Climate Science Forum


	*Reliable News and Analysis in Climate Science*
	SUMMER 2002 Volume 1 Number 2

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Forests That Now Absorb Carbon Dioxide May Not Do So in Future

Many policies for limiting future levels of greenhouse gases depend on the ability of forests, grasslands, and organic soil to absorb and "sequester" atmospheric carbon dioxide, as these ecosystems convert the carbon to wood and organic matter. A report in Nature¹ by Richard A Gill and others dashes such hopes.

In a field experiment in a Texas grassland, the authors modified the concentration of CO₂ in the ambient air from 200 parts per million (ppm) - well below the concentration observed in the pre-industrial age before 1800 - to 550 ppm, a level that some expect the atmosphere to reach by 2100. The ability of the grassland to absorb more carbon from the atmosphere depended on the availability of nutrients. The grassland apparently grew faster when CO₂ levels were lower than when they were higher. Researchers found that carbon storage in soil and cycling of nitrogen "are much more responsive to past atmospheric CO₂ concentration than those forecast for the coming century." They suggest that sequestration of carbon in soils "may have been important historically, but the ability of soils to continue as sinks is limited."

¹ Nature, v. 417, 16 May 2002, [www.nature.com/nature]

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