"So many people are coming together because climate change is really becoming crystal clear," said Refugio Mota with the Sierra Club. "It's coming home. You saw Superstorm Sandy, you saw the devastating effects."
Specifically, the protesters want Mr. Obama to take immediate action on what they say is a climate crisis. They also want him to reject the controversial Keystone XL pipeline. If approved, the pipeline would deliver oil from tar sand in Canada to refineries in Texas.
Some 300 people hit the streets for what organizers of the Forward on Climate Rally say was the largest public action on climate change in L.A.'s history.
"I'm here because like any parent who is looking to the future for their kids, future generations, we have an opportunity to make a stand here," said actor Orlando Bloom.
In Washington D.C., tens of thousands of protesters did all they could to get the president's attention Sunday. They too embarked on a march, though amid freezing temperatures, on the nation's capitol.
As for the pipeline, Mr. Obama has twice thwarted the project because of concerns over its route through sensitive land in Nebraska. But now that a new route has been selected, there is no word on what the president will decide.
The 1700 mile pipeline has become a flashpoint in the debate over climate change. Many say they will support it because of what it will bring in terms of jobs, but the opposition says it will only cause more harm than good.
The Associated Press contributed to this report.