Climate anomaly 536-550

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The cold anomaly 536-550 in the context of global temperatures since the beginning of the era

The 536-550 climate anomaly was a phase of relatively cool temperatures and other climatic anomalies in large parts of the northern hemisphere. It began with weak solar radiation and a marked cooling, the weather anomaly of 535/536 , and lasted until the late 540s. Droughts occurred in some regions. This climate anomaly was probably caused by several volcanic eruptions, the first of which is dated to 535 or 536. The climate event falls within a longer period rather changeable and cool climate, especially in Europe and in the North Atlantic region (→  Pessimum the migration period ), and it marks the beginning of a Late Antique Little Ice Age ( Little Ice Age of the Late Antiquity ) period of 536 to 660 above.

Contemporary reports

In 1983 Richard Stothers and Michael Rampino, two scientists at NASA's Goddard Institute for Space Research, published a summary of ancient volcanic eruptions documented in historical Mediterranean sources. Also on their list was a persistent haze of dust or dry fog, reported by ancient authors and which must have appeared in the years 536-537:

The historians Prokopios , Michael the Syrian and Flavius ​​Cassiodorus report for the year 536 low temperatures with snow in summer as well as bad harvests. Even at noon, the sun only cast a dull shadow and the circumstances that usually accompany a solar eclipse lasted for almost a year.

“The sun, without any radiance, shone like the moon all year round and gave the impression that it was almost completely darkened. Besides, her light was not pure and as usual. But since the sign was seen, neither war nor plague nor any other evil that brings people to death. "

- Prokopios of Caesarea

The Eastern Roman official Johannes Lydos wrote from Constantinople that the sun had been darkened for almost a year and the harvest had been destroyed. Bishop Zacharias of Mytilene , who attended a synod in Constantinople in 536, reports that the sun and moon were darkened from March 536 to June 537, from stormy seas and harsh winters. Contemporary Chinese and Indonesian sources also speak of unusual atmospheric events, so that it was apparently a global phenomenon.

Since a real solar eclipse can never last longer than a few minutes, Prokop must have meant an eclipse of the sun that had other causes in his comparison. The most likely cause for months or years of attenuation in sunlight are dust particles or aerosols that have entered the upper atmosphere either through volcanism or the impact of a smaller celestial body on Earth.

With two popular science books published in 1999, larger circles became aware of the ancient reports.

According to a more recent thesis, the Rök rune stone, erected before or around 800, could recall a mythical battle between heat and cold or life and death nine generations before that time, in which the Fenris Wolf devoured the sun, which was subsequently reborn. Such an event could be the weather anomaly of 535/536 with its extreme cold (a so-called. Fimbulvetr , Fimbulwinter have been). Because of the extreme cold and bad harvests, around half of the inhabitants of Scandinavia died. The region around Rök was also affected. Here fertile arable land turned back into forest. The erection of the rune stone around 800 could have been in a temporal connection with unusual sky redness as a result of a magnetic storm or gamma-ray outbreak in 775 or the solar eclipse in 810.

Scientific evidence

An analysis of tree rings by the dendrochronologist Mike Baillie of Queen's University Belfast shows abnormally low growth in Irish oak for 536 and - after an incomplete recovery - a further sharp decline in 542. Similar patterns can also be seen in annual rings of various tree species in Sweden , Finland and California's Sierra Nevada as well as the Alerce in southern Chile . In a 2015 comparison of cold events over the past 1500 years in the northern hemisphere based on tree ring data, eruption 535/536 was followed by a cold anomaly of around −1.4 ° C, the second largest in the reconstruction. In Europe, summer temperatures of 536 and 541 were 1.5–2.7 ° C colder than in the previous 30-year period; the summers of the decade 536-545 were, on average, possibly the coldest of the past 1500 years.

An analysis of paleoclimatological global reconstructions, considering 50-year periods, shows in many, but not all regions around the mid-550s, temperatures are cooler than the mean of the last two thousand years. Overall, probably more than half of the earth's surface was affected.

Investigations of the δ13C isotope ratio were used to reconstruct summer solar radiation in the 6th century on the subfossil remains of Scandinavian Scots pine trees, the growth of which was probably not limited by a lack of moisture or temperatures . The reconstruction indicates a strong clouding of the atmosphere and, with −50 W / m 2 , considerably reduced irradiation in the years 536 and 541–544.

