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Putting aside questions of planetary consciousness and will (beloved as they were by an early wave of New Age Gaia acolytes), the theory may help us understand how the earth has managed to remain hospitable for life over billions of years even as the sun, because of its own stellar evolution, has become significantly hotter. Through a series of processes involving, among others, ice ages, ocean algae, and weathering rock, the earth has managed to keep the amount of heat-trapping carbon dioxide in the atmosphere, and hence the temperature, at a relatively stable level.
This homeostasis is now being disrupted by our brief binge of fossil fuel consumption, which has released a huge amount of carbon dioxide into the atmosphere. Indeed, at one point Lovelock predicts -- more gloomily than any other competent observer I am aware of -- that we have already pushed the planet over the brink, and that we will soon see remarkably rapid rises in temperature, well beyond those envisioned in most of the computer models now in use – themselves quite dire. He argues that because the earth is already struggling to keep itself cool, our extra increment of heat is particularly dangerous, and he predicts that we will soon see the confluence of several phenomena: the death of ocean algae in ever-warmer ocean waters, reducing the rate at which these small plants can remove carbon from the atmosphere; the death of tropical forests as a result of higher temperatures and the higher rates of evaporation they cause; sharp changes in the earth's "albedo," or reflectivity, as white ice that reflects sunlight back out into space is replaced with the absorptive blue of seawater or the dark green of high-latitude boreal forests; and the release of large amounts of methane, itself a greenhouse gas, held in ice crystals in the frozen north or beneath the sea.
Some or all of these processes will be enough, Lovelock estimates, to tip the earth into a catastrophically hotter state, perhaps eight degrees centigrade warmer in temperate regions like ours, over the course of a very few decades, and that heat will in turn make life as we know it nearly impossible in many places. Indeed, in the photo section of the book there is one picture of a red desert captioned simply "Mars now -- and what the earth will look like eventually." Human beings, a hardy species, will not perish entirely, he says; in interviews during his book tour, Lovelock has predicted that about 200 million people, or about one thirtieth of the current world population, will survive if competent leaders make a new home for us near the present-day Arctic. There may also be other survivable spots, like the British Isles, though he notes that rising sea levels will render them more an archipelago. In any event, he predicts that "teeming billions" will perish.
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