Observed Trends in Summertime Extreme Heat Events in the U.S. and China

Surface meteorological observations from the United States (for 1948-95) and China (for 1951- 94) reveal upward trends in seasonal mean temperature and humidity, particularly at night. These trends are accompanied by increases in the frequency of extreme summertime apparent temperature (a combination of temperature and humidity), both for single-day events and multi-day heat waves. Extreme summertime heat adversely affects productivity, human health, and mortality. Because of the possibility that the observed trends might continue into the next century, the public welfare would benefit from forecasts and warnings of extreme heat events and appropriate adaptation or mitigation efforts.