Editing Ice age (section)

==History of research==
{{See also|History of climate change science}}

In 1742, Pierre Martel (1706–1767), an engineer and geographer living in [[Geneva]], visited the valley of [[Chamonix]] in the [[Alps]] of [[Savoy]].<ref>{{cite journal |vauthors=Rémy F, Testut L |title=Mais comment s'écoule donc un glacier ? Aperçu historique |journal=Comptes Rendus Geoscience |language=fr |volume=338 |issue=5 |pages=368–385 |year=2006 |doi=10.1016/j.crte.2006.02.004 |url=http://remy.omp.free.fr/FTP/histoire_de_la_glaciologie/ecoulement_glacier.pdf |bibcode=2006CRGeo.338..368R |access-date=2009-06-23 |archive-date=2012-04-26 |archive-url=https://web.archive.org/web/20120426050144/http://remy.omp.free.fr/FTP/histoire_de_la_glaciologie/ecoulement_glacier.pdf |url-status=live }} Note: p. 374</ref><ref>{{harvnb|Montgomery|2010}}</ref> Two years later he published an account of his journey. He reported that the inhabitants of that valley attributed the dispersal of [[glacial erratic|erratic boulders]] to the glaciers, saying that they had once extended much farther.<ref>{{cite book |author=Martel, Pierre |chapter=Appendix: Martel, P. (1744) An account of the glacieres or ice alps in Savoy, in two letters, one from an English gentleman to his friend at Geneva; the other from Pierre Martel, engineer, to the said English gentleman |editor=Mathews, C.E. |title=The annals of Mont Blanc |chapter-url=https://books.google.com/books?id=oestAAAAYAAJ&pg=PA327 |year=1898 |publisher=Unwin |location=London |page=327}} See {{harv|Montgomery|2010}} for a full bibliography</ref><ref>{{cite book |last=Krüger |first=Tobias |year=2013 |title=Discovering the Ice Ages. International Reception and Consequences for a Historical Understanding of Climate (German edition: Basel 2008) |location=Leiden, Netherlands |publisher=Brill |page=47 |isbn=978-90-04-24169-5 |oclc=968318929 }}</ref> Later similar explanations were reported from other regions of the Alps. In 1815 the carpenter and [[chamois]] hunter Jean-Pierre Perraudin (1767–1858) explained erratic boulders in the Val de Bagnes in the Swiss canton of Valais as being due to glaciers previously extending further.<ref>{{harvnb|Krüger|2013|pp=78–83}}</ref> An unknown woodcutter from Meiringen in the Bernese Oberland advocated a similar idea in a discussion with the Swiss-German geologist [[Jean de Charpentier]] (1786–1855) in 1834.<ref>{{harvnb|Krüger|2013|p=150}}</ref> Comparable explanations are also known from the Val de Ferret in the Valais and the Seeland in western Switzerland<ref>{{harvnb|Krüger|2013|pp=83, 151}}</ref> and in [[Johann Wolfgang von Goethe|Goethe]]'s [[Goethean science|scientific work]].<ref>Goethe, Johann Wolfgang von: Geologische Probleme und Versuch ihrer Auflösung, Mineralogie und Geologie in Goethes Werke, Weimar 1892, {{ISBN|3-423-05946-X}}, book 73 (WA II, 9), pp. 253, 254.</ref> Such explanations could also be found in other parts of the world. When the Bavarian naturalist [[Ernst von Bibra]] (1806–1878) visited the Chilean Andes in 1849–1850, the natives attributed fossil [[moraine]]s to the former action of glaciers.<ref>{{harvnb|Krüger|2013|p=83}}</ref>

Meanwhile, European scholars had begun to wonder what had caused the dispersal of erratic material. From the middle of the 18th century, some discussed ice as a means of transport. The Swedish mining expert Daniel Tilas (1712–1772) was, in 1742, the first person to suggest drifting sea ice was a cause of the presence of erratic boulders in the Scandinavian and Baltic regions.<ref>{{harvnb|Krüger|2013|p=38}}</ref> In 1795, the Scottish philosopher and gentleman naturalist, [[James Hutton]] (1726–1797), explained erratic boulders in the Alps by the action of glaciers.<ref>{{harvnb|Krüger|2013|pp=61–2}}</ref> Two decades later, in 1818, the Swedish botanist [[Göran Wahlenberg]] (1780–1851) published his theory of a glaciation of the Scandinavian peninsula. He regarded glaciation as a regional phenomenon.<ref>{{harvnb|Krüger|2013|pp=88–90}}</ref>

