SAN FRANCISCO--Atmospheric scientists are keeping a wary eye on the high Arctic. New research suggests that the north pole's ozone layer, already fragile during the cold season, may dwindle further in winters to come. That could threaten people at high latitudes with increased exposure to UV light each spring, according to reports here on 16 December at a meeting of the American Geophysical Union (AGU).
The protective ozone layer is under attack from chlorine and bromine, which come from both synthetic chemicals and natural sources. The chemical reactions that break down ozone are particularly intense within cold, acidified clouds called polar stratospheric clouds. These clouds form over Antarctica in the winter and early spring when an isolated vortex of air grows bitterly cold, then dissipate as air temperatures rise. The cycle of destruction is less severe in the Arctic, because mountains in the Northern Hemisphere force air to mix more thoroughly. Still, arctic ozone levels fell during most winters in the 1990s, making researchers worry that a northern ozone hole might appear. Indeed, a "minihole" briefly opened over Europe last year (ScienceNOW, 3 December 1999).
To address those concerns, ozone specialists in two international campaigns scrutinized the arctic atmosphere between November 1999 and April 2000. Their work reveals that 60% of the ozone vanished in a layer from 16 to 22 kilometers high. That falls short of Antarctica's total loss at some altitudes, but it's one of the worst ozone wipeouts ever seen in the Arctic. Further, temperatures plunged to a near-record low of -85°C in the arctic stratosphere. That triggered vast polar stratospheric clouds, some of them as big as the continental United States.
Researchers don't expect the arctic ozone layer to mend soon. Although chlorine levels are falling, thanks to agreements that banned chlorofluorocarbons, levels of bromine--which is 45 times more effective at zapping ozone--are still rising, says atmospheric chemist Dale Hurst of the National Oceanic and Atmospheric Administration in Boulder, Colorado. Much of the bromine comes from compounds still used in fumigants and fire extinguishers. Hurst estimates that even with phaseouts of those chemicals, the arctic ozone layer won't recover to its 1980 levels until at least 2050.
Colder temperatures and weaker high-altitude winds may make the arctic polar vortex even more intense in future winters and trigger greater ozone loss, says atmospheric scientist Paul Newman of NASA's Goddard Space Flight Center in Greenbelt, Maryland, although the losses probably won't approach those in Antarctica. Still, because organisms at northern latitudes have evolved in a world of high ozone, "they may be susceptible to even a few percent increase in UV," Newman says.