3-1-tragedy of commons.pdf

7/30/2019 3-1-Tragedy of Commons.pdf

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The Earth is made up o large, connected systems. As we discussed in the

introduction, human activity is changing many o these systems - especially

those involving the surace o the planet the atmosphere, oceans, orests

and ecosystems. For each o these systems, take a moment to think o and

describe a way in which you believe the system has been degraded or other-

wise negatively eected by human activity. Make a note o your answers well

come back to them at the end o this lecture.


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There are o course many answers. For example, you may have said that the

atmosphere is being polluted by greenhouse gases or smog, or that surace

lights have obscured the stars in the night sky. Forests have been logged, pre-

vented rom going through natural orest re cycles, and suered introduced

species, such as the emerald ash borer. Oceans have suered over-shing,

plastic pollution and run-o rom arms. Ecosystems have been transormed

by human land use, while some species have even become extinct. I we

wish to live sustainably, we must solve these problems.

This seems hard, as it is a long list o problems but while the details

change, there is oten an underlying principle that each o these problemshave in common.


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Is there some kind o general hidden me

these dierent problems? I we nd a gene

nd a general solution.


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There is a uniying model, or concept, that can help us

understand many o the environmental problems that we

ace. This concept was rst described by Garrett Hardin in

1968 and is known as the Tragedy o the Commons.


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In this case, commons means a shared area open to all. An early ex-

ample would be a common grazing area. No one herdsman owned the

land, but all the herdsman shared the land and its resource odder or

their livestock.


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The tragedy reers to the inevitable destruction o the

in this case, overgrazing will cause all the grass to be

that it will not recover, and wind and rain will remove

mons topsoil, degrading it rom lush rangeland to a panse. It is a central part o this concept that this des

inevitable. I overgrazing is the result o too many ani

many sheep, goats, cattle, reindeer or anything else

o a nite plot o land, why might overgrazing be inev


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Lets illustrate this tragedy sequence with a simple model.


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Consider a single common pasture.


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I it is overgrazed, the pasture will become steadily more degraded, as the

cattle eat the grass aster than it can grow. I the pasture is denuded o grass, it

is vulnerable to topsoil loss when conditions are unusually dry or wet.


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I the top soil is lost, the grass will never recove

will be supported in the uture.


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As a group, the armers do not want to overgraze the commons.


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The individual incentive is

Its in each armers own

many cattle as possible, a

the amount o meat and

a subsistence armer, ev

could really help by ma

between having well-ed

children, or example.


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And i one o your neighbors grazes three cattle and you have only have two, it

would only be air to add to your herd even i your other neighbor has only one

cow.


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Each extra cow degrades

degradation is shared.


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I ty armers have a total o 100

cows on the commons , adding a

single cow will increase your pro-

ductivity by 50% (rom 2 to 3 milk

producers), but the commons is only

1% more utilized (rom 100 cows to

101). So or every individual armer,

its well worth adding livestock.


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Its especially well worth doing

ers have the same incentive

way and take the same action


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I you do nothing, the commons will still be degraded, and your long-term uture is still blea


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The Tragedy o the Commons con-

cept is now used metaphorically to

describe many Earth systems.

The Tragedy reers to the inevita-

bly o the destruction o the naturalsystem, and the Commons reers

to any shared resource that is open

to all. So the Tragedy o the Com-

mons claims that i a resource is

open or use by anyone, it will be de-

stroyed.


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Examples o Commons include the atmosphere we

all share the same air oceans theyre all connected,

and owned by no one and many orests.


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Global sheries are perhaps the strongest evidence that the Tragedy o the Commons

concept has some validity.

The oceans are a shared resource with many individual sherman but i too many sh are

extracted, the shery collapses there are not enough mature sh let to repopulate. The

Tragedy o the Commons would predict that sherman would increase their catches past

the sustainable limit. It is in the interests o each individual sher to catch as many sh as

possible but when all shers maximize their own catch by purchasing more and bigger

boats rates o extraction can exceed rates o repopulation.


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This has been observed in

world. As an example, here

northwest Atlantic. Notice h

o improved shing techniqu

in the shing feet in the 50s

creased catch, at rst, until o

the supply. The decline in th

only a tiny raction o sh is t

compared to hal a century a


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And this pattern is repeated everywhere. Note on this graph that the number o over-exploited or collapsed sheries (o

and red portions o the graph) have increased rom almost nothing to around hal o all sheries. The northwest Atlant

shery is an example o a collapsed shery. The other hal are currently ully exploited. The overshed and collapsed

ies are clearly bad or the sh and their ecosystem, but theyre also a disaster or coastal communities the rational ac

o individual have created a collective disaster, devastating the livelihoods o millions and destroyed valuable resource


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Greenhouse gas warming o the atmosphere by

ossil uels can also be thought o as a Tragedy o

the Commons. In this case, using ossil uels has

a private benet individual countries and peoplegain the use o cheap energy, while the carbon di-

oxide produced pollutes the common resource o

the atmosphere.

So individual users gain all o the benet but experi-

ence only an innitesimal part o the cost. Collec-

tively, however, the atmosphere is degraded. Does

this mean that there is no hope in preventing large-

scale climate change, just as we have been unable

to prevent the collapse o sheries? Perhaps but

we will examine potential solutions to the Tragedy

o the Commons in the next lecture.


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3-1-tragedy of commons.pdf

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