In 2016, an interdisciplinary group led by the climate historian Ulf Büntgen proposed that the cold period beginning in 536, which lasted until the middle of the 7th century in parts of the northern hemisphere as a result of ocean and sea ice feedback , was called the Late Antique Little Ice Age (LALIA) to call.

Possible causes

The climate anomaly from 536 onwards was probably caused by sulphate aerosols, ashes and dust, which clouded the atmosphere and reduced solar radiation . With some certainty, these suspended matter came from two volcanic eruptions, one in the northern hemisphere in 536 and the Tierra Blanca Joven eruption of the Ilopango ( El Salvador ) in 540, which caused a volcanic winter . Other volcanic eruptions and an impact winter following a comet impact have also been discussed as possible causes.

There are no known contemporary reports pointing to the actual cause. It is therefore to be assumed that the triggering event took place in a region of the world that was remote from the Eurasian and African written cultures of the time, but not necessarily uninhabited before the event, and therefore did not flow into the traditional records of this time.

volcanic eruptions

Volcanic radiative forcing over the past 2500 years. Eruptions 536 and 540 are now considered the likely cause of the weather anomaly from 535/536.

As early as 1857, the philologist Valentin Seibel interpreted the veil of dust that Prokop had reported as an atmospheric cloudiness caused by volcanic eruptions. Stothers and Rampino's work, which established modern exploration of the climate anomaly in the early 1980s, saw evidence of a volcanic cause in the ancient reports and in the acidic layers of Arctic ice cores. Analyzes of ice cores from Antarctica carried out at the end of the 2000s reveal sulfate maxima at 542, which “fits very well with the maximum at 536 AD in Greenland” and suggests a huge volcanic eruption near the equator. In 2015, the ice cores, which use sulfate concentrations to indicate volcanic eruptions, were precisely synchronized with tree ring archives that are used for temperature reconstructions. A reconstruction of the radiative forcing of the volcanic eruptions was also possible. The authors of the work concluded that the cold anomaly must have been mainly caused by two volcanic eruptions, one in high latitudes in the northern hemisphere and, four years later, one in the tropics.

Northern Hemisphere Eruption 536

In an ice core extracted at Colle Gnifetti in the Swiss Alps , a group of scientists found traces of rhyolitic tephra and volcanic glass , suggesting an Icelandic volcano as the most likely source. This eruption recorded in the glacial ice matches that of 536. The volcanologist Michael Sigl suspects that the eruption of 536 occurred in North America.

Tavurvur (Papua New Guinea) or Krakatau (Indonesia)

As early as 1984, the astronomer and climate researcher Richard Stothers (1939–2011) attributed the climate change of 536 to an eruption of the Tavurvur volcano near Rabaul in Papua New Guinea .

1999 suggested the science journalist David Keys, supported by the work of the American volcanologist Ken Wohletz before, that climate disturbances caused by the eruption of between Sumatra and Java lying volcano proto-Krakatau, a precursor of today's Krakatoa may have been caused. According to a controversial theory, "Krakatau before 535 could have been a high mountain (approx. 2000 m)", which "largely disappeared into the sea in a super-eruption" and separated Sumatra and Java, which it had previously been part of.

Geochemical, volcanological and radiocarbon-based evidence clearly speak against a Proto-Krakatu or the Tavurvur as a trigger.

Ilopango (El Salvador)

The volcanologist Robert Dull published research results in 2001, according to which he was able to date the last huge eruption, the Tierra Blanca Joven eruption, of the Ilopango in El Salvador with the help of the radiocarbon method to a time between 408 and 536 AD. Due to the temporal and geographical location as well as the size of this eruption, he considered it to be the cause of the weather anomaly of 535/536.

A simulation from 2016 simulated the effect of two volcanic eruptions of the presumed strength in 536 and 540. The simulated climatic effects agreed very well with the assumption of an eruption of the Ilopango as the second volcanic event in 540.

In 2019, three tree trunks found in the pyroclasts of the Ilopangos were able to narrow the eruption period to 500-540. The magnitude of 7.0 and sulfur emissions of 9–90 million tons make the eruption probably the largest in Central America in the last 84,000 years. During this period, the Greenland and Antarctic ice cores only saw the signal of a tropical eruption in 540. According to Dull and co-authors, this proves that the second, tropical eruption that caused the climate anomaly around 540 was that of the Ilopango.

