In the first three months of this year, something unprecedented happened in the skies over the Arctic. A large hole appeared in the ozone layer, far bigger than any seen there before.
The Arctic ozone layer suffers a little damage every winter, but the effect is normally short-lived. "This is a clear step beyond that," says Neil Harris of the University of Cambridge. As the measurements came in, ozone researchers began to debate whether the loss could be compared to that seen over the Antarctic. "It's the first time we've even discussed that question," says Harris.