The Medieval Warm Period – a global phenomenon, unprecedented warming, or unprecedented data manipulation?

“ “Who controls the past controls the future: who controls the present controls the past.” – George Orwell, 1984

We live in an age of superlatives. When you turn on the TV nowadays, you get offered the choice of best films, the greatest hits or the dumbest opening lines of all time. And even with a detergent it is long ago not sufficient when it  washes whiter than white.  Again, the constant sale appeal to the consumer can be maintained only if the product is billed as “The best thing ever.”

Naturally, also the reporting on climate change must follow this trend. Therefore the upcoming conference in Copenhagen is optionally about  the salvation of mankind, of whole ecosystems, or for those who like it even more bombastic, the salvation of the planet. To achieve this, we continue to learn, enormous changes in our economic and financial system are needed. Production companies and countries should put on bureaucratic manacles to control their CO2 emissions. Best with the help of worldwide dedicated government-like organizations.

What is the purpose of all this? You suspect or know it already. We are experiencing a warming, which has not existed in the history of mankind, or even in the history of the earth. And as a result we will experience the greatest disasters of all time. Honestly!

Medieval Warm Period thesis contradicts the unprecedented warming

However, one must mention that, already the first half of the statement, that about the unprecedented warming, elicits significant question marks in many climate scientists and even at many historians. Wasn’t there something like the medieval warm period? And in the opinion of many scientists, wasn’t it warmer during this period than today?

The idea of a medieval warm period  was formulated for the first time in 1965 by the English climatologist Hubert H. Lamb [1].  Lamb, who founded the UK Climate Research Unit (CRU) in 1971, saw the peak of the warming period from 1000 to 1300, i.e. in the High Middle Ages. He estimated that temperatures then were 1-2 ° C above the normal period of  1931-1960. In the high North, it was even up to 4 degrees warmer. The regular voyages of the Vikings between Iceland and Greenland were rarely hindered by ice, and many burial places of the Vikings in Greenland still lie in the permafrost.

Glaciers were smaller than today

Also the global retreat of glaciers that occurred in the period between about 900 to 1300 [2] speaks for the existence of the Medieval Warm Period. An interesting detail is that many glaciers pulling back since 1850 reveal plant remnants from the Middle Ages, which is a clear proof that the extent of the glaciers at that time was lower than today [3].

Furthermore, historical traditions show evidence of unusual warmth at this time. Years around 1180 brought the warmest winter decade ever known. In January 1186/87, the trees were in bloom near Strasbourg. And even earlier you come across a longer heat phase, roughly between 1021 and 1040. The summer of 1130 was so dry that you could wade through the river Rhine. In 1135, the Danube flow was so low that people could cross it on foot. This fact has been exploited to create foundation stones for the bridge in  Regensburg this year [4].

Clear evidence of the warm phase of the Middle Ages can also be found in the limits of crop cultivation. The treeline in the Alps climbed to 2000 meters, higher than current levels are [5]. Winery was possible in Germany at the Rhine and Mosel up to 200 meters above the present limits, in Pomerania, East Prussia, England and southern Scotland, and in southern Norway, therefore, much farther north than is the case today [6]. On the basis of pollen record there is evidence that during the Middle Ages, right up to Trondheim in Norway, wheat was grown and until nearly the 70th parallel/latitude barley was cultivated[4]. In many parts of the UK arable land reached heights that were never reached again later.

Also in Asia historical sources report that the margin of cultivation of citrus fruits was never as far north as in  the 13th century. Accordingly, it must have been warmer at the time about 1 ° C than today [7].

Archeology and history confirm interglacial

Insects can also be used as historical markers for climate. The cold sensitive beetle Heterogaster urticae was detected during the Roman Optimum and during the Norman High Middle Age in York. Despite the warming of the 20th century, this beetle is found today only in sunny locations in the south of England [8].

During the medieval climate optimum, the population of Europe reached hitherto unknown highs. Many cities were founded at this very time with high-altitude valleys, high pastures and cultivated areas, which were at the beginning of the Little Ice Age again largely abandoned [9].

The Middle Ages was the era of high culture of the Vikings. In this period their expansion occurred into present-day Russia and the settlement of Iceland, Greenland and parts of Canada and Newfoundland. In Greenland even cereals were grown about this time.. With the end of the Medieval Warm Period the heyday of the Vikings ended. The settlements in Greenland had to be abandoned as well as in the home country of Norway, during this time, many northern communities located at higher altitudes [10]. The history of the Vikings also corresponds very well to the temperature reconstructions from Greenland, which were carried out using ice cores. According to the reconstructions, Greenland was  at the time of the Vikings at least one degree warmer than in the modern warming period [11].

