Scientists say a hole in the Arctic’s protective ozone layer last winter was the largest ever recorded, reaching an extent typically observed above Antarctica. While so-called ozone “holes” have occurred each summer since the mid-1980s over Antarctica — where extreme cold and powerful wind patterns trigger reactions that convert chlorine from human-produced chemicals into ozone-destroying compunds — warmer stratospheric temperatures in the Arctic have typically limited ozone loss. According to a new study, published in the journal Nature, unusually low stratospheric temperatures and powerful high-altitude wind patterns above the Arctic earlier this year created the conditions for an unprecedented ozone hole over northern Russia and parts of Norway and Greenland, exposing populations across the region to high levels of ultraviolet radiation.