The UnAustralian

Monday, May 26, 2003
More on Castles/Henderson and the IPCC

The journal Energy and Environment have finally published Ian Castles and David Henderson's critique of the IPCC SRES (emission scenarios) + a response from the IPCC. Unfortunately, I only have access to the abstracts.

From Castles and Henderson:

This set of papers chiefly presents a critique of the IPCC's Special Report on Emissions Scenarios (SRES), which claims to "provide the basis for future assessments of climate change and possible response strategies". The 40 scenarios are technically unsound in that, contrary to accepted international practice, they convert national GDP data to a common measure using market exchange rates. Because of this procedure and built-in assumptions about the extent to which the gap between rich and poor countries will be closed, the scenarios yield projections of GDP for developing regions which are improbably high: this includes the scenarios which give the lowest figures for projected cumulative emissions in the course of the century. Hence the SRES projections do not, as is claimed for them, encompass the full range of uncertainties about the future. Because of these and some other defects that we have noted, the SRES should not be taken as the accepted basis for the IPPC's coming Fourth Assessment Review. More broadly, the IPCC should try to ensure a more balanced, informed and professional treatment of the economic and statistical aspects of its work. In particular, there should be a greater involvement of economic ministries and statistical agencies.

From the IPCC response (by Nebojsa Nakicenovic; Arnulf GrĂ¼bler; Stuard Gaffin; Tae Tong Jung; Tom Kram; Tsuneyuki Morita; Hugh Pitcher; Keywan Riahi; Michael Schlesinger; P. R. Shukla; Detlef van Vuuren; Ged Davis; Laurie Michaelis; Rob Swart; and Nadja Victor):

Mr. Castles and Mr. Henderson have criticized the Special Report on Emissions Scenarios (SRES) and other aspects of IPCC assessments. It is claimed that the methodology is "technically unsound" because market exchange rates (MER) are used instead of purchasing power parities (PPP) and that the scenarios themselves are flawed because the GDP growth in the developing regions is too high. The response is:
The IPCC SRES reviews existing literature, most of which is MER based, including that from the World Bank, IEA and USDoE.

Scenarios of GDP growth are typically expressed as MER (the preferred measure for GDP growth, as opposed to PPP which is a preferred measure for assessing differences in economic welfare).

IPCC scenarios did include PPP-based scenarios, which Mr. Castles and Mr. Henderson have conveniently ignored.

Contrary to what Mr. Castles and Mr. Henderson claim, IPCC scenarios are consistent with historical data, including that from 1990 to 2000, and with the most recent near term (up to 2020) projections of other agencies.

Long-term emissions are based on multiple, interdependent driving forces, and not just economic growth. Mr. Castles and Mr. Henderson need to look beyond GDP.

The IPCC scenarios provided information for only four world regions, and not for specific countries. Mr. Castles' and Mr. Henderson's critique is not of IPCC scenarios but of ongoing unpublished work in progress that is not part of SRES.

We therefore show that Mr. Castles and Mr. Henderson have focused on constructing a "problem" that does not exist. SRES scenarios are sound and the IPCC has responded seriously and conscientiously.

We detail our response below in nine sections. After an introduction (Section 1), we outline the SRES methodology for measuring economic output (Section 2). Section 3 compares SRES to long-historical economic development and provides five responses to the critics. Section 4 addresses the issue of country-level economic projections even if not part of SRES. Sections 5, 6 and 7 validate the SRES scenarios by comparing them with recent trends for economic and CO2 emission growth, as well as more recent scenarios available in the literature. Section 8 refutes the argument that lower economic growth in developing countries would lower GHG emissions correspondingly. Section 9 concludes.

At face value, the IPCC rebuttal correlates well with some of the points that I've been trying to make. The next step for me, is to hunt down a copy of both papers.

Incidentally, both papers are in Energy and Environment , 14 (2,3) May 2003

| 7:31 PM