The 2021 Antarctic ozone hole reached its maximum area on Oct. 7 and ranks 13th largest since 1979.
Credits: NASA Ozone Watch
There has been much speculation around the 2021 Antarctic ozone hole and whether this year would result in a record-breaking large hole. On 27 October, NASA and NOAA confirmed the 2021 ozone hole reached its maximum area on October 7, peaking at 9.6 million square miles (24.8 million square kilometers) – roughly the size of North America – ranking it the 13th largest since 1979. The hole will likely persist into November, even early December.
“This is a large ozone hole because of the colder than average 2021 stratospheric conditions, and without a Montreal Protocol, it would have been much larger,” said Paul Newman, chief scientist for Earth Sciences at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The Montreal Protocol was set up in 1987 to protect human health and the environment from the adverse effects of ozone layer depletion caused by several man-made substances such as chlorofluorocarbons (CFCs). With the universal support of 198 nations, the Montreal Protocol led to the phase-out of almost 99 per cent of ozone-depleting substances.
While initial measurements in September caused concern, the overall trend is towards the ozone hole slowly closing. Estimates predict that it will return to pre-1980 levels by the 2060s.
Very low winter temperatures in the Antarctic stratosphere during August to October lead to the formation of polar stratospheric clouds. Special reactions that occur in these clouds lead to the formation of reactive forms of chlorine and bromine, derived from man-made ozone-depleting substances, which then initiate ozone-destroying reactions with the help of sunlight in the Antarctic at the end of winter. The size of the 2021 ozone hole, therefore, is more a reflection of the colder than average temperatures and strong winds circling the Antarctic from August up until now.
In contrast, abnormally warmer temperatures in the Southern Hemisphere in 2019, for example, dramatically limited ozone loss in September and October that year, resulting in the smallest ozone hole observed since 1982.
While the 2021 Antarctic ozone hole is larger than average it is consistent with the continued decline of ozone-depleting substances and the colder meteorological conditions. Current ozone hole recordings are less severe than the extreme ozone holes observed during the 1990-2010 period, indicating the implementation of the Montreal Protocol and the healing of the ozone layer remain on track.
For a more in-depth analysis of the state of the ozone hole for 2021 click here