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

In this way, the researchers said, the Chinese rogue production had contributed to the “banks” of chlorofluorocarbons that were produced worldwide before bans 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.”

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 Meteorology Organization, the United Nations 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, meant to cool the atmosphere. The method, called stratospheric aerosol injection, would use airplanes or other means to distribute sulfur aerosols high in the atmosphere, where they would reflect some of the sun’s rays before they reached 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.