As climate change becomes an ever hotter topic in the run-up to the Copenhagen summit in December, some US companies are finding that the environment and business lobbying go together like oil and water.

Several large energy companies - including Pacific Gas and Electricof San Francisco and Exelon, the biggest operator of nuclear power plants in the US - have quit the US Chamber of Commerce over its position on climate change. A slew of others have left the American Coalition for Clean Coal Electricity (ACCCE), a trade group for coal and utility companies, for the same reason.