Climate Change in the Pacific Northwest
In the Pacific Northwest, we are collaborating with climate researchers at the University of Washington’s Climate Impacts Group (CIG), the U.S. Geological Survey, the U.S. Forest Service (USFS) and many others to develop an understanding of climate change effects in the Pacific Northwest, and how to manage fish and wildlife resources in light of these effects.
The University of Washington’s Climate Impacts Group (CIG) is an interdisciplinary research group studying the impacts of natural climate variability and global climate change in the Pacific Northwest. Most of the following information is summarized from CIG's published work, including a recent assessment released in February, 2009 and published in June, 2009, titled The Washington Climate Change Impacts Assessment.
The assessment used 20 different global climate models for greenhouse gas emissions under a “medium” emissions scenario and 18 models for a “low” scenario. The assessment focuses on the “medium” scenario which is based on estimates that are lower than current rates of greenhouse gas emissions. In other words, the assessment is far from a “worse case” scenario or even a “business as usual” scenario.
Typical Climate in the Pacific Northwest
Climate and ecology in the Pacific Northwest are largely influenced by the interactions between seasonally varying atmospheric circulation patterns, or weather, and the mountainous terrain within the region.
Large-scale atmospheric circulation occurring over the Pacific Ocean, including the Gulf of Alaska, is the driving influence of seasonal variations in precipitation and weather. Approximately two-thirds of the Pacific Northwest precipitation occurs during half of the year (October-March) from the Pacific storm track, and much of this precipitation is captured in the region’s mountains. Precipitation declines from late spring to early fall with high pressure systems to the west, generally keeping the northwest fairly dry.
Contrasts in Pacific Northwest climate can be stark owing to the region’s mountains, especially the Cascade mountain range. The Cascades create a barrier between the maritime climate influences to the west, where temperatures are generally mild year-round, and the continental climate influences to the east, with more sunshine and larger daily and annual ranges in temperature.
(Littell et al., 2009; and University of Washington’s Climate Impacts Group website)
West of the Cascades
Climate in the low-lying valleys west of the Cascades is characterized by mild year-round temperatures, abundant winter rains, and dry summers. Average annual precipitation in most places west of the Cascades is more than 30 inches. Precipitation in the mountains is much higher with average annual accumulation typically exceeding 100 inches or more. The Cascades are often among the snowiest places on Earth. (Littell et al., 2009)
East of the Cascades
Climate east of the Cascade crest is more continental, with more sunshine and drier conditions, creating a sharp contrast to the maritime climate of the western Pacific Northwest. Average annual precipitation occurs during the warm half of the year and is generally less than 20 inches, with some places receiving as little as 7 inches. Annual and daily temperature ranges are considerably greater than west of the Cascades as well. (Littell et al., 2009)
The graph is excerpted from The Washington Climate Change Impacts Assessment , University of Washington, Climate Impacts Group, June 2009 |
Naturally Occurring Variations in Pacific Northwest Climate
Important fluctuations in regional climate are related to the El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) phenomena. In their warm phases, ENSO, El Nino and PDO increase the odds for a warmer-than-average Pacific Northwest winter and spring and decrease the odds for a wetter-than-average winter. The opposite tendencies are true for cool phase ENSO (La Niña) and PDO.
Figure 1 Warm Phase ENSO (El Niño). The spatial pattern of anomalies in sea surface temperature (shading, degrees Celsius) and sea level pressure (contours) associated with the warm phase of ENSO (i.e., El Niño) for the period 1900-1992. Contour interval is 1 millibar, with additional contours drawn for +0.25 and 0.5 millibar. Positive (negative) contours are dashed (solid).
