Advocates of New York’s Local Law 97 refer to it as the most ambitious climate legislation for buildings enacted by any city in the world. The claim might sound like hyperbole, but John Mandyck, CEO of the Urban Green Council, a nonprofit that helped shape the regulation, points to its scope and scale. It applies to 50,000 existing buildings—any that are 25,000 square feet or larger. These structures amount to 60 percent of the city’s floor area and are responsible for 40 percent of total greenhouse-gas emissions. By 2030, the law is expected to reduce emissions from large buildings by at least 40 percent compared to a 2005 baseline, which means cutting 5.3 million metric tons of carbon dioxide from current levels, the equivalent of San Francis­co’s citywide emissions.

The most consequential piece in a package of bills known as the Climate Mobilization Act, the law was passed by the City Council in April last year. It sets increasingly stringent limits for the amount of CO₂ facilities can emit based on building type. The first set of regulations go into effect in 2024, targeting the most carbon-intensive 20 percent of buildings, while the 2030 limits target the most carbon-intensive 75 percent. (Subsequent limits will be set by the Department of Buildings to achieve an 80 percent reduction in emissions citywide by 2050.) These thresholds are not aspirational but statutory, points out Mandyck: owners who fail to meet the limits face steep fines.