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Could we help plants remove more CO2 from the atmosphere by harvesting them and storing their carbon?
Yes—it’s called “bioenergy with carbon capture and storage” (BECCS). But it would take a lot of land to make a meaningful difference on climate change this way.
March 8, 2023
Plants take in carbon dioxide (CO2) as they grow, which is why forests are valuable carbon “sinks” that keep CO2 out of the atmosphere and stop it from contributing to climate change. But plants absorb CO2 fastest when they’re young and growing, and when they burn or decompose, their stored CO2 is released. Is it possible, then, to accelerate the process by harvesting plants early and storing their carbon safely out of the atmosphere?
Yes, although we wouldn’t want to do this in natural ecosystems. The most practical version of this idea is called “bioenergy with carbon capture and storage” (BECCS), which is being studied by MIT researchers including Jennifer Morris, a principal research scientist at the MIT Joint Program on the Science and Policy of Global Change and the MIT Energy Initiative. The idea of BECCS is that plants would be grown, harvested, and then combusted to create energy in the form of electricity or liquid biofuels. The CO2 created when the plants are burned would be captured and stored underground. The end result is the removal of some CO2 from the atmosphere.
“As we look at the growing focus on net zero emissions, there comes a point where you have to start thinking about negative emissions,” Morris says. “So what are carbon dioxide removal technologies that could potentially be feasible? That’s where something like BECCS comes in.”
A BECCS project would not remove towering old trees from established forests, Morris says. That would disrupt and harm ecosystems in countless ways. Instead, she says, BECCS would involve planting crops such as switchgrass or miscanthus that grow (and take in carbon) quickly, while needing neither prime cropland nor a large amount of fertilizer or irrigation.
Morris says most of the necessary technology already exists. Carbon capture systems for grabbing CO2 when plants burn are already mature, because they were developed to reduce the carbon emissions from fossil fuel power plants. So when a plant like switchgrass is burned to make electricity, more than 90 percent of the resulting CO2 can be captured. In addition, Morris says, the planet is abundant in the kind of geologic formations where captured CO2 could be injected underground to keep it out of the atmosphere.
All in all, BECCS works a lot like “direct air capture” of CO2—except that instead of using energy-intensive machines to suck CO2 out of the air, we would let plants do it for us (and even get some energy when we burn them).
The biggest question for BECCS is simply where to find enough land to make a difference on climate change. Morris coauthored a study that modeled the impacts of BECCS on a global scale,1 and found that the planet has enough under-utilized land to make the project possible with only a small effect on prices for food and livestock. However, she says, much of the best land for growing BECCS crops lies in Africa. This raises ethical issues about whether the developing world should have to “undo” carbon emissions created mostly by richer industrialized countries.
On the other hand, many landowners could make a profit trying BECCS—at least, in a future where governments are willing to pay them for the service of permanently taking CO2 out of the atmosphere.
“The carbon credit value that these negative emissions would create far overshadows the value of the energy product that it would create,” Morris says. “So even if you took away the electricity that you would be generating in the process … you would still want to produce tons of BECCS because of the carbon credit. That's the economic driver."
Thank you to Hans van Dam of Veenendaal, Netherlands, and Andrew Carver of Oxford, United Kingdom, for sending in variations of this question. You can submit your own question to Ask MIT Climate here.
1 Fajardy, Mathilde, et al. "The economics of bioenergy with carbon capture and storage (BECCS) deployment in a 1.5 °C or 2 °C world." Global Environmental Change, Vol. 68, May 2021, doi:10.1016/j.gloenvcha.2021.102262.