eric_cherry blossomsBackyard trees may not accomplish much, but forests soak up vast amounts of carbon. In fact, some people argue that trees and native plant communities may be one of our best remedies for climate emissions. Unfortunately, forests not only store a lot of carbon, they can also emit a lot carbon.

Take California’s redwood country, for example. Data from the North Coast Air Basin shows astonishing carbon emissions from a typical year of forest fires in just three counties. Enough, in fact, to equal 367,000 average American cars on the road. And this in a region with just 167,000 souls.

Here’s the down-low. Experts estimate that forest fires in Del Norte, Humboldt, and Trinity Counties were responsible for more than 1.8 million tons of carbon-dioxide over the decade from 1994 to 2003. Not only that, but fires kicked out more than 56,000 tons of methane, which is roughly 23 times as climate-potent as carbon-dioxide. All that adds up to nearly 2 million tons of carbon-dioxide-equivalent climate pollution. (Major hat tip to Lynn Jungwirth, who emailed me the data.)

Of course, the emisions from fires is really only half the story of forests. It’s debits, but not the credits. Northern California’s forests stored carbon during that period too (“sequestered” it, as they say in the biz). Just how much? Well, it’s hard to be certain. And that’s part of the problem.

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  • As North America gets serious about climate change, there’s growing interest in understanding the role of forests (and land use change more generally). That’s as it should be. But we should also acknowledge the big uncertainties that are inherent in dynamic ecosystems.

    One big risk is counting forest carbon storage as a plus—an “offset” to our emissions—but then not counting their emissions when they burn. We shouldn’t treat trees as permant carbon storage if, in fact, they’re not.

    And in truth, at least as I understand the state of play, it’s very hard to know the extent to which forests are permanent carbon storage vehicles. In fact, some research suggests that climbing temperatures may turn big carbon sinks, like Pacific Northwest forests, into carbon sources.

    Depending on how climate change plays out, hotter (and drier and longer) summers could lead to more wildfires, and therefore more emissions. Spreading forest pests, probably linked to warmer winters, can kill vast tracts of forest, simultaneously reducing carbon uptake and increasing susceptibility to fires and logging.

    So before we start banking on forests to do our climate work for us, we need to get serious about answering some quesions. Do forests permanently store carbon? And, if so, how can we verifiy the amount (and changes to the amount over time)?

    Surely afforestation adds to the world’s carbon storage, but what about a mature forest? Is it a carbon sink, a source, or a steady state?

    Now, I’m not saying that the right solution to ignore forests. Not at all. The questions I’m posing all have answers. We just need to figure out what they are.

    Timely update, 2/13: In yesterday’s throne speech, BC premier Gordon Campbell announced that the province will use forest offsets to help address climate emissions. The Vancouver Sunarticle is pretty short on details, but it sounds like the offsets would come mostly from afforestation projects.