The day I arrived in London a few weeks back, temperatures cracked 100 degrees at Heathrow airport. It was the hottest month on record—again. Melting Arctic sea ice had sent the jet stream wandering, allowing hot air from the Sahara to drift north over Europe. The usually buttoned-down city had an almost tropical languor to it. Everyone was going about their business, only more slowly, and sometimes without shirts, even on the subway: it did not occur to the engineers who built London’s underground that it would ever get so hot, and most trains are not air-conditioned. The mayor’s office put up posters in the stations, instructing residents to carry water, and to help heat-sick passengers off the trains.

If you looked for them, there was another set of alerts all over town, these ones taped to windows, stuck on lampposts, wheat-pasted to walls. I saw them everywhere I went in England—in London, in Bristol, in sleepy Suffolk hamlets. Some were just runes: a circle around two right triangles joined at the point, the stylized hourglass that has become Extinction Rebellion’s icon. It means time is running out. Others bore a deceptively simple message: “ACT NOW.”

It was those two messages—and the seemingly unbridgeable gulf between them—that made me seek out the activists behind Extinction Rebellion, the grassroots movement that’s working to halt the climate crisis by means of massive shows of civil disobedience. What could it mean to “act now,” when we have so little time? How to find the will to fight when everything seems doomed? It’s hard even to move when temperatures break 100, and harder still when you know that the sweat soaking your shirt means the Gulf Stream is failing, the permafrost melting, that Alaska’s sea ice is already gone, that we’re running out of arable land, out of water, out of time.

The left has rarely been comfortable talking about despair, much less about faith—of the religious sort or any other. But who ever expected to have to mourn a planet, to watch the shadow of extinction fall on so many living things? Our demise is not yet fated, but even without Bolsonaro and Trump, we are running headlong towards it. Carbon emissions continue to climb. Despair hangs heavy, stifling, grey as meltwater rushing off a Greenland glacier. Sometimes it feels more frantically debilitating, a roaring orange, like the Arctic and the Amazon in flames. It has its own feedback loops, too: If we don’t act, we know that all will certainly be lost; but all action feels inadequate, so we muddle on as the ground collapses in front of us.

From the beginning, Extinction Rebellion—“XR” in movement shorthand—has sought a way out of this bind. It helps that there is far more environmental consciousness and far less overt climate denialism in the UK than in the US. It made the problem easier to isolate: Nearly everyone understands what is happening, but the machine is powerful and chugs on nonetheless. XR’s solution was simple: The machine functions only because we will it to, if only tacitly, by submitting to business as usual. So the answer is to stop submitting, and to do so in sufficient numbers that the machine would begin to wheeze and choke.

A lot can happen in a year. For their inaugural action, on Halloween of 2018, they met in Parliament Square—not thousands yet, just hundreds. The event was meant to be symbolic, to announce a campaign of civil disobedience that would begin the following month, and then to go away. Greta Thunberg gave a speech. She had only started her school strike three months earlier. “It is time to rebel,” she said.

Donnachadh McCarthy gave a speech that day too. McCarthy is 60 and spry, a onetime ballet dancer who, after a career-ending accident on the stage of the Royal Opera House, traveled to the Brazilian Amazon. That was in 1992: Climate change was still largely an abstraction, but a month living with the Yanomami gave him a quick and intimate education in our inseparability from nature, and in what it means for a people to lose their world. “I came back to London gutted,” he said. He threw himself into environmental activism. In desperate times, he learned, despair is sometimes the only path forward.

Last Halloween, he recalled, “I spoke about the grief that’s in my heart, about this loss.” The memory made him laugh. XR had no plans for direct action that day, he said, and when police gave the crowd 30 minutes to leave or face arrest, people began to pack up. That is when he “jumped on the platform and said, ‘Who’s going to sit in the road with me?’ Hilariously, one person put their hand up.”

But then someone else, the writer George Monbiot, “sat down with a group of people” to block the road leading to Parliament “and 15 of us sat in a circle and suddenly the whole crowd surrounded that.” Fifteen were arrested. “That was the start of our rebellion.”

The next month made them famous. Thousands of activists blocked five bridges across the Thames, shutting down traffic in much of central London. The mood was festive and defiant. Eighty-five were arrested. The arrests were part of the strategy, the idea being that only massive disruption can break the entrenched momentum of the status quo, that only by showing that they were willing to sacrifice would activists be taken seriously, and only by transmuting solitary despair into collective joy could they inspire others to join them.

Every month since has brought something new. In April, they occupied Parliament Square and three major London intersections. They held them for days, stopped trains, blockaded the Stock Exchange, glued themselves to the Treasury. McCarthy was moved to tears. “It was like the reinforcements finally arrived,” he said, referring to the masses of new activists, most of whom are considerably younger than he is. More than 1,100 were arrested in London alone, and more across the planet from Australia to the Hague.

Less than two weeks later, Parliament formally declared a climate emergency. It was a symbolic victory—the UK still invests heavily in fossil fuels—but the discourse, at least, had shifted. Since then, chapters have formed around the world, from Accra to Bhopal to Adelaide. Organization is horizontal, viral even. Larger actions are coordinated, but so long as activists abide by a few basic principles, nonviolence first among them, chapters can do what they like without asking anyone’s permission.

And so, the protests continue: “die-ins” in Portsmouth and Perth, highways blocked in Birmingham, Brisbane, Madrid. October 7, a planned global day of action, McCarthy promised, will bring a tremendous escalation.

XR’s tactics won’t fit everywhere. They have taken heat from the left for relying on a strategy that counts on the benevolence of the state—co-founder Roger Hallam has described London’s Metropolitan Police as “probably one of the most civilized forces in the world”—and excludes and endangers populations vulnerable to police violence, i.e., people who are black and brown. In the UK, XR has remained a largely white and middle-class movement. It should not be impossible, though, to forge more flexible models of resistance, to borrow what works and discard whatever doesn’t.

The lesson here is not that any one strategy is particularly efficacious. It’s that collective action is the surest antidote to solitary despair. This is something that Americans have largely forgotten. When I asked Clare Farrell, another founding XR organizer, how she managed to keep afloat despite the ever-rising tide of apocalyptic news, she answered by recalling an early XR slogan: “Hope dies, action begins.”

We act, in other words, on the terrain of hopelessness, and by acting we transform the terrain. Faith is not about belief. It’s a leap into action—despite it all, for each other, and for a future that we cannot yet see. Anyway, Farrell said, “to not act is surely hopeless.” So we might as well fight while we can.