Richard Musgrove
A new Massachusetts Institute of Technology-led study confirms that the Antarctic ozone layer is healing as a direct result of global efforts to reduce ozone-depleting substances.
Our planet’s natural ozone layer is the earth’s version of 50+ sunscreen — its presence reduces UV and its carcinogenic effects. Complex life could not exist on this planet without the ozone layer.
But from early last century we started pouring refrigerants such as chlorofluorocarbons (CFCs) into the atmosphere. In 1986 studies revealed a “hole” over Antarctica, with evidence suggesting CFCs were to blame — destroying ozone (O3) faster than it could be naturally replenished, and reducing its protective effects.
Which lead to a global CFC ban in 1992, known as the Montreal Protocol.
Watch NOAA’s animation of the daily progression through the 2024 season (Above). The purple and blue colours are where there is the least ozone, and the yellows and reds are where there is more ozone.
Since then, the hole has been healing, but it hasn’t been clear whether this was due to the reductions in ozone-depleting chemicals; natural weather variability; or increased greenhouse gas emissions in the stratosphere.
The answer builds confidence in the strategy.
Ozone depleted regions sit over both poles, but mostly Antarctica.
The Antarctic hole was relatively small during 2024’s peak depletion season — September 7th to October 13th — compared to other years, says NOAA. Small is relative — it was still 22.4 million square kilometres, 3 times the size of Australia.
Last year the National Oceanic and Atmosphere Administration of the US predicted full recovery by 2066.
Now MIT researchers have added granularity and a little optimism to that prediction.
Coauthor Professor Susan Solomon of Environmental Studies and Chemistry at the MIT, and colleagues, noticed significant ozone hole recovery in 2016. The hole seemed to be shrinking each year, she says. Solomon was part of the original research team that gave evidence of CFC harms that lead to the Montreal Protocol.
But why was the hole shrinking? Was it CFCs, or was it weather variability from El Nino, La Nina or the polar vortex?
“While detecting a statistically significant increase is relatively straightforward, attributing these changes to specific forcings is more challenging,” says lead author of the current study, Peidong Wang, of the MIT’s Department of Earth, Atmospheric and Planetary Sciences.
Fingerprinting the ozone evidence
To resolve this question the MIT team borrowed a ‘fingerprinting’ technique used by the climate change community to isolate specific climate factors from natural meteorological “noise” — in this case attempting to remove the static from the CFC reduction-ozone hole recovery argument.
“The atmosphere has really chaotic variability within it,” Solomon says. “What we’re trying to detect is the emerging signal of ozone recovery against that kind of variability, which also occurs in the stratosphere.”
Computer model simulations were run with ‘parallel worlds’ generated using the same global atmosphere with different starting conditions, say without greenhouse gases (GHGs) or CFCs, to isolate natural weather variability. Or with or without GHGs or CFCs to determine possible effects of both. Questions included how ozone changed with altitude and season, and with different starting conditions. From these simulations they mapped out times and altitudes of monthly recovery.
The pattern was there — a fingerprint showing that ozone recovery was due to declining ozone- depleting chemicals. In the model, at least.
So, they knew what to look for, but did this fingerprint appear in the real world? Fifteen years of observational data on the Antarctic ozone hole were mined for this telltale sign. They saw it, becoming clearer and clearer, peaking in 2018.
“After 15 years of observational records, we see this signal to noise with 95 percent confidence, suggesting there’s only a very small chance that the observed pattern similarity can be explained by variability noise,” Wang says. “This gives us confidence in the fingerprint.
“It also gives us confidence that we can solve environmental problems. What we can learn from ozone studies is how different countries can swiftly follow these treaties to decrease emissions.”
Solomon says there will soon be a year when the ozone layer stays entirely intact, here and there, and eventually shuts for good.
“By something like 2035, we might see a year when there’s no ozone hole depletion at all in the Antarctic. And that will be very exciting for me,” she says. “And some of you will see the ozone hole go away completely in your lifetimes. And people did that.”
Slow pace of Ozone improvement poses threat to Antarctic life
