Studies of the Little Ice Age: II, Changes in the winds and ocean currents in the north-east Atlantic region
This chapter is included at this point to show the evidence we have of fundamental changes in the ocean during the time of colder climate in recent centuries and how the conditions of the seas so close to the coasts of Europe affected the climate. This study uncovers an underlying critical point for the development of human society in the countries close to the north-eastern Atlantic, which has not been recognized. Western and northern Europe today, as is well known, enjoy a climate which is many degrees warmer than the average for the latitudes concerned. And from the Atlantic seaboard to places even as far inland as central Europe the variability of temperature from year to year is also low for the latitude (see Lamb 1972, p. 280, fig. 7.13). This adds up to a sheltered regime, which is widely acknowledged (and taken for granted) and commonly put down to the stabilizing effect of the nearby ocean. What the examination reported in this chapter reveals is that when the ocean currents vary, and cause the boundary between the warm water of Gulf Stream origin and the polar water to shift, the ocean ceases to stabilize the situation and in fact becomes responsible for amplifying the climatic changes in the region. (The substance of this writing was published as a paper entitled, 'Climatic variation and changes in the wind and ocean circulation: the Little Ice Age in the north-east Atlantic', Quaternary Research, 11, 1979, pp. 1-20. The opening section has here been re-written to avoid repetition in other chapters.)
The surface currents in the world's oceans are largely driven by the drag of the winds. Variations must, and do, take place when the prevailing wind-pattern varies. And these variations have effects on the climate through changes in the ocean's heat transport, and hence its thermal and moisture input into the atmosphere. Opportunities to reconstruct conditions in the ocean in the past are more limited than in the case of wind-pattern
changes. But in the sea areas with which this chapter is concerned the records of measurements with meteorological and oceanographic instruments are unusually long; and a first search of available fisheries, whaling and naval records suggests that it is possible to derive estimates of prevailing oceanic and atmospheric conditions back to the seventeenth century AD, perhaps even into the sixteenth century in some cases. The results of the survey here presented, which are supported by other kinds of circumstantial evidence, indicate a major anomaly in the ocean in those times in this area, registering ocean current changes, which clearly had important effects on the climate of Europe.