The church ruins at Hvalsey, Greenland constructed during the
Medieval Warm Period. A new study says that the period was the
result of a regional warming and not an event that covered a
larger area of the globe. (Wikipedia)
A new study to be published in this week’s issue if “Science” tackles the controversial Medieval Warm Period (MWP) and Little Ice Age (LIA). By analyzing a variety of proxy data, the study authors believe that while these events were naturally driven, they were regional events and not comparable to the global warming we see today.
The Medieval Warm Period was a period of time from approximately 800 to 1300 AD during which temperatures were above average. It was during this event that the Vikings were able to colonize far previously inhospitable northern areas including Greenland and prolonged droughts are believed to have affected parts of North America.
Following that event was the period termed the Little Ice Age from 1400 to 1800 when temperatures were below average. In Europe and North America, colder and harsher winters were documented allowing rivers to freeze that normally would not, an increase in glacial ice was realized and the choice of crops grown in some areas had to be changed to account for cooler temperatures.
The study authors, led by Michael Mann of Penn State, explained that the events were not global in nature but do have applicability to today. In a press release Mann said, "Studying the past can potentially inform our understanding of what the future may hold."
By using proxy data tree ring samples, ice cores, coral and sediments, scientists try to reconstruct temperature records for centuries past. In the case of the Medieval Warm Period, the authors said that while the northern parts of the Northern Hemisphere were warmer, the tropical Pacific was cooler indicating La Niña was at work. The opposite effect was experienced during the Little Ice Age according to Mann and his colleagues.
Similar to how ‘climate change’ is the preferred term over ‘global warming’ and other terms in the climate change debate have been changed to improve public perception, Mann indicated a change in the Medieval Warm Period’s name was preferred, presumably to help steer the all important public opinion. Mann said, “we prefer to use 'Medieval Climate Anomaly'.”
Much debate surrounds these two events and how they relate to the warming of the earth in recent decades. Skeptics of the manmade climate change theory point to these two events as indication that the recent warming of the globe is not all that unusual. They say that temperatures in the Medieval Warm Period were comparable to today, if not warmer. Further, they argue that since the Little Ice Age, the globe has been consistently warming and the warming experienced today is a continuation of that warming.
Michael Mann along with a number of other climate scientists have recently come under a great deal of scrutiny due to contents of email messages to and from him as part of the Climategate episode. Mann wrote in various messages discussing withholding climate data and attempts to prevent publication of dissenting opinions. He discussed the Medieval Warm Period in one such message saying that “it would be nice to try to "contain" the putative "MWP"."
On the net:
- Science: Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly
- Wikipedia: Medieval Warm Period
- Wikipedia: Little Ice Age
- Complete Climategate coverage from Examiner.com
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Comments
The good people at climate audit would like to know how a serious error in this study was not noticed by the genius peers who reviewed this study but the error was detected by Steve McIntyre within minutes of publication. According to McIntyre, " Tiljander series(one of the proxies used in the study) are still used as inverted. This can be seen from the positive screening correlation values reported in the file 1209proxynames.xls. In fact, going quickly through the screening code, it seemed to me that they have really "moved on" from the screening employed in Mann et al (2008): only "two-sided test" is used! This means that if a proxy has a strong inverted correlation to the (two-pick?) local temperature, it gets picked - no matter what the physical interpretation is! Since RegEM doesn't care about the sign, it is now really so that the sign does not matter to them anymore. Anything goes!"
Most of the other proxy studies find this same result: regional effects.
Please, no ululating or garment rending about the Hockey Stick(TM). There is a ton of other corroborating evidence. By dozens of other authors. Across the planet. Unless, of course, the entire planet is conspiring against the small minority of deniers and pseudoskeptics.
Best,
D
If the 400 year Medieval Warming was warmer than the present, how did the 5000 year old remains of Oetzi, the Ice Man found on a rocky slope in the Alps, persist?
It would be instructive to everyone, I believe, to read about the British Green Party politician who has virtual control of the Wikipedia articles on global warming -- William Connelley.
It is fairly clear, reading Wikipedia, that articles are being colored to maintain the politically motivated arguments for pending disaster due to the climate continuing to warm up after several cold centuries (the Little Ice Age).
Michael Mann is the "hockey stick" creator -- producing a chart that the IPCC used to show that the temperature was stable for a thousand years before going up sharply in the last century. A false picture intended to justify extreme measures.
Mann is now attempting to cover his tracks by denying that there ever was a warm period when the Vikings came to Vinland and settled Greenland. The beginnings of the Renaissance coincided with a warming temperature, and famine, war and disease coincided with the following cold period. Politicians would rather you not know.
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