Medieval climate anomaly

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The reconstructed global temperature course of the last two thousand years does not provide any evidence for a simultaneous worldwide medieval warm period lasting several decades

The medieval climate anomaly (Engl. Medieval Climate Anomaly , shortly MCA), especially in terms of temperatures and the medieval warm period (Engl. Medieval Warm Period , shortly MWP) or the medieval climate optimum was an interval relatively warm climate and other environmental variations, such as extensive continental droughts . A MWP can only be determined indistinctly in terms of region and time; according to most reconstructions, it probably started after 900 and ended before 1400. The warmest period in the northern hemisphere was between 950 and 1250.

During the Medieval Warm Period, there was a high probability that some regions were roughly as warm at the time as they were towards the middle, and sometimes also at the end of the last century. The warm periods of the Middle Ages, however, were temporally and regionally inconsistent, unlike the global warming that has been advancing simultaneously since the 20th century . In the 21st century, the earth has continued to warm. The mean temperatures of the last thirty years are now probably higher than those of all equally long periods in the Middle Ages. The rate of global warming is also faster than it has ever been in at least 2000 years, probably without a comparable example in recent geological history .

Development of the research area

Notes and first systematic work for the North Atlantic area

Grænlendingar in the fight with Inuit: The importance of the climate for the Scandinavian Greenland settlements in relation to other influences has been discussed since the 18th century.

As early as the 18th century, anecdotal evidence has been used to discuss whether there could have been temporarily higher temperatures in various regions of the North Atlantic in the Middle Ages. The Danish missionary Hans Poulsen Egede , who in 1721 searched in vain for inhabited medieval Viking settlements in Greenland that had not been heard of for 200 years, considered the climate as a possible cause of their disappearance:

"Were they destroyed by an invasion of the natives ... [or] perished by the inclemency of the climate, and the sterility of the soil?"

"Were they destroyed by a native invasion ... [or] did they perish from the ruthlessness of the climate and the sterility of the soil?"

- Hans Egede : Description of Greenland.

The Swedish diplomat Fredrik von Ehrenheim declared the end of the Viking settlements in 1824 with a cooling from a high point in the 11th century to a low point in the 15th century. Bernhard Studer , 1847, François Arago , 1858, and others interpreted the end of the Greenlandic settlements in the 15th century as evidence that a previously warmer region was getting colder, while Conrad Maurer rejected this view and saw the reason in the advance of Inuit . Poul Nørlund , who was investigating Grænlendingar graves in Herjólfsnes , in southwest Greenland, found abundant plant roots in shrouds under the permafrost and concluded from this that the summer temperatures had temporarily thawed the ground and were therefore higher than around 1921. Changes in the tree lines became partly interpreted as an indication of climate change, partly as caused by human intervention. Eduard Brückner pointed out in 1895 that earlier viticulture in areas like northern Germany, where there was none around 1900, was influenced not only by climatic, but also by economic conditions: “The expensive freight was advantageous because of the poor harvests To buy than to import wine from the south. "

The systematic investigation of a possible medieval climate anomaly - especially in Europe - was initially primarily a field of historical climatology . For in Europe in the Middle Ages, long before the beginning of instrumental measurements, conclusions about climatic conditions and their consequences could be drawn from historical documents and archaeological finds, even before palaeoclimatology began increasingly providing high-quality reconstructions from natural climate archives in the 1990s . So there are reasonably complete historical reports on summer and winter weather for the period from around 1300. It was the pioneering work in this field, for example by the English climatologist Hubert Lamb or the French historian Emmanuel Le Roy Ladurie , which provided the first comprehensive overviews of higher temperatures and social relationships for the North Atlantic region and especially Europe.

According to act. According to research, there were fewer glacier advances worldwide at the beginning of the Medieval Warm Period than in the 2nd millennium, until the current, unusual decline.

