Nnimmo Bassey, chair of Friends of the Earth International, called Copenhagen "an abject failure."
"By delaying action, rich countries have condemned millions of the world's poorest people to hunger, suffering and loss of life as climate change accelerates," he said.
"The blame for this disastrous outcome is squarely on the developed nations."
The Sierra Club, a leading US environmental group, said that the blame lay largely with the US Senate which has yet to approve legislation backed by Obama to curb carbon emissions in the world's largest economy.
"President Obama and the rest of the world paid a steep price here in Copenhagen because of obstructionism in the United States Senate," said Carl Pope, the Sierra Club's executive director.
"That a deal was reached at all is testament to President Obama's leadership -- all the more remarkable because of the very weak hand he was dealt," he said.
Pierre Radanne, an advisor to African countries on climate change who is a veteran observer of the negotiation process, told AFP: "It is a breakdown of the United Nations."
The WWF environmental group voiced concern that the Copenhagen summit does not bind nations to action.
"A gap between the rhetoric and reality could cost millions of lives, hundreds of billions of dollars and a wealth of lost opportunities," said Kim Carstensen, the leader of the WWF's Global Climate Initiative.
But it said that the pledges by individual countries could lead to more action in the future.
"We are disappointed but remain hopeful," he said.
Josef Leinen, a German representative in the European parliament, said that it was a disappointing outcome.
"I think it is a rather weak agreement. It is not meeting our expectations for the Copenhagen conference, because there are no real commitments beyond the financing," he said.
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