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Soil carbon sequestration

March 21, 2016 | A version of this story appeared in Volume 94, Issue 12

Following the United Nations climate meetings in Paris, soil carbon sequestration has again emerged as a cure for climate change (C&EN, March 7, page 40). This is not a new idea. The potential amount of carbon that can be stored in global soils has been tabulated in numerous Intergovernmental Panel on Climate Change reports. Tens of millions of dollars have been spent on research determining the amounts of carbon that can be stored, the permanence of the storage, and the difficulty of measuring the actual gains in soils.

The recent surge in interest surrounding carbon sequestration has been facilitated by the French 4 per 1,000 (4 parts per thousand) Initiative, which correctly assumes that if all the soils of the world gained 0.4% carbon each year, this will sequester all anthropogenic carbon emissions. It’s an attractive concept: We can temporally keep burning fossil fuel but store the emitted CO2 in soil until the root problem is solved.

There is a flaw with this idea—it’s the equivalent of proposing a perpetual motion machine to solve the problem. No machine can run forever. Friction ultimately holds sway. The same is true for soil carbon.

One can prime the soil carbon sequestration machine by adding more carbon, but the amount of carbon stored in soils is governed by the “friction” of microorganisms, which are stimulated by the additional carbon. Simply, the biggest sequestration of carbon occurs at the beginning of a management change, and it quickly (within tens of years) grinds down to no net gain. Unlike a mechanical machine, the soil carbon sequestration machine has an undesirable additional quality. If—after the soil has ceased to gain more carbon—the farmer gives up on the management schemes, the soil machine will start running in reverse, pumping the stored carbon back into the atmosphere as CO2. Additionally, global warming is already thawing previously frozen reservoirs of carbon in the northern latitudes, reservoirs that dwarf the amount of carbon that can be sequestered by land management.

It is said by advocates of soil carbon sequestration that it is a “bridge” for society as we transition to a carbon-free economy. But now comes the rub: Soil management is not a top-down directive—with all farmers falling in line; it is conducted by billions of individual land managers (farmers) in a complex array of political, economic, and ecological conditions. The unstated assumption that all of these individuals will act in concert for decades is unrealistic. Most of the recent publicity surrounding carbon sequestration comes from government officials or from journalists and environmental advocates. It is a disservice to scientists to ask them to promise what is unrealistic. While improved soil management has many benefits, the solution to atmospheric greenhouse gas concentrations is to rapidly transition from a carbon-based energy sector.

Ronald Amundson
Berkeley, Calif

Editor’s note: To assist educators, C&EN and ACS released an infographic illustrating new National Fire Protection Association guidance for conducting demonstrations and experiments, as well as a video showing how to conduct flame tests using aqueous salt solutions. The resources are available at



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