Due to the Africans' demands, most of the rest of this week's talks in Barcelona will be devoted to discussing carbon-cutting pledges rather than other issues including carbon offsets and action by developing countries, said John Ash, chairman of the negotiations on emissions.
The Africans, supported by about 70 other developing countries, said industrial nations were making weak commitments to stave off dramatic temperature rises while Africa was being devastated by droughts and floods blamed on global warming.
Scientists say industrial countries should reduce emissions by 25 to 40 percent from 1990 levels by 2020, but targets announced so far amount to far less.
The walkout by some 50 African countries from committee work at the U.N. talks in Barcelona forced only some technical meetings to be canceled, but sent a clear signal that the developing countries would be tough negotiators at next month's final U.N. climate conference in Copenhagen, Denmark.
Negotiators hope to adopt a treaty in Copenhagen on regulating carbon emissions.
"It's really good that the Africans have finally been able to stand up together," said Fiona Musana of Johannesburg-based Greenpeace Africa. "That sends a strong signal."
German Chancellor Angela Merkel was in Washington on Tuesday, urging both chambers of a skeptical Congress to "overcome the walls of the 21st Century" and.
"We have no time to lose," she said. She said that while she recognized no deal could be successful without support from China and India, those fast-growing economies could be persuaded to sign on to a deal once it is struck.