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Peer Reviewed Paper Challenges IPCC Analysis of Medieval Warm Period
In their 2007 report, IPCC working group 1 refers to an increased heterogeneity of climate during medieval times about 1000 years ago. This conclusion would be of relevance, as it implies a contrast in the spatial signature and forcing of current warmth to that during the Medieval Warm Period. Our analysis of the data displayed in the IPCC report, however, shows no indication of an increased spread between long-term proxy records. We emphasize the relevance of sample replication issues, and argue that an estimation of long-term spatial homogeneity changes is premature based on the smattering of data currently available.
The IPCC on a heterogeneous Medieval Warm Period
Jan Esper and David Frank
Climatic Change (2009) 94:267–273
DOI 10.1007/s10584-008-9492-z
Full paper available here.
CO2 Science.org’s take is here:
In an important paper recently published in the peer-reviewed journal Climatic Change, Swiss scientists Jan Esper (of the Swiss Federal Research Institute) and David Frank (of the Oeschger Centre for Climate Change Research) take the Intergovernmental Panel on Climate Change (IPCC) to task for concluding in their fourth assessment report (AR4) that, relative to modern times, there was “an increased heterogeneity of climate during medieval times about 1000 years ago.”
This finding, if true, would be of great significance to the ongoing debate over the cause of 20th-century global warming, because, in the words of Esper and Frank, “heterogeneity alone is often used as a distinguishing attribute to contrast with present anthropogenic warming.” On the other hand, if the IPCC’s contention is false, it would mean that the warmth of the Current Warm Period is not materially different from that of the Medieval Warm Period (MWP), suggesting there is no need to invoke anything extraordinary (such as anthropogenic CO2 emissions) as the cause of earth’s current warmth, which does not yet appear to have reached the level experienced a thousand years ago (when there was much less CO2 in the air than there is today), as is indicated by the materials archived in our Medieval Warm Period Project. And, of course, this outcome would also be of great significance.
So what did the two Swiss scientists find? By means of various mathematical procedures and statistical tests, Esper and Frank were able to demonstrate that the records reproduced in the AR4 “do not exhibit systematic changes in coherence, and thus cannot be used as evidence for long-term homogeneity changes.” And even if they could be thus used, they say “there is no increased spread of values during the MWP,” and that the standard error of the component data sets “is actually largest during recent decades.” Consequently, the researchers concluded that their “quantification of proxy data coherence suggests that it was erroneous [for the IPCC] to conclude that the records displayed in AR4 are indicative of a heterogeneous climate during the MWP.”
Nevertheless, the homogeneity issue remains unresolved, for as Esper and Frank also note, “an estimation of long-term spatial homogeneity changes is premature based on the smattering of data currently available.” And that is why we continue to post the results of one new study each and every week that provides additional data on the Medieval Warm Period. We are determined to see this question — and others associated with it — clearly resolved, one way or the other. And as may be seen from the ever-expanding results of our Interactive Map and Time Domain Plot, the MWP is looking ever more global and substantial with every passing week.
Sherwood, Keith and Craig Idso
Reference
Esper, J. and Frank, D. 2009. The IPCC on a heterogeneous Medieval Warm Period. Climatic Change 94: 267-273.
June 11th, 2009 at 4:06 am
Yet another baseless claim made by the IPCC that has been exposed by further research. This parallels Ross McKitrick’s experience with his research showing bias in the temperature records from socioeconomic activity. They made statistical claims without having any statistical basis that the significance of his predictors disappeared when accounting for natural circulation changes. He tested this and it was plain false:
http://ross.mckitrick.googlepages.com/CircEffects.rev.pdf
June 13th, 2009 at 5:37 am
Have to agree with Andrew. I’m not an expert statistician, but I do hold A Level Maths & Statisics.
I trust Ross Mck., if they could bury him they would and they havent.
Trouble is spin, spin and more spin aligned closely with a younger generation street wise is some respects, but naive in others and sadly lacking in proper scientific education, and on many occassions supremely over confident
June 13th, 2009 at 2:11 pm
Hey, I’m a “younger generation” guy myself!
Haha, no, I get it. Plus, I think you mean mostly individuals much older than me.
December 17th, 2009 at 2:10 am
I don’t get why past climate change not being due to greenhouse gases (or not greenhouse gases emitted by humans) would imply that the currently added gases do not cause greenhouse effect and can’t be the main factor in the more recent warming. The qualification of this hypothesis as “extraordinary” is striking. If sun output is ruled out, as not only climatologists but even solar centers agree, what would be the factor then? Are we seeing “dark warming”?
December 17th, 2009 at 2:51 am
We’d expect man-made CO2 to enhance the greenhouse effect – the question is how much – the IPCC modelled scenarios range from 1.1C to 6.4C for a doubling of CO2 to 560ppmv, depending how much positive feedback is fed into models. The sun isn’t ruled out – the IPCC have ‘low’ ‘level of scientific understanding’ of ‘total solar irradiance’ and climate, and ‘very low’ for other solar factors. There are papers linking the sun with recent climate change, including the past 50 years. Also Tsonis et al’s natural ‘climate shifts’ may help explain natural climate variability.