The Intergovernmental Panel on Climate Change has seriously underestimated the technological challenges involved in lowering man-made greenhouse gas emissions, a Canadian economist and two U.S. experts on climate change argue in the journal Nature.

Assumptions in the IPCC's climate models divert attention from greenhouse gas reduction policies, they allege in a commentary published online Wednesday.

The authors are McGill University economist Christopher Green, University of Colorado climate policy expert Roger Pielke Jr. and U.S. National Center for Atmospheric Research climatologist Tom Wigley.

Last year, reports by the panel, which was established in 1988 by the World Meteorological Organization and the United Nations Environment Programme, spelled out the consensus on climate change from scientists and policy makers, arguing global warming was unequivocally occurring and was very likely man-made in origin.

The reports also presented several scenarios for what impact climate change would have on regions around the world and what measures could be taken to mitigate the damage caused by further warming.

Although largely praised for bringing climate change to the international forefront — the IPCC shared the 2007 Nobel Peace Prize with former U.S. vice-president Al Gore — the panel's reports have been criticized by some environmental scientists as being watered down and overly optimistic in some of the warming scenarios, particularly those concerning rising temperatures in the Arctic and Antarctic regions.

Pielke, Wigley and Green take issue with how the IPCC estimates future energy use and energy efficiency, arguing even their baseline scenarios assume "spontaneous technological change and related decarbonization."

The authors analyzed the panel's six scenarios and found the IPCC assumes 57 per cent to 96 per cent of reductions needed to stabilize carbon dioxide emissions at around 500 parts per million will occur automatically through natural technological advances. 

That assumption leaves a much smaller emission-reduction target for policy makers to tackle.

"The IPCC implicitly assumes that the bulk of the challenge of reducing future emissions will occur in the absence of climate policies," Pielke and his colleagues write.

"We believe that these assumptions are optimistic at best and unachievable at worst, potentially seriously underestimating the scale of the technological challenge associated with stabilizing greenhouse-gas concentrations."

To more accurately reflect the difficulty of reducing greenhouse gas emissions, they argue, the IPCC models should assume a "frozen technology" baseline, one in which energy efficiency and intensity projections are assumed to remain the same.

This, they say, would give policy makers a truer sense of the enormity of the task of reducing emissions and spur policies that encourage innovation.