Abstract

The average warming rate in the Pacific Northwest during the next ~50 yr is expected to be in the range 0.1-0.6°C (0.2-1.0°F) per decade, with a best estimate of 0.3°C (0.5°F) per decade. For comparison, observed warming in the second half of the 20th century was approximately 0.2°C per decade. Trends in temperature already stand out above natural variability. Projected warming is greater in summer than in other seasons.

Present-day patterns of greenhouse gas emissions constrain the rate of change of temperature for the next few decades: humans are committed to some degree of additional climate change. Beyond mid-century, the projections of warming depend increasingly on emissions in the next few decades and hence on actions that would limit or increase emissions.

Projected precipitation changes are modest, and are unlikely to be distinguishable from natural variability until late in the 21st century. Most models have winter precipitation increasing and summer precipitation decreasing. Early results suggest an increase in intense precipitation but little change in coastal upwelling.