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Scientists Discover Carbon Cycle Is Out Of Whack


Next we'll report on another of those signs that scientists monitor as they try to track global climate change, among other things. They're tracking carbon, which is everywhere. It's in our bodies. It's in trees. It's in the oceans. There is, in fact, a carbon cycle as it moves around, and carbon has been moving in an unusual way. NPR's Christopher Joyce reports.

CHRISTOPHER JOYCE, BYLINE: The so-called carbon cycle is kind of like a treadmill. An animal or tree dies and its carbon rises into the atmosphere and floats around for a while. Eventually it comes back down where new plants and animals suck it up and use it to grow. Normally a big slice of the carbon that comes back ends up on land, mostly absorbed by big trees in big forests, in the Amazon or in North America or Siberia.

But something weird happened in 2011.

BENJAMIN POULTER: The land took up over 40 percent of the emissions. It was a massive increase.

JOYCE: Benjamin Poulter is an ecologist at Montana State University. He chases carbon the way some people chase tornadoes. Poulter looked for where this big increase in the so-called carbon sink took place. He expected it to be in those big temperate and tropical forests. It wasn't.

POULTER: We were really surprised to see that about 70 percent of the carbon sink was located in South America, South Africa and Australia.

JOYCE: And not in big forests at all, but in dry places, even deserts, places where the only green things are shrubs or tall grass. Poulter wondered, hey, this isn't how the carbon cycle is supposed to work. Well, satellite photos and weather data showed the answer. The year before this southern hemisphere greening, it rained a lot down there. Okay, plants like rain, but they also like carbon dioxide. It's plant food and there's a lot more CO2 in the air now because of all the fossil fuels we humans are burning.

POULTER: And what this does is the plants become more efficient with their water use under elevated CO2 in the atmosphere.

JOYCE: So the deserts feasted on all this water and CO2 and bloomed. That should be good news. CO2 in the atmosphere warms the planet so if it ends up in plants instead, you won't get as much warming. But it's not that simple. Ecologist Daniel Metcalfe at the University of Lund in Sweden says there are good places to store carbon and not so good places.

DANIEL METCALFE: For example, in rain forests, the trees there can live for tens or hundreds or sometimes even thousands of years, and that basically locks away that carbon.

JOYCE: Putting carbon in big forests is like investing in long term bonds. Put your carbon in shrubs and grasses, though, well, that's like risky stocks. They are often short-lived or they burn.

METCALFE: That carbon's locked away for one year, two years, maybe a whole decade and then it goes back out into the atmosphere again.

JOYCE: Writing in the journal Nature, Metcalfe and Poulter say 2011 could've been just a rainy fluke, or not. If not, then it could mean the planet's carbon treadmill may be speeding up a notch. Christopher Joyce, NPR News. Transcript provided by NPR, Copyright NPR.

Christopher Joyce is a correspondent on the science desk at NPR. His stories can be heard on all of NPR's news programs, including NPR's Morning Edition, All Things Considered, and Weekend Edition.