A particularly sensitive issue in the negotiations is finance. Poorer nations are demanding billions of dollars in support to undertake costly measures intended to limit climate change over the next decade or so as well as longer term policies aimed through the second half of the century.

A failure by wealthy nations to come up with adequate amounts would “create a very emotional context for Copenhagen that, if not handled with sensitivity, could derail the summit as well,” Achim Steiner, the head of the United Nations Environment Program, warned in an interview over the weekend.

The differences between the rich and poor world are starkly visible at the talks.

The stuffy and overcrowded office of Lumumba Stanislaus Di-Aping, a Sudanese diplomat who speaks on behalf of the Group of 77 developing countries, is dwarfed by the airy E.U. cafe, with its huge television screen, and the U.S. center, featuring loud and colorful multimedia presentations about the claimed achievements of Americans in lowering carbon emissions.

For Mr. Di-Aping, the Copenhagen climate conference is a once-in-a-generation opportunity to push forward key projects that could translate into hundreds of billions of dollars in fresh aid and help transform their economies and energy systems. Beyond that, the money is needed, he and others say, to help nations like his adapt to the harsher conditions they already are suffering.

Scarcity of food sources from destruction of farmland and pastoral areas because of changing climatic conditions, he said, had helped foment wars in his country, including in Darfur.

He was particularly dissatisfied by a so-called fast-track plan, supported by the U.N. climate chief, Yvo de Boer, for wealthy nations to hand over $10 billion annually between 2010 and 2012.

He described the offer as a wholly inadequate “bribe” that made climate change “less important than the financial crisis,” which he argued had already cost the G-20 nations, including the United States, about $1.1 trillion in borrowed funds to prop up ailing financial institutions and revive economic growth.