Little ice age

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The painting IJsvermaak (" Ice Pleasure ") by Hendrick Avercamp shows people on a frozen canal in the Netherlands in the cold winter of 1608. Today, however, the canals are mostly ice-free in winter. Artistic representations of such scenes are only known from the period between 1565 and 1640.

The Little Ice Age was a period of relatively cool climates from the early 15th century to the 19th century. It was different regionally and temporally. Only during a core period, from the end of the 16th century to the last third of the 17th century, can a cooler phase be identified globally.

The Little Ice Age is part of more recent climatic history and the subject of research in historical climatology . In today's climate debate, it is considered the classic example of natural climate variation characterized by short-term fluctuations .

Observations

The Little Ice Age was preceded by a period known as the Medieval Warm Age . The middle of the 15th century is often given as the beginning of the Little Ice Age, from which regionally and chronologically different cooler conditions occurred. A globally cooler phase can only be identified in a later period, from the end of the 16th century to the last quarter of the 17th century. Even in this core period of the Little Ice Age, there were still considerable fluctuations: In the northern hemisphere, the periods from around 1570 to 1630 and 1675 to 1715 were particularly cold. In the southern hemisphere, the focus was shortly after the beginning and in the second half of the 17th century. Depending on the region and time, the temperatures during the Little Ice Age in the period 1400–1800 were around 0.1 K lower worldwide  than during the previous centuries 1000 -1400. Over shorter periods of a few decades, the temperatures could have been down to 0.8 K, in some European regions 1 to 2 K lower.

During the Little Ice Age, very cold, long winters and rainy, cool summers often occurred . In the middle of the 17th century and also until the middle of the 19th century, glaciers penetrated the Alps twice and destroyed farms and villages. Glacier growth during the Little Ice Age was the strongest since the long-lasting glaciation of the last Ice Age.

Various historical reports and events are associated with the Little Ice Age and are used to illustrate it:

  • Due to his bird watching, the lawyer and ornithologist Marcus zum Lamm (1544–1606) , who worked at the court of Heidelberg, registered the increasing change in the climate around 1580 and advised his sovereign, Count Palatine Johann Kasimir (Palatinate-Simmern) , to put up food supplies for them Population.
  • In France, the drop in temperature led to hungry winters - prolonged low temperatures that made sowing almost impossible and largely ruined harvests: 1659/60, 1694/95 and 1708/09. The climax was the cold period from 1692 to 1698, which was also often referred to as the "Little Ice Age".
Temperature anomaly winter 1708/1709
  • In London , a “ frost fair” took place several times on the frozen Thames - this was also made possible by the different flow conditions of the river at the time. Even in the Middle Ages, the Thames froze over several times.
  • In the winter of 1780, the port of New York could be safely crossed on the ice. On the Great Lakes in North America, the ice sometimes stayed until June.

The last mark of the Little Ice Age is seen as the Great Famine in Ireland 1845–1852. The rise in mean temperatures is skewed through the year without a summer (1816) and some abnormally cool years thereafter; The cause was the eruption of the Tambora volcano on the island of Sumbawa east of Java in 1815.

From around 1850 it became warmer worldwide; this is considered to be the end of the Little Ice Age. Since then, global mean temperatures close to the surface have risen by around 1 K and are therefore probably warmer than they have been for at least 1300 years (based on a period of 50 years).

Since the middle of the 19th century, a clear decline in glaciers has been observed almost worldwide (see glacier retreat since 1850 ).

Climate witnesses

Temperature history over the past 1000 years, reconstructed from various sources. The red line marks the reconstructed course in the northern hemisphere. The black rise on the right is measured instrumentally.

The Little Ice Age is documented in many natural climate archives by a series of proxy data (indirect climate data), such as:

Some paintings from that time can also be used as indicators of past climatic conditions. The depictions of winter landscapes by Pieter Brueghel , Hendrick Avercamps and other Dutch masters from the 16th and 17th centuries are known for this. Many of them show scenes in which frozen canals can be seen in the Netherlands. Vivaldi's winter concert with the accompanying sonnet addresses e.g. B. ice skating on the lagoon of Venice . This period ended in the 19th century, the (average) temperatures have been higher since then and there have been fewer observations that the above-mentioned canals or Venice's lagoon were frozen over.

