Restoration of the Ozone Layer Is Back on Track, Scientists Say

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…

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.

In a report for the United Nations, scientists said 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 the 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.

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“The recovery of the ozone layer is on track,” said David W. Fahey, director of the National Oceanic and Atmospheric Administration’s Chemical Sciences Laboratory and a co-chairman 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.”

In 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.

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The 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.

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“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 Dr. Montzka. Investigations by The New York Times and others strongly suggested that small factories in Eastern China were the source of the rogue emissions.

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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 very 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 the 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.

Dr. 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.

Durwood 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, Mr. 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.”

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Under the protocol, assessments like 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.

Dr. 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.

There is a lot of uncertainty in their findings, Dr. Fahey said, but the basic message is that trying to cool the planet by 0.5 degree Celsius (0.9 degree Fahrenheit), say, through the use of sulfur aerosols, would have some effect on ozone. But it “will not destroy the ozone layer and create catastrophic consequences,” he said.

“We actually already knew that because Mount Pinatubo did the experiment for us,” he said, referring to the huge volcanic explosion in the Philippines in 1991 that sent enormous amounts of sulfur gas into the stratosphere, creating an aerosol haze akin to a geoengineering effort.

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That eruption temporarily cooled the planet by about 0.5 degree Celsius, Dr. Fahey said. But the ozone layer did not collapse. “It has resilience,” he said.

More on China and the Ozone Layer

Study Pinpoints Source of Banned Gas That Saps Ozone Layer: Eastern China
May 22, 2019

In a High-Stakes Environmental Whodunit, Many Clues Point to China
June 24, 2018

More Evidence Points to China as Source of Ozone-Depleting Gas
Nov. 3, 2018
A correction was made on Jan. 9, 2023: An earlier version of this article misidentified one of the agencies whose researchers contributed to the ozone assessment. It is the World Meteorological Organization, not the World Meteorology Organization.
Henry Fountain specializes in the science of climate change and its impacts. He has been writing about science for The Times for more than 20 years and has traveled to the Arctic and Antarctica. @henryfountain • Facebook

A version of this article appears in print on Jan. 10, 2023, Section A, Page 5 of the New York edition with the headline: Ozone May Be Fully Restored in Decades. Order Reprints | Today’s Paper | Subscribe