Medieval Warm Period?

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6 responses to “Medieval Warm Period?”

1. 

   Naum

   November 30, 2009

   http://www.scientificamerican.com/article.cfm?id=seven-answers-to-climate-contrarian-nonsense&page=2
   It is hard to know which is greater: contrarians’ overstatement of the flaws in the historical temperature reconstruction from 1998 by Michael E. Mann and his colleagues, or the ultimate insignificance of their argument to the case for climate change.
   First, there is not simply one hockey-stick reconstruction of historical temperatures using one set of proxy data. Similar evidence for sharply increasing temperatures over the past couple of centuries has turned up independently while looking at ice cores, tree rings and other proxies for direct measurements, from many locations. Notwithstanding their differences, they corroborate that the earth has been getting sharply warmer.
   A 2006 National Research Council review of the evidence concluded “with a high level of confidence that global mean surface temperature was higher during the last few decades of the 20th century than during any comparable period during the preceding four centuries”—which is the section of the graph most relevant to current climate trends. The report placed less faith in the reconstructions back to 900 A.D., although it still viewed them as “plausible.” Medieval warm periods in Europe and Asia with temperatures comparable to those seen in the 20th century were therefore similarly plausible but might have been local phenomena: the report noted “the magnitude and geographic extent of the warmth are uncertain.” And a new research paper by Mann and his colleagues seems to confirm that the medieval warm period and a “little ice age” between 1400 and 1700 were both caused by shifts in solar radiance and other natural factors that do not seem to be happening today.
   After the NRC review was released, another analysis by four statisticians, called the Wegman report, which was not formally peer reviewed, was more critical of the hockey stick paper. But correction of the errors it pointed out did not substantially change the shape of the hockey stick graph. In 2008, Mann and his colleagues issued an updated version of the temperature reconstruction that echoed their earlier findings.
   But hypothetically, even if the hockey stick was busted… what of it? The case for anthropogenic global warming originally came from studies of climate mechanics, not from reconstructions of past temperatures seeking a cause. Warnings about current warming trends came out years before Mann’s hockey stick graph. Even if the world were incontrovertibly warmer 1,000 years ago, it would not change the fact that the recent rapid rise in CO2 explains the current episode of warming more credibly than any natural factor does—and that no natural factor seems poised to offset further warming in the years ahead.

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2. 

   Michael W. Kruse

   November 30, 2009

   Thanks for the counterpoint, Naum.

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3. 

   Josh Rowley

   November 30, 2009

   Thank you, Naum!

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4. 

   Michael W. Kruse

   November 30, 2009

   I did forget to add, Naum, if the truth about Medieval Warm Period is so insignificant then when does the IPCC find it necessary to refute it and staunchly defend the Mann Hockey Stick?
   I do find it interesting how arguments like unprecedented warming are promoted as convincing evidence and then when it is brought into question it is dismissed by those who originally raised it as important. Critics are accused of majoring in minors. It is a bit like nailing jello to the wall. The goal post keeps moving.

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5. 

   Dave

   November 30, 2009

   Actually to set the records straight, Naum didn’t say any of that. It was a quote straight from John Rennie’s article.
   The whole article is filled half truths.
   Let’s start with a real question. The hockey stick appears to be accurate to within about 1/50th of a degree for temperatures in the 10th and 11th centuries. This is clearly ridiculous, as there is no way to get that degree of accuracy from tree rings and ice cores. Second, the hockey stick shown doesn’t show the significant drop in temperatures between 1998 and the present.
   The most important point though is that although there may be more than one hockey stick graph, and their reliability is dubious given the data manipulation not only but the CRU folks, but James Hansens admitted manipulation of data. The particular graph and data that was used for the vaunted IPCC report is crap.
   That is the important fact here.
   One more thing. Using the UAH dataset. Plotting the global temperatures gets one result. However plotting the temperature of the continental 48 states yields an interesting graph.
   One might reasonably think that, if the CO2 models, (and that is ALL that they are, models, and inacurate ones at that) are correct that there must be some more warming over the highest areas of CO2 production. But that is absolutely not the case.
   Here is the data. http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt If you graph out the last column you’ll see that there is no warming in the last 40 years in the area of highest CO2 pollution. Go figure.

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6. 

   phil_style

   December 3, 2009

   David,
   “One might reasonably think that, if the CO2 models, (and that is ALL that they are, models, and inacurate ones at that) are correct that there must be some more warming over the highest areas of CO2 production”
   This assumption might be reasonable prima facie, but is not correct. The atmosphere doesn’t operate at the local level like that. Atmospheric mixing is so prevalent (due to winds and convection) that reginoal emissions are soon dispered acrross vast geographic areas, and concentrations diluted to a more ‘mean’ level. This is (allegedly), in part, why the non-emitting parts of the world are expected to cop more than their share of impacts.

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