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2. QUOTE FOR THE WEEK. Life is what happens when you are making other plans [John Lennon].. 3. To a certain extent, awareness of the fragile nature of our surroundings was triggered by talk of the
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1. 1 POPULATION GROWTH AND THE ENVIRONMENT ARE WE OVERWHELMING MOTHER EARTH?
2. 2 QUOTE FOR THE WEEK
Life is what happens when you are making other plans [John Lennon].
3. 3 To a certain extent, awareness of the fragile nature of our surroundings was triggered by talk of the population bomb. These concerns arose in the late 1960s as demographers began to notice quite large annual rates of population growth following the end of World War II.
In the U.S. the baby boom that began in 1945 and continued until around 1960 was a major source of concern to those who worried about the planet being overrun with people.
Population growth was, at that time, a reflection of new-found prosperity and of confidence in the future.
Fertility (births) is quite sensitive to economic outlook and following World War II optimism was quite high.
4. 4 With the exception of a few years between 1955-1962, the annual addition to the worlds population was increasing and this trend continued until the 1990s. At this time, the annual increments to population began to shrink.
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8. 8 Notice that even though the annual percent growth (the growth rate) began to fall around 1965, the actual growth in population continued until around 1990. This result follows from the fact that a slightly smaller percentage increase on a larger population base will continue to imply larger populations each year until the growth rate falls enough to overcome the larger number of people. The period between 1962 and 1990 was just such a period of transition. Since then we have been on a trend of reduced annual growth, but continued growth in total population.
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11. 11 A focus on total population growth obscures important differences among regions of the world. As a general rule, the industrialized countries of the world are experiencing very low rates of population growth, while the developing countries are where we find high rates of population growth. Consider the following graphs.
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14. 14 There is an interesting and profound relationship between income levels in a country and birth rates. Consider the following graph of per capita GDP (an indicator of national income) for a large number of nations.
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16. 16 Now let us see how national income levels correlate with annual rates of population growth The following graph shows a regression relationship between rates of population growth and per capita GDP.
The R2 of 0.4133 tells us that per capita GDP accounts for 41 percent of the variation across countries in the rate of population growth.
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18. 18 Now for a few more graphs of population-related data World population by regions of the world.
Life expectancy in different countries.
Infant mortality across countries.
19. 19 WORLD POPULATION BY REGION
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23. 23 We see that most of the worlds population increase is coming from the poorest nations. And we see that some of the richer nations have a negative rate of population growth, while many others are close to the replacement rate (zero population growth).
24. 24 We now turn our attention to the theory of population dynamics. That is, how might we model population changes?
25. 25 We start by positing a simple model of births. This model is informed by some general patterns we know to be pertinent: Birth rates = f(Ef, Y, U, SS)
Ef = years of female education
Y = per capita income
U = degree of urbanization
SS = government social security programs
26. 26 We then hypothesize that births vary with respect to these four factors as below: Years of female education: ?B/?Ef < 0 [read this to say that as years of female education increase we expect birth rates to fall].
Per capita income: ?B/?Y < 0 [read this to say that as per capita incomes rise we expect birth rates to fall].
Degree of urbanization: ?B/?U < 0 [read this to say that as a country becomes more urbanized we expect birth rates to fall].
Government Social Security: ?B/?SS < 0 [read this to say that as the government plays a more important role in the economic security of the elderly we expect birth rates to fall].
27. 27 Now consider a simple model of deaths. Death rates = f(Y, M)
Y = per capita income
M = access to good medical care
28. 28 Deaths as a function of:
Per capita income: ?D/?Y < 0 [read this to say that as per capita income increases we expect death rates to fall].
Access to medical care: ?D/?M < 0 [read this to say that as better access to medical care increases we expect death rates (especially of infants) to fall].
29. 29 These two general relationships combine to form a model of the demographic transition. This model is historical in the sense that it captures the empirical experience of the industrialized countries as they moved through three distinct periods. Phase I: high birth and death rates Phase II: high birth rates but falling death rates Phase III: low birth and death rates
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31. 31 Consider (in the following graph) the changing age structure in the U.S. as we went through our own demographic transition since 1900. At the turn of the 20th century we were an agrarian nation with a very large share of the work force engaged in what is called primary activitiesagriculture, mining, forestry.