The term medieval warm period was primarily coined by Lamb's work in the 1960s and later adopted by other research fields. Lamb used it to describe global warming, which he stated regionally as up to 1 to 2 ° C and whose peak he suspected between the years 1000 and 1300. Lamb found indications of such warming mainly around the North Atlantic , while at almost the same time there were indications of relatively low temperatures for the North Pacific . He assumed the displacement of the arctic polar vortex as the cause .

Occasionally, a medieval warm period was also defined based on the extent of glaciers. In this perspective, the MWP was characterized by a presumed extensive glacier retreat between approx. 900 and 1300.

A global heat anomaly?

Scott Stine published paleoclimatological analyzes in 1994, according to which there had been periods of extreme drought lasting several centuries from around 900 to 1350 in the Sierra Nevada of California and in Patagonia . Stine suspected that hydrological deviations in the Middle Ages could have been even more significant than temperature deviations. In order to include such hydrological anomalies as well, he proposed the more general term medieval climate anomaly for the time interval .

Around the same time, Hughes and Diaz (1994) came to the conclusion in a review that no clear evidence for a uniform hemispherical or global heat anomaly existed. At this point in time, high-resolution proxy data that could have provided extensive information about the temperature curve before 1500 were only sparse. Such proxy data only became available for other regions from the mid-1990s, so that numerous reconstructions were possible for the middle and high latitudes by 2011, while the tropics and the southern hemisphere are still only covered by relatively few data series. The IPCC concluded in its summary of the status of research in 2001 also to the conclusion that there was no clear evidence of global concurrent periods of unusual heat or cold at this time.

Questions about the causes, uniqueness and potential consequences of current global warming drew some attention to a possible medieval climate anomaly as a benchmark. The social indications and consequences of a medieval heat anomaly in the North Atlantic area were taken up in popular scientific presentations. With the emergence of the media and political controversy about global warming , climate change deniers argued , especially on the basis of Lamb's description of the medieval warm period, that the temperatures of the last few decades were still within the natural fluctuation range of the climate and therefore could not be taken as evidence that the observed Warming is a result of increased greenhouse gas concentrations. The existence and the extent of a supraregional medieval warm period were also controversial in science at the beginning of the 21st century.

Term and research since 2010

Inconsistent use of the term "medieval warm period" (red bars)

Further reconstructions, for example from the Pages 2k project, with increasingly better regional coverage, meanwhile allow a clearer classification of at least the northern hemisphere temperatures. In 2013, the Intergovernmental Panel on Climate Change came to the conclusion that there were regionally and chronologically inconsistent medieval climate anomalies, which in some regions could have been as warm as in the 20th century. In the last thirty years, however, the mean temperatures were probably higher than in all equally long periods in the Middle Ages.

The use of the term “medieval warm period” or “medieval climate anomaly” is inconsistent. The American climate researcher Raymond S. Bradley saw a kind of confirmation effect at work here. Many works also use the term if “their” climate deviation is clearly outside the time window of the years 950 to 1250 and includes periods of time throughout the Middle Ages between 500 and 1500. Such episodes, referred to as the Medieval Warm Period, occasionally also include periods of time that are counted as part of the later small Ice Age in other works or to previous episodes of the early Middle Ages, often characterized as more changeable or cooler (→ pessimum of the migration period ).

Rudolf Brázdil u. a. warned in 2005 against the use of the term Medieval Warm Period in comparing climatic conditions with historical and social developments. The term is not very helpful because it covers up complexity and leads to hasty conclusions. Even the term medieval optimum can easily be misinterpreted, because it is a value-free convention in the systematics of climate fluctuations and not a positive value judgment . The term medieval climate anomaly for the various climate deviations is now the most common in science.

