266 CLOUD 



global ecosystem. The answer to that question is the answer to the question that 

 titles this paper: "Is there intelligent life on Earth?" 



Just what are the characteristics of the global ecosystem that impose limits 

 on its use and abuse? First is the indivisibility of the environment. Hardin (1959) 

 has phrased this as "you can't do only one thing." Whatever happens to any part 

 of the environment has repercussions on other parts of it — not only on adjacent 

 parts but in some sense eventually on all other parts of the whole ecosystem. A 

 second limiting characteristic of our global ecosystem is the impossibility of 

 continued exponential growth within it. Nothing can increase infinitely in a 

 finite system. This is the crux of the Malthusian doctrine — often maligned but 

 never invalidated. Another factor that constrains our flexibility of choices has to 

 do with the idea that a sequence of actions, each individually justifiable on the 

 basis of evidence on which a particular action is taken, may have cumulatively 

 adverse effects. 



Let us begin our examination of the ways in which the limiting characteris- 

 tics of our global ecosystem are being tested with a look at the growth of world 

 populations through the Christian Era (Fig. 1). Graphically this takes the form 

 of a typical exponential curve with a doubling time that for the world as a whole 

 is now about 35 years. With the advent of the industrial revolution and modern 

 medicine, the doubling times have been getting shorter and the quantities larger. 

 In the lower right-hand corner of Fig. 1 is shown one possibility for the way the 

 industrial era may eventually look to our descendants in the historical 

 perspective of hundreds or a few thousands of years hence. If present trends of 

 population growth and rising consumption of material goods continue without 

 leveling off and coming into some kind of equilibrium, they must eventually 

 reach a peak and descend on the other side. We may all hope, of course, that this 

 is just an alarmist nightmare and that it will not work out that way, but to avert 

 such a peaking and collapse is likely to require conscious effort on our part both 

 to stretch the limits of the ecosystem within reason and to accommodate 

 ourselves within those limits where their stretching is impossible or inadvisable. 



Figure 2 illustrates a distinctive index of the industrial revolution which 

 coincided with the rapid increase in global population — pig-iron production. 

 Increase in production of pig iron and other mineral commodities made possible 

 increases in nearly everything else. Mechanization grew; farms became more 

 efficient; we could feed more people; and larger labor forces were needed for 

 more factories, plantations, and agencies to produce more of all kinds of goods 

 and services. Figure 2 shows the growth of pig-iron production, which, for the 

 world at large, has now reached about 400 million metric tons/year. The various 

 lines for nations and the world as a whole reflect the vagaries of war, depression, 

 and national fortune. You can see that the present leading producers of pig iron, 

 in order of rank, are: 



1. The USSR, which passed the United States during the last year. 



2. The United States. 



