Climate Change

Background

CMP Direct Threats 11.1, 11.2, 11.3, 11.4, 11.5

The Earth’s climate has changed throughout history due to a variety of factors, with corresponding changes to natural systems. However, in recent centuries, humans have significantly altered the composition of the atmosphere by burning fossil fuels for energy and clearing forests and other natural habitats, contributing to accelerated changes in climate conditions.

There is clear and growing evidence that our continued use of fossil fuels and conversion of natural lands for other uses is increasing the concentration of carbon dioxide and other greenhouse gases in the atmosphere and contributing to the significant rise in global temperatures that has been observed since about 1950. This increase in greenhouse gases in the atmosphere is primarily because humans have burned and continue to burn fossil fuels for transportation and energy generation. Industrial processes, deforestation, and agricultural practices also increase greenhouse gases in the atmosphere. According to the Intergovernmental Panel on Climate Change (IPCC), the United Nations body for assessing the science related to climate change, the evidence is unequivocal that the earth is warming at an accelerated rate due primarily to human activities, and that there have been and will be significant changes to the global climate this century.

Rising temperatures and other direct and indirect climate effects of increased greenhouse gases make up the body of interrelated trends referred to as climate change or global warming. These substantial shifts in global climate variables are observable in today’s climate, and they are expected to increase and accelerate through at least the next century or until well after human-caused emissions of greenhouse gases are returned to much lower levels. As a result, climate change will cause irreversible alterations to both human communities and ecological systems globally.

Climate change will bring significant impacts not only to fish, wildlife, and their habitats, but also to working landscapes and rural, urban, and tribal communities. These impacts include threats to water resources, rangeland degradation due to invasive species and increased drought, increases in wildfire, pest outbreaks in forests, alteration of oceanographic regimes, and changes to aquatic, terrestrial, and marine communities. Many of the available approaches to help fish and wildlife adapt to climate change can also help human communities cope with these changes.

Changes to the global climate system

Atmospheric concentrations of planet-warming gases are increasing, including the three main greenhouse gases produced by human activities: carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). Since 1850, carbon dioxide concentrations have increased by more than 47%, nitrous oxide by 23%, and methane by more than 156%. The concentration of CO₂ in the atmosphere as of 2024 (about 425.5 parts per million) is the highest known level in at least the past 2 million years, and probably much longer, and it continues to rise rapidly. In the absence of strong mitigation measures, 21st century emissions are projected to approximately double the current atmospheric concentrations of CO₂ by 2100. Substantial efforts to reduce or stabilize emissions could help limit the concentration to 600 ppm CO₂ or less.

The most direct effect of the rise in carbon dioxide and other greenhouse gas concentrations is a warming of the air and water. Global average temperatures over the past decade were about 2°F warmer than the pre-industrial period. Each of the years from 2014-2022 was ranked globally as one of the nine warmest on record.

In addition to warming temperatures, major impacts from increases in greenhouse gases include ocean acidification and sea level rise. The ocean is a natural carbon sink and has absorbed 20-30 percent of atmospheric CO₂ increases. Dissolved CO₂ then forms carbonic acid and subsequently dissociates into bicarbonate and hydrogen ions, which increase sea water acidity. The surface of the open ocean is the most acidic since at least 26,000 years ago, and current rates of change in acidity are unprecedented since at least that time. Additionally, global average sea levels over the past decade were between 7 and 9.5 inches higher than in the preindustrial period, with more than half of this rise occurring since 1980. Relative to 2020, an additional 11 inches of sea level rise is expected along the U.S. coastline by 2050, with a likely range of 9–13 inches. Sea level rise will vary across U.S. coasts, with greater impacts expected to the East and Gulf Coasts than the West Coast.

Climate Change in the Pacific Northwest

The Pacific Northwest, including Oregon, contains diverse ecosystems and landscapes encompassing nearshore kelp forests, estuaries, rocky shorelines, wet temperate forests, snow-packed volcanic mountains, dry coniferous forests, and large expanses of dry sagebrush steppe. In addition to supporting thousands of native species, these ecosystems also provide food, housing, recreation, and income that support the health and well-being of almost 14 million residents. Communities in the region have been employing various climate adaptation strategies, but additional efforts to mitigate climate change will be essential for the long-term effectiveness of adaptation actions. Climate change has already impacted ecosystems across the Pacific Northwest, and these effects will continue to drive transformational change across the region.

