May 7, 2010

No Help from the Plant Kingdom

For those of you hoping that plants would somehow come to our rescue and save us from global boiling by sucking all that extra carbon dioxide out of the atmosphere, I'm afraid you're out of luck (via Science Daily):
Trees and other plants help keep the planet cool, but rising levels of carbon dioxide in the atmosphere are turning down this global air conditioner. According to a new study by researchers at the Carnegie Institution for Science, in some regions more than a quarter of the warming from increased carbon dioxide is due to its direct impact on vegetation.

This warming is in addition to carbon dioxide's better-known effect as a heat-trapping greenhouse gas. For scientists trying to predict global climate change in the coming century, the study underscores the importance of including plants in their climate models.

Plants give off water through tiny pores in their leaves, a process called evapotranspiration that cools the plant, just as perspiration cools our bodies. On a hot day, a tree can release tens of gallons of water into the air, acting as a natural air conditioner for its surroundings. The plants absorb carbon dioxide for photosynthesis through the same pores (called stomata). But when carbon dioxide levels are high, the leaf pores shrink. This causes less water to be released, diminishing the tree's cooling power.
That is what's a called a negative feedback loop -- and it's not helpful. Do note that current climate models don't take plants' effects on climate into account -- which means we continue to underestimate the pace of climate change. The good news? There is one plant that seems to respond to higher levels of carbon dioxide by growing more enthusiastically and thus absorbing more of our emissions: Poison Ivy. What, you're not one of the 15% of people with natural immunity? Ah, well. I guess you're really out of luck then.

Photo credit: Noel Zia Lee

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