Climate scientists want to eliminate contradictions

Until about the mid-90s of last century the Medieval Warm Period was for climate researchers an undisputed fact. Therefore in  the first progress report of the IPCC from 1990 on page 202, there was the graphics 7c [12], in which the Medieval Warm Period was portrayed as clearly warmer than the present. However, the existence of this warm period became quickly a thorn in the side for the scientists responsible. When in 12th century without human influence the climate has been even warmer than at the height of industrialization, why should the current warming have non-natural causes?

Thus, the Medieval Warm Period was soon declared an odious affair. Meanwhile, an e-mail is legendary, which was sent to a U.S. climate researcher David Deming [13] in 1995. This scientist  published an article in the prestigious journal Science in which he had presented research on climate change in North America based on cores [14].

With this publication, he was immediately known among climate researchers, and some of them obviously thought that he was toeing their line [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 would be one of them, someone who would pervert science in the service of social and political causes. So one of them dropped his guard. An important person working in the field of climate change and global warming sent me an astonishing email with the words: ‘We must get rid of the Medieval Warm Period’. ”

Meanwhile, the climate machinery for the eradication of the Medieval Warm Period has already started. In 1995, the English climatologist Keith Briffa published in the journal Nature a study with sensational results. According to his studies of tree rings in the Siberian Polar-Ural, there had never been a Medieval Warm Period and the 20th century, suddenly appeared as the warmest of the last 1000 years [16]. The real breakthrough was the thesis of 20th Century experience as the warmest of the millennium, but not until three years later, and that with the release of Michael Mann’s infamous Hockeystick [17, 18].

Warm period is extinguished

In this diagram that became the icon of human-induced global warming in the 3rd IPCC Assessment Report, the Medieval Warm Period has now been completely eradicated. However, this curve was quickly under attack, mainly because the Canadian mathematician Steven McIntyre had serious doubts about the correctness of the representation and those pursued with the meticulousness of an auditor [19]. McIntyre showed not only that Mann had used an algorithm that resulted in 90 percent of the cases to a hockey stick, but found also serious errors in the selection of the data and the location of places, as well as the use of incorrect data [20].

Of course, the Mann’s gang could not let these allegations unanswered. In response, Realclimate.com was founded, a name intended to suggest the truth, but somehow reminiscent of the Real Ghostbusters, a poorly made copy of the genuine, which in contrast to the original only pretends to be the right thing. This webpage was henceforth used for accusations and slanders against the non-“believers” [21]. It took also increasingly care not to call McIntyre, in the meantime identified as the main enemy, by his name.

Following the publication of Michel Mann’s hockey stick and the criticism, whole series of further studies was published to demonstrate that the results of Mann’s actually represented the real temperatures over the last 1000 years. The highpoint of the debate was the forced disclosure of the raw data from tree ring studies long held under lock and key, which served as one of the principal witnesses for the correctness of the thesis of the unusually warm 20th century. It turned out that clearly the data were selected intently to get the desired result [22].

Conflicting data

Regardless of the debate over the proper or improper use of proxy data like tree rings to determine the temperature history, mainstream climate researchers, however, are still 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 documented that in the Middle Ages, there was an unusually warm period? Quite simply, the attempts to refute these arguments were made based on claims that all these phenomena indeed existed, but only as geographically limited events [23]. If the Middle Ages was warmer somewhere than today, then maybe it was only in England, the Alps, Greenland or North America. Globally, however, as shown in the many hockey stick charts, it has been colder than at the end of the 20th century.

If one, however, provides an overview of the literature on the subject of Medieval Warm Period, which has been published in recent years, there will be a completely different picture. There are now quite a number of studies from around the world, showing all one thing. And indeed, that the High Middle Ages were warmer than today. An excellent overview can be found on the website CO2 Science, which has set up a whole section for studies of this kind [24]. There are now  765 different scientists from 453 research institutes listed that have worked on the medieval warm period. A small portion of these studies is shown in the figure below [Click 25] (by the graph, you get a larger image where you can select individual work).

This survey shows one thing quite clearly. At the time of the Middle Ages, that is, from 1000 to 1300 it was almost everywhere in the world warmer than today. There have been periods of warming, that exceeded 0.6 degree Celsius rise in temperature in the 20th century and totally without the man-made increased emissions of the supposed “climate killer” of CO2. The statements, that there has not been any Medieval Warm Period, or it was merely a localized phenomenon, can safely be regarded as untenable.

It is therefore not surprising that there are influences on the climate, which can by far exceed the CO2 as a driver of climate variability. This hypothesis is massively supported by the observations made during the last 10 years. Finally, we have been experiencing no increase since 2002, the temperatures have dropped slightly [26]. And that even though the emissions of CO2 from fossil fuels in exactly the same period increased to previously unmatched dimensions.

Google translation in English of the full article is here.