China will overtake the US to become the world's biggest source of carbon dioxide emissions by 2009, nearly 10 years ahead of earlier predictions, the International Energy Agency (IEA) has said. Emissions of the gas, thought to be the key cause of global warming, are being driven up by China's dependency on coal, the South China Morning Post reported. As a developing country, China is exempt from the requirements set out in the Kyoto Protocol for reduced greenhouse gas emissions. Beijing predicted four years ago that its carbon dioxide emissions would not reach US levels until 2020 and Xu Huaqing, the National Development and Reform Commission's climate change expert, said the IEA's revised projection will only stand if China fails to reduce its reliance on coal. Another NDRC official said developing nations were dependent on technology transfers from the West to achieve this.