On September 20, the Antarctic ozone hole reached an extent of
24 point 8 million square kilometers. 2020 was the 12th
largest hole on record in 2019. The peak extent was the second
smallest hole on record, but this stark contrast doesn't mean
the hole is worsening. That's where weather patterns come in.
Colder temperatures are one of the factors that activate ozone
depletion, which means that weather patterns play a vital
role in determining the ozone holes extent each year. The
Antarctic ozone hole peaks during the southern hemisphere's
late winter, when temperatures are at a low and the sun's rays
return. The 2020 ozone hole was exceptionally large due to a
stable and cold Antarctic vortex, the stratospheric low
pressure system that flows clockwise in the atmosphere
above Antarctica. It's there that the colder conditions help
support formation of polar stratospheric clouds, whose
cloud particles activate ozone layer destroying forms of
chlorine and bromine compounds. These compounds stem from
years of human production and used to be found in things like
aerosol sprays and refrigerants. Unfortunately, it took years to
realize how damaging they are to the ozone.
If chemically active forms of chlorine and bromine are
present, and there are both cold enough temperatures and sun
rays, a reaction occurs on the surfaces of cloud particles that
form in cold stratospheric layers, leading ultimately to
runaway reactions that destroy ozone molecules. The Antarctic
ozone hole was first discovered by researchers at the British
Antarctic Survey in 1985. Just a few years later, in 1987, the
international community signed the Montreal Protocol on
substances that deplete the ozone layer. Countries as small
as the Vatican and as far as North Korea signed the deal,
regulating the consumption and production of ozone depleting
compounds. Since 2000, human made ozone depleting substances
have slowly declined, but remain high enough to produce
significant ozone loss. These compounds have lifetimes of more
than 50 years, which is why we're still seeing their effects
on the environment today. The ozone hole over Antarctica is
expected to gradually become less severe, as
chlorofluorocarbons continue to decline. And because of
scientifically supported international action. Scientists
expect the Antarctic ozone to recover back to 1980 levels
around the year 2070.