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Burying Trees: Brilliant Or Crazy?

Usually, when anyone claims to have a simple, elegant solution to the problem of runaway greenhouse-gas emissions that doesn't require a massive restructuring of the world's energy policies, well, I narrow my eyes and keep a hand on my wallet. But New Scientist has a story that sounds... well, let's just call it "eyebrow raising." Ning Zeng, a climatologist at the University of Maryland, recently published a paper suggesting that if we just buried enough trees underground, we might be able to sequester enough carbon to offset most (or even all) of the world's fossil-fuel emissions.

Wait... what? Zeng estimates that, each year, some 60 gigatons of carbon is temporarily sequestered in plant life, which is then continuously returned to the atmosphere when those plants die and decompose. If you could bury, say, a bunch of trees underground before they decompose, that carbon would be stored for a significantly longer period of time—and voila, you've pulled it out of the cycle. In theory, you could bury a good portion of the dead trees lying around on forest floors for a massive one-time reduction, and then start (very selectively) thinning out existing forests and entombing some of those trees underground to create a continuous carbon sink. No fancy technology necessary.

Fine, but would this make sense as a policy? Zeng estimates that a "sustainable" harvest of this sort could, potentially, sequester up to 10 gigatons of carbon per year (by comparison, fossil-fuel consumption coughs up about 8 gigatons of carbon per year). Offsetting the world's manmade emissions would require about 2 million people to get to work—still less than are employed by the U.S. forestry industry alone—and cost about $250 billion per year. Of course, that's far, far less than the damage that would be caused by unchecked global warming, and less, it seems, than it would cost to pump the carbon captured from coal-burning plants down into disused oil wells and underground caverns—the big idea of the moment.

But that's just the theory. There are some huge potential problems here. As Zeng himself concedes to New Scientist, burying wood in the wrong types of soil could generate methane—an even more potent greenhouse gas than carbon dioxide. In some areas, termites could start munching on the buried wood and release the carbon back into the atmosphere. Not to mention the fact that you're taking key nutrients out of the ecosystem. Even worse, clearing dead wood away from forest floors on such a large scale could, if done clumsily, wreak havoc on a number of habitats. That's probably my biggest worry: This isn't mass deforestation, but a forest-management scheme of this sort could very easily be abused, and almost certainly would in practice.

So, no, there's no free lunch after all, and it would need a lot more scrutiny before governments ever decided to try this—the ongoing biofuels fiasco should act as a cautionary tale here. And it'd be extremely short-sighted for the world to pursue something like this instead of curtailing its fossil-fuel consumption. My guess is that biomass burial, if done right, could play a very modest complemetary role—make the task of mitigating climate change a wee bit less impossible—but certainly isn't a major solution. Still, I have to admit, this sounds more promising than some of the other ideas that have been floated lately, especially since the technology to capture and sequester carbon from coal-fired plants remains... well, "elusive" is putting it gently.

--Bradford Plumer