Press release and comment on the NAS report "Surface Temperature Reconstructions for the last 200 Years"

22 June 2006

Hans von Storch, Eduardo Zorita, Fidel González-Rouco

We welcome the National Research Council’s Report, which clarifies that the discussion about the technical qualities of the hockeystick-methodology is insignificant for the overall conclusion that the presently ongoing warming is likely related to elevated greenhouse gas concentrations in the atmosphere. We are pleased to read that the NRC shares our view that the methodology behind the hockeystick is questionable. We stick to our view that the methodology was not sufficiently described when published and independently tested thereafter.

1) We welcome the conclusion of the analysis by the NRC committee, which separates between two issues, namely firstly the claim that the last few decades (the last decade, the year 1998) were unprecedented in their warmth compared to a previous time horizon, and secondly the certainty we place into the published estimates of temperature variations in the past 1000-2000 years.

2) The assessment that the last few decades have exhibit a warming likely beyond the range of natural variations has been made on a variety of scientific findings, of which the Mann et al study was possibly the most publicly “sold” one, but other studies have provided better evidence (“detection and attribution studies”).

3) We share the assessment of the NRC committee that the evidence for unprecedented warming of a single decade or even a single year in times prior to 1500, or so, is stretching the scientific evidence too far. However, this was the key claim made in the contested 1998-“nature” and 1999-GRL-papers by Mann et al.

4) With respect to methods, the committee is showing reservations concerning the methodology of Mann et al.. The committee notes explicitly on pages 91 and 111 that the method has no validation (CE) skill significantly different from zero. In the past, however, it has always been claimed that the method has a significant nonzero validation skill. Methods without a validation skill are usually considered useless.

5) Other independent efforts (e.g., inversion of borehole temperatures) to reconstruct past temperatures find different temperature ranges albeit qualitative agreement. These quantitative differences underline the methodological limitation of the Mann et al approach, which are described in the sections 9 and 11 of the NRC report.

6) We welcome the major conclusion of the report that further scientific efforts are needed to sort out a variety of problems with respect to methods and data ; also the uncertainty must be assessed in a more objective manner. Thus, the public perception that the hockeystick as truthfully describing the temperature history was definitely false.

7) We find it disappointing that the method of Mann et al. was not sufficiently described in the original publication, and thus not peer-reviewed prior to publication, and that no serious efforts were made to allow independent researchers to check the performance of the methods and of the data used.

Climate Audit » NAS Panel Report

file: pressrelease_vonStorch_NAS_report.html