Writing in the May issue of the Journal of Environmental Economics and Management, researchers at the University of California, Berkeley, and UC San Diego said China's CO2 emissions will grow at least 11 percent annually between 2004 and 2010.

Previous estimates, including those used by the UN's Intergovernmental Panel on Climate Change, say the region that includes China will see a 2.5 to 5 percent annual increase in CO2 emissions during the same period.

The release of the article comes as energy and environment ministers from the world's 20 major greenhouse gas emitting nations prepare to meet in Japan from Friday to discuss climate change, clean energy and sustainable development.

The G20, ranging from top polluters the United States and China to Indonesia, Brazil and South Africa, emit about 80 percent of mankind's greenhouse gases.

Pressure is growing on these nations to hammer out a pact to halt and reverse growing emissions of CO2, the main gas blamed for global warming.

In the journal report, the US researchers said that by 2010, there will be an increase of 600 million metric tonnes of CO2 emissions in China over levels in 2000.

They said that figure from China alone would overshadow the 116 million metric tonnes of carbon emissions reductions pledged by all the developed countries under the Kyoto Protocol during the pact's 2008-2012 first commitment phase.

China is not obliged under Kyoto to cut greenhouse gas emissions during 2008-12. But it joined nearly 190 nations in Bali in December in agreeing to launch two years of UN-led talks to create a global emissions-fighting pact to replace Kyoto from 2013.

The authors used pollution data from 30 provinces and China's official waste gas emissions data to get a more detailed picture of CO2 emissions up to 2004.

"It had been expected that the efficiency of China's power generation would continue to improve as per-capita income increased, slowing down the rate of CO2 emissions growth," said Maximillian Auffhammer, UC Berkeley assistant professor of agricultural and resource economics.

"What we're finding instead is that the emissions growth rate is surpassing our worst expectations, and that means the goal of stabilising atmospheric CO2 is going to be much, much harder to achieve."

Part of the problem was also a shift to give provinces more say in building power plants after 2000, the report said.

"Wealthier coastal provinces tended to build clean-burning power plants based upon the very best technology available, but many of the poorer interior provinces replicated inefficient 1950s Soviet technology," said Richard Carson, UC San Diego professor of economics.

"The problem is that power plants, once built, are meant to last for 40 to 75 years," said Carson.

"These provincial officials have locked themselves into a long-run emissions trajectory that is much higher than people had anticipated. Our forecast incorporates the fact that much of China is now stuck with power plants that are dirty and inefficient."

(Reporting by Tan Ee Lyn; Editing by David Fogarty and Emma Graham-Harrison)