Today's summit on climate change at the United Nations is more of a show and tell for world leaders than anything else. No negotiations are planned. Xi Jinping, Narendra Modi and Vladimir Putin -- the heads of three of the four states that produce the most carbon dioxide emissions -- all apparently have better things to do. The international community is scheduled to continue negotiations formally in Paris next year, but the chances for a comprehensive binding agreement on carbon dioxide look slim at best.

"When you really look at the numbers, when you really look at what’s going on, there is absolutely no genuine deep political drive toward reducing carbon dioxide emissions," said Kevin Anderson of the University of Manchester.

But President Obama's most important achievement on global warming could well be an addition to an old treaty called the Montreal Protocol, which actually has nothing to do with carbon dioxide.

Ratified in 1987, the treaty was written to protect the ozone by regulating chemicals used in aerosol cans and refrigerators. Not only did the treaty succeed in stabilizing the ozone, but many of the chemicals it regulated are potent greenhouse gases as well. The Montreal Protocol has been enormously beneficial to the climate already. Without it, worldwide annual emissions of greenhouse gases would be around 30 percent greater, according to a U.N. report.

Back in June, Obama and Xi agreed to press the case for adding another class of chemicals to the treaty. They're coolants called hydrofluorocarbons, and you might find them in your car's air conditioner. Since there are perfectly good alternatives in many applications, getting rid of hydrofluorocarbons is diplomatically feasible. If the treaty is revised to include them, the earth in 2100 could be cooler by 1 degree Fahrenheit than it would be otherwise.

"This the most realistic, the fastest, the biggest, the cheapest piece you could do," said Durwood Zaelke, president of the Institute for Governance & Sustainable Development. He added that he felt that with international action on hydrofluorocarbons, Obama had a chance to make up for the inconclusive Copenhagen talks in 2009, widely perceived as a failure.

"They’re doing what they can, and it’s adding up fast. I’m impressed," Zaelke said. Last week, the administration also announced a voluntary agreement with major manufacturers, including Coca-Cola, DuPont and Honeywell, to limit hydrofluorocarbons.

Carbon dioxide has understandably received more public attention in the debate about climate change, since it constitutes the bulk of emissions and will remain in the atmosphere for centuries. Hydrofluorocarbons are one of several other pollutants, including methane, that persist in the atmosphere for anywhere from a few weeks to a dozen years. The hope is that by focusing on these other gases, humans can at least put a check on rising temperatures in the near term.

One degree Fahrenheit is not nearly enough to make the world safe from climate change, but at least it is something. Compared to this initiative, the administration's rules on exhaust from American cars, trucks and power plants are just a drop in the increasingly acidic proverbial ocean.