Cosmic small bodies

Compared to the Tunguska event of 1908, an asteroid or comet that triggered the climate changes from 536 onwards must have been many times larger. The size of the asteroid should have been about 500 meters and it should have exploded at a height of 20 kilometers.

The dendrochronologist Mike Baillie, who had identified reduced growth by 536 and 540 in tree ring rows from Ireland, Europe and North America, suspected in 1999 that a comet or other small cosmic body had caused the climate anomaly. Baillie distanced himself from this explanation by more precisely dating new rows of tree rings and layers of volcanic sulfates from ice cores.

Other research since the 2000s has attributed the climate changes to the possible impact of multiple comet fragments or the combination of a volcanic eruption and a meteorite. The theory of the impact of small cosmic bodies is supported by finds of tiny spheres in the Greenland ice, which consist of condensates of evaporated rock material ( spherules ). The double crater discovered in 2006 by the Holocene Impact Working Group research group in the Gulf of Carpentaria off Australia and a smaller one in the North Sea off Norway are viewed as possible impact sites . The impact of a small body as the main cause of the climate anomaly was considered unlikely at the end of the 2010s.

Possible consequences

The mostly very cold years up to 550 caused bad harvests in northern and high-altitude regions. In addition, even in the Mediterranean region, where plant growth is not limited by temperatures to the same extent, the reduced solar radiation itself could have reduced the photosynthetic capacity of the plants.

Numerous parallels to significant historical events of the following decades were drawn and hypotheses about causal connections were made. In 2020, the American anthropologist Peter N. Peregrine systematically examined whether crises had occurred particularly often during that time. Using the climate episode as a naturalistic quasi-experiment , he examined the connection between the event or the extent of the cold anomaly 536-546 and social upheavals in 20 societies in Central and North America, Europe, North Africa and Asia. To do this, he used an index of social change ( Social Change Index ), which quantifies statements about changes in demographic development, migration, famines and diseases, conflicts and social order. He found a significant deviation in the rate of social change compared to the decades before the climatic event, but it did not correlate regionally with the extent of the cooling. Peregrine interpreted regional deviations as an indication of the lower vulnerability of some societies.

For example, there are considerations that the movement of associations known as Avars in the 550s from the area north of the Black Sea in the direction of the Eastern Roman Empire, which is often attributed to the pressure of Kök Turks , is also related to droughts in previous years could.

The Justinian plague broke out for the first time in the Mediterranean world between 541 and 544 . Some researchers argue that the sudden change in weather conditions disturbed rodents, which are the reservoir for the plague pathogen, and brought them into contact with other rodents and humans, who then spread the pathogen. The cooler climate could also have allowed the plague to spread across the Mediterranean to Europe, where it encountered a population weakened by food and possibly vitamin D deficiencies . Italy was also devastated by the Gothic Wars (535–552 / 562). After these events, the final decline of ancient civilization began in Italy .

Bracteates from the hoard find in Darum, western Jutland , 6th century.

Climate simulations suggest particularly severe crop losses in Scandinavia and the Baltic States. In Scandinavia many settlements were abandoned in the 6th century, in some regions 75% and more, on Öland all of the 1,300 houses discovered so far were apparently abandoned. The climate anomaly lies at the transition to the Swedish Vendelzeit . The Danish archaeologist Morten Axboe sees a connection between the accumulation of hoard finds , which are dated to the first half of the 6th century, and the climatic episode from 536 onwards. The hoards often contained gold bracteates , thin, one-sidedly shaped platelets that were probably powerful Protective amulets were used. According to Axbo, particularly valuable objects were sacrificed in order to let the dark and weak sun shine brightly again. In addition, the hoard could have been set up at a time of turmoil and turmoil, which made people leave home and yard and hide their valuable belongings in order to recover them when they return. Some authors suspect that the cold event in the Fimbulwinter of the Nordic Ragnarök legend was processed.

However, the social impacts were inconsistent and dependent on the vulnerability of the regions affected. The cold anomaly does not seem to have had any impact on the settlements in Northern Norway, which are more dependent on marine resources. And on the Arabian Peninsula, the unusually heavy rainfall may have increased agricultural yields and thus promoted the rise of Islam.

