A bulletin on greenhouse gas levels by the World Meteorological Organization (WMO) said there were 377 parts per million of carbon dioxide in the atmosphere in 2004, up from around 280ppm before the industrial revolution.

One of the highest year-on-year rises ever in the level of carbon dioxide was recorded at 1.8ppm.

But the US National Oceanic and Atmospheric Administration, using a slightly different methodology, said last year's rise was even greater at 2.6ppm, and overall carbon dioxide levels were at 381ppm.

Carbon dioxide - produced by burning fossil fuels - is the most abundant greenhouse gas in the atmosphere, and is the gas that most concerns climate scientists, because of its warming effect on the earth.

But levels of methane and nitrous oxide, both of which have a much greater effect on the climate but are present in the air in much smaller quantities, have also risen.

Nitrous oxide is a potent greenhouse gas, the concentration of which has been rising by about 0.8 parts per billion per year since 1988.

At least a third of the amount of the gas in the atmosphere is the result of human activities such as fuel combustion, biomass burning, fertilizer use and some industrial processes.

But the levels of methane - produced by human activity such as oil and gas production and agriculture, as well as some natural processes - were showing signs of reaching a plateau, the WMO said.

Tony Juniper, director of the campaigning group Friends of the Earth, said urgent action was needed to curb emissions: "If we take action now we can still avoid the worst impacts of climate change by investing in clean renewable technology and energy efficiency.

"The attempts by government and business to reduce emissions have lacked ambition and there hasn't been the effort put in that is needed."