Paintings from the early Manchurian Qing dynasty (from 1644) show snow landscapes. The collapse of the preceding Ming dynasty was caused by crop failures as a result of repeated droughts since the 16th century and particularly an extreme drought from 1638–1641. The droughts were caused by changes in the monsoons during a chronically documented cold spell, possibly caused by volcanic eruptions. Comparable droughts have only reappeared since the second half of the 20th century.

Spatial and temporal occurrence

Temperature anomalies over the past two thousand years, by continent

When the first indications of the Little Ice Age became apparent, it was assumed that there was a global climate phenomenon. Today this is partly seen differently. In order to obtain secure data from around the world, hundreds of scientists have traveled to all continents in several national and international collaborative projects since the 1990s and compiled thousands of observations and proxy data there .

From various climate archives , cooler periods in the northern and southern hemisphere, i.e. on all continents and the two polar caps , could be documented. Periods of significantly cooler climates were regionally and temporally but not distributed uniformly. At least for a main phase of the Little Ice Age from the end of the 16th to the 19th century, one can speak of a phenomenon in the northern hemisphere with an average deviation in summer temperatures of −0.5 K compared to the reference period 1960 to 1991. However, particularly low temperatures did not occur globally simultaneously for a period of more than a few decades. Significantly cooler phases with temperature deviations of more than 0.8 K in summer occurred in Northwest Asia in the 17th century and in North Asia at the beginning of the 19th century. A cold snap in China is documented for around 1650 (transition from Ming to Qing dynasty ). In Greenland there were particularly cool periods in the 14th, 15th, 17th and first half of the 19th century. In Europe at the time of the late Maunder minimum , at the end of the 17th century, it was significantly cooler, in Eastern Europe by up to 1.2 K. However, cooler average temperatures were also very unevenly distributed in Europe at this time, and a slight warming was also reconstructed in northern Scandinavia .

causes

The causes of the Little Ice Age were considered to be increased volcanism , reduced sun activity and reforestation of agricultural areas after a population decline due to disease. If the ocean currents change as a result of the cooling, a reinforcing role is assumed. In addition to these short-term influences, there was a millennia-long cooling trend that was caused by changes in the earth's orbit.

Increased volcanic activity

Reconstructed volcanic radiative forcing from the last 2500 years

The Little Ice Age was preceded by a series of strong volcanic eruptions , Plinian eruptions , which hurled dust and ash as well as gases, including sulfur dioxide (SO 2 ), high into the earth's atmosphere .

The processes taking place in the higher atmosphere, the stratosphere , are known through studies of current volcanic eruptions . Volcanic solids and gases can stay there for a few years and affect the climate. The sulfur dioxide is converted into sulfuric acid (H 2 SO 4 ) in a photochemical reaction . The acid becomes a cloud of aerosol , airborne droplets in the stratosphere , which absorbs solar radiation and reduces insolation . In the shadow of the aerosol cloud, the lower atmosphere, the troposphere , cools down .

In a study published in 2011, the reaction of the world's climate to a series of volcanic eruptions from the end of the 13th century onwards, as evidenced by ice cores, was simulated with the help of climate models. It was shown that a rapid and strong cooling triggered by this can be caused by feedback processes such as For example, ice-albedo feedback persists for many years, long after the causative aerosols have disappeared from the atmosphere. Large changes in solar activity are not necessary for such a reaction of the climate. By examining the date of death of fossil plants on Baffin Island in the Canadian Arctic, the years from 1275 to 1300 and 1430 to 1455 were found to be periods with relatively suddenly dying vegetation and a consequent increase in glacier growth.

The end of the Little Ice Age was marked by a number of major volcanic eruptions. The eruption of the Laki crater in Iceland in 1783 caused the harsh winter of 1783/84 in the northern hemisphere. In 1808 or 1809 an as yet unidentified volcano erupted in the tropics. In 1815 the Tambora broke out on the island of Sumbawa ( Indonesia ). In the following year, 1816, the " year without a summer ", snow and frost were observed in June and July in northern Europe and eastern North America. Another tropical eruption occurred in 1835. The ten coldest summers in temperature reconstructions for the northern extra-tropical latitudes in the period 1750–1900 all occurred after volcanic eruptions.

Decreased exposure to sunlight

Sunspot activity of the last 2000 years: After 20 to 60 years, the minima of 14 C formation caused by the maxima of sunspots can be detected with the help of the radiocarbon method .

