Ronald Prinn, the director of the Center for Global Change Science at MIT and a co-author of the new research, said the data was “tremendously encouraging.” CFC gases are also potent greenhouse gases and they stay in the atmosphere for a long time, which is why the recovery of the ozone layer will take decades.
“If emissions of CFC-11 had continued to rise or even just leveled off, there would have been a much bigger problem building up,” Prinn said.
Ozone molecules are made of three oxygen atoms. When CFC-11 is released into the atmosphere, radiation breaks it down into chlorine, which then eats into the ozone molecules, breaking them down and creating the more stable oxygen molecules made of two atoms.
Once commonly used in refrigeration and insulation, CFC-11 was banned by global agreement in the late 1980s, and was meant to be phased out internationally by 2010. Initially, the agreement worked: the concentration of the substance was declining and scientists estimated the ozone layer would recover by 2050.
“The global monitoring networks really caught this spike in time, and subsequent actions have lowered emissions before they became a real threat to recovery of the ozone layer,” Prinn said.
While the study says the emissions coming from China have declined, those only account for roughly half the global total. Figuring out where the rest is coming from is the scientists’ next challenge.
“We will need to expand measurements and modeling to identify new sources, and continue to keep watch,” Prinn said. “Clearly this story shows that … continuous vigilance is required. You can’t stop measuring these chemical species and assume the problem is solved.”