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 big was in October 2015, when it reached a whopping 10.8 million square miles (27.9 million square km), records from the Copernicus Atmosphere Monitoring Service show. So why is the hole in the ozone layer — the shield that protects life on Earth from harmful ultraviolet solar radiation — so big this year, despite other clues telling scientists that it is recovering as expected from the damage human-made chemicals did in the 20th century?The ozone hole's extent is due to extremely low ...