Yesterday, NASA announced that the annual “hole” in the ozone layer over Antarctica was the smallest they’ve measured since 1988.
Ground and balloon measurements conducted by scientists from the National Oceanic and Atmospheric Administration found that at its peak in September, the area of thinning ozone was 7.6 million square miles—about 2.5 times as large as the area of the United States. As CBS News reports, that is 1.3 million square miles less than the size of the hole in 2016 and 3.3 million square miles less than the 2015 hole. But it may be too soon to celebrate environmental success.
“In the past, we’ve always seen ozone at some stratospheric altitudes go to zero by the end of September,” Bryan Johnson, NOAA atmospheric chemist tells CBS. “This year our balloon measurements showed the ozone loss rate stalled by the middle of September and ozone levels never reached zero.”
While the reduced hole is good news generally, human efforts to heal the thinning ozone layer aren’t responsible. Instead, NASA reports that the decrease was caused by warmer-than-average temperatures in the Antarctic stratosphere over the last two years. That led to stormy conditions in the stratosphere that prevented some of the atmospheric chlorine and bromine that reacts with and destroys the ozone from reaching the molecules.
That’s not to say human intervention hasn’t helped the ozone layer. According to National Geographic, ozone—a molecule composed of three oxygen atoms—is constantly created and destroyed in the upper atmosphere, up to 31 miles above the ground in a region known as the stratosphere. Ozone acts as an atmospheric sunscreen, filtering out lots of the sun's ultraviolet B radiation, which can cause skin cancer and kill phytoplankton, the base of the food chain in the ocean.
In the 1980s, researchers began recording an annual thinning of ozone concentrations above Antarctica. Scientists found that a type of chemical called chlorofluorocarbons, used in refrigerants and as a propellant for things like hairspray, were collecting in the polar stratosphere. And during the southern spring and summer, when sunlight beams down during long hours of the day, the compounds were converted to chlorine, which reacted with and destroyed the ozone.
In 1987, the Montreal Protocol to ban ozone-depleting chemicals was ratified. As at National Geographic reports, without the implementation of the protocol, studies suggest that the Earth’s entire ozone layer would have collapsed by 2050, leading to 280 million extra cases of skin cancer as well as a spike in cataracts and other health problems. Climate change would have also worsened without the reduction of these compounds, which Leahy reports are now known to be super-greenhouse gases. Rolando Garcia, a senior scientist at the National Center for Atmospheric Research tells Leahy that the climate today would be 25 percent hotter without the Montreal ban.
“In 1987 I don’t think anyone knew about the full climate implications,” he says. “The Protocol saved our bacon a little bit.”
If all goes according to plan, the thinning of ozone should completely heal by 2050, Erin Blakemore reported for Smithsonian.com last year. In fact, after the thinning reached a peak in 2000, researchers found the first clear evidence that the layer was healing in a study published last year.
But the fate of the ozone layer is not completely secure just yet. As Matt McGrath at the BBC reports, other recent studies show that the rise in the manufacture of another class of chemicals, PVCs, used as industrial solvents and paint thinners, could set back the repair of the hole by up to 30 years. Currently, many of those chemicals are made in China where they are not regulated.
Celebrate the latest minor triumph, whether humanity deserves the credit or not. But it's clear more work is needed to ensure the fate of the ozone.