PROBLEMS FROM LAND OCCUPANCY 173 



tures at the stations of longest record have been increasing 

 progressively for 80 years or more, and drawing upon records 

 from Canada, Europe, Asia, South America, and the East 

 Indies, concludes that "the practically unanimous testimony 

 of these graphs not only establishes the realness of these up- 

 ward trends but shows that they are operative on an extensive 

 geographical scale." In the years since 1940 there has been a 

 slight downward trend at many localities, but it is not yet 

 known whether this represents a reversal of the long-term 

 trend. The argument that most records are obtained in cities 

 where an upward temperature trend might result from man's 

 occupancy has been anticipated by Kincer, and he has shown 

 that the increase in temperature is as marked in Lynchburg, 

 Va., Dale Enterprise, Va., and Easton, Md., as in the city of 

 Baltimore. 



Glaciers provide excellent evidence as to the balance be- 

 tween precipitation and evaporation: if the precipitation is 

 heavy enough or the temperature low enough to hold down 

 the rate of evaporation, the glacier will advance. If precipita- 

 tion is light and temperatures sufficiently high, the glacial 

 front will recede. The long-term trends as shown by glacial 

 advances and recessions result entirely from natural con- 

 ditions and need not be adjusted for man's activity. Glaciers 

 provide evidence as to long-term climatic trends in very few 

 places in the United States, and except for the Nisqually 

 Glacier on Mt. Rainier, the measurements of annual advances 

 and recessions did not begin until 1930. Longer records are 

 available in Europe, and data have been collected from areas 

 distributed over the globe (Switzerland, Sweden, Iceland, 

 Greenland, Alaska, Africa, South America, New Guinea, New 

 Zealand, Antarctica). The data summarized by Matthes 15 

 show that glacial recession has been general since the middle 

 of the nineteenth century and that it is world-wide. The data, 

 like those of temperature, suggest a rough synchronism in 



is Matthes, F. E., Glaciers, pp. 190-215 in "Hydrology," edited by O. E. 

 Meinzer, McGraw-Hill Book Company, Inc., New York, 1942; Report of the 

 Committee on Glaciers, Trans. Am. Geophys. Union, vol. 27, pp. 219-233, 1946. 



