If Earth had no greenhouse effect, it would be a frozen ice ball, far too cold for advanced life. If it had a 100% greenhouse effect, it might well be like its near-twin Venus, whose runaway greenhouse effect gives it a surface temperature hotter than molten lead. Instead, we live on a planetwide Garden of Eden, delicately balanced between those extremes.
Our atmosphere is transparent to the white-hot radiation from the sun, but it is nearly opaque to the much cooler radiation with which Earth tries to send its received energy back out into space. The result is a balmy average temperature of 57 degrees Fahrenheit. In those benign conditions, we evolved, climbed down from the trees and began drilling oil wells.
Over the last 150 years, we have evolved a civilization firmly anchored in the mathematically impossible promise of an endless supply of cheap oil. Now there is good reason to believe that sometime in the next decade or two, the world's oil fields will start to be depleted faster than new ones can be tapped. When that happens, a gap will begin to grow between the supply of fuel and the need for it.
If we lived in an orderly, rational world, it might be possible for some other fossil fuel to fill the gap. But anyone who was alive in 1973 knows that we don't live in such a world, especially when it comes to a shortage of our precious gasoline. In 1973, a temporary, artificial shortage immediately caused mile-long lines at gas stations and panic and despair for the future of our way of life. When worldwide oil supplies reach their natural peak, the shortages that follow will be neither temporary nor artificial.
It is technically possible to make a substitute fuel out of coal or natural gas, and as the price of oil skyrockets (along with the price of all petrochemicals and everything that has to be transported), more oil at this higher price will be grudgingly extracted from oil sands, tar sands and depleted oil fields. So, ignoring the effects of runaway inflation, possible armed conflict and the like, it might be possible to muddle on for a while.
How long? We are told by countless studies that there is enough coal in the ground to last for hundreds of years or more, but that estimate is surely flawed. For one thing, if we use coal as a substitute for oil, it will have to be mined many times faster than now. In addition, the world's population continues to increase, the poorer peoples want to live more like the richer ones, using far more energy, and coal supplies, like those of any mineral resource, will peak and begin to decline long before the last ton is dug out of the ground. It's a pretty good bet that the peak will happen before the end of this century.
And, if we let all that happen, the increased greenhouse effect produced by burning all those fossil fuels may well destroy the delicate balance that makes it possible for us to live on this planet.
President Bush has asked us to think beyond our mundane concerns and dream of placing humans on the hostile surfaces of the moon and Mars. He would do better to offer a far more visionary and courageous challenge: to kick the fossil fuel habit now, before we have made Earth hostile to humans.
Beyond fossil fuels there is only sunlight and nuclear energy. Finding ways to run a civilization as complex as ours on those resources alone would be exceedingly difficult, but not entirely impossible. The scientific principles on which the new technologies would have to be based are well known.
We are very good at solving technical problems when we put our minds to it. The task to be accomplished is enormous, but we could do it. What's lacking now is leadership.
David Goodstein is a professor of physics and vice provost at Caltech. His latest book, "Out of Gas: The End of the Age of Oil," was published recently by W.W. Norton.