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Crop irrigation could be cooling Midwest

Drop in hot days blamed on moisture from Great Plains

2:02pm, January 22, 2010

ATLANTA — If summers seem cooler and wetter in parts of the Midwest in recent years, you can thank — or blame — farmers, two new studies contend.

While average global temperatures rose about 0.74 degrees Celsius during the past century, the U.S. Midwest has experienced a noticeable slump in summer temperatures in recent decades, reported David Changnon, a climatologist at Northern Illinois University in DeKalb, on January 19 at the annual meeting of the American Meteorological Society.

On average, daily high temperatures in Chicago rise above 90° Fahrenheit (32.2° Celsius) on 24 days each summer. But from 2000 through 2009, only two years tallied more than 24 days hotter than 90°— the lowest decadal total in 80 years, Changnon noted.

Rather than being just a statistical anomaly, the recent cool temperatures seem to be part of a steady long-term decline in summertime highs in Chicago, Changnon and his colleagues found. Th

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