I always thought the Midwest has hot summers appropriate for growing sweet corn. Still, I wonder about the accuracy of the government charts. Satellite data since the 1970s shows a temperture increase worldwide of 0.13 degrees C. A lot of the so-called warming in the U.S. is because many weather stations once in rural areas have had cities grow up around them. It's called the heat island effect. If I were writing this article, I would first check old newspapers of the 1900s and then of the 1930s to see what actually was going on. The 1930s was Dust Bowl time, but the government map shows it to be rather cool. Actually it was the hottest recent period in the U.S.