These ruins belong to the great Mayan civilization. Mayan history has been briefly summarized by Huntington as follows: “First we have a long period of active development, during which the calendar was evolved and the arts of architecture and sculpture were gradually developed.... This time of marked growth must have preceded the Christian era. Then comes ... the building of the great cities of Copan, Quirigua, Tikal and others. These first great cities were in the southern part of the Maya area, on the borders of Honduras or in eastern Guatemala. They lasted perhaps three or four centuries; then quickly declined. So far as we have any evidence, civilization never revived in this southern area, for the structures of the great period have not been rebuilt by later inhabitants. Towards the end of the period of greatness the centre of Mayan culture moved northward.... The great period, according to Bowditch, lasted from 100 B.C. to A.D. 350 ... then came a time of very low civilization, lasting for centuries.... A revival ensued about A.D. 900 or A.D. 1000, and architecture once more reached a high pitch, but ... only in northern Yucatan; all the rest of the country seems to have remained in darkness. Moreover, this mediæval revival was relatively shortlived. Since that time the condition of the Mayas has fluctuated more or less, but on the whole there has been a decline.”
Now at the present day the densest and most progressive population in Yucatan is found in the driest part of the country, where the forest gives place to jungle. If the line of separation between jungle and forest were moved southward 300 miles, the former would include all the districts where ruins are now found. We see from the above summary that the prosperous periods of Mayan history were just those periods which in California were moist; in Yucatan they must have been dry. Huntington’s explanation is the theory of the “shifting of climatic belts”; during the rainy period in California the temperate storm-tracks were shifted further southward. At the same time the sub-tropical high-pressure belt, which at present lies over the West Indies, was also shifted southwards, and this brought a dry cool winter to Yucatan, with an increased contrast of seasons, and consequently a more invigorating climate.
In Asia, Huntington and other explorers have found similar traces of past variations of climate, a fascinating account of which is given in “The Pulse of Asia.” Space will not permit of a summary in detail, but the following general conclusions may be quoted:[6]
“If we omit the Volga and the European portions of the Caspian drainage area, the limits (of the six basins considered) lie over sixteen hundred miles apart from north to south and over three thousand from east to west. All this great area seems to have been subject to the same great waves of climatic change.
“In the ancient days when the Oxus River entered the Scythian Gulf of the expanded Caspian Sea, and Lake Gyoljuk discharged permanently to the Tigris, the lake of Seyistan had not been converted into dry land by the giants. Kashmir was so cold and snowy that agriculture was impossible.... In the Lop basin the rivers were full of water; Lop-Nor was the “Great Salt Lake”; the desert was comparatively small and the zone of vegetation extensive; and on all sides there was a density of population and a degree of prosperity far beyond those of to-day. And in the Turfan basin the same was probably true.
“A great change took place throughout the six basins during the early centuries of the Christian era. The lakes of Gyoljuk, Seyistan, the Caspian, Lop-Nor and presumably Turfan were greatly reduced in size. In the case of the first three, parts of the old lake-beds were used as sites for villages. Except in Kashmir, the change of climate appears to have brought disaster....
“Again there came a change (about A.D. 700). The process of desiccation gave place to a slight but important tendency toward increased rainfall and lower temperature. Kashmir became colder and more snowy, and hence more isolated; the rivers of Lop and Turfan gained greater volume; and the lakes of Lop, the Caspian and Turfan expanded once more. The habitability of the arid regions began to increase; migrations came to an end; and central Asia was prosperous for a time. Finally (about 1350) a latest and slightest change took place in the other direction, and we seem to-day to be in the midst of an epoch of comparative equilibrium, with no marked tendency towards climatic change in either direction.” There was, however, a period of comparatively high water in the Caspian in the early part of the seventeenth century.
In Europe the evidence for climatic changes during historical times is more difficult to follow, since variations of rainfall leave fewer traces in a moist than in an arid or semi-arid country. A certain amount of material is given by Brückner in his “Klimaschwankungen.” He finds that there was a great advance of the Alpine glaciers from 1595 to 1610, while two Italian lakes without outlet, the Lago di Fucina and Lake Trasimeno, attained a high level about the same time. Other evidence for western Europe is derived from the date of the wine-harvest and from the records of severe winters. Like the growth-curves of the big trees, they need a secular correction to alter the general slope of the curve, especially in the case of severe winters, but the larger irregularities probably correspond to real variations of climate. I have added in column 4 the numbers of winters with sea-ice on some part of the Danish coast, as tabulated from the records compiled by Captain C. I. H. Speerschneider. The results are in general agreement with column 3, particularly as showing that the period 1401-50 was relatively mild; but the first half of the seventeenth century is less instead of greater than its two neighbours in this column.
The figures for the wine-harvest refer to the average for the period 1816-80; - indicates that the harvest was so many days earlier than normal, corresponding to a high summer temperature (May to August). The table shows that cold winters were especially numerous in the first half of the twelfth century and again in the thirteenth. The end of the fifteenth century was marked by hot summers and mild winters, or a warmer climate; the beginning of the seventeenth century by cold (presumably snowy) winters and cool summers. Thus the periods of increased rainfall in the arid regions of Asia and America were marked by a colder climate in the rainy regions of western Europe.
| 1. | 2. | 3. | 4. | 5. |
| Period, 50 years about. | Date of Wine Harvest. | No. of Severe Winters. | Winters with Ice on Danish coast. | Remarks. |
| 825 | 4 | |||
| 875 | 7 | |||
| 925 | 5 | |||
| 975 | 6 | |||
| 1025 | 6 | |||
| 1075 | 10 | |||
| 1125 | 15 | Cold winters | ||
| 1175 | 10 | |||
| 1225 | 13 | } | ||
| 1275 | 13 | } | Cold winters | |
| 1325 | 13 | 7 } | ||
| 1375 | 11 | 4 | ||
| 1425 | +5 | 13 | 7 | |
| 1475 | +1 | 7 | 2 | Warm |
| 1525 | +2.9 | 10 | 5 | |
| 1575 | +2.2 | 14 | 14 } | |
| 1625 | +4.1 | 17 | 11 } | Cold |
| 1675 | +2.7 | 15 | 14 } | |
| 1725 | +0.1 | 10 | 5 | |
| 1775 | - 0.2 | — | 22 | |
| 1825 | - 0.9 | — | 21 | |