Aleading British government scientist has warned the UN’s climate panel to tackle its blunders or lose all credibility.

Robert Watson, chief scientist at Defra, the environment ministry, who chaired the Intergovernmental Panel on Climate Change from 1997 to 2002, was speaking after more potential inaccuracies emerged in the IPCC’s 2007 benchmark report on global warming.

The most important is a claim that global warming could cut rain-fed north African crop production by up to 50% by 2020, a remarkably short time for such a dramatic change. The claim has been quoted in speeches by Rajendra Pachauri, the IPCC chairman, and by Ban Ki-moon, the UN secretary-general.

This weekend Chris Field, the new lead author of the IPCC’s climate impacts team, said he could find nothing in the report to support the claim. The revelation follows the IPCC’s retraction of a claim that the Himalayan glaciers might all melt by 2035.

The African claims could be even more embarrassing for the IPCC as they appear not only in its report but, unlike the glaciers claim, are also repeated in its Synthesis Report. This report is the IPCC’s most politically sensitive publication, distilling its most important science into a form accessible to politicians and policy makers. Its lead authors include Pachauri himself. SUNDAY TIMES, LONDON