Lecture 6 - Lecture 6: What is carrying capacity?...

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1 Lecture 6: What is carrying capacity? Introduction. Today we have the modest task of finishing the second half of the Cohen text and coming to some conclusion about what the carrying capacity of the earth is. The way I’m going to get there is by thinking about the different concepts of carrying capacity in the Cohen text, seeing what the problems with these concepts have proven to be and what these problems tell us. I want to start with several mathematical models of carrying capacity, look at one of these models--the Law of the Minimum--in some detail, and then do a long summing-up of the question and basically of the past two weeks. Estimates of human carrying capacity The text warns us that arriving at a consensus about the maximum size of the population that the Earth can support is not easy. Figure 11.1 gives another illustration of this. The point is not only the huge spread--from one billion to one trillion is a good spread-- but also that the spread does not seem to be decreasing as time goes on. Estimates of carrying capacity range from just over a billion to 40 or fifty billion. The estimates do center around the range 8 to 16 billion; meanwhile, as we were saying last week, estimates of population are projecting stabilization in the 9 to 10 billion range, with estimates edging downward as time goes on. Estimates of human carrying capacity : methodology . The text presents eight former estimates of carrying capacity. The point here is not to memorize each of the eight or the numbers they each came up with, but to look at them from the point of view of methodology, of how they came up with the numbers they did and what these methods tell us about how to calculate the carrying capacity of the earth. Algebraic methods of calculating the carrying capacity of the Earth Ravenstein. Writing in 1893, Ravenstein divided the surface of the earth into three types of covers-- fertile, steppe or grassland and desert, calculated the maximum population density of each type of land and the amount-- the area of each type on the earth’s surface and decided that the carrying capacity of the earth was a bit under 6 billion. What was wrong with that? Why aren’t the Ravenstein calculations the last word? Well, his method was to assume that the population density of Europe in 1893--about 80 people to the square kilometer or 0.8 people per hectare--is the carrying capacity of fertile land, or that Europe had then achieved its maximum population. Moreover, since fertile land was supposedly responsible for almost all food production--steppes were supposed to support 4 people to the square kilometer, or one-twentieth the density of fertile land, and deserts one-quarter of that--supposing that European fertile land of 1893 represented the maximum meant that maximum world population could be was approximated by multiplying the then-current European population density by the amount of fertile land in the world. The problem was that, by assuming that then-current European populations were at
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This note was uploaded on 09/28/2009 for the course GEOG 130 taught by Professor Staff during the Summer '08 term at University of California, Berkeley.

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Lecture 6 - Lecture 6: What is carrying capacity?...

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