See also

literature

  • Timothy P. Newfield: The Climate Downturn of 536-50 . In: The Palgrave Handbook of Climate History . Palgrave Macmillan, ISBN 978-1-137-43020-5 , pp. 447-493 , doi : 10.1057 / 978-1-137-43020-5_32 .
  • Ulf Büntgen et al .: Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD . In: Nature Geoscience 9, 2016, 231-236.
  • Joel D. Gunn (Ed.): The Years without Summer. Tracing AD 536 and its Aftermath. Archaeopress, Oxford 2000, ISBN 1-84171-074-1 ( BAR. International Series 872).
  • David Keys: When the sun went out. 535 AD: A natural disaster changes the world. Karl Blessing Verlag, Munich 1999, ISBN 3-89667-035-2 . English original edition: David Keys: Catastrophe. A Quest for the Origins of the Modern World. Ballantine Books, New York NY 1999, ISBN 0-345-40876-4 .

Web links

Individual evidence

  1. ^ 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. ↑ Timothy P. Newfield: The Climate Downturn of 536-50 . In: The Palgrave Handbook of Climate History . Palgrave Macmillan, 2018, ISBN 978-1-137-43020-5 , pp. 447-493 , doi : 10.1057 / 978-1-137-43020-5_32 .
  3. ↑ a b Markus Stoffel, Myriam Khodri, Christophe Corona, Sébastien Guillet, Virginie Poulain, Slimane Bekki, Joël Guiot, Brian H. Luckman, Clive Oppenheimer, Nicolas Lebas, Martin Beniston, Valérie Masson-Delmotte : Estimates of volcanic-induced cooling in the Northern Hemisphere over the past 1,500 years . In: Nature Geoscience . October 2015, doi : 10.1038 / ngeo2526 .
  4. ↑ Samuli Helama, Phil D Jones, Keith R Briffa: Dark Ages Cold Period: A literature review and directions for future research . In: The Holocene . February 2017, doi : 10.1177 / 0959683617693898 .
  5. ^ Richard B. Stothers, Michael R. Rampino: Volcanic eruptions in the Mediterranean before AD 630 from written and archaeological sources . In: Journal of Geophysical Research - Solid Earth . September 1983, doi : 10.1029 / JB088iB08p06357 .
  6. ↑ a b Antti Arjava: The Mystery Cloud of 536 CE in the Mediterranean Sources . In: Dumbarton Oaks Papers . tape 59 , 2005, pp. 73-94 , doi : 10.2307 / 4128751 .
  7. ^ Prokopios, Historien IV 14 (German translation from: Vandalenkriege. Greek-German , translated by Otto Veh , Munich 1971, p. 263).
  8. ↑ Michael Sigl, M. Winstrup, JR McConnell, KC Welten, G. Plunkett, F. Ludlow, U. Büntgen, M. Caffee, N. Chellman, D. Dahl-Jensen, H. Fischer, S. Kipfstuhl, C. Kostick, OJ Maselli, F. Mekhaldi, R. Mulvaney, R. Muscheler, DR Pasteris, JR Pilcher, M. Salzer, S. Schüpbach, JP Steffensen, BM Vinther, TE Woodruff: Timing and climate forcing of volcanic eruptions for the past 2,500 years - Extended Data Table 3 Historical documentary evidence for key volcanic eruption age markers 536-939 CE . In: Nature . No. 523 , July 2015, doi : 10.1038 / nature14565 ( nature.com ).
  9. ↑ a b Mike Baillie: Exodus to Arthur. Catastrophic Encounters with Comets . = Batsford, London 1999, ISBN 0-7134-8352-0 .
  10. ↑ a b David Keys: Catastrophe. A Quest for the Origins of the Modern World . Ballantine Books, New York 1999, ISBN 0-345-40876-4 . See also: Ken Wohletz: Were the Dark Ages Triggered by Volcano-Related Climate Changes in the 6th Century? (If so what Krakatau volcano the culprit?). Los Alamos National Laboratory, 2000, accessed June 19, 2020 .
  11. ↑ Per Holmberg, Bo Gräslund, Olof Sundqvist, Henrik Williams: The Rök Runestone and the End of the World . In: Futhark: International Journal of Runic Studies . tape 9-10 , 2020, ISSN  1892-0950 , pp. 7-38 , doi : 10.33063 / diva-401040 (open access).
