CAUSES OF CLIMATAL CHANGE 39 1 



in tropical America were to allow the equatorial current to pass 

 through into the Pacific. The effect would at once be to re- 

 duce the temperature of Norway and Britain to that of Green- 

 land and Labrador at present, while the latter countries would 

 themselves become colder. The northern ice, drifting down 

 into the Atlantic, would not, as now, be melted rapidly by the 

 warm water which it meets in the Gulf Stream. Much larger 

 quantities of it would remain undissolved in summer, and thus 

 an accumulation of permanent ice would take place, along the 

 American coast at first, but probably at length even on the 

 European side. This would still further chill the atmosphere, 

 glaciers would be established on all the mountains of temperate 

 Europe and America, the summer would be kept cold by 

 melting ice and snow, and at length all eastern America and 

 Europe might become uninhabitable, except by Arctic animals 

 and plants, as far south as perhaps 40° of north latitude. This 

 would be simply a return of the glacial age. I have assumed 

 only one geographical change ; but other and more complex 

 changes of subsidence and elevation might take place, with 

 effects on climate still more decisive.^ 



We may suppose an opposite case. The high plateau of 

 Greenland might subside, or be reduced in height, and the 

 opening of Baffin's Bay might be closed. At the same time 

 the interior plain of America might be depressed, so that, as 

 we know to have been the case in the Cretaceous period, the 

 warm waters of the Mexican gulf might circulate as far north as 

 the basins of the present great American lakes. In these cir- 

 cumstances there would be an immense diminution of the 

 sources of floating ice, and a correspondingly vast increase in 

 the surface of warm water. The effects would be to enable a 



^ According to Bonney, the west coast of Wales is about 12° above the 

 average for its latitude, and if reduced to 12° below the average, its moun- 

 tains would have large glaciers. So near is England even now to a glacial 

 age. 



