Population Growth and Need for Advanced Technologies

1
Population Growth and Need for Advanced
Technologies

• Population, Carrying Capacity

2
Population Terminology

• Biotic potential - ability of populations to
  increase
• Environmental resistance - combination of all
  biotic and abiotic factors that may limit
  population increase
• Critical number - minimum population required to
  sustain a species

3
Nebel/Wright, Environmental Science, 7th,
Prentice Hall, NJ, 2000, 85
4
Types of Growth

• Arithmetic (linear) growth - constant amount of
  increase per unit time (difference between points
  is constant) 5, 10, 15. (Graph is linear)
• Geometric (exponential) growth - constant rate of
  increase per unit time (points are constant
  multiples) 2, 4, 8, 16 (Graph is J-shaped,
  J-curve)

5
Cunningham/Saigo, Environmental Science, 6th,
McGraw Hill, MA, 2001, 130
6
Population Curves

• For most species the biotic potential is
  geometric, however, it is not unlimited
• Carrying capacity - maximum population of an
  animal that a given habitat will support without
  the habitat being degraded over the long term
• Environmental resistance modifies the geometric
  J-curve to an S-curve

7
J- and S-Curves
Cunning-ham/Saigo, Environmental Science, 6th,
McGraw Hill, MA, 2001, 132
8
World Population Curve a J-Curve
Joesten,Essentials,Saunders, 1993,324
9
Population Predictions

• Total Fertility Rate or Replacement level no.
  of offspring per pair of parents
• Zero population growth occurs when replacement
  level 2
• Models have been constructed using estimated
  replacement levels
• Models predict a population of 10.4 B by 2100,
  8.9 B in developing countries

10
Population Growth
Turk, Intro to Envir. Studies, 3rd, Saunders,
NY, 1989, 85
11
Significance of Carrying Capacity

• If the population of a species exceeds its
  carrying capacity, a dieback occurs, usually
  followed by recovery
• If the dieback takes population below its
  critical number, however, it can result in the
  extinction of the species

12
Population Growth and Carrying Capacity
Critical
Recovery
Number
Cunning-ham/Saigo, Environmental Science, 6th,
McGraw Hill, MA, 2001, 131
13
Earth's Carrying Capacity for Humans

• The carrying capacity of Earth for humans is not
  known
• In 1970, J.A. Campbell made rough calculations of
  several factors that might limit Earth's carrying
  capacity for humans assuming that society is
  unwilling/unable to control population growth

14
Estimating Carrying Capacity

• Crude estimates of carrying capacities for some
  variables do not require chemical knowledge
• Rainfall on entire earth is 2 x1019 L/yr of which
  3 x1017 L falls on land and serves as potential
  source of drinking water for humans
• Consumption in developed countries is 107
  L/person/yr.

15
Continued

• Estimate the carrying capacity for humans on
  earth with respect to available water
• (3 x1017 L/yr)/(107 L/person/yr) 3 x1010
  persons carrying capacity with respect to water
• Other variables require knowledge of chemical
  equation to estimate carrying capacities

16
Use of Chemical Equations to Estimate Carrying
Capacity

• Coefficients in a balanced equation express
  ratios in which moles of substances react
• 2 H2 O2 gt 2 H2O
• 2 moles 1 mole 2 moles
• 4 g 32 g 36 g
• 2 moles 1 mole 2 moles

17
Continued...

• Find moles of water that can be obtained by
  reacting 4 moles of oxygen with hydrogen
• 2 H2 O2 gt 2 H2O
• 2 moles 1 mole 2 moles
• (4 mol O2)(2 mol H2O /1 mol O2)
• 8.0 mol of H2O

18
Weight-Weight Calculation

• Given the weight of one participant in a chemical
  reaction, calculate the weight of another
  participant in same reaction
• Assuming that photosynthesis produces 6.4 x 1017
  grams of O2 per year, estimate the weight of
  glucose that is produced by photosynthesis
  annually

19
Continued...

• 1. Write balanced equation 6
  CO2 6 H2O gt C6H12O6 6 O2
• 2. Convert grams of the given substance to moles
  of the given substance
  (6.4 x 1017 g of O2)(1 mole of
  O2/32 g of O2) 2.0 x 1016 moles of O2

20
Continued...

• Using mole ratio implied by the balancing
  coefficients of the equation, 6 CO2 6 H2O gt
  C6H12O6 6 O2, convert moles of the given
  substance to moles of the sought substance
  (2.0 x 1016 mol O2)( l mol C6H12O6/ 6 mol O2)
  3.3 x 1015 mol C6H12O6

21
Continued...

• Convert moles of sought substance to grams of
  sought substance (3.3 x 1015 mol
  C6H12O6)(180 g/mol C6H12O6 ) 6.0 x 1017 g of
  C6H12O6

22
1970 Estimates of Limiting Factors in Carrying
Capacity
10
Campbell concluded in 1970 that heat probably
would be the ultimate limiting factor and urged a
switch to solar power
Campbell, J.A., Chemical Systems, Freeman, CA,
1970, 16
23
Need for Advanced Technologies

• Increase in population seems likely
• This increase will require additional food,
  materials, and energy to avoid a dieback (or
  extinction)
• The water cycle and the gaseous parts of C-cycle
  appear to be sufficiently fast to fulfill needs
  except for fossil fuel formation which takes 1 M
  years

24
Continued...

• The N-cycle, however, is significantly slower due
  to stability of N2 molecule (N?N triple bond
  has bond energy of 225 kcal/mole)
• The P-cycle is the slowest natural cycle since it
  involves no gases and ionic solid phosphates are
  only sparingly soluble in water

25
Continued...

• N and P are not supplied at sufficiently fast
  rates to supply food for the current population
  of the world, ? advanced technology required
• Fossil fuels are not produced rapidly enough by
  the C-cycle to be a renewable source of energy,
  ? advanced technology required