Big Rise in UV Rays Linked to Ozone Loss

Measuring radiation over a heavily populated region, Canadian scientists have made a compelling case that large increases in harmful ultraviolet rays over the past four years are linked to the depletion of the ozone layer.

Scientists Jim Kerr and C.T. McElroy reported Thursday in the journal Science that from 1989 through 1993, ultraviolet radiation over Toronto rose 5.3% every winter, when the ozone layer is thinnest, and nearly 2% every summer, when ultraviolet rays are most intense.

“We saw large increases in ozone depletion and large increases in ultraviolet radiation over the same period,” said Kerr, who heads ozone research and monitoring at Environment Canada, a government agency that oversees the country’s weather service. “Before, we didn’t have long records (measuring) ultraviolet radiation. This is the first link which attributes it directly to ozone.”

The study said radiation may not continue to increase at such a rapid pace because measures to protect the ozone layer could trigger a slow healing process by the end of the decade. The scientists also speculated that the 1991 eruption of Mt. Pinatubo in the Philippines may have contributed to the recent ozone loss.

Until now, the argument that ozone depletion intensifies human exposure to ultraviolet rays has depended largely on measurements taken in Antarctica and the Arctic, where the hole in the ozone layer is most pronounced.

But this week, Kerr and McElroy documented what many other scientists have suspected for some time, that depletion of the ozone layer carries radiation risks for other parts of the world.

“By detecting those increases in a populated area, they show that the ozone depletion is beginning to increase ultraviolet light in places where harm to living systems may result,” said John Firor, director of advanced studies at the national Center for Atmospheric Research in Boulder, Colo.

In addition to causing skin cancer, increased ultraviolet radiation at certain wavelengths is believed to harm animals and alter vegetation and crops. Intact, the ozone layer shields the Earth from the sun’s harmful rays.

Chlorofluorocarbons, or CFCs, used mainly in industrial solvents and refrigeration, have been linked to depletion of the Earth’s protective ozone shield since the mid-1970s. Most nations, including the United States, are phasing them out.

Firor said the latest research is “particularly important at this time because of the doubts expressed from earlier, cruder studies that UV light was increasing. Because these latest measurements are more precise, they should dispel the doubts.”

Previous studies have not proven that ozone depletion is a major cause of increased radiation because a variety of other factors, such as clouds, haze and pollution, could be involved. Those variables have prompted skeptics to question campaigns to ban the use of industrial and agricultural products that deplete the ozone layer.

But Kerr and McElroy showed a link between the ozone hole and rising radiation levels by using techniques that distinguish between the effects caused by ozone and those caused by the other influences. They did so by measuring UV rays at many different wavelengths, finding that radiation was the worst at the short wavelengths where ozone depletion is the most severe and the other factors are not present.

Largely as a result of the meticulous research, some other scientists are expressing confidence in the findings.

“Now, we have good data we can point to,” said F. Sherwood Rowland, a UC Irvine atmospheric chemist who is considered one of the world’s foremost ozone researchers.

Rowland said he was distressed, but not surprised, by the high levels of ultraviolet radiation detected by Kerr and McElroy. Although Rowland said the winter increase of “5% a year is a lot,” he said it was not unexpected because about 10% of the ozone over the north temperate zone, which includes Canada, has disappeared over the past decade.

Kerr said the amount of summertime radiation over Toronto in the wavelengths that produce sunburn increased nearly 8% over the four years studied. The summer levels are most important because that is when people spend most time outdoors.

“It is a large increase. If it kept on that 2% per year indefinitely, it would eventually accumulate quite a lot. But we don’t know what will happen in future years,” Kerr said.

The four-year data “may not be representative of longer-term changes,” so it should not be used to predict future radiation increases, the scientists’ report warns.

One cause for the high radiation readings may be the 1991 volcano eruption in the Philippines because atmospheric scientists suspect that it caused chlorine to eat away more of the ozone layer.

“The future is rather difficult to predict because we really don’t understand the mechanisms involved. There is a possibility that the volcano had very small effects, or large effects,” Kerr said.

One reason for optimism, he said, is that atmospheric scientists believe that the damaging effects of CFCs will peak about the year 2000, spurring “a long, slow recovery” of the ozone layer.

Environmentalists said the study shows the need to step up the gradual, international ban on ozone-depleting chemicals, and they encouraged the Clinton Administration to lead the way. Although manufacture of CFCs ends in 1996, other chemicals that deplete the ozone layer, including an agricultural fumigant, will be produced beyond that.

“This study points up the need to move quickly to eliminate ozone-depleting chemicals,” said Michael Oppenheimer, a senior scientist with the Environmental Defense Fund, a national environmental group. “A thinning ozone layer which causes increased . . . radiation on our planet will have significant impacts on people, wildlife and natural ecosystems.”

Kevin Fay, executive director of the Alliance for Responsible CFC Policy, an industry group, said “the new data certainly sends a message to all of us that we need to continue our efforts” to eliminate CFCs.