Introduction and Human Population Growth

Chapters 1 & 2

Unit Organization:

• Introductory Remarks
• History of Human Population Size
• Population Growth
• Carrying Capacity and Overpopulation
• Malthus and the Demographic Transition
• Population Policy
• Ancillary Resources and Links

Reading:

Textbook:  Chapters 1 & 2

Ancillary Reading on the meaning of exponential growth: Stead growth and doubling time

Some introductory comments on Environmental Science

I will not spend much class time on the first chapter, as it is fairly general but not difficult

Points I want to emphasize

• Why environmental science now?  Pollution has been around for a long time
  • Human population is so large that we can alter large systems, including the entire planet
  • This makes all of us interconnected in ways we have never been (Globalization is not just an economic term)
• How do we approach the topic in this class?
  • We are either scientists or those who wish to be scientists here (I am including a view of medicine in which doctors contribute to as well as benefit from science)
  • Because of the above, we will focus on the scientific basis of the problems we face
• However, our focus on the science does not allow us to ignore other aspects of any environmental problem
  • Garret Hardin:  The law of unintended consequences
  • This observation links all human activities and natural processes.  Such a complex web of interactions means that, when one attempts to think about or to affect any one part of the web, one necessarily must either consider or affect many other parts of the system
• The interconnectedness of the system means we will encounter both types of feedback
  • Negative feedback, where increasing output acts to slow the system down
    • Negative feedback leads to regulation about some steady point
  • Positive feedback, where increasing output acts to speed the system up
    • Positive feedback leads to exponential growth
• Environmental Impact depends on the per capita effects (how much does each person use or produce) and the populations size
  • Impacts are discounted in two ways:
    • Future Discounts:  impact felt all or partially in the future
    • Distance Discount:  impact felt in another place or in only a small part of home
• Hardin's Law of the common: If not regulated, each consumer of the common benefit will act to maximize individual benefit, without regard to other's benefits, until the common provides no positive benefits (also known as the tragedy of the commons)

History of Human Population Size

• Agricultural (Neolithic) Revolution - ~10,000 YBP (surplus production and culture, no drastic change in growth rate)
• Lag Period until Industrial Revolution (~1800 A.D.)
• Germ Theory and public sanitation and drop in death rate
• Since 1900, world growth rate has undergone large fluctuations but, has generally declined from a peak in the 1960's (around 2.3%) to the present (about 1.2%)

Distribution of Human Population

Geographic Distribution of Human Population

• North America has experienced most change since Industrial Revolution (the onset of rapid increase)
• Europe the least
• Currently, Africa is experiencing greatest growth rate (with the Middle East included)
• Most of humanity experiences a density of between 100 and 1000 per square kilometer
  • US density is 34 ppsk (people per square km)
  • Tennessee has 59 ppsk
  • NJ (most dense state) has 461 ppsk, Wyoming (least dense of lower 48) has 2.3 ppsk, and Alaska (least dense) has 0.5 ppsk
  • Washington, D.C. (just the district, no including the surrounding communities) density is 3801 ppsk

Economic Distribution of Human Population

• The recent trend has caused a shift away from industrially developed countries to less developed countries
  • MDCs are the US, Canada, the European Union, Japan, Russia, Australia, and New Zealand
  • The distinction between the MDCs and the LDCs is becoming harder to draw, as China and several other LDCs are becoming more industrialized

Future of Human Population

• Recent decline in growth rate
• Predictions of growth generally reflect the recent decline and show a slowing of growth
  • Most show us reaching at least 9,000,000,000 from the current 7,000,.000,000 by 2050 but that the time to add additional billions will be increasing (not decreasing as it has been)
• Predictions beyond 2050 reflect outlook of those doing the prediction
  • Some will show a "maximum" population, others will assume no limit

Population Growth Theory

• Exponential growth
• constant growth rate
• Doubling time
• Implications of exponential growth

Carrying Capacity and Overpopulation

Logistic Growth vs Exponential Growth

• Lag period
• Exponential period
• Inflection point
• Carrying Capacity

Does the Earth have a carrying capacity

• Ecological Footprint
• Role of technology

Regional versus Global impact

Population Age Structure

• Growing populations have a "pyramid"
• Declining populations are narrower at base than at middle
• For stable populations, a stable age distribution results
• Growing populations tend to be young, declining or stable populations are older

Malthus and the Demographic Transition

Sampling Variation

Robert Malthus (1766 to 1834 - at start of population increase) was a clergyman, an economist, and an influential essayist on social problems in England

• Essay on the Principle of Population
  • resources increase incrementally, population increases exponentially
  • resource limitation will check population growth
  • checks can be
    • Positive
      • increase in death rate
      • war, famine, disease
    • Preventative
      • decrease in birth rate
      • abstinence before marriage, birth control, abortion, late marriage, celibacy, prostitution
  • argued that virtue would lead to moral restraint and effect those preventative checks

Demographic Transition

• Europe and North America experienced a fall in death rates at the onset of industrialization
• Both then experienced a fall in birth rates to a level roughly equal to the death rate
  • These two events constitute a demographic transition from non-industrial to industrial society
• During the time between fall in death rate and fall in birth rate, population will grow rapidly but will level off after transition is completed
• Reasons given for transition focus on role of women in society and attitudes toward children
  • Some feel that overpopulation will not be a problem as all societies will eventually undergo the transition and the human population will stabilize
  • Others point out that the ecological footprint of industrial societies is too large for all societies to undergo the transition

Population Policy

Is there a population problem?

• Approach depends on whether or not you assume a carrying capacity and how close you think we are to reaching that number
  • Those who believe that no attempt to limit population should be made argue that
    • we are far from any possible carrying capacity
    • growth rate is slowing and the human population will eventually stop growing
    • technology will increase the carrying capacity in time alleviate any resource limitation
  • Those who believe that we must solve a population problem point out that
    • we can detect human impacts in every ecosystem on Earth
    • the ecological footprint of societies that have undergone the demographic transition indicates that, were all alive today to increase their ecological footprint to that level, we will exceed Earth's carrying capacity
    • argue that technology has not decreased the footprint but has increased it

If there is a population problem:

Many policy approaches are possible

• Some take direct action on growth
  • Legislation limiting or favoring small family size
  • Often seen as coercive
• Some aim at changing attitudes and encouraging changes associated with decline in fertility associated with the demographic transition
  • Making family planning available
  • Increasing educational opportunities, especially for women

Ancillary Materials and Links

• Materials posted to the myTSU website (on the files page)
  Small, Christopher.  2004.  Global Population Distribution and Urban Land Use in Geophysical Parameter Space.  Earth Interactions 2(8). pp: 1-18.

Last updated January 25, 2012