Tuesday should have been a day of unmitigated joy for America’s oil and gas executives. The new G.O.P. tax bill treats their companies with great tenderness, reducing even further their federal tax burden. And the bill gave them something else they’ve sought for decades: permission to go a-drilling in the Arctic National Wildlife Refuge. But, around four in the afternoon, something utterly unexpected began to happen. A news release went out from Governor Andrew Cuomo’s office, saying that New York was going to divest its vast pension-fund investments in fossil fuels. The state, Cuomo said, would be “ceasing all new investments in entities with significant fossil-fuel-related activities,” and he would set up a committee with Thomas DiNapoli, the state comptroller, to figure out how to “decarbonize” the existing portfolio. Cuomo’s office even provided a handy little Twitter meme of the type that activists often create: it showed three smoke-belching stacks and the legend “New York Is Divesting from Fossil Fuels.” The pension fund under Albany’s control totals two hundred billion dollars, making it one of the twenty largest pools of money on Earth.

Not to be outdone, half an hour later the comptroller of the city of New York, Scott Stringer, sent out a similar statement: he, too, was now actively investigating methods for “ceasing additional investments in fossil fuels, divesting current holdings in fossil-fuel companies, and increasing investments in clean energy.” Stringer’s pension funds add up to a hundred and ninety billion dollars—that’s in the top twenty, too.

Climate advocates—many of them at 350.org, the nonprofit that I founded—have been working for years to spur divestment from fossil-fuel stocks, and this was perhaps the biggest single day of that campaign, which in turn is the largest divestment campaign in history. With Tuesday’s announcements, the endowments and portfolios engaged in the process collectively manage more than six trillion dollars in assets. More important, Cuomo and Stringer sent the signal that, in the very center of world finance, sentiment is turning sharply against fossil-fuel investing. Activists have urged divestment for what you might call moral reasons: if it’s wrong to wreck the planet, it’s wrong to profit from the wreckage. But pension funds are willing to divest because they’ve come to believe that the future is not about coal and oil and gas—that these are now on the decline. The future lies elsewhere.

These divestments won’t happen overnight; Cuomo will have to persuade DiNapoli to coöperate, and in any event no one wants a fire sale of stocks at depressed prices. But the announcements offered an encouraging echo of other recent developments. Norway, for instance, last month began work to divest its giant sovereign-wealth fund, which is bigger even than New York’s combined pensions. The World Bank, last week, said it would no longer be lending money for oil and gas exploration. It’s not that the fossil-fuel industry will go bankrupt overnight; its supporters, including Donald Trump and Vladimir Putin, will give it all the love they can. But the shift in the Zeitgeist has been dramatic. The same day that Cuomo was pumping out divestment memes, the President of France, Emmanuel Macron, sent out a tweet announcing that his country would no longer grant any licenses for oil and gas exploration in its various territories. He concluded with “#keepitintheground,” a hashtag until now confined to campaigners.

Tuesday’s news is also a reminder that, as thoroughly as Trump and the G.O.P. have captured D.C., there are other arenas in which to fight them. New York State is, obviously, smaller than the federal government, but it’s not that small. Attorney General Eric Schneiderman, for instance, has been using state statutes to bedevil ExxonMobil, investigating the company’s sordid coverup of our climate peril. It’s likely that the actions of the pension funds will prove contagious to some degree. Other states and cities will begin to wonder whether they’re going to be left holding the bag.

It would make the most sense, of course, to have a concerted global battle against climate change—it is, after all, the first truly global problem we’ve ever faced. But this Administration will not fight it, as Trump’s recent pullout from the Paris climate accords showed. So if the battle, instead, is going to be local, three hundred and ninety billion dollars is a pretty good haul for one day. New York may be an empire in name only, but on Tuesday it demonstrated a global reach.