GENEVA — A nearly three decade-old international treaty appears to be paying off: Earth’s protective ozone layer has been slowly mending.
A new scientific assessment shows damage to the ozone layer from aerosol sprays and coolants started recovering in parts of the stratosphere at a rate of 1 to 3 percent per decade since 2000. The treaty known as the Montreal Protocol was adopted to protect the ozone layer by eliminating the use of ozone-depleting substances such as aerosol sprays and coolants.
The ozone layer, which starts at about 10 kilometers above Earth and stretches for nearly 40 kilometers, is made up of molecules with three oxygen atoms and protects Earth against harmful levels of ultraviolet rays from the sun.
Life could not exist without solar radiation splitting oxygen into ozone, which converts back to oxygen when it absorbs radiation. Ozone at ground level acts as an air pollutant in smog, formed from the byproducts of car exhaust and other fossil-fuel burning.
“At projected rates, Northern Hemisphere and mid-latitude ozone is scheduled to heal completely by the 2030s followed by the Southern Hemisphere in the 2050s and polar regions by 2060,” two United Nations agencies, the World Meteorological Organization and U.N. Environment, said in a joint statement.
The study, produced by an international team of scientists, also involved the U.S. National Oceanic and Atmospheric Administration, U.S. space agency NASA and the European Commission.
The scientific assessment of the #ozone layer shows at projected rates that northern hemisphere and mid-latitude ozone will heal by the 2030s, southern hemisphere in the 2050s and polar regions by 2060. Ozone action also benefits the #climate. https://t.co/z1NmValXhY pic.twitter.com/p0h0ECy7V7
— World Meteorological Organization (@WMO) November 5, 2018
Success, so far
Since it took effect in 1989, the Montreal Protocol has been widely viewed as one of the most successful environmental treaties, because it essentially eliminated the use of chlorofluorocarbons, or CFCs, that were blamed for thinning the ozone layer above the Northern Hemisphere and poking a giant hole in the Antarctica ozone layer since the late 1970s.
The use of CFCs to cool refrigerators, air conditioners, cars and many other devices was broadly replaced with the use of hydrofluorocarbons, or HFCs, because they do not affect the ozone layer.
But since HFCs contribute to global warming, an addition to the Montreal Protocol known as the Kigali Amendment, which takes effect in 2019, aims to cut the use of some of those gases.
The scientists’ new 70-page report shows the progress made since the worst effects in the late 1990s, when as much as 10 percent of the upper ozone layer was depleted, and in 2006 when the biggest hole, covering 29.6 million square kilometers, was recorded over the South Pole. The seasonal hole peaks in September and October, then vanishes by late December until the next spring.
But there were concerns, too, over the lag in ridding the atmosphere of some ozone-depleting substances like chlorofluorocarbon-11, or CFC-11, which are banned under the Montreal Protocol. Because they persist for decades, the damage will come in the future.
Which is why, scientists said, it is important that the Kigali Amendment succeeds, because it addresses some of the chemicals that are used to replace those banned under the Montreal Protocol.
“We know the Montreal Protocol was a huge success,”said NASA research scientist Qing Liang. But she said “there are some industrial compounds that are not banned by the Montreal Protocol and as they enter the atmosphere, they will also hurt the ozone layer.”
Another NASA research scientist, Susan Strahan, said the big unknown factor in the ozone layer recovery is climate change.
“There are many naturally produced ozone-depleting substances that are emitted by the ocean,” she said, “and as the oceans continue to warm due to climate change, those emissions will increase, and that will further delay ozone recovery.”