To mitigate climate change, cities need to target buildings—the “mother lode” of greenhouse gas emissions, as New York Mayor Bill De Blasio called them last week.

At a news conference, he announced a pathbreaking proposal to set stricter energy efficiency standards in the city’s aging buildings—and to fine building owners who don’t comply with the codes.

Other cities may need to crack down, too, if they are to meet their climate goals. Across the U.S., cities have pledged to reduce emissions, with some (like New York) aiming ambitiously for 80 percent reductions by 2050.

“If you’re a city that’s concerned about climate change, you have to focus on buildings, because that’s where the carbon is,” says Cliff Majersik, executive director of the Institute for Market Transformation, a Washington, D.C.-based nonprofit focused on climate and energy.

Read more (Inside Climate News)