents an energy surplus. The temperature 

of the surface and lower atmosphere will then increase and in turn increase the amount of infrared 

radiation being emitted into space, thus establishing a new energy balance. The amount that

emissions of infrared radiation to space increases for a given increase in temperature is known as 

the radiative damping.(IPCC)

Radiative Forcing. A change in the balance between incoming solar radiation and outgoing infrared radiation. Without any radiative forcing, solar radiation coming to the Earth would continue to 

be approximately equal to the infra-red radiation emitted from the Earth. The addition of

greenhouse gases traps and increased fraction of the infra-red radiation, reradiating it back toward 

the surface and creating a warming influence (i.e., positive radiative forcing because incoming 

solar radiation will exceed outgoing infra-red radiation). (EPA)

Radiocarbon age. The age of plant or animal remains determined by measuring the remaining 

activity of the 14C atoms in the sample: A=A0e-ltwhere A is the measured activity, A0 is the 

initial activity, l is the decay constant, and t is the sample age. (NOAA Paleo)

Relative dating. Dating methods that determine time with respect to stratigraphic position, for 

example deeper layers being older, or with respect to some changing quantity or property, such as 

magnetic polarity. (NOAA Paleo)

Residence Time. The average time spent in a reservoir by an individual atom or molecule. Also, 

the age of a molecule when it leaves the reservoir. With respect to greenhouse gases, residence 

time usually refers to how long a particular molecule remains in the atmosphere. (EPA) Reservoir. 

A component or components of the climate system where a greenhouse gas or precursor of 

greenhouse gas are stored. (Australia) 

Respiration. The process by which animals use up stored foods (by combustion with oxygen) to 

produce energy. (EPA)

Salt Wedge. The layer of salt water that penetrates upriver under the freshwater layer to the 

head of the estuary. Because the estuary is deeper near the ocean, and shallows upstream, the 

layer is typically wedge-shaped

Sea surface temperatures. Temperature of the ocean's surface used in collaboration with other 

data to predict an El Niño occurrence. (NOAA Paleo)

Sink. A reservoir that uptakes a pollutant from another part of its cycle. Soil and trees tend to 

act as natural sinks for carbon. (EPA)

Soil moisture. Water stored in or at the continental surface and available for evaporation. In 

IPCC 1990 a single store (or bucket) was commonly used in climate modes. Today's models 

which incorporate canopy and soil process view soil moisture as the amount held in excess of 

plant "wilting point." (IPCC)

Solar Radiation. Energy from the Sun. Also referred to as short-wave radiation. Of importance 

to the climate system, solar radiation includes ultra-violet radiation, visible radiation, and infrared radiation. (EPA)

Solar variability. Changes in the sun's radiation due to the sun's internal dynamics. (NOAA 

Paleo)

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Southern Oscillation (ENSO). Shifting of pressure zones in the Pacific during an El Niño 

event. (NOAA Paleo)

Stratification. Increase in water density with depth caused by changes in salinity and/or 

temperature. 

Stratosphere. The part of the atmosphere directly above the troposphere. See Atmosphere.

Sulfate Aerosol. Particulate matter that consists of compounds of sulfur formed by the 

interaction of sulfur dioxide and sulfur trioxide with other compounds in the atmosphere. Sulfate 

aerosols are injected into the atmosphere from the combustion of fossil fuels and the eruption of 

volcanoes like Mt. Pinatubo. Recent theory suggests that sulfate aerosols may lower the earth's

temperature by reflecting away solar radiation (negative radiative forcing). Global Climate 

Models which incorporate the effects of sulfate aerosols more accurately predict global 

temperature variations. (EPA)

Sulfur Dioxide (SO2). A compound composed of one sulfur and two oxygen molecules. Sulfur 

dioxide emitted into the atmosphere through natural and anthropogenic processes is changed in a 

complex series of chemical reactions in the atmosphere to sulfate aerosols. These aerosols result 

in negative radiative forcing (i.e., tending to cool the Earth's surface). (EPA)

Sulfur Hexafluoride (SF6). A very powerful greenhouse gas used primarily in electrical 

transmission and distribution systems. SF6 has a global warming potential of 24,900. (EPA)

Thermal expansion. Expansion of a substance as a result of the addition of heat. In the context 

of climate change, thermal expansion of the world's oceans in response to global warming is 

considered the predominant driver of current and future sea-level rise. (Pew)

Thermocline. The region of the world's ocean, typically at a depth of lkm, where temperature 

decreases rapidly with depth and which marks the boundary between the surface and Deep 

Ocean. OPCC).

Thermohaline Circulation. Large-scale density-driven circulation I the oceans, driven by 

differences in temperature and salinity. (IPCC)

Trace Gas. Any one of the less common gases found in the Earth's atmosphere. Nitrogen, 

oxygen, and argon make up more than 99 percent of the Earth's atmosphere. Other gases, such 

as carbon dioxide, water vapor, methane, oxides of nitrogen, ozone, and ammonia, are 

considered trace gases. Although relatively unimportant in terms of their absolute volume, they 

have significant effects on the Earth's weather and climate. (EPA)

Tradewinds. A system of low-level winds occurring in the tropics; the tradewinds blow from

the northeast to the equator in the Northern Hemisphere and from the southeast to the equator in 

the Southern Hemisphere. (NOAA Paleo)

Transient Climate Response. The tirne-dependent response of the climate system or model to a 

tirne-varying change of forcing. (IPCC)

Troposphere. The lowest layer of the atmosphere. The troposphere extends from the Earth's 

surface up to about 10-15 km. See also Atmosphere.

Tropospheric Ozone (O3). Ozone that is located in the troposphere and plays a significant role 

in the greenhouse gas effect and urban smog. See Ozone for more details. (EPA)

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Turn-over time. The ratio between the mass of a reservoir (e.g. mass of N20 in the atmosphere) 

and the rate of removal from the reservoir (e.g. for N20, the rate of destruction by sunlight in the 

stratosphere (q.v.). (IPCC)

Uncertainty. Uncertainty is a prominent feature of the benefits and costs of climate change. 

Decision makers need to compare risk of premature or unnecessary actions with risk of failing to 

take actions that subsequently prove to be warranted. This is complicated by potential 

irreversibilities in climate impacts and long term investments. (Pew)

Upwelling. Rising of cold, nutrient-rich water towards the surface. (NOAA Paleo)

Urban Heat Island (UHI). Refers to the tendency for urban areas to have warmer air 

temperatures than the surrounding rural landscape, due to the low albedo of streets, sidewalks, 

parking lots, and buildings. These surfaces absorb solar radiation during the day and release it at 

night, resulting in higher night temperatures. (Pew)

Volatile Organic Compounds (VOC). Any one of several organic compounds which are 

released to the atmosphere by plants or through vaporization of oil products, and which are 

chemically reactive and are involved in the chemistry of tropospheric ozone production. 

Methane, while strictly falling within the definition of a VOC, is usually considered separately. 

(IPCC)

Water Vapor. The most abundant greenhouse gas, it is the water present in the atmosphere in 

gaseous form. Water vapor is an important part of the natural greenhouse effect. While humans 

are not significantly increasing its concentration, it contributes to the enhanced greenhouse 

effect because the warming influence of greenhouse gases leads to a positive water vapor 

feedback. In addition to its role as a natural greenhouse gas, water vapor plays an important role 

in regulating the temperature of the planet because clouds form when excess water vapor in the 

atmosphere condenses to form ice and water droplets and precipitation. (EPA)

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