Increases in air and water temperatures

As of 2025, average annual air temperatures in Oregon have warmed by 2.5°F since 1900. Over the 21st century, annual average temperatures are projected to increase by an average of 4.7°F under a low emissions scenario (SSP1-2.6) and by an average of 10.0°F under a very high emissions scenario (SSP5-8.5).

Seasonal coastal upwelling causes nearshore sea surface temperatures off the Oregon and Washington coasts to be cooler than offshore surface temperatures. Nonetheless, annual average coastal sea surface temperatures in the Northwest have warmed approximately 1.2°F since 1900, and the northern California Current, which extends northward from northern California to the northern tip of Vancouver Island in Canada, is projected to warm by an additional 4.6°–7.3°F by the end of the century under a very high emissions scenario (RCP 8.5).

Warming has also been observed in freshwater ecosystems, with warming trends in stream temperatures throughout the Pacific Northwest, including Oregon. Average annual water temperatures in lakes and streams are projected to continue to rise. Increases in stream temperatures are more pronounced during summer and early fall months when stream flows are lowest.

Changes in water and snow availability, streamflow, and drought

As air temperature increases, the capacity of the atmosphere to hold water vapor increases and the rate of evaporation increases. These changes impact the timing, form, and quantity of precipitation, which alters hydrology in lakes, rivers, streams, aquifers, wetlands, and upland systems. In general, a greater share of precipitation falls in fewer events, which simultaneously increases the frequency and severity of both floods and droughts.

Between 1915 and 2024, average snowpack declined by 21% in the western U.S., representing a loss of water storage capacity that is twice as large as that of Crater Lake. Mountain snowpack has been declining as winter temperatures increase, particularly in areas with warm maritime climates, and a greater proportion of winter precipitation is falling as rain rather than snow. Snow-line elevation is also increasing as snow-dominated watersheds transition to mixed rain-and-snow watersheds and mixed rain-and-snow watersheds transition to rain-dominated watersheds. More frequent, longer, and more severe regional drought conditions will increase as summer precipitation continues to decrease, exacerbating wildfire risk and reducing water availability.

Interannual variability in precipitation is projected to persist, and summer streamflow is expected to decrease further due to reduced snow storage, increased evapotranspiration, and longer lags between summer rain events. It is projected that some permanent streams will transition to ephemeral streams, affecting aquatic species and ecosystems as well as regional water supplies.

Changes in wildfire frequency and intensity

In the Pacific Northwest, wildfires are increasing in size, frequency, and intensity. Area burned has increased steadily and dramatically across the western U.S. since the 1980s. Warming temperatures lead to an increase in evaporative demand. When evaporative demand is high, the land loses more water to the atmosphere through evaporation and transpiration, leading to drier vegetation and increased fire risk. Concurrent heat and drought have become more common, resulting in higher fuel loads as amounts of stressed or dead vegetation in many landscapes continue to increase. Additionally, many previously burned forests are reburning. Reburns can produce abrupt shifts in forest structure and composition, including transition to non-forest vegetation when they occur over shortened intervals. Indeed, in low-elevation and drier areas, some forests are converting to shrubland after wildfires. These ecosystem transitions are becoming more common across the Northwest.

The average annual area burned in Oregon’s forests is expected to increase by at least 50%, and fire seasons are expected to become more extreme than any in recorded history. From 1979 through 2019, the duration of the fire weather season in forests in Washington, Oregon, Idaho, and California increased by 43%, and the annual number of days when fire danger was extreme increased by 166%. In fire-prone areas of the western United States, including the mountains of Oregon, the annual number of extreme, single-day wildfire expansions is projected to increase by 100% if annual average temperatures increase by 3.6°F above the 2002–2020 average. The number of wildfires in national forests in the Pacific Northwest is projected to increase by 20–140% by 2070–2099 under a very high emissions scenario (RCP 8.5), varying based on forest characteristics and regional weather patterns. Furthermore, the total area at risk of high fire danger in summer in the Northwest is projected to increase by 345% under RCP 8.5.

