WATERVILLE — The effects of global warming are materializing more quickly than expected, according to author and environmentalist Bill McKibben, who told a Colby College audience Thursday night that humans need to act now to address climate change.

McKibben, the founder of the grass-roots climate change organization 350.org, was the keynote speaker at the Community, Culture and Conservation Conference at Colby, which runs through Saturday.

“Climate change is the biggest thing humans have done, and we have to stop it at all costs,” McKibben told about 300 people gathered in Lorimer Chapel. “We have to figure out how to stop it before it breaks everything around us.”

Founded on the belief that mass mobilization can lead to change, 350.org started as a response to lobbying efforts by the fossil fuel industry against action on climate policy. Renewable energy such as solar power and efforts to reduce carbon emissions are potential solutions to slowing climate change, but they have been hindered by corporate fossil fuel interests, McKibben said.

He said 350.org has held about 20,000 rallies “almost everywhere” around the world in support of addressing and preventing climate change.

“We’re winning an increasing number of these fights,” he said.