Published on 5 November 2018
The ozone hole that forms over the Antarctic each September is primarily driven by two factors: the amount of ozone-destroying chlorine in the polar stratosphere and the availability of ice crystals in stratospheric clouds for the chlorine to bind to. This year, the super-cold stratospheric temperatures measured by NOAA and NASA meant conditions were ripe for the development of ice clouds - and a big ozone hole.
But the size of the 2018 ozone hole seen by NASA satellites was just a little larger than average, covering 8.83 million square miles (almost three times the size of contiguous United States). That’s because chlorine levels have been falling thanks to a 30-year-old global environmental treaty known as the Montreal Protocol.