N. America's Open Spaces
Soaking Up Much
Carbon From Atmosphere
By Randolph E. Schmid
AP Writer
WASHINGTON (AP) -- There may be a bit of good news on the global-warming front. North America seems to be removing almost 2 billion tons annually of the excess carbon in the atmosphere.
A team of government and university researchers speculates that the carbon is being soaked up, at least partly, by the regrowth of plants and vegetation on abandoned farmland and previously logged forests.
But the report, in Friday's edition of the journal Science, could mean more controversy for the global-warming debate.
In particular, environmentalists worry that groups opposed to the global climate treaty negotiated last year in Kyoto, Japan, will use the findings to argue that the United States doesn't need to reduce emissions of so-called greenhouse gases, as it agreed to do.
"There is a huge concern that this result will be misinterpreted," ecologist David Schimel of the National Center for Atmospheric Research in Boulder, Colo., said in a telephone interview.
"I don't believe this result," said Schimel, commenting that other research indicates the amount of carbon taken up by North America can be no more than 700 million tons, rather than the 1.2 billion to 2.2 billion tons estimated by the new report.
Pieter Tans, one of the scientists who worked on the paper, admitted the "uncertainties are still large."
"This is not ironclad. We say in the paper the evidence is still somewhat tentative," he said.
But "we do think that we have used good models. ... We think we've used data in a proper way. ... We've tried to look at all the uncertainties, and this is what we get," said Tans, an atmospheric chemist at the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory in Boulder.
Carbon dioxide released by burning fossil fuels such as coal and oil has been increasing in the atmosphere. That has led to the conclusion by many scientists that it might cause excessive warming of the Earth by trapping heat from the sun, somewhat like the glass of a greenhouse.
The measured increase in carbon dioxide has been less than was expected, leading scientists to wonder where the excess was going.
The Science paper measures carbon dioxide levels around the world and concludes that whatever is absorbing the gas is in the temperate region of the northern hemisphere, roughly between 25 degrees and 51 degrees north latitude.
Comparing carbon dioxide levels in America, Europe and Asia led the scientists to believe that the major absorption is occurring in North America.
Regrowth on farmland and previously cut forests is a strong possibility, since growing plants absorb carbon dioxide, use the carbon for growth and release oxygen into the air.
Tans also speculated that increases in carbon dioxide have spurred plant growth, which caused them to grow faster and remove more of the gas from the air. Fertilization by increased nitrogen in the air might have had the same effect, he said.
The analysis looked at carbon dioxide levels between 1988 and 1992, measured at 63 atmospheric sampling stations.
"The current uptake of carbon by terrestrial ecosystems is helping to slow down the rise of CO2 in the atmosphere, but we need to know why it is happening. Only then may we be able to project for how long into the future this process may continue," Tans said.
Jerry Mahlman, director of NOAA's Geophysical Fluid Dynamics Laboratory at Princeton University, a co-author of the paper, said that while the North American carbon sink may prove important in worldwide management of atmospheric carbon absorption, its value will come at a global level, not regional.
In addition to Tans and Mahlman, co-authors of the article in Science are Song-Miao Fan, Emanuel Gloor, Stephen Pacala and Jorge Sarmiento of Princeton University and Taro Takahaski of Columbia University's Lamont-Doherty Earth Observatory.