A US-led plan to let all countries set their own goals for fighting climate change is gaining grudging support at UN talks, even though the current level of pledges is far too low to limit rising temperatures substantially.
The approach, being discussed this week at 160-nation talks in Bonn, Germany, would mean abandoning the blueprint of the 1997 Kyoto Protocol, which set central goals for industrialized countries to cut emissions by 2012 and then let each work out national implementation.
Attempts to agree a successor to Kyoto have foundered above all on a failure to agree on the contribution that developing countries should make to curbing the industrial emissions responsible for global warming — greenhouse gases. The next ministerial conference to try to reach a deal is scheduled for Paris in 2015.
The United States, recently overtaken by China as the world's biggest carbon polluter, never ratified Kyoto because it set no binding emissions cuts for rapidly growing economies such as China and India.
President Barack Obama's administration now says each nation should define its "contribution" to a new UN accord — a weaker word than past US demands for national "commitments."
Elliot Diringer, executive director of a Washington-based think-tank, the Center for Climate and Energy Solutions, said there was "a growing acceptance of nationally defined approaches, with a big 'But.'"
Trigg Talley, head of the US delegation, noted that the agreement "will need to be applicable to all."
And even if all countries agree to participate, all sides say the initial national promises will be insufficient to rein in greenhouse gases, which are rising by about 3 percent a year even though economic growth is weak in many regions.
Under the US plan, contributions might be submitted 6 months before the Paris summit, giving some time for a non-binding review to strengthen plans. The pact is due to enter into force from 2020.
Christiana Figueres, head of the UN Climate Change Secretariat, said it was already clear that promised emissions cuts would fall short of the level needed to prevent the global temperature rising more than 2 degrees Celsius above pre-industrial times.
Temperatures are already up by about 0.8 degree C.
"The challenge for the 2015 agreement is precisely to bridge that gap," she said. "The process is not on track with respect to the demands of science."
International scientists say it is highly likely that high levels of greenhouse gases are already changing the climate and that it is at least 90 percent probable that human activities are the main cause.
In Geneva, the World Meteorological Organization said on Thursday that 2012 was the ninth warmest year since records began in the 19th century. Among extremes, Arctic sea ice shrank to a record low and Superstorm Sandy battered the United States.
Many emerging nations are still holding out in Bonn for binding common targets, especially for rich countries. But securing a bigger role by the United States might mean accepting a relatively weak accord in 2015.
Jennifer Morgan of the World Resources Institute think-tank said the negotiation process was a "dance."
"People want to make sure the United States is in, but many are deeply worried about what that may mean," she said.
The United States and China did agree last month to work more closely together on climate change, saying they hoped it would inspire action by others. Many delegates welcomed the plan, but said the two emitters have not led in the past.
"We have to see the developed countries taking the lead," Brazil's delegate Andre Correa do Lago said. "This need — I'm not hearing here."
Ronald Jumeau of the Seychelles, a spokesman for the 44-nation Alliance of Small Island States where many low-lying atolls fear they will be swamped by rising sea levels, said pledges so far were "woefully inadequate."
Japan, Canada and Russia have dropped out of the Kyoto accord this year, leaving a dwindling core of countries led by the European Union and Australia.
But a collapse in carbon dioxide prices on a European Union market has weakened EU leadership on climate change.