NATURAL HISTORY EST ICELAND — HUXLEY 



337 



it is world-wide, and due to increased lieat from the sun, which in its 

 turn operates by altering the world's great system of atmospheric 

 circulation. 



The evidence is of every sort — increased temperatures, spectacular 

 regression of glaciers, changes in the position of main low-pressure and 

 high-pressure areas, alterations in rainfall and snowfall, desiccation 

 in lower latitudes (including the drying up of East African lakes), 

 enormous shrinkage of the polar pack ice, enlarged growth rings of 

 trees, and finally changes in the distribution of many animals and 

 plants. 





&^&%" \ 41) 



Figure 4. — Breeding distribution of the great skua, a circumpolar species from the 

 Southern Hemisphere, which has given rise to one Northern Hemisphere sub- 

 species. The shaded parts represent the actual breeding areas of the various 

 Southern Hemisphere subspecies. (Based on map compiled by James Pisher.) 



On this last point Iceland provides a great deal of evidence, since 

 it lies on the sensitive limit between sub- Arctic and Arctic conditions. 

 We know from historical records that for over 400 years the early 

 colonists successfully grew barley, but that soon after 1300 this became 

 impossible. But now, to quote Ahlmann, "the present shrinkage of 

 the glaciers is exposing districts which were cultivated by the early 

 medieval farmers but were subsequently overridden by ice." 



The ensuing cold spell of about 600 years has been called the Little 

 Ice Age ; it seems to have been the coldest period since the retreat of 

 the ice after the last major glacial period. At any rate, about 1880 

 the Iceland glaciers reached their maximum extension for some 10,000 

 years, while the warmest period since the end of the Ice Age seems 

 to have been the few centuries just before our present era. 



As showing how sensitive animals may be as climatic indicators, 

 Finnur Gudmunsson told me that in the warm spell just before the 

 Christian Era, the dog-whelk (Pu/rpura) was found all along the 

 north and east coasts of Iceland, while today it stops dead at the 



