The protective ozone layer over the Arctic has thinned this winter to the lowest levels since records began, alarming scientists who believed it had begun to heal. The increased loss of ozone allows more harmful ultraviolet light to reach the Earth's surface, making children and outdoor enthusiasts such as skiers more vulnerable to skin cancer -- a disease that is already dramatically increasing. Scientists Tuesday reinforced the warning that people going out in the sun this summer should protect themselves with creams and hats.
Research by Cambridge University shows that it is not increased pollution but a side effect of climate change that is making ozone depletion worse. At high altitudes, 50 percent of the protective layer has been destroyed.
The research has dashed hopes that the ozone layer was on the mend. Since the winter of 1999-2000, when depletion was almost as bad, scientists had believed an improvement was under way as pollution was reduced. But they now believe it could be an additional 50 years before the problem is solved.
What appears to have caused the further loss of ozone is the increasing number of stratospheric clouds in the winter, 15 miles above the Earth. These clouds, in the middle of the ozone layer, provide a platform that makes it easier for rapid chemical reactions that destroy ozone to take place. This year, for three months from the end of November, there were more clouds for longer periods than ever previously recorded.
Cambridge University scientists said Tuesday that, in late March, when ozone depletion was at its worst, Arctic air masses drifted over the U.K. and the rest of Europe as far south as northern Italy, creating significantly higher doses of ultraviolet radiation and sunburn risk.
The results, which were announced at a Geophysical Union meeting in Vienna, Austria, Tuesday, are part of a European venture coordinated by Cambridge University's chemistry department, which has been studying the relationship between the ozone layer and climate change since May 2004.
Tuesday, professor John Pyle of the university said: "These were the lowest levels of ozone recorded since measurements began 40 years ago. We thought things would start to get better because of the phasing out of CFCs and other chemicals because of the Montreal protocol, but this has not happened. The pollution levels have leveled off, but changes in the atmosphere have made it easier for the chemical reactions to take place that allow pollutants to destroy ozone. With these changes likely to continue and get worse as global warming increases, ozone will be further depleted even if the level of pollution is going down."
The relationship between the depletion of the ozone layer and climate change is so complex that the European Union is investing 11 million pounds in a five-year project to try to understand and predict what is happening. Reporting the results of the first year, scientists told the meeting in Vienna Tuesday that "the atmospheric lifetime of these [ozone-depleting] compounds is extremely long, and the concentrations will remain at dangerously high levels for another half century."
Increased greenhouse gases in the air trap more heat in the lower atmosphere, but the stratosphere far above the Earth is getting colder. As a result, ice clouds form between 14 and 26 kilometers above the Earth, exactly in the region where the protective ozone is found.
The European scientists reported the first signs of ozone loss in January. As sunlight returned to northern latitudes, the rate of ozone depletion increased, and rapid destruction of ozone occurred throughout February and March. In the altitude range where the ozone layer usually reaches its maximum concentration, more than half of the ozone was lost. In the lower atmosphere losses were not so great.
"Overall, about 30 percent of the ozone layer was destroyed," said Markus Rex, from the Alfred Wegener Institute in Potsdam, Germany, another member of the team. He said the cold conditions that created polar stratospheric clouds were four times more extensive in 2005 than in the 1960s and 1970s.
Professor Pyle said overall the mixing of the air in the Northern Hemisphere was far more rapid than in the Antarctic, so a "hole" in the ozone layer did not occur. Instead, as the air mixed in spring, there was a general thinning of the protective ozone over the whole of the Northern Hemisphere. "It just means we have less natural protection than we should have and we are used to. It means that we should be careful about exposing ourselves to the sun, but that is already the case -- this just makes things slightly worse," he said.