American climate negotiators refused to back down in their opposition to mandatory cuts in greenhouse gas emissions on Thursday, even as a US Senate panel endorsed sharp reductions in pollution blamed for global warming.

The US, the world’s largest producer of such gases, has resisted calls for strict limits on emissions at the UN climate conference, which is aimed at launching negotiations for an agreement to follow the Kyoto Protocol when it expires in 2012.

That stance suffered a blow when the Senate Environment and Public Works Committee passed a bill on Wednesday to cut US emissions by 70 per cent by 2050 from electric power plants, manufacturing and transportation. The bill now goes to the full Senate.

US climate negotiator Harlan Watson, however, said that would not impact Washington’s position at the international gathering in Bali.

“In our process, a vote for movement of a bill out of committee does not ensure its ultimate passage,” he said. “I don’t know the details, but we will not alter our posture here.”

It was the first bill calling for mandatory US limit on greenhouse gases to be taken up in Congress since global warming emerged as an environmental issue more than two decades ago.

Republican critics of the bill argued that limiting the emissions could become a hardship because of higher energy costs.

Washington’s isolation in Bali has increased following Australia’s announcement on Monday that it has reversed its opposition to the Kyoto pact and started the ratification process. That left the US as the only industrialised nation to oppose the agreement.

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