Climatic conditions

Temperatures

Global and hemispherical temperature course of the last 2000 years in different reconstructions, compared to temperatures measured up to and including 2004

Overall, the evaluations show a long-term slight cooling trend globally over the last 5000 years or so into the 19th century, which was interrupted in different regions in the Middle Ages by warmer intervals. A globally simultaneous, clearly definable medieval warm period is not recognizable. The slight cooling trend of the late Holocene was only ended in the last approx. Two hundred years by an unusually strong warming that is now globally synchronous . The mean northern hemisphere air temperatures of the last three decades are probably higher than the same periods in the Middle Ages. In the southern hemisphere, too, the warmest decade of at least the last 1000 years is likely to be in the late 20th and early 21st centuries.

Temperature anomalies over the past two thousand years, by continent

During the medieval climate anomaly, large parts of the middle and high latitudes of the northern hemisphere were warmer than during the subsequent Little Ice Age . This is what a large majority of paleoclimatological evidence suggests. Some regions could even have been as warm as in the past 20th century over a period of 100 years. The data are sparse for the southern hemisphere. An evaluation of 511 time series from tree rings, pollen, corals, lake and ocean sediments, glacier ice, speleothems and historical documents shows a warmer interval in Europe, North America, Asia and the Arctic for the period 830–1100. In South America and Australasia there was a warmer interval later, from 1160 to 1370.

Parts of the tropics could have been comparatively cool; a data series from shallow waters in East Antarctica shows no clear signal of a medieval warm period. In southern South America, according to a reconstruction, there were summer temperatures over several decades in the 13th and early 14th centuries, which could have reached those in the late 20th century. Data series from Africa paint a mixed picture. Overall, around the year 1000 there was a stronger warming signal in some areas of South Africa, while for Namibia, Ethiopia and Tanzania a more pronounced warming can only be seen later, from 1100. A synthesis of 111 time series confirmed for the entire southern hemisphere, based on average temperatures between 1000 and 1200, a warmer interval between 1200 and 1350, the subsequent cooling trend and the current global warming.

In the North Atlantic area, the sea ​​surface temperatures were comparatively high. However, a synthesis of 57 reconstructions of sea surface temperatures over the last two thousand years found no global medieval climate anomaly.

Hydrosphere

Changes in sea level over the past 2000 years

In addition to regional temperature anomalies , large-scale hydrological anomalies occurred.

In the period 1000–1200, southern Europe was dry compared to the mean conditions of the 20th century, while southern Scandinavia and northern central Europe were significantly drier. North-western Europe, the Balkans and the western Levant had rather humid conditions. There is evidence that fewer droughts occurred in the area of ​​influence of the East Asian monsoons compared to the period of the Little Ice Age .

There have been severe and long mega-droughts in parts of North America .

In Africa, historical sources for the Sahel zone indicate wetter conditions, but south of the Sahel it appears to have been relatively dry. In the western Congo Basin, the data available do not show a clear signal. In the east, from Ethiopia to Malawi , it was dry; From 900 on the Nile showed a very strong increase of years with low water, from around 1150 years with high water were added. In southern Africa, most of the reconstructions show rather humid conditions overall.

The sea ​​level has fluctuated by about ± 8 cm over the past two thousand years. It rose up to around the year 700, from 1000 to 1400 it sank slightly, accompanied by a global cooling of approx. 0.2 ° C over this period. Only in the 19th century did the sea level begin to rise again , the rise being much faster than during the Middle Ages.

Cryosphere

Reconstructed arctic sea ice extent in late summer since 560 (red line) and observed values ​​since 1870 (blue line, smoothed); current unsmoothed values ​​are between 3.5 and 5 million km 2

Reconstructions suggest that the Arctic sea ​​ice extent was less before 1200 than during the Little Ice Age. The minimum before the beginning of industrialization, however, fell in the period around the year 640, well before the most assumed core period of a medieval warm period.

