Climate and Time in their Geological Relations; a theory of Secular Changes of the Earth's Climate

Abstract

II.

MR. CROLL's own theory about the distribution of heat by means of ocean currents is in intimate connection with his ideas as to the variation of climate in past time. His theory may be summarised as follows:— The Gulf Stream and other warm or cold currents are due entirely to the prevailing system of winds, which force the water along the surface, or even make it take a lower course; the return of the colder water from the Arctic regions being assisted by the difference of level caused by driving up the waters into a narrow basin, such as he supposes those regions to be. The result of this theory is, that if one hemisphere is colder than the other, the trades on that hemisphere will be strongest, and the resulting warm current will flow into the warmer hemisphere; any difference, therefore, in the mean temperature of one hemisphere from that of the other is augmented according to this theory by ocean circulation, whereas on Dr. Carpenter's theory the latter would have a counteracting influence. When, however, we take both theories into account, and also the effect of the distribution of land and sea, which is remarkably manifested by the two facts of the South Atlantic being coldest and the North Pacific also coldest, we see that we are not in a position to estimate the effect, if any of much consequence, of the different forms of ocean circulation on the occurrence of a glacial epoch, but must look for the causes of the latter independently.

Climate and Time in their Geological Relations; a theory of Secular Changes of the Earth's Climate.

By James Croll Geological Survey of Scotland. (London: Daldy, Isbister, and Co., 1875.)