(CNN)The ozone hole that typically grows over the Antarctic each September and October has become one of the largest and deepest in recent years -- just one year after scientists recorded its smallest size since it was discovered.
The Antarctic ozone hole is one of the largest and deepest in recent years
The 2020 ozone hole grew rapidly from mid-August and had grown to about 9.2 million square miles when it peaked in early October, according to a statement from the World Meteorological Organization (WMO).
It then shrank to about 8.9 million square miles -- more than twice the size of the United States -- covering almost the entire Antarctic continent, the agency said.
The WMO's Global Atmosphere Watch program works closely with the Copernicus Atmospheric Monitoring Service (CAMS), NASA, Environment and Climate Change Canada and other partners to monitor the Earth's ozone layer.
The ozone layer in our atmosphere protects the Earth from ultraviolet radiation.
"There is much variability in how far ozone hole events develop each year. The 2020 ozone hole resembles the one from 2018, which also was a quite large hole, and is definitely in the upper part of the pack of the last fifteen years or so," said CAMS Director Vincent-Henri Peuch in a statement.
The depletion is directly related to the temperatures in the stratosphere, where the ozone layer sits, because the polar stratospheric clouds that play an important role in the process only form at temperatures below -78 degrees Celsius (-108.4 Fahrenheit).
Ice crystals in the clouds react with compounds in the atmosphere that can then rapidly destroy ozone when they are exposed to sunlight, the WMO said.
NASA said last year's ozone hole was particularly small because of unusual weather patterns that cause warmer stratospheric temperatures over Antarctica.
The Antarctic ozone hole will shrink as temperatures warm up in the Southern Hemisphere, where it's spring, and will return to normal by December, the WMO said.
Peuch said this year's data confirms the need to continue enforcing the 1987 Montreal Protocol, which banned the emission of ozone depleting chemicals.
It banned chlorofluorocarbons, or CFCs, which were common in refrigerators, aerosol cans and other products before scientists realized they were damaging to the ozone layer.
A 2018 report by the UN Environment Programme and the WMO predicted that ozone values over Antarctica would return to pre-1980s levels by 2060.
CORRECTION: An earlier version of this story incorrectly identified the meteorological group. It is the World Meteorological Organization.