On Sept. 20, the Antarctic ozone hole peaked at 10.6 million square miles (27.4 million square kilometers), the second-largest size ever observed for this time of the year.

The last time the ozone hole was this huge remained in October 2015, when it reached a massive 10.8 million square miles (27.9 million square km), records from the Copernicus Atmosphere Monitoring Service program. Why is the hole in the ozone layer– the guard that safeguards life on Earth from damaging ultraviolet solar radiation– so huge this year, in spite of other ideas informing researchers that it is recuperating as anticipated from the damage human-made chemicals did in the 20th century?