Three million years ago, there were no humans, global temperatures were possibly four degrees celsius warmer and sea levels were high enough to cover most of modern-day Manhattan. This was also the last time in geologic history that global atmospheric carbon dioxide (CO2) levels exceeded 400 parts per million (ppm), a benchmark that was permanently and ominously passed once again in 2016.
Carbon emissions, largely as a result of burning fossil fuels, are not likely to halt anytime soon. Some scientists have started organizing backup plans; most notably, finding a way to grab some of this atmospheric carbon and store it in the Earth.
“The critical thing at this point in time is to reduce emissions as rapidly as we are able to do so. However, in the event that we cannot, as a global community, manage to reduce emissions fast enough, we will still end up with a surplus of CO2 in the atmosphere that we need to deal with,” said Dr. Dominic Woolf, soil and crop sciences, and lead author of a recent study that focussed on a new way to sequester more CO2 into the Earth and out of the atmosphere.
“We need a plan B, because it looks like we may not get there fast enough or quick enough. Plan B is how we get that carbon back down out of the atmosphere,” Woolf said.
Plan B, in Woolf’s case, is to use a “Biochar-Bioenergy System” . BCBES involves using a technique called pyrolysis, the burning of plant material in the absence of oxygen. By doing so, half of the original carbon in the plant remains in the leftover biomass, now called biochar.
BCBES has been proposed by Woolf and other researchers as a substitute for “Bioenergy with carbon capture and storage” , a similar method of carbon sequestration that captures CO2 from plants through combustion.
Although BECCS may be a more effective way to remove and store CO2, there are several advantages to using BCBES instead. A bioenergy capture system requires a large carbon transportation network and therefore a lot of capital for infrastructure, while a biochar system could be implemented in more remote areas.
Biochar can also be added to infertile soils in order to increase agricultural productivity, which could be used to offset some of the costs associated with BCBES.
“Plants already draw down 10 times as much carbon as we’re emitting at the moment globally,” Woolf said.
Under normal conditions, approximately 90 percent of that carbon would be returned to the Earth or atmosphere through burning or plant decay over a three year period. Pyrolysis, on the other hand, releases 50 percent of plant carbon instantly, but stores the rest in biochar for a significantly longer duration.
Woolf suggests using BCBES and BECCS in tandem for now, transitioning to using BECCS once it becomes more economically viable. Other carbon sequestration techniques, such as reforestation or direct carbon capture, either require too much land and money to implement or are too under-developed to be used immediately.
However, Woolf stresses that the main goal right now must be to reduce CO2 emissions and said that these proposed techniques are not a panacea for the warming climate. Keeping CO2 levels under 450 ppm is critical, as scientists have warned that crossing that threshold will likely have irreversible effects on the environment. In order to do so, Woolf urges that “we’ve got to move rapidly and drastically as a global effort.”
“By 2100, our key driving motivation must be to keep any change that does happen within manageable levels and the more we can mitigate, the better it is. And it’s clear that bioenergy-biochar systems will have a role to play in that,” he said. “The less we manage to reduce emissions, the larger the role these other technologies will have to have. But we shouldn’t see them as a get-out or a substitute for reducing emissions.”