The annual output of solar radiation , the energy source of the earth's climate, fluctuates with solar activity in the order of 0.1%. Phases of lower solar activity go hand in hand with lower radiation output and have a cooling influence on the earth's climate. By observing sunspots , solar activity can be reconstructed as far back as the year 1610; for the period before that, one can approximately deduce solar activity by measuring radioisotopes, which are generated by cosmic radiation that increasingly penetrates the earth's atmosphere when solar activity is weaker ( cosmogenic radioisotopes 14 C and 10 Be as proxy ).

During the Little Ice Age there are phases of particularly low solar activity . The second half of a particularly cool phase of the Little Ice Age in the northern hemisphere, which began before 1600 and lasted until around 1710, coincides with the Maunder Minimum . During this period, from 1645 to 1715, the sun showed a minimum of sunspots , which was accompanied by a somewhat reduced radiation intensity. Even a slight weakening can lead to significant regional cooling symptoms. The Spörminimum , around 1420 to 1550, and the significantly shorter and less pronounced Dalton minimum , around 1800, also fall during the Little Ice Age.

Globally, however, according to the result of more recent work, the changes in solar activity can only have been accompanied by comparatively small changes in the radiation output. This means that the weaker activity of the sun was probably not the main cause of the Little Ice Age in the 16th and 17th centuries. Resulting temperature changes are estimated globally to be less than 0.3 K, with a most likely value of approx. 0.1 K. A significantly stronger regional influence, especially in the middle latitudes of the northern hemisphere, for example indirectly via an influence on the winter North Atlantic Oscillation and thus on the climate in Europe, is possible.

Reforestation as a result of population decline

In 2003, the paleoclimatologist William F. Ruddiman proposed the hypothesis that massive population decline could have led to reforestation. This would have bound enough carbon from the air to trigger the Little Ice Age through the resulting reduction in CO 2 concentrations (→ Ruddiman's hypothesis ). Ruddiman specifically suspects the plague epidemics of the late Middle Ages to be the trigger. It has also been suggested that the massive population decline on the American continents , triggered by diseases brought in by Europeans, exacerbated the aforementioned causes. After America's population was decimated by approximately 95%, large parts of previously fire-cleared arable land were reforested, which is estimated to have sequestered 2 to 5 gigatons of carbon from the atmosphere. This corresponds to approx. 4 to 14% of a decrease in CO 2 concentrations of 7 ppm, which falls in the period 1550–1750. The resulting reduced greenhouse effect would have resulted in the 0.1 K cooler period in the period.

The decline in fires in America began as early as 1350, however, the sharpest decline in burned biomass was localized precisely in regions of America with a low population density and late contact with Europeans. On the other hand, coal residues found correlate well with the temporally and spatially inconsistent climatic fluctuations of the Little Ice Age. Other authors conclude from this that local climate fluctuations, rather than population decline, were the main cause of reforestation. Overall, there is no high global correlation between fires and CO 2 concentrations in the Holocene . According to other researchers, the decrease in CO 2 concentrations is more likely to be explained by CO 2 uptake in bogs and the deposition of calcium carbonate in shallow waters.

Weaker Gulf Stream

According to studies by Jean Lynch-Stiglitz and her colleagues, the Gulf Stream was around 10% weaker than usual at the time of the Little Ice Age. The basis for the calculation were the 18 O / 16 O ratios in mussel shells, which come from the Florida street. Studies of mussel shells from the shelf north of Iceland also showed a weaker current in the upper water layers. The weaker Gulf Stream likely exacerbated other cooling factors, such as weaker solar radiation, in the North Atlantic region.

Changes in the earth's orbit around the sun

Starting about 5000 years ago and into the 19th century - especially in the middle and high latitudes of the northern hemisphere - there was a long-term cooling trend of a little more than 0.1 K per millennium. According to climate simulations, this cooling trend can be traced back to changes in the earth's movement relative to the sun, above all to a change in the inclination of the earth's axis. This changes the seasonal and regional distribution of the solar radiation arriving on earth . Such changes in solar radiation can change the snow and ice cover as well as vegetation in middle and high northern latitudes and thereby trigger climatic feedback such as ice-albedo feedback , which leads to long-term cooling, especially in the north.

