COPENHAGEN -- Developing countries at the United Nations climate summit demanded that rich nations commit money and accept sharper cuts in their emissions, highlighting the divisions among the world's rich and poor nations that stand in the way of a new global climate deal.

Representatives of China, the world's largest greenhouse-gas emitter, said President Barack Obama's proposal that the U.S. reduce its greenhouse-gas emissions by 17% from 2005 levels by 2020 isn't ambitious enough. Su Wei, the Chinese chief negotiator,...