The UnAustralian

Tuesday, March 18, 2003
 
A New Low in Climate Pseudoscience: Part 6

This section concerns Daly's collection of regional studies which show a MWP and Little Ice Age with a considerable larger magnitude than indicated by the Mann (and subsequently others) paper.

It is important to note that the Mann paper was a multiproxy (ie. multiple techniques) temperture reconstruction which looked at multiple sites around the Northern Hemisphere. The paper's which Daly cites are all regional studies.

As can be seen in this IPCC diagram, these is considerable differences in temperture changes between different areas of the world. Hence we would expect certain regional studies to show significantly larger trends than the global average.

So a good question would be, are the studies selected by Daly cherry picked to support his case or are they representative of global trends.

To test this, I've only looked at one of his examples (sorry, but I?ve already spent far too much of time on this), that of China.

If one only read Daly's selected studiers on China, you would see evidence for a MWP and Little Ice Age (erroneous interpreted by Daly as support for his theories), and the following statement:

"They estimated the temperature between 1100 and 1200 AD at around 2°F warmer than today, matching the Medieval Warm Period, confirmed by the existence at that time of plant remains from species that normally exist only in southern China. They found very cold temperatures between around 1550 and 1750, matching the Little Ice Age found elsewhere."

I've done some very basic looking around and found a paper (Yang, 2002) which looks at multiproxy temperture reconstructions of China. They use 6 data sets (plus 2 more from Taiwan, and another from Japan) to do their reconstructions. The data sets are from the Guliya ice core, the Dunde ice core, Dulan tree rings, Tibet tree rings, Eastern Chinese temperatures, the Big Ghost Lake (Taiwan), the Jiaming Lake (Taiwan), and Japanese tree ring data. Their data shows that by 1950's it was warmer in China than during the MWP, something at odd with Daly's selected studies.

This is supportive of Daly's selected regional studies not being representative of larger scale trends.

I'll end this post with the abstract of paper (Crowley, 2000) which came out as about the sametime as Daly wrote his essay:

A frequent conclusion based on study of individual records from the so-called Medieval Warm Period (similar to 1000-1300 A.D.) is that the present warmth of the 20(th) century is not unusual and therefore cannot be taken as an indication of forced climate change from greenhouse gas emissions. This conclusion is not supported by published composites of Northern Hemisphere climate change, but the conclusions of such syntheses are often either ignored or challenged. In this paper, we revisit the controversy by incorporating additional time series not used in earlier hemispheric compilations. Another difference is that the present reconstruction uses records that are only 900-1000 years long, thereby, avoiding the potential problem of uncertainties introduced by using different numbers of records at different times. Despite clear evidence for Medieval warmth greater than present in some individual records, the new hemispheric composite supports the principal conclusion of earlier hemispheric reconstructions and, furthermore, indicates that maximum Medieval warmth was restricted to two-three 20-30 year intervals, with composite values during these times being only comparable to the mid-20(th) century warm time interval. Failure to substantiate hemispheric warmth greater than the present consistently occurs in composites because there are significant offsets in timing of warmth in different regions; ignoring these offsets can lead to serious errors concerning inferences about the magnitude of Medieval warmth and its relevance to interpretation of late 20(th) century warming.
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