<!--[[File:AntarcticaDomeCSnow.jpg|thumb|left|upright=1.15|The [[Antarctic ice sheet]]. Ice sheets expand during an ice age.]]
[[File:Vostok Petit data.svg|thumb|left|upright=1.15|Variations in temperature, {{CO2}}, and dust from the [[Vostok, Antarctica|Vostok]] ice core over the last 400,000 years]]-->
[[File:Haukalivatnet.JPG|thumb|Haukalivatnet lake (50 meters above sea level) where [[Jens Esmark]] in 1823 discovered similarities to [[moraine]]s near existing glaciers in the high mountains]]

Only a few years later, the Danish-Norwegian geologist [[Jens Esmark]] (1762–1839) argued for a sequence of worldwide ice ages. In a paper published in 1824, Esmark proposed changes in climate as the cause of those glaciations. He attempted to show that they originated from changes in Earth's orbit.<ref>{{harvnb|Krüger|2013|pp=91–6}}</ref> Esmark discovered the similarity between moraines near [[Haukalivatnet]] lake near sea level in [[Rogaland]] and moraines at branches of [[Jostedalsbreen]]. Esmark's discovery were later attributed to or appropriated by [[Theodor Kjerulf]] and [[Louis Agassiz]].<ref>{{Cite journal|last=Hestmark|first=Geir|date=2018|title=Jens Esmark's mountain glacier traverse 1823 − the key to his discovery of Ice Ages|journal=Boreas|language=en|volume=47|issue=1|pages=1–10|doi=10.1111/bor.12260|bibcode=2018Borea..47....1H |issn=1502-3885|quote=The discovery of Ice Ages is one of the most revolutionary advances made in the Earth sciences. In 1824 Danish-Norwegian geoscientist Jens Esmark published a paper stating that there was indisputable evidence that Norway and other parts of Europe had previously been covered by enormous glaciers carving out valleys and fjords, in a cold climate caused by changes in the eccentricity of Earth's orbit. Esmark and his travel companion Otto Tank arrived at this insight by analogous reasoning: enigmatic landscape features they observed close to sea level along the Norwegian coast strongly resembled features they observed in the front of a retreating glacier during a mountain traverse in the summer of 1823.|doi-access=free|hdl=10852/67376|hdl-access=free}}</ref><ref>{{Citation|last=Berg|first=Bjørn Ivar|title=Jens Esmark|date=2020-02-25|url=http://nbl.snl.no/Jens_Esmark|work=Norsk biografisk leksikon|language=nb|access-date=2021-02-28|archive-date=2021-03-07|archive-url=https://web.archive.org/web/20210307220710/https://nbl.snl.no/Jens_Esmark|url-status=live}}</ref><ref>{{Cite web|last=Hverven|first=Tom Egil|title=Isens spor|url=https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|access-date=2021-02-28|website=Klassekampen|archive-date=2021-04-17|archive-url=https://web.archive.org/web/20210417172110/https://arkiv.klassekampen.no/article/20170805/ARTICLE/170809976|url-status=live}}</ref>

During the following years, Esmark's ideas were discussed and taken over in parts by Swedish, Scottish and German scientists. At the University of Edinburgh [[Robert Jameson]] (1774–1854) seemed to be relatively open to Esmark's ideas, as reviewed by Norwegian professor of glaciology [[Bjørn G. Andersen]] (1992).<ref>{{cite journal |first=Bjørn G. |last=Andersen |year=1992 |title=Jens Esmark—a pioneer in glacial geology |journal=[[Boreas (journal)|Boreas]] |volume=21 |pages=97–102 |doi=10.1111/j.1502-3885.1992.tb00016.x|title-link=Jens Esmark |issue=1 |bibcode=1992Borea..21...97A }}</ref> Jameson's remarks about ancient glaciers in Scotland were most probably prompted by Esmark.<ref>{{cite book |author=Davies, Gordon L. |title=The Earth in Decay. A History of British Geomorphology 1578–1878 |url=https://archive.org/details/earthindecayhist0000herr |url-access=registration |location=London |year=1969 |pages=267f|publisher=New York, American Elsevier Pub. Co |isbn=9780444197016 }}<br />{{cite book |author=Cunningham, Frank F. |title=James David Forbes. Pioneer Scottish Glaciologist |publisher=Scottish Academic Press |location=Edinburgh |year=1990 |isbn=978-0-7073-0320-8 |page=15}}</ref> In Germany, Albrecht Reinhard Bernhardi (1797–1849), a geologist and professor of forestry at an academy in Dreissigacker (since incorporated in the southern [[Thuringia]]n city of [[Meiningen]]), adopted Esmark's theory. In a paper published in 1832, Bernhardi speculated about the polar ice caps once reaching as far as the temperate zones of the globe.<ref>{{harvnb|Krüger|2013|pp=142–47}}</ref>

