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Conservation Science for a Healthy Planet

Intensive agriculture caused cooler temps and more rain in US Midwest from 1950-2000

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February 14 2018  read full ScienceDaily article here

…The team showed that there was a strong correlation, in both space and time, between the intensification of agriculture in the Midwest, the decrease in observed average daytime temperatures in the summer, and an increase in the observed local rainfall. In addition to this circumstantial evidence, they identified a mechanism that explains the association, suggesting that there was indeed a cause-and-effect link between the changes in vegetation and the climatic effects.

Eltahir explains that plants “breathe” in the carbon dioxide they require for photosynthesis by opening tiny pores, called stoma, but each time they do this they also lose moisture to the atmosphere. With the combination of improved seeds, fertilizers, and other practices, between 1950 and 2009 the annual yield of corn in the Midwest increased about fourfold and that of soybeans doubled. These changes were associated with denser plants with more leaf mass, which thus increased the amount of moisture released into the atmosphere. That extra moisture served to both cool the air and increase the amount of rainfall, the researchers suggest….

…The findings suggest the possibility that at least on a small-scale regional or local level, intensification of agriculture on existing farmland could be a way of doing some local geoengineering to at least slightly lessen the impacts of global warming, Eltahir says. A recent paper from another group in Switzerland suggests just that.

But the findings could also portend some negative impacts because the kind of intensification of agricultural yields achieved in the Midwest are unlikely to be repeated, and some of global warming’s effects may “have been masked by these regional or local effects. But this was a 20th-century phenomenon, and we don’t expect anything similar in the 21st century,” Eltahir says. So warming in that region in the future “will not have the benefit of these regional moderators.”

Ross E. Alter, Hunter C. Douglas, Jonathan M. Winter, Elfatih A. B. Eltahir. Twentieth Century Regional Climate Change During the Summer in the Central United States Attributed to Agricultural Intensification. Geophysical Research Letters, 2018; DOI: 10.1002/2017GL075604

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