To hear some climate skeptics say it, you'd think the greenhouse effect was just a theory, concocted by dangerous radicals to undermine the American way of life; and to hear some of the climate alarmists, you'd think 100 percent of the science was nailed down, with nothing new to learn and nothing left to argue about. Well, a report by French and Russian scientists in Physical Review Letters, the world's premier publisher of new physics discoveries, finds that the mechanisms responsible for trapping the Sun's radiation in the Earth's atmosphere have been imperfectly understood. (Journalists can obtain pre-publication copies of the article at the American Institute of Physics' physics news/select.)
As every basic textbook in atmospheric science will tell you on page 1, the greenhouse effect is something of a misnomer: in an actual greenhouse, warming occurs because the glass roof stops the convection currents that normally carry warmer air up and away; in Earth's atmosphere, warming occurs because the infrared radiation reflected back from the Earth's surface is trapped by the greenhouse gases in the atmosphere--natural water vapor is by far the most important among them but human-generated carbon dioxide is increasingly significant.
Michael Chrysos and colleagues at the University of Angers and collaborators at the University of Saint Petersburg confirmed that absorption of IR radiation by triatomic carbon dioxide molecules is governed by the laws of quantum physics, involving their internal vibrations. But they found that IR absorption also occurs in collisions between CO2 molecules--and in collisions of diatomic molecules such as O2 and N2 as well--and that this kind of absorption is explained by Newtonian mechanics.
The Chrysos team estimates that the collisional IR absorption accounts for about 10 percent of the total greenhouse effect on Earth. On Venus, which has a super-hothouse climate, they believe the collisional absorption explained by classical mechanics may account for more than half the effect.