Comments on “An Exchange on Climate Science and Alarm” between Lindzen and Rahmstorf

March 10, 2008

Lubos Motl’s blog recently highlighted an exchange between Stefan Rahmstorf and Ricbard Lindzen.  this peaked my interest because I have already picked apart another paper by Rahmstorf.  Rahmstorf’s part of the exchange is from chapter 3 (which he wrote) of the book Global Warming: Looking Beyond Kyoto,published in paperback in December of 2007.  You can see Rahmstorf’s chapter here.

 Rahmstorf shows the same CO2 vs. time and temperature vs. time data overlay that Al Gore used in An Inconvenient Truth.  Figure 1, below, shows part of page 36 of Rahmstorf’s chapter in the book.  The image shown in Rahmstorf’s paper notes the source of his data as “Climate and Atmospheric History of the Past 420,000 Years from the Vostok Ice Core, Antarctica, Nature 399 (June 1999): 429-36” by Petit, et. al.

Figure 1. Excerpt from Rahmstorf’s chapter in Global Warming: Looking Beyond Kyoto.  Rahmstorf added the points for 1959 and 2005 in a similar fashion to Al Gore.

But Rahmstorf forgot to mention that original source of his data included insolation vs. time, along with CO2 vs. time and temperature vs. time.  Figure 2, below, shows an excerpt from Petit’s original paper, in Nature, in which I have highlighed all three parameters vs. time.  Note that Rahmstorf puts the present at the right and the past at the left.  Petit has present at the left and the past at the right.  Other than that, and the fact that Rahmstorf leaves out the insolation data, they are the same.


Figure 2.  Excerpt from Petit’s Nature paper.  This is Rahmstorf’s source, but Rahmstorf leaves out the insolation vs. time data

It is not possible for the CO2 level or the temperature to control the insolation.  It is clear that the temperature and the CO2 can only follow the insolation.  There doesn’t seem to be any likely mechanism for the insolation to directly impact the CO2 level.  Therefore, the insolation must influence the temperature, and the temperature influences the CO2 level.  There may be a small feedback to the temperature from the CO2, but it cannot be large.  This is evidenced by the fact that no matter how high the CO2 goes the temperature still follows the insolation back down. 

In figure 3, below, I have digitized the temperature, CO2 level and insolation from Petit’s data and plotted the temperature series with the CO2 series and again with the insolation series for the last 150,000 years.  Temperature obviously correlates better with insolation than with CO2


Figure 3.  Digitized versions of Petit’s data.  Why does Rahmstorf leave the insolation out of his presentation?


  1. A more detailed version of this arguement can be seen at:


  2. Damn, that sound’s so easy if you think about it.

  3. Looking at an abstract of the Petit paper at http://www.cnrs.fr/cw/en/pres/compress/mist030699.html, it says:

    “The sunshine variations are not significant enough to explain the amplitude of the observed climate changes. These findings confirm the idea, suggested a decade ago, that greenhouse gases, by amplifying the variations initiated by the orbital variations of the Earth, were also responsible for the glacial/interglacial changes.”

    The insolation graph shows no scale info, so we can’t tell whether the variation in insolation is 1%, or 0.1%, etc. I would like to know how much it is exactly, but given the Milankovitch cycles make only subtle changes to the earth’s orbit, I suspect the variation is small. So Petit et al would appear to agree with Rahmstorf that the insolation changes trigger the temperature changes but are not strong enough to completely drive them, and that therefore CO2 must be amplifying the changes via positive feedback.

    • Topquark,

      Thank you for your comment.

      The problem with your explanation is that the temperature leads the CO2 on both the upswing and the downswing, as indicated…

      Hubertus Fischer (1999)(Scripps Institution of Oceanography) “Ice core records of Atmospheric CO2 Around the Last Three Glacial Terminations”

      Manfred Mudelsee (2001) Quaternary Science Reviews in 2001

      Lowell Stott (2007)Science, Southern Hemisphere and Deep-Sea Warming Led Deglacial Atmospheric CO2 Rise and Tropical Warming

      Best regards

      • If I understand you correctly, your problem is not that the temperature change precedes the CO2 rise on the upswing, but that it also precedes the CO2 drop on the downswing?

        I don’t see why this is a problem. In fact, it’s what I would expect. In the reverse of the warming phase, why can’t small insolation changes cause a small drop in temperature, which causes a drop in CO2, initiating a feedback which amplifies the insolation change?

        What alternative explanation is there? The insolation changes are surely too small to drive large temperature changes on their own.

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