Soil organic carbon tends to be concentrated in the topsoil. 11ġ Most of the soil mass is not plant matter-it is inorganic material like sand, silt and clay. To stop global warming, these efforts to store carbon must be coupled with drastic cuts in greenhouse gas emissions. Ultimately, scientists say soil-based carbon sequestration, like other negative emissions technologies, can help fight climate change, but cannot take carbon out of the atmosphere as fast as we are currently adding it. This release of CO 2 to the atmosphere could become a self-reinforcing feedback loop, where lost soil carbon warms the Earth, causing soils to release even more carbon. We are already seeing this happen in the Arctic as permafrost, or permanently frozen soil, thaws. The warming of the planet could lead to widespread soil carbon losses by speeding up the decay of soil organic matter. 7-9Ĭlimate change is also making it harder for soils to naturally store carbon. This is a big social and economic challenge, and experts debate how much soil-based sequestration is really possible over the long term.
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To take full advantage of soil-based sequestration as a climate solution, we would need many of them to change the way they farm, now and for hundreds of years in the future. There are hundreds of millions of farmers around the world, mostly farming small plots of land. 6 Limitations of soil-based carbon storage Proponents argue that farming practices that store more carbon can also improve soil health and food production. By breaking up the soil, tilling prepares land for new crops and helps control weeds, but also releases a lot of stored carbon.
Farmers can also do less intensive tilling. “Cover crops” like clover, beans and peas, planted after the main crop is harvested, help soils take in carbon year-round, and can be plowed under the ground as “green manure” that adds more carbon to the soil. For example, perennial crops, which do not die off every year, grow deep roots that help soils store more carbon. Farmers can add more carbon to agricultural soils by planting certain kinds of crops. 5Ĭropland, which takes up 10% of the Earth’s land, is a major target for soil-based carbon sequestration. 4 This has led policymakers to increasingly look to soil-based carbon sequestration as a “negative emissions” technology-that is, one that removes CO 2 from the air and stores it somewhere it can’t easily escape. Scientists have estimated that soils-mostly, agricultural ones-could sequester over a billion additional tons of carbon each year. 3 The question is: Can this trend be reversed at the global scale as part of a strategy to help fight climate change? Storing carbon in agricultural soils Over the past 12,000 years, the growth of farmland has released about 110 billion metric tons of carbon from the top layer of soil 2-roughly equivalent to 80 years’ worth of present-day U.S. If not for soil, this carbon would return to the atmosphere as carbon dioxide (CO 2), the main greenhouse gas causing climate change.īut converting natural ecosystems like forests and grasslands to farmland disturbs soil structure, releasing much of that stored carbon and contributing to climate change.
Especially in colder climates where decomposition is slow, soils can store-or “sequester”-this carbon for a very long time. 1 This means they contain a lot of carbon that those plants took in from the atmosphere while they were alive. Soils are made in part of broken-down plant matter.
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