The weakened ozone layer, which is
vital to protecting life on Earth, is on track to be restored to full strength
within decades — the latest success of a global effort by nations to stop using
chemicals that had been destroying the critical layer in the upper atmosphere.
اضافة اعلان
In a report for the United Nations,
scientists said on Monday that China had largely eliminated rogue emissions of
one of those chemicals, known as CFC-11.
Once widely used as a refrigerant and in
foam insulation, CFC-11 was first synthesized a century ago. Along with similar
chemicals, collectively called chlorofluorocarbons, CFC-11 destroys ozone,
which blocks ultraviolet radiation from the sun that can cause skin cancer and
otherwise harm people, plants, and animals. Chlorofluorocarbons were banned
under the Montreal Protocol, a landmark environmental agreement that took
effect in 1989.
If countries continue to maintain bans on chlorofluorocarbons and other chemicals, ozone levels between the polar regions should reach pre-1980 levels by 2040.
If countries continue to maintain bans on
chlorofluorocarbons and other chemicals, ozone levels between the polar regions
should reach pre-1980 levels by 2040. Ozone holes, or regions of greater depletion
that appear regularly near the South Pole and, less frequently, near the North
Pole, should also recover, by 2045 in the Arctic and about 2066 in Antarctica.
“The recovery of the ozone layer is on
track,” said David W. Fahey, director of the US National Oceanic and
Atmospheric Administration’s Chemical Sciences Laboratory and a co-chair of the
protocol’s scientific assessment panel. “The peak destruction of the global
ozone layer is behind us due to the effectiveness of the control measures of the
Montreal Protocol that have been adopted by all nations.”
The emissions timelineIn the 1970s, scientists first determined
that chlorofluorocarbons were depleting ozone high in the atmosphere. By the
mid-1980s, researchers discovered a hole in the ozone over the Antarctic,
sparking an urgent international effort to repair it. More than 100
ozone-depleting compounds were eventually banned and phased out.
Chinese emissions had threatened to delay
restoration of the ozone layer by a decade, but the new report said it had only
been put off by a year.
“The emissions dropped amazingly abruptly,”
said Stephen A. Montzka, a NOAA research chemist and one of the report’s
authors. The delay in recovery “is a lot smaller than it could have been if the
emissions persisted,” he added.
Emissions of CFC-11 began increasing after
2012 and appeared to come from East Asia, according to a 2018 study by Montzka.
Investigations by The New York Times and others strongly suggested that small
factories in eastern China were the source of the rogue emissions.
At the time, the head of the United Nations
Environment Program, which oversees the protocol, called illegal production of
CFC-11 “nothing short of an environmental crime which demands decisive action.”
But a follow-up study in 2019 showed that
emissions were declining, a sign that the Chinese government was cracking down
on new production of CFC-11.
The Chinese CFC-11 was likely used as a
blowing agent in making foam insulation. During foam production, some of the
CFC-11 escapes into the atmosphere, where it can be detected and measured, but
much of it is contained within the foam as it hardens.
In this way, the researchers said, the
Chinese rogue production had contributed to the “banks” of chlorofluorocarbons
that were produced worldwide before ban went into effect and are in foams as
well as refrigeration equipment and fire-extinguishing systems. These existing
chemicals are not yet in the atmosphere, but are being released slowly through
foam deterioration and destruction, leaks or other means.
“Without admitting guilt, the offending parties got their act together,” he said. “And the measurements are back where they should be.”
Montzka said the size of the Chinese
contribution to the banks was not known. “But if the banks have been built up
substantially, that would add a few more years to that expected delay in
recovery,” he said.
Re-assessing climate impactDurwood Zaelke, president of the Institute
for Governance & Sustainable Development, a Washington-based research and
advocacy organization, said the elimination of the rogue emissions was another
example of the success of the protocol, which is generally considered to be the
most effective global environmental pact ever enacted.
Atmospheric monitoring, which is required
by the protocol, detected the problem, Zaelke said, and brought it to the
attention of the treaty’s directorate. “Without admitting guilt, the offending
parties got their act together,” he said. “And the measurements are back where
they should be.”
Under the protocol, assessments such as the
one issued Monday are required at least every four years. In addition to NOAA scientists,
contributors included researchers with NASA, the World Meteorological
Organization, the United Nations Environment Program, and the European
Commission.
The new assessment also considered, for the
first time, the effects on ozone of a potential type of climate intervention,
or geoengineering. The method, known as stratospheric aerosol injection, is
meant to cool the atmosphere by using airplanes or other means to distribute
sulfur aerosols to reflect some of the sun’s rays before they reach the
surface.
The idea has drawn fierce opposition. Among
other objections, opponents say that intervening in the climate in this way
could have severe unintended consequences, potentially altering weather
patterns worldwide. But many scientists and others say that at the least,
research is needed, because warming may reach a point where the world becomes
desperate to try such an intervention technique, perhaps temporarily to buy
time before greenhouse gas reductions can have a significant effect.
Fahey of NOAA said that some studies had
shown an impact on ozone of sulfur aerosols, so the assessment team was given
the task of looking into it.
The protocol “exists to protect the ozone
layer, and we’ve done a pretty good job of it in dealing with ozone-depleting
substances,” he said. Looking at stratospheric aerosol injection, “is in our
wheelhouse,” he added.
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