September's Ozone Hole Was the Biggest It Has Been in 25 Years

In September, the Antarctic ozone hole peaked at 10.6 million square miles—the second largest ever observed for this time of year. Using data from the Copernicus Atmosphere Monitoring Service, scientists found that the ozone hole started growing earlier than usual in August. By September 20, it reached a size close to its October 2015 peak, when it was 10.8 million square miles.

To understand what’s happening, we first need to understand the ozone layer. The ozone layer lies in the Earth’s stratosphere and protects our planet from harmful ultraviolet (UV) radiation that can harm humans, plants and animals. The infamous ozone hole is actually a patch of depleted ozone in the stratosphere over Antarctica that is mainly caused by chemicals called chlorofluorocarbons, or CFCs.

While the 1987 Montreal Protocol phased out the use of CFCs globally, they can persist in the atmosphere for decades. The ozone hole’s size fluctuates every year. For about three months each fall—the Southern Hemisphere’s spring—the hole opens inside the stratospheric polar vortex, a large band of fast-spinning westerly winds that encircles Antarctica and the Southern Ocean.

The vortex traps freezing air inside and leads to the formation of polar stratospheric clouds, writes a New Zealand-based research team in The Conversation. This year brought a stronger and colder polar vortex. By late January, the hole will shrink again.

Wildfires can destroy the ozone layer So, should we be worried? It’s something we need to keep a close eye on.” Kessenich and other experts underscore the fact that the ozone hole size we’re currently seeing isn’t a sign that the Montreal Protocol isn’t working. In fact, this year’s hole isn’t as deep as it has been in previous years, and year-to-year variability is to be expected.

There will, however, be impacts on weather across the Southern Hemisphere. A larger ozone hole shifts the Southern Annular Mode into a positive phase, which affects winds and precipitation in different areas. In Australia, for example, it causes increased rainfall on the country’s southeast coast, Kessenich and her colleagues write in The Conversation.