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Harvest Public Media is a reporting collaboration focused on issues of food, fuel and field. Based at KCUR in Kansas City, Harvest covers these agriculture-related topics through an expanding network of reporters and partner stations throughout the Midwest.Most Harvest Public Media stories begin with radio- regular reports are aired on member stations in the Midwest. But Harvest also explores issues through online analyses, television documentaries and features, podcasts, photography, video, blogs and social networking. They are committed to the highest journalistic standards. Click here to read their ethics standards.Harvest Public Media was launched in 2010 with the support of a grant from the Corporation for Public Broadcasting. Today, the collaboration is supported by CPB, the partner stations, and contributions from underwriters and individuals.Tri States Public Radio is an associate partner of Harvest Public Media. You can play an important role in helping Harvest Public Media and Tri States Public Radio improve our coverage of food, field and fuel issues by joining the Harvest Network. Learn more here.

Study: Intensive Agriculture Drives Midwest Climate Changes

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Amy Mayer/Harvest Public Media
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A study tries to understand how much intensive agriculture has contributed to climate change in the Midwest.

As agriculture intensified in the 20th century, summers in the Midwest became wetter and cooler.  An MIT study published this month looked at whether vegetation from crop production, rather than greenhouse gas emissions that are an established source of climate changes, could have driven these regional impacts.

“We provided very strong evidence that agricultural intensification is a stronger forcing of these observed changes than greenhouse gas emissions were,” says lead author Ross Alter, who conducted the research as a postdoctoral associate at MIT and is now a research meteorologist with the U.S. Army Corps of Engineers in New Hampshire.

“People don’t often put agricultural changes and greenhouse gas emissions in the same vein,” Alter says. “The greenhouse gas emissions are a much larger, globally, forcing.”

In the central United States — a region the study defines as a box encompassing the eastern Dakotas and Nebraska through Michigan and western Ohio, then stretching north to mid-Minnesota and south into Kansas and Missouri — the significantly higher number of plants on the landscape produced changes inconsistent with other parts of the world at similar northern latitudes, which don’t have the combination of temperature decreases and rainfall increases.

Alter says more crops equals more photosynthesis and more water used by plants. All of that contributes to increased rainfall and humidity and cooler temperatures because of increased evaporation — rainfall consumes so much sunlight (solar energy), there isn't enough left to raise the air temperature. 

Iowa State University agronomist Rick Cruse, who also is the director of the Iowa Water Center, has worked on projects with climate scientists in the past, though he was not involved with the MIT study.

“This study suggests that there’s evidence that, yeah, we might ought to be considering agricultural impacts" when using models to predict how the climate may continue changing, he says.

But Cruse also suggests that irrigation is a place to look at, considering it has allowed crops like corn and soybeans to grow in arid environments where previously they couldn’t.

To compare current and historical land use for this purpose, he says, it’d be important to know the type and density of historical vegetation and where water is coming from to allow row crops today. It’s the movement of water on the landscape and the resulting transpiration of water from the plants that puts more moisture in the air, he says, leading to increases in rainfall and moderating the temperature.

“I don’t know that you can question bushels per acre as a means of water that’s being lost to the atmosphere,” Cruse says, “especially if you’ve had complete canopy cover in those areas in the past. It’s the expansion in areas that didn’t have water before that I think will have a bigger impact.”

The research also indicates agriculture may have masked potential increases in temperature that the greenhouse gas emissions alone might have caused.

You can watch a video about the study here.

Follow Amy on Twitter: @AgAmyinAmes.