Transcript 04_Population and Tragedy f10 (6)

Population
The power of population is infinitely greater than the power in the earth to
produce subsistence for man. – Malthus - 1798
Since last class – world population increased by ~ 1,090,000
Rule of thumb for exponential growth
Amount doubles in:
t = 70/growth rate (%)
If population is growing at 2%/year, it doubles in 35 years…
P(t) = (1 + g)n p(0) ~ en g p(0)
Linear vs. exponential growth
Both curves have same increase in first year
Carrying Capacity
How many people can the Earth hold?
Page 5
Thomas Malthus
 1798 Essay on the Principle of Population
- Population grows exponentially
- Food grows linearly
- Eventually there will be a problem
- Leading to misery, vice, and poverty
- Underestimated human ability to increase food production…
- But…
Population Density (people/km2)
1
2
3
4
5
6
 172
Monaco
21,781
Singapore
6,814
Vatican City 1,877
Bahrain
1,454
Malta
1,309
Bangladesh 1,211
United States 31
 NY City
 Manhattan
 World
10,606
27,490
?
13
Population Density
 To get 1pers/m2 NYC would only have to go up a factor of 100
 Is the world population doubling rate steady?
1600
1720
1804
1875
1927
1961
1974
1999
2024
250mi 375
500
750
1.0
1.5
2.0
3.0
4
6
8
llion
million
million
million
billion
billion
billion
billion
billion
billion
billion
650
300
204
155
123
86
47
38
~50
Year
950
Pop.
Time to
next
double
1420
Population
 When I was your age – the world’s population was ~3 billion
 When you are my age – the world’s population will be 9 billion
 How many people can the earth hold - “carrying capacity”?
- The surface area of the earth is ~5 x 1014m2 - but 2/3 is ocean so let’s say
there are 2 x 1014m2 available.
- So there is 1 person in 2 x 1014 / 7 x 109 = ~3000 m2 over the land area of the
earth – 1pers/.003km2 or ~35 people/km2
- This room has 1pers/m2 – that looks like enough for me…
 How long will it take for the population to go up by a factor of 3000 to 27 trillion
(2x1013) assuming a 35 year doubling period?
- Every doubling period the pop. goes up 2 so after m periods the population is
2m higher.
- 211 is 2048 – 212 is 4096 – so it will take ~11.5*35 = ~400 years
Population
 Another way – energy
- To survive we need about 2000 kcal – 8400kJ of food/day
- The solar energy (used to grow food) is about 8x1018kJ/day
- So if we use all solar energy to produce just food 100% efficiency
– we can support ~1015 people
Estimates of Human Population
Estimates of Human Population
Green revolution
Industrial revolution
Fire, tool-making
UN Population Scenarios
Converting solar energy into food
The Trophic Pyramid
 Trophic (feeding order) Pyramid
The Trophic Pyramid
 Why so little passed
on?
The Trophic Pyramid
The Trophic Pyramid
 Photosynthesis is about 5% efficient in turning sunlight to sugars
 In the US about 1/3 are primary consumers and 2/3 are either
secondary or tertiary so take an average of 5%
 So take this and we get 5 x10-2 x 5 x10-2 = 2.5x10-3 as the fraction
of energy available for people and get
 ~1014 people x 2.5x10-3 = 2.5 x 1012 =250 billion people
Arable land
 Only 25% of the Earth’s land is capable of sustaining crops
- Its currently expensive to increase the amount of arable land
- Israel did it, but it was expensive. Israel's land primarily
consisted of desert until the construction of desalination plants
along the country's coast.
Another calculation
 Need to share some food with animals that aren’t directly in our
food chain
- Say another factor of 2
 We have a factor of 4 from arable fraction and another factor of 2
from sharing
 So we take our 250 billion people and cut it down by a factor of 8
and we get to 30 billion
 These represent some sort of absolute upper limits
 With a 35 year doubling we would hit this limit in your lifetime…
Where the People Are
How Many Humans Have Ever Lived?
