The United States and China announced Friday they would seek to eliminate some of the world's most potent greenhouse gases through the 1987 Montreal Protocol, the landmark treaty that successfully phased out ozone-depleting substances decades ago.
The move, announced at the Group of 20 summit in St. Petersburg, is significant because it provides a clear path for curbing a major contributor to global warming in the near term as world leaders grapple with the more challenging task of cutting carbon dioxide in the coming decades.
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President Obama and Chinese President Xi Jinping said they would work to phase out hydrofluorocarbons (HFCs) -- a class of chemicals commonly used in refrigerators and air conditioners -- through the Montreal Protocol, even as they tried to make progress through the annual climate talks held by the United Nations. The U.N. Framework Convention on Climate Change has yet to produce a broad, binding, global warming accord that many scientists say would be needed to limit the world's growing carbon output.
Other G-20 leaders also endorsed the approach Friday in a joint statement.
Durwood Zaelke, president of the Institute for Governance & Sustainable Development, a Washington-based nonprofit group, called HFCs "the biggest climate prize available to the world in the next few years."
In an email, Zaelke estimated that the accord could cut the equivalent of 100 billion tons of carbon dioxide by 2050 and would avoid up to nearly 1 degree in global warming.
"This high-level agreement during the G-20 in St. Petersburg shows how effective climate policy can be when it's done at the leader level," he wrote.
The new effort builds on the accord Obama and Xi struck in June, when they said for the first time that they would work together to persuade other countries to cut HFCs. Brazil and India have resisted deep cuts in the past.
In announcing his climate action plan in June, Obama said he would pursue this sort of international action even as he worked to cut greenhouse gas emissions at home.
"We reiterate our firm commitment to work together and with other countries to agree on a multilateral solution," the two leaders said in a joint statement.
The Montreal Protocol succeeded in phasing out nearly 100 chemicals, but an unintended consequence was that it spurred the production of HFCs, which are short-lived and do not damage the ozone but are far more potent greenhouse gases than carbon dioxide. In addition to being used as refrigerants, they are used in insulating foams, solvents and aerosol products.
Left unabated, HFC emissions could grow to nearly 20 percent of carbon dioxide emissions by 2050.