More than 400,000 climate protestors marching through Manhattan yesterday turned out because, as Bill McKibben, Eddie Bautista, and La Tonya Crisp-Sauray, wrote last week, the world has left the Holocene behind: scientists tell us that we’ve already raised the planet’s temperature almost one degree Celsius, and are on track for four or five more degrees by century’s end.

Other than nuclear weapons, man-made climate change is the only existential threat confronting all of humanity, and the massive march was an organized attempt to raise public awareness and turn up the heat on the United Nations, which hosts a climate summit this week.

McKibben, a former journalist who has made addressing climate change his life’s mission, has dedicated the last 10 years to building a movement. He told The New Yorker’s online science and tech editor Jay Caspian Kang that yesterday’s march was part of the process of building that movement.

U.N. Secretary General Ban Ki-Moon joined the march (as did Al Gore and New York Mayor Bill de Blasio). But McKibben is looking beyond the U.N. climate summit, which will devote a great deal of rhetoric to climate change while accomplishing little else.

Attempts to reach an international climate accord, from Kyoto to Copenhagen, have been unsuccessful, largely because the United States and China, the two largest producers of greenhouse gasses, have refused to sign onto international protocols. Among the 195 signatories to the Kyoto climate accords, the United States and China are noticeably absent.

The next attempt to reach a global accord is the U.N. sanctioned Conference of Parties scheduled for December 2015 in Paris.

“This is a warmup for the big negotiating session in Paris,” McKibben said.

The march itself, which involved 1,200 organizations, drew protesters from far beyond New York, and far beyond the U.S., has to be considered a singular success for McKibben, along with the other organizers involved.

“Eight years ago to the month, I organized, without any idea how to do it, a March across Vermont,” McKibben told The New Yorker. “We walked for five days, and when we ended up in Burlington there were a thousand people with us. The papers the next day called it the biggest climate-change demonstration that had taken place in the United States.”

McKibben then realized that “we’re getting our butts kicked.”

We had, he said, the superstructure of a movement. But there was no movement. There were no people.

Yesterday what New York saw was a movement.

Lou Dubose is the editor of The Washington Spectator.