Non-native annual grasses, including highly flammable cheatgrass, ventenata, and medusahead have rapidly expanded in perennial grass systems, arid woodlands, and sagebrush ecosystems. The establishment of these invasive species is associated with relatively high precipitation during autumn and spring and with ground disturbance from wildfire, livestock grazing, recreation, and other types of land use. These species grow in spaces between sagebrush or other shrubs and perennial grasses that were historically bare of vegetation, which significantly increases fuel loads, fire spread, and fire intensity.

Additional stressors to habitat, including recreation, development, transportation, and energy transmission, will also continue to affect wildfire frequency in both shrubland and forested systems. The length of the wildfire season and the potential for human-caused ignitions in all Pacific Northwest ecosystems are expected to increase as drought frequency, duration, and intensity increase.

Wildfire smoke also poses a major threat to human and wildlife health. Due to increasing wildfire activity in late summer and autumn in the Pacific Northwest, air pollution from wildfire smoke is projected to double under a moderate emissions scenario (SSP2-4.5) or triple under a high emissions scenario (SSP5-8.5) by the end of the century.

Extreme events

In addition to changes in long-term averages in temperature and precipitation, climate change is increasing the frequency and severity of extreme weather events, including heatwaves, drought, and severe storms. Along with the increased water-holding capacity of warmer air, higher air temperatures indicate an increase in the average energy of air molecules; this energy can manifest as movement, resulting in higher wind speeds and more powerful weather.

The frequency and intensity of extreme precipitation events are projected to increase across the region, particularly because of an expected rise in the number of strong atmospheric river events, producing significant amounts of rain or snow for longer durations. An atmospheric river is a flowing column of condensed water vapor in the atmosphere responsible for generating substantial quantities of rain and snow, especially in the Western United States, which can lead to flooding, landslides, and other damage. Impacts of atmospheric rivers are also projected to reach farther inland and last longer as the climate continues to warm. Understanding how climate change alters the frequency, intensity, duration, and reach of atmospheric river events will be critical for estimating how the region’s water supply will change.

The frequency and intensity of heatwaves are also expected to increase in both terrestrial and marine systems and will have broad-ranging impacts. Terrestrial heatwaves refer to a period of abnormally hot weather lasting two or more days. In terrestrial systems in the Pacific Northwest, an “extremely warm day” is a day on which the maximum temperature is 90°F (32°C) or above. The number of “extremely warm days” has increased significantly across Oregon since 1951, and the magnitude and duration of heatwaves are expected to continue to increase. Marine heatwaves refer to a period during which water temperature is abnormally warm for the time of the year relative to historical temperatures, with that extreme warmth persisting for days to months. The phenomenon can manifest in any place in the ocean and at scales of up to hundreds of square miles. Widespread and persistent high sea surface temperatures have been shown to temporarily increase onshore temperatures by up to 11°F above regional averages, resulting in short-term shifts in species distributions and mortality of many seabirds and marine mammals. These heatwaves also increase the toxicity of harmful algal blooms, posing significant risks to fish and wildlife, as well as people who consume crabs and other shellfish.

Sea level rise

Under all future climate scenarios, sea level is projected to increase across the Pacific Northwest, although net sea level changes will vary by location. Long-term climate cycles, such as El Niño, also influence sea level and can raise sea levels up to an additional 7.9 inches for periods of several months. Wave height and tidal surge are also projected to increase. Relative to the 1991–2009 average, sea levels in the Pacific Northwest are projected to rise 0.6 to 1.0 feet by 2050 for intermediate- and high-emissions scenarios, respectively, placing physical structures and communities at risk. This expected rise will cause total water levels to increase and change coastal flood regimes, with major and moderate high-tide flood events occurring as frequently as moderate and minor high-tide flood events occur today.

Higher sea levels also contribute to erosion and tidal flooding, increase the likelihood of damaging storm surges during storm events, and increase the salinity of surface water and groundwater systems. Furthermore, mechanisms to protect infrastructure from rising seas, like shoreline armoring, can have additional negative effects on coastal and marine ecosystems. As sea levels rise, coastal species and habitats will need to migrate inland, which may not be possible for species in locations adjacent to developed communities or transportation infrastructure.

