(Posted by Olive on behalf of Hans)

In October 2004 we were lucky to publish in Science our critique of the ‘hockey-stick’ reconstruction of the temperature of the last 1000 years. Now, two and half years later, it may be worth reviewing what has happened since then.

The publication in 2004 was a remarkable event, because the hockey-stick had been elevated to an icon by the 3rd Assessment Report of the IPCC. This perception was supported by a lack of healthy discussion about the method behind the hockey-stick. In the years before, due to effective gate keeping of influential scientists, papers raising critical points had a hard time or even failed to pass the review process. For a certain time, the problem was framed as an issue of mainstream scientists, supporting the concept of anthropogenic climate change, versus a group of skeptics, who doubted the reality of the blade of the hockey stick. By framing it this way, the real problems, namely the ‘wobbliness’ of the shaft of the hockey-stick, and the suppressing of valid scientific questions by gate keeping, were left out.

Hopefully, sociology of science will later study this unfortunate period of climate science, but we may conclude now that science itself has indeed corrected claims of premature knowledge. We see now a healthy and broad discussion of the issue. We had the opportunity to respond to no less than four comments on our 2004 Science paper, but unfortunately only two comments were published. Similarly, Michael Mann and his coworkers had to respond to at least 2 comments to their Journal of Climate article in 2005.

At the EGU General Assembly a few weeks ago there were no less than three papers from groups in Copenhagen and Bern assessing critically the merits of methods used to reconstruct historical climate variable from proxies; Bürger’s papers in 2005; Moberg’s paper in Nature in 2005; various papers on borehole temperature; The National Academy of Science Report from 2006 – al of which have helped to clarify that the hockey-stick methodologies lead indeed to questionable historical reconstructions. The 4th Assessment Report of the IPCC now presents a whole range of historical reconstructions instead of favoring prematurely just one hypothesis as reliable.

When looking back we are satisfied with what has been achieved – namely an open, open-minded exciting discussion about the merits and problems related to different methods; an atmosphere where mere claims about the informational content of proxy-data meet a more critical response; an evolving practice of testing the skill of reconstruction methods in the laboratory of millennial forced global climate model simulations, where the formation of proxy-data is simulated in – so far too simplified – models.

Hans von Storch and Eduardo Zorita