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Thursday, June 10, 2010

John Abraham on Skeptical Science hammers the myth that the Medieval Warm Period was as warm as today in his "Monckton Chronicles Part IV– Medieval Warm Period?"

Monckton Chronicles Part IV– Medieval Warm Period?

Guest post by John Abraham, Skeptical Science, June 11, 2010

Now we will turn the clock back to a time that is often referred to as the medieval optimum, or the Medieval Warm Period. It is well known that approximately 1000 years ago, there was a warm period which spanned at least part of the northern hemisphere. This warm period is often used by climate deniers such as Christopher Monckton to incorrectly assert that today’s warmth is not unusual. Since there were no thermometers around at the time, researchers have to use what are often called “proxies” to measure temperatures. Proxies are indirect measurements, they are never as accurate as real thermometer data, however, they at least give us an idea about past climate.

A graph showing different researchers’ temperature estimations is shown in Figure 1. The measurements extend back to 800 AD. Modern time is on the right side of the graph. Each line represents a different researcher’s reconstruction. What you can see is that there is a lot of uncertainty in the proxies. You will also notice that as we approach modern times, the amount of uncertainty decreases significantly. What you should also notice is that the curves generally agree that there was a warm period from about 950-1150 AD. This period is the so-called Medieval Warm Period.

Figure 1. Various temperature reconstructions.

In his recent presentations, Mr. Monckton has claimed that “700 scientists” have shown that the medieval warm period was real. While we don’t know who those 700 scientists are, at least Monckton shows a few of them. Figure 2 is an image taken directly from Monckton’s slideshow. In his audio, he states that these papers show the Medieval Warm Period “was real, was global, and was warmer than the present.” Let’s investigate this claim just a bit.

Figure 2. Image from Monckton’s slide show of a representative set of researchers that claim the Medieval Warm Period was warmer than today.

In the investigation, I focused on the more recent articles. First, articles from 1969 and 1979 are based on older measurement techniques which are less accurate. Also, since much of the warming has occurred in the last 30 years, it doesn’t make sense to use papers older than 30 years. Next, I attempted to contact some of the authors listed above. Since Monckton did not present full citations, it was not possible to accomplish this. I was able to successfully contact some of the authors, and here is what I found.
  1. I contacted Dr. Schweingruber. He indicated that he was no longer working in the field but he referred me to a colleague, Dr. David Frank who is active in this area. Dr. Frank recently wrote this paper:

    D. Frank, J. Esper, C. Raible, et al., Ensemble reconstruction constraints on the global carbon cycle sensitivity to climate, Nature, 463, 527-532, 2010.

    I wrote to Dr. Frank and here is his reply…

  2. Next, I contacted Lloyd Keigwin, here is what he told me…

  3. I went further and identified the paper by Noon et al. Here is an image of the title page:

    You will notice that one of the authors is V. J. Jones. Dr. Viv Jones works at the University College of London Environmental Change Research Center. Here is her website:

    If you go there, you will find the following statement:

    It doesn’t sound like Dr. Viv Jones thinks global warming isn’t happening.
  4. Last, I determined that the Huang mentioned in Monckton’s talk is S. P. Huang who, incidentally, wrote a recent paper titled:

    S. P. Huang, H. N. Pollack, and P. Y. Shen, A Late Quaternary Climate Reconstruction Based on Borehole Heat Flux Data, Borehole Temperature Data, and the Instrumental Record, Geophys. Res. Lett., 35, 2008.

    Here is a screenshot from the paper and a quotation taken directly from the manuscript.

    The relevant text is… “The reconstructions show temperatures… the maximum of the MWP at or slightly below the reference level and the end-of-20th century temperatures about 0.5 °C above the reference level….. consistent with the amplitudes estimated from other climate proxies as summarized by the IPCC.”
After seeing that four out of the first four papers were not as they had seemed, I concluded that Monckton has misinterpreted the data. It turns out that these authors did not say the Medieval Warm Period was warmer than today and that they truly are concerned about global warming. When you combine this finding with the fifteen other investigations that I show in Figure 1, it becomes pretty clear that the Medieval Warm Period does not disprove today’s global warming.


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