Ocean acidification

Ocean acidification is the process by which the pH measurement of ocean water becomes more acidic due to the absorption of carbon dioxide. Human-caused carbon emissions have already influenced ocean acidification of waters off the coast of Oregon. Since the beginning of the Industrial Revolution, roughly one-third to one-half of the CO₂ released into Earth’s atmosphere by human activities has been absorbed by the oceans. During that time, scientists have estimated that the average pH of seawater declined from 8.19 to 8.05, which corresponds to a 30% increase in acidity. Concentrations of atmospheric CO₂ are expected to continue to rise, leading to more CO₂ absorbed by the oceans and further increases in ocean acidity.

Ocean acidification has significant negative effects on marine organisms. As ocean acidity increases, it becomes more difficult for species such as oysters, clams, mussels, crabs, sea urchins, corals, and certain types of plankton to build and maintain shells. Larger animals, such as squid and fishes, may experience negative impacts from increasing acidity as acid concentrations rise in their body fluids. This condition, called acidosis, may cause problems with respiration as well as with growth and reproduction. Further, some algal species benefit from more acidic conditions, with increased growth and toxin production as ocean acidification increases, contributing to more frequent and severe harmful algal blooms. Increases in ocean acidity commonly co-occur with other stressors like warmer temperatures or reduced oxygen, leading to cascading effects on food webs and human communities.

Ocean hypoxia

Hypoxia, or the condition of low levels of dissolved oxygen within the water column, is a naturally occurring phenomenon that has increased in frequency over the last century. Hypoxia can be caused by a variety of factors but changing climate conditions have increased the frequency of occurrence of hypoxic conditions in the ocean. Anoxic events (zero oxygen) have also started to occur. Hypoxic conditions are harmful to marine life, as low oxygen levels directly affect the fish and invertebrates that live in these areas, which require dissolved oxygen in the water to breathe. The effects of ocean hypoxia on fish and shellfish are varied and differ by species. As dissolved oxygen content decreases, mobile organisms will avoid or move out of the area, shifting species distributions. Species that cannot move to more oxygenated waters may die during hypoxic events.

Warming sea surface temperatures also increase stratification of the water column, which affects oxygen availability. Stratification is a condition in which surface and subsurface waters are separated by differences in temperature or salinity. This layering prevents oxygen-rich surface waters from replenishing the oxygen in the bottom waters, increasing hypoxic conditions in subsurface waters. Warming sea surface temperatures also reduce oxygen saturation in the water column and increase species’ metabolic rates, which can further diminish oxygen availability. Climate-induced changes in wind patterns and intensity affect coastal currents, altering patterns of upwelling which can bring deoxygenated water to the sea surface. Shifts in upwelling patterns may also cause mismatches in the timing of important life cycle events for marine species. Increased precipitation contributes to more water, sediment, and nutrient runoff into coastal zones, where they are likely to increase eutrophication, leading to further stratification and increases in hypoxia.

Compounding stressors

Climate change interacts with other stressors, often amplifying effects and complicating management responses. Species, habitats, and ecosystem processes are threatened by multiple longstanding and ongoing stressors, including habitat loss, fragmentation, degradation, overharvest and destructive harvest, pollution, invasive species, and disease agents. Alone or in combination, these compounding stressors can reduce a species’ potential to adapt to changing conditions, making it more difficult for species to persist. Climate change acts as a “threat multiplier” by magnifying the effects of existing stressors on species and ecosystems. The severity of these compounding stressors and their interactions with climate change will drive the overall vulnerability of most ecosystems. Resource managers must therefore confront climate impacts in the context of the other natural and human-induced changes that are already significantly affecting species, habitats, and ecosystems. Successful species and habitat conservation will require an increased understanding of these complex interactions of climate change and compounding stressors.

As climate change intensifies existing threats to species and ecosystems, resource managers must confront many uncertainties. No single strategy will ensure that ecological communities can adapt and survive. However, reducing the impact of compounding stressors is often one of the most effective strategies to increase the resilience of species and ecosystems. For example, reducing habitat fragmentation and increasing connectivity of intact habitats makes it easier for wildlife to move and track shifting resources as climate conditions change.

