The recovery of Earth’s ozone layer is a rare environmental story in which a global response has produced measurable progress. It is also a story best told with patience: harmful chemicals can remain in the atmosphere for a long time.
A NASA study announced in 2018 provided an especially useful piece of evidence. Satellite measurements connected declining chlorine with reduced ozone destruction over Antarctica, supporting the expected benefit of restrictions on ozone-depleting chemicals.
The chemical measurement behind the good news
The 2018 article named Susan Strahan and Anne Douglass as the researchers examining the Antarctic record. Their work went beyond comparing the outlined size of the ozone hole: it investigated the chemicals involved in wintertime ozone destruction. That distinction is why the results offered evidence about the effects of the Montreal Protocol rather than merely another annual map.
Atmospheric scientist Bill Randel, quoted in the contemporary reporting, welcomed the consistency between declining chlorine and the expected policy effect:
“They’re seeing net decreases in chlorine that are very consistent with the Montreal Protocol,”
“That’s a big take-home message, that the Montreal Protocol is doing what we think it should be doing.”
Strahan’s reaction was more personal: “It’s nice to have some positive environmental news for a change.” The original optimistic closing belongs beside the measurements. Its older 2060s–2080s recovery horizon is a historical estimate; the later regional projections below provide a more specific assessment without making recovery unconditional.
The measurement involved more than watching the hole’s outline. NASA’s 2018 explanation describes how, after most available ozone has been depleted, chlorine reacts with methane and accumulates as hydrogen chloride, HCl. Measuring that gas around mid-October gives a way to estimate total chlorine. Comparing it with nitrous oxide helped distinguish changing chlorine abundance from variations in the sampled air. The study found an average decline of about 0.8 percent per year; its ozone-loss comparisons covered 2005–2016.
What the 2018 study measured
Researchers used the Microwave Limb Sounder aboard NASA’s Aura satellite to examine Antarctic stratospheric chemistry. Their published account of the findings reported about 20% less ozone depletion during the Antarctic winter in 2016 than in 2005, linked to a decline in chlorine.
Chlorofluorocarbons can reach the stratosphere, where ultraviolet radiation breaks them apart and releases chlorine that participates in ozone-destroying reactions. Restricting those chemicals addresses the cause, but their long atmospheric lifetimes mean the response unfolds over decades.
The result was evidence of recovery under way. It did not mean that the Antarctic ozone hole had disappeared.
Why one year’s hole can still be large
The ozone hole is a region of severe seasonal depletion, rather than a literal opening in the atmosphere. Antarctic conditions help enable the chemistry that destroys ozone during the Southern Hemisphere spring.
Year-to-year weather and stratospheric conditions affect its size and duration. A single large or small season therefore needs to be placed within a longer record.
The historical comparison image accompanying this article shows earlier years. It is not a current monitoring map, and its sequence should not be read as a perfectly smooth year-by-year recovery.
Recovery dates are projections with conditions
The 2022 Scientific Assessment of Ozone Depletion projected a return to 1980 total-column ozone levels around 2040 for the near-global average, around 2045 in the Arctic and around 2066 over Antarctica, under the assessment’s assumptions.
These are regional estimates, not a single deadline for the whole atmosphere. Continued compliance with the controls on ozone-depleting substances remains part of the recovery story.
Ozone depletion and climate change are connected through atmospheric processes and some shared chemicals, but they are different problems. Progress on one does not establish that the other has been solved.
The 2025 ozone hole
The trend the 2018 study pointed to has continued. NASA and NOAA ranked the 2025 Antarctic ozone hole the fifth smallest since 1992, averaging about 18.7 million square kilometres between 7 September and 13 October, roughly 30% smaller than the record hole of 2006; Europe’s Copernicus service said it closed on 1 December, the earliest since 2019. NOAA’s Stephen Montzka noted that ozone-depleting substances in the Antarctic stratosphere had fallen by about a third since peaking around 2000. NASA’s Paul Newman estimated that without the reduction in those chemicals, the 2025 hole would have been more than a million square miles larger. (The roughly 30% comparison applies to the season’s largest single-day extent, 8.83 million square miles (about 22.9 million km²) on 9 September, against the record hole of 2006; the 7 September–13 October average was about 7.23 million square miles, and NASA projects recovery around the late 2060s (NASA, 24 November 2025).) One small season is not the trend on its own, but it fits the long record described above.
Good environmental news benefits from a long view
The most encouraging feature here is the chain from identifying a problem to changing emissions and measuring the atmosphere’s response.
For another Antarctic image that becomes clearer with its history attached, see NASA’s rectangular iceberg. And Costa Rica’s forest recovery offers a land-based example of why definitions, time periods and continuing stewardship belong beside a hopeful headline.
More images
Earth’s stratosphere, from space. Image: NASA
Video and posts
The hole is a measurement threshold, not empty sky
NASA’s Ozone Watch describes the Antarctic ozone-hole boundary using total column ozone at 220 Dobson units. “Total column” refers to the ozone amount through the atmospheric column above a location. The outlined region marks unusually low ozone; the word “hole” does not mean that the atmosphere or every ozone molecule has vanished there. NASA explains the threshold and its historical basis.
Area and amount answer different questions
A map can show how much territory falls below a selected threshold. A separate measurement can describe how low ozone levels become. These are related but distinct: the largest outlined area need not coincide with the lowest value at any one point.
For a simple analogy, imagine mapping places where a temperature falls below a chosen value. The area of that map and the coldest reading are not the same statistic. The analogy explains threshold mapping; it does not imply that ozone behaves like temperature.
This distinction helps when comparing headlines. One may discuss a season’s maximum hole area, another the minimum ozone amount, and a third a long-term assessment. Those statements can coexist without contradicting one another. Keep the measurement, geographic scope, and time interval beside the claim. Doing so makes the recovery story clearer and avoids treating a single striking map as a verdict on decades of atmospheric change.
Original feature credits and references: Atmosphere.Copernicus.eu · new study · slowly healing · firm scientific understanding · Earther.
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