A new global agreement to tackle climate change was announced by politicians yesterday, on the day that greenhouse gas concentrations reached a record high.

The world's major industrial nations, including the US, signed a resolution urging the G8 governments to commit to setting new targets for limiting greenhouse gas emissions.

They want an agreement ready by 2009, to succeed the Kyoto Protocol which is set to expire in 2012.

Although the declaration is non-binding, it is seen as representing a mood shift over global warming, particularly in America, where the administration refused to sign up to Kyoto.

The two-day meeting brought together legislators from the G8 nations plus Brazil, China, India, Mexico and South Africa.

It was organised by British-led environmental group Global Legislators Organisation for a Balanced Environment.

The delegates called for a new worldwide carbon trading scheme to cap CO2 emissions and urged developing world countries to sign up to emissions cuts. However, Greenpeace warned that the group's agreed target for global atmospheric CO2 concentration, which is 450-550 parts per million, could result in "a climate catastrophe".

At those levels, climate scientists predict there would be an increase in temperature of between two and four degrees - enough to leave an extra billion people without water.

Meanwhile, levels of the greenhouse gas widely blamed for causing global warming have jumped to record highs in the atmosphere. Kim Holmen, research director of the Norwegian Polar Institute, reported that concentrations of carbon dioxide had risen to 390 parts per million (ppm) from 388 a year ago.

Levels have hit peaks almost every year in recent decades, bolstering theories of warming, and are far above 270 ppm before the industrial revolution of the 18th century. This year's unusually high rise is apparently stoked by rising emissions from Asian industry, said Mr Holmen.