More than 400,000 people took to the streets of New York City on Sunday for the People’s Climate March. Calling for action on climate change, organizers say it was one of the largest environmental demonstrations ever held.

From scientists to activists to parents concerned for the future of their children, this massive grassroots event attracted people from across the country and around the world. It even included some boldface political names like former U.S. Vice President Al Gore (founder of the Climate Reality Project), NYC Mayor Bill DeBlasio, U.N. Secretary-General Ban Ki-Moon, as well as high profile environmentalists like Jane Goodall and Leonardo DiCaprio.

The message of this enormous rally was aimed at the more than 120 heads of state that will be attending the U.N. Climate Summit this Tuesday in NYC.  The summit is an effort to mobilize political will ahead of the U.N. Climate Change Conference in Paris next year where the objective is a binding global agreement on greenhouse gas emissions.

Demonstrators making their down Sixth Ave in mid-town Manhattan during the People’s Climate March.  Image Credit: Fox News/AP