The publication of false claims by the IPCC has been compounded by its imperious attitude, says professor of climate change Mike Hulme.

The incorrect statement in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) that the Himalayan glaciers could completely disappear by 2035 is remarkable in many ways.

First, how could such a physically implausible claim have entered an early draft of an assessment undertaken by 'the world's leading experts', as IPCC authors are frequently described? Second, how did the claim survive several rounds of peer review from other IPCC authors and outside experts? Third, how did the claim, published in April 2007, remain unchallenged for more than two years before hitting the news headlines?

But perhaps most remarkable of all was the reaction of the IPCC chairman, Rajendra Pachauri, when the results of a specially commissioned Indian study of the glaciers challenged the IPCC's claim. He dismissed the new study as "voodoo science".

Pachauri's haughty attitude helps explain why the controversy surrounding the mistaken claim — which, after all, is a rather minor piece of the picture of climate change impacts — is now filling newspapers, blogs and broadcast media.

But to fully understand the timing of this affair we must reflect on the unexpected turn of events in the politics of climate change science over the past three months.

Under fire

The seminal moment was 'Climategate', when more than a thousand emails from the Climatic Research Unit (CRU) at the University of East Anglia, United Kingdom, were made public, either stolen or leaked (see Lessons about science from 'Climategate').

The emails made front-page news for several weeks and prompted a torrent of allegations about the conduct of some climate scientists and their attempts to withhold data.

Crucially, although the leaked emails hardly constituted evidence of a global warming conspiracy, they legitimised those commentators who have challenged the scientific orthodoxy and the IPCC.

The emails gave such commentators unprecedented credibility in the eyes of the mainstream media and the public to question even more sharply, and less deferentially, the science underpinning human-induced climate change. Is the scientific evidence sound? Or have scientists been sexing up the risks and playing down the uncertainties?

The IPCC is the obvious target for such questions. It gained public status and stature through its Nobel Peace Prize, its outspoken chairman and its key role in forging consensus on the effects of climate change, and it has become the ultimate source of authority for scientific claims about climate change.

Many of its pronouncements have been used by political advocates to justify their policy prescriptions. "As the science demands" was the cry echoing around the UN climate talks in Copenhagen in December, and, indeed, for months and years before.

Inaccurate claims

Both Climategate and the unexpected outcome of the Copenhagen talks have enabled critics to openly attack the IPCC. As a result, the false claim about the Himalayan glaciers has taken on considerable symbolic significance.

It is not so much that an error was made, whether this is attributed to the original maverick scientist who made it, to the lapse in the IPCC's peer-review process, or even to Pachauri's rather arrogant defiance.

No, the error's significance lies in the fact that it proves definitively that not everything written by the IPCC — or declared by its senior spokespersons — is true. So sceptics and bloggers are now scrutinising other chapters in the IPCC report as never before to find further evidence of inaccurate or poorly warranted statements and claims.

And some have been found — for example, attributing the rise in disaster costs to climate change and claims that up to 40 per cent of the Amazon rainforest could react drastically to drought.

Time for change

What does all this mean? Well, it doesn't mean that the well-authenticated, headline conclusions about human impacts on the climate system are undermined. Nor does it mean that concerns about the risks of future climate change are misplaced.

But it does mean that the IPCC in its next assessment must be more scrupulous in adhering to its basic ground rules.

It also probably means that the rules must be revised, especially regarding the use of non-peer-reviewed sources and the ways that reviewers' comments are handled.

The danger of claiming, or being offered, ultimate authority — whether for determining how people should live or how policies should be made — is that it can leave you vulnerable to human error and poor practice.

By setting itself up as the impeccable and authoritative source of ultimate scientific knowledge about climate change, and with advocates justifying their case for action with "as the [IPCC's] science demands", the IPCC's fall was almost inevitable.

A little less hubris from the IPCC might have made Pachauri more careful about using phrases such as 'voodoo science'. And a little less deference to science that 'demands action', and a more honest articulation of the ethical and political reasons for their proposed actions, would have left climate change campaigners in a stronger position.

Mike Hulme is professor of climate change in the School of Environmental Sciences at the University of East Anglia, Norwich, United Kingdom.