Cold temperatures and a strong polar vortex allowed chemicals to gnaw away at the protective ozone layer in the north.
A vast ozone hole — likely the biggest on record in the north — has opened in the skies above the Arctic. It rivals the better-known Antarctic ozone hole that forms in the southern hemisphere each year.
Record-low ozone levels currently stretch across much of the central Arctic, covering an area about three times the size of Greenland (see ‘Arctic opening’). The hole doesn’t threaten people’s health, and will probably break apart in the coming weeks. But it is an extraordinary atmospheric phenomenon that will go down in the record books.
“From my point of view, this is the first time you can speak about a real ozone hole in the Arctic,” says Martin Dameris, an atmospheric scientist at the German Aerospace Center in Oberpfaffenhofen.
The hole’s formation
Ozone normally forms a protective blanket in the stratosphere, about 10 to 50 kilometres above the ground, where it shields life from solar ultraviolet radiation. But each year in the Antarctic winter, frigid temperatures allow high-altitude clouds to coalesce above the South Pole. Chemicals, including chlorine and bromine, which come from refrigerants and other industrial sources, trigger reactions on the surfaces of those clouds that chew away at the ozone layer.
The Antarctic ozone hole forms every year because winter temperatures in the area routinely plummet, allowing the high-altitude clouds to form. These conditions are much rarer in the Arctic, which has more variable temperatures and isn’t usually primed for ozone depletion, says Jens-Uwe Grooß, an atmospheric scientist at the Juelich Research Centre in Germany.
But this year, powerful westerly winds flowed around the North Pole and trapped cold air within a ‘polar vortex’. There was more cold air above the Arctic than in any winter recorded since 1979, says Markus Rex, an atmospheric scientist at the Alfred Wegener Institute in Potsdam, Germany. In the chilly temperatures, the high-altitude clouds formed, and the ozone-destroying reactions began.