WORLDWIDE — Atypical weather conditions caused the Antarctic ozone hole to grow to an unusually large size in 2026, NOAA and NASA scientists reported today, though they said the protective ozone layer is still on track to recover by later this century. 

Fueled by a powerful polar vortex, the 2026 ozone hole became the seventh-largest in 48 years of monitoring, based on NOAA and NASA analysis of the seasonal mean area. However, scientists noted that this year’s hole would have been larger still if levels of ozone-destroying chemicals in the atmosphere had not been reduced through international cooperation.

NOAA scientists launch a weather balloon carrying an ozonesonde at the South Pole on October 1, 2023. Credit: Marc Jaquart/IceCube

During peak ozone depletion season between September 7 and October 13, 2026, the average extent of the hole covered about 9.6 million square miles (25 million square kilometers) — more than twice the area of the United States. Scientists continually track the amount of ozone in the stratosphere because it acts as Earth’s “sunscreen,” helping shield life from harmful solar radiation. This is distinct from ground level ozone, which is an air pollutant commonly resulting from human activities. 

“The annual ozone hole has been forming later in the season in recent years, which tells us the ozone layer is healing,” said Paul Newman, a senior scientist at the University of Maryland and longtime leader of NASA’s ozone research team at the agency’s Goddard Space Flight Center. “But an unusually powerful polar vortex has extended ozone depletion in the Antarctic this season, allowing the hole to grow to proportions we haven’t seen in a decade.” 

The hole reached its greatest extent for the year on September 18 at 10.5 million square miles (27.1 million square kilometers). That’s about 90% as large as the largest ozone hole ever observed, which occurred on September 9, 2000.

This data visualization shows the area and shape of the ozone hole on September 18, 2026, the day of its annual maximum extent. Scientists define the ozone hole as the area in which ozone concentrations drop below the historical threshold of 220 Dobson units. Credit NASA Earth Observatory

“The 2026 ozone hole is large but could have been 1 to 2 million square miles (3.5 million square kilometers) larger if ozone-depleting substances were as prevalent in the atmosphere today as they were at their year 2000 peak,” Newman said.

How does ozone loss occur?

The ozone depletion process begins when human-made compounds containing chlorine and bromine are released into the environment. Air currents carry the gases up into the stratosphere, where they’re broken down by ultraviolet radiation. The freed chlorine and bromine atoms interact with cloud particles in the Antarctic stratosphere to enable ozone destruction. The stratospheric polar vortex, a seasonal stream of wind encircling Antarctica, plays a key role by corralling the frigid air necessary to produce polar stratospheric clouds.

“The polar vortex was unusually large this year in part because planetary-scale weather systems that typically well up from the lower atmosphere and break up the vortex were especially weak in August and September,” said Amy Butler, a research scientist at the NOAA Chemical Sciences Laboratory. “That weak wave action kept the strongest polar vortex winds further from the South Pole by several degrees of latitude, creating a larger area for conditions ideal for ozone depletion to occur.” 

How do scientists measure and monitor the ozone hole?

The depletion of  ozone within the hole was not as severe as record-breaking holes that occurred 10 or 20 years ago. Deploying balloon-borne instruments from the South Pole Baseline Atmospheric Observatory, and using an optical instrument called the Dobson Ozone Spectrophotometer, NOAA scientists found that ozone concentrations directly overhead reached their lowest value for the year — 105 Dobson units — on October 17. 

The Dobson unit is the commonly used standard of measurement for expressing ozone concentration. One hundred Dobson Units represents a column of ozone that would be 1 millimeter deep – about as thick as a dime – if compressed under standard temperature and pressure conditions at sea level. The lowest value ever recorded over the South Pole was 92 Dobson units in October 2006.

Since 1979, satellites have also been integral to monitoring the health of the ozone layer. Instruments aboard NASA’s Aura satellite, the NOAA-20 and NOAA-21 satellites, and the Suomi National Polar-orbiting Partnership satellite, jointly operated by NASA and NOAA, all contributed to the annual monitoring.

NOAA and NASA scientists said that the ongoing monitoring shows that controls established by the Montreal Protocol in 1987 continue to drive long-term recovery of stratospheric ozone. 

An essential element the Montreal Protocol is the international commitment to replacing ozone-depleting substances like chlorofluorocarbons with less-harmful alternatives. Since their peak, chlorine levels in the Antarctic stratosphere derived from ozone-depleting substances have declined by about a third relative to levels reached in the 1980s, said Stephen Montzka, senior scientist at NOAA’s Global Monitoring Laboratory. 

What chemicals can cause the loss of ozone?

Chlorofluorocarbons and other ozone-depleting compounds were once widely used in consumer goods such as refrigerators, air conditioners, and building insulation. They can linger in the atmosphere or leach out of old products and landfills for many decades. As those older compounds break down, scientists estimate that the ozone hole will recover by the 2070s.

More: View the latest status of the ozone layer over the Antarctic by visiting NOAA’s South Pole Ozone website and NASA’s Ozone Watch.