The 2026 Antarctic ozone hole ranked as the seventh-largest in 48 years of observations, based on its average seasonal area. Scientists attributed the expansion primarily to an exceptionally strong polar vortex, a large circulation of winds that influences atmospheric conditions over Antarctica. They also emphasized that international efforts to reduce harmful chemicals have prevented the hole from becoming even larger.

Between September 7 and October 13, 2026, when ozone depletion was at its seasonal peak, the hole covered an average of approximately 9.6 million square miles (25 million square kilometers). That is more than twice the size of the United States. Scientists closely monitor ozone in the stratosphere because it serves as Earth's natural "sunscreen," protecting living organisms from dangerous solar radiation. Unlike this beneficial layer high in the atmosphere, ozone near Earth's surface is a pollutant frequently associated with human activities.

Antarctica's Ozone Hole Reaches Its Largest Size in a Decade

The ozone hole reached its maximum extent on September 18, spreading across 10.5 million square miles (27.1 million square kilometers). This was approximately 90% of the size of the largest ozone hole ever measured, which occurred on September 9, 2000.

"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."

Although the hole expanded to an extraordinary size, the results also demonstrate the benefits of decades of international environmental protections. Without reductions in chemicals known to destroy ozone, the affected area could have been substantially greater.

"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 a Powerful Polar Vortex Accelerates Ozone Loss

Ozone depletion begins with chemicals released through human activities, particularly compounds containing chlorine and bromine. Atmospheric circulation transports these substances into the stratosphere, where ultraviolet radiation breaks them apart. The released chlorine and bromine atoms then participate in chemical reactions involving particles in Antarctic stratospheric clouds, leading to the destruction of ozone.

A major factor in this process is the stratospheric polar vortex, a seasonal band of strong winds that circles Antarctica. This circulation traps extremely cold air over the region, allowing the formation of the special clouds that help trigger ozone destruction. When the vortex becomes unusually strong or expansive, conditions favorable for ozone loss can persist across a larger area.

In 2026, atmospheric disturbances that would normally weaken the vortex were unusually subdued. This allowed the circulation to remain powerful and helped create a broader region where ozone could be destroyed.

"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."

NASA and NOAA Measure the 2026 Ozone Hole

Despite its exceptional geographic size, the 2026 ozone hole did not experience the same extreme levels of ozone loss observed during record-breaking events 10 or 20 years earlier.

To measure ozone concentrations, NOAA researchers launched instruments attached to weather balloons from the South Pole Baseline Atmospheric Observatory. They also collected readings using the Dobson Ozone Spectrophotometer, an optical device designed to measure atmospheric ozone. Their observations showed that ozone levels directly above the South Pole fell to their lowest reading of 2026 on October 17, reaching 105 Dobson units.

The Dobson unit is the standard measurement used to describe the total amount of ozone above a particular location. To illustrate the scale, 100 Dobson units would produce a layer of ozone just 1 millimeter thick, approximately the thickness of a dime, if all the ozone in the atmospheric column were compressed to standard temperature and pressure at sea level. The lowest ozone concentration ever measured over the South Pole was 92 Dobson units in October 2006.

Satellites provide another essential source of information. Since 1979, spaceborne instruments have helped scientists observe changes in the ozone layer and track its condition over time. The 2026 measurements included data from NASA's Aura satellite, NOAA-20, NOAA-21, and the Suomi National Polar-orbiting Partnership satellite, a joint NASA and NOAA mission.

Why Earth's Ozone Layer Is Still Recovering

Scientists say the latest observations reinforce evidence that international restrictions on ozone-destroying chemicals are working. Much of that progress can be traced to the Montreal Protocol, a global agreement adopted in 1987 to phase out substances responsible for damaging the ozone layer.

Under the agreement, countries committed to replacing harmful compounds such as chlorofluorocarbons with alternatives that pose less danger to atmospheric ozone. According to Stephen Montzka, a senior scientist at NOAA's Global Monitoring Laboratory, chlorine concentrations in the Antarctic stratosphere associated with ozone-depleting chemicals have declined by approximately one-third compared with their peak levels in the 1980s.

These reductions are significant because chlorofluorocarbons and other ozone-depleting compounds were once common in refrigerators, air conditioning systems, building insulation, and other everyday products. Although many of these substances have been phased out, they can remain in the atmosphere for decades. Additional emissions can also occur when older equipment, materials, and landfill waste release chemicals that were manufactured years ago.

Because these compounds break down so slowly, repairing the ozone layer takes many decades. Nevertheless, continued monitoring by NASA and NOAA indicates that the long-term recovery is progressing. Even with unusually large seasonal ozone holes such as the one observed in 2026, scientists expect the Antarctic ozone hole to recover by the 2070s.

The latest findings illustrate how exceptional atmospheric conditions can temporarily produce severe ozone depletion without reversing decades of environmental progress. They also highlight the lasting impact of international cooperation in protecting Earth's atmosphere.