The first effort to spatially quantify global soil carbon loss revealed that agriculture has removed 133 billion tons of carbon from the top 2 meters of soil, with the rate of loss increasing dramatically in the past 200 years. Those soil carbon losses are nearly equal to total carbon emissions due to forest clearing.
The study was published this week in PNAS, and was led by Dr. Jonathan Sanderman of the Woods Hole Research Center and Tom Hengl of the soil data organization ISRIC.
“The spread of agriculture has created a large carbon debt in soils,” Sanderman said. “It has been difficult to estimate the size and spatial distribution of soil organic carbon loss from land use and land cover change but that is a critical step in understanding whether soil carbon sequestration can be an effective climate mitigation strategy.”
The large soil carbon debt can be thought of as the maximum potential for soils to remove carbon from the atmosphere and act as a natural climate solution. Even realizing only a fraction of this potential would be an important climate mitigation strategy, Sanderman said.
The study also showed that cropping causes more soil carbon loss on a particular parcel of land but because grazing covers so much land surface, total losses from cropping and grazing are nearly equal.
For the study, the scientists used a machine learning-based model, a global compilation of soil carbon data, and the History Database of the Global Environment (HYDE) land use data.