Is the Ozone Layer Finally Healing Itself?
Earth
is currently experiencing a host of environmental problems. Air and water
pollution continue to plague much of the world; exotic plants, animals, and
other organisms pop up in parts of the globe that have no natural defense
against them; and, all the while, climate change lingers in the headlines. It’s
often difficult to find good environmental news, but environmentalists and
scientists have reported one bright spot: the countries of the world rallying
to combat the problem of ozone depletion.
Earth’s protective ozone
layer sits some 15 to 35 km [9 to 22 miles]
above Earth’s surface, in the stratosphere. Stratospheric ozone loss is worrisome because the
ozone layer effectively blocks certain types of ultraviolet (UV) radiation and
other forms of radiation that could injure or kill most living things. For 30
years countries around the world had worked together to reduce and eliminate
the use of chlorofluorocarbons (CFCs) and
other ozone-destroying chemicals (ODCs). However, scientists
still could not say whether these efforts were helping. Was the ozone layer actually
healing itself?
Before getting to the answer, it helps to have some
background on the problem. In 1974 American chemists Mario Molina and F. Sherwood Rowland and Dutch chemist Paul Crutzen discovered that
human-produced CFCs could be a major source of chlorine in the stratosphere. They also noted that
chlorine could destroy extensive amounts of ozone after it was liberated from
CFCs by UV radiation. Since then, scientists have tracked how the ozone layer
has responded to CFCs, which, since their creation in 1928 had been used as
refrigerants, cleaners, and propellants in hairsprays, spray paint, and aerosol containers. In 1985 a paper by the British
Antarctic Survey revealed that stratospheric ozone concentrations over Antarctica had been dropping precipitously (by more than
60% compared with global averages) since the late 1970s. Throughout the 1980s
and early 1990s, observations and measurements from satellites and other
instruments showed that this “hole” over Antarctica was growing larger year
after year, that a similar hole had opened over the Arctic, and that
stratospheric ozone coverage worldwide had dropped 5% between 1970 and the
mid-1990s, with little change afterward.
In response to the growing problem, much of the world came
together in 1987 to sign the Montreal Protocol on Substances That Deplete the Ozone Layer, an agreement that allowed the world to begin to
phase out the manufacturing and use of CFCs—molecules containing only carbon,
fluorine, and chlorine atoms—and other ODCs. Follow-up meetings throughout the
1990s and early 2000s produced amendments aimed at limiting, reducing, and
eliminating hydrobromofluorocarbons (HBFCs), methyl bromide, carbon
tetrachloride, trichloroethane, hydrofluorocarbons
(HFCs), hydrochlorofluorocarbons (HCFCs), and other ODCs. Even though nearly
all of the planet’s governments had been working diligently toward a common
goal—good news in itself—it was unclear whether these unprecedented efforts
were having much of an effect.
In 2014, however, scientists received the first bit of good
news on this topic: the first small increases in stratospheric ozone in more
than 20 years had been detected, along with evidence that ODCs had declined by
10–15% in the atmosphere. Yet they remained cautious. Some two years
later, scientists got sufficient data to confidently reveal proof that the
ozone layer was indeed on a path to recovery. The
2016 study, which tracked the evolution of the size of the ozone hole over
Antarctica, observed that stratospheric ozone concentrations were continuing to
increase and that the size of the Antarctic ozone hole had declined by half the
size of the continental U.S. between 2000 and 2015. They expected the ozone
layer to fully heal sometime between 2040 and 2070.
In 2023, a United Nations study brought these estimates into
further focus. It found that if countries continued to adhere to the limits
imposed by the Montreal Protocol and its follow-on agreements, the world could
expect that ozone concentrations would largely return to their pre-1980 levels
by 2040, with the Arctic reaching pre-1980 levels by 2045 and the Antarctic
following suit by 2066.
