Mandatory US emission cuts moved a step closer yesterday after the Lieberman-Warner bill passed its first vote, in defiance of the White House's long-standing opposition to binding emission cuts.

The vote, in a Senate subcommittee, marks the first time a congressional body has voted in favour of legislation mandating cuts in greenhouse gas emissions and paves the way for a full committee vote later this month.

Independent senator Joe Lieberman, who proposed the Climate Security Act alongside Republican John Warner, said that the vote represented a turning point in the US government's attitude to climate change.

"Today, this committee made history," he said. "This is potentially a landmark event, the moment at which the United States finally began a serious fight against the threat of unchecked global warming."

Under the bill, the US would commit to a 15 per cent reduction in emissions by 2020 and a cut of up to 63 per cent by 2050. It would also introduce a European-style emissions trading scheme covering the energy, manufacturing and transportation sectors of the economy that would effectively put a price on carbon emissions and provide a financial incentive for firms to reduce their emissions.

The vote was broadly welcomed by environmentalists and many business groups who argued that it represents a growing willingness in the US to address the issue of climate change.

Elizabeth Thompson, legislative director at green group Environmental Defence, welcomed the move, claiming that there was now a "real chance" of a mandatory cap on emissions being imposed within this Congress.

However, it remains unclear when and if the bill will make it into law, with many commentators maintaining that despite his softening stance on climate change, George Bush would still likely veto the bill if it hits his desk before a new president takes office in 2009.