Nate Mantua

University of Washington

Co-authors: Philip Mote, Eric Salathe, Valerie Duliere, Emily Jump

Abstract: Historical climate observations for the Pacific Northwest region indicate that temperatures increased approximately 1 degree C in the 20th century, while trends in precipitation were less prominent than interannual and interdecadal variations. Additional evidence in support of the observed changes in temperatures includes widespread declines in the ice mass and length of PNW glaciers, declines in springtime snowpack at low elevations, and advanced runoff timing in snowfed rivers. Recent projections for climate change in the 21st century taken from the climate models used in the IPCC's Fourth Assessment Report of 2007 indicate that the average warming rate for PNW temperatures will be in the range of 0.1 to 0.6 deg C/decade, with a best estimate of 0.3 deg C/decade. For comparison, the observed PNW warming in the 2nd half of the 20th century was approximately 0.2 deg C/decade. In contrast, projected changes in annual average precipitation from most climate models are modest with respect to historical variations, ranging from a 10% decrease to as much as a 20% increase, but with an average of +4% by the late 21st century. On average, the climate models have winter precipitation increasing and summer precipitation decreasing.

Video Length: 16 Minutes, 25 Seconds

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Observed and Projected Climate Trends in the Pacific Northwest