Thousands of protesters gathered in Washington Sunday for a rally to press President Barack Obama to take concrete measures to help fight global warming.
The protesters want Obama to reject the proposed Keystone XL pipeline that would bring oil from Canada's tar sands to Texas and order the Environmental Protection Agency (EPA) to set carbon standards for power plants, among other things.
The event has been organized by scores of local and national environmental groups, including the Sierra Club, under an umbrella group named Forward on Climate.
"Your legacy as 44th president of the United States rests firmly on your leadership on climate disruption," protest organizers say on their website.
"Only the president has the power to lead an effort on the scale and with the urgency we need to phase out fossil fuels and lead America, and the world in a clean energy revolution."
Organizers claim the event will be the largest climate rally in US history, and includes protesters who have arrived aboard buses from 28 states.
The crowd was to rally at the National Mall at noon, then march to the White House.
The president mentioned climate change during his inauguration speech in January, and in Tuesday's State of the Union he vowed to take action "for the sake of our children and our future" if Congress fails to do so.
"I will direct my cabinet to come up with executive actions we can take, now and in the future, to reduce pollution, prepare our communities for the consequences of climate change, and speed the transition to more sustainable sources of energy," Obama said in his speech.
Celebrities who have signed a petition supporting the protesters include Alec Baldwin, Susan Sarandon, Morgan Freeman, Robert Kennedy Jr and Yoko Ono.
The rally comes after the United States last year endured record high temperatures and lengthy droughts, as well as superstorm Sandy, which devastated the New York-New Jersey coastline.
To demand action against the $7 billion Keystone XL pipeline protesters said they will form a "a human pipeline" -- a chain of people -- between the National Mall and the White House.
Soon after taking office in 2009 Obama presented an ambitious measure aimed at reducing carbon dioxide emissions -- the United States is the world's second largest CO2 emitter after China. But the bill ran into stiff resistance from the Republican opposition.