The Minnesota-born brothers previously collaborated on the movies "Burn After Reading," "No Country for Old Men," "The Big Lebowski" and "Fargo."
Their new TV spot for the Reality Coalition, which features the tag line, "In reality, there's no such thing as clean coal," started airing last week on CNN, MSNBC and Comedy Central, as well as the Web site www.thisisreality.org, the Los Angeles Times reported.
"We were excited to be part of this important project and tell another side of the 'clean' coal story," the Coens said in a statement.
Environmentalists have said the coal industry's marketing campaign is misleading because it has left people thinking "clean coal" technology is further along than it is, The Times noted.
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