Uncertain Future: Climate Change and Its Effects on Puget Sound

Released October 18, 2005

Overview Report

Overview report (4.9 MB)

The Overview report provides a summary of climate impacts to Puget Sound and the implications to ecosystem management.

Foundation report (3 MB)

The Foundation Document provides additional technical detail on the information presented in the overview report. For improved image quality, we recommend downloading the high resolution (14 MB) version of the report.

Media coverage of the report | PSAT News Release (10.18.05)

Uncertain Future: Climate Change and Its Effects on Puget Sound is a new report prepared by the Climate Impacts Group at the University of Washington that examines the projected impacts of climate change on Puget Sound. Combining a review of current scientific literature and new research, the report provides a detailed assessment of how climate change has affected - and will continue to affect - the Puget Sound environment. Specific areas of focus include changes in regional climate, snowpack, streamflow, sea level rise, water quality, nearshore habitat, and salmon. The importance of planning for climate change is also discussed. The report was commissioned by the Puget Sound Action Team in the Washington State Office of the Governor.

Research Highlights


Uncertain Future highlights important changes for the Puget Sound region, including the following:

  • Average annual temperature in the Puget Sound region warmed 2.3°F (1.3°C) during the 20th century, a rate substantially greater than the global warming trend.

  • Projected 21st century average warming rates for the Pacific Northwest are on the order of 1.8°F (1.0°C) by the 2020s and 3.0°F (1.7°C) by the 2040s, relative to 1970-1999 average temperature. Even the lowest estimated warming would change Pacific Northwest climate significantly.

  • Puget Sound river and stream flows are changing in ways consistent with projected climate change impacts.

  • Glaciers in the Cascade and Olympic Mountains have been retreating for over 50 years.

  • Lake Washington has warmed substantially and there is evidence of rising temperatures in the Strait of Juan de Fuca.

  • Scientists project that Puget Sound waters will warm in the future, potentially putting many species at risk including plankton, the foundation of Puget Sound’s food web.

  • More of the region’s winter precipitation is likely to fall as rain rather than snow, increasing flooding in Puget Sound watersheds.

  • The rate of sea-level rise in the Pacific Northwest is projected to be faster than the global average, and is likely to increase both the pace and extent of the erosion and nearshore habitat loss already affecting Puget Sound shorelines, especially in south Puget Sound.

  • Puget Sound salmon are likely to be further stressed by lower summer and fall streamflows, warmer water temperatures, and an increased potential for winter flooding.
  • The potential for harmful algal blooms and low oxygen concentrations in bottom waters may increase due to warmer water temperatures, increased temperature stratification, and other factors.

  • Changes caused by a warming climate are likely to reverberate across the Puget Sound ecosystem in complex and unpredictable ways, disrupting crucial interactions between Puget Sound plants and animals and their environment.

Planning for Climate Change


Planning for climate change is needed if the region is to adapt to the coming changes. The report suggests that in order to plan for future climate, policy makers, planners, and resource managers should:

  • Recognize that the past may no longer be a dependable guide to the future,

  • Take actions to increase the adaptability of regional ecosystems to future,

  • Monitor regional climate and ecosystems for ongoing change, and

  • Expect surprises and design for flexibility to changing conditions.

By starting now to plan for climate change, the region can build the capacity required to prepare for and cope with climate impacts in the Puget Sound region.

For more information, please contact:

Brad Ack, Director
Puget Sound Action Team
360-725-5437
Ed Miles, Director
Climate Impacts Group
Center for Science in the Earth System
University of Washington
(206) 616-5348

For questions related to the technical and scientific aspects of the document, please contact:

Amy Snover, PhD
Research Scientist (CIG)
206-221-2997
Philip Mote , PhD
Research Scientist (CIG) & State Climatologist
206-616-5346