Don’t count on forests to keep us cool

Scientists have discovered that over the past 25 years, many trees in the far north have been growing more slowly in the summertime.

And that’s bad news if you’re concerned about global warming. Andy Bunn is an ecologist at the Woods Hole Research Center in Massachusetts. Bunn studies boreal forests: conifer trees growing in Alaska, Canada, and northern Eurasia. He told EarthSky that scientists expected to find trees growing faster as Earth warms. In other words, he said, these trees should be ‘greening.’ Instead, biologists say, they’re growing more slowly or ‘browning.’

Andy Bunn: One of the few things that could make global warming less intense than it is is the assumption that as the climate warms, the boreal forests are going to be able to grow more intensely and soak up more carbon dioxide from the atmosphere.

As plants grow faster, they breathe in more of the heat-trapping gas carbon dioxide and store more of it in their roots, leaves, and wood. But the northern forests aren’t growing faster, as expected. They appear to be stressed by increasingly drier air and soil in the summer, which slows their growth and makes them more susceptible to fire and pests. Bunn told us he’s worried.

Andy Bunn: We thought that forests were going to be able to take more carbon dioxide out of the atmosphere and store it in the ground, and we’re in fact seeing that that might not be the case.

Our thanks to NASA: explore, discover, understand.

Our thanks to:
Andy Bunn
Post Doctoral Fellow
Woods Hole Research Center
Falmouth, MA

June 24, 2006

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