Soaring carbon dioxide emissions from China and the US have driven the world's output of greenhouse gases to its highest level, alarming new figures reveal.  Global CO2 emissions in 2010 reached 33.51 billion tonnes, up from 31.63 billion tonnes in 2009 - an increase of nearly 6 per cent. This is believed to be the highest-ever percentage increase year on year, despite growth in many industrial economies being sluggish or non-existent.  However, the figures from the US Department of Energy show clearly that it is the surging Chinese economy that is driving the growth: China's emissions in 2010 were 8.15 billion tonnes, up from 7.46 billion tonnes the year before - a 9.3 per cent increase in 12 months.  The 694-million-tonne increase alone dwarfs all the carbon emissions that Britain produces in a year. China now accounts for 24.3 per cent of global carbon emissions and has taken over the role, held by america for decades, of the world's biggest polluter.  The US, whose emissions totalled 5.49 billion tonnes in 2010, up from 5.27 billion tonnes in 2009 - an increase of 4.1 per cent - now accounts for 16 per cent of emissions worldwide. So although the Chinese did not overtake the US in carbon emissions un