Agriculture and the Abatement of "Record" CO2 Emissions Levels - Pt. 2

This is Part 2 of the series on agriculture's contribution to the mitigation of global climate change. Here we'll be discussing the value of agricultural soil carbon sequestration in reducing atmospheric levels of carbon dioxide.

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There are three ways to reduce fluxes of carbon dioxide to the atmosphere.

1. Stop producing as much electricity and other industrial output, and stop driving your car. 
2. Use technological advances to make electrical production and fossil fuel combustion less carbon-intensive.
3. Figure out a way to stick that carbon someplace where it cannot contribute to global climate change.

Option #1 is completely undesirable, although, certainly, we could all afford to scale back on our electricity and gasoline consumption. Option #2 is very promising, but technological advances take time and lots of research, so as a solution, it's hit-or-miss. Option #3 sounds like science fiction. How would you even go about sticking carbon someplace where it can't contribute to global warming?

Turns out that, of all the options, #3 is both the most possible and practical. In fact, row crop farmers all over the world have been doing this for decades by using no-till production systems on their land or by retiring their land from agricultural production.

No-till is a farming practice which, obviously, eliminates or reduces the amount of tillage operations performed by a farmer. Keeping the corn stalks, cobs, and other residues on the surface of the soil creates numerous benefits for the farmer by lessening erosion of valuable topsoil and reducing labor and equipment costs associated with several passes of tillage equipment. No-till also encourages carbon sequestration; by not tilling the land, carbon stored in agricultural soils stays in the soil, rather than drifting up to the atmosphere upon disturbance from plows and disks.

The use of no-till has the potential to sequester vast amounts of carbon, as agricultural soils are a massive carbon sink. Further, farmers can potentially save significant amounts of time, labor, and equipment wear and tear through reducing the number of passes over their fields. As such, carbon trading schemes both in the U.S. and abroad have been more than eager to include no-till as an eligible offset-generating practice.

If all of this sounds too good to be true, though, it is. Plenty of research on the subject has shown that the greenhouse gas (GHG) benefits that result from implementation of no-till are small or even nonexistent. Some research has shown that no-till actually increases global warming potential by increasing fluxes of nitrous oxide (N2O), a GHG that is nearly 300 times as potent as carbon dioxide. Further, carbon stays sequestered in the soil profile only as long as the soil remains undisturbed by tillage implements; the second someone plows their no-till field, all of those benefits from carbon sequestration are lost. Finally, soils can only hold so much carbon, meaning that one essentially has to pay farmers forever to maintain no-till systems even after those systems stop sequestering new carbon. All of these considerations may limit the usefulness of agricultural carbon sequestration.

Fortunately, there are other means to achieve more permanent soil carbon sequestration. The journal Environmental Science & Technology published an article online this morning that talks about the potential for capturing carbon dioxide emitted from power plants and sticking it in deep geological formations, thereby effectively preventing it from contributing to global climate change. Even more impressive, this process has the potential to sequester 500 years worth of carbon emissions from every stationary source in the country at 2009 emissions levels. While still a long way away from practical reality, geologic carbon sequestration (GCS) has some serious potential to help limit contributions to global climate change. Because the sequestration is permanent, this type of mitigation strategy has some serious potential to steal agriculture's thunder as an instrument to fight climate change.

The general conclusion is that more research is needed before agricultural carbon sequestration can be included as a carbon-mitigating practice with any confidence. Fortunately, agriculture still has the potential to play a significant role in the abatement of greenhouse gases, particularly through the abatement of N2O. The next post in the series will further delve into this role.

For more on this series:
Part 1