Effects of Climate Change on Washington State

After reading my recent article on the effects of climate change on Nebraska, my birthplace and home, my mother, who grew up in Seattle, asked me to write one up on Washington state.

Nebraska is expected to see the second largest increase in average annual temperature of any state in the United States by 2100. Washington, in contrast, is expected to see one of the lowest levels of warming: "only" 7.8° F under the business-as-usual A2 high emissions scenario and about 5.7° under the lower B2 emissions scenario, which projects an atmospheric carbon dioxide level of about 538 parts per million (ppm) by 2100. (Current CO2 levels are about 390 ppm, an increase of approximately 110 ppm over pre-industrial levels.) This places Washington in 44th place among the US states for projected temperature increases. Even these comparatively moderate increases in temperature, however, can be expected to cause some major changes in Washington's climate and ecosystems.

This article will attempt to lay out some of the projected effects of climate change on the state of Washington in simple, accessible language, and discuss some of the actions Washington residents can take to adapt to these changes.

As I discussed above, Washington state can expect a comparatively moderate increase in average temperature of about 5.7-7.8° F, depending on the emissions scenario used to calculate the proposed increase. If certain climate feedback loops are triggered, these figures could be much higher, but they could also be much lower, if we are able to restrict atmospheric CO2 levels to levels of 450 ppm or even reduce them back down to the "safe" level of 350 ppm. Unpredictable natural events, such a major volcano eruption or a decline in the amount of solar energy reaching the Earth, could also keep temperatures lower than these projected figures.

Assuming a moderate or high emissions scenario with no change in other natural factors, however, the impacts of warmer temperatures on Washington state could be widespread.

One immediate concern is the impact of higher temperatures on snowpack. Washington is highly dependent on natural snowpack to store water used for drinking, irrigation, recreation, and many other purposes. Unfortunately, April 1st snowpack, a key indicator of natural water storage available for the warm season, has already declined by about 25% in the Cascade mountains over the last 40-70 years due to average temperature increases of up to 4°F in high altitude regions (well over the average 1.5° increase experienced in the Pacific Northwest as a whole). It is expected to decline an additional 40% by the 2040s. This could lead to declines in warm season runoff of 30% or more by mid-century, creating warm season water shortages and increasing the severity of droughts.

Warmer temperatures can also affect the timing of peak runoff. Many regions of the state have already seen peak runoff shift anywhere from a few days to nearly a month earlier over the last century. Projected increases in winter precipitation - and declines in summer precipitation - for Washington state could also have a serious effect on runoff. More precipitation falling as rain in the winter time, especially in the warmer western Cascades, could lead to increased risk of winter flooding. Faster, earlier snowmelt could also increase flooding risk in spring, while exacerbating droughts in summer and fall.

Changes in runoff could in turn cause a decline in salmon populations, which are already under stress due to a combination of factors including water pollution, habitat destruction, and over-fishing.

Increased winter stream flows can scour streambeds, damaging nests and washing away eggs, while earlier peak streamflows can wash immature salmon out to sea before they are physically ready to make the transition. Additionally, warmer air temperatures raise water temperatures, degrading stream and ocean habitat for salmon and other cold water fish and benefiting pests and diseases that flourish in warmer water. Salmon populations have already declined by more than 90% in the Columbia River basin and are expected to decline even further as up to 1/3 of their current habitat becomes too warm for this coldwater fish to thrive.

Another concern related to increased winter precipitation and stream flow is increased risk of erosion and landslides. In heavily populated regions of Western Washington, many coastal bluffs have been developed. Increased winter precipitation could saturated soils, increasing the risk of major landslides on these bluffs and hillsides. Higher streamflows can also cause increased streamside erosion.

A projected rise in global sea levels caused by melting of the Greenland and Antarctic ice sheets could also put parts of coastal Washington at risk. At higher emissions scenarios, experts are projecting sea level rise as high as 5 feet by 2100, which would inundate low-lying coastal areas such as Harbor Island in Seattle and increase erosion along the coast.

Further inland, Washington can expect to see increased risk of forest fires and damage to forest ecosystems as a result of disease and pest outbreaks benefiting from warmer temperatures. The mountain pine beetle is already wrecking havoc on the forests of neighboring British Columbia, where it has destroyed 33 million acres of trees so far and is expected to kill more than 78% of all mature pines before running its course. Forests already vulnerable to the effects of drought, pests, and disease due to logging and habitat fragmentation will be hard hit by warming temperatures and increased evaporation from soil and vegetation.

Finally, warmer temperatures can threaten human health as a result of heat stress and reduced air quality. The effects will be especially severe in Washington's urban areas, and among the most vulnerable populations, including the very young, the very old, and the low income.

Fortunately, King County, Washington - home of Seattle and 38 other municipalities - has been one of the global leaders of municipal efforts to mitigate and prepare for the effects of climate change. King County's 2007 Climate Plan is available free online as a PDF document, and the county website offers recommendations for individuals, businesses, and fellow governments seeking to prepare for the effects of climate change. For governments, urban planners, and other interested individuals, King County's publication Preparing For Climate Change: A Guidebook for Local, Regional, and State Governments is also available free online.

Some of King County's preparations include:

• repairing and improving levees and bridges
• incorporating permeable pavement and rain gardens into urban designs to reduce stormwater runoff
• relocating water treatment facilities to higher ground
• continuing improvements to public transportation systems, as well as infrastructure for pedestrians and bikers, to maintain better air quality
• promoting green building practices to reduce carbon emissions while maintaining indoor comfort levels in a hotter climate
• encouraging rainwater harvesting, greywater reclamation, and other strategies to reduce the effects of drought
• increasing forest cover and take steps to improve forest health to increase resistance to fires, pests, and diseases and maintain forest ecosystem services such as flood mitigation
• and more