Environmental groups announced a major ad campaign targeting “key Senators” to support a climate and energy bill. But while the outcome is uncertain, the main bill on the table would likely either eliminate completely a carbon cap or substitute it with a utilities-only cap. And that has been deemed totally insufficient by the biggest environmental actor, the Sierra Club.

One of the leading environmental groups in the country offered its most forceful opposition yet to a leading compromise on climate change legislation, raising questions as to whether there is a broad enough coalition to get even a watered-down bill passed.

Michael Brune, Executive Director of the Sierra Club, said on a conference call on Thursday that a cap on greenhouse gas emissions that only affects the utility sector would fall short of both the president’s goals and the definition of effective reform.

“A utility-only bill does not meet the standard that the president set in Copenhagen last year,” said Brune. “We feel it will not produce the emissions [standards] the planet needs to begin to address the threat of climate change. Moreover it misses an opportunity to address more clean energy jobs… The Sierra Club does not support a bill that is limited in scope to utilities.”

As recently as a couple days earlier, top officials at the Sierra Club urged caution. That caution has been thrown, as they say, to the wind.

So exactly what will that $11 million dollar ad campaign say? Sierra Club is one of the main groups funding it, along with The League of Conservation Voters, SEIU and VoteVets.org. It’s designed to go up when the Senate bill reaches the floor. Will the ads urge a No vote, if lawmakers decide on the utilities-only approach? Will they make the carbon cap as central to their critique of the bill as the public option was for health care? The ads will supposedly begin next week. With these debates about the carbon cap happening now, isn’t that too late?

UPDATE: So will the Sierra Club support with $11 million dollars a bill that has “broad bipartisan support,” which will necessarily never have an industry-wide carbon cap, if it has a carbon cap at all.