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?

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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 Monaco 21,781 2 Singapore 6,814 3 Vatican City 1,877 4 Bahrain 1,454 5 Malta 1,309 6 Bangladesh 1,211 172 United States 31

NY City 10,606 Manhattan 27,490

World 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?

Year 950 1420 1600 1720 1804 1875 1927 1961 1974 1999 2024

Pop. 250million

375 million

500 million

750 million

1.0 billion

1.5 billion

2.0 billion

3.0 billion

4 billion

6 billion

8 billion

Time to next double

650 300 204 155 123 86 47 38 ~50

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

Fire, tool-making

Industrial revolution

Green revolution

UN Population Scenarios

Converting solar energy into food

The Trophic Pyramid

Trophic (feeding order) Pyramid

The Trophic Pyramid

Why so little passedon?

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?

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US GDP Growth last quarter? 1%

China GDP Growth last quarter?

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US GDP Growth last quarter? 1%

China GDP Growth last quarter?9.5%

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Tragedy of the Commons

Garrett Hardin 1968- Article is on ELMS

A commons is an open spaceavailable 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?

PrivatizationIf I own the land, it is in my interest to adjust the

number of cows to prevent catastrophe

RegulationAn 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.”

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Challenged the conventional wisdom by demonstrating how local property can be successfully managed by local commons without any regulation by central authorities or privatization.

Larry David explains Elinor Ostrom's work

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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