To the Editor

The calculations offered by Quinton et al.1 raise the unfortunate notion that soil erosion generates an unintentional benefit for climate, owing to the long-term burial of soil organic carbon. But limiting the assessment of the impact of soil erosion on climate change to organic carbon burial ignores, apart from economic and social damages, the coupling between biogeochemical cycles. For example, the eroded nitrogen has to be replaced, at least in part by artificial fertilizers, to maintain soil fertility. At this point the carbon and nitrogen cycles meet, because the production of fertilizer generates greenhouse gases; the production of one ton of fertilizer in the United States generates more than 850 kg of carbon dioxide2. Applying this number to the estimate by Quinton et al. of the amount of nitrogen lost owing to erosion each year1 yields carbon dioxide emissions of 0.02–0.04 Pg yr−1. These emissions correspond to 15–30% of the organic carbon buried owing to soil erosion1,3. Obviously the full complexity of biogeochemical cycling on agricultural land is not reflected by the crude calculation above. However, the example illustrates that all greenhouse gas fluxes affected by agriculture should be considered when assessing the impact of soil erosion on global biogeochemical cycles and climate.