Every winter, over Antartica, scientists track the size and shape of the "hole" in the ozone layer, about 13 miles above the ground. A ring of strong winds around the south pole during the winter isolates the air over the pole. In this polar vortex, chlorine ions break off from CFC molecules that make it into the upper atmosphere, and breaks down the ozone.
But, this year, a similar ozone hole was detected over the North Pole.
Ozone is a chemical usually present in the upper atmosphere that blocks harmful ultraviolet radiation that can cause skin cancer. An unusually cold winter around the North Pole is blamed for the hole. The article appears in the scientific journal Nature.