Now we are a post-industrial economy with less than 3-4 percent of the labor force engaged in primary activities, a somewhat larger share engaged in secondary activities (manufacturing), and a growing share of the labor force engaged in tertiary activities such as real estate, insurance, legal affairs, transportation, government jobs, communications, teachers, etc.
All of the concern for the loss of manufacturing jobs reflects the fact that the U.S. is now post industrial in nature and we will never again have the level of manufacturing employment that we had at the beginning of the 20th century.
32. 32 CHANGES IN DEMOGRAPHIC COMPOSITION OVER TIME: UNITED STATES
33. 33 In the next slide I show the situation for the 84 poorest countries in the world. Notice the strong relation between income rank of birth rates;
And the somewhat weaker relation between income rank and death rates.
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35. 35 Next we see the actual data from one developing countrySri Lanka.
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37. 37 Let us now consider population dynamics and the danger of exceeding the natural carrying capacity of the planetor perhaps our ability to produce food. This brings us to the work of Parson Thomas Robert Malthus, a mathematician of the first rank in his class at Cambridge (1784), but alas, not a very good empirical researcher. He was good with mathematical models, but not very good with data.
38. 38 Consider a simple model of population growth Assume two periods: t and t+1. Let t be the end of this year, and t+1 be the end of next year.
Population (N) at the end of next year (t+1) is a function of population at the end of this year (t) times some growth factor R.
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40. 40 We see here the issues that concerned Malthus. Specifically, he worried that since food supply was able to grow at a linear rate (an assumption based on historical conditions), and population would grow at an exponential rate (something derived from mathematics with particular assumptionsas above), he foresaw immiserization setting in as hunger and squalor reduced both fertility rates (Ft) and the survival rates (St) of the youngand even of adults. Let us now consider the Malthusian model.
41. 41 A linear function for food production might be: Ft+1 = ?Ft where ? = some constant. Malthus thought population growth would be exponential until population outstripped food supply and then starvation would reduce population. So population would follow a path such as: Pt+1 = Ptedt where: e = 2.718 (the base of the natural logarithm) d = rate of growth of population (in percentage) t = time period
42. 42 The nice aspect of this formulation is that it gives us the percentage population change directly in the form of the parameter d Pt+1 = Ptedt
So the parameter d can be read directly as the percentage change in population between period t+1 and t.
43. 43 Recall our earlier formulation had R = Nt+1 Nt so that R is the ratio of next years population to this years population. R depicts the actual change in population. In contrast, the parameter d is the percentage change in population between two periods.
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45. 45 The parameter d captures all of the factors that will influence population change. These are: (1) fertility; and (2) survival.
46. 46 Fertility is largely endogenous to the family, while survival is largely exogenous. The family is in control of fertility decisions, while social conditions national economic circumstances, access to (and quality of) health care, and old-age insurance tend to be external to the family.
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49. 49 We can think of this relationship between food grain production and population growth in a broader sense ~~~~~~~~~~~~~~~~~ Specifically, think of food production as the ability of the earth to support people and our lifestyle, including our consumption and disposal of stuff. To the extent that natural resources are degraded or depleted through human activity then the ability of nature to keep providing for us is diminished. We can degrade the earth just as food production can reach its limits.
50. 50 In the following graph I depict a situation of a gradual increase in annual food supplies, a gradual decline in the rate of population growth leading to a general increase in grain supplies per person, then a serious crop failure in year 12, followed by a predictable impact on population growth rates, and then followed by a slow recovery in the rate of population growth as food production recovers.
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52. 52 In the following graph we see a gradual increase in food supplies per person, then the crop failure and accompanying famine, then followed by a gradual increase in the standard of living as measured by food availability. But before long per capita grain consumption (availability) begins to drop off (in year 18) as population growth picks up after the famine years.
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55. 55 The point here is that when the ability of naturebroadly defined to include food productionto provide materials and services can no longer keep up with our demands for those materials and services then something has to give. ~~~~~~~~~~~~~~~~~~ This is what people worry about under the general heading of sustainability, or sustainable development.
