New Studies Show Heat Waves to Move Toward Coasts

A new study by researchers at Scripps Institution of Oceanography, UC San Diego, suggests that the nature of California heat waves is changing due to global warming. Climate researchers detected a trend toward more humid heat waves that are expressed very strongly in elevated nighttime temperatures, a trend consistent with climate change projections. Moreover, relative to local warming, the mid-summer heat waves are getting stronger in generally cooler coastal areas. Classic California heat waves have been characterized as interior desert and valley events that are hot during the day and marked by dryness and strong nighttime cooling. Researchers Gershunov and Guirguis said their analysis of observations and computer model data indicates that the emerging flavor of heat waves marked by greater humidity, greater expression in nighttime temperatures, and greater expression in coastal areas relative to the generally cooler coast are intensifying and will keep intensifying in coming decades. Both coastal and desert heat waves will continue to be more common as climate changes relative to the past, but the desert heat waves are becoming less intense relative to strong average warming observed and projected for the interior of the state. The study, "California heat waves in the present and future," will appear in the American Geophysical Union journal Geophysical Research Letters. The "non-stationary" approach reflects an acknowledgment by scientists that what has been considered extreme heat is gradually becoming commonplace. The rate of climate warming necessitates a measure of extreme heat relative to the changing average climate rather than to historical climate norms. So, instead of defining heat waves relative to fixed temperature thresholds, the researchers projected heat wave intensity against a backdrop of increasing average summertime temperature. This causes the definition of heat waves -- temperatures in the warmest 5 percent of summertime conditions -- to evolve with the changing climate and reflect extreme conditions relevant to the climate of the time.