The Climate of the Pacific Northwest
Over the last 110 years, average annual temperatures have risen by 1.5°F in the Pacific Northwest. Consistent with climate changes worldwide, the Climate Impacts Group of the University of Washington cited, in 2008, the following changes observed in the 20th century in the Pacific Northwest:
- Increase in winter average temperature
- Greater variability in precipitation in the cool season
- Snowpack on April 1 declined from 1950 to 2000
- Timing of the peak water runoff has shifted to earlier in the season
The Office of the Washington State Climatologist has made available a tool to examine trends in 20th century temperature, precipitation and snow water equivalent in the Pacific Northwest.
Every global climate model used by the Intergovernmental Panel on Climate Change (IPCC) projects an annual temperature increase for the Pacific Northwest over the 21st century. The amount of the increase ranges from about 3°F under a low emissions scenario to about 9°F under a high emissions scenario by 2080. Changes in precipitation are less certain. Summer temperatures are projected to increase the most of any season. Many models show a drier summer and a wetter winter.
The table below is a summary of projected changes in temperature and precipitation for the Pacific Northwest for the 21st century. Two IPCC emissions scenarios are represented, labeled A1B and B1 (see their report for details). The “low”, “high”, and “REA average” values represent the range and average of projected values based on a comprehensive suite of climate simulations.
To learn more about the limitations of using global models for regional predictions, see our Climate Modeling page.