By examining weather data over the past 50 years from just off the U.S.'s Atlantic coast, Cerveny and ASU colleague Robert Balling found that air pollution caused by big-city commuters builds up over the workweek, warming the air, which rises to spawn clouds and rain. "It wasn't one of those ta-da! things," says Cerveny, whose study shows that on the East Coast it's 22 percent more likely to rain on Saturdays than on Mondays. "The more we studied the patterns, the more intriguing it got." Though some critics say the theory that pollution seeds clouds is not new, Cerveny's hypothesis that it causes rotten weekend weather has brought him considerable attention.
Cerveny's data also suggest that hurricanes hitting the coast on weekends may be less powerful than those making landfall on weekdays, perhaps because pollution-induced rain tends to lessen their intensity. "To think that we humans could have an effect on these storms—that was surprising," says Cerveny. "Even a little frightening."
Weather has fascinated Cerveny since he was a boy in Nebraska, where he chased tornadoes with his letter-carrier father. "I loved the lightning and the thunder," he says. These days, Cerveny, who has taught at ASU's Tempe campus since 1987 (and whose previous research includes the discovery that Christopher Columbus lucked out by sailing to the New World during a decade-long lull in hurricanes), monitors tempests at his computer, avoiding Arizona's blistering heat in the comfort of his office. "I tend to like my air-conditioning," he says. Even on weekends.