An increase in the release of carbon dioxide from soils could speed up the greenhouse effect, according to a new analysis by Gundolf Kohlmaier of Frankfurt University. He warned that the response of forests and their soils to an increase in temperature could introduce unexpected feedbacks in the progress of the greenhouse effect that are not currently included in models of climate. Kohlmaier presented his findings to a conference on Climate and Development, held in Hamburg last month.
The concentration in the atmosphere of greenhouse gases, principally carbon dioxide, will probably be double that of pre-industrial times by 2030. Most models of climate predict that the increase will result in an atmosphere that is approximately 4C warmer than today and up to 10 C warmer in polar regions. But the current generation of models ignores two factors. The first is the response to warming and the changing chemistry of the air over the oceans. Oceans and the organisms in them currently absorb around half of the carbon dioxide released into the air. The second is the response of plants and soils on land.
Both oceans and plants on land are major sources and sinks for carbon. Their response to the changing atmosphere above them could set in chain either devastating positive feedbacks or stabilizing negative feedbacks. It is not certain which way the feedbacks will work..
The destruction of forests in the past two centuries, mostly in temperate lands, has contributed almost as much to the greenhouse effect as the burning of fossil fuels. But large uncertainties about the rate of destruction of tropical rain forests and the speed of re-growth mean that no one is sure how much carbon flows between the forests and the atmosphere. Recent estimates, taking account of the rapid planting of trees in many developed countries, put the release at perhaps 1 billion tonnes a year one-fifth of the release from the burning of fossil fuel.
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