Figure 1 is excerpted from The Washington Climate Change Impacts Assessment , University of Washington, Climate Impacts Group, June 2009 |
For more information on climate variation in the Pacific Northwest due to El Niño/Southern Oscillation and Pacific Decadal phenomena, visit Climate Impact Group’s websights: El Niño/Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)
Climate Change: Temperature and Precipitation
Temperature records indicate that Pacific Northwest temperatures increased 1.5°F since 1920. Regionally downscaled climate models project increases in annual temperature of, on average, 2.0°F by the 2020s, 3.2 °F by the 2040s, and 5.3°F by the 2080s (compared to the 1970-1999 period), averaged across all climate models. Projected changes in annual precipitation, averaged over all models, are small (+1 to +2%), but some models project wetter autumns and winters and drier summers. Increases in extreme high precipitation (falling as rain) in the western Cascades and reductions in snowpack are key projections from high-resolution regional climate models. (Littell et-al., 2009)
Table 1 is excerpted from The Washington Climate Change Impacts Assessment , University of Washington, Climate Impacts Group, June 2009 |
Hydrology
Changes in temperature and precipitation will continue to decrease snow pack, and will affect stream flow and water quality throughout the Pacific Northwest region. Warmer temperatures will result in more winter precipitation falling as rain rather than snow throughout much of the Pacific Northwest, particularly in mid-elevation basins where average winter temperatures are near freezing. This change will result in:
- Less winter snow accumulation,
- Higher winter streamflows,
- Earlier spring snowmelt,
- Earlier peak spring streamflow and lower summer streamflows in rivers that depend on snowmelt (most rivers in the Pacific Northwest)
The decline of the region's snowpack is predicted to be greatest at low and middle elevations due to increases in air temperature and less precipitation falling as snow. The average decline in snowpack in the Cascade Mountains, for example, was about 25% over the last 40 to 70 years, with most of the decline due to the 2.5 degrees F increase in cool season air temperatures over that period. As a result, seasonal stream flow timing will likely shift significantly in sensitive watersheds. (Littell et-al., 2009)
Forests
Studies and the results of vegetation change modeling suggest that a number of different scenarios are possible for Pacific Northwest forests. These scenarios differ dramatically, ranging from projections of forest expansion to forest dieback, as a result of uncertainty regarding how projected temperature and precipitation changes will interact to affect drought stress in trees or otherwise modify total annual productivity. Other major uncertainties are whether increased levels of carbon dioxide (CO2) in the atmosphere would increase primary productivity or help trees withstand reduced soil moisture. The likeliest scenario seems to be that increased forest growth could occur during the next few decades, but that at some point temperature increases would overwhelm the ability of trees to make use of higher winter precipitation and higher CO2.
In any case, the changes in climate are likely to cause plant communities to undergo shifts in their species composition and/or experience changes in densities. Species range shifts are expected to be individualistic rather than primarily as collections of currently associated species. In other words, species won't all move together. Extinction of local populations and, potentially, species are expected with climate change. Species with poor dispersal ability may have particular difficulty in shifting their spatial distributions in response to climatic changes. Loss of biological diversity will occur if environmental shifts outpace species migration rates and interact with population dynamics to cause increased rates of local population extinction. (Littell et al., 2009)
Wildfire
Virtually all future climate scenarios predict increases in wildfire in western North America, especially east of the Cascades, due to higher summer temperatures and earlier spring snowmelt. Fire frequency and intensity have already increased in the past 50 years, and most notably the past 15 years in the shrub steppe and forested regions of the West. The area burned by fire regionally is projected to double by the 2040s and triple by the 2080s. The probability that more than two million acres will burn in a given year is projected to increase from 5% (observed) to 33% by the 2080s. USFS and CIG researchers have linked these trends to climate changes. Drought and hotter temperatures have also led to an increase in outbreaks of insects, such as the mountain pine beetle, increasing the risk of fire. (Littell et al., 2009)
Sea Level Rise
The melting of mountain glaciers and the Greenland and Antarctic ice sheets along with the thermal expansion of the oceans will likely continue to increase sea level for many hundreds of years into the future. The consensus estimate of sea level rise by 2100, published in the Intergovernmental Panel on Climate Change’s Fourth Assessment, was estimated at 0.6 to 2.0 ft. Improved estimates of the range of sea level rise by 2100, which now include estimated effects of ice dynamics, lie between 2.6 and 6.6 ft, a significantly higher estimate.
As a result of sea level rise, low lying coastal areas will eventually be inundated by seawater or periodically over-washed by waves and storm surges. Coastal wetlands will become increasingly brackish as seawater inundates freshwater wetlands. New brackish and freshwater wetland areas will be created as seawater inundates low lying inland areas or as the freshwater table is pushed upward by the higher stand of seawater. (Pfeffer, W.T., et al., 2008)
Ocean Acidification
The ocean will eventually absorb most carbon dioxide released into the atmosphere as a result of the burning of fossil fuels. Dissolving of carbon dioxide into ocean surface waters will increase the acidity of ocean surface waters. Oceanic absorption of CO2 from fossil fuels may result in larger acidification changes over the next several centuries than any inferred from the geological record of the past 300 million years (with the possible exception of those resulting from rare, extreme events such as meteor impacts).
Virtually every major biological function has been shown to respond to acidification changes in seawater, including photosynthesis, respiration rate, growth rates, calcification rates, reproduction, and recruitment. Much of the attention has focused on carbonate-based animals and plants which form the foundation of our marine ecosystems. An increase in ocean acidity is likely to result in a decline in the ability of coral reefs to maintain their calcium carbonate structure. Phytoplankton that utilize calcium carbonate are also likely to decline in abundance, along with other carbonate-dependent animals such as marine snails and carbonate-dependent plants such as red marine algae.
(Smith and Baker, 2008, and Ocean Carbon and Biogeochemistry Program, 2008).
