The Planet’s Natural Air Filters

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The Earth as one great organism has always been one of the most appealing metaphors of the green movement. From the moment environmentalist James Lovelock first articulated his so-called Gaia hypothesis—after the Greek goddess of the Earth—in the 1970s, the theory has continued to charm environmentalists.

It doesn’t stand up to much scrutiny, of course. With the exception of a sort of biofilm covering the surface or shallow subsurface of the world, the vast majority of the planet is nothing but inorganic rock and water and gas and metals. And yet the Earth as a whole does have a remarkably lifelike ability to heal itself when it’s been hurt.

For all the booms and berms and chemical dispersants thrown at the Gulf oil spill last year, for example, it was the bacteria in the Gulf feasting on the oil that did the most to clean up the mess. For all the damage human beings can do to coastlines or rivers, once we get out of the way, the waters soon run clear again and natural deposits of silt soon rebuild the shores.

The same is true in many ways with global warming, thanks mostly to trees. It’s not for nothing that jungles like the Amazon—which inhale the CO2 we produce so profligately and exhale pure oxygen—are referred to as the lungs of the planet.

Now, a new study by the National Science Foundation and the U.S. Department of Energy reveals just how powerful U.S. forests can be in ameliorating the polluting effects of our fossil fuel addiction. According to figures released this week, the green ecosystems in the 48 contiguous states can capture and sequester a staggering 40% of the carbon emissions we produce each year. That number, huge as it is, wasn’t a complete surprise: earlier analyses had already put the figure at 30%. But the 10% overall boost—or a full third over the original estimate—makes a very big difference.

“There’s some uncertainty in these data,” said Beverly Law, a professor of forest ecosystems at Oregon State University and a co-author of the new study. “But it does appear that the terrestrial carbon sink is higher than believed in earlier studies.”

That’s not to say that all you have to do is look at aerial photos of the country and see how much green there is and how much carbon capture is thus going on. For one thing, not all green patches could be included in the survey. Farms, for example, may be great carbon sinks while crops are growing, but as soon as they’re harvested and the biomass left behind is burned or decomposes, the carbon escapes right back into the atmosphere. It’s only the land mass that’s more or less steadily covered—at least in the spring and summer—that does the real good.

What’s more, land that’s capturing carbon one year may do little or nothing the next due to seasonal fluctuations or natural disasters. Droughts can turn millions of acres of thriving green to a dead brown inside of a single summer. (Droughts in 2002 and 2006 slashed natural terrestrial carbon capture in half.) Wildfires can do the same kind of damage in a single day. And hurricanes can claw away whole ecosystems in one violent stroke.

Confounding things more, climate change can sometimes be good for greenery, turning cool, dry regions to warn and humid ones and causing an explosion of new plant growth. The problem, of course, is that most of that new biomass may be devoted just to sopping up the excess carbon that caused the growth in the first place, leading to no net greenhouse gas change at all.

None of this is to say that we can keep fouling the skies as much as we want and let the forests pick up after us. Clear-cutting and development are denuding the Earth faster than hand plantings or warming climates ever could. The true good-news message of the new study may be that if we ever do get control of our fossil fuel appetites—a very big if—the planet may be a lot more forgiving than we have a right to expect it to be.

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