Consequences for the people

Distress, social tension, persecution of minorities

Weather and climate fluctuations are seen, above all by British and Scandinavian researchers, as a trigger for the late medieval agricultural crisis in Europe in the 14th and 15th centuries. Individual authors, such as Hubert Lamb, see the crisis as a transition period from a medieval warm period to a small ice age, which they start early with. The growing seasons were reduced by deep and long winters . The summers were cold and wet, so that the wheat was rotting on the stalks. The food production declined, and there was famine. Wolfgang Behringer pointed out the increasing price increases, malnutrition and epidemics, which ultimately exacerbated social tensions in the population.

Social minorities and marginalized groups were repeatedly blamed for the bad harvests. A series of black magic was often seen in the falling yields. During the Little Ice Age both the early modern witch persecutions in Central Europe and the frequent persecution of social minorities (especially the Jews and smaller Christian denominations such as the Anabaptist ) fall . In many witch trials , the defendants were u. a. Accused of damaging the weather (e.g. frost in wine-growing areas and hail).

Power political events

The Little Ice Age marked an epoch of significant historical events in Europe and beyond. Knowing about the climate-related problems would lead to a clearer picture of that time. To what extent these problems not only aggravated the living conditions at the time, but also contributed to the major conflicts, will also have to be clarified by historical research. The outbreak of the Thirty Years' War and - much later - the French Revolution give rise to considerations with regard to exogenous causes.

Thirty Years' War

Ten years after the end of the war, the Swedes and Danes were at war again : in 1658 the army of the Swedish King Charles X advanced across the frozen Belt to the Danish islands

After the population in the German states had almost doubled from 1500 to 1618 and the temperatures had been falling steadily from around 1570, a catastrophic situation arose for the people in the country, which expressed itself in despair, distrust and doomsday mood. Several crop failures, hurricanes and hard winters are known from the period from 1560 to 1610. This time was marked by famine . These grievances prepared a radical change in society and are - among other things - seen as a breeding ground for wars in the first half of the 17th century such as the Thirty Years' War .

French Revolution

In pre-revolutionary France there was an increase in population from around 1770, which was not offset by a sufficient increase in food production. In addition to the subsequently rising food prices, there was an economic crisis that was exacerbated by the wrong policies. The years 1787 and 1788 were therefore marked by the simultaneity of an agricultural, industrial and social crisis.

In this situation, one of the clusters of climatic extremes characteristic of the Little Ice Age was added in 1788 and 1789. In 1788, as a result of an extreme drought and a severe hailstorm, grain yields in France fell by over 20 percent compared to the average for the previous ten years. This caused prices to rise more than a year before the French Revolution . The extremely cold winter of 1788/1789 was followed by floods with the thaw in spring, with subsequent cattle epidemics . In some areas there were hunger riots and attacks on grain transporters. In response to rumors about brigands , farmers were armed ( Grande Peur ) in the summer . The drought of 1789 shut down water mills and the decreased flour production led to a further increase in bread prices. The common rural and urban populations suffered most from the food shortages as a result of the deteriorating climate, and it was the starving masses who helped make the French Revolution a breakthrough. Thus the Little Ice Age was one of the many reasons for the outbreak of the revolution, albeit indirectly.

Follow the advancing pack ice

During the Medieval Warm Period, among other things, the pack ice in the northern Atlantic retreated to the north and some land glaciers had disappeared. This heating allowed the Vikings , Iceland (from about 870) and coastal areas of Greenland to colonize (from 986).

As a result of the cooling, the pack ice border moved south again in the 15th century and from around 1700 until the 19th century , interrupted by a phase of particularly low ice expansion. The advancing pack ice temporarily isolated Iceland from the outside world, causing the population to decline sharply. The worsening climate is one possible reason why the Scandinavian colony on Greenland , which around 1300 belonged to around 3000 people, went extinct in the 16th century .

