In the city that never sleeps, the lights burn all night. And New York City needs energy for those lights, as well as for heating, air-conditioning and many other services. To meet these demands, the Big Apple belched nearly 60 million metric tons of greenhouse gases into the atmosphere in 2005.

Eight years later, despite a rise in population and new construction, emissions of greenhouse gas pollution had dropped by more than 11 million metric tons. How did Gotham manage to go so green? By banning the dirtiest oil used for heating and benefiting from a switch to natural gas for generating electricity.

New York is not alone in taking climate change seriously. Cities across the globe are stepping into the leadership vacuum left by nations, which have failed to take meaningful action on global warming for more than two decades. Coastal cities, which are particularly vulnerable to sea-level rise and other ill effects of rising temperatures, are leading the charge. Copenhagen, Melbourne and a handful of others have laid plans to go carbon-neutral. The “Compact of Mayors,” a group of 228 cities representing 436 million citizens around the world made commitments at the United Nations Climate Summit earlier this year to avoid two billion metric tons of greenhouse gas pollution per year. Even Chinese cities are in on the action: cap-and-trade markets for carbon pollution opened in 2013 in seven regions, including Shenzhen, which reduced carbon dioxide emissions by 2.5 million metric tons this past year, says Vice Mayor Tang Jie.

That forward motion is in contrast to China's failure as a nation to reduce carbon intensity—the pollution associated with economic activity—as it promised in the five-year plan that ends next year. China, the U.S. and the rest of the world spew more than 36 billion metric tons of greenhouse gases a year—and the number continues to rise.

In response to this lack of progress, at least 100,000 people took to the streets of New York this past September to demand action from leaders. Participants in the People's Climate March expressed hope that when country representatives meet in Paris in December 2015 for the 21st iteration of international talks, they will hash out a new, legally binding treaty to curb emissions. Many climate policy experts fear the meeting will not achieve nearly enough, however.

Regardless of how international talks go, the world's cities could cut eight billion metric tons of greenhouse gases by 2050, according to an analysis by the C40 group of cities. That is significant but delivers only slightly more than the Montreal Protocol of 1987, the single biggest step ever taken to restrain climate change. That one treaty accomplished what it would take hundreds of local laws to do. An international solution is important, but until one arrives, the cities will strive to keep the lights on and the pollution down.

FURTHER READINGS AND CITATIONS ScientificAmerican.com/dec2014/advances