Viewed over millennia, most glaciers showed a development that was in accordance with long-term, gradual changes in the earth's axis ( Milanković cycles ), in large parts of the northern hemisphere this corresponded to a slow advance. Over the period of individual centuries or decades, reliable statements about past, simultaneous glacier changes can only be made for individual regions. From around 900, for example, the advancement of glaciers in Alaska came to a temporary standstill, and some glaciers in the western Alps were also less active from around 760 until the 12th century. A uniform glacier retreat in the period of a medieval climate anomaly is not discernible. In the study period between 1050 and 1150, many high mountain regions of the world, such as the Alpine regions, Canada, Patagonia, Alaska and others, grew. a., the glaciers or it is, for example for the area of Baffin Bay or Southeast Greenland, no difference to the Little Ice Age. Only in the last few decades has a global glacier retreat that takes place almost simultaneously , which is very unusual for the period of the Holocene and is advancing rapidly.

causes

Changes in ocean-atmospheric circulation systems likely played an important role in the inconsistent occurrence of medieval climate anomalies. Human influences from disturbances in the atmosphere or land use were - on a global scale - of little importance. The absence of significant changes in the primary climate factors greenhouse gas concentration, solar and volcanic activity in the period 725 to 1025 prompted Bradley, Wanner and Diaz (2016) to speak of a medieval dormant period during which the climate could have been almost in a state of equilibrium.

Internal variability

The regional and temporal inconsistencies in the occurrence of climate anomalies suggests that internal variability in the climate system plays an important role, i.e. changes in the atmospheric circulation or ocean currents .

At the end of the 12th century up to 1400 there were more frequent positive phases of the North Atlantic Oscillation.

Some studies support the thesis that changes in ocean-atmospheric circulation systems, such as more frequent or more intensive occurrences of La Niña- like events, played a role. This thesis coincides with reconstructions of a relatively cool tropical Pacific. Warmer sea surface temperatures in the North Atlantic, in line with positive phases of the North Atlantic Oscillation (NAO), could explain the relatively warm climates in northern and western Europe and droughts in parts of the world. However, positive phases in the NAO are usually associated with colder climates in Greenland. More recent studies on the basis of significantly more data series indicate that the positive phases of the NAO were noticeably more frequent only around 1150–1400.

The hypothesis of the "wobbly oceanic conveyor belt " (Engl. Wobbly ocean conveyor hypothesis ) refers to periodic fluctuations (approximately 1000 to 2000 years) of the North Atlantic stream as the cause. The evaporation of 0.25 × 10 6  m³ / s of water, which is transported into the Pacific, increases the salinity of the Atlantic. The circulation of the global conveyor belt is expected to increase sharply every 1500 years to compensate for the salt content. This is associated with temperature fluctuations of the sea water in the order of 4 to 5  K , which could also change the temperatures on land. Positive phases of the Atlantic Multi-Decade Oscillation may have contributed to the droughts of the time. Why circulation systems could have changed persistently during a medieval warm period is not clear.

Volcanism

Caldera of the Samalas eruption in 1257

From the 8th to the 11th centuries there were unusually few strong volcanic eruptions. If gases and ash get into the stratosphere during volcanic eruptions , this can lead to the formation of aerosols, reduced solar radiation and the associated cooling. Eruptions in the tropics can have a global effect, while in eruptions at higher latitudes the ejected particles are less widely distributed and the effect is more regional. Between 682 and 1108 no strong eruptions were seen in the tropics and only one at higher latitudes, around the year 939 in Iceland , which may have had only a limited effect on global temperatures. Only with large eruptions in 1108, 1171, 1230 and 1257 ( eruption of the Samala ) near the equator did the phase of low volcanic activity end. The lack of volcanic influence on the climate could have contributed to relatively high temperatures in the period up to the 12th century.

Solar activity

Reconstructed solar activity over the past 2000 years

The radiation intensity of the sun seems to have fluctuated only slightly between approx. 725 and 1025; it was roughly in line with the long-term average. After a minimum of solar activity in the 11th century, the local minimum , it rose again to the previous level. The solar activity from around 1150 to 1300 was sometimes referred to as the medieval maximum . Solar activity that was below average over long periods of time can be observed at the end of the 13th century, beginning with the wolf minimum . Even if the direct influence of the sun via the intensity of its radiation was probably relatively small in the past millennium, it could have been of greater regional importance indirectly, for example via its influence on the ozone layer.

