Tropical forests release about a quarter of their carbon as trees are destroyed-for instance, during the burning of forests that happens in the Amazon rainforest each year. Deforestation will continue to exacerbate the greenhouse effect, warns Kohlmaier. But it could also have a more possible consequence, weakening one of the planets most effective mechanisms for damping the greenhouse effect.
Optimists believe that living organisms will find means to stabilize unwanted changes to their environment. They believe that the extra carbon dioxide in the atmosphere will often fertilize plants, allowing them to grow faster, and thus absorb still more carbon dioxide from the atmosphere.
Some data from tree rings, from as far apart as Canada and Tasmania, suggest that this may already be happening. The fertilization effect could also be reflected in a recent increase in the difference in levels of carbon dioxide in the atmosphere between summer and winter. Forests are effectively breathing harder by taking up more carbon dioxide during the summer.
But Kohlmaier warns that destruction of the naturally occurring biota by deforestation. . . may alter or stop this stabilizing negative feedback . A solution could be to plant trees. More trees would both absorb more carbon dioxide and increase the potential for this negative feedback to stabilize temperatures.
Kohlmaier estimates that if all the forests of the Amazon basin were destroyed, they would release 73 billion tonnes of carbon, but if allowance were made for possible extra absorption of carbon dioxide from the air as a result of the fertilization effect, this could amount to a loss of 133 billion tonnes. The loss of all the worlds tropical forests would result in 300 billion tonnes more carbon dioxide being released into the air.
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