Scientists at the Mauna Loa observatory in the US state of Hawaii say that CO2 levels in the atmosphere now stand at 387 parts per million (ppm), up almost 40 per cent since the industrial revolution and the highest for at least the last 650,000 years.

Based on some 11,000 ft high volcano, the Mauna Loa observatory is regarded as producing among the most reliable data as its remote location ensures that its sensors are not confused with other possible sources of the gas.

According to the US National Oceanic and Atmospheric Administration, the latest figures also confirm that carbon dioxide, the chief greenhouse gas, is accumulating in the atmosphere faster than expected.

"Despite all the talk, the situation is getting worse. Levels of greenhouse gases continue to rise in the atmosphere and the rate of that rise is accelerating. We are already seeing the impacts of climate change and the scale of those impacts will also accelerate, until we decide to do something about it," Martin Parry, co-chair of the Intergovernmental Panel on Climate Change's working group on impacts, was quoted as saying by the British daily The Guardian on Tuesday.

According to the report, the annual mean growth rate for 2007 was 2.14ppm - the fourth year in the last six to see an annual rise greater than 2ppm. From 1970 to 2000, the concentration rose by about 1.5ppm each year, but since 2000 the annual rise has surged to an average 2.1ppm.