THE END OF NATURE By Bill McKibben (Anchor: $9.95). Bill McKibben argues that by altering the chemistry of the atmosphere with pollutants, humans have so profoundly changed the Earth that the natural world no longer exists: Every square inch of the planet has been irrevocably altered. Sadly but rationally, he reflects on the biological, environmental and psychological implications of his thesis. The greenhouse effect is causing the climate to change more quickly than it ever has in the past, and no one knows whether animals and plants (and humans) will be able to adapt to the rapidly rising temperatures, highly acidic rain and increased exposure to ultraviolet radiation. The most frightening aspect of this scenario is its irreversibility. The recently passed Clean Air Accord only slows the rate at which pollutants are added to the atmosphere. Even if the burning of fossil fuels ceased today, the climate would continue to warm and the ozone layer to deteriorate for decades (the chlorofluorocarbons already in the air will remain there for at least another century). Mankind has casually launched a juggernaut, and McKibben offers a warning of what will follow and an elegy for what has passed.