The Medieval Warm Period – a global phenomenon. Unprecedented warming or unprecedented data manipulation?30. November 2009 | Von Rudolf Kipp | Kategorie: Blog
We live in an age of superlatives. If you switch on the TV nowadays you have the choice of either the best movies, the greatest hits or the dumbest pick-up lines of all times. And if you buy a detergent you are now longer satisfied if it washes “whiter than white”, it needs to be the “best ever”.
And of course the news coverage about climate change has to follow this trend as well. So now, with the upcoming Copenhagen-Conference we have either the choice between saving mankind, the whole ecosystem, or if you like it even more dramatic, the entire planet. To reach this goal, we learn, giant upheavals in our eco- and finance system are to be introduced. Every country and each single company has to be applied with bureaucratic shackles, to be able to fully control their CO2 output. Even the formation of a world government is seriously being discussed these days.
Why all this? You might already know it already. Today, we are told, we see a warming that exceeds everything we have experienced in the history of mankind or even in the history of the earth. And as a result from that, we will undergo the greatest catastrophe of all times. For real!
Medieval Warm Period thesis contradicts the unprecedented warming
However, one has to mention that already the first half of the above statement, the one about the undescended warming, leaves many open questions when discussed with climate scientists or historians. Hasn’t there been once something like a medieval warming period? And wasn’t this time period, according to many researchers, warmer than today?
The idea of a medieval warming period was for the first time written out in full by the English climatologist Hubert H. Lamb . Lamb, who founded the British Climate Research Unit (CRU) in 1971, saw the climax of this warm period between 1000 and 1300, in the High Middle Ages. He estimated that temperatures that time were about 1-2 °C higher than the normal period 1931-1960. In the high north he expected even 4 °C warmer temperatures. The continuous traveling of vikings were not disturbed by drifting ice and many of the burial places of the vikings in Greenland are even today still in permafrost regions.
Glaciers were smaller than today
Another indicator for the existence of the medieval warming period is the global retreat of glaciers in the time between about 900 and 1300 . Here a further notable detail is, that many of the glaciers retreating since 1850, nowadays release plant remains from the middle ages, which is obvious evidence that the extend of the glaciers was lower that time than today .
Historical tradition, too, testify to extraordinary warmth in that time. The 1180s brought the warmest ever reported winter-decade. In January 1186/87 in the region of Strasbourg the trees where in flower. And even before that time evidence of longer lasting heat periods can be found, for instance between 1021 and 1040. The summer of 1130 was so dry, that the river Rhine could be waded through. In the year 1035 the Danube was carrying so little water, that it could be passed by foot. This circumstance was taken advantage of. In this year the fundament of the first stone bridge in Regensburg was layed .
Explicit evidence for the warm period in the High Middle Ages can also be found in the agricultural borders of the horticultural crop. The tree limit in the alps raised up to 2000 meters, being above todays values . Winegrowing in Germany in the Rhine and Moselle was possible up to 200 meters above today limits. Wine was grown in Pomerania, East Prussia, in England and in southern Scotland as well as in Noway, far more in the north than today . On the basis of ancient pollen records it can be proven, that in the medieval time in Norway wheat was grown even in Trondheim. And up to almost 70th degree of latitude certain species of barley were cultivated . In many parts of great Britain cropland reached an altitude, unequaled until today.
And not only from Europe, but as well from Asia we have historical data reporting, that the limit of agriculture for citrus fruits has never reached so far north than in the 13th century. Accordingly, temperatures must have been about 1 °C higher in that region compared to modern times .
Archeology and history confirm warm period
Insects can be used as good historic climate markers. The cold sensitive bug Heterogaster urticae could be archaeologically proven being present in the city of York while the Roman Optimum and the Norman medieval time. Despite the 20th century warming, this bug nowadays can only be found at sunny places in the south of England .
During the medieval climate optimum the population in Europa reached until then unseen high levels. Many Cities were founded in that time and in the alps and in many high valleys have been made arable, which had to be abandoned later during the Little Ice Age .
The medieval was the era of the high culture of the Vikings. During this period their expansions to Russia and the colonization of Iceland, Greenland and parts of Canada and Newfoundland took place. In Greenland even certain species of cereals could be cultivated. With the end of the medieval warm period the heyday of the Vikings ended. The settlements in Greenland had to be abandoned and as well in the mainland Norway many settlements to far north or in to high altitude were left .
Climate scientists want to eliminate contradictions
Until about the mid-90s of last century the medieval warm period was an undisputed fact among climate researchers. Accordingly, in the first IPCC assessment report from 1990 on page 202 figure 7c  could be found, showing the medieval warm period clearly warmer than modern times. However, for the responsible scientists the existence of this warm period soon became a thorn in their sides. If in the 12th century it was even warmer, with the absence of human influence, than today at the so far peak of industrialization, why should the today warming not be primarily driven by mainly natural causes.
Thus, the Medieval Warm Period was soon declared an odious affair. Of meanwhile legendary status is an email, which the American climatologist David Deming received in 1995 . In that year he had published a paper in the prestigious journal Science, in which he had presented his research about climate change based on borehole data . With this publication he became well known amongst climate scientists and some of them assumed obviously, that he was in line with them [13, 15].
