When summer temperatures turn brutal along the Gulf Coast in the deepest depth of the American South, locals always say, “It’s not the heat, it’s the humidity.” Iowa has been suffering through that one-two punch of heat and humidity this week, but here it’s not just the humidity, it’s also the “corn sweat.”
Corn sweat is the colloquial term for evapotranspiration, which is when plants release water vapor from their leaves. Corn is a particularly sweaty plant, hence the slang name for the multi-syllabic scientific term. An acre of corn can release as much as 4,000 gallons of water vapor every day. According to the last report from the U.S. Department of Agriculture, there are currently approximately 12.4 million acres of corn planted in Iowa.
All that corn sweat adds to other sources of water vapor in the atmosphere, driving the dew point higher.
“This influx of moisture is pushing dew points as high as the 60s and 70s F (upper teens and low to mid-20s C), ”Scientific American explained in an article on corn sweat published this week, noting, “The dew point is the temperature that the air would have to be cooled to in order to let water vapor start condensing out of the atmosphere.”
“In some places dew points are even reaching the low 80s F (mid- to high 20s C). Those below about 55 degrees F (13 degrees C) can feel reasonably dry and pleasant, but things start getting sticky at around 60 degrees F (16 degrees C) — and downright miserable if this measurement reaches the 70s F.”
Corn sweat exacerbates the problem of humidity, but it’s not the biggest humidity-related problem Iowa is facing. Climate change is.
“The rise in ‘absolute humidity’ (moisture in the air) is likely to become the most pervasive factor in climate change across the state,” according to the 2017 Iowa Climate Statement, endorsed by 190 scientists, researchers and educators from 39 of the state’s colleges and universities.
In Dubuque, absolute humidity during springtime increased 23 percent between 1970 and 2017, and increases in “humidity have been measured across the Midwest and in Iowa across all seasons and at all long-term monitoring stations.”
Humidity makes it harder for humans and other animals to cool off and accelerates corrosion of metal and the warping and rotting of wood. It also aggravates some of Iowa’s worst agriculture problems as “increased warm-season humidity leads to increased rainfall, extreme rain events, water-logged soils during planting season, soil erosion, and runoff of chemicals to waterways,” the Iowa Climate Statement said.
The recent blanket of humidity smothering Iowa has been extreme enough to attract the attention of a meteorologist in one of America’s most humid (and sweatiest) cities, New Orleans. WWL-TV meteorologist Payton Malone was so impressed he posted about Iowa’s corn sweat-driven humidity on Twitter/X.
Addressing the increasing humidity means addressing climate change, and until that’s done, Iowans will have to keep sweating, just like the corn. Of course, it’s not just corn that’s engaged in evapotranspiration. The state’s other top crop, soybeans, is also pretty damn sweaty.
According to the USDA, this year Iowa farmers planted 10 million acres of soybeans.
