High above the Arctic, winds swirling around the pole in the winter darkness are isolating an air mass that will grow colder and colder over the coming weeks.
It will create what James Drummond, an atmospheric physicist at Dalhousie University, likes to describe as a "chemical cauldron" around the pole — one that can do nasty things to the Earth's protective ozone layer.
Last year, the cauldron chewed an unprecedented hole in the Arctic ozone. It is anyone's guess what will unfold this winter.
The 2011 hole is thought to have been a rare one-off occurrence. And there will be plenty of concern if there is a repeat in 2012.
"If we were to have ozone holes on a regular basis, that would imply that we don't understand what is going on," says Drummond, one of Canada's leading atmospheric scientists. "And when you don't understand, then you start worrying."
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