Environment
4:51 pm
Wed August 8, 2012

July Was the Hottest Month Ever Recorded in Continental U.S.

It's official: last month's heat wave (which cooked Louisville as well as most other states in the region) was the hottest ever on record in the continental U.S. According to an Associated Press story, this beats the record set during the Dust Bowl in the 1930s.

And climate change could be at least partially responsible. AP reporter Seth Borenstein looks at the U.S. Climate Extreme Index, which is a measurement developed by the National Oceanic and Atmospheric Association. The index for this past July was 37 percent. The average is 20 percent.

For the first seven months of the year, the extreme index was 46 percent, beating the old record from 1934. This year's extreme index was heavily driven by high temperatures both day and night, which is unusual, Crouch said.

"This would not have happened in the absence of human-caused climate change," said Pennsylvania State University climate scientist Michael Mann.

Crouch and Kevin Trenberth, climate analysis chief of the National Center for Atmospheric Research, said what's happening is a double whammy of weather and climate change. They point to long-term higher night temperatures from global warming and the short-term effect of localized heat and drought that spike daytime temperatures.

Drought is a major player because in the summer "if it is wet, it tends to be cool, while if it is dry, it tends to be hot," Trenberth said.

In Kentucky, statewide, this wasn't quite a record year. It was second to July 1901. But this year's January through July period was the hottest on record in the state.