“A source told the BBC: ‘The measurements from the natural world on all parts of the globe have been anomalous over the past decade.
“’If a few were out of kilter we wouldn’t be too worried, because the Earth changes naturally. But the fact that they are virtually all out of kilter makes us very concerned.’
He said the report would forecast that a doubling of greenhouse gas concentrations in the atmosphere would bring a temperature rise of 2-4.5C, or maybe higher.
This is an increase on projections in the last IPCC report, which suggested that the rise could be as little as 1.5C.