In [[Val de Bagnes]], a valley in the [[Swiss Alps]], there was a long-held local belief that the valley had once been covered deep in ice, and in 1815 a local chamois hunter called Jean-Pierre Perraudin attempted to convert the geologist [[Jean de Charpentier]] to the idea, pointing to deep striations in the rocks and giant erratic boulders as evidence. Charpentier held the general view that these signs were caused by vast floods, and he rejected Perraudin's theory as absurd. In 1818 the engineer [[Ignatz Venetz]] joined Perraudin and Charpentier to examine a [[proglacial lake]] above the valley created by an ice dam as a result of the [[1815 eruption of Mount Tambora]], which threatened to cause a catastrophic flood when the dam broke. Perraudin attempted unsuccessfully to convert his companions to his theory, but when the dam finally broke, there were only minor erratics and no striations, and Venetz concluded that Perraudin was right and that only ice could have caused such major results. In 1821 he read a prize-winning paper on the theory to the Swiss Society, but it was not published until Charpentier, who had also become converted, published it with his own more widely read paper in 1834.<ref>{{cite book|last=Wood |first=Gillen D’Arcy  |title=Tambora, the Eruption that Changed the World|pages=160–167 |publisher=Princeton University Press |location =Princeton, NJ |year=2014|isbn=978-0-691-16862-3}}</ref>

In the meantime, the German botanist [[Karl Friedrich Schimper]] (1803–1867) was studying mosses which were growing on erratic boulders in the alpine upland of Bavaria. He began to wonder where such masses of stone had come from. During the summer of 1835 he made some excursions to the Bavarian Alps. Schimper came to the conclusion that ice must have been the means of transport for the boulders in the alpine upland. In the winter of 1835–36 he held some lectures in Munich. Schimper then assumed that there must have been global times of obliteration ("Verödungszeiten") with a cold climate and frozen water.<ref>{{harvnb|Krüger|2013|pp=155–59}}</ref> Schimper spent the summer months of 1836 at Devens, near Bex, in the Swiss Alps with his former university friend [[Louis Agassiz]] (1801–1873) and Jean de Charpentier. Schimper, Charpentier and possibly Venetz convinced Agassiz that there had been a time of glaciation. During the winter of 1836–37, Agassiz and Schimper developed the theory of a sequence of glaciations. They mainly drew upon the preceding works of Venetz, Charpentier and on their own fieldwork. Agassiz appears to have been already familiar with Bernhardi's paper at that time.<ref>{{harvnb|Krüger|2013|pp=167–70}}</ref> At the beginning of 1837, Schimper coined the term "ice age" (''"Eiszeit"'') for the period of the glaciers.<ref>{{harvnb|Krüger|2013|p=173}}</ref> In July 1837 Agassiz presented their synthesis before the annual meeting of the Swiss Society for Natural Research at Neuchâtel. The audience was very critical, and some were opposed to the new theory because it contradicted the established opinions on climatic history. Most contemporary scientists thought that Earth had been gradually cooling down since its birth as a molten globe.<ref>{{harvnb|Krüger|2013|pp=177–78}}</ref>

In order to persuade the skeptics, Agassiz embarked on geological fieldwork. He published his book ''Study on Glaciers'' ("Études sur les glaciers") in 1840.<ref>{{cite book |first1=Louis |last1=Agassiz |author-link=Louis Agassiz |first2=Joseph |last2=Bettannier |title=Études sur les glaciers. Ouvrage accompagné d'un atlas de 32 planches, Neuchâtel |url=https://books.google.com/books?id=fTMAAAAAQAAJ |year=1840 |publisher=H. Nicolet}}</ref> Charpentier was put out by this, as he had also been preparing a book about the glaciation of the Alps. Charpentier felt that Agassiz should have given him precedence as it was he who had introduced Agassiz to in-depth glacial research.<ref>{{harvnb|Krüger|2013|pp=223–4.  Charpentier, Jean de: ''Essais sur les glaciers et sur le terrain erratique du bassin du Rhône,'' Lausanne 1841.}}</ref> As a result of personal quarrels, Agassiz had also omitted any mention of Schimper in his book.<ref>{{harvnb|Krüger|2013|pp=181–84}}</ref>

It took several decades before the ice age theory was fully accepted by scientists. This happened on an international scale in the second half of the 1870s, following the work of [[James Croll]], including the publication of ''Climate and Time, in Their Geological Relations'' in 1875, which provided a credible explanation for the causes of ice ages.<ref>{{harvnb|Krüger|2013|pp=458–60}}</ref>