PART III — CLIMATIC CHANGE 



other for differentiating between the 

 various time-scales of climatic change. 

 Similar glossaries are needed for other 

 aspects of the physical matrix making 

 up the environment. 



"Operational" definitions are used 

 here. "Environment" is considered to 

 be the physical matrix in which orga- 

 nized and unorganized matter exists. 

 The term "cycle" refers to the com- 

 plete course of events or phenomena 

 that recur regularly in the same se- 

 quence and return to the original 

 state; in this sense, a cycle has a true 

 harmonic course. "Cyclic" (or "cycle- 

 like") refers to something that only 

 roughly approximates a harmonic. 



Aside from "seasonal" patterns, no 

 true harmonic behavior has been 

 found in global or regional climatic 

 patterns; the latter are cyclic patterns 

 but they vary in duration and inten- 

 sity. Several biological and natural 

 processes reach such a degree of 



harmonics that they are sometimes 

 called rhythms, but these rhythms are 

 generally tied to seasonal climatic 

 changes. 



Tree growth and pollen production 

 are, in a certain sense, a physiological 

 response to the climatic conditions 

 prevailing at the time these processes 

 occurred. A thorough understanding 

 of these processes leads to a better 

 understanding of the immediate envi- 

 ronment, and when old samples of 

 tree rings (the long chronologies) and 

 pollen production (the pollen profiles) 

 can be located and studied, past local 

 environmental conditions can be de- 

 termined for those specific areas. Pub- 

 lications are now appearing on cli- 

 matic conditions over the past 15,000 

 years or so, as interpreted by various 

 authors. Although cyclical patterns 

 appear in many of these interpreta- 

 tions, the patterns are so obscure that 

 little credence can be put on their 

 meaning. 



Tree Rings and Environmental 

 Cyclic Behavior 



Certain species of trees respond to 

 physiological behavior by doing all of 

 their yearly growth in a particular 

 period of time. Thus, growth itself 

 is harmonic. The amount of growth 

 produced each year, however, varies 

 in response to environmental changes. 

 Trees in a uniform environment, or 

 one that remains fairly constant year 

 in and year out, produce tree rings 

 of a uniform width over a given 

 period of years. In contrast, trees 

 growing in areas where environmen- 

 tal changes are quite pronounced will 

 reflect those changes in variable ring- 

 widths for a given period of years. 

 (See Figure III-5) In areas where one 

 growth-controlling factor assumes 

 dominance over the others, this factor 

 can be isolated; variations of ring- 

 widths then permit study of this par- 

 ticular type of variable environmental 

 condition. In certain areas the con- 



Figure III -5 — PRECIPITATION PATTERNS FROM TREE RINGS 



1700 



17S0 



1800 



1900 



The photograph shows tree rings beginning about 1690 and ending about 1932. 

 The rings were used to estimate whether the year was wet or dry; moisture was 

 then computed to provide the graph in the lower part of the diagram. Since varia- 

 tions in atmospheric circulation cause periods of wetness and dryness, the ring- 

 width records can be calibrated with surface pressure and used to map anomalies 

 of the atmospheric circulation for periods of time in which few if any historical 

 data exist. 



60 



