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Arboreal storage for carbon dioxide.

Arboreal storage for carbon dioxide

As carbon dioxide levels in the atmosphere continue to rise, researchers are taking a closer look at potential methods for limiting the increase in order to avoid adverse changes in global climate. "What is required," says Gregg Marland of the Oak Ridge (Tenn.) National Laboratory, "is some way to collect carbon and some place to put it so that it does not accumulate in the atmosphere as carbon dioxide." One possibility, at least in the short term, would be to stimulate the growth of forests. Recently, Marland evaluated what it would take -- by increasing either forest area or tree growth rates -- to remove an additional 5 billion tons of carbon per year from the atmosphere.

His study shows that increasing the area of land covered by forest does not look promising. Although the amount of forested land in the United States and a few other countries has actually increased slightly in recent years, in many parts of the world, especially the tropics, forests are still being cleared without being replaced. Even if the loss of existing forests were halted, it would still take an area roughly the size of Australia planted with a fast-growing tree species such as American sycamore to meet the target reduction in carbon dioxide. "Where would we put the trees?" asks Marland. "This ultimately becomes a political question."

A better approach may be to concentrate on increasing forest productivity, says Marland. "There is much one can do to raise yields," he notes. Techniques such as fertilization, irrigation, and weed, fire and pest control have a great impact on growth rates. Genetic engineering may also contribute to increased yields. The trouble is that young trees take up carbon dioxide much more quickly than mature trees. This means having to harvest trees regularly while finding ways to keep the wood from oxidizing back into carbon dioxide, perhaps by using it for construction. Even then, the net annual yield of all of the world's forests would have to be doubled to remove enough carbon from the astmosphere.

"The cost of such a scheme is immense," says Marland, "but it needs to be compared with the costs of other approaches to dealing with atmospheric carbon dioxide or of coping with the attendant changes in climate." He adds, "This analysis suggests that although looking to forests to solve the carbon dioxide problem is unrealistic, reforestation could indeed play a significant role as one component among a variety of measures taken to address increasing carbon dioxide."
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Title Annotation:atmospheric carbon dioxide may be controlled by increasing forest productivity
Author:Peterson, Ivars
Publication:Science News
Date:Feb 27, 1988
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