A changing climate for the IPCC

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.