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A South American hockey stick

Posted on 18 September 2010 by John Cook

A new paper has just been published employing a new technique for reconstructing past temperatures (Kellerhals 2010). It uses Ammonium concentration from an ice core in tropical South America (the eastern Bolivian Andes) as a proxy for temperature. This enables them to build a temperature record going back 1600 years in a region which has had little proxy data available until now. They find a distinguishable Medieval Warm Period and Little Ice Age in the record. Nevertheless, they also find the last few decades show unprecedented warmth over the last 1600 years.

Figure 1: Reconstructed tropical South American temperature anomalies (normalized to the 1961–1990AD average) for the last 1600 years (red curve, smoothed with a 39?year Gaussian filter). The shaded region envelops the ±2 standard deviation uncertainty as derived from the validation period. Poor core quality precluded any chemical analysis for the time interval between 1580 and 1640 AD.

Note that Figure 1 shows only the proxy record from the ice core - no instrumental data is included. Of course, the usual caveat applies when looking at a single proxy record - this is a temperature record for a single location.To get a better feel for past climate, you need to look at proxy records from a range of locations.

When we combine all the various temperature records, we find the same result: modern temperatures are significantly warmer than medieval temperatures. This is demonstrated in Moberg's reconstruction of Northern Hemisphere temperature (which happens to bear a striking resemblance to the South American proxy record).

Figure 2: Northern Hemisphere Temperature Reconstruction by Moberg et al. (2005) shown in blue, Instrumental Northern Hemisphere Temperatures from Hadley shown in Red. Thanks to Robert Way for providing this graph.

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Comments 51 to 55 out of 55:

  1. HR, the word would be laughable but, really, what is there to hang on? What paper since Duplissy has been published using CLOUD data? Do you have something of any substance? The point was not to reveal problems in the epxerimental design, but the problems were uncovered nevertheless.
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  2. John, can you correct the mis-spelling of Moberg's name in the article, please.
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    Response: Fixed. You'd think I'd have noticed the correct spelling in the graph :-(
  3. Looking at the link identified in #19 is quite interesting if one takes the time to examine the records from around the globe. Unless I'm mistaken it appears that the mini ice age was widespread and not confined to Europe as sometimes asserted.
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  4. JC, who has asserted that the Little Ice Age was confined to Europe? I believe I have read that it was more pronounced there but never that it was absent elsewhere.
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  5. John, sorry to labour this, but I think that a global search and replace on the articles on your site for the word "Moburg" might be in order. I found another one here in the Figure 1 caption and title.
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    Response: Thanks for spotting that, have updated the Medieval Warm Period page.

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