A Montana State University researcher says no-till practices and a trend toward removal of fallowed acres may be contributing to cooling in the northern Plains that contradicts the so-called global warming trend. 

Paul Stoy’s current research focuses upon the benefits believed to be brought about through planting crops instead of leaving fields unplanted for a growing season, a practice known as fallowing. 

In the Northern Great Plains, farmers have reduced the amount of land held in fallow in favor of no-till planting techniques, which may be responsible for the region’s decades-long cooling trend, says the assistant professor of land resources and environmental sciences at Montana State’s College of Agriculture. 

“There is a large region in the Dakotas that extends well into Canada that has been cooling in summer, which bucks the global warming trend,” Stoy says. “Very few people have studied the mechanisms that underlie this, and that’s partly because it’s so difficult to model cloud formation and convective precipitation.”

A fallow field can only lose carbon to the atmosphere because there’s no carbon input, only respiration of carbon dioxide into the atmosphere, he says. Soil with lower carbon content is of lower quality. 

“Tens of millions of hectares that used to be kept fallow in the summertime are now planted, so there’s more water entering the atmosphere and less heat,” Stoy says. “This is likely underlying the increase in cloudiness and precipitation, and the cooling trend that people have been seeing only in the summertime.”

The elimination of fallow may have brought about a “win-win-win” situation for farmers and other inhabitants of the region, he adds.

“If you’re practicing no-till agriculture rather than fallowing, you’re probably conserving soil, you’re probably making money because you’re planting and harvesting a crop, and you’re probably helping bring about summertime cloudiness and rain,” Stoy said. “There’s a decrease in the number of extreme temperature events that can cause crop damage, and it’s adding some moisture to the system, which can benefit crop yield.”

Linking what Stoy describes as the “fallow reduction phenomenon” to the 40-year summertime cooling trend throughout the Northern Great Plains could help people make land-management decisions that benefit crops as well as climate.

“If the maximum temperatures are decreasing and there is an increase in summertime precipitation, that can be huge,” he said. “Some places are seeing a net gain of about an inch of precipitation during summer, which is a lot for a dry region. The more we understand these trends, the more we can make concrete recommendations to producers. Because, after all, this February was the warmest month on record and the previous warmest month was January.”

Stoy recently received a $500,000 CAREER Award from the National Science Foundation, the NSF's most prestigious award to support early career development of faculty researchers. The grant will further the work of Stoy, who studies the exchange of water, energy and trace gases between the land surface and the atmosphere. His work quantifies how land-use change and land management, including conservation, impact climate.