Foreword: Dr Sebastian Lüning and Prof. Fritz Vahrenholt, authors of a new controversial skeptic book now hitting German bookstores, have asked me to post their response to comments made by climate scientist Georg Feulner of the Potsdam Institute for Climate Impact Research in an interview by NTV television. Feulner insists that CO2 plays the major role in climate change and that the sun has little impact.

You can read about the new book just published in Germany that is causing an uproar in the German green establishment here. The response is so vitriolic that one is newspaper (TAZ) is headlining “Skeptics are like viruses“. Greenpeace Germany has now gotten into the act, denoucing Lüning and Varrenholt (formerly a champion of the global warming cause) as an Ice Cold Denier.

The website (in German) for the new book (that has become a bestseller on three outlets) from Lüning and Vahrenholt is here. An English version is also planned which I will announce at WUWT. Sincere thanks to Pierre Gosselin of notrickszone.com for translation. -Anthony

Georg Feulner of the PIK runs in circles

Guest post by Sebastian Lüning and Fritz Vahrenholt

On the Germany television website Georg Feulner of the Potsdam Institute for Climate Impact Research comments on our recently published book “Die kalte Sonne”. As we have criticized his work in our book, we are not at all surprised by his rejection of our position.

First he disputes global warming has stopped for the time being. To do this he uses a special chart from a blog depicting a stepwise temperature development, which makes no sense for the particular topic at hand. The temperature plateau that we’ve had since the year 2000 is disputed by Feulner. However, the missing warming of the last 12 years is no fabrication made up by the authors of “Die kalte Sonne“. Anybody can plot it by going over to Woodfortrees.org. Or you can read up about it up in the peer-reviewed scientific literature, e.g. Kaufmann et al (2011). Even Prof. Ottmar Edenhofer of Feulner’s own Potsdam Institute for Climate Impact Research seems to see it the same way. Climate researcher Prof. Jochem Marotzke of Hamburg just confirmed it once again in a recent interview with the German TAZ daily (9 February 2012).

Next, Feulner tries to score points by using the 30-year climate rule. In some official definitions, climate is defined as the 30-year mean of weather. While this makes sense for some considerations, this rigid rule obstructs the discussion on the mechanisms that are involved in climate. It’s becoming increasingly clear that natural decadal cycles have been greatly under-estimated in the past. For example the Pacific Decadal Oscillation (PDO) is characterized by a warm and a cold phase, each lasting 20 to 30 years. They have a significant impact on global temperature. Should that 30-year-climate window unfortunately get placed between both phases, then the trends get mixed up and we end up comparing apples and oranges. The corresponding “climate“ results end up depending more on the choice of the start point of the 30-year window and less on the real, shorter-scale temperature trends. Consequently, looking at 10-year temperature trends is not only legitimate, but it also makes sense.

In discussing the sun, Feulner attempts to show that in the event of an impending significant drop in solar activity to Dalton or Maunder Minimum-levels, which he foresees as well, no considerable cooling is to be expected. Here he fails to mention that he forgot to include any solar amplification in his climate models. This is essential because it is only with such solar amplifiers that one is able to explain the synchronicity between the sun and the temperature, with at least a 1°C pulsating climate development, over the last 10,000 years. The climate model used by Feulner cannot explain the past, and therefore naturally is not suitable for projecting the future. To explain the Maunder-Minimum 300 years ago, Feulner resorts to the dubious volcano joker. But this still does not explain the overlying fundamental problem that there is a good sun-climate coupling over the other well-documented millennial cycles of the last 10,000 years.

When it comes to the Svensmark solar amplification effect, whose existence is supported by much evidence in peer-reviewed literature (see Chapter 6 and Svensmark guest contribution on page 209 in “Die kalte Sonne”), Feulner simply pushes it off the table without providing a good argument. Not a word on the independent confirmations of the important sub-processes of the effect (e.g. Usoskin et al. 2004, Laken et al. 2010, Kirkby et al. 2011).

The NTV interview illustrates just how much Georg Feulner runs in circles with his arguments. The arguments he presents are weak. When will the Potsdam Institute get around to addressing the millennium cycles of the last 10,000 years? On page 68-75 of our book (“The sun’s impact over the last 10,000 years”) we find one of the most important keys to the climate discussion. Strangely not a single media report following publication of our book has looked into this. Day eight and counting.

Example for millennial climate cycles: Studies of dripstones in Oman for the period 7500-4500 BC show a high degree of synchronicity between solar activity and temperature development. Figure modified after Neff et al. (2001)

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