Last September 21st, two days before a United Nations summit on climate change, more than three hundred thousand people flocked to Manhattan for the People’s Climate March. The protest stretched for more than two miles and featured indigenous communities, labor groups, students, scientists, politicians, celebrities, and thousands of others. The next day, a much smaller group, made up of about a thousand people who sought a more pointed, confrontational approach, gathered at Bowling Green, in Lower Manhattan, to protest Wall Street’s investments and campaign contributions in support of the fossil-fuels industry. The action, which they called Flood Wall Street, was not approved by the city, but police blocked traffic on Broadway, allowing the march to proceed northward. When the protesters reached barricades that prevented them from turning onto Wall Street, they sat down in an intersection and remained for several hours. After defying a police order to leave the area, a hundred of them were arrested, most of them on charges of disorderly conduct. The majority received adjournments in contemplation of dismissal, meaning that the charges would be dropped if they stayed out of trouble for six months. Eleven, however, decided to take their case to Manhattan Criminal Court.

The Flood Wall Street 11, as the group was called, included a student, an Army veteran, and a nonprofit fund-raiser with a five-year-old son. They decided to attempt a necessity defense, or justification, which holds that otherwise illegal activity is legal in certain situations, in addition to a First Amendment case related to the police’s dispersal of the protest. The necessity defense goes back centuries; the classic example is someone who breaks and enters a house in order to save someone’s life. Under New York State’s penal code, it encompasses conduct necessary “as an emergency measure to avoid an imminent public or private injury which is about to occur by reason of a situation occasioned or developed through no fault of the actor.” For the defense to be successful, however, it cannot rest solely on moral considerations: the “desirability and urgency” of avoiding injury has to outweigh the harm caused by the illegal act, and there can’t have been a reasonable legal alternative to the illegal act. The argument isn’t unprecedented in environmental cases: anti-nuclear protesters have been invoking it since at least the nineteen-seventies, for example, and in 2009 the climate activist Tim DeChristopher attempted the necessity defense after interrupting an oil-and-drilling lease auction by bidding up prices with no intention to pay. He was found guilty and served twenty-one months in prison. Last September, two men invoked the same defense to justify their attempt to blockade a forty-thousand-ton coal shipment off the coast of Somerset, Massachusetts. The outcome that time was more favorable: the prosecution dropped the charges, saying it agreed that climate change “is one of the gravest crises our planet has ever faced.”

By the time the trial in Manhattan began, on March 2nd, the Flood Wall Street 11 had become only ten; a medical emergency had led one defendant to take an adjournment in contemplation of dismissal. Martin R. Stolar, one of two defense attorneys and a longtime member of the National Lawyers Guild, an organization that provides pro-bono representation to progressive activists, had prepared each defendant to speak on a different aspect of climate change, including carbon-dioxide emissions, alternative sources of energy, and the lack of meaningful legislative action. Judge Robert Mandelbaum allowed only one defendant to speak on the necessity defense, however, and he ultimately decided against allowing Stolar to present the defense in full. Although climate change presents a kind of “generalized and continuing harm,” he said, this is not the sort of imminent threat of injury established by a 1991 case, People v. Craig, as meeting the necessity defense’s qualifications.

The judge next addressed the defense’s First Amendment case, which contended that the police officer’s order for the protesters to disperse was unlawful because he had ordered them completely out of the area, rather than allowing them to move to an adjacent location where they would not be obstructing traffic. This approach ultimately succeeded; the judge acquitted all ten defendants. The ruling was itself significant, insofar as it reinforced the right of protesters to express dissent in proximity of their target and held law enforcement accountable for the policing of civil disobedience. But it was the attempt to invoke the necessity defense—coupled with its use in the recent Massachusetts case—that has roused enthusiasm in progressive legal circles.

“Any time a tactic is brought and receives attention, I believe it starts to spark in the public consciousness and, in the judiciary, a greater awareness,” Heidi Boghosian, who directed the National Lawyers Guild for fifteen years and who now directs the A.J. Muste Memorial Institute, a nonprofit that provides grants to activist organizations, said. “When defense attorneys raise the necessity defense, I think that it starts a trend,” she continued. She added that she believes this might especially prove to be true as climate activists escalate their actions. The necessity defense has yet to succeed on its own in a civil-disobedience case relating to climate, but it nevertheless forces judges to focus on the larger social and political issues of a case, rather than only its technical aspects. For this reason, protesters and defense attorneys view it as a useful way of bringing the protest into the courtroom, regardless of how slim the chances that they will win the legal argument.

Although Mandelbaum ruled out the necessity defense in the Flood Wall Street case, he did take judicial notice of climate change, indicating the seriousness with which he viewed the underlying issue, and marking it as one whose existence no longer warrants lengthy debate. Judicial notice allows a court to consider a fact proven without evidence being submitted, and is typically invoked with reference to common knowledge or facts whose accuracy cannot reasonably be disputed. “On the questions of the existence of climate change as a result of human activity and the grave environmental dangers posed by a failure to address it, no such expert testimony would be necessary,” he said.

The significance of the notice is a matter of debate—though it was a rare step in a case relating to climate change, it is not binding, and other judges are not obligated to follow his lead. Stolar told me that he believes it could factor into future cases involving climate change. “It could be used in some other proceeding where there’s a contest about whether or not climate change is real.... Once one judge does it, then other judges feel comfortable doing it,” he said, sitting in his office two weeks after the trial. But numerous instances of courts acknowledging climate change, including in three Supreme Court cases, already exist. Michael B. Gerrard, the director of the Sabin Center for Climate Change Law at Columbia Law School, told me, “The reason why the litigation seeking certain kinds of relief has not advanced is for a lot of reasons other than courts not accepting that climate change is a real problem.” He referred to Flood Wall Street as “a political advocacy tactic, as opposed to a legal strategy.”

Certainly, Flood Wall Street illuminates the obstacles facing the necessity defense as a legal tactic. But the defendants were well aware that the line between “generalized and continuing harm” and imminent threat of injury is a matter of perception, especially as the dangers of climate change become more evident. Often, the courts are slow to reflect shifting public consciousness; the necessity defense has become a tool to that end, and with the Somerset case, and again with Flood Wall Street, the judiciary appeared to keep pace.

Two weeks after he was acquitted, John Tarleton, one of the defendants, who is forty-seven years old and the executive editor and co-founder of the newspaper The Indypendent, returned with me to the spot at the intersection of Broadway and Wall Street where the protesters had staged their sit-in. After recounting for me the events that had led to his arrest, we headed to the atrium at 60 Wall Street, which was frequented, in 2011 and 2012, by Occupy Wall Street organizers. He told me that he had been following the issue since 1988, when the NASA scientist James Hansen testified about climate change before the Senate. He’d seen Flood Wall Street as a complement to the People’s Climate March, and he discussed with me the recent examples of the necessity defense in the courtroom. “As the climate crisis unfolds, the logic of what we were arguing, I think, will make more and more sense,” he said. “And at some point, I think we will see a breakthrough in a courtroom. I can’t say when or where, but I think the long-term arc is moving in that direction.”