Possible Future Climates: National Assessment climate model results show regional warming continuing at an increased rate this century, in both summer and winter. Average warming over the region is projected to reach about +3 degrees F by the 2020s and +5 degrees F by the 2050s. Annual precipitation changes projected through 2050 over the region range from a small decrease (-7%) to a slightly larger increase (+13%). Projected changes in precipitation are within the range of year-to-year variability that has been experienced over the past 100 years.
After 2050, the projected trend to a warmer, wetter regional climate continues with substantially more warming likely to occur in winter. By the 2090s, projected average summer temperatures rise by +7.3 degrees F to 8.3 degrees F, while winter temperatures rise +8.5degrees F to 10.6 degrees F. Projected precipitation increases over the region range from 0 to 50% depending on the model. Warmer temperatures, though, mean less winter precipitation will fall as snow and, therefore, there will be less snowpack for later melting and use.
Glaciers: The US Geological Survey has monitored mass balance of South Cascade Glacier for nearly 50 years. The Pacific Northwest South Cascade Glacier has lost mass since USGS monitoring began more than four decades ago and mass loss has accelerated during the past 15 years. Glaciers on Mount Adams show a period of retreat during the first half of the century, followed by a period of little change or advance, and then another period of rapid retreat in latter part of the century.
Forests Ecosystem Impacts: Climatic change is likely to affect PNW forests in several important ways. Spatial patterns of productivity will change. Species composition will be affected by climate and consequences for lower elevation forests and for species susceptible to mountain pine beetle are potentially substantial. Regional fire area burned may increase two- or three-fold. Fire regimes in different ecosystems in the PNW have different sensitivities to climate. Due to climatic stress on host trees, mountain pine beetle outbreaks may increase in frequency and levels of tree mortality. Mountain pine beetles will reach higher elevations due to a shift in favorable temperature conditions in these areas as the region warms.
For Example: In western North America, projections were made for climates expected for the decades beginning in 2030, 2060, and 2090 and for the decade beginning in 2030, whitebark pine contemporary climate profile is projected to decline 70 % while moving upward in altitude by 333 m on average. By end of century, its contemporary climate profile is projected to diminish to an area equivalent to less than 3% of its current distribution.
Currently, stands of dead and dying whitebark pine trees can be seen in several western states as well as Mt. Adams. Ecologically, high elevation white pines play a critical role in maintaining a range of wildlife and plant species. As these pines continue to decline, it can affect the diversity of wildlife and plant species that depend on them for food and cover. The large seeds produced by many of these species are an important food source for the Clarks nutcracker and similar birds and black bear. The decline of pine species will likely affect squirrel populations and carnivore species that depend on them.
For example: Mountain meadows in the Pacific Northwest, as in much of western North America, have experienced recent and rapid invasion by conifers. Changes in climate, cessation of sheep grazing, and long-term suppression of wildfire likely contribute to the observed replacement of meadow by forest. Knowledge of factors that influence invasion, and of their varying importance across gradients in environment and vegetation, is critical to predicting future changes in these dynamic systems.
For example: The wolverine is a candidate for Endangered Species Act endangered species protection because it is primarily threatened by impact of climate warming on its habitat.
For example: Although the US Fish and Wildlife Service has not listed the pika under the Endangered Species Act based on an assessment of changing conditions out to 2050. However, cumulative evidence available so far suggests that pikas are sensitive indicators of climate variability and change and unpublished surveys indicate pikas are disappearing in the Cascades.
Climate Change Resources
Forest Service Climate Change Resource Center
USF&W Service PNW Climate Change
University of Washington Climate Impacts Group