Another nasty surprise is the recent discovery that rainforest plants are not heat tolerant: if they get too hot, they die. Who could have predicted this? It now appears some rainforests will become carbon dioxide sources rather than sinks. The rainforests are also being burned like garbage like an annoying nuisance. A 1995 study published in Nature showed that, unlike our expectations that rainforests absorb carbon dioxide, in 1992, tropical regions between 30 degrees north and 30 degrees south were a net source of about 1.7 billion tons of atmospheric carbon. It was suggested that this could reflect biomass burning. This means the Amazon basin, most of tropical Africa, much of Southeast Asia and even some of southern Europe could become barren deserts if global temperatures reach a certain level and Brazil and Southeast Asia continue their bold plans for economic development. If this occurs, the present biomass of the Earths tropics will rot or burn and become more carbon dioxide and a great desert will girdle the world.
Already the Amazon desert is emerging in Rondonia. As far as the eye can see there is only red, cracked ground. The red dust fills the air and sky itself turns red. Ten years ago this area was jungle, then it was slashed and burned to form farmland. But the jungle soil is notoriously poor, so it was used for pasture. Once overgrazed it became desert. Now even the landless poor who created it have moved on. They have moved west, to begin the process deeper in the land that used to be the Amazon rainforest. We are recreating the Amazonian desert of Mars right here on the Earth. The only ludicrously absurd virtue in this is that, with the Amazon desert, the computer simulations of the greenhouse effect on weather will be simpler, and thus it will be easier to convince skeptics of the reality of global warming.
The surprises keep coming. As we go to press, ABC News reported on a new study, published in Arctic and Alpine Research, which shows that a temperature increase of only 2 °C causes significant releases of carbon dioxide from Arctic tundra soil, thus accelerating global warming. Only 2 °C!
The Gaia principle is one of the most powerful and mystical ideas to appear in modern planetary biology. Essentially a principle of large complex ecosystems, it says that life alters its own environment to make it more hospitable to life, and that if outside forces alter the environment, life will react to minimize the negative impact of this alteration. A simple example: a rainforest spreads because its vegetation holds moisture, thus attracting more rain clouds which hover over it, circulating the moisture up from the ground, through the cycles of plant life, into the clouds and back down again as rain. According to the Gaia principle, the biospheres response to increased carbon dioxide, and the global warming it produces, would be to increase plant growth so as to reflect more heat to the sky and absorb more carbon dioxide. Gaia also represents the hope that the biosphere will mitigate whatever negative changes humanity induces. However, on Mars, Gaia failed. Whatever life Mars had sustained could not overcome the forces that made Mars a frozen desert. The Gaia principle represents, at best, the tendency of a planetary biosphere to rebound from disaster. But its power is not limitless. Some form of the Gaia principle is probably at work on Earth now, but Gaia cannot take the place of intelligent foresight and action, nor overcome all of our excesses.
The Amazon provides one quarter of the Earths oxygen. Rainforest is highly efficient in trapping light and thus promoting photosynthesis. Photons that penetrate the top canopy of the forest have usually two more canopies to go before they can be absorbed by the ground or reflected. Anywhere they go they run into something green. Grass lands, by contrast, allow most light to reflect or be absorbed by the ground; thus they are less efficient per acre in producing oxygen or trapping carbon dioxide. The fact that carbon dioxide and oxygen are exchanged one for one in photosynthesis and combustion-respiration was part of what led to the discovery that oxygen levels are dropping.
Copyright 2000 Dr. John Brandenburg and Monica Rix Paxson. All rights reserved. No part of this book may be reproduced without written permission from the publisher - The Crossing Press.
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