Social consequences

Ever since medieval climate anomalies have been studied, the question of their impact on societies has also arisen. Much of the work identified temporal parallels between climatic anomalies and social developments and attempted to derive causal relationships, often through the influence of the climate on the agricultural yields that were particularly important for most medieval societies.

Sometimes the medieval climatic conditions were rated as a “ climatic favor” with a view to a European high Middle Ages that was regarded as a heyday . The Canadian environmental historian Richard Hoffmann warns against an overly simplistic representation of medieval civilization as one that was brought about by harsh environmental conditions in late antiquity, flourished during favorable climatic conditions and collapsed with the beginning of the Little Ice Age. This smacks of environmental determinism . A Eurocentric perspective can lead to a distorted evaluation of the medieval climate. In tropical southern China there was a pronounced, in North America even extreme drought. The droughts of that time went hand in hand with agricultural crises, famines, conflicts and social crises. Detailed analyzes of how climate fluctuations, as differentiated from and in conjunction with other factors, could have led to social developments are still difficult and rare - despite increasingly high-resolution precipitation and temperature reconstructions.

Europe

In the period in which the medieval warm period was located, there was a real population explosion in Europe. This is attributed, among other things, to a favorable climate development. As a result of the warmer climate in Europe, there was an expansion of the agricultural economy, the cultivation of grain was now possible in areas much more northerly as well as in higher areas. Grain farming as far as Norway and in the mountains of Scotland has been proven, which was stopped again in the subsequent Little Ice Age and the associated cooling of the climate. The pests weevils and grain beetle and the human flea were detected between the 9th and 15th centuries much more common in Western and Northern Europe, warmer and humid weather could have favored her with deposits.

However, the climatic conditions were not the only reasons for the rapid increase in the population and the associated expansion with its development. Wilhelm Abel mentions agricultural progress both in the use of technical equipment, such as B. the collar for draft horses, as well as in land use and the diversification of grain. This interaction made it possible to supply a rapidly growing population with food. It is assumed that the population in Europe almost tripled between 1100 and 1400. As a result, there was an interaction between population growth and the production of new arable land. The population began with an expansion of the settlement area, in which huge forest areas were converted into arable land (e.g. in the train of the German East Settlement ). Numerous cities emerged as new centers of trade and industry that shared work with the agricultural areas.

Despite the changeable climate, the Byzantine Empire expanded and flourished in the 12th century.

For southeastern Europe and Asia Minor , the development of the agricultural Byzantine Empire , a review comes to the cautious conclusion that the climate, among many other factors, may have played a role. From the 9th to the 10th centuries, mild, humid weather favored agriculture and population growth. The climatic conditions persisted in the 11th century, but Byzantium in Anatolia came under pressure from the Seljuks and could no longer expand its agriculture there. Although the climate became more changeable in the 12th century, sometimes warmer, with dry periods in the autumn and winter months, which are particularly important for the local agriculture, there was a new expansion and social and economic boom in Byzantium in the Comnenian period , what the researchers considered Sign for the resilience of society was interpreted. Cooler summers and drier winters at the beginning of the 13th century, as well as the eruption of Samala in 1257 with the cool years that followed, could have contributed to the instability and the end of the late Byzantine Empire.

Africa

From 930–1070 and 1180–1350 there was a sharp increase in years in which the Nile carried significantly less water due to reduced rainfall in East Africa. From around 1150 onwards there were also more years of flooding. Years of low water led to famine from Egypt to the area around Lake Victoria . According to the Arab historian al-Maqrīzī (1364–1442) there was an extreme famine with cannibalism in the years 962–967. The Arab scholar Abd al-Latif al-Baghdadi reported low water around 1200 and a subsequent famine in the years 1200–1202, which he witnessed and which, according to him, killed over 100,000 people in Cairo alone .

The hill of Mapungubwe .

