No. It wasn't global warming. There was a huge hole in the Arctic ozone layer last winter because the stratosphere was colder than previous years. It is the largest ever recorded, but we have only been recording since the age of satellites.
ScienceDaily — A NASA-led study has documented an unprecedented depletion of Earth's protective ozone layer above the Arctic last winter and spring that was caused by an unusually prolonged period of extremely low temperatures in the stratosphere. University of Toronto physicist Kaley Walker was part of the international team behind the study to be published online on October 2 in Nature.
The researchers found the amount of ozone destroyed in the Arctic in 2011 was comparable to that seen in some years in the Antarctic, where an ozone "hole" has formed each spring since the mid 1980s. The stratospheric ozone layer, extending from about 15 to 35 kilometres above the surface, protects life on Earth from the sun's harmful ultraviolet rays.
The scientists found that at some altitudes, the cold period in the Arctic lasted more than 30 days longer in 2011 than in any previously studied Arctic winter, leading to the unprecedented ozone loss. Further studies are needed to determine what factors caused the cold period to last so long.