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Losses of up to $2 billion per year (10%) in soybean yield is due to rising surface ozone, according to satellite measurements by NASA, as outlined in a recent study. 

Above a threshold concentration, ozone inhibits photosynthesis and reduces yield in soybeans, one of the more sensitive crops to high surface ozone levels. On the left are plants that have been exposed to “clean air” and are healthy, while on the right are plants exposed to ozone that are showing injury.

The study, presented at the American Geophysical Union Joint Assembly meeting, May 24 in Toronto, is based on five years of soybean yields, surface ozone, and satellite measurements of tropospheric ozone levels in Indiana, Illinois and Iowa. It revealed summertime ozone concentrations consistently exceeded threshold levels at which crops are negatively affected. The states, three of the biggest soybean producers in the U.S., account for a large chunk of the country’s $27 billion annual soybean crop. The study estimates damage to the soybean crop – by a yield reduction of approximately 10 percent – of at least several hundred million in some years in those states alone, and possibly more than $2 billion nationwide. 

Climate change scenarios present numerous global problems for agriculture in this century, with the probability of more severe and extended droughts. But there’s also the strong likelihood that as cars, factories and power plants both here and abroad continue to change the fundamental chemistry of the air, the altered atmosphere will negatively impact the biological processes of important crops. 

“In the 19th and early 20th century, background surface ozone concentrations were relatively low so that an increase of 25 percent, (5 to 10 parts per billion), didn’t affect living organisms,” said Jack Fishman, a research scientist at NASA’s Langley Research Center. “But now, we’ve crossed the line where you can expect to see modest increases in surface ozone result in crop growth being stunted.” 

Since the early twentieth century, surface ozone levels in rural areas in the Midwest have doubled, Fishman said. The U.N.’s Intergovernmental Panel on Climate Change (IPCC) predicts that surface ozone concentrations will rise another 25 percent by 2050. In the southern region of the three states studied, peak daytime concentrations often surpassed 60 parts per billion. And so the yields in the southern region definitively suffered. In the northern region of the area studied, averaged concentrations were nearly 20 percent lower, and the impact of ozone was less. 

“Background conditions are rising. Precursor emissions are rising,” said Elizabeth Ainsworth, a professor of crop biology at the University of Illinois. “This is likely to get worse in the future and impact a greater area of the Midwest.”