Rahmstorf et al. 2007 Update 8


Well it is almost 24 hours since I posted the comment below to RealClimate at the post by Stefan Rahmstorf, about the inconsistency in the methodology used in their Science Brevia article to show that climate is trending higher than IPCC models. As yet the post has not appeared. I can’t see how it breeches their moderation policy, so I guess I am being told to go pound sand.

Update: Stefan Rahmstorf replied at the post here.

To provide a bit more clarity, I have drawn a couple of lines on the figure at issue to illustrate possible trajectories of the trend. The thin red line is where I think the trend should have gone if the method described in the figure caption had been used — SSA+MRC. The thin blue line is where I think the trend line should have gone if SSA only had been used.

Slide1.png

Figure: Annotated Rahmstorf et al. 2007 Science Brevia figure showing global temperatures and trend line. SSA is where the trend line should be for SSA method only, SSA+MRC is the trend line for SSA with the ‘minimum roughness criterion’ applied. The published trend line passes between these possible outcomes.

The actual trend on the figure passes between these two obvious choices. So at this stage I don’t know what method was used. It seems clear that if they had used the method SSA+’maximum roughness criterion’ as described, the trend line would not have supported their argument that ‘temperatures may be responding more quickly to climate change than our current generation of models indicates’.

Below is my post to RealClimate.org:

Stefan

I would be grateful if you would clarify for me a
puzzling aspect of your Rahmstorf et al. ’07 Science
paper. You state in the figure caption that the
‘minimum roughness criterion’ was used to get the
temperature trend line. Use of this method of data
padding as described by Mann 2004 should ‘pin’ the
trend line to the 2006 temperature value. However,
while the 2006 value lies in the center of the IPCC
range, the trend line shown on the figure lies above
the 2006 value, in the upper IPCC range.

I would like to clarify this apparent inconsistency.
This an important paper for the case that ‘the climate
system is responding more quickly than climate models
indicate’ and it is important to verify its technical
correctness. More details and graphs can be found
here:

http://landshape.org/enm/rahmstorf-et-al-2007-ipcc-error/