Dissidents aren't the only ones being forced off Beijing's streets during the Olympics. The Chinese government has also pushed drivers off the roads—about 3.5 million of them—and shuttered hundreds of factories, steel mills and coal plants in an effort to reduce the city's notorious smog. But while better air in Beijing may be good news for athletes, it could for worse for the earth's environment. "When you clean up very polluted air, as China is doing during these Olympics, it has a direct impact on global warming," says Veerabhadran Ramanathan, a leading climate researcher from the University of California, San Diego, who is studying Beijing's atmosphere for the Games' duration.
Here's how it works: particles in polluted air cool the planet by shielding it from the sun's radiation (which bounces off the particles back into space). By getting rid of smog, it eliminates the protective barrier—and temperatures rise.
Scientists are painfully aware of the irony, but so far, no one's found a solution. It's also unclear how closely smog and lower temperatures are linked. "We know that air pollution masks the effects of global warming. But to what percentage, we are still not certain," says Ramanathan. "If it's 80 percent, that would be bad news."