A large ozone hole can occur during recovery

The Antarctic ozone hole was unusually large in 2026 while the ozone layer's longer recovery remained on track.

Ozone-depleting chemicals change over decades. Atmospheric conditions can vary enough between seasons to produce a larger hole within that longer trend. A sequence of progressively smaller satellite images is therefore an incomplete test of recovery.

Researchers need to separate annual conditions from the chemical change. Hole size supplies one measure, with other observations needed to explain what happened.

The 2026 seasonal mean was unusually large

NASA's November 4, 2026 update with NOAA ranks the hole seventh largest by seasonal mean area in the monitoring record. The average during the defined peak-depletion period was about 25 million square kilometers. Its depth was less severe than that of some other large holes. The November 2026 update

Area measures extent, while depth measures depletion within it. A seasonal average also covers a different period from the largest daily value. A trend comparison needs the same measure across years.

My older note focused on the smaller 2024 hole. Evaluating recovery after the larger 2026 season requires accounting for the annual conditions before drawing a conclusion about the underlying change.

A selected satellite image leaves that explanation to the measurements behind it.

Ozone absorbs ultraviolet radiation

Most atmospheric ozone is in the stratosphere, where it absorbs part of incoming ultraviolet radiation. EPA describes that protective role. Its overview also explains natural variation with season or latitude. Basic ozone-layer science

An ozone hole is a region of severe seasonal depletion. Its mapped area is defined by an ozone threshold, making observations comparable across dates. The atmosphere remains above the depleted region.

A map therefore needs its date with the definition of the measured quantity. Extent describes one change; total ozone loss describes another. The duration of depletion adds a time measure.

Identify which quantity a headline describes before comparing its result with another report. Two accounts may concern different observations even when their maps look similar.

The polar vortex affects the season

NOAA attributes part of 2026's ozone loss to an unusually strong polar vortex. Human-made compounds release chlorine and bromine in the stratosphere. Cold polar conditions help those chemicals destroy ozone. NOAA's explanation

The chemical burden follows a slower trajectory than the weather. A different vortex can therefore change a season's depletion while the amount of ozone-depleting material continues its longer-term change.

The agencies also model what the hole could have looked like under an earlier, higher chemical burden. That counterfactual estimates an effect of the chemical change. It needs the model's assumptions alongside its result.

Comparing annual observations examines changes between seasons. Modeling the earlier chemical burden examines a different cause. Both can inform the recovery account when their questions remain explicit.

Match the bulletin to its observation year

WMO's September 2026 bulletin describes the 2025 Antarctic hole as one of the smallest in recent decades. It places annual variation within the recovery trend. November's account concerns the 2026 season, so the two publications report different observation years. The September 2026 bulletin

Keep the observation period beside the publication date. A report published in 2026 may assess measurements collected in 2025.

Recovery projections also need their defined region. Each projection uses a reference level with assumptions about the atmosphere's future behavior. Different regions can reach their reference levels at different times.

I'd describe each recovery date as a conditional estimate for that region. Assessing whether the projection needs revision requires evidence about its assumptions beyond the size of one season's hole.

Continue testing the recovery account

The Montreal Protocol controls ozone-depleting substances. Monitoring agencies examine the atmosphere over time to assess the recovery under those controls.

Continued observations can detect an unexpected chemical signal. They can also reveal atmospheric behavior outside the projected pattern. Such findings give researchers a reason to investigate whether the explanation needs revision.

The account of progress is that international controls changed the conditions driving ozone damage. Continuing ultraviolet exposure remains relevant, with the atmosphere's response still measured as recovery proceeds.

The difficult 2026 season belongs in that record. Explaining it against the longer measurements gives the next observation a testable account to extend or revise.