Around 1000 on the Limpopo , the first more complex societies and urban centers developed from small chiefdoms in southern Africa. A wetter climate in this semi-arid region could have encouraged this development. Around 1220 the elite of this society shifted their political center to nearby Mapungubwe . In this procession, changed worldviews could reveal themselves: The leadership of the state probably also drew its legitimacy from its spiritual role, to conjure up the dwindling rain from the hill. The South African archaeologist Thomas Huffman argued that the lack of rain had weakened the power of the leaders, contributed to the fragmentation of the state and thus also to the fact that the state around Mapungubwe behind Greater Zimbabwe , which from the 11th century onwards became another major regional power had developed, fell behind.

America

The Salmon Great House , near Bloomfield, New Mexico: built from 1068, possibly after drought-related migration ; after two subsequent droughts, like almost all other settlements in the region, abandoned.

For the Southwest of what is now the United States, several studies have examined a possible connection between exceptional warmth, droughts and the development of Indian tribes and cultures. For example, parallels have been identified between the decline of the Anasazi , Fremont , and Lovelock cultures and three distinct medieval droughts.

The Anasazi culture on the quadrangle of today's US states Utah, Colorado, New Mexico and Arizona was heavily dependent on corn cultivation. Sufficient rainfall in the years 700–900 and 1050–1130 allowed a sedentary lifestyle, cultural development and rapid population growth. Pueblos with large multi-story buildings were erected, including those of the Chaco Canyon culture and the Cliff palace in what is now Mesa Verde National Park . However, after periods of medieval drought in the middle of the 12th century and in the late 13th century, almost all settlements were abandoned. Archaeological evidence of a sharp rise in cannibalism was found in the mid-12th century.

In Central America, droughts from the 8th to the 11th centuries were likely one of the factors that contributed to the end of the Mayan centers in the central lowlands . Declining rainfall led to the end of the pre-Inca Empire of Tiahuanaco in what is now Bolivia; despite sophisticated irrigation systems, it was probably no longer possible to feed the population in the barren Altiplano .

Greenland

Medieval chess pieces carved from walrus teeth. Increased ice drift and the resulting more difficult walrus hunt, but also competition from Africa and Russia, could have made the ivory trade and thus the Greenland settlement unprofitable.

The extent to which climate changes contributed to the end of the medieval Scandinavian Greenland settlement (western settlement around 1350, eastern settlement in the 15th century) is still not clear. More recent work on medieval climate changes in the West and South Greenland area paints a complex picture. Overall, they indicate a period of cold climate for the period between approx. 1140 and 1220 in the area of ​​the western settlement and the walrus hunting grounds. Regionally and temporarily, there may have been cold periods before, i.e. already during the core period of the medieval climate anomaly. In the Baffin Bay and in the Disko Bay there were for the period from 1000 to 1250 caused by lower summer temperatures glacier advances that may even approach ranged to the subsequent degree from the 1400th Analyzes of lake sediments paint a partly contradicting picture: An examination of sediments from a lake near Kangerlussuaq indicates increasing temperatures between 900 and 1150, then - well before the end of the settlements - rapid cooling and then warming again, which again began around 1300 reached the 900 level and lasted into the 17th century; An analysis of mosquitos from lake sediments near the southern Narsaq indicates relatively high temperatures between 900 and 1400, with the climate becoming more changeable towards the end of this period.

It had long been assumed that the Vikings stubbornly stuck to their traditional agriculture and that their inflexibility, including against climatic fluctuations, as well as environmental degradation, had contributed to their decline. More recent excavations since the mid-2000s indicate, however, that from around 1300 onwards the sea as a source of food predominated over the previously more important agriculture and animal husbandry. Researchers interpret this as an adaptation to lower winter temperatures.

