Ozone hole smallest on record, but there’s a catch
The Antarctic ozone hole hit its smallest annual peak on record since tracking began in 1982, the National Oceanic and Atmospheric Administration and NASA announced Monday. Although we’re making progress in cutting down on the use of ozone-depleting chemicals, the milestone doesn’t mean we’ve solved the problem, the agencies cautioned. Instead, scientists attribute the relatively tiny ozone hole to unusually mild temperatures in that layer of the atmosphere.
According to NASA and the NOAA, the annual ozone hole — which consists of an area of heavily depleted ozone high in the stratosphere above Antarctica, between seven and 25 miles above the surface — reached its peak extent of 6.3 million square miles on Sept. 8 and then shrank to less than 3.9 million square miles during the rest of September and October.
“During years with normal weather conditions, the ozone hole typically grows to a maximum of about 8 million square miles,” the agencies said in a news release. This is the third time in 40 years that weather systems have caused warm stratospheric temperatures that put the brakes on ozone loss, the federal science agencies said. Similar weather patterns led to unusually small ozone holes in 1988 and 2002, they reported. “It’s a rare event that we’re still trying to understand,” Susan Strahan, an atmospheric scientist at the NASA’s Goddard Space Flight Center in Maryland, said in a news release. “If the warming hadn’t happened, we’d likely be looking at a much more typical ozone hole.”
The stratospheric ozone layer helps deflect incoming ultraviolet radiation from the sun, shielding life on Earth from its harmful effects, such as skin cancer, cataracts and damage to plants. However, chemicals used for refrigeration purposes, such as chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs), break down stratospheric ozone molecules, thereby exposing the planet’s surface to greater amounts of UV radiation.
The Montreal Protocol, a landmark international environmental treaty that took effect in 1988, has reduced CFC emissions worldwide. These chemicals have an atmospheric lifetime of several decades and can destroy extraordinary amounts of ozone over that time. The ozone layer has been slowly but steadily recovering since the Montreal Protocol took effect, but it still has a long way to go.
Each year, an ozone hole forms during the Southern Hemisphere’s late winter as the sun’s rays initiate chemical reactions between the ozone molecules and man-made chemically active forms of chlorine and bromine. These chemical reactions are maximized on the surface of high-flying clouds, but milder-than-average conditions in the stratosphere above Antarctica this year inhibited cloud formation and persistence, according to a NASA statement.
This helped prevent the loss of a considerable amount of ozone. The weather systems that minimized ozone depletion in September, known as “sudden stratospheric warming” events, were unusually strong this year. About 12 miles above Earth’s surface, temperatures during September were 29 degrees higher than average, NASA reported, “which was the warmest in the 40-year historical record for September by a wide margin.”
As can occur with stratospheric warming events in the Northern Hemisphere, this weather event helped to weaken the Antarctic polar vortex, a ribbon of high-speed air encircling the South Pole that typically concentrates the coldest air near or over the pole itself.