The concentration of carbon dioxide in the atmosphere has reached a record high, according to a Norwegian measuring station. Levels of the gas at the Zeppelin research station last week peaked at over 397 parts per million (ppm), an increase of more than 2.5ppm on 2008. The findings suggest that greenhouse gas emissions are continuing to increase at an alarming rate. Experts say that it is not the level of CO2 that is the real problem, but the speed of change, and warn that the world must prevent CO2 levels from rising higher than around 450ppm to avoid a 2 degree celsius increase on preindustrial temperatures.