26 



METEOROLOGY AND CLIMATOLOGY: 



altitude cannot be denied. However, latitudinal and 

 altitudinal changes are only a part of the total cli- 

 matic picture. Each climate is not merely an arbi- 

 trary geographic subdivision of continuous trends 

 in the various climatic factors; rather, a climatic 

 type is somewhat uniform throughout its area of oc- 

 currence. For this reason, areas of transition between 

 adjacent climatic types are often subject to rela- 

 tively abrupt changes in temperature, precipitation, 

 and other factors. 



PAST CLIMATES 



Perhaps the greatest climatic mystery is that in- 

 volving climatic change through the ages. The fac- 

 tors causing such fluctuations through eons of time 

 can hardly be guessed. Why are climates always mi- 

 grating geographically? Only the most tentative hy- 

 potheses — probably no more than wild guesses — as 

 to the processes involved can be made. Some of the 

 causes might involve solar system cycles. For ex- 

 ample, the sun might produce variable amounts of 

 heat through time. To some extent such a variation 

 could follow an irregular cycle of heat increase and 

 decrease. Although each cycle might be of different 

 duration, increase and decrease would probably be 

 regular, with long periods of alternate warming 

 and cooling. This would account for the regular as- 

 pects and different durations of past cycles of earth 

 climate. A second possibility is a cyclic change in 

 tilt of the earth's axis. This would definitely af- 

 fect climate, because tilt is of' major importance in 

 influencing the angle of solar rays reaching different 

 parts of the earth's surface. A third possibility is a 

 change of earth's orbit from nearly circular to fairly 

 elliptical. If earth had a circular orbit, seasonal dif- 

 ferences in solar radiation that result from earth's 

 varying distance from the sun would be eliminated. 

 The maximum ellipse (ignoring axis tile) would cause 

 a 30 per cent seasonal differential. However, at the 

 present time the seasonal difference is 7 per cent, with 

 the greatest heat being received during the December 

 solstice — recall that our winter is the time when the 



sun is closest, but the solar rays are least direct. This 

 present condition causes relatively mild winters and 

 summers. In spite of these possibilities, actually no 

 more than intelligent guesses, the poor state of knowl- 

 edge about the cause of climatic changes is indicated 

 by the lack of good explanation for the warmest 

 recent times having been 6000 years ago. 



SEtECTED READINGS 



Bates, D. R., ed. 1957. The Earth and its Atmosphere. Basic 

 Books, New York. 



Battan, Louis J., 1961. The Nature of Violent Storms. Double- 

 day & Co., Garden City, N. Y. 



Byers, Horace R., 1959. General Meteorology. 3d ed. 

 McGraw-Hill Book Co., New York. 



Clausse, Roger, and Leopold Faey, trans, by J. Ferrante, 

 1961. The Clouds. Grove Press, New York. 



Haynes, B. C, 1947. Techniques of Observing the Weather. 

 John Wiley & Sons, New York. 



Fisher, Robert M., 1960. How to Know and Predict the 

 Weather. New American Library, New York. 



Lehr, Paul E., R. Will Burnett, and Herbert S. Zim, 1957. 

 Weather. Golden Press, New York. 



Z-j/c Editorial Staff and Lincoln Barnett, 1955. The World 

 We Live In. Time Inc., New York. 



Loebsack, Theodore, 1959. Our Atmosphere. Pantheon, New 

 York. 



Orr, Clyde, Jr., 1959. Between Earth and Son. The Macmil- 

 lan Co., New York. 



Petterssen, Sverre, 1958. Introductory Meteorology. 2d ed. 

 McGraw-Hill Book Co., New York. 



Shapley, Harlow, ed., 1954. Climatic Change: Evidence, 

 Causes and Effects. Harvard University Press, Cam- 

 bridge, Mass. 



Trewartha, Glenn T., 1954. An Introduction to Weather and 

 Climate. 3d ed. McGraw-Hill Book Co., New York. 



United States Weather Bureau. 1949. Cloud Code Chart. 

 U. S. Government Printing Office, Washington, D. C. 



, 1949. Manual of Cloud Forms and Codes for States of 



the Sky. U. S. Government Printing Office, Washing- 

 ton, D. C. 



, 1952. Weather Forecasting. U. S. Government Print- 

 ing Office, Washington, D. C. 



Yearbook of Agriculture, 1941. Climate and Man. U. S. 

 Government Printing Office, Washington, D. C. 



