Leonardo DiCaprio, Edward Norton, Mark Ruffalo Join People's Climate March ...

We're not sure how you spent your Sunday, but celebrities from Leonardo DiCaprio to Edward Norton were busy trying to save the planet.

Among the estimated 400,000 participants in the People's Climate March in New York City - a crusade to demand climate-change action - were the two Hollywood heavyweights as well as Jennifer Connelly and Paul Bettany, Sting and Trudie Styler, Mark Ruffalo, Evangeline Lilly, Russell Brand, and former vice president Al Gore. Their mission? To demand that the United Nations, which is holding a summit on climate change this week, take action on global warming. And they were already a success because it was the largest climate protest in history and biggest social demonstration of the past decade, according to Time magazine. (The event was held primarily in NYC, but there were 2,808 solidarity events in 166 countries.)

Long-time environmental activist DiCaprio, who was recently named the UN Messenger of Peace on Climate Change, walked with an aboriginal group trying to stop the Keystone XL pipeline. (He recently visited the controversial Canadian tar sands with director Darren Aronofsky, which they documented here.) Although the Wolf of Wall Street star, 39, was wearing a hat, sunglasses, and, yes, that bushy beard, he was still easy to pick out of the crowd as he stood front and center, carrying the organization's banner for much of the time. He marched alongside Ruffalo, who has been big on the anti-fracking movement, and his pal Norton, who was there with his wife, Shauna Robertson.

Connelly and Bettany, a New York pair who married after meeting on the set of A Beautiful Mind, made it a family affair, bringing along their 3-year-old daughter, Agnes, whom the British actor carried for much of the walk. Sting and his wife, who have long supported earthy causes, were another star couple on the scene.

Lost alum and The Hobbit actress Evangeline Lilly documented her day in a series of Instagram photos and even spoke out to a group of ralliers. 'Shout out of #thanks to all of you who were there at the #peoplesclimatemarch today and to those of you who were there with us in spirit,' she wrote. 'It was a very powerful demonstration that could be felt all through the city. Xoxo.'

British comedian Brand infused some humor into the cause - and even joked while posting photos from the event. 'A lot of people on the #climatemarch were eccentric,' he captioned a photo of himself with a masked protestor.

Gore, who earned a Nobel Peace Prize for his work in climate change activism, was also on hand and marched with New York City Mayor Bill de Blasio and UN Messenger of Peace Jane Goodall.

The 50-block march, which took several hours, didn't tire out DiCaprio. On Sunday night, the actor, who owns an environmentally-friendly condo in Manhattan along with a number of hybrid and electric vehicles, attended Bill Clinton's 8th Annual Clinton Global Citizen Awards along with Sting, Eva Longoria, Seth Meyers, Uma Thurman, Idris Elba, and a very pregnant Chelsea Clinton to continue to put a spotlight on the cause.

So yesterday DiCaprio walked the walk - literally.