Trade probably played a crucial role in the Greenland settlement. The settlers had to import important goods such as iron. The export of the coveted walrus ivory , which they captured on regular hunting expeditions to Disko Bay, was an important economic factor. More frequent and more intense storms, falling temperatures and, in particular, increased ice drift along the west coast - not only a regional cooling, but also increased ice drift from the Greenland Sea and Denmark Strait may have been the cause - could have significantly impaired hunting and trade relations. But also increasing competition from Russia (walrus) and Africa (elephants), which pushed onto the European market and led to falling ivory prices, and a decrease in demand for ivory in the course of late medieval crises could have ruined the economic basis of the settlement. Confrontation with the Inuit is also still considered a possible factor.

Controversy over comparing it to current warming

Medieval warm periods are sometimes cited by climate deniers as supposed evidence that it is by no means certain that the current warming is caused by greenhouse gases emitted by humans. Since the greenhouse gas concentrations in the Middle Ages were not higher than before or after, only other causes could have been responsible for warm periods at that time. They argue that these causes alone could explain 20th century warming. They ignore the fact that medieval warm periods were probably only regional phenomena. Even the well-known scientific justifications that the factors that were effective at the time could not explain today's warming are left out of this argument.

In doing so, they are making a logical fallacy by arguing that some factor that was solely responsible for a change in the past must also be today. Just as the occurrence of natural forest fires in the past does not rule out that forest fires can also be triggered by arson, natural medieval warm periods are no proof against anthropogenic warming. In climate research, in addition to the changes in greenhouse gas concentrations - currently caused by humans - the study of other factors that have an impact on the history of the climate also play a major role . Of all the known factors that can cause global warming, only the concentration of greenhouse gases changed so much in the 20th century that it can essentially explain the observed warming.

Occasionally, even with Eurocentric recourse to a medieval warm period, it is claimed that warm phases are generally favorable times. When the discussion about the medieval warm period began in the mid-1960s, it was a phase of global cooling that lasted until the mid-1970s. A warming to the level of the medieval warm period at that time would have been beneficial in some regions. However, there is much evidence that by the end of the 20th century it was warmer in Europe than during the medieval warm period. Climate historians point out that the crisis consequences of past climate fluctuations, such as the medieval climate anomalies, can rather serve as parables for the dangers of global warming or that it is the rates of change and variability of the last millennia that call for climate protection.

If massive reductions in greenhouse gas emissions were not to take place, the global average temperatures expected with a high degree of probability at the end of the 21st century would be higher than they have been over the last several hundred thousand years and possibly even higher than they have ever been since Homo sapiens existed . The rapid global warming observed at the end of the last ice age was a warming of about one degree Celsius per 1000 years. Even if the 2-degree target were reached (which is considered unlikely), global warming expected by the end of the 21st century would be an order of magnitude faster.

The discussion about the extent and consequences of the current and the likely expected man-made global warming thus relates to a historically unique process, both in terms of the speed and extent of the warming, for which empirical values ​​are largely lacking and for which - as due to a large number of climate proxy is proven - also from a geological and paleoclimatological point of view no equivalent is known.

See also

literature

Web links

Commons : Medieval Warm Period  - Album with pictures, videos and audio files
  • On klimafakten.de the claim is refuted that it was globally warmer than today during the Medieval Warm Period.

