Now it seems that the problem is far graver than anyone thought. Last week Environmental Protection Agency chief William Reilly announced that ozone loss over the United States since 1978 has amounted to a “stunning” 4 to 5 percent. The preliminary satellite data, which scientists have been analyzing since last autumn, show that Europe, the Soviet Union and northern Asia experienced similar losses, while areas at the latitude of Sweden and Hudson Bay saw losses of 8 percent. “Past studies had shown about half that amount,” said Reilly. “As a result, there could be 200,000 deaths from skin cancer in the United States over the next 50 years” in addition to the 400,000 otherwise expected over that period. The fatality estimate was 21 times what the EPA had forecast earlier. Ultraviolet radiation can also cause cataracts, weaken the immune system, damage crops and disrupt the reproduction of plankton that anchor the marine food chain.

And the ozone loss is almost certain to get worse. CFCs stay in the atmosphere for decades. The EPA’s Eileen Claussen told NEWSWEEK that the agency’s models show ozone loss of 10 to 12 percent over the next 20 years - “and we’ve already thrown out those estimates because they are far too conservative.”

Reilly vowed that the EPA would intensify its efforts to find substitutes for ozone-eating substances. Researchers have made progress in finding benign chemicals that do the job of chlorine-based solvents, but they have been less successful in replacing the CFCs used in refrigerators and air conditioners. If substitute chemicals can be found, developing nations might be persuaded to phase out CFCs by 2000 rather than 2010. Right now, countries such as China and India believe that abandoning CFCs too quickly would cripple their economies. Eliminating CFCs before 2000, though, would not make much difference, because so many of the chemicals are already on their way to the stratosphere. In effect, regulators are running out of ideas. “Because such aggressive steps have already been taken,” Claussen says, “it’s hard to come up with anything more that can make a difference.”

Every 1 percent drop in ozone allows 2 percent more ultraviolet light to reach Earth’s surface.

Every 1 percent reduction in ozone raises the incidence of skin cancer by 5 to 7 percent.

The 5 percent loss of ozone over the U.S. is expected to cause 4,000 more skin-cancer deaths a year.

The ozone loss is greater at higher latitudes. Over Leningrad, it is as much as 8 percent.