In the near future, China could increase its winter crop yields by roughly 25% and its summer crops by 15%, while Western Europe could increase winter yields by roughly 9% and summer crops by about 11%. The catch? They’d have to cut the air pollutant class of nitrogen oxides—found in both vehicle exhaust and industrial emissions—by half of their current levels.
This is the takeaway from research recently published in the journal Science Advances by David Lobell, PhD, the Gloria and Richard Kushel Director of the Center on Food Security and the Environment at Stanford in Palo Alto, Calif., and his team.
The main message of the paper is that nitrogen dioxide, a principal form of nitrogen oxides and key indicator of the presence of others, is consistently harming crop yields around the world, says Dr. Lobell. “Losses from nitrogen dioxide are often 10% or more, which is a big number in agriculture; 10% is roughly the yield loss that a significant drought would cause,” he says. “This finding is significant because this study is the first time we have been able to measure the exposure of crops to nitrogen dioxide over large scales in many regions.”
Dr. Lobell notes that, due to the U.S. Clean Air Act and other North American environmental protections, limits to nitrogen oxides have already brought crop yield gains to this continent. His team’s findings centered on potential gains in crop yields in China, but also predicted significant yields in Western Europe, as well as India, which could see crop yield gains of 8% in summer and 6% in winter following a 50% reduction in nitrogen oxides.
Thomas Sharkey, PhD, a professor in plant biology at Michigan State University in East Lansing, says the research by Dr. Lobell and his team connects a series of dots that have always been present. “But I would say they’ve never been connected so well,” he says.
Dr. Sharkey says that this research begins with the need to reduce the production of ozone, which inhibits crop growth. Ozone is generated through the combination of hydrocarbon, nitrogen oxides in the air, and sunlight. “A lot of work has been done showing how ozone inhibits crop growth,” he says, “but the people studying the ozone haven’t gone that next step and said, ‘Where did that ozone come from?’ It comes from nitrogen oxides that are around.”
The other half of the equation is hydrocarbon, which is produced by trees and other plant matter. “The hydrocarbons are unavoidable; that means that we need to address the nitrogen oxide pollution,” Dr. Sharkey says. “That’s how we can get rid of ozone. This paper now connects for us in a way that hadn’t been explicit that, because you have nitrogen oxides you have ozone, and because you have ozone, you have crop damage.”
Dr. Lobell’s paper also contained a wholly unexpected finding: Nitrogen oxide has the capacity to reduce crop yields on its own, independently of its role in ozone production. “That was a surprise,” says Dr. Sharkey. “I don’t think anyone would’ve necessarily predicted that.”
Fortunately, Dr. Lobell believes that the boosts to crop yields are achievable, noting that nitrogen oxides is the product of fossil fuel sources that are already the target of reductions from many sides; however, he says, “I don’t think crop yield gains alone would have to justify the investment, since the benefits for local human health are often many times the cost of changes. The crop yield gains are more like icing on the cake.”