Amazon Forest May Take Some Heat off Global Warming

John Roach
for National Geographic News
(March 27, 2001)

Add the possible control of global warming to the list of incentives for silencing the chain saws and dousing the flames in the Amazon rain forest.

The forest, which is home to the richest diversity of species on Earth and thousands of indigenous peoples, is currently destroyed at a rate of two million acres per year to make way for roads, agricultural fields, and urban dwellings.

This rapid loss of species diversity and displacement of indigenous peoples focused international conservation efforts on the Amazon region following the 1992 Earth Summit in Rio de Janeiro-but the loss and displacement continues today unabated, according to Amazon Watch, an environmental organization based in Topanga, California.

An additional incentive to protect the forests, and perhaps turn the tide of destruction to one of conservation, may lie in the ability of the forests to help meet the goals of the Kyoto Protocol, an international treaty to combat global warming, said Jeffrey Chambers, a researcher at the University of California, Irvine, who explains this incentive in the March 22 issue of Nature.

Carbon Sink
Some scientists who study climate suspect that forests grow faster for a period in response to increased carbon dioxide in the atmosphere. If that picture is correct, as several studies indicate, then trees in the Amazon rain forest may absorb carbon dioxide from the atmosphere at a higher rate than they release it for more than a hundred years after the period of increasing growth, according to the research.
Carbon dioxide, which humans produce at a rate of nearly six billion tons per year via the burning of fossil fuels such as gas and coal, is one of the most important of the greenhouse gases-gases that trap heat in the atmosphere, leading to global warming. Some experts say that the ability of forests to act as a carbon sink ought to be capitalized upon to help meet the goals of the Kyoto Protocol.

Climate Model
Working on the assumption that the growth of forests will accelerate by 0.25 percent per year for 50 years in response to increased carbon dioxide in the atmosphere, Chambers ran two decades worth of forest carbon-cycling data through a computer model, which predicted the forest's carbon dioxide absorption into the future.

Chambers found that the trees would grow larger, exceeding the mass they might have otherwise reached. Once the trees establish a new higher growth rate, the forest continues to absorb additional carbon for more than a century.

"What we showed was that if you have an increase in productivity, the forests will continue to accumulate carbon for more than a hundred years after the productivity increase," said Chambers. "Forest productivity cannot increase continuously. So, even if forest productivity is increasing in response to increased atmospheric carbon dioxide, eventually other factors, such as nutrient limitation, will put a limit on the productivity increase."

The result, though not conclusive, suggests another practical reason to protect the Amazon rain forest from destruction-the trees lock up carbon dioxide that would otherwise contribute to global warming long after rapid growth stimulated by excess carbon dioxide stops.

"Yet, there is no question that fossil fuel emissions must be reduced to control global warming," said Chambers. "Preserving forests helps in important ways, but getting anywhere even close to what is called for in the Kyoto Protocol will require substantial reductions in fossil fuel emissions."