BARCELONA, Spain (AFP) — Some 50 African nations staged a show of force at world climate talks here Tuesday, demanding that rich countries commit to deep cuts in the carbon emissions that stoke global warming.

Talks were suspended throughout the day in one of the twin negotiation tracks under the 192-nation UN Framework Convention on Climate Change (UNFCCC) before delegates hammered out a procedure for addressing the demand.

In an exceptional show of unity, African countries blamed advanced economies for using fossil fuels to take the fast track to prosperity but at the cost of unleashing today's climate nightmare.

They accused rich countries of backsliding on saying how deep they will rein in their greenhouse-gas pollution in the medium term.

They demanded emissions curbs from them of 40 percent by 2020 over 1990 levels to show good faith in the effort to craft a post-2012 climate treaty.

"We consider the quality of ambition stated by the developed countries unacceptable and cannot proceed on the substance of 20 to 30 percent cuts," said Gambian chief delegate Pa Ousman Jarju, speaking for the African bloc.

"We have to consider ambitious targets and numbers, and Africa's official opinion is that (developed countries) cut by a minimum of 40 percent."

The African boycott stalled negotiations in several groups meeting under the Kyoto Protocol, the UNFCCC's cornerstone treaty. Other developing countries, including China, voiced support for the protest.

The negotiations' other track includes Kyoto countries and the United States, which has refused to ratify the Protocol.

Delegates have until Friday to whittle down a sprawling text into a manageable draft for December 7-18 talks in Copenhagen.

The goal is a treaty that will spell out curbs on carbon gases and channel billions of dollars to poor countries, empowering a switch to a low-carbon economy and shoring up defenses against climate change.

Scientists warn Earth's climate system could be catastrophically damaged by higher temperatures, leading to more frequent and brutal droughts, higher sea levels, and floods and storms.

The hardest-hit countries will be poor nations that are least to blame for global warming. Africa accounts for only around four percent of global carbon emissions.

To limit warming to around two degrees Celsius (3.6 degrees Fahrenheit), rich nations must cut emissions by between 25 and 40 percent by 2020 compared with 1990 levels, the UN's Intergovernmental Panel on Climate Change (IPCC) says.

So far, only two big economies — the EU and Japan — ww have got anywhere near the target.

The EU has unilaterally decided to cut its emissions by 20 percent by 2020, and offered to go to 30 percent if another major player follows suit. Japan has offered a cut of 25 percent but has not spelt out conditions.