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Legions of demonstrators frustrated by international inaction on global warming descended on New York City on Sunday, marching through the heart of Manhattan with a message of alarm for world leaders set to gather this week at the United Nations for a summit meeting on climate change.

Coursing through Midtown, from Columbus Circle to Times Square and the Far West Side, the People's Climate March was a spectacle even for a city known for doing things big, and it was joined, in solidarity, by demonstrations on Sunday across the globe, from Paris to Papua New Guinea.

"I'm here because I really feel that every major social movement in this country has come when people get together," said Carol Sutton of Norwalk, Conn., the president of a teachers' union. "It begins in the streets."

From the scientists holding an oversize chalkboard to the Hurricane Sandy victims toting life preservers, the march was a self-consciously inclusive affair, with the organizers intent on creating a very big tent, which they hoped would hammer home the relevance of climate change and its effects.

The march attracted leading lights in the environmental movement, most notably former Vice President Al Gore. It drew the secretary general of the United Nations, Ban Ki-moon, who will preside over this week's United Nations climate summit meeting. And it included Mayor Bill de Blasio of New York, fresh off his announcement that he was committing the city to an 80 percent reduction in greenhouse gases by 2050.

But it was mostly an event for concerned ordinary people, many of them veterans of climate change efforts, others relative newcomers. Continue reading the main story Related in Opinion

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From as close as the Bronx and as far as at least Rome, the demonstrators came in vast numbers. At one point early in the afternoon, the march came to a halt because the entire 2.2-mile route was full, and more than two hours into the procession, people were still setting out from the starting point near Columbus Circle.