As the United States struck a climate deal with India, China and South Africa, President Barack Obama's supporters hailed it as a "powerful signal", but many some US environmental groups debunked it as "sham".
Calling Obama and leaders of the three major emerging economies as "the four horsemen of a climate change solution," Senator John F. Kerry, chairman of the Senate Foreign Relation Committee, said the Copenhagen accord set the stage for domestic legislation.
"It's a powerful signal to see President Obama, Premier Wen (Jiabao), Prime Minister (Manmohan) Singh, and President (Jacob) Zuma agree on a meeting of the minds, he said. "These are the four horsemen of a climate change solution."
But Kumi Naidoo, executive director of Greenpeace International, disagreed saying world leaders had lost a once in a generation chance. "The city of Copenhagen is a climate crime scene tonight, with the guilty men and women fleeing to the airport in shame," he was quoted as saying by Boston Globe "World leaders had a once in a generation chance to change the world for good, to avert catastrophic climate change. In the end they produced a poor deal full of loopholes big enough to fly Air Force One through," he said.
Edward J. Markey, chairman of the House Select Committee on Energy Independence and Global Warming, said a "ground-breaking agreement by critical nations is not the end of this process, it is the beginning."
"It signifies a new era of action where America is willing to be a leader in the fight to combat global warming. This provides an opportunity for the rest of the world to build a comprehensive agreement that so many have been working to achieve for so long."
But Erich Pica, president of Friends of the Earth US, said "climate negotiations in Copenhagen have yielded a sham agreement with no real requirements for any countries."
"This is not a strong deal or a just one-it isn't even a real one. ... The actions it suggests for the rich countries that caused the climate crisis are extraordinarily inadequate.
"This is a disastrous outcome for people around the world who face increasingly dire impacts from a destabilizing climate."
"The failure of the UN climate conference should surprise no one," said Republican Senator James Inhofe, who challenges the premise human activity is affecting the climate in potentially dangerous ways. "The same major issues that have plagued any UN global-warming treaty for over a decade remain today."
White House officials disagreed, saying bipartisan legislation being drafted by Democrat John Kerry, Independent Joe Lieberman and Republican Lindsey Graham would include cap and trade.
The accord in Copenhagen comes as Obama is trying to persuade senators to pass legislation cutting greenhouse-gas emissions by more than 80 per cent by 2050.