Our recent oppressive heatwave that swept through the Upper Midwest has a lot of people referring to our extreme humidity levels as 'tropical'. But in all reality, the excessive moisture in our air was impacted by something much closer than the tropics.

In fact, it's growing all around us in this part of the world.

Our main cash crop is to blame. Weather experts call it 'corn sweat'.

It's a phenomenon that is actually called 'evapotranspiration', but whatever you call it it's caused by the gaseous vapor released by corn growing in the fields. High levels of humidity transported in from the Gulf of Mexico pass over these fields and absorb that extra moisture along the way.

That leads to extreme dew point levels (a measure of how much moisture is in the air) and outrageous heat index values.

The National Weather Service estimates that corn can add enough water to the atmosphere and to boost dew points by five to 10 degrees.

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