Thousands of people concerned about climate change descended on Washington, D.C., on Sunday.Organisers  claim more than 35,000 attendees.

The Forward on Climate rally called forPresident Obama to take immediate action on climate change, and asked  the government to block the construction of the oil pipeline known as Keystone XL.

Protestors marched through the streets bearing placards and massed on the National Mall, where speakers addressed the crowd. 

"Today was one of the best days of my life, because I saw the movement come together finally, big and diverse and gorgeous," 350.org President Bill McKibben tweeted after speaking at the rally.

The Keystone XL pipeline which would bring so-called tar sands oil from Canada into the United States  is regarded as such a serious issue in climate terms because it has the ability to create the tipping point. In order to be built this TransCanada project has a legal hurdle it must pass - U.S. law requires federal approval for new pipelines crossing international borders, making the pipeline more vulnerable to concentrated political pressure.

Sierra Club's director Michael Brune was arrested at a Wednesday protest outside the White House.

Picture from The Nation