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United Nations Development Programme
United Nations Environment Programme

Are Climate Change Measurements Wrong?

By Sanjay Suri*

There is a stir in the scientific community as two experts challenge the widely accepted climate change reports issued by an intergovernmental panel. One of the critics, David Henderson, explained their doubts in a conversation with Tierramérica.

LONDON - The Intergovernmental Panel on Climate Change (IPCC) should not base its next climate report on its flawed greenhouse gas emissions projections, says David Henderson, former chief economist of the Organization for Economic Cooperation and Development (OECD) and now a visiting professor at the Westminster Business School in London.

Henderson and Ian Castles, of the National Center for Development Studies at Australian National University and formerly head of Australia's national office of statistics, have co-authored a critique of the IPCC's Special Report on Emissions Scenarios, which is to be used as a basis for future assessments of climate change.

Henderson and Castles's analysis, to be published in the next edition of Energy and Environment journal, argues that the methodology used to estimate the accumulation of greenhouse gases (produced from combustion of petroleum, natural gas and coal) in the atmosphere by 2100 is erroneous and assumes an exaggerated level of economic growth for developing countries.

The two experts' challenge was published recently in the British magazine the Economist, and comes as a sharp blow to the credibility of the IPCC, whose opinions on the human causes of climate change have otherwise been considered the consensus of the international scientific community on the matter.

According to the Third Assessment Review on climate change, published in 2001 by the IPCC, it is likely that within a century the average earth surface temperatures will have risen by 1.4 to 5.8 degrees centigrade with respect to 1990 averages, and that sea level would rise 0.09 to 0.88 meters as a result of melting polar icecaps.

In an exclusive dialogue with Tierramérica, Henderson calls on the IPCC to give economic and statistical issues greater weight in the climate change calculations and expresses hope for a "full and open debate" on the issue.

On what basis do you challenge the IPCC's Special Report on Emissions Scenarios?
Contrary to accepted international practice, the 40 scenarios presented in the Report convert GDP (gross domestic product) data for the countries of the world to a common measure using market exchange rates, rather than purchasing power parity rates. Because of this flawed procedure, and also because of built-in assumptions about the extent to which the gap between rich and poor countries will be closed over this century, the scenarios yield projections of GDP for developing regions which are improbably high.

Does this mean that the figures for prospective emissions are too high?
What it means is that the even the scenarios which show the lowest cumulative emissions over the century do not in fact represent reasonable lower limits. These projections do not, as is claimed for them, encompass the full range of uncertainties about the future. They should not be taken as the accepted basis for the IPCC's coming Fourth Assessment Review of climate change issues.

The IPCC met last week in Paris. What do you think should have emerged from that meeting in relation to the future work of the Panel?
For a start, I hope that the Panel will recognize that our critique of the Special Report on Emissions Scenarios is well founded. What we are saying does not merely represent the views of two isolated persons -- neither I nor my co-author (Castles) have any official status. What we are saying would receive wide professional backing.

But what action would you want the IPCC to take? Should the whole emissions scenarios exercise be redone?
I understand that it would be difficult to repeat an exercise on this scale in time for the IPCC's Fourth Assessment Review. But a more limited exercise should begin now to review the basis for the work on emissions, and to arrive at a new set of projections which, though less elaborately derived, would give a sounder basis than the present figures.

There are very great uncertainties in these and the other projections that the IPCC makes because in keeping with its mandate from governments, it has to look a century ahead. Would what you propose do much to reduce these uncertainties?
No, because economists can't claim to be able to see the future at all clearly. But what we suggest would provide a basis, a starting point, which was more professionally watertight than the present report.

Do you have any other suggestions for the IPCC?
Yes, what we are saying goes beyond the work on emissions scenarios. More generally, we think that the IPCC should try to ensure a more balanced, informed and professional treatment of the economic and statistical aspects of its work. On the official side, there should be a greater involvement of economic ministries and statistical agencies. Among the academics who take part, there should be better representation of economic historians and historically minded economists.

Has the IPCC responded in any way to what you have been saying?
Yes it has. We started by writing to the Chairman of the Panel, Dr R.K. Pachauri, and as a result we were invited to a special IPCC experts' meeting last month. Although the meeting already had a full agenda, we were given the chance to make presentations to it, and technical discussions were held outside the main meetings to consider the points we were making.

Will the IPCC be making a more formal response to your critique?
Yes, I believe that will happen soon, and we hope it will. We would like t o see a full and open debate. The various communications that we have sent to the IPCC are to be published soon in Energy and Environment journal. When the editor there offered to publish what we had written, we made it a condition that she should invite the IPCC to publish an article by way of response. She accepted our proposal, and I understand that the IPCC has accepted her invitation.

* Sanjay Suri is an IPS editor.

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