Coastal and Marine Environments
In addition to temperature and rainfall changes, researchers and others have observed rising sea levels and changes to ocean conditions. Some important climate-related factors to consider are sea level, air and sea surface temperatures, winter precipitation, and storminess. These factors influence coastal erosion, landslides, flooding and inundation, estuarine water quality, and invasion of exotic species. In particular, the following conditions increase the risk associated with various coastal hazards:
- Increased sea level (associated with El Niño events during winter and spring) increases the risk of coastal erosion,
- Increased winter precipitation (associated with La Niña years, and cool phase PDO years) increases the risk of coastal river flooding and landslides,
- Southeasterly winter storms (associated with El Niño events during winter and spring) increase the risk of coastal erosion, and
- The co-occurrence of these three conditions increases the likelihood of large, damaging coastal erosion and flooding events.
In the Pacific Northwest, climate change may affect the coastal marine environment by increasing ocean temperature, increasing the vertical stratification of the water column (reducing mixing which is important to the marine food chain), and changing the intensity and timing of coastal winds and upwelling. Wind-driven coastal upwelling and mixing are particularly important to productive marine ecosystems that support diverse marine life, major fisheries and seabirds. Upwelling usually brings cold, nutrient-rich water to the surface in nearshore areas, supporting highly productive food webs. However, too much wind may transport planktonic organisms offshore and away from coastal areas. These coastal systems are highly variable in both locality and time. Natural changes can occur daily, weekly, seasonally, yearly or even every ten years. And upwelling can vary greatly due to El Niño-Southern Oscillation events which occur on average every 2 to 7 years, as well as decadal shifts known as cool or warm phases of the Pacific Decadal Oscillation. For example, El Niño events often result in reduced upwelling and productivity.
(Littell et-al., 2009)
The Fish and Wildlife Service’s 2009 5-year review of the Marbled Murrelet (pp. 42-45) contains a thorough evaluation of climate change affects to the marine environment. The review concludes that climate change is likely to result in changes to the murrelet’s marine environment. While physical changes to the near-shore environment appear likely, much remains to be learned about the magnitude, geographic extent, and temporal and spatial patterns of change, and their effects on coastal and marine species.
Salmon
Climate change affects salmon throughout its life stages. Historically, warm periods in the coastal ocean have coincided with relatively low abundances of salmon, while cooler ocean periods have coincided with relatively high salmon numbers.
Salmon productivity in the Pacific Northwest is clearly sensitive to climate-related changes in stream, estuary, and ocean conditions. In the past century, most Pacific Northwest salmon populations have fared best in periods having high precipitation, deep mountain snowpack, cool air and water temperatures, cool coastal ocean temperatures, and abundant north-to-south "upwelling" winds in spring and summer.
Rising stream temperatures will likely reduce the quality and extent of freshwater salmon habitat. The duration of periods that cause thermal stress and migration barriers to salmon is projected to at least double and perhaps quadruple by the 2080s for most analyzed streams and lakes. The greatest increases in thermal stress (including diseases and parasites which thrive in warmer waters) would occur in the Interior Columbia River Basin and the Lake Washington Ship Canal. The combined effects of warming stream temperatures and altered stream flows will very likely reduce the reproductive success of many salmon populations in Washington watersheds, but impacts will vary according to different life-history types and watershed-types. As more winter precipitation falls as rain rather than snow, higher winter stream flows scour streambeds, damaging spawning nests and washing away incubating eggs for Pacific Northwest salmon. Earlier peak stream flows flush young salmon from rivers to estuaries before they are physically mature enough for transition, increasing a variety of stressors including the risk of being eaten by predators.
Studies suggest that one third of the current habitat for either the endangered or threatened Northwest salmon species will no longer be suitable for them by the end of this century as key temperature thresholds are exceeded.
(Littell et-al., 20009)
Figure 9 is excerpted from The Washington Climate Change Impacts Assessment , University of Washington, Climate Impacts Group, June 2009
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References
Littell, J.S., M. McGuire Elsner, L.C. Whitely Binder, and A.K. Snover (eds). 2009. The Washington Climate Change Impacts Assessment: Evaluating Washington's Future in a Changing Climate, (PDF 14.1 MB) Climate Impacts Group, University of Washington, Seattle, Washington.
Ocean Carbon and Biogeochemistry Program, Subcommittee on Ocean Acidification. December 2, 2008. Ocean Acidification- Recommended Strategy for a U.S. National Research Program.
Smith, Ellen and Baker, Jason. August 2008. Pacific Island Ecosystem Complex chapter, Climate Impacts on U.S. Living Marine Resources: National Marine Fisheries Service Concerns, Activities and Needs. Osgood, K. E. (editor). U.S. Dept. Commerce, NOAA Tech. Memo. NMFS-F/SPO-89, 118 p.
Pfeffer, W.T., et al. September 5, 2008. Kinematic Constraints on Glacier Contributions to 21st- Century Sea Level Rise. Science AAAS. W.T. Science 321.
United States Global Climate Change Research Program. May, 2009. Global Climate Change Impacts in the United States - Northwest Region
