Oregon continues to warm in all seasons, in part due to human activity.
The entire Pacific Northwest has warmed about 2°F since 1900. The last three years (2016-2018) were all warmer than the 1970-1999 average, and 2015 still stands as Oregon’s warmest year on record. Annual precipitation varies between wet and dry years, with no discernible trend. The year 2018 was much drier than normal, and 11 counties received an emergency drought declaration, even coastal Lincoln County, because of historically low flows in the Siletz River.
Oregon is projected to warm by about 4-9°F by 2100, depending in part on whether global emissions follow a lower (RCP 4.5) or higher (RCP 8.5) path. Warming is likely to be enhanced in mountainous areas in winter and spring, and muted on the coast in summer.
Future warming rates will increasingly depend on global greenhouse gas emissions, as can be seen by comparing the red (high emission RCP8.5) and yellow (low emission RCP4.5) thick curves and shaded regions.
The Paris Agreement seeks to achieve warming no greater than 2°C, but even the yellow curve and shaded region are higher than the scenarios consistent with the Paris Agreement.
Changes in rainfall will accentuate extremes.
Annual precipitation is not projected to change, but models suggest modest increases in winter precipitation and decreases in summer precipitation. Extreme precipitation may change more (~20%) in eastern Oregon than western Oregon (~10%) by mid-century.
Annual precipitation, unlike temperature, has no long-term
trend toward wetter or drier.
Years of abnormally low precipitation and extended drought conditions are expected to occur throughout the century, and extreme events, like heavy rainfall associated with atmospheric rivers, are also anticipated to occur more often.
By the end of the century, sea level could rise to 8.2 feet.
Sea level rise projections have not changed substantially through mid-century, though estimates of the maximum plausible sea level by the end of the century (2100) have increased to 8.2 feet.
Hot days will become more frequent in Oregon in a changing climate.
Most locations, except the cooler mountains and the coast, will see an increase of about 30 days over 86°F by mid-century compared with the recent past.