Carbon dioxide emissions from fossil fuels and cement manufacturing are rising faster than the worst-case scenario drawn up by the Intergovernmental Panel on Climate Change (IPCC). According to the latest worldwide carbon budget, released by the Global Carbon Project, CO2 levels rose by 3.5% a year between 2000 and 2007, compared with 2.7% as calculated by the IPCC. During the 1990s, emissions rose at 0.9% a year.

"For a decade we've been using the [IPCC] middle-ground scenario, while we're actually in a different realm of emissions," says Pep Canadell, the project's executive director.

China is now the biggest emitter of CO2 and responsible for 21% of the world's emissions — up from 14% in 2002. This knocks the United States into second place, contributing 19% of global emissions. India is fourth, but looks set to take third place from Russia this year.