Headline last week: Plants Making Global Warming Worse!
Headline this week: Plants Cooling Midwest!
Both studies state that plants affect climate via water vapor - but last week the water vapor was to be increasingly retained by plants thus increasing warming, and this week water vapor is being increasingly released by plants to decrease warming.
Are farmers cooling Chicago's summers?
May 11, 2010|By Joel Hood, CHICAGO TRIBUNE
Amid one of the warmest springs on record in Chicago, and renewed worries about our warming planet, how is that late summer days across the Midwest are cooling?
The answer may be in the towering, tightly packed rows of corn that blanket Illinois at harvest and the ripple effects from industrialized farming that scientists are only beginning to understand.
In the last 80 years, those lazy, late summer days in July and August have been getting cooler and wetter throughout much of the Midwest. In Chicago, temperatures reached 90 degrees or higher 344 days during the 1930s, but only 172 days in 2000-09.
In place of those dry, 90-degree scorchers are the kind of lingering 80-degree days with higher humidity that don't cool down much at night. Climate scientists say the cause is rising dew-point levels — the measure of water vapor in the atmosphere.
These high dew-point levels are important, said David Changnon, a climate scientist at Northern Illinois University who helped pioneer this research, because even though the temperature is lower, the heat index is higher. And that's bad news for many city dwellers, since those conditions contributed to the deadly heat waves that hit Chicago in 1995 and 1999.
Already, these cooler but muggy late-summer days are likely to be producing more powerful thunderstorms and periods of heavier rain that bear watching, Changnon said.
"While we're seeing fewer really hot days, we've created dew points in Chicago and around the Midwest that are unheard of," Changnon said. "And it begs the question, 'How the heck can we do that?'"
Changnon's theory, backed by more than a decade of research, is that more densely planted corn and soybean fields scattered across the Midwest are changing the regional climate by releasing more water vapor into the atmosphere. The more water vapor that reaches the atmosphere, the higher the dew point, and the fewer extremely hot summer days.
In other words, while some still question whether people are to blame for changing weather patterns around the globe, farmers around the Midwest are already altering the region's climate in significant ways, Changnon said.
"It's a different type of human-induced climate change that has certainly played a role in the changes to Illinois' weather," said Jim Angel, a climatologist at the Illinois State Water Survey in Champaign. "It's kind of an interesting way to look at all this."
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