Oct. 21 (UPI) -- The ozone hole is the smallest its been since scientists first began monitoring the human-caused phenomenon in 1982.
After reaching an annual maximum measuring 6.3 million square miles in early September, the smallest maximum ever, the ozone hole quickly shrank. By early October, the ozone hole measured 3.9 million square miles. Scientists expect the hole to continue to dissipate in the coming weeks before closing completely -- for now.
In a pair of news releases published Monday, scientists at NASA and NOAA confirmed that the ozone hole was the smallest in recorded history. Weather systems near the South Pole triggered an influx of warm air into the stratosphere during September and October, curbing the depletion of ozone gas.
Similar climate patterns produced unusually small ozone holes during the autumns 1988 and 2002.
"It's important to recognize that what we're seeing this year is due to warmer stratospheric temperatures," Paul Newman, chief scientist for Earth Sciences at NASA's Goddard Space Flight Center, said in a news release. "It's not a sign that atmospheric ozone is suddenly on a fast track to recovery."
The space and weather agencies use a combination of 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 -- to measure the dimensions of the ozone hole from space. NOAA scientists stationed near the South Pole also regularly deploy high altitude weather balloons to measure the vertical dimensions of the ozone layer, or the lack there of.
This year's record low bests the record set in 2017. Then, as now, scientists credited natural variability, not permanent repair.
The ozone hole is created when solar rays catalyze manmade chemicals like chlorine and bromine. These chemical reactions destroy ozone molecules. The chemical reactions are encouraged by polar stratospheric cloud formation, but in recent years, warmer stratospheric air has helped limit these reactions and curtailed the growth of the ozone hole.
Scientists first noticed the ozone layer was weakening in the 1970s; they quickly fingered a class of chemicals called chlorofluorocarbons, or CFCs, commonly used in refrigerants and aerosol cans, as responsible.
The hole itself was discovered by scientists with the British Antarctic Survey in 1985, intensifying the concerns of scientists and the general public. Strict regulation followed.
In 1987, world leaders signed the Montreal Protocol, which helped phase out CFC use around the world. The ban has apparently helped the ozone layer regain its strength.
Most studies suggest the ozone layer has slowly healed as a result of the Montreal Protocol and the adoption of more environmentally friendly alternatives to CFC, but last year, scientists observed rising CFC emissions in Asia. Investigators determined the continued production and use of CFCs in China and its foam industry were to blame for the emissions increase.
Scientists have also found evidence that the increased use of dichloromethane, a popular substitute for CFCs, could also undermine the recovery of the ozone layer. Though the ozone-eating chemical has a much shorter lifespan than chlorofluorocarbons, its use remains unregulated.