R. M. Deeley — Polar Climates. 453 



distinct layers ; a lower troposphere and an upper stratosphere. In 

 the troposphere, as we ascend, the temperature falls at a rate which 

 closely agrees with that of rising and adiabatically expanding moist 

 air, i.e. about o- 5 C. for each 100 metres of rise near the earth's 

 surface. At Eatavia, 1 about 7° south of the Equator, it falls some- 

 what irregularly until a height of 17 kilometres is reached, where 

 the temperature has been found to be — 89 0, 6 C. At 26 kilometres 

 the temperature has risen to — 57 0, 2 C. On the other hand, at 

 Pavlovsk, near Petrograd, 2 in about latitude 59° 40', the lowest 

 temperature, the mean for the year, was reached at a height of 

 11 kilometres, and was only —53° C, rising to about —42 C, at 

 19 kilometres. 



The following table shows the heights and temperatures at these 

 two places : — 



"We thus have opposing temperature gradients in the troposphere 

 and stratosphere respectively. The upper side of the troposphere is 

 that point where the temperature either only changes very slowly 

 with increasing height or actually gets warmer as we rise. Its level 

 is much higher in the Tropics than in Polar areas or middle latitudes, 

 and is lower over low-pressure areas than over high -pressure areas. 

 The upper layer is the stratosphere, and it rests upon the troposphere. 

 The reason why the stratosphere in high latitudes has such a high 

 temperature we need not here discuss. 



Now if the lower atmosphere, or troposphere, should, from any 

 cause, get warmer in Polar regions, then less opposition would be 

 offered to the flow of the upper atmosphere towards the Equator, 

 and the winds blowing towards the Poles from the high-pressure belts 

 would be strengthened. Such warming of the troposphere in high 

 latitudes would still further decrease the surface temperature adverse 

 to winds blowing from the high-pressure belts at latitude 30° towards 

 the Polar regions. There would thus be brought into operation 

 a secondary effect which would powerfully assist still further to 

 raise the temperature in high latitudes. 



Warm seas in Polar regions would mean less cold conditions in the 

 ocean and sea bottoms and would favour the existence of certain 

 kinds of life at greater depths than that at which they now exist. 



At the present time the South Polar area is occupied by a continent 

 which is placed nearly concentrically with the Pole. The collection 

 of snow and ice upon this land area keeps the troposphere temperature 

 low, even in summer, and it here contends on fairly equal terms 

 with the opposing temperature gradient in the stratosphere. Outside 

 the Antarctic Continent, however, Ave have the seas warmed by the 

 prevalent north - westerly winds. Over the sea, therefore, the 

 temperature of the troposphere is less in conflict with that of 



1 W. van Bemmelen, Nature, March 5, 1914, p. 6. 



2 Gold, Meteorological Office Geophysical Memoir, No. 5, 1913 (M.O., 

 No. 210e). 



