'Corn sweat': How Illinois crops are adding to the heat and humidity

CHICAGO - As the Midwest grapples with sweltering heat, you may hear the term ‘corn sweat’ making its rounds.

Climate experts say ‘corn sweat’ is something they are often asked about this time of year. It’s even trending in online searches this week.

While it's not something you can see, ‘corn sweat’ is certainly something we can all feel — it is a factor contributing to the oppressive humidity across Illinois.

As the Midwest gets warm and humid air from the Gulf of Mexico, millions of acres of crops across the state are also increasing dew points.

"If anybody were to go into a cornfield – be outside of the cornfield and then go into the cornfield – they’ll feel a difference in the humidity," said Illinois State Climatologist Trent Ford.

Climate experts explain that ‘corn sweat’ refers to the process of transpiration, where water is drawn from the roots of corn plants, moves through the plant, and is then released into the atmosphere in the form of vapor.

"Most plants don’t transpire a significant amount of water. Corn plants are really, really effective at transpiration," said Ford, who is based at the University of Illinois – Urbana-Champaign.

The added humidity from transpiration can push the heat index even higher, making it feel significantly muggier.

Duane Friend, a climate specialist with the University of Illinois Extension, says this process still impacts how it feels outside now, but the peak effect occurred mid-summer.

"As the corn crop continues to mature right now, and yes, we’re having a really hot stretch of weather at the moment, the actual amount of moisture being put out by the corn crop right now is very small compared to what it was like a couple of months ago," Friend explained. "If you were talking six weeks ago, it could have been putting several thousands of gallons per acre of water into the air each day."

While less intense now, Ford and Friend say each corn plant is still working hard to ‘break a sweat.’

"This time of year, it’s closer to maybe – at maximum – a tenth of an inch per day (per plant)," said Ford.

"Up in the northern part of the state, the corn crop is not as far along, so you are still getting some of that added moisture up there," said Friend. "Here in the central part of the state, a lot of the crop is very mature."

There are currently more than 11 million acres of planted corn in Illinois.