The Natural Born Killers star fears environmentalists, who warn of natural crises decades before they occur and offer ways of avoiding them, don't do enough and aren't taken seriously.
But, after last month's Gulf Coast hurricane tragedy and the tsunami disaster in south east Asia in December, Harrelson insists Earth lovers have to act like clever oil barons and do whatever it takes to succeed.
He explains, "Those guys, when the gas goes up half a cent at Chevron, it goes up half a cent at Shell. They've got every move coordinated. They're totally in control. They're working in unison.
"I think all the environmental groups have to focus on at least one main issue together. And now is the time. Hurricane Katrina is a direct by-product of global warming. We all knew that.
"Scientists 20 years ago were saying we'll get increased severity of storms and bigger and bigger hurricanes. It's all happening exactly the way they predicted, except a little bit faster. So, now's the time for all of us to get together."
And Harrelson wants to be at the forefront of an environmental coalition - he has set up a website, www.voiceyourself.com, and is asking those keen to follow his lead to sign up online.
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