The ozone hole over the Antarctic in 2025 was the fifth smallest since 1992 — "the year a landmark international agreement to phase out ozone-depleting chemicals began to take effect," per a new NOAA-NASA report.
Why it matters: While the ozone hole varies in size from year to year, the report says this year's monitoring shows "controls on ozone-depleting chemical compounds established by the landmark Montreal Protocol and subsequent amendments are driving the gradual recovery of the ozone layer."
- The ozone layer shields Earth's inhabitants from the sun's harmful ultraviolet radiation as it sits in the stratosphere 9-22 miles above Earth. Its depletion "increases the amount of UVB that reaches the Earth's surface" — and this can impact plants, marine ecosystems UVB causes non-melanoma skin cancer, per the EPA.
- Thanks to the protocol that was signed in 1987 and subsequently ratified by all United Nations member states, the ozone layer "remains on track to recover fully later this century," the NASA-NOAA report notes.
Context: Countries agreed in the Montreal Protocol on Substances that Deplete the Ozone Layer to restrict the production and import of ozone-depleting substances after large seasonal ozone losses linked to chlorofluorocarbon chemicals (CFCs) were recorded over Antarctica.
- The agreement led to the phasing out of CFCs that were found in refrigerants and aerosol cans.
- "Still, the now-banned chemicals persist in old products like building insulation and in landfills," the report notes. "As emissions from those legacy uses taper off over time, projections show the ozone hole over the Antarctic recovering around the late 2060s."
State of play: Atmospheric scientist Laura Revell told Axios Wednesday the ozone hole varies in size due to factors related to climate variability, with wildfires and large volcanic eruptions driving the hole to be larger than normal, but overall "we are starting to see ozone recovery."
- Tuesday's report found that a "weaker-than-normal polar vortex this August helped keep temperatures above average and likely contributed to a smaller ozone hole."
- Stephen Montzka, a senior scientist with NOAA's Global Monitoring Laboratory, noted in the report that since peaking around the year 2000, "levels of ozone-depleting substances in the Antarctic stratosphere have declined by about a third, relative to pre-ozone-hole levels."
What they found: A the height of this year's depletion season, from Sept. 7 through Oct. 13, when the ozone layer develops a thin spot, the average extent of the hole was about 7.23 million square miles — twice the area of the contiguous U.S.
- The hole reached its greatest one-day extent for the year on Sept. 9 at 8.83 million square miles, about 30% smaller than the largest hole ever observed, the report notes.
What they're saying: "As predicted, we're seeing ozone holes trending smaller in area than they were in the early 2000s," said Paul Newman, a senior scientist with the University of Maryland, Baltimore County, and leader of the ozone research team at NASA's Goddard Space Flight Center in Greenbelt, Maryland.
- "They're forming later in the season and breaking up earlier. But we still have a long way to go before it recovers to 1980s levels," added Newman, in a statement shared in the NASA-NOAA report.
- "This year's hole would have been more than one million square miles larger if there was still as much chlorine in the stratosphere as there was 25 years ago."
The bottom line: The Montreal Protocol is "one of the most effective environmental treaties to date," said Revell, who's an associate professor at the University of Canterbury in New Zealand.
- "Through this mechanism, ozone-destroying gases have been phased out, and this is a double win, since ozone-destroying gases tend to be very effective greenhouse gases, too," she said.
- "I don't think it can be overstated what a success story the Montreal Protocol is, since if we'd kept on emitting ozone-depleting gases at the rate we were in the 1970s and early '80s, the entire ozone layer would been almost entirely destroyed by the mid-21st century. Instead, it's on track to recovery."
Yes, but: Revell noted that there are "emerging threats to ozone recovery" that scientists are monitoring, including the rapid intensification of the space-launch industry.
Go deeper: The Montreal Protocol saved the ozone layer