  12. ↑ a b c d Michael Sigl, M. Winstrup, JR McConnell, KC Welten, G. Plunkett, F. Ludlow, U. Büntgen, M. Caffee, N. Chellman, D. Dahl-Jensen, H. Fischer, S. Kipfstuhl, C. Kostick, OJ Maselli, F. Mekhaldi, R. Mulvaney, R. Muscheler, DR Pasteris, JR Pilcher, M. Salzer, S. Schüpbach, JP Steffensen, BM Vinther, TE Woodruff: Timing and climate forcing of volcanic eruptions for the past 2,500 years . In: Nature . No. 523 , July 2015, doi : 10.1038 / nature14565 . Press release: Researchers find new evidence that large eruptions were responsible for cold temperature extremes recorded since early Roman times. Desert Research Institute, July 8, 2015, archived from the original on July 16, 2015 ; accessed on August 9, 2015 .
  13. ^ 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 .
  14. ↑ a b c Samuli Helama, Laura Arppe, Joonas Uusitalo, Jari Holopainen, Hanna M. Mäkelä, Harri Mäkinen, Kari Mielikäinen, Pekka Nöjd, Raimo Sutinen, Jussi-Pekka Taavitsainen, Mauri Timonen, Markku Oinonen: Volcanic dust veils tree-ring isotopes linked to reduced irradiance, primary production and human health . In: Scientific Reports . No. 1339 , 2018, doi : 10.1038 / s41598-018-19760-w (open access).
  15. ↑ a b Ulf Büntgen, Vladimir S. Myglan, Fredrik Charpentier Ljungqvist, Michael McCormick, Nicola Di Cosmo, Michael Sigl, Johann Jungclaus, Sebastian Wagner, Paul J. Krusic, Jan Esper Jed O. Kaplan, Michiel AC de Vaan, Jürg Kirdyanov : Cooling and societal change during the Late Antique Little Ice Age from 536 to around 660 AD . In: Nature Geoscience . 2016, p. 231-236 , doi : 10.1038 / ngeo2652 . See also about the work:
  16. ↑ Valentin Seibel: The great plague in Justinian's time. and the unusual natural events that precede and accompany it. A contribution to the history of the sixth century Christian calendar . Printed by A. Kranzle'schen Officin, Dillingen 1857, II. Atmospheric phenomena ( verbodengeschriften.nl ).
  17. ^ A b c John Moreland: AD536 - Back to Nature? In: Acta Archaeologica . January 2019, doi : 10.1111 / j.1600-0390.2018.12194.x .
  18. ↑ LB Larsen et al. a .: New ice core evidence for a volcanic cause of the AD 536 dust veil . In: Geophysical Research Letters . tape 35 , L04708, doi : 10.1029 / 2007GL032450 . Blog post about it: Gavin A. Schmidt : What was going on in 536 AD? In: scilogs.de - klimalounge. March 25, 2008, accessed June 19, 2020 .
  19. ↑ Christopher P. Loveluck, Michael McCormick, Nicole E. Spaulding, Heather Clifford, Michael J. Handley, Laura Hartman, Helene Hoffmann, Elena V. Korotkikh, Andrei V. Kurbatov, Alexander F. More, Sharon B. Sneed, Paul A. Mayewski: Alpine ice-core evidence for the transformation of the European monetary system, AD 640-670 . In: Antiquity . tape 92 , no. 366 , December 2018, ISSN  0003-598X , p. 1571–1585 , Supplementary material - S1 data on Colle Gnifetti tephra from AD 536 volcanic event - L. Hartman & AV Kurbatov , doi : 10.15184 / aqy.2018.110 ( cambridge.org [accessed April 14, 2020]). Popular scientific article on Loveluck et al. a. (2018): Spectrum of Science. Worst year for Europeans? SdW , November 19, 2018
  20. ↑ Ann Gibbons: Why 536 was 'the worst year to be alive'. AAAS , November 15, 2018.
  21. ^ Richard Blair Stothers: Mystery cloud of AD 536 . In: Nature . tape 307 , 1984, pp. 344-345 , doi : 10.1038 / 307344a0 .