IMPACTS OF CLIMATE CHANGE ON FISH AND WILDLIFE

Climate change is causing innumerable direct and indirect impacts on species and their habitats. Consequently, species must respond by either shifting in space (seeking more suitable conditions elsewhere) or persisting in place (adapting to tolerate changing conditions). Populations that fail to move or adapt risk extirpation or extinction. A growing body of scientific literature has documented species responses to climate change, including altered abundances, distributions, health, morphology and growth, timing of life cycle processes, and behavior. These species-level changes are having cascading impacts on the overall structure and function of ecosystems.

Each of these impacts has the potential to significantly alter fish and wildlife populations and their habitats. Some climate stressors will directly jeopardize the success of species that are dependent on specific habitat components, while other impacts may be indirect. For example, ocean acidification may lead to direct loss of organisms that build shells or other calcified structures, such as oysters, clams, sea urchins, and corals. Loss of these species may then destabilize food webs, as well as economies that depend on marine harvests.

Although some species and ecosystems are undoubtedly being harmed by climate change, others may prove surprisingly durable. Species that can move to more climatically suitable locations will do so by migrating or shifting their ranges. Range shifts have already been noted for many species, including poleward and elevational movements of many insects, birds, fish, and vegetation communities. However, the rapid rate of change and the fragmentation of habitat will make it more difficult for many species to move. Additionally, some species may not be able to shift because they have limited mobility, movement is blocked by geographic or anthropogenic barriers, or because suitable habitat is not available elsewhere. These species may need to alter their behavior or the timing of life cycle processes, like reproduction, to respond to changes in habitat conditions such as food availability, habitat loss, and novel species interactions.

While some generalist species may continue to thrive in a changing climate, the rapid rate of climate change, compared to past shifts in climate, means that species adaptation may have to occur very quickly for species to be successful. Evidence indicates that most species will not have the capacity to keep pace with the rate and magnitude of climate change through evolutionary adaptation alone, particularly since adaptive capacity is often constrained by factors such as barriers to movement, disease, or invasive competitors. Species that are negatively affected by climate change will likely include species with limited movement and dispersal and those with very specific habitat and/or diet requirements, including species that depend on high elevation, cold water, or wetland habitats. Low reproductive rates, long generation times, low genetic diversity, and complex life histories are additional traits that tend to increase vulnerability and have already led to threatened or endangered status for some species. Migratory species are also likely to be strongly affected by climate change, as these animals require multiple habitats along movement pathways (increasing the chances of reliance on an impacted resource) and often rely on environmental cues to trigger migration (which may become misaligned with resource availability).

Maintaining and recovering species that are already imperiled are expected to become increasingly difficult. If species are unable to adapt to the rapidly changing environment caused by climate change, they could become locally extirpated. Native species that are adapted and restricted to certain conditions may face extinction. For example, the ranges of small mammals in mountaintop habitats are contracting along with the snow caps, and some of the state’s native frog populations are declining due to the seasonal increases in temperature and associated drying of wetlands.

Resources for supporting climate adaptation:

GOALS AND ACTIONS

Goal 1. Use the best available information, technology, and management tools to determine the vulnerability of species and habitats to climate change at a landscape scale.

Climate change is a global issue, and the responses of fish, wildlife, and habitats to changing climate conditions will play out across political boundaries and will require a new, more integrated approach to management. As a result, evaluation and planning needs to be done at a landscape scale that can be applied to range-wide conservation planning for fish, wildlife, and their habitats. Landscape-scale conservation recognizes the importance of large, interconnected land- and seascapes in maintaining biodiversity, and considers the needs of wildlife, ecological processes, and human communities holistically to achieve conservation goals. Many species may shift ranges so that they are no longer found within the borders of a particular state or protected area. Therefore, efforts to evaluate and mitigate vulnerability should focus on how a species or their habitat will respond across its range, accounting for the full array of life cycle functions.

Action 1.1. Work with partners to increase information on climate change vulnerability of habitats and species.

Building a body of information on climate change impacts and the vulnerability of Species of Greatest Conservation Need and Key Habitats is an important first step to guiding management and policy decisions on climate change. Management priorities should drive the scientific information that is gathered to inform decision making. Collaboration with research institutions, such as the Oregon Climate Change Research Institute, Northwest Climate Adaptation Science Center, NOAA Northwest Fisheries Science Center, and University of Washington’s Climate Impacts Group, nonprofits, tribes, and government agencies can help increase understanding of climate change vulnerability without overtaxing limited budgets. Many of these institutions are leading ongoing efforts to identify the most vulnerable species and habitats and develop assessment models for these species. Meaningful, multi-sector stakeholder engagement will be essential to advance our understanding of these complex issues.

