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: wzforum.de/forum2/msg-2768981.
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”.