Record ozone depletion over the Arctic early this year rivals what was observed in the Antarctic when holes in the protective atmospheric layer first appeared there during the 1980s.

The observation raises concerns that portions of the Northern Hemisphere might periodically begin experiencing potentially harmful levels of ultraviolet radiation during early spring, an international team of scientists reports online October 2 in Nature.

“It was significantly worse than anything we have ever seen,” says Geir Braathen of the World Meteorological Organization in Geneva, who was not one of the authors of the Nature paper. Typically, spring Arctic ozone depletion has maxed out at a drop of between 20 and 30 percent, the atmospheric chemist notes. “But in 2011, we had a loss of around 40 percent.”