Studies Measure Capacity of "Carbon Sinks"

By John Roach
for National Geographic News
June 21, 2001

After years of wide disagreement, scientists are getting a better grip on how much carbon Earth's forests and other biological components suck out of the atmosphere, thus acting as "carbon sinks." New research in this area may be highly useful in efforts to devise international strategies to address global warming.

The emission of carbon dioxide from the combustion of fossil fuels is the leading cause of the buildup of greenhouse gases in the atmosphere, which many people believe is the main culprit behind an increase in Earth's temperatures.

For a long time, scientists have known that forests, crops, soils, and other organic matter soak up some of that carbon, thereby slowing down the rate of global warming. Yet their calculations of how much carbon is absorbed have differed, in some cases significantly.

A team of scientists led by Stephen Pacala, a professor of ecology and evolutionary biology at Princeton University in New Jersey, set out to resolve this discrepancy in calculations. Their research is reported in the June 22 issue of Science.

Different Measuring Techniques

While some carbon is absorbed by organic matter such as trees and shrubs, carbon is also regularly emitted into the atmosphere by activities on land such as the burning of fossil fuels.

Researchers' lack of agreement on how much carbon is "stored" has been rooted in the use of two different methods of measurement—one atmosphere based, the other land based.

The first method involves measuring concentrations of carbon dioxide in the air as the air moves across landmasses from Point A to Point B. The second method entails making an inventory of all the carbon in a given area of ground and calculating the difference between the levels of carbon recorded from year to year.

Although there is wide variation among different atmospheric models of carbon measurement, their results have consistently indicated that higher levels of carbon are absorbed than the land-based models show.

Pacala said his team's land-based analysis was more thorough than earlier studies. "We did the first exhaustive analysis of the land sink," he said.

Previous land-based models inventoried mainly the amount of carbon absorbed by trees, he explained. He and his colleagues included measures of carbon absorbed by landfills, soils, houses, and even silt at the bottom of reservoirs.

"We found out that the land sink was bigger than had been reported by other analyses, about twice as big, and the atmosphere [models] gave numbers that were consistent," he said.

Continued on Next Page >>


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