As a result, ozone is depleted 100 times faster in an area affected by thunderstorms than in an area that is not. About 13 to 21 percent of the ozone is destroyed after four days, with losses of 4 to 6 percent over the next few days. All told, 25 to 30 percent of the ozone over a 60- by 60-mile area could be destroyed, with the effect persisting for weeks. Sunlight eventually replenishes the molecule, converting ordinary oxygen into it; one big remaining question is whether ozone destruction or replenishment will come out ahead. The region the storm-tossed water reaches, 9 to 12 miles up, contains about 20 percent of the ozone column in the summer over the U.S.
“The system reacts much more quickly than we expected,” says Anderson. “We don’t know how long that lasts, but it may be many days or weeks.” If the intensity and frequency of powerful summertime thunderstorms increased as a result of climate change, he and his colleagues wrote, then “decreases in ozone and associated increases in UV dosage would also be irreversible”—at least until there are no more manmade chlorine or other ozone-eating chemicals in the atmosphere.
In 80 years or so, CFCs from the air conditioner in your 1965 Mustang, the spray cans that were part of your morning grooming and every other source will have finally dissipated, eliminating the threat to ozone. Accordingly, that means we’ll have to hang on for another eight decades with possibly more people dying from skin cancer and more crops wilting under the intense UV rays.
To be sure, the idea of ozone-killing storms is not a slam-dunk at this point. The weakest link in the chain of evidence is whether climate change is indeed bringing more powerful and more frequent thunderstorms. “We haven’t a clue whether that’s happening,” says MIT’s Emanuel, “but Jim’s work shows that we better pay attention to the connection” between climate change and thunderstorms.
Anderson acknowledges the uncertainty—“we can’t write down a precise equation between carbon dioxide and storms”—but is convinced the link is there, partly because rising levels of greenhouse gases have already been accompanied by weird rainfall patterns: Since the late 1950s, the percentage of rainfall coming in deluges has increased some 70 percent in the Northeast and 30 percent in the Midwest, for instance. Climate scientist James Hansen believes Anderson is right: “What we call ‘moist convection’ will penetrate higher into the atmosphere as the climate becomes warmer,” he says.
Anderson’s work brings the science of ozone loss full circle. Years before some scientists suspected that chlorine from CFCs attacked stratospheric ozone, others warned that supersonic aircraft such as the now-retired Concorde could deplete the ozone layer because its exhaust left water molecules in the stratosphere. Jim Anderson showed that something much more common—the thunderstorms that characterize American summers as reliably as watermelon and hot dogs—can provide the ozone-destroying water. “We thought we’d solved the problem of ozone depletion,” says Anderson, “but we haven’t. If anything, it could be made much worse than we thought by climate change.”