The past two months have been an unnerving time for the international climate community. Once seen as one of the most esteemed scientific organizations in the world, the Intergovernmental Panel on Climate Change has, of late, suffered some serious blows to its reputation.

The first of these — dubbed 'Climategate' — saw thousands of emails obtained illegally from the University of East Anglia in the United Kingdom and posted on the Internet. Carefully timed ahead of international climate policy negotiations, the emails showed apparent attempts by a handful of IPCC climatologists to withhold data from climate deniers and to exclude contentious information from the panel's report. Unsurprisingly, this cast doubt on the credibility of the UN body.

Now, the process by which the IPCC assesses climate science has again been called into question. Over the past two weeks, the panel has admitted that a key statistic quoted in its 2007 report — that Himalayan glaciers could disappear by 2035 — was in error, and its source of dubious origin. Hard on the heels of 'Glaciergate' are fresh claims that the same report oversold the link between increasing natural disasters and human-induced warming.

None of these unfortunate events calls into question the evidence that warming is unequivocal and that human activity is the primary cause. But they undoubtedly create confusion among the public and, in this regard, their timing could not be worse. The UN negotiations in December failed to deliver an agreement that would prevent dangerous climate change, and the world now lacks a unified vision of the way forward for climate policy (See page 15). The passage of US domestic legislation also hangs in the balance.

To some extent, the end of the IPCC's exaltation was inevitable. Any organization or individual that is placed on a pedestal will eventually come a cropper. That hard lesson is being learnt as much by the Nobel prize-winning US President as by the Nobel prize-winning IPCC. But there are also more sobering lessons for scientists in all of this. Withholding information from those who question your views or scientific rationale, as was the case in Climategate, does little to instil public trust. The same holds true of responding defensively. When initially confronted with independent evidence on the melting of Himalayan glaciers, IPCC head Rajendra Pachauri retorted that it was "voodoo science".

For the IPCC, the challenge is clear. Faced with political inertia and denialism, they must communicate their results clearly and their message constructively. The 2007 report — and the Summary for Policymakers in particular — represented a giant leap forward for science communication. For the next report — due out in 2013 — the challenge will be greater still. In trying to understand the climate system more fully, scientists could reveal greater uncertainty about the range of possible climate outcomes (See page 20). At the same time, policymakers and the public will demand greater certainty so that they can plan accordingly. The climate research community recognizes this problem. Now it must make a priority of addressing it.