A British economist is at the centre of a row over his controversial contribution to an international report on global warming.

Campaigners, who claim that David Pearce's methods rate third world lives at one 15th of the value of first world lives, are stepping up their actions, which will include picketing his offices on Wednesday.

David Pearce, an environmental economist at University College London, was leading author for a chapter in the report, for approval next month, of the Intergovernmental Panel on Climate Change's working group three. Group three assesses the social and economic consequences of global warming.

He and his co-authors produced a result that suggests it would cost more to alleviate the damage caused by global warming than the damage itself will cost.

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The chapter successfully passed both governmental and scientific peer review but then upset the writers of its summary, which is read by policymakers around the world. The summary now says that the authors would have drawn the opposite conclusion if they had valued all lives equally.

Aubrey Meyer, of the Global Commons Institute, which has sparked much of the protest, said publishing the chapter "will taint the IPCC irreparably and permanently". He said that the first working group's report, assessing climate change, "is clearly a scientific effort. To suggest that the third group's report is equally scientific is aggrandising their work and the economics profession in general". Some UK environmental scientists have privately agreed with him.

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Critics also say that monetary value cannot be attached to lives.

Professor Pearce, who is director of the Centre for Social and Economic Research of the Global Environment, said that critics did not understand the methodology of the chapter. "The report simply says that people value risks differently. That valuation is affected by the level of their incomes."

He said that the alternative - to assess everyone equally - would increase the amount spent on disaster aversion and foreign aid: "We would end up allocating all our national income to life-saving."