Extremes and Attribution (Invited Presentation)

Changes in the characteristics of weather and climate extremes are particularly important for human safety, infrastructure, agriculture, water quality, and natural ecosystems. A variety of extremes have become more frequent and/or intense over the past century, and climate model simulations indicate that many extremes will continue to increase or worsen over the coming decades. This presentation will summarize observed and projected changes in extremes (and their attribution) in the United States, focusing on temperature and precipitation. Key observed changes since the early-1900s include a decrease in the frequency of cold waves and an increase in the intensity of heavy rainfall, with recent decades experiencing an increase in the frequency of heatwaves and record-setting high temperatures. Over the 21^st Century, extreme temperatures are projected to increase even more than average temperatures, with substantial decreases in the number of days below freezing and increases in the number above 90°F nationwide. The frequency and intensity of heavy precipitation events are also projected to increase, as are the frequency and severity of land falling atmospheric rivers on the Pacific Coast.