A key Senate panel on Thursday passed a sweeping climate change bill despite a boycott of deliberations by Republicans opposed to the measure.

The Senate Environment and Public Works Committee approved the legislation by a vote of 10 to one, with the seven Republicans on the committee absent from the discussion and vote.

"We are pleased that despite the Republican boycott we have been able to move this bill forward," said committee chair Democrat Barbara Boxer.

Republicans said they would oppose the bill until they had a "comprehensive analysis" of the economic impact of the legislation from the federal watchdog agency, the US Environmental Protection Agency (EPA).

The Senate legislation faces a long and contentious process ahead, and must be reconciled with a US House bill that calls for cutting US greenhouse gas emissions by 17 percent from 2005 levels by 2020, and by 83 percent by 2050.

The Senate's slightly more ambitious bill calls for a 20-percent cut by 2020. Both bills would create a cap-and-trade regime, aimed at setting the total level of domestic emissions allowable and then allocating quotas to companies.

Firms that emit less than their quota would be allowed to sell their surplus allocation to others that exceed theirs. Those in excess could also face fines.