Why is the Antarctic ozone hole still so big in December?

 

The Antarctic ozone hole, a seasonal phenomenon that occurs every year from August to December, is still persisting well into the summer months, according to satellite and balloon-based measurements by NASA and NOAA. The ozone hole reached its maximum size of 10 million square miles (26 million square kilometers) on September 21, 2023, making it the 12th largest single-day ozone hole on record. The average size of the ozone hole from September 7 to October 13 was 8.9 million square miles (23.1 million square kilometers), ranking as the 16th largest over this period¹.

The ozone layer is a thin layer of gas in the stratosphere that protects life on Earth from harmful ultraviolet (UV) radiation from the Sun. UV rays can cause sunburns, cataracts, skin cancer, and damage to plants and animals. The ozone hole is caused by human-made chemicals containing chlorine and bromine, such as chlorofluorocarbons (CFCs), that destroy ozone molecules through chemical reactions. These chemicals were widely used in aerosols, refrigerators, air conditioners, and other products until they were banned by the Montreal Protocol in 1987 and its subsequent amendments¹.

The size and duration of the ozone hole depend on several factors, such as the amount of ozone-depleting substances in the atmosphere, the temperature and circulation of the stratosphere, and the presence of polar stratospheric clouds that facilitate the chemical reactions. Scientists have observed that the ozone hole has been shrinking and healing since the late 1990s, as the levels of chlorine and bromine have declined due to the Montreal Protocol. However, the ozone hole can still vary from year to year due to natural variability in the weather and climate¹².

This year, the ozone hole was larger and lasted longer than expected, mainly due to colder-than-average temperatures in the stratosphere and stronger-than-usual polar vortex winds that isolated the Antarctic air from the rest of the world. These conditions allowed the ozone-depleting substances to accumulate and persist over the South Pole, resulting in more ozone loss. The ozone hole also shifted slightly towards the South Atlantic Ocean, exposing parts of South America and Antarctica to higher levels of UV radiation²³.

Scientists are monitoring the ozone hole closely and expect it to close by the end of December or early January, as the stratosphere warms up and the polar vortex weakens. They are also studying the long-term trends and impacts of the ozone hole on the climate, the biosphere, and human health. While the ozone hole is expected to recover by the middle of this century, it is still a reminder of the fragility of the Earth’s atmosphere and the need to protect it from human activities¹²³.