What is corn sweat? Extreme heat and sun makes humidity in the Midwest soar

Ah, sure, late July within the Midwest: a time for popsicles by the lake, a visit to the county honest, and, in fact, excessive humidity made extra depressing by…corn sweat.Corn sweat. It’s a factor!The time period refers back to the moisture launched by fields of corn throughout scorching and sunny climate. Like all different vegetation, corn transpires — that means, it sucks up water from the bottom and expels it into the air as a solution to keep cool and distribute vitamins. Moisture additionally enters the air when water within the soil evaporates. Along with transpiration, this course of is named evapotranspiration.So, the place you discover a great deal of vegetation packed tightly into one place, whether or not the Amazon rainforest or Iowa, humidity can skyrocket throughout scorching and particularly sunny intervals, making the air really feel oppressive.That’s what’s occurring this week: An enormous warmth dome is bringing dangerously excessive temperatures to a lot of the US, together with elements of the Midwest the place there additionally occurs to be huge fields of corn. Together with loads of daylight, that warmth is sufficient to make corn sweat, producing extraordinarily uncomfortable climate and, in some areas, a warmth index of 110 levels or increased.It’s not that corn sweats greater than different vegetation — an acre releases much less moisture on common than, say, a big oak tree — however the Midwest has a variety of corn in late July. In Iowa, for instance, greater than two-thirds of the realm is farmland, and corn is the highest crop (adopted by soybeans, which, by the best way, additionally sweat).“The mix of upper temperatures and elevated humidity from corn sweat can result in extra intense warmth waves, making it tougher for folks to remain cool and growing the chance of heat-related sicknesses,” Bruno Basso, a crop and agriculture scientist at Michigan State College, advised me final summer season.Sweating corn is a very pure course of; it’s not prefer it harms the crop. However when it causes humidity to spike, a great deal of evapotranspiration could be harmful for many who work exterior, susceptible teams just like the aged or pregnant, and those that can’t afford air con.Is corn sweat a rising concern?One complicated factor to bear in mind is that evapotranspiration tends to chill the encircling air, Basso mentioned, as a result of the method absorbs warmth. That is one motive why a forest or prairie sometimes feels cooler than a parking zone on a scorching day.But throughout excessive warmth waves, which have gotten extra frequent as corporations spew carbon dioxide into the air, “the dynamics change,” Basso mentioned.“Regardless of the cooling impact of evapotranspiration, the heightened humidity can offset it, making warmth waves really feel much more intense,” Basso advised me. It additionally prevents temperatures from cooling off at evening, he added, if you may usually really feel reduction.In a single 2020 research, researchers from the Harvard-Smithsonian Middle for Astrophysics analyzed a previous summer season warmth wave within the Midwest and located that cropland — most of which comprised corn on this a part of the nation — can enhance moisture within the air above it by as much as 40 %.A cornfield in southwest Iowa. Darcy Maulsby/Getty Pictures/iStockphotoAgain, it’s not simply crops throughout the Midwest that launch moisture, enhance humidity, and make summers really feel disgusting (I do know firsthand; I grew up in Iowa). The hundreds of thousands of acres of prairie that industrial farmland changed — largely to feed livestock and make ethanol — would have additionally produced a great deal of moisture, Basso mentioned.However there are some key variations between native ecosystems and industrial farmland, he added. “Native prairies are numerous ecosystems with a wide range of plant species, every with completely different root depths and water wants, serving to to create a balanced moisture cycle,” he advised me. “In distinction, corn and soy monocultures are uniform and may draw water from the soil extra rapidly.”Densely planted rows of corn drain water from the soil, which may deepen droughts, he mentioned. Droughts have gotten extra excessive in some elements of the US, although that is much less of a priority within the Midwest, which is projected to get wetter within the coming a long time.Whenever you put all of this collectively, you’ve gotten large fields of corn grown to feed cows that make the Midwest extra humid throughout warmth waves and worsen different local weather extremes.Mainly, corn sweat is simply as disgusting because it sounds.Replace, July 23, 2025, 4:50 pm ET: This story was initially revealed on August 29, 2024, and has been up to date with details about the 2025 summer season warmth wave within the Midwest.