A new topic of dinner-party conversation was introduced yesterday with the launch of a personalised carbon calculator.

Guests who would once have vied to report having holidayed in the most exotic location or having bought the latest designer handbag can now compare their carbon footprints.

David Miliband, the Environment Secretary, said the calculator was designed to help individuals and families to work out how much carbon they were responsible for producing.

The calculator is intended to show individuals where they are wasteful and how they can change their behaviour to reduce their impact on climate change.

Carbon dioxide is the main greenhouse gas, and bringing down the quantity pumped into the atmosphere is regarded by many scientists as the world’s biggest challenge. Sir David King, the Government’s chief scientist, has described global warming as a bigger threat than terrorism, but many people are unaware of how they produce CO2 .

“We want to cut through that confusion,” said Mr Miliband. “This carbon calculator will help people decide what they can do – and be sure it will make a difference. Using it, people can work out the impact of their actions and, with the tailored recommendations provided by the calculator, identify the best way to reduce their footprint.” He said his personal carbon footprint was 2.76 tonnes per year, which is below the national average.

The calculator became available online yesterday and immediately ran into difficulties because of the number of people trying to use it. More than 22,500 people had used, or tried to use, it by yesterday afternoon. Officials at the Department for Environment, Food and Rural Affairs (Defra) were trying to double its capacity. The site was developed by Defra and other departments with the Energy Saving Trust and The Climate Group.

Carbon footprints can be worked out for an individual and a household, and emissions are broken down into three categories – home, transport and appliances. A summary page then makes a comparison with the national average and the Government’s target.

For a household, the national average is emissions of 10.22 tonnes, with a target of 4.23 by 2050, while for an individual the average is 4.48 tonnes and a target of 1.99 tonnes. The climate change Bill proposed by Mr Miliband aims to impose a target of a 60 per cent reduction in emissions by 2050.

The initiative was welcomed by Friends of the Earth (FoE), despite the calculator showing Tony Juniper, its director, to have slightly higher-than-average household emissions. “Carbon calculations can play a useful role in helping people take simple measures to cut their contribution to climate change,” Martyn Williams, of FoE, said. However, he added: “This must not distract from the crucial role that Government must play in cutting carbon dioxide emissions.”

John Sauven, of Greenpeace, was concerned that it was a gimmick. “CO2 emissions are higher now than when Labour came to power. That’s a damning indictment of a Government that says this is the biggest problem we all face.”

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