HFCs are just a small percentage of greenhouse gases in the atmosphere, but they function as a sort of supercharged greenhouse gas, with 1,000 times the heat-trapping potency of carbon dioxide.
The Kigali deal was seven years in the making, and is a compromise between rich nations and poorer, hotter ones, including some where rising incomes are just starting to bring air-conditioners within reach. Wealthier nations will freeze production of HFCs more quickly than poorer countries, though some nations, including those in Africa, elected to phase the chemicals out more rapidly than required, citing the grave threats they face from climate change.
While the Paris pledges are broad, they are also voluntary, often vague and dependent on the political will of future world leaders. In contrast, the Kigali deal includes specific targets and timetables to replace HFCs with more planet-friendly alternatives, trade sanctions to punish scofflaws, and an agreement by rich countries to help finance the transition of poor countries to the costlier replacement products.
So, narrow as it is, the new accord may be more likely to yield climate-shielding actions by industry and governments, negotiators say. And given the heat-trapping power of HFCs, scientists say the Kigali accord will stave off an increase of atmospheric temperatures of nearly one degree Fahrenheit.
That would be a major step toward averting an atmospheric temperature increase of 3.6 degrees Fahrenheit, the point at which many experts think the world will be locked into a future of rising sea levels, severe droughts and flooding, widespread food and water shortages, and more powerful hurricanes.
Over all, the deal is expected to lead to the reduction of the equivalent of 70 billion tons of carbon dioxide from the atmosphere — about two times the carbon pollution produced annually by the entire world.
The Kigali accord is “much, much, much stronger than Paris,” said Durwood Zaelke, the president of the Institute for Governance and Sustainable Development, a research organization. “This is a mandatory treaty. Governments are obligated to comply.”
The deal is an amendment to the Montreal Protocol, the landmark 1987 pact designed to close the hole in the ozone layer by banning ozone-depleting coolants called chlorofluorocarbons, or CFCs. That means the Kigali amendment maintains the legal force of a treaty, even if that treaty was ratified by the Senate during the Reagan administration.
Chemical companies responded to the 1987 agreement by developing HFCs, which do not harm the ozone layer but do trap heat in the atmosphere.
The Kigali deal came about in part because Mr. Obama, as he sought to build a legacy of tackling climate change, elevated the obscure effort to amend the Montreal Protocol to a top White House priority. The final agreement is also consistent with the president’s efforts to push his climate change agenda while using creative ways to bypass a hostile Congress.
Mr. Obama began paving the way to the HFC deal at a 2013 get-acquainted meeting with the Chinese president, Xi Jinping, at the Sunnylands golf estate in California. The two leaders agreed to make a deal to reduce the use of HFCs a priority, a major concession from China, the world’s largest HFC producer.
Since then, American and Chinese companies have increased production of HFC replacement chemicals, and major chemical makers in both countries stand to emerge as winners in the deal.
Top officials from the chemical industry were in Kigali to push for the deal. “Our industry is hard at work doing the research on the HFC alternatives,” said Stephen Yurek, the chief executive of the Air-Conditioning, Heating and Refrigeration Institute, an advocacy group. “Getting that right is certainly as important as reaching agreement.”
