It’s not that corn sweats more than other plants — an acre releases less moisture on average than, say, a large oak tree — but the Midwest has a lot of corn in late July. In Iowa, for example, more than two-thirds of the area is farmland, and corn is the top crop (followed by soybeans, which, by the way, also sweat).

Dangerous temperatures will persist across parts of the U.S. through July, and in some areas, there's an unexpected contributor.