Publication Date July 18, 2016

What in the world is ‘corn sweat’ and is it really causing this heat wave?

United States
Corn is not what’s behind this heat wave. Photo: iStock

Is corn sweat the cause of the coming heat wave? Definitely not. At most, it could make it more uncomfortable for some places.

“Corn sweat” is an extremely simple way of referring to evapotranspiration, the process by which moisture in plant leaves evaporates into the air. Plants draw water out of the ground through their roots for photosynthesis, and the water in the plant cells is exposed to the air once it gets above the ground. It evaporates off the leaves just as sweat evaporates off our skin — although it doesn’t take place to keep the plant cool, like it does for us.

So evapotranspiration is not making things hotter. But it is making things more humid — which can certainly be just as bad.

In regions where there are vast swaths of any plant, corn in particular, humidity can be notably higher than it otherwise would be. And the Midwest is covered in corn. Over 94 million acres of corn was planted in 2016, the USDA reported last month, up 7 percent from 2015 and the third-highest corn acreage in the United States since 1944.

Corn acreage by county in 2015. (USDA)

These regions are where the humidity is more likely to be higher because of evapotranspiration. During big heat waves, this translates into a higher heat index — or what the temperature feels like to our living bodies