Contact: Barbara McGehan EMBARGOED UNTIL
(303)497-6286 6 P.M. THURSDAY, 8/24/95
Unexpected evidence that a large area of the Northern Hemisphere is a "sink" or depository for carbon dioxide, a greenhouse gas that is closely associated with global warming, was released today by the Commerce Department's National Oceanic and Atmospheric Administration.
The evidence published in the Aug. 25 issue of Science magazine gives the first factual information that a depository for carbon dioxide exists on land, NOAA scientists said. The previous scientific view was that the ocean was a major sink for carbon dioxide, or CO2.
The term "sink" refers to areas where greenhouse gases are absorbed either by land or ocean processes.
According to the Science magazine article, during the time period 1992-93, measurements of carbon 12 and carbon 13 were used to determine the net removal of carbon dioxide from the atmosphere by the oceans and by vegetation on land. The measurements point to a large land depository for carbon dioxide in the temperate latitudes of the Northern Hemisphere during this time period.
This means that trees and other vegetation in the northern latitudes are storing carbon instead of releasing it into the atmosphere.
Carbon dioxide is the most important of the greenhouse gases produced through 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. For instance, activities such as the burning of fossil fuels and deforestation can release significant amounts of carbon into the atmosphere, upsetting the natural balance. Excess carbon dioxide in the atmosphere/ocean system lasts over a hundred generations.
The region of the study lies in the latitudes between 30 degrees north and 60 degrees north. This area includes most of the northern latitude temperate forests such as those found in the U.S., Europe and Russia. During the two years of the study, this area stored the equivalent of 3.5 gigatons of carbon or more than half of the total global fossil fuel burned for those years.
One of the important dilemmas facing scientists is to determine where the carbon dioxide emitted by human activities goes when it is released into the atmosphere. It is known that approximately half remains in the atmosphere, while the other half is divided between the oceans and the land. The question facing scientists and policy makers is: how is the half that is absorbed by ocean/land processes divided between these two sinks? Without a good understanding of these processes, projections of CO2 levels and of global warming are uncertain.
The authors of the paper include Philippe Ciais and Pieter Tans, NOAA's Climate Monitoring and Diagnostics Laboratory, Boulder, Colo.; Michael Trolier, NOAA and the Institute of Arctic and Alpine Research (INSTARR); James White, University of Colorado; and Roger Francey, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Victoria, Australia.
According to co-author Pieter Tans, observations, such as those taken at the 43 NOAA sites, must form the basis for our understanding of the carbon cycle and, therefore, of our predictions of future increases of this greenhouse gas.
"The carbon cycle is still the long term driver in global climate change," said Tans. The challenge now, he said, is to identify those processes that cause the land to absorb CO2 in such large quantities.
"Because CO2 is a major greenhouse gas and has a very long life in the atmosphere, it is important to understand this process. If we understand it, we can make projections of the amount of CO2 present in the atmosphere in future years," Tans said.