The ozone hole in Anatartica's upper atmosphere shrunk to 3.9 million square miles between September and October, due to warmer conditions this year. The 2019 ozone hole is the smallest on record since its discovery in 1982. This may give the impression that the ozone is heading towards recovery. Except that it is not, say experts.

"It’s not a sign that atmospheric ozone is suddenly on a fast track to recovery,” says Paul Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center in Greenbelt, Maryland, in a report released by NASA and NOAA. He adds that the shrinking can be attributed to warmer temperatures in the stratosphere: the layer of the atmosphere between 10 and 50 kilometers altitude.

Ozone, which is made of three oxygen atoms, is dubbed as the nature's sunscreen. It screens us from the sun's harmful ultraviolet radiation, which can cause skin cancer and cataracts, suppress immune systems and also damage plants.

But the ozone layer has been depleting due to certain chemicals that humans introduced into the atmosphere. The most notorious of them all was chlorofluorocarbons (CFCs), used primarily in refrigerators. When scientists realized these chemicals were creating a hole in the ozone layer, the world leaders got together to sign the Montreal Protocol in 1987, banning all ozone-depleting chemicals, including CFCs.

Though other ozone-depleting chemical levels have come down, NASA says, they remain high enough to produce significant ozone loss.

The ozone-depleting chemicals are found all over the globe, and yet Antarctica is the only region to bear the brunt of human-induced pollution. This is because the conditions in the continent make the region vulnerable. Every winter, scientists see the Antarctic ozone hole taking shape. Human-manufactured chemically active chlorine and bromine stick to cloud particles. The cold temperature in the stratospheric layers trigger the destruction of the ozone molecules. But in warmer conditions, the opposite occurs: they restrict fewer polar stratospheric clouds to form and as they don’t persist as long and limit the ozone-depletion process.

Monitoring ozone

Scientists could make these observations, thanks to satellite data. Over the years, scientists from NASA and  National Oceanic and Atmospheric Administration (NOAA) have been keeping a watch over the ozone hole in Antarctica. Using satellites, including NASA’s Aura satellite, the NASA-NOAA Suomi National Polar-orbiting Partnership satellite and NOAA’s Joint Polar Satellite System NOAA-20 satellite, they measure ozone from space. The Aura satellite’s Microwave Limb Sounder also estimates levels of ozone-destroying chlorine in the stratosphere. 

There are other ways of monitoring the ozone layer too. The NOAA staff launch weather balloons, which carry ozone-measuring “sondes”. They, in turn, measure ozone levels through the atmosphere.  

“This year, ozonesonde measurements at the South Pole [Antarctica] did not show any portions of the atmosphere where ozone was completely depleted,” says atmospheric scientist Bryan Johnson at NOAA’s Earth System Research Laboratory in Boulder, Colorado.

This is not the first time that the Antarctic is witnessing warm temperatures. According to Susan Strahan, an atmospheric scientist with Universities Space Research Association, who works at NASA Goddard, this is the third event in the last 40 years. "Similar weather patterns in the Antarctic stratosphere in September 1988 and 2002 also produced atypically small ozone holes, she adds.

In the future, scientists will try to understand what drives such warm conditions in Antarctica. “There is no identified connection between the occurrence of these unique patterns and changes in climate," says the report.

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