Mark Ruffalo and Leonardo DiCaprio marched for climate change in New York City’s People’s Climate March, which has attracted thousands to walk the streets of New York.

People's Climate March NYC

The People’s Climate March in New York City on Sunday, Sept. 21, was organized as a message to the United Nations summit on climate change, scheduled to take place on Tuesday in New York City.

“We are demanding the world we know is within our reach: a world with an economy that works for people and the planet; a world safe from the ravages of climate change; a world with good jobs, clean air and water, and healthy communities,” reads the official march website.

Ruffalo and DiCaprio joined thousands on Sunday, including actors Kevin Bacon and his wife Kyra Sedgwick, who have been live-tweeting the march.

Al Gore Joins People's Climate March

Al Gore, a longtime climate change activist, is marching alongside New York City Mayor Bill De Blasio and UN Secretary General Ban Ki-moon.

Though not in attendance, President Barack Obama tweeted his support of the march.

Emma Thompson Marches In London

People’s Climate March also took place worldwide, with marches in London and Paris, among others. Emma Thompson was spotted at the People’s Climate March in London earlier today, and Russell Brand also tweeted from the London event.