Considerable contribution of Montreal Protocol to declining US greenhouse gas emissions

At last, a bit of good news on the climate front.

A new study published in the latest issue of Geophysical Research Letters found that the 1989 Montreal Protocol—the treaty designed to cut down the gasses that cause dangerous holes in the Earth’s protective ozone layer—has had another major benefit. It turns out that the protocols have also been surprisingly effective at curtailing global warming—even though climate change was not even a consideration during initial treaty negotiations in the ’80s.

That’s because the ozone-depleting substances controlled by the treaty—chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs)—are also potent greenhouse gases, with heat-trapping abilities up to 10,000 times greater than carbon dioxide over the course of a century. So, when the level of CFCs and HCFCs was reduced, so were their effects on the climate.

The researchers project that by 2025, the Montreal Protocol will have reduced US greenhouse gas emissions by the equivalent of 500 million tons of carbon dioxide per year compared with 2005 levels. This reduction would be equivalent to about 10 percent of the current US emissions of carbon dioxide.

CFCs, HCFCs, and their substitutes, the hydrofluorocarbons, had been widely used as refrigerants, foam blowing agents, aerosol propellants, fire retardants, and solvents. Chlorine from CFCs was first identified as capable of destroying stratospheric ozone in 1974. The Montreal Protocol has controlled the production and consumption of these chemicals since the late 1980s. Implementation of the Montreal Protocol in the United States, largely through the Clean Air Act, led to a near complete phase-out of US production and consumption of CFCs beginning in 1996, and a 95 percent decline of HCFC production since 1998. As a result, total emissions of CFCs in the United States have decreased by two-thirds from 2008 to 2014, while emissions of HCFCs declined by about half, the study authors said.

Previous studies, such as one published in the Proceedings of the National Academy of Sciences, had demonstrated that the Montreal Protocol has been more effective at curtailing global greenhouse gas emissions than any other international effort so far, but the latest study is the first to quantify the effect.

“This shows what can be achieved by concerted and thoughtful international effort,” commented Scott Lehman of the Institute of Arctic and Alpine Research at the University of Colorado Boulder, and co-author of the new study.