Scientists call for action to tackle CO2 levels

Scientists are calling on world leaders to take action on climate change after carbon dioxide levels in the atmosphere broke through a symbolic threshold.

Daily CO2 readings at a US government agency lab on Hawaii have topped 400 parts per million for the first time.

Sir Brian Hoskins, the head of climate change at the UK-based Royal Society, said the figure should "jolt governments into action".

China and the US have made a commitment to co-operate on clean technology.

But BBC environment analyst Roger Harrabin said the EU was backing off the issue, and cheap fossil fuels looked attractive to industries.

The laboratory, which sits on the Mauna Loa volcano, feeds its numbers into a continuous record of the concentration of the gas stretching back to 1958.