Individual evidence

  1. ↑ a b c PAGES 2k Consortium: Consistent multidecadal variability in global temperature reconstructions and simulations over the Common Era . In: Nature Geoscience . July 24, 2019, doi : 10.1038 / s41561-019-0400-0 .
  2. ↑ a b c Raphael Neukom, Nathan Steiger, Juan José Gómez-Navarro, Jianghao Wang, Johannes P. Werner: No evidence for globally coherent warm and cold periods over the preindustrial Common Era . In: Nature . July 24, 2019, doi : 10.1038 / s41586-019-1401-2 .
  3. ↑ a b c Valérie Masson-Delmotte u. a .: Information from Paleoclimate Archives . In: IPCC (Ed.): Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change . 2013, 5.3.5, p. 409-414 .
  4. ↑ Robert Tardif, Gregory J. Hakim, Walter A. Perkins, Kaleb A. Horlick, Michael P. Erb, Julien Emile-Geay, David M. Anderson, Eric J. Steig, David Noone: Last Millennium Reanalysis with an expanded proxy database and seasonal proxy modeling . In: Climate of the Past . July 2019, doi : 10.5194 / cp-15-1251-2019 .
  5. ↑ a b Shaun A. Marcott: A Reconstruction of Regional and Global Temperature for the Past 11,300 Years . In: Science . tape 339 , March 8, 2013, doi : 10.1126 / science.1228026 .
  6. ↑ a b c d Eli Kintisch: Why did Greenland's Vikings disappear? In: Science . November 10, 2016, doi : 10.1126 / science.aal0363 .
  7. ^ Franz Mauelshagen: Climate history of the modern age . Scientific Book Society, Darmstadt 2010, ISBN 978-3-534-21024-4 , pp. 25 .
  8. ^ Eduard Brückner: Climate fluctuations since 1700 (1890) . In: Nico Stehr and Hans von Storch (eds.): Eduard Brückner: The history of our climate: climate fluctuations and climate effects . 2008, p. 95.96 .
  9. ↑ Niels Lynnerup: The Human Skeletons from Herjólfsnes . In: Journal of the North Atlantic . 2009, p. 23 .
  10. ^ Eduard Brückner: The Influence of Climate Variations on Harvest Yields and Grain Prices in Europe (1895) . In: Nico Stehr and Hans von Storch (eds.): Eduard Brückner: The history of our climate: climate fluctuations and climate effects . 2008, p. 172 .
  11. ↑ a b c d Rudolf Brázdil, Christian Pfister, Heinz Wanner, Hans von Storch and Juerg Luterbacher: Historical Climatology in Europe . In: Climatic Change . 2005, Chapter 5.3 Defining the Medieval Warm Period and the Little Ice Age ( 144.122.146.136 [PDF]).
  12. ↑ a b Olga N. Solomina u. a .: Glacier fluctuations during the past 2000 years . In: Quaternary Science Reviews . 2016, doi : 10.1016 / j.quascirev.2016.04.008 .
  13. ↑ Hubert Lamb: The Medieval Warm Epoch and its Sequel . In: Palaeogeography, Palaeoclimatology, Palaeoecology . January 1965, doi : 10.1016 / 0031-0182 (65) 90004-0 ( psu.edu [PDF]).
  14. ↑ Hubert Lamb: Climate and cultural history: the influence of the weather on the course of history . Reinbek 1989, p. 189-206 .
  15. ^ Scott Stine: Extreme and persistent drought in California and Patagonia during mediaeval time . In: Nature . tape 369 , June 16, 1994, pp. 546-549 , doi : 10.1038 / 369546a0 .
  16. ↑ a b c d e f g Henry F. Diaz: Spatial and Temporal Characteristics of Climate in Medieval Times Revisited . In: Bulletin of the American Meteorological Society . November 2011, doi : 10.1175 / BAMS-D-10-05003.1 ( climates.com [PDF]).
  17. ^ A b Thomas J. Crowley and Thomas S. Lowery: How Warm Was the Medieval Warm Period? In: AMBIO: A Journal of the Human Environment . tape 29 , no. 1 , February 2000, p. 51-54 , doi : 10.1579 / 0044-7447-29.1.51 .
  18. ^ A b Raymond S. Bradley: Climate of the Last Millennium . Presentation, Holocene Working Group Workshop, Bjerknes Center for Climate Research. August 2003: "... numerous studies have used the term to frame whatever climatic anomaly might have occurred at some time within the more broadly define Medieval period (AD 500–1500) - even if the record is unrelated to temperature. This has led to a classic reinforcement syndrome, in which ill-defined evidence for adverse range of climatic anomalies - occurring over a wide range of time intervals has created the notion that the MWE [Medieval Warm Epoch] was a definitive global phenomenon. However, a careful examination of long-term paleoclimatic data shows that this is not the case. "
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