Yesterday I found myself wrapped in a pale blue plastic poncho, arm in arm with my friend Kate on one side and a total stranger on the other. Hundreds of people rushed toward us as we stood squinting in the late afternoon sunlight—and then, in time with the music echoing over the sound system, they all turned as one, raising both arms to point at the sky. As a sea of extended arms lowered, beat by beat, an ominous countdown echoed overhead: “Tck. Tck. Tck.”

That’s what it looked like from where I stood, anyway—one among the thousands who turned out for Oxfam’s Human Countdown event in New York’s Central Park.

Viewed from above, the carefully choreographed spectacle makes more sense. An army of volunteers transform themselves into a massive, perfectly rendered planet earth, which trickles down through an hourglass, then forms the words “tck tck tck.” Our group was the bottom of the hourglass, while the blue- and green-clad dancers in front of us formed the earth’s oceans and continents.

But beyond just looking really cool, yesterday’s event sends a clear message: Time is running out for our leaders to act on climate change.

Though the problem is global, the countdown to climate action begins right here in New York, just blocks from the empty ice skating rink where we assembled. Tomorrow President Obama and other world leaders will gather for a special UN climate summit, the first in a series of key decision moments about the future of our planet.  This meeting could generate the momentum we need for leaders to deliver fair, ambitious, and binding climate treaty at the UN Conference on Climate Change in Copenhagen this December.

Many of the volunteers I met yesterday came ready to have fun, but were also aware of the significance of the day’s events.

“As long as there are people who care enough to stay out in the sun and make an hourglass, this issue will get attention,” said New York University student Kate Cordry, who stood next to me in the formation.

Her friend Rosemary Devine, from New Brunswick, New Jersey, agreed. “A small group of people can change the world,” she told me quietly as we ran through our moves one more time, media cameras filming us from above. “Today shows that they can.”