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A new study finds that scaling back grazing on most pastureland worldwide would dramatically increase the amount of carbon stored in soils.
By thinning grasses, cows, sheep, and other animals reduce competition for sunlight and nutrients. This spurs the growth of new grass, which conveys carbon from the air into the soil. But too much grazing can denude fields and dredge up carbon stored in the ground.
“When you cross a threshold in grazing intensity, or the amount of animals grazing there, that is when you start to see sort of a tipping point,” study coauthor César Terrer, of MIT, said in a statement. “Basically you lose a lot of the carbon that you have been locking in for centuries.”
For the research, scientists gathered data on the impact of grazing from dozens of studies undertaken across the globe. They then built a computer model to determine the point at which pastureland shifts from carbon sink to carbon source. The model showed that, since the 1960s, excessive grazing has let loose 46 billion tons of carbon. By comparison, the burning of fossil fuels unleashes around 10 billion tons yearly.
Scientists also gauged how much carbon soils would store with the optimal amount of grazing. If farmers scaled back grazing on 75 percent of pastureland worldwide and scaled up grazing on the rest, the study found, those lands would lock away 63 billion tons of carbon. The findings were published in Nature Climate Change.
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