„With the publication of the article in Science, I gained significant credibility in the community of scientists working on climate change. They thought I was one of them, someone who would pervert science in the service of social and political causes. So one of them let his guard down. A major person working in the area of climate change and global warming sent me an astonishing email that said ‚We have to get rid of the Medieval Warm Period.‘“
In the meantime the machinery for the deletion of the medieval warm period was already running on full power. Also in 1995 the English climatologist Keith Briffa published an article in Nature with sensational results. According to his findings from tree-rings in the Siberian “Polar-Ural”, the medieval warm period had never existed and the 20th century appeared as the warmest of the last 1000 years . But the real breakthrough of the thesis of the 20th century as warmest in the millennium should be seen not until three years later. Namely with the release of Michael Mann’s infamous hockey-stick [17, 18].
Warm period is being erased
In this figure, which appeared as the icon on man made global warming in the 3rd IPCC assessment report, the medieval warm period had been totally eradicated. However, this curve was quickly under attack, mainly because the Canadian statistician Steve McIntyre had doubts about the scientific strength of the hockey stick graph and decided to unravel the numbers behind it with the diligence of an auditor . Not only that McIntyre could show that the algorithm Mann had used leads to a hockey-stick in 90 percent of the time even with random data, he also could prove that data selection, attribution of data and data usage was often erroneous .
Following the publication of Michel Mann’s hockey stick and the criticism, a whole bunch of studies were published, which all should prove that Michael Mann’s results correctly represent the temperatures of the last 1000 years. Preliminary climax of the debate was was the forced disclosure of the tree ring data from the british climatologist Keith Briffa, which he for years had refused to make available to the public. This data was used in several scientific papers, all proving the correctness of the thesis of a unprecedented warm 20th century. With the publication of the data it emerged, that obviously some trees were selected on purpose to achieve the favored result .
Regardless of the debate over the proper or improper use of proxy data like tree rings to determine the temperature history, the mainstream climatologists were struggling with a whole series of problems. What was with all the archaeological data, the records of weather events in church records and historical facts, which clearly suggested that there was an extraordinary warm period in the medieval? The scientists simply tried to refute these arguments claiming all these phenomena might have existed, but these had only been geographically limited events [23, 24]. If it should have been somewhere warmer in the middle ages than today, them maybe in England, the Alps, Greenland or North America. Globally, however, it has for sure been colder than in the 20th century, as shown in so many hockey-stick diagrams.
If one, however, tries to get an overview of the literature on the subject of the Medieval Warm Period published in the last years, a completely different picture appears. There is quite a number of studies from all around the world, showing all the same. Namely, that during the time of the High Middle Ages the temperatures were higher than in the modern times. An excellent overview can be found on the website CO2 Science, which has set up a whole section for these kind of scientific studies. The current count is 768 individual scientists from 454 separate research institutions in 42 different countries having published papers about a warmer than today medieval warming period. A small portion of these studies is shown in the figure below.
This overview clearly underlines one point. At the time of the Middle Ages, that is from 1000 to 1300 it was almost everywhere in the world warmer than today. here have been periods of warming, which clearly exceeded the 0.6 °C warming in the 20st century. And this happened totally without human influence by increased emission of the supposed „climate killer“ CO2. The statement that there had not been a Medieval Warm Period, or that it was merely a localized phenomenon can safely be regarded as untenable.
It therefore can be safely assumed that there are other factors influencing the climate, by far exceeding CO2 as main driver for climate change. Furthermore this thesis is supported by observations of the last 10 years. Since then we are not seeing any increase in temperature, which is even slightly dropping since 2002 . Even though the emissions of CO2 by burning fossil fuels have increased to previously unreached levels in very much the same time period.
 Hubert H. Lamb, The Early Medieval Warm Epoch and Its Sequel, in Paleogeography, Paleoclimatology, Paleoecology 1 (1965) 13-37
 Jean M. Grove, Roy Switsur, Glacial geological evidence for the medieval warm period
 Klimanews, Die Alpengletscher und der Eisman Ötzi
 Wolfgang Behringer, Kulturgeschichte des Klimas: Von der Eiszeit zur globalen Erwärmung (auch Google Books)
 Hubert H. Lamb: Klima und Kulturgeschichte, Reinbeck 1989
 Wilfried Weber, Die Entwicklung der nördlichen Weinbaugrenze in Europa
 De’Er Zhang, Evidence for the existence of the medieval warm period in China
 John M. Steane, The Archeology of Medieval England and Wales
 Thomas Gale More, Global Warming: a Boon to Humans and Other Animals
 Science Skeptical, Wird es in Grönland wärmer? Nein – kälter
 Climate Audit, Where did IPCC 1990 Figure 7c Come From?
 David Deming, Climatic Warming in North America: Analysis of Borehole Temperatures
 Michael E. Mann et al., Global-scale temperature patterns and climate forcing over the past six centuries. Nature 392 23 April 2008
 Michael E. Mann et al., Northern Hemisphere Temperatures During the Past Millennium: Inferences, Uncertainties, and Limitations 1999
 Stephen McIntyre, Auditing Temperature Reconstructions of the Past 1000 Years 2008
 Stephen McIntyre und Ross McKitrick, Corrections to the Mann et al (1998) Proxy Data Base and Northern Hemisphere Average Temperature Series Energy & Environment 14 2003
 Realclimate, False Claims by McIntyre and McKitrick regarding the Mann et al. (1998) reconstruction 2004
 Bishop Hill, The Yamal Implosion
 Valérie Trouet et al., Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly, Science 3 April 2009
 Michael E. Mann et al., Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly, Science 27 November 2009