Ozone layer expected to recover in four decades, says new study

The protective ozone layer in the upper atmosphere could be restored within several decades, scientists said Monday, as China’s recent illegal emissions of ozone-depleting chemicals have mostly been phased out.

In a UN-sponsored assessment, scientists said global emissions of CFC-11, a banned chemical used as a refrigerant and in insulating foams, have declined since 2018 after rising for several years. CFC-11 and similar chemicals, collectively called chlorofluorocarbons, destroy ozone, which blocks ultraviolet radiation from the sun that can cause skin cancer and harm people and other living things.

Scientists said that if current policies remain in place, ozone levels between the polar regions should reach pre-1980 levels by 2040. Ozone holes, or regions of increased weathering that regularly appear near the south pole and, with less near the North Pole are also expected to recover, by 2045 in the Arctic and around 2066 in Antarctica.

“Things continue to move in the right direction,” said Stephen A. Montzka, a research chemist with the US National Oceanic and Atmospheric Administration (NOAA) and one of the authors of the report. Montzka led a study in 2018 that warned the world that CFC-11 emissions had been rising since 2012 and that they appeared to be coming from East Asia.

Investigations by The New York Times and others strongly suggested that the source was small factories in eastern China that were flouting the global ban.

The new emissions threatened to undermine the Montreal Protocol, the treaty negotiated in the 1980s to phase out the use of chlorofluorocarbons in favor of more benign chemicals, after chlorofluorocarbons were found to be destroying atmospheric ozone.

At the time, the head of the UN Environment Program, which oversees the protocol, called the illegal production of CFC-11 “nothing short of an environmental crime that demands decisive action”. Montzka and others said that if the dangerous emissions continued they could delay the recovery of the ozone layer by up to a decade.

But follow-up studies showed that emissions were decreasing, a sign that the Chinese government was successfully cracking down on new CFC-11 production. The report said the hazardous emissions likely delayed the ozone layer’s recovery by a year.

Chinese CFC-11 would have been used as a blowing agent in the manufacture of 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 in the foam as it hardens.

In this way, the researchers said, illegal Chinese production contributed to the “banks” of chlorofluorocarbons that were produced around the world before the bans took effect and are in foams, refrigeration equipment and fire extinguishing systems. These existing chemicals are not yet in the atmosphere, but are slowly released through foam decay and destruction, leaks, or other means.

Montzka said the size of the Chinese contribution to banks is not known. “But if the banks were increased substantially, it would add a few more years to the expected recovery delay,” he said.

Durwood Zaelke, president of the Institute for Governance and Sustainable Development, a Washington-based research and advocacy organization, said the elimination of illegal emissions was another example of the success of the protocol, which is generally considered the most effective global environmental compact ever enacted. .

Atmospheric monitoring, required by the protocol, detected the problem, Zaelke said, and brought it to the attention of the treaty board. “Without admitting guilt, the offending parties acted together,” he said. “And the measurements are back where they should be.”

Under the protocol, assessments like the one released on Monday are required at least every four years. In addition to NOAA scientists, collaborators included researchers from NASA, the World Meteorological Organization, the UN Environment Program and the European Commission.

The new assessment was the first to consider the effects on ozone of a potential type of climate intervention, or geoengineering, aimed at cooling the atmosphere. The method, called stratospheric aerosol injection, would use airplanes or other means to spread sulfur aerosols into the atmosphere, where they would reflect some of the sun’s rays before reaching the surface.

The idea generated strong opposition. Among other objections, opponents say that intervening in the climate in this way could have serious unintended consequences, potentially altering weather patterns around the world. But many scientists and others say that at least the research is needed, because warming could reach a point where the world is desperate to try such an intervention technique, perhaps temporarily, to buy time before reductions in greenhouse gases have a significant effect.

David W. Fahey, director of NOAA’s Chemical Sciences Laboratory and co-chair of the protocol’s scientific evaluation panel, said that some studies had shown an impact of sulfur aerosols on ozone, so the evaluation team was tasked to investigate it.

The protocol “exists to protect the ozone layer, and we’ve done a good job of dealing with substances that deplete the layer,” he said. Examining stratospheric aerosol injection “is in our control room,” he added.

There is a lot of uncertainty in their findings, Fahey said, but the basic message is that trying to cool the planet by 0.5°C, for example through the use of sulfur aerosols, would have some effect on ozone. But “it won’t destroy the ozone layer and it will have catastrophic consequences,” he said.

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

That eruption temporarily cooled the planet by about 0.5°C, Fahey said. But the ozone layer did not collapse. “She has resilience,” he said.

_{Translated by Luiz Roberto M. Gonçalves}