USCOC LOSING FRIENDS FAST…. The U.S. Chamber of Commerce has been one of the leading conservative opponents of climate change legislation, operating on the assumption that a looming environmental catastrophe isn’t nearly as important as the short-term profit margins of some of its members.

It’s a position that some Chamber of Commerce affiliates are no longer willing to accept.

Exelon, one of the country’s largest utilities, said Monday that it would quit the United States Chamber of Commerce because of that group’s stance on climate change. It was the latest in a string of companies to do so, perhaps a harbinger of how intense the fight over global warming legislation could become.

“The carbon-based free lunch is over,” said John W. Rowe, Exelon’s chief executive. “Breakthroughs on climate change and improving our society’s energy efficiency are within reach.”

A wave of departures from the chamber has been building for weeks. It was heralded Monday by some Congressional Democrats and environmentalists as a sign that the business community’s opposition to global warming legislation is weakening. In their view, that improves the chances that a global warming bill that narrowly passed the House in June might also pass the Senate.

Last week, Pacific Gas and Electric and PNM Resources also quit the Chamber over the group’s efforts to derail energy reform, but Exelon is an even bigger prize. “There will be significant vibrations from this,” Rep. Jay Inslee (D-Wash.) said. “It’s a bit of an earthquake.”

One of the driving factors in the shift away from the Chamber is a recent announcement that the group wants a “Scopes monkey trial of the 21st century” about the science of climate change. The remarks made clear that the Chamber of Commerce, even now, simply doesn’t accept the scientific evidence.

It’s important to note that Exelon, which sold many of its coal-fired plants in 2000, is the nation’s biggest operator of nuclear power plants. It’s hardly unreasonable to suspect the company’s position on climate change legislation is motivated, at least in part, by business considerations.

But Exelon’s move is nevertheless welcome, and comes at a fortuitous time for supporters of cap-and-trade legislation — Sens. John Kerry (D-Mass.) and Barbara Boxer (D-Calif.) intend to introduce a Senate version of the already-passed Waxman/Markey bill today.

A global climate crisis will invariably be bad for business. The more the business community acknowledges this fact, the more likely meaningful reform will pass.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.