The ?? ???ozone hole grew pretty large this year — but that's expected.

Researchers from the European Union's Copernicus Atmosphere Monitoring Service announced Tuesday that the ozone hole — a big zone of depleted ozone over the Antarctic region — reached its maximum extent for the year. It swelled to some 23 million square kilometers in size, or 8.9 million square miles, one of the largest and deepest holes of the last 15 years. That's well over twice the size of the U.S.

It's an above-average sized hole, but certainly not extreme or unprecedented, explained Richard Engelen, the deputy director of the Copernicus Atmosphere Monitoring Service.

The Antarctic ozone hole, which exists annually between September through December, wavers in size from year-to-year as it's strongly influenced by weather events in the atmosphere. The recurring ozone hole, however, is a consequence of civilization having released bounties of ozone-depleting chemicals into the atmosphere (like from refrigerants used in things like air conditioners and fridges) during the 20th century.

The 2020 ozone hole, massive and continent-sized, is what we would expect, based on the amount of ozone-depleting chemicals currently in the atmosphere, explained Paul Newman, the chief scientist in the Earth Sciences Division at NASA's Goddard Space Flight Center.

"This is not a good thing," Newman said, noting these chemicals are long-lived in the atmosphere. There's no quick fix. "It's going to be with us for many decades," he said.

Critically, global nations signed an international treaty (the Montreal Protocol) in the late 1980s that banned these chemicals, allowing the ozone layer to slowly repair. (Though some rogue operators still illegally release these chemicals into the atmosphere.)

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Without this landmark global environmental pact, ozone depletion would be much more widespread today.

"If we had done nothing, this would have gotten much worse," said Engelen.

The ozone layer is critical for life on Earth. It blocks damaging ultraviolet (UV) radiation from the sun. We know how UV rays burn our skin, but might not always appreciate that much of surface-dwelling life on land and in the oceans depends on the ozone layer for protection, too. UV radiation impairs functions of both plants and phytoplankton, and damages the DNA of living organisms. Many organisms can't hide from a depleted ozone layer. "It impacts life on Earth," noted Engelen.

The orange line shows the extent of the ozone hole in 2020. Credit: eu copernicus / cams The ozone hole on Sept. 27, 2020. Credit: Eu Copernicus / cams

Each year, a depleted area of ozone, or hole, grows over the Antarctic region in September and October. Sunlight returns to Antarctica this time of year, and the light reacts with ozone-depleting chemicals high up in the atmosphere where ozone lives, a place called the stratosphere. These reactions make chlorine, the chemical that ultimately destroys ozone.

The reactions happen in extremely cold conditions (below -78 degrees Celsius, or -108 degrees Fahrenheit) in icy clouds. This year, conditions have been colder than usual in the stratosphere, thanks to a stronger polar vortex (a whirling jet of air that forms over the poles) in the region, which confined cold air over the area. As a result, the environment was favorable for ozone-killing chemicals to react with sunlight. "Things are a little colder than normal and that leads to a bigger and deeper ozone hole," said NASA's Newman.

"There’s bad news and good news."

In stark contrast, temperatures in the stratosphere last year were abnormally warm, leading to a record low size for the ozone hole.

The good news in 2020, noted Newman, is the ozone hole is some 3 to 4 million square kilometers smaller than it would have been 20 years ago. Then, levels of ozone-destroying chemicals in the atmosphere were much higher.

The ozone hole will take at least decades longer to fully repair. But it's only repairing because global society listened to scientists and banned ozone-killing chemicals some 30 years ago.

"There’s bad news and good news," said Newman.

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