The European Space Agency (ESA) reported this month that the ozone hole—known more officially as the “ozone depleting area”—over Antarctica fluctuated in size this year more than most. Lingering ozone-depleting substances and last year’s eruption of the Hunga Tonga volcano could be to blame.
The ozone hole naturally fluctuates in size throughout the year. When sunlight starts to return to Antarctica between September and October, it activates chlorine and bromine in the stratosphere, resulting in a somewhat rapid depletion of ozone. This results in a bigger ozone hole. Typically, the ozone hole shrinks again around December, when the southern hemisphere’s polar vortex weakens and eventually breaks, prompting a slowdown in ozone depletion.
This is all to say that it’s normal to see the ozone hole expand during part of the year—but that a particularly significant ozone hole could still signal concerning stratospheric trends. According to data from the ESA’s Copernicus Sentinel-5P, the first Copernicus satellite dedicated entirely to atmospheric monitoring, the ozone hole reached a size of 26 million square kilometers (more than 10 million square miles) on Sept. 16, 2023. That’s roughly three times the size of Brazil, the ESA writes.
Though it’s a bit early to know why this fluctuation was so steep, the ESA has some ideas. When Hunga Tonga-Hunga Ha'apai, an underwater volcano in the South Pacific, erupted in early 2022, it threw water vapor into the stratosphere. This vapor might have taken until the end of 2022 to reach the south polar regions, where it boosted the formation of polar stratospheric clouds. These clouds transform benign forms of chlorine into reactive, ozone-destroying forms. Because human-made chlorofluorocarbons (CFCs) contain chlorine and tend to linger in the stratosphere, the Hunga Tonga volcano’s polar clouds might have exacerbated what ozone depletion was already occurring.
Hope is not lost, however. Thanks to widespread CFC bans from decades past, the ozone hole reached its smallest recorded size in 2019, and it’s said to be on a slow yet encouraging path to recovery.
“Based on the Montreal Protocol and the decrease of anthropogenic ozone-depleting substances, scientists currently predict that the global ozone layer will reach its normal state again by around 2050,” Copernicus Sentinel-5P mission manager Claus Zehner told the ESA.
