In a sign that US electricity companies are recognising that the Democratic-controlled Congress will seek to impose aggressive climate change initiatives, six companies, including Exelon, one of the largest utility companies, on Wednesday endorsed a bill that would reduce their projected emissions by 25 per cent below projected levels by 2020.

Dianne Feinstein, the Senate Democrat from California, and co-sponsor of the cap and trade bill with Tom Carper, a Democrat for Delaware, said the bill was the first time “major industry groups have endorsed a cap and trade bill which establishes emissions reductions as deep and aggressive as this bill”.

The six companies, which have broken ranks with the rest of the industry, represent 15 per cent of the US electricity market and operate in 42 states. They include Calpine, Entergy, Florida Power and Light and PG&E Corporation.

However, critics say that the six companies have a comparative advantage over rival power companies, in that they are less dependent on creating power from coal and have been more active in moving to nuclear power and wind power.

Peter Darbee, chief executive of PG&E, which operates California’s largest utility company, acknowledged there was a degree of self interest by the companies. “There was a lot of push-back against global warming, but in the last few weeks there has been a view of the need to take proactive action to deal with this, otherwise we will be viewed as unconstructive. We want to be at the table.”

Ms Feinstein said electricity companies accounted for a third of all US emissions, and that the bill was the first of five bills that would address global warming, including one to raise fuel economy standards by 10 miles per gallon over the next 10 years and a cap and trade proposal for the industrial sector.

“You’ve got a cap and trade in seven north-eastern states, and in Europe and also California is looking to enter a cap and trade system.”

She acknowledged resistance on Capitol Hill. “Coal dominates and is in 40 states, which makes garnering votes here in the Senate very difficult, so we decided whether there was some parts of industry with which we could work.”

The White House also remains firmly opposed to cap and trade.

The proposal underlines rising interest in cap and trade on Capitol Hill.