New study finds the spatial extent of U.S. summer heat waves increasing substantially by mid-century

By the middle of this century, the average spatial extent of summer heat waves in the United States could be up to 80% larger than they are today if greenhouse emissions continue unabated, according to a new study led by a University of Maine climate scientist.

Bradfield Lyon, associate research professor with the UMaine Climate Change Institute and School of Earth and Climate Sciences, led a research team that applied an algorithm to daily temperature data to identify contiguous heat wave regions across the U.S. during May to September in both the current climate (1979–2009) and in climate model projections for 2031–55.

The researchers found that by mid-century, in a middle-of-the-road greenhouse gas emissions scenario, the average size of heat waves increases by 50% relative to the current climate. Under high greenhouse gas emissions, the average size increases by 80%, with the more extreme heat wave events more than doubling in size. 

“Larger spatial extent of heat waves strongly suggests larger human exposure and increased energy demand, and could also have implications for fire risk and air quality,” according to the researchers, who published their study in Environmental Research Letters. 

Previous studies have shown that heat waves — consecutive days with extreme daily temperatures — are expected to increase in duration, intensity and frequency as the climate system warms in response to increasing greenhouse gas concentrations. An important physical attribute that has not been systematically analyzed is the spatial extent of contiguous heat wave regions. 

A NOAA news release on the study is here.