The odds that the oil industry will have to pay billions of dollars in legal damages soared today when New York City Mayor Bill DeBlasio announced a one-two punch that positions the city at the front of the global fight against climate change. The city is suing five of the industry’s biggest companies—ExxonMobil, BP, Shell, Chevron, and Conoco Phillips—both for past climate-change damages and for the city’s ongoing investments in climate resilience, said de Blasio, who estimated the total costs at well above $20 billion. The city’s pension funds will also divest all of their holdings in oil and gas companies, estimated at $5.5 billion, de Blasio told a press conference at the Manhattan Youth Downtown Community Center in Tribeca, where flooding from Hurricane Sandy in 2012 put 20 feet of saltwater in the sub-basement, knocking the center out of commission for months.

“This city is acting, and we want other cities and states to act,” said the mayor of one of the world’s leading financial centers. “People watch what New York does. We are going to lead the fight against climate change as if our lives depended on it. Because they do.”

De Blasio explicitly linked New York’s actions to the plethora of lawsuits against the tobacco industry that led in 1997 to the largest corporate legal settlement in US history: a $246 billion pay-out to all 50 states to fund medical care and smoking-prevention programs. “Those lawsuits were crucial to changing the public perception of tobacco and the industry behind it, and that change helped drive new policy,” de Blasio said. “If we no longer assume that fossil fuels are innocent, if we no longer assume we have to keep investing in them, that changes the conversation.”

The walls aren’t tumbling down on Big Oil just yet, but they may be closing in. More and more big players in the world economy have distanced themselves from fossil fuels in recent months. In November, Norway’s central bank urged the Norwegian government to divest oil and gas stocks from the country’s $1 trillion sovereign wealth fund, the world’s largest. Universities, churches, philanthropies, and institutional investors that manage assets estimated at $6 trillion have divested from oil and gas, Clara Vondrich of the DivestInvest campaign told The Nation. The World Bank announced in December that it would no longer finance oil and gas exploration.

“This is one of a handful of the most important moments in the 30-year fight against climate change,” said Bill McKibben, the 350.org activist and Nation contributor, who joined de Blasio in addressing the press conference. “Today, the mightiest city on our planet takes on its richest, most powerful, and most irresponsible industry. Science and economics and morality are on the side of the city, and so eventually it will win. We hope it will win in time.”

“The bar for being a climate leader has just been dramatically raised,” author and Nation contributor Naomi Klein told the conference. Invoking the imperative of climate justice, she noted that “the costs of sea-level rise and ferocious and unprecedented weather events are being offloaded onto the public with taxpayers stiffed with the ever-ballooning costs,” leaving less money for social needs, while “the extravagant profits from destabilizing our planet’s life support system are systematically privatized…. It is a world upside-down, but today we take a major step in turning it right side up.”

New York City’s lawsuit, filed in the Southern District of New York federal court, makes the city by far the largest entity yet to sue oil and gas companies for climate damages. The lawsuit includes an exhibit of evidence—a letter sent on November 12, 1982, to Exxon’s management and personnel by M. B. Glaser, the company’s manager of environmental-affairs programs, which projects average global temperatures rising by as much as 3 degrees Celsius by the year 2100, a level climate scientists today say would be catastrophic.

San Francisco, Oakland, and seven other cities and counties in California have filed similar suits in state court. Exxon has fought back, filing counter-suits against the municipalities and the attorneys and public officials representing them. “We will not be intimidated,” John Beiers, the legal counsel to San Mateo County in California, said in response to Exxon’s counter-suit.

Such David versus Goliath bravery becomes easier now that an entity as rich and powerful as New York City has joined the fight. “We understand what climate change does, we’ve been victims of it,” Michael Mulgrew, president of the United Federation of Teachers, told the press conference. “I lost my house [on Staten Island during Hurricane Sandy], two of my neighbors died, and all of my neighbors lost their houses.” Addressing the oil companies, Mulgrew added, “We are going to hurt you in your pocketbook because your whole world and every decision you make is about your greed…. I understand [these companies]. If somebody sues, they say, ‘We’ll squash.’ Well, come on, people, try to squash us.”

The American Petroleum Institute, the oil and gas company’s trade association, did not respond to The Nation’s request for comment.