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 Published by the American Geological Institute
Newsmagazine of the Earth Sciences

August 2000

News Notes
 Climate Change

Loophole in the carbon cycle

   When clear cutting was a common agri-
   cultural practice 150 years ago, many 
   forested regions on the East Coast were
   not as lush as they are today. In recent
   decades reforestation has played a 
   major role as a carbon sink in the eastern
   United States. Photo taken east of 
   Elkins, W.Va. Photo by Kristina Bartlett,
The importance of the carbon cycle to Earth’s future can be summed up by considering the uptake of carbon as a “subsidy from Nature,” says Chris Field, head of the Science Steering Panel of the U.S. Carbon Cycle Research Program. “If the oceans and land were not taking carbon out of the atmosphere, we would have to cut fossil-fuel emissions by one half.” Because that amount is so huge, he says, scientists need to gain a better understanding of how, and to what extent, natural carbon sequestration will continue into the future.
Of the 7 billion tons of carbon emitted into the atmosphere each year, half stays in the atmosphere. Of the other half, some is stored in the ocean and the rest is stored on land. Carbon-cycle scientists are looking at a variety of mechanisms working in concert to remove carbon from the atmosphere. But they are left with many questions about the processes involved and their implications for global sustainability, especially in regard to terrestrial mechanisms. At the spring meeting of the American Geophysical Union in Washington, Field and other scientists met to discuss the important role that carbon-cycle science plays in achieving global sustainability.

 To understand the carbon cycle, scientists need to look at all aspects of the Earth system from hydrologic and climatic dynamics to ecological systems. Using eddy flux technology — a mechanism by which carbon can be measured in the atmosphere at different locations above a forest canopy — Steve Wofsy of Harvard University works to quantify the amount of carbon stored in the Harvard Forest in Massachusetts. Wofsy is co-chair of the Carbon and Climate Working Group of the U.S. Global Change Research Program in Washington, and he and many others believe something is missing in scientists’ understanding of the terrestrial sinks. Measuring atmospheric carbon dioxide over forested regions and tallying forest mass allow scientists to estimate carbon accumulation on land. “But there is a missing sink not on the books,” Wofsy says.

 “Every two years you ought to be burying a Cadillac — or a Cadillac’s weight in carbon — in your backyard,” Wofsy says. “That is what would be required to equal the amount of carbon estimated to disappear into the terrestrial sink. But the estimated 200 to 300 million tons of carbon stored in trees each year is too small by a factor of two or three.”
Wofsy has generated a 10-year log of data from the Harvard Forest. He stressed the importance of long-term measurements to understand the carbon cycle. “We can’t presume that measurements from 1993 apply over a decade,” he says. Some scientists find results consistent over 10 to 15 years, he says, but 20 years back they find no correlation.
To find out whether or not Earth’s loan of sequestered cabon will carry us through the millennium, scientists must identify the mechanisms by which the gargantuan amount of carbon spewed into the atmosphere is stored. There is no one government agency established to monitor climate, so finding the direction and funds for such a task is difficult, Wofsy says. Field agrees.
 “We don’t really have the basic science to understand the impacts and long-term effects.”

Laura Wright

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