The Shutter Island star was scouting for volunteers to join him at an upcoming rally against the Keystone XL Pipeline, which would stretch from Canada to America's Gulf Coast.
Ruffalo told the crowd the project would be built at the cost of citizens' health and wellbeing, according to the Huffington Post.
He said, ""We are fighting against climate change. Climate change is real; it is happening now, not tomorrow. They want to keep us addicted to oil, to gas, to coal, to nuclear. We are the sunlight revolution.""
Ruffalo plans to protest at the White House in Washington, D.C. on 6 November (11).