New data reveals one of the smallest ozone holes in decades: Study

Washington DC [US], December 4 : This year's ozone hole over Antarctica ranked among the smallest since the early 1990s, reflecting steady progress from decades of global action under the Montreal Protocol.

Declining chlorine levels and warmer stratospheric temperatures helped limit ozone destruction. Scientists say the layer remains on track to recover later this century.

Scientists from NOAA and NASA report that this year's ozone hole over Antarctica is the fifth smallest seen since 1992, the year that the Montreal Protocol, a landmark international agreement to phase out ozone-depleting chemicals, began to take effect.

During the peak of the 2025 ozone depletion season, from September 7 through October 13, the ozone hole covered an average of about 7.23 million square miles (18.71 million square kilometres).

It is already breaking apart almost three weeks earlier than the typical timing over the past ten years.

"As predicted, we're seeing ozone holes trending smaller in area than they were in the early 2000s," said Paul Newman, a senior scientist at the University of Maryland system and longtime leader of NASA's ozone research team.

"They're forming later in the season and breaking up earlier."

Peak size and long-term ozone records

On September 9, the ozone hole reached its largest single-day size for 2025, spanning 8.83 million square miles (22.86 million square kilometers).

That area is roughly 30% smaller than the largest ozone hole on record in 2006, which had an average size of 10.27 million square miles (26.60 million square kilometers).

In earlier assessments, NASA and NOAA rated ozone hole severity using records that extend back to 1979, when satellites first began tracking ozone levels above Antarctica.

Using this longer 46 year record, the 2025 ozone hole ranks as the 14th smallest in terms of area.

Montreal Protocol helps drive ozone layer recovery

According to NOAA and NASA scientists, this year's measurements support the conclusion that restrictions on ozone-depleting chemicals set by the Montreal Protocol and its later amendments are steadily helping the ozone layer recover.

They note that the layer is still expected to return to pre-ozone hole conditions later this century as countries worldwide continue to replace ozone-depleting substances with less harmful alternatives.

"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," said Stephen Montzka, senior scientist with NOAA's Global Monitoring Laboratory.

"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," added NASA's Newman.

Weather balloon observations showed that in 2025, the ozone layer directly over the South Pole dropped to a minimum of 147 Dobson Units on October 6.

For comparison, the lowest value ever measured over the South Pole was 92 Dobson Units in October 2006.

What ozone is and why it matters for life on Earth

Earth's ozone-rich layer functions like a global sunscreen that protects living things from harmful ultraviolet (UV) radiation from the sun. This layer resides in the stratosphere, which lies between 7 and 31 miles above Earth's surface.

When ozone levels drop, more UV rays reach the ground, increasing the risk of crop damage and contributing to higher rates of skin cancer and cataracts, along with other negative health effects.

Ozone depletion begins when certain chlorine- and bromine-containing compounds reach the stratosphere, where intense UV radiation breaks them apart and releases reactive forms of chlorine and bromine. These reactive substances then interact with ozone molecules and destroy them.

For many years, compounds such as Chlorofluorocarbons (CFCs) and other ozone-depleting substances were widely used in aerosol sprays, foam products, air conditioners and refrigerators, and the chlorine and bromine in these chemicals can remain in the atmosphere for long periods.

American leadership in science, technology, and policy has been central to identifying these risks and driving actions that protect the ozone layer as well as the health and prosperity of the American people.

Legacy chemicals and projected ozone hole recovery

Although these chemicals are now banned, many still linger in older materials such as building insulation and in landfills. As emissions from these legacy sources gradually diminish, scientists expect the ozone hole over Antarctica to recover (get smaller) by around the late 2060s.

Laura Ciasto, a meteorologist with NOAA's Climate Prediction Center and a member of the ozone research team, noted that conditions such as temperature, overall weather patterns and the strength of the band of winds circling Antarctica known as the polar vortex also affect ozone levels and the size of the ozone hole from year to year.

"A weaker-than-normal polar vortex this past August helped keep temperatures above average and likely contributed to a smaller ozone hole," said Ciasto.

Global network tracks ozone from space and the surface

Keeping an eye on the ozone layer takes a team of observing systems spread across the globe. Scientists monitor ozone using instruments aboard NASA's Aura satellite, the NOAA-20 and NOAA-21 satellites, and the Suomi National Polar-orbiting Partnership satellite that is jointly operated by NASA and NOAA.

NOAA scientists also rely on instruments carried by weather balloons, along with upward-looking surface-based instruments, to directly measure stratospheric ozone above the South Pole Atmospheric Baseline Observatory.

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