Rahmstorf 7 Finale

“According to a new U.N. report, the global warming outlook is much worse than originally predicted. Which is pretty bad when they originally predicted it would destroy the planet.” –Jay Leno

If ever there was a good example of alarmists views being given a free ride by a major journal, then the publication in Science of “Recent Climate Observations Compared to Projections” by Stefan Rahmstorf, Anny Cazenave, John A. Church, James E. Hansen, Ralph F. Keeling, David E. Parker, and Richard C. J. Somerville is it.

This paper claimed to show that:

The data available for the period since 1990 raise concerns that the climate system, in particular sea level, may be responding more quickly to climate change than our current generation of models indicates.

By way of recap, this paper figured prominently in the Interim Report of the Garnaut Review where it is clearly used as a source of mainstream scientific opinion:

“Developments in mainstream scientific opinion on the relationship between emissions, accumulations and climate outcomes, and the Review’s own work on future business-as-usual global emissions, suggest that the world is moving towards high risks of dangerous climate change more rapidly than has generally been understood.”

Interest in the current weather has been growing since people have been observing either sharp declines in temperatures since last year, or relative stability in temperatures over about the last 10 years and wondering how these fit into the picture of global warming. I did some posts putting it into context showing last years temperature drop was not unusual here, that a particular 10 year period has been flat here, and that a number of climate indicators are showing decadal stability here.

The Blackboard has been spear-heading rigorous statistical methods for checking IPCC projections and finding post 2001 TAR consistently falsified by climate trends.

Contradicting these findings was the paper by Rahmstorf et al 2007, published in Science, by seven of the leading members of the IPCC scientific team. So, I started to audit this paper to see if this paper does in fact provide a more reliable perspective on the issue of whether climate is changing faster or slower than expected.

A number of bloggers ‘raised concerns’ about the vague description of the methodology, and argued at Niche Modeling and The Blackboard that there were important sources of uncertainty unaccounted for. Other blogs picked up the issue including Peter Gallagher and Mark Lawson.

Stefan Rahmstorf and I exchanged comments at RealClimate.org and here.

His main defense was that the end point uncertainty would only affect the last 5 points of the smoothed trend line with an 11 point embedding. Here the global temperatures were smoothed using a complex method called Singular Spectrum Analysis (SSA). I gave examples of SSA and other methods where the end point uncertainty affected virtually ALL points in the smoothed trend line, and particularly more than 5 end points. Stefan clearly had little idea of how SSA worked. His final message, without an argument, was:

[Response: If you really think you’d come to a different conclusion with a different analysis method, I suggest you submit it to a journal, like we did. I am unconvinced, though. -stefan]

So much for the recap. Keep in mind that the purpose of a scientific exchange like this is to clarify the points of agreement and disagreement and attempt to arrive at a resolution on the validity of the claims. Note the problem I raised is not the only obvious problem either, but just one I worked on. This is not meant to be a personal process. I am grateful for someone to point out errors in my work and would try to understand them, as I would rather not be blowing smoke unintentionally.

This example highlights the power of numbers to resolve an issue. Stefan can have his opinion, and I have opinions too, but the thing I love is the power of numbers to arbitrate and discriminate, and ultimately eliminate the unjustified ones.

Also I was wanting to address the Garnaut Review, as I feel that they are abrogating a duty of diligence by not paying more critical attention to papers such as these. Here was an opportunity to give a specific example of a paper with flaws so obvious that it SHOULD have been dismissed by anyone with statistical training, or background knowledge.

So thank you readers for your patience with this process. I have put a submission into the Garnaut Review supported by documentation from the web sites involved.

Here is a good example of the use of blogs. As the time for comments has closed, I could not submit a critique to Science. It is also better to have a through and open discussion of the issues at hand anyway, before rushing to publication of critical comments, so both can gain a deeper understanding of the finer points. It is unfortunate that Stefan cut the discussion off, but to his credit he was responsive to the actual concerns in the replies he did make.