  22. ↑ a b Robert A. Dull, John R. Southon, Steffen Kutterolf, Kevin J. Anchukaitis, Armin Freundt, David B. Wahl, Payson Sheets, Paul Amaroli, Walter Hernandez, Michael C. Wiemann, Clive Oppenheimer: Radiocarbon and geologic evidence reveal Ilopango volcano as source of the colossal 'mystery' eruption of 539/40 CE . In: Quaternary Science Reviews . tape 222 , 2019, doi : 10.1016 / j.quascirev.2019.07.037 .
  23. ↑ Robert A. Dull, John R. Southon and Payson Sheets: Volcanism, Ecology and Culture: A Reassessment of the Volcán Ilopango Tbj eruption in the Southern Maya Realm , in: Latin American Antiquity Vol. 12, No. 1 (March 2001), pp. 25-44, JSTOR 971755
  24. ↑ News about FUNDAR's Investigations and other activities. Fundación Nacional de Arqueología de El Salvador (FUNDAR), 2012, archived from the original on September 24, 2015 ; accessed on April 30, 2016 .
  25. ↑ a b Matthew Toohey et al. a .: Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages . In: Climatic Change . 2016, doi : 10.1007 / s10584-016-1648-7 . See also: Two volcanoes trigger crises in late antiquity. On: idw-online.de from April 19, 2016
  26. ↑ Dallas H. Abbott, Dee Breger, Pierre E. Biscaye, John A. Barron, Robert A. Juhl, Patrick McCafferty: What caused terrestrial dust loading and climate downturns between AD 533 and 540? In: GSA Special Papers . 2014, doi : 10.1130 / 2014.2505 (23) . For a conference contribution by Abbott, who had already presented the hypothesis, see: Comet smashes triggered ancient famine . In: New Scientist 2689 (January 7, 2009), p. 9, and geologists explain the greatest catastrophe of the Middle Ages . spiegel.de, December 21, 2010
  27. ↑ See seshatdatabank.info.
  28. ^ Peter N. Peregrine: Climate and social change at the start of the Late Antique Little Ice Age . In: The Holocene . 2020, doi : 10.1177 / 095968362094107 .
  29. ↑ Mischa Meier : History of the Great Migration - Europe, Asia and Africa from the 3rd to the 8th century AD. C.-H. Beck, 2019, ISBN 978-3-406-73959-0 , pp. 813, 953-973, 995 .
  30. ↑ Michael McCormick, Ulf Büntgen, Mark A. Cane, Edward R. Cook, Kyle Harper, Peter Huybers, Thomas Litt, Sturt W. Manning, Paul Andrew Mayewski, Alexander FM More, Kurt Nicolussi, Willy Tegel: Climate Change during and after the Roman Empire: Reconstructing the Past from Scientifc and Historical Evidence . In: Journal of Interdisciplinary History . 2012, doi : 10.1162 / JINH_a_00379 .
  31. ↑ Timothy P. Newfield: Mysterious and Mortiferous Clouds: The Climate Cooling and Disease Burden of Late Antiquity . In: Late Antique Archeology . tape 12 , no. 1 , October 2016, doi : 10.1163 / 22134522-12340068 .
  32. ↑ a b c Morten Axboe: Amulet Pendants and a Darkened Sun . In: KVHAA Konferenser . tape 51 . Stockholm 2001 ( academia.edu ).
  33. ↑ a b Bo Gräslund and Neil Price: Twilight of the gods? The 'dust veil event' of AD 536 in critical perspective . In: Antiquity . tape 86 , no. 332 , January 2012, doi : 10.1017 / S0003598X00062852 ( Html ).
  34. ↑ A detailed and critical consideration: Mathias Nordvig and Felix Riede: Are There Echoes of the ad 536 Event in the Viking Ragnarok Myth? A critical appraisal . In: Environment and History . 2018, doi : 10.3197 / 096734018X15137949591981 .
  35. ^ Mats Widgren: Climate and causation in the Swedish Iron Age . In: Danish Journal of Geography . tape 112 , no. 2 , December 2012, doi : 10.1080 / 00167223.2012.741886 ( PDF (working version ) ).