literature

Web links

Commons : Little Ice Age  album with pictures, videos and audio files

Individual evidence

  1. ↑ a b c Raphael Neukom u. a .: Inter-hemispheric temperature variability over the past millennium . In: Nature Climate Change . March 2014, doi : 10.1038 / NCLIMATE2174 .
  2. ^ A b Mathew J. Owens, Mike Lockwood, Ed Hawkins, Ilya Usoskin, Gareth S. Jones, Luke Barnard, Andrew Schurer and John Fasullo: The Maunder Minimum and the Little Ice Age: an update from recent reconstructions and climate simulations . In: Journal of Space Weather and Space Climate . tape 7 , A33, 2017, doi : 10.1051 / swsc / 2017034 .
  3. ↑ a b c Ahmed et al.: Continental-scale temperature variability during the past two millennia . In: Nature Geoscience . tape 6 , 2013, p. 341 , doi : 10.1038 / ngeo1797 .
  4. ^ Climate Change 2007: Working Group I: The Physical Science Basis . In: Intergovernmental Panel on Climate Change (Ed.): Fourth Assessment Report (IPCC AR 4) . 2007, 6.6.1.1 ( ipcc.ch ).
  5. ↑ They are no substitute for rigorously determined, long climatic time series, cf. Philip D. Jones : Historical climatology - a state of the art review . In: Weather . tape 63 , no. June 7 , 2008.
  6. ↑ see also list of weather events in Europe , sortable z. B. for cold anomalies
  7. ^ The bird books from the Thesaurus picturarum, Marcus zum Lamm (1544-1606) , ed. with interpretation and commentary by Ragnar K. Kinzelbach u. a .; Eugen Ulmer Verlag, Stuttgart 2000, 404 pp., Ill .; ISBN 3-8001-3529-9 ; Volumes 29–31 are dedicated to birds.
  8. ^ J. De Vries: Histoire du climat et économie: des faits nouveaux, une interprétation différente . In: Annales. Économies, Sociétés, Civilizations . No. 32 , 1977, pp. 198-227 (French, persee.fr ).
  9. ↑ HM van den Dool, HJ Krijnen, CJE Schuurmans: Average Winter Temperatures at De Bilt (The Netherlands): 1634-1977 . In: Climatic Change . tape 1 , no. 4 , 1978, p. 320 , doi : 10.1007 / BF00135153 .
  10. ^ Walter Lenke: Investigation of the oldest temperature measurements with the help of the severe winter 1708–1709. In: Reports of the German Weather Service. No. 92, 1964.
  11. ↑ There are reports of the Thames freezing over in the years 998, 1061, 1063 and 1092 for the Medieval Warm Period in England, although this period is less historically developed than the Little Ice Age, cf. JB Rigg: Influence of Local Conditions on the Freezing of the River Thames . In: Weather . February 1964, doi : 10.1002 / j.1477-8696.1964.tb02732.x .
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  13. ↑ Michael Budde et al. (Ed.): The "Little Ice Age". Dutch landscape painting in the 17th century . Gemäldegalerie, Staatliche Museen zu Berlin Preußischer Kulturbesitz, Berlin 2001, ISBN 3-88609-195-3 . Catalog for the exhibition, September 19, 2001 to January 6, 2002 ( bib.gfz-potsdam.de PDF; 18.48 MB).
  14. ↑ The city of Venice diverted tributaries to the lagoon from the 14th to the 19th century. This created additional conditions under which the lagoon could more difficult to freeze over. For this and for years in which the lagoon froze, see: Dario Camuffo: Freezing of the Venetian Lagoon since the 9th century AD in comparison to the climate of western Europe and England . In: Climatic Change . tape 10 , no. 1 , February 1987, p. 45-46 .
  15. ↑ Caiming Shen include: Exceptional drought events over eastern China during the load-five centuries . In: Climatic Change . tape 85 , 2007, p. 453-471 , doi : 10.1007 / s10584-007-9283-y .
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  25. ↑ Stefan Brönnimann, Jörg Franke, Samuel U. Nussbaumer, Heinz J. Zumbühl, Daniel Steiner, Mathias Trachsel, Gabriele C. Hegerl, Andrew Schurer, Matthias Worni, Abdul Malik, Julian Flückige, Christoph C. Raible: Last phase of the Little Ice Age forced by volcanic eruptions . In: Nature Geoscience . July 2019, doi : 10.1038 / s41561-019-0402-y .
  26. ↑ a b At the 24th General Assembly of the International Astronomical Union in 2015, a revised series of data from 1750 was presented after the observation conditions were checked again, which gave less low and higher sunspot numbers around 1885 and 1945. This so-called Group sunspot number , V.2, is shown in blue. Corrected Sunspot History Suggests Climate Change since the Industrial Revolution not due to Natural Solar Trends. International Astronomical Union press release, iau1508, August 7, 2015 (iau.org, accessed August 20, 2015);
