CONTACT:  Barbara McGehan                      For Release
                                               Thursday, Oct. 15, 1998

A study by government and university scientists indicates that the land mass in North America is absorbing a large amount of carbon dioxide from the atmosphere. During the past decade, evidence had already suggested the existence of a large land "sink " of atmospheric carbon dioxide at temperate latitudes in the Northern Hemisphere.

Carbon dioxide is a greenhouse gas that is closely associated with global warming. The term "sink" refers to areas where greenhouse gases are absorbed either by land or ocean processes.

In an article appearing in the Oct. 16 issue of Science magazine, scientists from the Commerce Department's National Oceanic and Atmospheric Administration, Princeton University, and Columbia University say that they have now, tentatively, identified that "sink" as being mostly North America, at least during the period studied, from 1988-1992.

Pieter Tans, an atmospheric chemist at NOAA's Climate Monitoring and Diagnostics Laboratory in Boulder, Colo., and a co-author of the paper, says that "the North American land surface appears to be absorbing possibly as much as between one and two billion tons of carbon annually, or a sizeable fraction of global emissions of carbon dioxide from fossil fuel burning."

The data used in the study was obtained from 63 atmospheric sampling stations taken from the GLOBALVIEW database. GLOBALVIEW includes stations from NOAA's Climate Monitoring and Diagnostics Laboratory, and 12 other laboratories located around the world. The ocean and atmospheric models used were developed at NOAA's Geophysical Fluid Dynamics Laboratory located at Princeton University, and the air-sea fluxes were developed at Columbia's Lamont-Doherty Earth Observatory. The study was funded by NOAA's Office of Global Programs.

According to the Science article, the researchers developed a three- dimensional grid of the earth to model the flow of carbon dioxide. The expectation was that carbon dioxide would increase over North America as the winds moved from west to east, due to the large amounts of carbon dioxide produced by fossil fuel burning. Instead, carbon dioxide tended to decline slightly in crossing North America from the Pacific to the Atlantic oceans during the period of the study.

The researchers are not sure what is causing this decline of carbon dioxide. But they theorize that it is partly due to the regrowth of plants and vegetation on abandoned farmland and previously logged forests in North America, and may be enhanced by human-induced nitrogen deposition - a diluted form of acid rain - and increasing CO2 levels, which can act as fertilizers for plants. However, the actual cause remains unknown. The researchers do believe that plants and soils are a major factor in CO2 absorption and will continue to exert considerable influence on atmospheric carbon dioxide in the future.

Tans emphasizes that even when researchers can account for most of the carbon dioxide that has been emitted globally, the future remains uncertain. "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."

Jerry Mahlman, director of NOAA's Geophysical Fluid Dynamics Laboratory and a co-author of the paper, said that while the North American sink may prove important in worldwide management of atmospheric carbon absorption, its value will come at a global level, not a regional one.

Excess carbon dioxide in the atmosphere/ocean system lasts more than a hundred generations. Carbon dioxide is the most important of the greenhouse gases produced due to human activities. Because it is closely associated with global warming, how carbon is distributed throughout the world and how it is absorbed or released is of major significance.

"This finding will assist us in better understanding the global fate of carbon dioxide," said Tans.

In addition to Tans and Mahlman, the article in Science was co-authored by Song-Miao Fan, Atmospheric and Oceanic Sciences Program; Emanuel Gloor, Ecology and Evolutionary Biology; Stephen Pacala, Carbon Modeling Consortium; and Jorge Sarmiento, professor of Geosciences, all from Princeton University; and Taro Takahaski, from Columbia University's Lamont-Doherty Earth Observatory.

More information on the data sampling can be obtained from the CMDL home page at http://www.cmdl.noaa.gov
Information on the modeling can be accessed at the GFDL home page at : http://www.gfdl.gov