FUTURE OF MAN — ^MATHER 217 



is a time of unusually rugged and extensive lands, with notably 

 varied climate ranging from the glacial cold of Greenland and 

 Antarctica to the oppressive warmth and humidity of certain equa- 

 torial regions. Such conditions have apparentily recurred many 

 times at long-spaced intervals since the oldest known rocks were 

 formed, but added together the time thus represented cannot be as 

 much as a fourth of geologic time. Much more characteristic of 

 earth history as a whole have been the conditions illustrated by those 

 periods when corals thrived in shallow seas occupying the site of 

 Baffin Land and North Greenland, and coal-forming plants flour- 

 ished on Antarctica. The probability is strong that eventually, say 

 in 5 or 10 million years, the earth will display again the physical 

 conditions of many past geologic periods that were characterized by 

 broad low lands, wide shallow seas, and uniform genial climate. 



But most of us have a greater interest in the next few centuries than 

 in the subsequent millions of years. Minor changes in climate will 

 doubtless occur just as they have in the last few thousand years. 

 Unfortunately, or perhaps fortunately, there is no basis for predic- 

 tion concerning their nature, whether for better or for worse. There 

 is really no good reason for referring to the present as "a post- 

 glacial epoch"; it may prove to be an interglacial epoch. But our 

 ancestors weathered ice ages in the past, and presumably we are 

 better equipped for such contingencies than they were. Should the 

 average annual temperature of the earth as a whole be reduced some- 

 thing like 10° F. and remain at that lower level for a few millennia, 

 it is likely that once more the greater part of Canada, the northern 

 United States, and the Scandinavian countries would be buried be- 

 neath great ice sheets. But in consequence of the removal of water 

 from the sea as vapor to form the snow to produce the glacial ice, con- 

 siderable areas now shallowly submerged along the coast lines in middle 

 and equatorial latitudes would emerge as dry land. Indeed, it is 

 likely that the area of land suitable for human abode would be 

 nearly or quite as great at the climax of a glacial period as it is 

 today. 



By the same token, the disappearance of existing bodies of glacial 

 ice as a result of rapid amelioration of climate in the not-distant 

 future would, if it occurred, be a decidedly mixed blessing. Eeturn 

 to the sea the water now imprisoned in the ice on the Arctic islands, 

 Greenland and Antarctica without any compensating changes in 

 crustal elevation, and sea level would be raised 150 to 160 feet the 

 world around. Considering the number of people who now work or 

 sleep in buildings in metropolitan communities not over 150 feet 

 above sea level, the importance of such a change is readily apparent. 

 But from the geologists' point of view these are relatively trivial 



