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By Root 365 0

things could happen, and the universe of terrible things is so large that some of them probably will." This quote is by Steve Pacala, a Princeton University ecologist. The other followed a discussion about the immense reservoirs of organic carbon stored away in the permafrost in Arctic regions—perhaps two hundred billion tons of the stuff, "safely" stored for thousands of years, because frozen. "Now," says Terry Chapin of the University of Alaska, "it's potentially a very large time bomb." If the Arctic thaws, rising sea levels will be the least of our worries, in this view. Instead, we'll be smothered in C02 and in short order the planet will become as steamy as Venus, ending life as we know it, and most important, our own.14

This is bad enough, but perhaps the most depressing thought of all is to contemplate not so much what is happening but how rapidly it might happen. The potential time line is unnervingly short. The global climate, like its component parts, is a chaotic system with its own strange attractors. Theory suggests that there might be at least three such attractors. One is the current climate model, another is a White Earth model (the deep freeze of an ice age), and a third is the Venus model (with dense clouds and surface temperatures high enough to evaporate the oceans). If climate is indeed chaotic, it would tend to hover around one of these three, and have the ability to bounce unpredictably from one to another. If we are close to such a bounce, a very small effort on our part, such as an increase of a few parts per million of C0, might be a sufficient trigger. Unlike conventional global warming theories, these bounces wouldn't happen in a reassuring one hundred or two hundred years. They could be complete within a decade. We would have no time to prepare. Flip! The Venus effect . . . Or flip! The deep freeze . . . Fry or freeze. An evil choice.

The greenhouse effect is simple enough to understand, though not quite as simple as in the popular imagination. It is really the tipping point at which the air will become dangerously oversaturated with moisture vapor and carbon dioxide that is causing all the fuss. What concentration of CO2 is too much? Where's the true danger point?

In the present mix of atmospheric gases, a little more than half the sun's energy reaching the outer atmosphere strikes the surface directly The other half is distributed through scattering, "bouncing" off other molecules in the same way odor molecules disperse themselves in the air. Much of the energy that does reach the surface directly is absorbed, but it is then reradiated upward again. The reradiated energy has much longer wavelengths than solar energy, somewhere between i and 30 micrometers. Between them, carbon dioxide and water vapor absorb radiation at these wavelengths efficiently, except for a small window that is transparent to radiation, which lies between 8 and 11 micrometers. It is through this window that some of the reradiated heat is able to escape back into space.

The half of the sun's energy that doesn't reach the surface is absorbed by the same two substances, water vapor and carbon dioxide. The CO molecules become agitated and therefore warmer by the process of absorption, and they then reradiate the energy they took in, some of it down to the surface, some out to space. That energy reaching the surface is treated the same way as the other half—it is absorbed and then reradiated spaceward. Some of it is trapped yet again and sent back down . . . and so on and so on, setting up an oscillating feedback effect not unlike a game of Ping-Pong.

The net effect of all this is that the atmosphere has been gradually heated to a relatively constant temperature with a relatively constant variation by altitude, somewhere around 6.50 Celsius for every 3,300 feet of altitude. It is this constant feedback effect that makes the proportion of carbon dioxide in the air so important—the more there is, the more absorption there is, and the greater the heat gain in the atmosphere. 15 This is pretty straightforward, complicated