The Antarctic ozone hole has mysteriously shrunk to one-third its usual size and last week split in two. The only explanation so far is that unprecedented large-scale weather patterns have warmed the stratosphere, inhibiting the atmospheric chemistry favoring ozone destruction and importing extra ozone. The additional ozone is blocking harmful ultraviolet radiation--good news for penguins as well as humans living in the far southern Southern Hemisphere, although this dramatic shrinkage isn't expected to continue.
Satellite-borne ozone monitors, operated by NASA and the National Oceanic and Atmospheric Administration (NOAA), have been watching the ozone hole since 1979. Caused by pollutants such as chlorine-bearing compounds once common in refrigerators and air conditioners, the hole has steadied at about 24 million square kilometers over the previous 6 years.
The ozone monitors have seen nothing like this year's variation before. Through September, the hole became elongated and slid off the South Pole. Last week it broke in two, with one lobe on the Antarctic coast toward Africa and the other near South America. Over the last 2 weeks, the hole has spanned a mere 15 million square kilometers, the smallest measured since 1988. Yesterday, according to atmospheric physicist Paul Newman of NASA's Goddard Space Flight Center in Greenbelt, Maryland, it had dropped to a measly 2 million square kilometers.
Meteorologists trace the hole's odd behavior to the great globe-girdling atmospheric waves that steer Earth's weather. The waves are the only lower-atmosphere weather that can penetrate the stratosphere and alter ozone patterns, and in the Southern Hemisphere, the waves have been exceptionally strong this year. They're believed to be warming the stratosphere; that discourages chemical ozone destruction by inhibiting the formation of icy cloud particles that help these chemical reactions along. And by carrying ozone-rich air, the waves also patch up parts of the hole.
“It's like Minnesota jumping to 80°F in January,” says Newman. “The whole community's trying to figure out what's happening.” But like any Indian summer, the extra ozone is a temporary reprieve. Only the slow self-cleansing of the atmosphere's store of ozone-destroying pollutants and continued reductions in their emission will finally do in the ozone hole.