It’s not the heat, it’s the corn

Are row crops making summers unbearable?


Here it is July again, and the General Assembly still hasn’t done anything about summer. Summers in the Midwest have never been pleasant, unless you own stock in a water park, but lately they have gotten worse – not just more unpleasant but more unpleasant in ominous ways. Windstorms have become so common that people have put roof shinglers and tree removal firms on their speed dials. When I was a boy, anyone who was asked, “Did you remember your trunks?” on his way out the door was planning to go swimming, not driving.

It is natural to assume that hotter weather hereabouts must be a result of a hotter planet, a side effect of humans treating the atmosphere like a midnight dumper treats a county roadside. There have been heat waves in the past, however, when atmospheric concentrations of greenhouse gases were much lower. A nasty one occurred in Illinois in the 1930s. Highs reached at least 100 degrees on 29 different days in 1936, including a record 12 consecutive days after July 4; nighttime lows were higher than 80 nearly every day during that hellish span.

It was nearly as bad in the 1950s. The all-time record high for Springfield – 112 degrees F. – was set in 1954. I remember we were watching the Milton Berle show, and what sounded like applause could be heard even during the performers’ routines. Turned out the sound wasn’t coming from the TV at all. It was the the noise of sweat drip-dripping from Mom and Dad and us three kids onto our TV trays.

The recent extreme summer weather is consistent with what climatologists’ models say are the likely effects of global warming. They predict that central Illinois will gradually turn into southeast Texas, weatherwise – hotter and wetter in spring and fall (a recipe for more and more violent storms and floods) and drier in the summer. As I write on this July morning it is 85 F. in Springfield, on its way to forecast high of 87; down in Houston it is 96.

Whatever the effects of planetary climate change, there seems no question that people have altered the ecosystems of Illinois and the Midwest in ways that affect the local summer weather. Urban heat islands are one well-documented impact, but might not be the only one. These days there are fewer very hot days (as measured by the thermometer) compared to 80 years ago. Julys and Augusts are actually cooler (comparatively), as well as wetter.

Yet even though the heat is less severe, it is more lethal. The heat wave in July of 1995 caused approximately 525 deaths in northeastern Illinois. That made it one of the worst weather-related disasters in Illinois history, even though those three consecutive days of highs over 99 degrees and lows in the upper 70s and lower 80s didn’t come close to matching 1936 for high temperatures.

What turned funky weather into fatal weather was record humidity levels. The likely source of that airborne moisture, argues Northern Illinois University climatologist David Changnon, might lay not on the other side of the planet but on the other side of the county line. Corn plants (and to a lesser extent soybeans) pump massive amounts of water from the soil through their roots and out of their leaves in the form of vapor. And while Illinois has had corn fields for a very long time, it has never had corn fields with so much corn on them. Changnon points out that average corn yields in Illinois have more than doubled since 1950 while the number of corn plants per acre have increased by two-thirds. Higher yields means more water is taken up per plant; higher plant densities means more plants per acre taking up water. A corn field come July and August has much the same kind of effect on the local atmosphere that running a vaporizer would have on the atmosphere of your living room on an August afternoon.

Interestingly, Changnon also found that a bad heat wave in 1988 saw Chicagoland temperatures of 90 degrees or greater on more than 40 days. But that heat coincided with a drought that had slowed down corn growth, with the result that the humidity stayed low enough that the heat was not a mass killer.

This is not merely a matter of spoiled picnics. More people die during hot spells in the U.S. than are killed by all other weather events combined, including floods and tornadoes. Add higher summer heat deaths and higher electricity bills to such unwelcome environmental effects of corn production as soil wastage, polluted lake water and dead zones in the Gulf of Mexico, and you begin to ask why corn fields are not regulated by the EPA.

Contact James Krohe Jr. at

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