He plans to officially launch the Footprint Coalition in April 2020 and vowed to spend the next 11 years working on making some kind of difference in what he called "a massive threat to our future and the mess we leave behind."
Downey made the announcement late Tuesday at the start of Amazon's re:Mars conference in Las Vegas, where the online retailer and other companies are showing off how they use artificial intelligence and other technology.
As Downey talked on stage, images of plastic bottles and other litter flashed on the screens behind him. The actor, who has played Iron Man in several superhero movies, admitted that he hasn't been kind to the environment in the past.
"I am a one-man carbon footprint nightmare colossus," he said. "I want to change."
Contact Joseph Pisani at http://twitter.com/josephpisani