Stefan Rahmstorf Pulls Warming Out Of His Hat – Uses Curve-Designing Tricks For September Mean Temperatures

It seems every time Stefan Rahmstorf makes a claim about climate, there’s almost always something very creative and acrobatic about the statistical approach he uses on which to base that claim. Rahmstorf seems to feel very much at home with the climate-Armageddon-theorists at his ultra-alarmist Potsdam Institute.

By Sebastian Lüning and Fritz Vahrenholt
(Translated, edited by P Gosselin)

Wringing his hands, Potsdam Climate Impact research Institute’s Stefan Rahmstorf keeps up his efforts to pour cold water on the warming pause. In an article at his Klimalounge blog on November 1, 2013 he posted a chart depicting the September temperatures over the last 130 years, represented by a bold red-colored moving average curve that shows no pause in warming (Figure 1). Rahmstorf has always said: The warming continues unabated.

Figure 1: Global September temperature for the last 130 years. Source: Klimalounge / Stefan Rahmstorf.

But wait, upon closer examination, September temperatures do show a plateau that is already more than 10 years long.

Weather Central Forum contributor DH7FB has taken a close look at the data and discovered where Rahmstorf used tricks to get warmer results. First with curve smoothing, if an especially long smoothing interval is used, then the plateau at the end disappears. Here Rahmstorf uses an enormously long period of more than 30 years without mentioning it in his blog. If one uses a smoothing period that is more common, say 5 years, then the warming pause becomes clearly visible also for September temperatures.

Using 5-year smoothing: light blue curve = September; bold blue mean = June, July, September, bold red = July-December. Source:

And why did Rahmstorf choose September and not some other month? DH7FB made a comparison with other monthly combinations and discovered that the Pinatubo-eruption in June 1991 had a significant impact on September and that it significantly steepened the global September mean value curve.

Reading tip: Take a look at the reader comments at Rahmstorf’s blog. It’s peppered with criticism.


It should be noted that in his blog article and comments, Rahmstorf repeatedly equates climate skeptics to the Tea Party, “the radical climate skeptical wing of the Republicans” and that “climate skeptic think tanks are financed mainly by the Koch brothers”.


11 responses to “Stefan Rahmstorf Pulls Warming Out Of His Hat – Uses Curve-Designing Tricks For September Mean Temperatures”

  1. Ric Werme

    Well, if you want to make a 17 year plateau disappear (which is mainly on RSS, not the surface datasets, starting out with a smoothing function that includes a warming period is a good first step.

    If he is using such a long smothing period, then there would be gaps at either end of the graph since it covers the typical “trusted” history. Are the end points smoothed with only half the period?

    1. DirkH

      “Are the end points smoothed with only half the period?”

      A centered 30 year smoother would have to end delivering output at 1998 if given data up to 2013.
      So what the climatists do in such a case is extrapolating beyond actual data. Some others, economists sometimes, also do that, but I’ve never seen it in actual signal processing applications; I guess it would be considered useless as signal processing actually needs to solve problems, not create them.

      So what they sometimes do – McIntyre caught Mann doing it once – is mirroring the past n years to get the next future n years. Or they somehow create imagined data by modeling the existing data using a Monte Carlo process with its parameters fitted to the past data.

      In any case, the output of a centered 30 year smoother beyond 1998 is as factual as a fairytale.

  2. Ed Caryl

    This think tank is still waiting for his first check!

  3. DirkH

    Looked into his forum. Pretty sycophant comments, maybe culled already?
    Notably in one of his answers Rahmstorff has no qualms spreading Kochtopus smears.
    “Im übrigen wird die Tea Party nach Medienberichten von den Koch brothers finanziert, die zu den größten Finanziers “klimaskeptischer” think tanks in den USA gehören.”

    He’s really the Seth Borenstein of science. What an obedient little EU lickspittle! Well done, Ramstorff!

    1. DirkH

      Oh I see you noticed already, Pierre, sorry. Headed over to Rahmstorff before reading all of your post.

  4. Manfred

    Wouldn’t it be appropriate for Rahmstorf

    (1) to clean up with his relationship with, among others, Munich Re and the infamous Umweltbundesamt,

    (2) to correct and/or retract some of his previous papers and

    (3) to apologize to various scientists and journalists

    before piling up again and again?

  5. Ike
  6. DirkH

    I found a bunch of German crazies that I didn’t know before. Lots of crazy over there. This writeup expresses some general concernedness about everything that we do including changing the climate. What we call Gutmenschen.

    1. Ike


      question: if you click on their Impressum, who are the people listed below “Fotografien”?

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