While they have a pretty good idea of how much carbon our factories and planes and cars are releasing, scientists are much less certain about the amount of carbon tree-planting will absorb. When you drain or clear the soil to plant trees, for example, you are likely to release some carbon, but it is hard to tell how much. Planting trees in one place might stunt trees elsewhere, as they could dry up a river that was feeding a forest downstream. Or by protecting your forest against loggers, you might be driving them into another forest. As global temperatures rise, trees in many places will begin to die back, releasing the carbon they contain. Forest fires could wipe them out completely. The timing is also critical: emissions saved today are far more valuable, in terms of reducing climate change, than emissions saved in 10 years' time, yet the trees you plant start absorbing carbon long after your factories released it. All this made the figures speculative, but the new findings, with their massive uncertainty range (plants, the researchers say, produce somewhere between 10% and 30% of the planet's methane) make an honest sum impossible.
Tuesday, January 17, 2006
Tree hugging not solution to global warming
George Monbiot has a good summary of recent research showing that tree-planting is not quite the tool for reducing global warming that had been thought: