On a recent drizzly, cold Saturday, a climate scientist named Gisela Winckler was standing at Beach Ninety-fourth Street, in Rockaway, Queens. The ocean behind her was gray-green, uninviting, confused, the wind blowing hard onshore. A flock of surfers bobbed in the waves, a scattering of people strolled. Next to her, a huge black-and-orange L.E.D. roadwork sign flashed a series of messages: “CLIMATE DENIAL KILLS”; “ABOLISH COAL ONIALISM”; “VOTE ECO LOGICALLY.” “I thought we would be getting a lot more questions, actually, about these specific messages,” Winckler said. “This one, for example, is pretty complicated.” The L.E.D. sign read “HUMAN AGENDA AHEAD.”

The sign, which was solar-powered, was part of “Climate Signals,” a citywide installation by the artist Justin Brice Guariglia, presented by the Climate Museum in partnership with the Mayor’s office. Winckler, in a red leather jacket, the wind whipping her long brown hair, was taking part in “Ask a Scientist,” an event co-hosted by the museum and Columbia University’s Earth Institute, where Winckler works. Other scientists were stationed at nine other roadwork signs, situated across the five boroughs, in prominent and iconic public spaces: the 1964 World’s Fair Unisphere, in Queens; a former illegal dumping ground in the Bronx; Governor’s Island. The scientists at each post had handouts with “climate-communication tips,” such as “How to deal with a climate skeptic.” (One suggestion: look for common ground, i.e., how “we all depend on the same planet for our survival, and all of us want a good outcome.”)

One man rode by on his bike, staring at Winckler, then circled back and dismounted. “It says I can ask a scientist a question?” he said emphatically, indicating a banner hanging from a table in front of Winckler. She nodded. “I just got back from a cruise on the Rhine River, from Amsterdam to Frankfurt. Whole time there, in Germany, it was eighty-five degrees. I’m, like, ‘Eighty-five degrees! What’s going on here?’ They haven’t had rain in two months. The water levels were so low! Only twenty-five inches of water! Why? I’m asking you, why?” He was practically shouting.

“I happen to actually come from Germany, so I know exactly what you’re talking about,” Winckler said. “There are changes to the climate system that we are seeing over longer time scales. This was a huge anomaly in Europe.”

Another curious passerby asked Winckler what, for her, was the biggest and scariest unknown in climate science.“What’s mostly occupying my mind right now, in terms of the importance of the question, is the contribution of Greenland to sea-level rise,” she said. She nodded at the L.E.D. sign, which now read, “50,000,000 CLIMATE REFUGEES.” “Sea-level rise is the big question that will affect pretty much everybody,” she continued. “Not just the coastal areas. Yes, there will be flooding. There already is flooding all over the place. But there are also all the indirect effects, like what the sign says: millions of climate refugees, forced migrations.”

Guariglia, the artist behind the roadwork signs, had been sitting in a traffic jam, waiting to go through the Holland Tunnel from New Jersey to Manhattan, when he saw a highway sign that was glitching on the side of the road. He recalled thinking, “Oh, L.E.D.s are flashing unreadable text, and my brain is registering it as something that’s out of place, and I cannot stop looking at it or thinking about it.” After thinking about it some more, he realized that the highway sign, which warns us to slow down and pay attention to what’s ahead, was “this great embedded metaphor.” “It’s exactly what we need right now across the planet,” he told me. The real challenge was then making his point at traffic-sign length. As he worked with the Climate Museum on the messages, the museum worked with the city to select locations for the signs and determined which languages—ultimately Spanish, French, Russian, and Chinese—should be included depending on local neighborhood demographics.

At Rockaway, the sign was flashing in Russian. An eight-year-old named Miriam Bird, who was riding a scooter with her parents and four siblings, approached. “Is climate change related to global warming?” she asked.

“Yes, absolutely it is,” Winckler responded. “Global warming just means that the temperature goes up, but there are other things that it causes, like the melting of ice, or the change in where it rains—more rain in places where it already rains a lot, or less rain in dry places, or no rain at all.” “In California, they are having a lot of wildfires because of global warming,” Bird said. Winckler nodded. Bird’s older brother, Cameron, asked whether climate change would affect all of the world’s biomes differently. It would. An elderly man stopped by and told Winckler that we were going to disappear in the next forty-eight years, at least Rockaway was: “We’re doomed.” He also wanted her to know that he had once met Jacques Cousteau, a scientist like her. “A very nice man,” he said.

Was the man right, a curious bystander asked. Was Rockaway going to be completely gone within half a century? Winckler, who can’t help but think in millions of years, not hundreds, returned to Greenland. A few years ago, she said, scientists at Columbia’s Lamont-Doherty Earth Observatory had analyzed a rock core that had been drilled from underneath a Greenland glacier that was a hundred and twenty-five thousand years old. When galactic cosmic rays—like the ones that hit us from the sky every time we step outside—hit rock surfaces, certain isotopes are produced. When the rock was covered by an ice sheet, there was no isotope production.

“So essentially you ask the rock beneath the ice sheet, ‘When did you last see the atmosphere?’ You want it to tell you ‘never’ or ‘ten million years ago.’ Then we wouldn’t have to worry about this,” Winckler said. That would mean, as scientists previously believed, that the sheet is stable, just a big ice cube sitting on top of the world. “But that was not the answer of the rock,” she said. The answer was that, in the last 1.2 million years, it was exposed for something like two hundred thousand years. “That’s a fairly long time,” Winckler said. “That means inherently there is something going on with the ice sheet that we weren’t aware of.” The new evidence suggests that the sheet—which would equal more than twenty feet of sea-level rise if it melted entirely—could thaw and flow into the Arctic Ocean at a potentially terrifying rate.

A woman wearing a trucker hat and carrying a surfboard appeared. “Have those people been screaming at you guys?” she asked, gesturing down the block. At the intersection of Beach Ninety-fourth Street and Rockaway Beach Boulevard, a Trump rally was under way. Winckler said no—that was a separate event, and they had ignored the scientists. As the afternoon passed and the rain picked up, the group, in “America First” and Trump 2020 T-shirts, continued chanting “U.S.A.!” and waving MAGA flags. Directly across the street, a group of counter-protesters had gathered, holding up signs like “Mermaids Against Misogyny” and “Rockaway Against Rape Culture.” On the MAGA side, a man with a blow horn began to sing “God Bless America.” The counter-protesters quickly joined in, singing at the top of their lungs. For a moment, the two groups seemed like one. Then the song ended, everyone cheered, and a cop yelled, “Play ball!”