Recent Climate Observations: Disagreement With Projections

Appearing in Energy and Environment (ee-20-4_7-stockwell2) is a note by myself on a paper by IPCC lead authors Rahmstorf, S., Cazenave A., Church J.A., Hansen J.E., Keeling R.F., Parker D.E., and R.C.J. Somerville, Recent climate observations compared to projections published in Science in 2007.

As shown by 102 citations in Google Scholar already, Rahmstorf et al 2007 has been one of the main references for alarmist calls to action because the “climate system is responding more quickly than the climate models indicate”. Taking the first one off Google:

The strong trends in climate change already evident, the likelihood of further changes occurring, and the increasing scale of potential climate impacts give urgency to addressing agricultural adaptation more coherently. There are …

Adapting agriculture to climate change – pnas.org, SM Howden, JF Soussana, FN Tubiello, N Chhetri, M … Proceedings of the National Academy of Sciences, 2007 – National Acad Sciences.

Respected on-line authors like Peter Gallagher, Mark Lawson and Lucia were concerned with the paper. Lucia attacked the ‘slide and eyeball’ approach. I engaged with Rahmstorf at RealClimate and wrote a number of articles on the uncertainty, until he told me in effect to ‘sod off and publish’. But rather than try to diagnose a sloppy methodology and be ignored, time and evidence has done the job instead. Here is my abstract.

Abstract: The non-linear trend in Rahmstorf et al. [2007] is updated with recent global temperature data. The evidence does not support the basis for their claim that the sensitivity of the climate system has been underestimated.

Its gratifying to read that the authors of the Copenhagen Synthesis Report do not seem to agree with Rahmstorf et al 2007 either, in reference to analysis in a figure that ostensibly used the same method as Rahmstorf et al 2007.

Figure 3 … shows the long-term trend of increasing temperature is clear and the trajectory of atmospheric temperature at the Earth’s surface is proceeding within the range of IPCC projections.

synthesis3

However, five days ago JeanS, a talented data analyst, pointed out an inconsistency in Figure 3 of the synthesis report at Lucia’s in a post, Fishy odors surrounding Figure 3 from “The (Copenhagen) Synthesis Report”, which he illustrated with replications of Figure 3 with different variations on a smoothing parameter. I did some replicating too. It turns out that the global temperature trend had a higher slope than it should have had if it was produced with an 11 year embedding period, as was reported in the caption.

rahm11-141

JeanS queried Stefan about the inconsistency at RealClimate. Five days later his comment was released from moderation and Stefan admitted:

Did you change the filter length from M=11 to M=14 in the temperature graph (Figure 3)?

[Response: Almost correct: we chose M=15.

The reason he gave was essentially to address the same concerns the bloggers had raised about Rahmstorf et al. 2007 in the first place, that Stefan had refused to acknowledge, and are the subject of my paper:

In hindsight, the averaging period of 11 years that we used in the 2007 Science paper was too short to determine a robust climate trend. The 2-sigma error of an 11-year trend is about +/- 0.2 ºC, i.e. as large as the trend itself. Therefore, an 11-year trend is still strongly affected by interannual variability (i.e. weather).

Obviously, I am glad he finally appears to have agreed. But as a later poster pointed out, the misrepresentation of the embedding period in the legend raises questions about the motivation:

Stefan’s inline comment implies that he changed the smoothing method only after he realized that m=11 showed a flattening of the trendline, while m=14 did not. Changing things on the fly like this and leaving the erroneous caption just gives skeptics more ammunition.

Indeed. Of course, Stefan claims it was an innocent error in the figure caption:

[Response: I hadn’t noticed the error in the caption of our graph yet, thanks for drawing my attention to it. I have notified the editors of the report of this mistake. Not sure why a small technical error in the caption would give ammunition to anyone except conspiracy theorists:

This error was not noticed despite the warrant concerning the extensive peer review of the Synthesis Report made in the preface.

This report has been critically reviewed by representatives of the Earth System Science Partnership (ESSP), by the parallel session chairs and co-chairs, and by up to four independent researchers from each IARU university. This extensive review process has been implemented to ensure that the messages contained in the report are solidly and accurately based on the new research produced since the last IPCC Report, and that they faithfully reflect the most recent work of the international climate change research community.

On the relevance, Stefan apparently finds no problem with arbitrarily changing the parameters of the smoothing, and regards the error in the caption as not important:

None of this has anything to do with the smooth trend line or is affected by whether one happens to choose 11-year or 15-year smoothing.

Apparently it does affect the message communicated by the figure enough to want to increase the smoothing from 11 years to 15 years.

So this raises a number of issues:

1. What is to be done with the many sources that already reference Rahmstorf et al 2007, and will in the future, to justify faster actions on controlling emissions, including Australia’s Garnaut Report?

2. Why were the obvious shortcomings of the original article, by a number of lead chapter authors of the IPCC, not pointed out (and defended even) by other members of the climate science community (with a comment in Science say), and only skeptical bloggers noticed or were concerned by it?

3. As Jan Pompe remarks, if temperatures continue to stay flat, is it justified to keep increasing the smoothing period of the trend lines to ensure the appearance of an increasing trend, as Stefan appears to think?

Call me a conspiracy theorist, but when a short smoothing gave a high warming, Rahmstorf and his coauthors were quick to cry ‘the sky is falling’. But when the trend turned down due to random fluctuations, he changed the parameters to stay on message. As Marcellus said, “Something is rotten in the State of Denmark” (Hamlet).

Update: Lucia does a fine job of explaining the history and issues in Source of fishy odor confirmed:
Rahmstorf did change smoothing.