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. 