    In particular, why the radiocarbon dating supports the old version must now be checked.
  27. ↑ Gerard Bond et al: Persistent Solar Influence on North Atlantic Climate During the Holocene . In: Science . tape 294 , December 2001, p. 2133 , doi : 10.1126 / science.1065680 . , Message from Axel Tillemans: Little Ice Age was caused by fluctuations in the strength of solar radiation. In: Image of Science. November 16, 2001, Retrieved September 7, 2019 .
  28. ^ Georg Feulner: Are the most recent estimates for Maunder Minimum solar irradiance in agreement with temperature reconstructions? In: Geophysical Research Letters . August 2011, doi : 10.1029 / 2011GL048529 ( edoc.gfz-potsdam.de [PDF]). , Press release: Study on the Little Ice Age: Low solar activity cools the climate only insignificantly. Potsdam Institute for Climate Impact Research, September 1, 2011, accessed on September 13, 2013 .
  29. ↑ AP Schurer et al. a .: Small influence of solar variability on climate over the past millennium . In: Nature Geoscience . 2015, doi : 10.1038 / NGEO2040 .
  30. ^ Mike Lockwood: Solar Influence on Global and Regional Climates . In: Surveys in Geophysics . 2012, chap. 6 , doi : 10.1007 / s10712-012-9181-3 (English, link.springer.com ).
  31. ^ William F. Ruddiman: The Anthropogenic Greenhouse Era Began Thousands of Years Ago . In: Climatic Change . tape 61 , no. 3 , December 2003, doi : 10.1023 / B: CLIM.0000004577.17928.fa ( PDF ).
  32. ↑ Dull et al: The Columbian Encounter and the Little Ice Age: Abrupt Land Use Change, Fire, and Greenhouse Forcing . In: Annals of the Association of American Geographers . tape 100 , no. 4 , September 2010, doi : 10.1080 / 00045608.2010.502432 .
  33. ^ Mitchell J. Power: Climatic control of the biomass-burning decline in the Americas after ad 1500 . In: The Holocene . 2013, doi : 10.1177 / 0959683612450196 .
  34. ↑ Jennifer R. Marlon et al .: Global biomass burning: a synthesis and review of Holocene paleofire records and their controls . In: Quaternary Science Reviews . tape 65 , 2013, 2.5, Global Summary , doi : 10.1016 / j.quascirev.2012.11.029 .
  35. ↑ David C. Lund et al .: Gulf Stream density structure and transport during the past millennium. In: Nature . 444, 2006, pp. 601-604. doi: 10.1038 / nature05277
  36. ^ Alan D. Wanamaker Jr et al .: Surface changes in the North Atlantic meridional overturning circulation during the last millennium . In: Nature Communications . June 2012, doi : 10.1038 / ncomms1901 ( nature.com ).
  37. ↑ Information from Paleoclimate Archives: Observed Recent Climate Change in the Context of Interglacial Climate Variability and Regional Changes During the Holocene - Temperature - Northern Hemisphere Mid-to-High Latitudes . In: Intergovernmental Panel on Climate Change [IPCC] (Ed.): Fifth assessment report (AR5) . 2013, 5, Executive Summary, and 5.5.1.1.
  38. ↑ 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 .
  39. ↑ a b Werner Rösener: The crisis of the late Middle Ages in a new perspective . In: VSWG: Quarterly journal for social and economic history . tape 99 , no. 2 , 2012, p. 196-207 .
  40. ^ Hubert Lamb: Climate, History and the Modern World . 2nd Edition. Routledge, 1995, ISBN 0-415-12734-3 , pp. 264 .
  41. ↑ Johannes Dillinger: Witches and Magic. A historical introduction. Frankfurt / New York 2007, p. 78f.
  42. ↑ Compare e.g. B. Georg Böhnisch with reference to the history professor Johannes Burkhardt
  43. ↑ See timetable - history and notes on climate, cultural history and migrations
  44. ↑ Famine. In: Meyers Konversations-Lexikon. 1888.
  45. ↑ Compare Georg Bönisch
  46. ↑ Wolfgang Behringer : Cultural history of the climate: From the ice age to global warming . CH Beck, 2007, pp. 215/216. ( Google Books, limited preview )
  47. ↑ Christopher Kinnard et al .: Reconstructed changes in Arctic sea ice over the past 1,450 years . In: Nature . tape 479 , November 2011, p. 511 , doi : 10.1038 / nature10581 .