China could overtake the US this year as the world's largest emitter of greenhouse gases, a leading international energy group has said.
The International Energy Agency had predicted China's carbon dioxide emissions would pass the US by 2010.
But IEA chief economist Fatih Birol said the rate of China's economic growth this year defied expectations.
His comments come days after a Chinese government report warned of the impact of climate change on the country.
The report, compiled by several government bodies, said that higher temperatures would lead to worsening droughts, spreading deserts and reduced water supplies.
But it stopped short of recommending cuts in greenhouse gas output and risking the country's economic growth.
Mr Birol, of the Paris-based IEA, which advises governments on energy policy, said: "China's economic growth and use of coal production over the last few months has surprised us all.
"If they continue to surprise us in terms of very high economic growth and corresponding coal production, China will overtake the US much earlier than 2009 - more like this year or the next."
Though that gap could widen considerably in the coming years, he said per capita emissions from China still remained well below those of the US and other developed countries.
But he warned that both China and India - another fast-developing nation - needed to be involved in global efforts to tackle greenhouse gas emissions, otherwise there would be "no chance the climate change fight can be won".
He also said slowing China's growth was not the answer to curbing high greenhouse gas emissions - rather it needed a change of approach to energy production.
"China is a developing country and it needs growth," he said. "The question is what kind of energy and policies will be used in order to get that high level of economic growth.
"If they were to use much more sustainable policies and energy efficiency it would be good both for China's economy and for the climate change issue."
China is heavily reliant on highly polluting coal for its energy, and mines far more coal than any other country.
While the Chinese government has pledged to try to develop alternative energy sources, it says wealthy nations are the most to blame for high gas emissions.