China, the world's number three economy, is the top greenhouse gas polluter, scientists say, and its emissions of the main greenhouse gas, carbon dioxide, are set to keep rising.
The United States' climate change policy envoy, Todd Stern, is in Beijing, the latest in a succession of officials hoping to nurture agreement with China on containing emissions.
But any climate deal with Beijing is not going to be easy, and half a year remains until nations gather in Copenhagen to work out the treaty, which will succeed the current Kyoto Protocol, whose first phase ends in 2012.
A senior official in China's National Coordination Committee for Climate Change, Gao Guangsheng, said bridging disputes on basic principles will probably push talks to the wire.
"I personally hope Copenhagen will reach an agreement with targets for developed countries and specific actions for developing countries," said Gao in a recent interview. "But at present, to judge from the stances of various countries, it will be difficult to reach an agreement that satisfies everyone.
The threat of global warming and pressure for a deal in Copenhagen are, nonetheless, driving Beijing to explore ways to reconcile development and minimizing greenhouse gas emissions.
Chinese thinktanks have been seeking to map a path to a low-carbon economy, and their ideas are likely to be part of what China might offer as a contribution to fighting global warming.
But these blueprints are still on the drawing board and would take years to be implemented, leaving decades before China's emissions begin to level off.
Uncertainties about what Beijing will do to control its greenhouse gas volumes, and what it will receive in return from rich countries, will make for fraught negotiations this year and beyond with Washington and other major powers.
"Reaching agreement at Copenhagen should be relatively easy, because nobody wants outright failure. But reaching an effective agreement will be more difficult," said Zhang Haibin, an expert on environmental diplomacy at Peking University.
The emissions numbers are daunting, with China's carbon output outpacing that of the United States.
Scientists say these mounting greenhouse gases from industry, transport and agriculture are dangerously overheating the atmosphere by retaining more solar radiation, and poorer countries such as China could be especially vulnerable to more intense droughts, floods and storms.
But Beijing also says it must not be distracted from growing its economy and, like other developing countries, should not accept a ceiling on greenhouse gas output, which even optimistic Chinese experts expect to keep rising until around 2030.
By then, China's annual emissions of carbon dioxide could reach 8 to 10 billion tons a year, unless stringent action is taken, said He Jiankun, a professor at Tsinghua University in Beijing who advises the Chinese government on emissions policy.
In 2007, China's CO2 emissions from fossil fuels amounted to about 6.6 billion metric tons, according to U.S. estimates.
China also wants rich nations to cut emissions by at least 40 percent below 1990 levels by 2020 far deeper than the cuts now on offer and to give up to one percent of their annual economic worth to help poor nations fight global warming.
"Ultimately, there will have to be compromise in Copenhagen, because these negotiations can't be allowed to collapse," said He, the Tsinghua professor. "If they do fall apart, that will be devastating, and nobody will be spared the repercussions."
But China is also looking to take some of the initiative in climate change politics by setting its own the path to lower greenhouse gas emissions and eventual outright reductions.
The nation's next five-year development plan, starting from 2011, will focus on creating a "low-carbon economy" by reducing coal use and encouraging clean energy, said Wang Yi, an expert on climate change at the Chinese Academy of Sciences.
"In the past, China has been reactive in policy-making, responding when the West has put forward its demands," said Wang, chief author of a recent 415-page study laying out a blueprint for a low-carbon economy.
"Now instead of others criticizing us, we're saying, 'Why don't we take the initiative by proposing our own policy goals?'"
These proposals build on China's goals to cut the amount of energy expended for each unit of economic worth by 20 percent between 2006 and the end of 2010, and to steeply lift use of wind, solar, nuclear and hydro power.
One idea backed by some experts calls for carbon intensity targets, spelling out goals for cutting the amount of CO2 emitted to create each unit of economic worth.
"We must incorporate addressing climate change and reducing the intensity of carbon dioxide emissions into national economic and social development plans," said the summary of a meeting on energy and climate change issues chaired by Premier Wen Jiabao, according to the central government website (www.gov.cn).
China could offer to halve its carbon intensity by 2020 compared to 2005 levels, given the right funding and technology incentives from rich nations, said Wang.
But Beijing will remain reluctant to incorporate many of its domestic initiatives into an international treaty, especially any vows on emissions levels, said experts.
China stresses that global warming has been caused by the historically high emissions of wealthy nations, and fears signing international commitments it may not be able to meet, said Wang.
Here, too, some experts said there was room for compromise if wealthy powers offer more in aid and emissions cuts.
"Ultimately what commitments the United States makes will have a big impact on what we offer," said Zhang, the Peking University professor. "If it can be more ambitious and cooperative before Copenhagen, then so can we."