Dr Rajendra Pachauri, chair of the UN Intergovernmental Panel on Climate Change (IPCC), said people should have one meat-free day to cut greenhouse gas emissions.

The economist, who is vegetarian, said diet change was important in reducing environmental problems associated with rearing cattle and other animals.

Dr Pachauri is due to give a speech in London on Monday under the title: "Global Warning: the impact of meat production and consumption on climate change".

The IPCC evaluates climate data for the world’s government and last year earned a joint share of the Nobel peace prize.

“Give up meat for one day (per week) initially, and decrease it from there," he told the Observer.

"In terms of immediacy of action and the feasibility of bringing about reductions in a short period of time, it clearly is the most attractive opportunity."

Other small-scale lifestyle changes would also help to combat climate change.

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