An Earth so hot that it looks like an egg yolk frying in a skillet— that's the image the editors of Time magazine offered on the cover of the April 9, 2001, issue.

Inside, the talk was deadly serious. "Except for nuclear war or a collision with an asteroid, no force has more potential to damage our planet's web of life than global warming," 1 it said. Time predicted higher temperatures, melting glaciers, rising seas, withered crops, and the spread of diseases due to the warmth.

The past fifteen years have seen the steady accumulation of evidence that the average temperature of the earth is going up. There is mounting concern that the cause is human activity and that these warmer temperatures could have severe effects.

Whether life on Earth is going to resemble a frying egg is another story, however. The theory underlying these predictions is that humans, by burning...