The alarmist warning appeared two years ago in a highly influential report by the United Nations Intergovernmental Panel on Climate Change.

At the time the IPCC insisted that its report contained the latest and most detailed evidence yet of the risks of man-made climate change to the planet.

But the experts behind the warning have now admitted their claim was not based on hard science – but a news story that appeared in the magazine New Scientist in the late 1990s.

That story was itself based on a telephone conversation with an Indian scientist who has since admitted it was little more than speculation.