 Answer depends entirely on when we start counting “humans”
 Lower limit: assume two “modern Homo sapien sapiens” in 50,000
BC
50 billion born before 1 AD
60 billion born after 1 AD, of which
6.9 billion alive today
Area Proportional to Population
Area Proportional to Population
Projections Trending Downward
Fertility Declining Faster Than Expected
Infant Mortality Rates
Life Expectancy: UN Medium
Life Expectancy Increasing
Population Pyramids
What are these bumps?
Population Pyramids
What Determines Carrying Capacity?
 Standard of living (what kind of life?)
 Technology
 Food and fiber (land, nutrients, fisheries)
 Water
 Energy (fossil, nuclear, solar?)
 Metals, minerals, other resources
 Waste assimilation
 Disease
 War
Estimates of Carrying Capacity
Economic growth
Q. Can we have economic growth forever?
- most economists see 3% growth as healthy
“any sustained period of GDP growth below 2.5% is a recipe
for rising unemployment and sluggish wage growth.”
Economic Policy Institute, April 2008.
3% growth would correspond to a 23 year doubling time
Q. How do we grow without consuming more resources?
“Sustainable growth” - an oxymoron
US GDP Growth last quarter?
China GDP Growth last quarter?
Page 38
US GDP Growth last quarter?
China GDP Growth last quarter?
Page 39
1%
US GDP Growth last quarter?
1%
China GDP Growth last quarter?
9.5%
Page 40
Tragedy of the Commons
 Garrett Hardin 1968
- Article is on ELMS
 A commons is an open space
available to all
 Hypothetical case of 10 dairy
farmers using the land
- In hard times everyone has a
few cows and there is plenty of grass for all
- As things improve we assume the that eventually we get 20 cows
each (total 200 cows) and we have reached the carrying capacity
of the land
Tragedy of the Commons
 What should a rational farmer do?
- If he adds a cow he gets the benefit of another cow
- However all the cows including his 21 now only get 200/201
(99.5%) of the nutrition it needs produce a full amount of milk
- Mathematically lets say his benefit is +1 from the extra cow but
each cow loses about 0.5% so he loses ~10% of one cow so his
net profit from adding the cow is 9/10 of a cow
- So he should do it
- And so should everyone else
 What happens next?
How do we deal with T.o.t.C?
Privatization
If I own the land, it is in my interest to adjust the number of
cows to prevent catastrophe
Regulation
An organization (usually governmental) set rules to make
sure catastrophe does not happen
G. Hardin - 1998
 "A 'managed commons' describes either socialism or the privatism
of free enterprise. Either one may work; either one may fail: 'The
devil is in the details.' But with an unmanaged commons, you can
forget about the devil: As overuse of resources reduces carrying
capacity, ruin is inevitable."
Crticisms of T.o.t.C?
 Often used as an excuse to argue for privatization
 Simplifies individual’s concept of self-interest to an extreme
 Used as an excuse for “excessive” regulation
 Neglects innovation that “expands” the common
2009 Nobel Prize in Economics
Elinor Ostrom
“for her analysis of economic governance,
especially the commons.”
Challenged the conventional wisdom by
demonstrating how local property can be
successfully managed by local commons
without any regulation by central authorities
or privatization.
Page 47
Larry David explains Elinor Ostrom's work
Page 48
Tragedy of the Commons as the Earth
 Uncontrolled human population growth leading to overpopulation.
 Water - Water pollution, Water crisis of over-extraction of
groundwater and wasting water due to overirrigation.
 Forests - Frontier logging of old growth forest and slash and burn.
 Energy resources and climate - Burning of fossil fuels and
consequential global warming
 Animals - Habitat destruction and poaching leading to mass
extinction.
 Oceans – Overfishing, depletion of populations
TANSTAAFL
 There ain’t no such thing as a free lunch
- Every thing has a cost
- This cost may not be obvious at first
- Ozone
- Industrialization
- Pollution
- Energy usage
- Cell phones
- Bad driving
- Nuclear Energy
- Waste
- Proliferation