For those of a sceptical disposition who have been persuaded by scientists to adopt the view that global warming is either a man-made phenomenon or has been exacerbated by human economic activity, these are unsettling times. Over the past week or so, some of the supposed evidence for what we are invited to believe is no longer a contestable truth contained in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) in 2007 has been called into question.
Last week, we learnt that an assertion that glaciers in the Himalayas were melting so fast that they would disappear by 2035 (always a far-fetched notion) was based on a single quote in a science journal news story, never repeated in peer-reviewed literature. The IPCC quickly admitted the error but dismissed it as an aberration carried on just one page of a report thousands of pages long.
However, the weekend brought further disclosures that claims in the report blaming rising temperatures for an increase in the number and severity of natural disasters such as hurricanes and floods had not been properly reviewed by other scientists. It is true that the first people to apologise for these errors and to promise to rectify them were the IPCC scientists themselves, who understand how important it is for the credibility of their case that the evidence on which it is based is copper-bottomed.
The continuing controversy over the dossiers compiled to justify the case for a war in Iraq are testament to the dangers of seeking to include conjecture as fact in order to reinforce a preferred conclusion. We have argued that a conservative case for preserving the planet's scarce resources should support much of the action demanded by concerned scientists, whether or not the case for man-made global warming can be proved. But it becomes difficult to resist the blandishments of the sceptics if a purportedly scientific document cannot be wholly relied on. The most charitable interpretation is that the drafters were sloppy.
Two things are now required. First, when the fifth IPCC report is prepared for publication, any errors must be fully acknowledged and others removed. In addition, the report should contain contrarian evidence produced by scientists to demonstrate that this is a serious document, not a holy writ. Second, the chairman of the IPCC, Rajendra Pachauri, should step down. This will please environmentalists since he was appointed after the uber-sceptic George W Bush objected to his predecessor, Dr Robert Watson; but Dr Pachauri no longer carries the credibility that is required to take this hugely important debate forward.