In the summer of 2019, the city council in Berkeley, California, made a bold and unprecedented move: They banned natural gas hookups in most new building construction.

Councilwoman Kate Harrison, who sponsored the new ordinance, had been on a hunt for ways to reduce the city’s carbon emissions. “We looked at where our emissions were coming from and found that natural gas in buildings played a significant role,” she says—they accounted for a whopping 37 percent of the city’s total. Cars are another big source, but the city has no authority to regulate tailpipe emissions. But buildings? “This is an area we can tackle,” Harrison says.

Berkeley’s pioneering ordinance spurred a wave of similar efforts. Since 2019, more than 40