The date of the break up of the River Dwina at Mitau was recorded intermittently from 1530 to 1709, and regularly since that date, and the figures have been discussed by Rykatchef. Recasting them in our unit of fifty years we find the mean dates to be:
| 1551-1600 | 1601-50 | 1651-1700 | 1701-50 | 1751-1800 | 1801-50 |
| March 29 | March 30 | March 5 | March 26 | March 26 | March 28 |
This again points to a cold period about the beginning of the seventeenth century.
The climate of Iceland and Greenland in the Middle Ages has been the subject of much controversy, the view that there were extensive changes during that period being warmly upheld by one party and as warmly combated by the other party. The case for climatic change has been well set out by O. Pettersson[7]. The Roman authors (Pliny, Solinus, etc.) wrote that there was a frozen sea about Thule (Iceland), but a party of monks who visited the island about A.D. 795 during the months of February to August, in which the ice is normally most abundant in Icelandic waters, found the coast free, though they met with a frozen sea a day’s journey to the northward. In the ninth century the Norsemen visited Iceland regularly, and at times sailed round it, apparently without interference from ice. The early settlers practised agriculture with some success. In the thirteenth century, however, the reports of ice off Iceland became frequent—apparently the conditions were worse than those of the present day, and much more so than in the eighth and ninth centuries. According to Rabot, it appears from ancient records that considerable areas cultivated in the tenth century are now covered with ice. The first spread of the glaciers took place in the first half of the fourteenth century. In the fifteenth and sixteenth centuries the climate of Iceland ameliorated somewhat, but in the seventeenth there was a readvance, which destroyed several farms about 1640 or 1650. Since then there has been a slight retreat.
The ice-conditions of Greenland are closely related to those of Iceland, and the records of the Norse colonization of Greenland bear out the conclusions drawn from the latter island. Up to the close of the twelfth century ice is hardly ever mentioned in the accounts of voyages, though it is now a great hindrance. Eric, the pioneer explorer of West Greenland, spent three successive winters on the islands in Juliaanehaab Bay (latitude 60° 45′ N.), and explored the country during the summer; “this cannot be explained otherwise than by assuming that the Polar ice did not reach Cape Farewell and the west coast of Greenland in those days.” In the thirteenth century ice is first specifically mentioned as a danger to navigation, and at the end of the fourteenth century the old Norse sailing route was on account of ice definitely abandoned in favour of one further south. Shortly afterwards the Norse colonies were wiped out by a southward migration of the Eskimos. Even in Norway itself the fourteenth century was a time of dearth, short harvests and political troubles, when corn had to be imported from Germany instead of being exported to Iceland as in former years.
It should be noted that Pettersson’s conclusions are considered invalid by H. H. Hildebrandsson[8] on the ground of the incompleteness of the records.
For the southern hemisphere our records are naturally much rarer and of less antiquity than for the northern hemisphere, and until the tree-rings are investigated we cannot carry our study back beyond the sixteenth century. From some researches into the municipal archives of Santiago de Chile, latitude 33½° S., published by B. V. Mackenna in 1877, we can infer, however, that the general course of variation since 1520 was similar to that of corresponding regions in North America. Santiago lies in a semi-arid region where a temporary shortage of water is severely felt, the average annual rainfall being only 364 mm. (14.3 inches). The early travellers, however, make no specific mention of drought, and in 1540 Pedro de Valdivia crossed the desert of Atacama with a column of troops and cattle without inconvenience—a feat which would be difficult nowadays. In 1544 there were heavy rains and great floods in June. The next record is for the year 1609, recording another heavy flood on the Mapocho, which was repeated nine years later in 1618. The first recorded drought occurred in the years 1637 to 1640; there was another flood in 1647, after which came a series of severe droughts interrupted by occasional floods, which lasted until the close of the eighteenth century. The first half of the nineteenth century was again comparatively rainy. The records thus indicate a wet period centred about 1600, followed by a dry period during the eighteenth century, exactly parallel to the records from the United States and Europe.
BIBLIOGRAPHY
Huntington, E. “The climatic factor as illustrated in arid America.” Washington, Carnegie Institution, 1914.