CAUSE OF MILD POLAR CLIMATES. 147 



power of the Gulf Stream had long been known, yet 

 no one had imagined that the warmth of our climate 

 was due, to such an enormous extent, to the heat 

 conveyed by that stream. The amount of heat received 

 by an equatorial zone 64 miles in breadth represents, 

 be it observed, merely the amount conveyed by one 

 current alone. There are several other great currents, 

 some of which convey as much heat polewards as the 

 Gulf Stream. On taking into account the influence of 

 the whole system of oceanic circulation, it is not 

 surprising that the difference of temperature between 

 the equator and the poles should be reduced from 

 200° to 80°. 



From these considerations, the real cause of former 

 comparatively mild climates in Arctic regions becomes 

 now apparent. All that was necessary to confer on, 

 say, Greenland a condition of climate which would 

 admit of the growth of a luxuriant vegetation is 

 simply an increase in the amount of heat transferred 

 from equatorial to Arctic regions by means of ocean- 

 currents. And to effect this change of climate no 

 very great amount of increase is really required ; 

 for it was shown that the severity of the climate of 

 that region is about as much due to the coolino- effect 

 of the permanent snow and ice as to an actual want of 

 heat. An increase in the amount of warm water 

 entering the Arctic Ocean, just sufficient to prevent 

 the formation of permanent ice, is all that is really 

 necessary ; for were it not for the presence of ice the 

 summers of Greenland would be as warm as those of 

 England. 



Were the whole of the warm water of the Gulf 

 Stream at present to flow into the Arctic Ocean, it 

 would probably remove the ice of Greenland. Any 

 physical changes, such as those that have been discussed 



