BRUSSELS/LONDON China, the world's biggest carbon emitter, could nudge the United States into more action on climate change, rescuing the latest round of global talks and improving its international reputation.
Expectations remain extremely low that a new global deal can emerge from a summit later this month in Durban, South Africa.
But it could lay the foundations for a future deal and desperate negotiators are looking to China to help isolate the United States in its stubborn climate change denial, even if it is only for reasons of enlightened self-interest.
"My sense is that if Durban fails it would be due to the lack of U.S. political will to deliver and if it succeeds it would be due to China's extra efforts," said Jennifer Morgan, director of the climate and energy program at environmental thinktank the World Resources Institute.
The United States has achieved local shifts on environment policy and developed emissions trading schemes at state and regional level.
However, it has twice delayed plans this year to regulate carbon dioxide from power plants and, under fuel efficiency standards for vehicles, automakers do not have to make improvements until 2018 or 2025.
A more far-reaching climate law failed last year to pass the U.S. Congress, where the environment has become a political battleground between Republicans and U.S. President Barack Obama's Democrats.
Obama, for all his personal commitment to the environment, has made clear the world's second biggest carbon emitter will not commit to a new legally-binding protocol at least until after the next presidential election.
NOT THE BIGGEST BOULDER
In China, a huge population and a series of devastating floods have underlined the risk of global warming and justified record-breaking investment in new energy technology.
Climate negotiators no longer see China as the biggest of the so-called boulder nations -- a group that also includes smaller boulders Japan, Canada and Russia, as well as the United States.
Within the European Union, which has spearheaded efforts this year to maintain momentum in the Kyoto process, officials say China has been helpful.
"We have great hopes with regard to China, which recently has been very constructive in its attitude towards Durban," Joanna Mackowiak-Pandera, Undersecretary of State at the Ministry of the Environment for Poland, said this week. Poland is current holder of the EU rotating presidency.
Some have gone further to say China can help to isolate the United States.
"I don't exclude the EU and China and other emerging economies making this strategic partnership for this climate issue and the U.S. being isolated," said Jo Leinen, chair of the environmental committee in the European Parliament.
CHINA HAS DEVELOPED
After the Kyoto Protocol was adopted in 1997, the United States signed, but never ratified it.
China was still regarded as a developing nation and not expected to carry a large share of the cost of cutting carbon emissions, blamed on decades of pollution by the industrialised world.
Since then, China has overtaken many developed nations in economic output and has leapfrogged the United States to become the greatest producer of carbon emissions.
But it has also powered ahead in the low-carbon technology race investing $54 billion, compared to the United States' $34 billion, the U.S. Pew Environment Group said.
In the framework of Kyoto talks, China is still arguing, along with the other members of the BASIC group of nations -- Brazil, South Africa and India -- it should be counted as developing.
Environmental negotiators think it is time China recognised that being a world power should also mean leadership of the green race -- and joining in with environmental diplomacy as well as scrambling for energy and technology.
Within Kyoto, it should be leading the cuts, instead of benefiting from the U.N.'s Clean Development Mechanism, through which rich nations invest in clean energy projects in developing countries in return for carbon credits.
China has become the world's number one country in terms of registered CDM projects since the scheme's launch in 2005, although the environmental integrity of some projects has been questioned.
The European Union has made a leap of faith saying it will sign up to a second phase of Kyoto -- but on the condition that other countries give a firm commitment, or in EU-speak, a road map, showing when they would sign up too.
The question is whether China will break the deadlock, said Morgan of the WRI, and "commit to commit".
"My hope would be Europe and China would be working together to build a pathway forward," she said.
The EU, with its mighty debts and dependence on China to help bail it out, has limited bargaining power.
Visiting Chinese officials have nevertheless acknowledged the EU, a vital trade partner, has expertise to share.
"We need to focus on the green sector, and in this regard, Europe has the talent and the knowledge," Zhang Yangsheng, director of the Institute of Foreign Economy, National Development and Reform Commission in Beijing, told a high-level EU-China forum in Brussels this month.
"We need to focus on energy saving. Europe is ahead of the others."
(Additional reporting by Juliane von Reppert-Bismarck, editing by William Hardy)