176 Concluding Remarks 



can we even discuss the hypotheses very satisfactorily; in particular, we 

 know very httle about the rates of formation of water masses. But these 

 arguments are of special interest, because they confound the popular idea 

 of the role of the Gulf Stream in European chmate. For all we know, the 

 European cUmate might actually be warmer if the direction of rotation of 

 the North Atlantic Eddy were reversed. 



During the past thirty years there has been an increase of about 2° in 

 the surface temperatures of the Norwegian Sea, and also a decrease of 

 perhaps 50 m. in the depth of the 10° C. isotherm throughout the Sargasso 

 Sea. (The statistical significance of this change of position of the isotherm 

 is doubtful.) These two isolated bits of information suggest that the North 

 Atlantic surface circulation is slowing do^^Ti and that the Gulf Stream 

 transport is consequently decreasing, and that this, in turn, results in 

 greater warming of the coast of Europe. This indication favors Isehn's 

 proposal. 



The theory of \\dnd-driven ocean currents suggests that the effect of 

 diminished winds would make the North Atlantic circulation shallower in 

 the middle, but would not change its radius. Toward the periphery of the 

 circulation the isotherms might become deeper. However, it is important 

 to remember that the theory, in its present state of development, deals only 

 with integrated velocities, and hence that there is no clear theoretical 

 indication of the ways in which temperature, heat transport, and surface- 

 current velocity might vary with the wind. Moreover, the chmate and 

 winds over the ocean are not unaffected by the state of ocean currents. 

 As a result, the theory of wind-driven currents permits us to draw in- 

 ferences about the change of currents resulting from only very slight 

 changes of the winds. It seems to me quite reckless to assert, for example, 

 that some current of the Carboniferous Glacial Period, flowing in an ocean 

 which does not even exist now, had a greater or lesser transport than the 

 present-day Gulf Stream. The more these hypothetical oceans of the past 

 depart from the configuration and chmate of the oceans of today, the less 

 we can hope to explain and describe their behavior.^ When the disparity 

 between supposed conditions of the past and observed conditions of the 

 present becomes as great as that envisaged in Chamberlain's theory of 

 the reversal of the deep circulation due to the sinking of highly saUne 

 water at the equator, the unhappy physical oceanographer can make no 

 constructive comment. 



^ Many examples of purely verbal theories that invoke physical processes with 

 which our present primitive theoretical models cannot yet cope are given in Chapter III 

 of C. E. P. Brooks's book Climate Through the Ages (1949). Another example, 

 published since this text was written, is 'A Theorj'^ of Ice Ages', by M. Ewing and 

 W. L. Donn, Science, 123 (1956) : 1061-1066. 



