CAUSES OF e; IANGE 



tion is improving rapidly, since the 

 High Resolution Infrared Radiom- 

 eters, of the type used on the Nimbus- 

 4 and ITOS-1 satellites, can obtain 

 pictures by day or night and even 

 provide an indication of the heights of 

 cloud tops. Nimbus-F, scheduled for 

 launching by the National Aeronau- 

 tics and Space Administration 

 (NASA) in 1974, may carry an ab- 

 solutely calibrated radiation experi- 

 ment that could mark the beginning 

 of direct quantitative measures of the 

 total heat budget of the earth. Mea- 

 surements of lower atmospheric com- 

 position, or pollution, from satellites 

 have been proposed, but at this time 

 they seem to be further in the future. 

 Ozone, a trace gas found mostly in 

 the stratosphere and upper tropo- 

 sphere, has been measured, but this 

 component may be of minor concern 

 in the present context. 



A Perspeciive on Man-Made Pollu- 

 tion — The possible change in the 

 radiative characteristics of the upper 

 atmosphere due to rockets can prob- 

 ably be dismissed, because even ex- 

 treme assumptions about numbers of 

 Saturn-class rockets being launched 

 lead to negligible changes. The con- 

 tribution of jets to water vapor and 

 aerosols in the stratosphere may also 

 be trivial. Recent studies by the Na- 

 tional Academy of Sciences, by Ma- 

 nabe and Weatherald, and by others 

 strongly suggest that it is. Contrails 

 are likely to have a climatic influence 

 only when they trigger the formation 

 of extensive bands of cirrus cloud 



which mature, with the passage of 

 time, to a sufficient optical depth in 

 the infrared to produce either signifi- 

 cant blanketing or reduction of in- 

 coming visible solar radiation. 



One cannot say for certain that, on 

 the occasions when jet-airplane con- 

 trails produce cirrus clouds, the cirrus 

 clouds would not have formed natu- 

 rally. But there are many occasions, 

 some lasting for several days, when 

 major portions of the United States 

 are crisscrossed by jet-airplane con- 

 trails that do not dissipate, but instead 

 spread out until major fractions of the 

 sky are covered by thin cirrus of suf- 

 ficient intensity to be of radiative sig- 

 nificance. What needs to be done 

 is to conduct quantitative studies, in 

 selected areas of the earth, of the 

 radiative losses to space that occur 

 with and without cirrus clouds. Then 

 there needs to be a rather careful ex- 

 amination of the degree to which 

 these cirrus can be artificially trig- 

 gered. The stability of the large-scale 

 circulation is an extremely important 

 matter. We know that large trough 

 developments occur in the 300-milli- 

 bar circulation, particularly in the late 

 winter and spring seasons, in a way 

 that is difficult if not impossible to 

 predict. It is quite conceivable that 

 cirrus cloud formations at high lati- 

 tudes over warm sources, as over the 

 Gulf of Alaska, may be important in 

 this regard. 



The atmosphere-ocean system de- 

 pends on the heat available to run it, 

 and this is the result of a delicate bal- 



ance between heat received from the 

 sun and re-radiated to space. There 

 are ways to disturb this balance, and 

 the ice ages of the past are proof that 

 nature sometimes does, in fact, alter 

 it. Man might do the same, and this 

 possibility deserves the most careful 

 study. There has been much hand- 

 waving of late by "prophets of doom." 

 While virtually none of these people 

 is a scientist, atmospheric scientists 

 have not been able to make convinc- 

 ing rebuttals so far. 



The earth actually has a remarkably 

 stable life-support system, and man 

 is unlikely to be able to move it far 

 from its equilibrium. To mention a 

 few examples: Aerosols, of the sort 

 that man or nature creates, only re- 

 main in the atmosphere for about a 

 week on the average. Thus, indus- 

 trial pollution in the United States 

 hardly has time to reach Europe be- 

 fore it is washed from the air. Further- 

 more, natural sources of contamina- 

 tion from vegetation, volcanoes, the 

 oceans, and the deserts still far out- 

 weigh all of man's contributions, 

 taken on a global scale. With respect 

 to the balance built into our highly 

 variable clouds, an increase in mean 

 temperature would probably cause an 

 increase in moisture and cloudiness, 

 which in turn would reflect more solar 

 radiation back to space. Such a nega- 

 tive feedback, forcing the situation 

 back to equilibrium, is only one of 

 several mechanisms that we are be- 

 ginning to identify in the complex 

 atmosphere-ocean system. 



Climatic Change and the Effects of Civilization 



A worldwide climatic change has 

 been taking place for the past decade 

 or two. Its reality has been estab- 

 lished by scientists of the United 

 States, the Soviet Union, and 

 England. 



The climatic amelioration that took 



place between the late 1800's and 

 1940 has ended, and the mean tem- 

 perature of the earth appears to have 

 fallen since the middle of the present 

 century. (See Figure III-8) Some 

 dramatic environmental changes have 

 followed — e.g., the return of mid- 

 summer frosts in the upper Midwest, 



record cold autumns in Ohio, rising 

 lake levels in East Africa, and mas- 

 sive encroachment of sea-ice on the 

 north shore of Iceland. With this 

 change, the circulation patterns of 

 the atmosphere also appear to have 

 changed. Any such changes on an 

 earth that is straining its capacity to 



69 



