In the summer of 1998, a heat wave punished the American South. Crops and cattle died en masse; Texas alone suffered $2.1 billion worth of agricultural damages, while Oklahoma lost $2 billion. College Station, Dallas-Ft. Worth, and Oklahoma City all saw weeks on end when the maximum temperature hit 100 degrees every day. In Corpus Christi, there was a 41-day stretch during which the temperature hit 95 every day. Nationwide, 200 people were killed by the heat.

Expect more summers like that.

A new report says that in the decades ahead, the Southwest, Southeast, and Upper Midwest could see stretches of months—not weeks—when the temperatures will consistently reach the mid-90s. "During these periods," the report cautions, "anyone whose job requires them to work outdoors, as well as anyone lacking access to air conditioning, will face severe health risks and potential death."

This has significant consequences for industries that largely operate outside, particularly construction, agriculture, landscaping, and utility maintenance. According to the report, the labor productivity of those sectors could fall by about 3 percent. "For context," the report adds, "labor productivity across the entire U.S. labor force declined about 1.5 percent during the famous 'productivity slowdown' in the 1970s."