Too Hot to Handle?

As prices at the pump have risen this year, so has the intensity of the debate over the relative abundance of Earth’s remaining oil (an issue, David Goodstein notes, on which reasonable people can and do differ). However heated that discussion ultimately becomes, it has some way to go before it reaches the level of commentary and vitriol that is routinely generated over the related question of what impact fossil fuels are having on the greenhouse effect, the atmospheric phenomenon that for eons has kept Planet Earth—like Baby Bear’s cereal—neither too hot nor too cold.

In Out of Gas, Goodstein takes on the seemingly thankless job of distilling the innumerable position papers, research studies, and policy debates on this issue down to a few immutable physical facts: At 93 million miles from the sun, Earth receives a flux of solar energy that, averaged over the face of the planet at the top of the atmosphere, comes to 343 watts per square meter. A portion of this energy is reflected, and the rest is absorbed and radiated back into space as infrared radiation. For Earth to radiate back energy equal to what it absorbs, its surface temperature would have to be roughly zero degrees Fahrenheit. At that temperature, its surface water would freeze, reflecting more of the sun’s light, and making Earth an even colder and less hospitable planet.

That this hasn’t happened is due to the fact that atmospheric trace gases—water vapor, methane, carbon dioxide, and the other so-called greenhouse gases—absorb infrared radiation that would otherwise escape and reradiate it both out to space and back to Earth, warming the planet’s surface overall to, in Goodstein’s words, a relatively “balmy, comfortable 57 degrees Fahrenheit, as a mean surface temperature. At that temperature we evolved, climbed down from the trees and started building steam engines.”

In the preindustrial era, Earth’s atmosphere absorbed 88 percent of the infrared radiation that would otherwise have been radiated away. In the last 150 years, however, that balance has been significantly altered by humans’ ever-growing reliance on fossil fuels. Says Goodstein, “Since the beginning of the industrial age, we have increased the amount of carbon dioxide in the atmosphere by about 30 percent.”

The net result of this tinkering, observes Goodstein “is not easy to predict. We don’t know exactly what would happen if by burning more fossil fuel, particularly more coal, and increasing CO2 in the atmosphere, we were to raise the greenhouse effect, let’s say, to 100 percent, but we have a good model to look at. The planet Venus is a little closer to the sun than Earth is, but the physics should permit Venus to be very earthlike in temperature. But it’s not.Venus has a runaway greenhouse effect and a surface temperature hotter than molten lead. As we have seen, distance from the sun is only one of several variables that determine habitability on Earth. At 93 million miles from the sun, our planet could be a frozen wasteland, or it could be a Venusian inferno. The fact is that it is neither. Instead it has this delicately balanced partial greenhouse effect that is ideal for creatures like us. We mess with that greenhouse effect at our peril.” -H.A.