Many developing states at 175-country talks in Bonn, working on a new UN climate pact, urged the rich to cut emissions by "at least 40 percent" below 1990 levels by 2020 to confront what they said were worsening signs of climate change.
The calls, part of negotiations on a new UN climate pact due to be agreed in December, marked a break with praise for President Barack Obama's promises to do more to fight global warming than former President George W. Bush.
"We believe that by 2020 the (developed nations) should reduce their emissions by at least 40 percent below 1990 levels," Chinese delegate Xu Huaqing told the March 29-April 8 meeting.
India was among other nations urging same level, far deeper than goals set by the United States, the European Union or other rich nations. Obama met Chinese President Hu Jintao in London, the eve of the G20 summit which will focus on ways to revive the world economy.
Obama's goal is to cut U.S. emissions, mainly from burning fossil fuels, back to 1990 levels by 2020, a cut of between 16 and 17 percent from current levels. Bush had foreseen a peak in emissions only in 2025.
Several developing nations said that scientific findings about global warming, ranging from a melt of the Arctic ice to signs of quicker sea level rise by 2100, were getting more alarming and so demanded tougher action.
"The strongest voice (for at least 40 percent) has come from the small island states. But it seems to have broad support," said Harald Dovland, a Norwegian official who chairs a group looking at ranges of future cuts by developed nations.
Small island developing states, who fear that some atolls will be wiped off the map by rising seas, agreed to call for at least 40 percent cuts in December last year. Delegates said that many poor nations had since lined up behind the number.
Rich and poor are deeply split about sharing out the burden of fighting warming, that could bring more floods, heatwaves, extinctions and droughts. The poor want new funds, and green technology as a price for slowing the rise of their emissions.
The UN Climate Panel said in a report in 2007 that developed nations would need to cut emissions on average by between 25 and 40 percent below 1990 levels by 2020 to avoid the worst of climate change.
"Recent scientific information and analysis has painted a bleaker picture," said Selwin Hart of Barbados, representing small island states.
Climate change "will result in the demise if we don't take urgent action of many small island states," he said.
China's Xu said that the rich had to do most to allow the poor a chance to burn more energy to end poverty.
Among the most ambitious goals by developed nations, the European Union has agreed to cut its emissions by 20 percent below 1990 levels by 2020 and to deepen the cuts to 30 percent if other developed nations join in.