Is Our Favorite Renewable Energy Source A Disaster?

by Bradford Plumer | July 8, 2010

When most people hear the phrase "renewable power," they tend to think of solar panels and wind turbines. But in the United States, the reality is quite different. Right now, the country gets about 8 percent of its power from renewables, and most of that is from large hydropower dams (2.6 percent) and biomass (2.3 percent). And even if Congress were to pass some sort of clean-energy legislation, that would remain the case for the foreseeable future. A recent IIE analysis of the Kerry-Lieberman climate bill found that much of the growth in renewable electricity through 2030 would come from burning wood for fuel. Likewise, if the EPA forced coal plants to limit their emissions, many operators would likely start mixing coal with biomass in their boilers.

On one level, this all makes sense. America has a lot of forests, and we're pretty skilled at chopping down trees. In some areas, like the Southeast, biomass is the most abundant renewable resource around. You can burn wood whenever it's needed—no need to worry about what happens when the wind dies down or the sun sets. And, in theory, it's carbon neutral. A tree grows and absorbs CO2 from the atmosphere. When it's burned for fuel, the CO2 is exhaled back into the air. And when a new tree is planted in the old one's place, the cycle can start anew. Simple, right?

Well, no, not so simple. For a variety of reasons, it's quite hard to make biomass carbon neutral. There's a timing problem, for one. Most trees have spent decades and decades absorbing carbon and growing to full size. Burning that tree sends up all that carbon in an instant. If you plant a new tree, it will again take decades to absorb an equivalent amount of CO2—and in that time lag, there's extra carbon in the air, heating up the planet.

And it gets even more complicated than that, as this excellent article over at Depleted Cranium explains. Yes, all trees eventually die, but they don't necessarily release all of their carbon on death. Acidic soils in pine forests can prevent a full decay of the wood. And some of the biomass can get absorbed into the subsoil, where it reaches a stable state and doesn't decay further. So if you're cutting down and burning a tree because you assume that all that carbon would've eventually gone up into the air anyway, you're running the risk of faulty accounting. (Likewise, many trees absorb carbon into their leaves, many of which then fall to the forest floor and become humus, which essentially keep the carbon locked in the soil.)

Moreover, it's true that many trees get logged anyway to make wood products—everything from paper to furniture—but this wood doesn't necessarily release as much carbon into the air as biomass fuel would. After all, a wooden chair is essentially sequestering its carbon for decades and decades. And discarded wood and paper products don't necessarily fully decay—large landfills help slow the rate of decay of trash down, which can keep carbon locked for decades or more. (Newspapers, for instance, can stay intact in a landfill for 15 years or longer.) At the margins, a higher demand for biomass energy could reduce demand for wood products that, on some level, help keep carbon out of the air.

So there are a lot of complications. Burning biomass can be an improvement over burning fossil fuels from a climate perspective, but it needs to be done carefully—otherwise, it could be even worse for the climate than burning coal. Last month, researchers at the Manomet Center for Conservation Sciences tried to develop a more rigorous accounting method for biomass that took into account a lot of the factors I mentioned above (particularly what the life cycle of the wood would've been in the absence of burning it for fuel). You can read an interview with lead researcher John Hagan here. He notes that, no, biomass isn't unambiguously carbon neutral, but it can be a useful renewable resource under the right conditions, especially if forests are managed properly.

And it looks like people are finally paying attention. Massachusetts, in particular, has been one of the more aggressive states in harnessing renewable power, and it relies fairly heavily on biomass. So it's pretty noteworthy that, this week, the state's energy/environmental secretary, Ian Bowles, ordered a new round of regulations that would force the state to take a closer look at whether the carbon benefits from burning wood for fuel outweigh the benefits of leaving those trees/plants in place. It seems like an arcane rule change, but seeing as how biomass is expected to play such a outsized role in a cleaner-energy world (at least for the next two decades), this sort of scrutiny is going to be hugely important.

More: And if you want to see how bad things can get, check out this new report from the Environmental Working Group. Thanks to the widespread assumption that any old method of burning trees and biomass is "carbon neutral," EWG warns, various renewable-power standards could lead to the clear-cutting of between 18 million and 30 million acres of forest by 2025. And, yes, that would kick up a lot of extra carbon into the air.

(Flickr photo credit: Steve Roe)

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