Climatic variation in historic and prehistoric time ((1914)) (20470049229)

Title: Climatic variation in historic and prehistoric time
Identifier: Climaticvariati00Pett (find matches)
Year: (1914) ((190s)
Authors: Pettersson, Otto
Subjects:
Publisher: Göteborg, W. Zachrissons boktr
Contributing Library: Smithsonian Libraries
Digitizing Sponsor: Biodiversity Heritage Library



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Introduction. In the last centuries of the middle ages a series of political and economic catastrophes occurred all over the then-known world. They synchronise with occurrences of a st artling and unusual kind in the kingdom of Nature. The coasts of Iceland and Greenland became blocked by Polar ice. Frequent volcanic eruptions occurred in Iceland and the surrounding seas. Violent storm-floods devastated the coast of the North Sea and Baltic. In certain cold winters Ore- sund and the Baltic were frozen over and the lucrative Hanseatic herring fishery of the early middle ages which had been carried on in the Baltic and Oresund ceased altogether. All these events are recorded in ancient chronicles which also depict the social and econo- mic state of the communities, which were greatly influenced by these violent climatic variations and their consequences: famine and disease. The ancient Sagas and convent chronicles give no hint of any sup- posed connection between the catastrophes in nature and the human world. The Icelandic chronicles from the 14th and 15teenth cent- uries abound in descriptions of catastrophes, such as »hall9eri micit vm allt land • hafis vmhserfis Island . landskialfte mikill vm allt land . elldz uppkoma j Heklu fialli • elldeyar — myrkr mikit sva at fal sol — bolnasot — mandaudi a. e. o. Simultaneously there occurred violent floods and inundations of the European continent and winters of unexampled severity. Such was that of the year 1322—1333 thus described in the history of Olaus Magnus. »ait Albertus Crantsius diligentissimus omnium regionum scrip- tor: anno MCCCXXIII gelidissimo frigore constringebatur mare ut pedestri itinere per glacie de littore Lubicensi in Daniam in Prussiam mare transiretur, dispositis per loca opportuna in glacie hospicii — —» etc. We are told in the Gronica Guthilandorum that in that winter it was possible to drive over the ice between Sweden and Gothland. The climatic variations recorded in mediaeval chronicles have given rise to much speculation lately, especially in Sweden. I here give the names of three wellknown Swedish papers on the subject: Ehren- heims speach on his resignation of the presidency of the Royal Aca- demy of Science in 1824 »Om Climaternas Rorlighet»; the chapter on climatic variations pag. 562—572 in »Lehrbuch der kosmischen Fysik» by S. Arrhenius and N. Ekholm's paper »On the variations of climate » etc. The historic material at hand is much more exten- sive than generally supposed. Only part of it is published, f. inst. the 10 Icelandic annal-series, by G. Storm and Hennig's »Katalog bemer- kenswerther Witterungserscheinungen von den altesten Zeiten bis zum Jahre 1800». The unpublished Danish and Norwegian records are being pre- pared for publication, the former by Captain C. J. Speerschneider of the Danish Met. Inst., the latter by Dr. E. Bull of Christiania. Till quite recently the opinion has prevailed among meteorologists and geographers that the old records are unreliable and exaggerated and that no real variation in the climate has occurred in historic time. This opinion is concisely expressed in Nansen's book »Paa ski over Gronland»: »The physical conditions of Greenland remained all through the middle ages approximately the same as they are to day » The same view characterises Nansen's latest, publication »Nord i Taakeheimen». Of late, however, dissenting opinions have been advanced in various countries, in Sweden by Ekholm and Sernander, in Germany by Bruckner and in America by E. Huntington. In Ekholms opinion the climate of Scandinavia has changed since mediaeval time and this change he attributes to a gradual transition from a continental to a more maritime climate. Such a change would manifest itself by variations in the mean temperature and precipita- tion at Stockholm, Lund, Copenhagen, Petersburg a. o. places when compared with earlier observations made in the 18th and 19th cen- turies and with the oldest observations we possess, i. e. those made by Tycho Brahe on the island of Hven in Oresund at the end of the sixteenth century. Such a comparison made by Ekholm will be referred to later. E. Huntington approaches the question from an archaeological point of view. In his extensive travels in Central Asia and the in- terior of North America he studied the former extension and gradual exsiccation of steppe-lakes as shown by ancient shorelines and rem- nants of cities abandoned in periods of drought. The climatic varia- tions which caused floods, inundations and ice-blockades in Green- land, Iceland and Europe manifested themselves in the interior of the continents by devastating periods of drought, forcing the popu- lation to emigrate. Huntington holds the invasion of the Tartars into China and Europe in the 14th century, as well as that of the Aztecs into Mexico, to be caused by such variations in the climate. We possess no actual observations of climatic variations in the countries on the western and northern shores of the Atlantic. Here we have only the ancient Sagas to go by, and what they have to say on the subject I will recapitulate later. It is neccessary, however, that I should say a few words now as to my own standpoint in this matter. In my opinion the ancient records of variations in the climate indicate that a change in the oceanic circulation and in the condi- tions of the Atlantic has occurred. No geologic alteration that could influence the climate has occurred for the past six or seven centuries. The changes due to cultivation of land, clearing of forests, draining of marshes and regulation of river-beds are too insignificant to ex- plain these phenomena. Their very nature, i. e. floods, inundations, ice-blockades, suggests a dislocation in the oceanic circulation, the ultimate cause of which must be ascribed to cosmic agents. The third part of this paper will contain the proofs in support of the theory here propounded as regards the countries west and north of the Atlantic. The fourth part will contain those pertaining to the European seas and coasts. In the first part I will endeavour to point out the cause of these climatic variations. My own researches and those made during the past thirteen years by the International Cooperation for the investigation of the sea, have enabled me to study the variations in the seas surrounding Sweden since 1891. The material collected by myself and by Dr. G. Ek- man, who in 1876 with A. W. Cronander and in 1877 with F. L. Ekman investigated the Baltic and Cattegat, and later by him- self carried out the first fundamental investigation of the con- ditions off the Bohuslan- coast in the first years of the present herring- period, have enabled me to study the causes of these variations. They appear to be of a periodic nature and ultimately ruled by cosmic agents, i. e. variations in the tide-generating force exercised by the sun and moon upon the waters of the ocean. I have also ascertained that the tide-generating force exhibits secular variations and that an absolute maximum occured 500 years ago accompanied by a series of secondary maxima and minima in the centuries immedi- ately before and after.