56. 56 Let us now add one more refinement to the simple Malthusian story That is, I will show you how to model fertility as endogenous.
57. 57 Malthus started with the exponential growth equation for population, but he dideventuallycome to recognize positive and negative checks on population growth. This is captured by the logistical growth equation from Verlhurst (and elaborated in biology by Lotka and Volterra). This is also called a Sigmoid curve.
58. 58 This relation demonstrates that population growth is itself influenced by the settings and circumstances (the environment) of the population under study. Perhaps the population has reached the carrying capacity (here denoted by K) of its environment. The presence of K in this equation means that population growth is endogenous.
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60. 60 Let us now look at the population experience of the place that was the laboratory for all of Malthuss writing (and hand wringing)England. I use England because I am working on the economic history of England starting in the 12th century. And we are fortunate to have reasonably good population data as far back as 1086 (though there are long gaps in those early years). First, we will see the early Medieval picture (1250-1450), and then one for the full sweep of recorded population data
61. 61 In the period between 1250 and 1300 Englands population was showing a gradual increase. Then, in 1315 there were very heavy rains throughout the summer that destroyed virtually the entire crop, and so 1315 and 1316 were hungry timesmillions of people starved. It is estimated that 10-15 percent of the population died.
62. 62 The population began to recover around 1320 and was on a general upward trajectory when the Black Death struck (arrived) in the summer of 1348. This catastrophe wiped out 30-40 percent of the population in the period of 12-18 months. The dead were everywhere. The plague re-appeared again and again over the ensuing centuries, though on a less dramatic scale. It was not until 1550two hundred years after the original outbreakthat Englands population began to increase again. There was one more serious instance around 1660.
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65. 65 We see several things here. Malthus was writing in the early stages of a quite rapid increase in population after nearly four-five centuries of population stagnation. The Industrial Revolution began around 1740 following several decades of marvelous weather, bounteous agricultural yields, improved diets, and some considerable new income. Family size fairly explodednot necessarily because people were suddenly having more children, though there was some of that. But infant mortality plummeted with the advent of better diets and improved health care.
66. 66 So Malthus was very worried that population would outstrip food supply. But there was more going onas there usually is. Specifically, with the industrial revolution came an increase in horrible living conditions for the poor. Read Charles Dickens. These grim conditions were also noticed by a German economist and historian living in London by the name of Karl Marx. There can be little mystery why Marx was appalled at the reality of un-restrained capitalism. It was barbaric and in-humane.
67. 67 England began to undertake poor reliefwhat we would call welfare. And Malthus was not too happy about the breeding habits of the poor who then were making claims on the public treasury for poor relief. He did not much care how many children the rich had, since they were comfortable enough to provide for them. It was the poor who concerned Malthus. Does this sound familiar?
68. 68 Current politics (welfare reform) aside, it also puts a new interpretation on contemporary fussing about population growth. Specifically, as you now see, most of the population growth in the world occurs in the poor countries, while the rich countries are not having very many children. And the ones we do have are, for the most part, well taken care of.
69. 69 Latter-day Malthusians who complain about population growth are quite ready to whine about family size among the poor (in the tropics), while overlooking the ostentatious and often obscene consumption patterns of those of us in the rich countries. The real threat to nature over the long run is not their numbers (family size). The serious threat is that they may someday be wealthy enough to consume and waste resources on a scale similar to our patterns of consumption. If you want to worry about nature, there is something to worry about.
70. 70 SUMMARY
1. World population will probably stabilize at 8-9 billion;
2. The faster we can help improve the living conditions (both economic and social) in the developing world, the quicker world population will stabilize;
3. It is a mistake for the U.S. government to oppose family planning programs in the poor countries;
Market-capitalism will be undermined by the prospects of zero-population growth unless fundamental changes occur in how we think of economic relations. This follows from the inherent aspect of capitalism which is the continued production of stuff in order to continue economic growth. If populations stabilize, consumption stabilizes and this can be problematic if all policies are predicated on growth. Several western European countries (Italy, Germany, others?) are now struggling with this problem.
