Biochar has the potential to offset 12 to 14 percent of global CO2 emissions. 2021-12-03 05:48:59
By Steve Wilent
Biochar is nothing new. The indigenous people of the Amazon Basin began using it at least 2,500 years ago, and the terra preta soils they created are still highly productive. Today, interest in biochar’s utility as a soil amendment and in stormwater filtration, environmental remediation, and other applications is strong—see the sidebar on page 9 for examples. In November 2021, a team of biochar producers, practitioners, scientists, and engineers produced Biomass to Biochar: Maximizing the Carbon Value, a paper describing their investigations into the many uses for biochar, including its potential as a means of slowing climate change by storing carbon in soils.
The authors conclude that the conversion of biomass to biochar shows significant promise as one of a suite of climate change mitigation strategies and offers the possibility of near-term, widespread deployment. They conclude that biochar has the potential to offset 8 percent to 19 percent of CO2 emissions in the state of Washington. In an interview for NRM Today, lead author Jim Amonette said that biochar has the potential to offset 12 percent to 14 percent of global emissions.
“That’s at maximum production rates, and we have a long way to go before we get there,” said Amonette, a researcher with Washington State University’s Center for Sustaining Agriculture and Natural Resources and the US Department of Energy’s Pacific Northwest National Laboratory. “There are some people who think we can get offset two or three times as much, though I haven’t yet seen full evidence to support that. But we don’t know all the things that we can do with biochar to offset emissions. We’re always looking for the silver bullet. With climate change, there just isn’t one. Biochar is what we call a ‘wedge’ that we can use to fight climate change.”
[Editor’s note: What’s the difference between atmospheric carbon dioxide and the carbon stored in biomass—trees and forest products? The Maine Woodland Owners Association explains in a brief article, “Carbon in Wood Products—Translated to Plain English.”]
Biochar is the carbon-rich solid produced by heating biomass—wood from forest thinning or fuels reduction projects, for example—under low-oxygen conditions to a temperature at which its chemical structure transforms to a more stable form. In addition to its climate benefits, the authors say, biochar has potential to improve forest and soil health, decrease wildfire risk, bolster ecosystem services, and revitalize rural economies. Their research was supported by the US Forest Service and the Washington Department of Ecology’s Solid Waste Management Program.
“It really boils down to what effects you’re looking for,” said Amonette. “If you’re just looking for a place to store some carbon, so that it doesn’t go back into the atmosphere for a while, you can make biochar and put it just about anywhere. It’s a stable form of carbon.”
For using biochar in agricultural applications, Amonette says his number one rule is, “First, do no harm.”
“You want to make sure that you don’t put a high pH biochar on a high pH soil, for example, because then you’ve just exacerbated your problem,” he said. “On the other hand, if you have an acid soil and you want to raise the pH—say, wheat land in the Palouse country of eastern Washington, where they’ve applied nitrogen fertilizers for something like a hundred years—using biochar is just another way of liming. That makes perfect sense. It may not make economic sense, but from the standpoint of using it as a liming agent, that might be a good option. If you’re looking for big yield increases, you generally see 10 percent to 15 percent yield increases on average, depending on the crop. It’s more the specialty crops, the high-value crops, where you’d want to focus on applying biochar.”
Cannabis is one such high-value crop. Cannabis growers, legal and otherwise, often use biomass as a soil amendment.
What about using biochar as a soil amendment in forests?
“There’s relatively little known about using biochar in forests. If you are thinning a forest, it might make sense to put the biochar right back into the forest that you got it from, rather than trying to haul it someplace else. But there is a lot of research that needs to be done in this area,” said Amonette.
Amonette and his coauthors discuss the avenues of biochar research that ought to be followed.
“We need to answer questions such as where we can get the maximum yield increase and which biochar production method will offer the best climate offsets,” he said.
Carbon Out, Carbon In
Examining the carbon storage potential of biochar in climate change mitigation was one of the authors’ main goals.
“You could have two [batches of] biochar that are identical from a chemical perspective and behave the same when put into soil, but the way they are made could have a huge difference in their carbon footprints. You need to look at carbon from the biomass all the way through to the application in the field as biochar—don’t just start with the biochar,” said Amonette, who is working on a paper in which he will assess the various means of producing biochar in terms of carbon emitted during the production process and carbon stored in the resulting biochar.
“The other issue, of course, is the ultimate fate of that biomass,” he said. “Say you’ve got a dead tree in a forest that was killed by beetles. It could be consumed by fire, it could be cut down and allowed to decay in place, or it could be harvested and used to make biochar. If it’s burned in a wildfire, there’s no question that biochar, almost no matter how you make it, is the better option.”
One indication of biochar’s effectiveness as a means of storing carbon is its half-life.
“You’re going to have 95 percent, if not 99 percent, of the carbon in the biochar that you started with still in the soil 100 years later, if the biochar is produced at the right temperature and you end up with a high-quality biochar,” Amonette said. “In our global model, we assumed about a 300-year half-life for biochar carbon, but there are some people who say it may be higher—perhaps a 1,000-year half-life—and some people who say it will be lower. We think a 300-year half-life is a good average.”
Regardless of the half-life of the carbon stored in the form of biochar, the sooner that carbon is stored, the better, he said.
“The way I view it is that we just need to get through the next century or two, and a lot is going to happen in the next 50 years. So if we can stash away a lot of carbon for 100 or 200 years, then we’re good.”
And soil isn’t the only place where biochar can be used as a store of carbon. For example, it can be added to concrete or asphalt.
“If we really crank up biochar production, we’re going to run out of places to put it in soil in the next 60, 70, 100 years,” said Amonette. “So we’re going to have to find other things to do with it. Asphalt and concrete are excellent places to put it, and I’m sure we’ll find other places for it. Biochar is a very interesting material.”
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