The Oscar-nominated Spotlight and Avengers actor spoke out at a rally in Los Angeles protesting against man-made climate change and, in particular, the controversial Dakota Access Pipeline, the site of escalating protests in recent weeks.
“President Obama, it is immoral for you to keep drilling in our state lands, in our federal lands, off our federal waters, while at the same time calling yourself a climate change leader,” he said.
Ruffalo, 48, recently narrated and produced Dear President Obama: The Clean Energy Revolution Is Now, a critical documentary on the outgoing head-of-state’s environmental legacy.
He was joined on stage by actresses Shailene Woodley, 24, and Susan Sarandon, 70, for a five-hour event featuring music and speeches in front of around 800 people at MacArthur Park in downtown LA.
The heavens opened as Grammy-nominated singer-songwriter Antonique Smith started playing Beatles hit Here Comes the Sun, and a prolonged downpour, rare in drought-hit Southern California, delighted the crowd.
Woodley, who stars in Oliver Stone biopic Snowden and the Divergent film franchise, was arrested at the Dakota Access Pipeline earlier this month.
She was charged with criminal trespass and engaging in a riot, and is due in court on Monday.
“Indigenous people, for the most part, and marginalised communities, are the first communities to get compromised and get taken out by the fossil fuel industry,” she said.
“Their lands are flooded from dams being built, their fish are taken and put in other countries, their mountains are compromised without any regard to their sacred ancestry and their traditions.”
Protests have drawn thousands of people to the area where Texas-based Energy Transfer Partners is trying to complete a 1,886km pipeline from a vast underground deposit in North Dakota southwards into Illinois.
More than 220 people have been arrested since demonstrations began in August.
Protesters say the $3.8bn pipeline will damage the environment and affect historically significant Native American tribal land.
The Standing Rock Sioux tribe, whose reservation in North Dakota is near the pipeline route, says the project would destroy some of their sacred sites.
“The world is a mess.
We’ve got wars, we’ve got the Mother Earth being raped constantly,” Sarandon told the crowd, to cheers.
“Not only is it an environmental, but it’s a problem in terms of social justice.
We can do it. We can stop fracking. We can stop the pipeline.”
Fracking, or hydraulic fracturing, is the extraction of natural gas from deep in the ground by blasting water and chemicals under extremely high pressure.
It is estimated to have offered gas security to the US and Canada for about 100 years, presenting an opportunity to generate electricity at half the CO2 emissions of coal.
But the process uses huge amounts of water, which must be transported to the fracking site at significant environmental cost, and critics say the potentially carcinogenic chemicals involved could contaminate groundwater.
The rally was part of a series of gatherings across the US organised by Josh Fox, best known for Oscar-nominated 2010 documentary Gasland and his opposition to fracking.
“No matter what happens in this election, we need a strong movement to fight the fossil fuel industry and to fight to preserve our planet against climate change,” he said, referring to next month’s presidential vote.
Sunday’s event included an outdoor screening of Fox’s How to Let Go of the World and Love All the Things Climate Can’t Change.
The film was produced by Deia Schlosberg, who is facing a possible 45-year prison sentence after she was arrested while documenting the shutdown of five major pipelines by environmental activists.
The pipeline, being built by a group of companies led by Energy Transfer Partners LP, would be the first to bring Bakken shale from North Dakota directly to refineries on the US Gulf Coast.
Supporters say the pipeline would provide a safer and more cost-effective way to transport Bakken shale to the US Gulf than by road or rail.
There were no reports of arrests at the Los Angeles rally, where demonstrators assembled into the evening decrying climate change, hydraulic fracturing and oil pipelines as a threat to the safety of future generations.
“I’d rather walk miles today to protest the building of the pipeline than have my children walk miles to get clean water in the future,” 22-year-old college student Steffany Urrea said.