Action 1.2. Support long-term research on climate trends and ecosystem responses.

To provide the necessary information about the impacts of climate on species and habitats, research and monitoring efforts will need to be conducted over longer periods of time. Funding and institutional support will be needed to encourage long-term research. Existing long-term ecological research programs, such as Oregon State University’s (OSU) H.J. Andrews Experimental Forest, the U.S. Forest Service’s (USFS) experimental forests, the Northwest Fisheries Science Center’s long-term ocean environment monitoring, and the ODFW’s Lifecycle Monitoring Sites can be a cornerstone of such efforts. The results from these research efforts should be used to inform and adapt management strategies, monitoring protocols, and objectives for Species of Greatest Conservation Need and Key Habitats.

Action 1.3. Develop and implement monitoring and evaluation techniques for vulnerable Species of Greatest Conservation Need and Key Habitats.

Because of the changes expected under future climates, new decision tools will be needed to help determine appropriate management actions. There is a need to develop monitoring protocols that can quickly detect climate-related shifts in populations and habitats, help tie existing and proposed management with on-the-ground results, and inform and refine vulnerability assessments. Evaluating actions will be critical to coping with future climate uncertainties. To make the most efficient use of available funding, monitoring should be coordinated and shared among relevant agencies and organizations. Monitoring across boundaries and jurisdictions will form the basis for decision-making in a variable and rapidly changing environment and allow habitat protection and restoration efforts to focus on vulnerable, high priority areas.

Goal 2: Identify, prioritize, and implement conservation strategies to mitigate the negative impacts of climate change on fish, wildlife, and habitats.

Action 2.1. Incorporate currently available climate change information into management plans for species and habitats. Focus on strategies that are robust to a range of potential future climates and that maintain or restore key ecosystem functions and processes.

Future climate conditions will vary in unpredictable ways; however, waiting for more details is not the best approach. Instead, it is important to make use of the best available information to immediately identify and implement adaptation strategies for Oregon’s species and habitats.

One way of coping with uncertainties about future climates and the responses of species and habitats is to focus on identifying and implementing management approaches that are likely to be successful under a range of climate scenarios. Efforts to identify robust adaptation strategies for a particular species or habitat might involve considering two or more climate scenarios with different degrees of warming and precipitation conditions. Management actions that are likely to be successful under multiple scenarios are preferable to those that only make sense under a narrow range of future conditions.

Because future climate conditions may not support the same fish, wildlife, and plant species found in Oregon today, another promising approach is to focus on restoring abiotic conditions in ecosystems.

Some researchers have even suggested that conservation planning should be based on geophysical classes rather than biological communities.

Action 2.2. Minimize other threats.

Many of the best available climate change adaptation strategies involve managing other threats to species and habitats. Because rapidly changing climate conditions will interact with, and may exacerbate, the other Key Conservation Issues (KCIs) described in Oregon’s SWAP, working to reduce these other threats is a good way of moderating the effects of climate change on fish, wildlife, and habitats. Reducing non-climate threats also tends to be a low-risk approach with a relatively high likelihood of success, because many non-climate threats are better understood, managers have more experience in applying action plans, and the actions taken are not as dependent on the accuracy of future climate predictions. For example, protecting an interconnected, representative network of natural and semi-natural lands for long-term conservation management is one of the most effective tools for coping with both climate change and other conservation threats, because relatively intact ecosystems are more likely to be more resilient to climate change, will better sustain fish and wildlife populations facing climate threats, allow wildlife to move to adapt to changes at their own pace, and may even transition more smoothly to future climate conditions.

Action 2.3. Develop regional and local partnerships to coordinate responses to climate change across political, cultural, and jurisdictional boundaries.

Climate change is a global phenomenon, and it greatly increases the importance of working across traditional boundaries to more effectively manage fish, wildlife, and natural systems. Coping with the challenges of a rapidly changing and less predictable climate will require stronger working relationships with both traditional and new partners at various scales.

REFERENCES