Marchers rally for climate change action

People gather near Columbus Circle before the People's Climate March in New York on Sunday, September 21. People from around the world are participating in what's billed as the largest march ever calling for action on global warming.

A man waves a rainbow flag as he marches in New York.

Marchers wave signs and banners as they fill a street in London.

Thousands of people joined the march from the Embankment via Whitehall to the Houses of Parliament in central London.

Marchers crowd a street in Brussels, Belgium.

Demonstrators gather in Place de la République in Paris.

Indian schoolchildren take part in a march in New Delhi.

• "Cut your emissions or you'll sleep with the fishes," marcher's sign warns


• "People's Climate March" in New York is one of several around the world Sunday


• Activist: Droughts, storms and floods are "a taste test of what's to come"


• World leaders converge on the U.N. to discuss climate policy Tuesday

(CNN) -- Tens of thousands of people marched through Manhattan sounding an urgent call for action to reverse global climate change Sunday.

One marcher's sign read "cut your emissions or you'll sleep with the fishes."

The "People's Climate March" in New York was billed as the largest of several protests held around the world two days before the start of the United Nations' Climate Summit.

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U.N. Secretary General Ban Ki-moon walked with former U.S. Vice President Al Gore along the two-and-a-half mile route. Celebrity protesters included comedian Chris Rock and actors Leonard DiCaprio and Mark Ruffalo, who said he was marching for his children's future.

"I see the world changing very quickly already, and I want to do my best to give them the best world that they deserve to have and that I was fortunate to come up into," Ruffalo told CNN.

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Ricken Patel, the founding executive director of march organizer Avaaz, told CNN the "solution is so clear. It's to get to a 100% clean energy power society and economy."

"We're seeing massive droughts across the Midwest and California," Patel said. "We're seeing storms that are devastating the East Coast and the Gulf Coast. We're seeing flooding that's threatened this city and many others. All of those impacts that are happening, but it is just a taste test of what's to come if we don't urgently reverse course."

The Environmental Defense Fund said it expected up to 100,000 people to walk, while the New York Police Department predicted about 30,000 would participate.

Rallies were also held in London, Paris, Berlin, Tokyo and Bogota, Colombia.

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World leaders converge on the U.N. headquarters in New York to offer and discuss climate change proposals starting Tuesday.

Speakers will include President Obama and DiCaprio, who was recently appointed as U.N. Messenger for Peace with a focus on climate change.

CNN's Alison Kosik contirbuted to this report.