Since Donald Trump’s election, the policies and agencies designed to protect people have been mercilessly gutted–from the EPA’s deregulation of toxic chemicals to the United States’ abrupt exit from the Paris Climate Treaty. Many states and dozens of cities have moved to pick up the slack left by the government on environmental and industrial regulations, including ones aimed at climate change. The latest comes from 19 mayors, half of which govern American cities, who are pledging to radically alter how buildings act in their metropolises.

More specifically, the pledge stipulates two major things: First, by 2030, every new building constructed in these cities will be net zero–in other words, they’ll produce as much energy as they consume (or get that energy from renewable sources). Second, by 2050, all buildings, new and old, will conform to the net-zero standards.

As part of the announcement, several mayors hinted at the rise of nationalist politics–and the attendant inaction on climate change policy. Clover Moore, Lord Mayor of Sydney, described the “shocking inaction by National Government here in Australia,” while Washington, D.C., Mayor Muriel Bowser noted that, “as the nation’s capital, Washington, D.C. has a unique responsibility to push for bold climate action.”

It’s an ambitious goal, considering that there are many hundreds of thousands of buildings in Manhattan alone, all of which would need to be retrofitted within the next three decades. On the other hand, as C40–the coalition of almost 100 mayors behind the pledge–points out, the stakes are high: Pollution from buildings can constitute up to 70% of overall emissions in some cities including Paris and Los Angeles, and research shows that hundreds of thousands of premature deaths are caused by increasing air pollution. (Even, as Curbed‘s Alissa Walker rightly points out, transit pollution is an even bigger hurdle for some cities.)

As many mayors also noted, there are economic benefits to be had in the process. L.A.’s Eric Garcetti called the pledge a “moral necessity, an environmental imperative, and an economic opportunity,” while Vancouver’s mayor, Gregor Robertson, reported a 53% increase in green building jobs since 2010 in the city.

There’s another opportunity for cities in adopting net-zero standards to focus on: Social and economic equity. The Rocky Mountain Institute’s Kelly Vaughn, writing about its national “Getting To Zero” forum focused on net zero standards in cities this spring, reports that these new standards could be an avenue for cities that want to raise the standard of living for all citizens. In many cities, poor and disinvested communities are among the most air-polluted. They also pay higher energy costs due to poorly insulated and inefficient building design; A recent report from the American Council for an Energy-Efficient Economy found that even making low-income housing as energy efficient as the average house in the U.S. would cut 35% of energy costs. Making all housing–especially affordable and low-income buildings–net zero could, feasibly, help make citizens healthier and cost them less to heat.

Time will tell if every city throwing its weight behind the pledge will do it in a way that promotes economic justice along with environmental justice.