Organizers of the march on Washington, D.C., for action on climate change estimate that about 35,000 people participated in the Feb. 17 protest.

The Sierra Club on Feb. 18 said protesters arrived to the capital from at least 30 states for the largest climate rally in U.S. history.

"For 25 years our government has basically ignored the climate crisis: now people in large numbers are finally demanding they get to work, said Bill McKibben, founder of the activist environmental group 350.org. "We shouldn't have to be here – science should have decided our course long ago. But it takes a movement to stand up to all that money.

Demonstrators on the National Mall focused on the proposed Keystone XL tar sands pipeline and called on President Barack Obama to reject the project, as well as to move forward on his State of the Union address declaration. In his speech, the president said, "For the sake of our children and our future, we must do more to combat climate change."

Michael Brune of the Sierra Club said, "Twenty years from now on President’s Day, people will want to know what the president did in the face of rising sea levels, record droughts and furious storms brought on by climate disruption. President Obama holds in his hand a pen and the power to deliver on his promise of hope for our children. Today, we are asking him to use that pen to to reject the Keystone XL tar sands pipeline, and ensure that this dirty, dangerous, export pipeline will never be built."

Brune's group maintains that Keystone XL would "pipe some of the dirtiest oil on the planet through the breadbasket of America to be shipped overseas through the Gulf of Mexico. It would be a disaster for our climate, producing tar sands crude that kicks out two or three times as much carbon pollution as producing conventional crude oil."

Protesters also urged the president, under the Clean Air Act, to cut the amount of carbon pollution emitted from power plants.

"This president has the power to achieve the single biggest carbon reduction ever, by holding our biggest carbon polluters – dirty power plants – accountable for what they dump into the air," said Van Jones, president of Rebuild the Dream. "Cleaning up this pollution and using more clean energy will provide jobs to thousands of Americans, save families real money when it comes to electricity bills and, most important, will make a real difference in our health and the health of our children."

Rally speakers also included the Rev. Lennox Yearwood of the Hip Hop Caucus; Democratic Sen. Sheldon Whitehouse of Rhode Island; Chief Jacqueline Thomas of the Saik’uz First Nation in British Columbia and co-founder Yinka Dene Alliance; Crystal Lameman of the Beaver Lake Cree First Nation; Maria T. Cardona of Latinovations; and Tom Steyer, of the Center for the Next Generation.