• How external costs and benefits affect tradeoffs.
• What effects externalities have on market price, quantity, and surplus.
• What private solutions to externalities exist.
• How taxes, subsidies, quantity regulations, and tradable allowances can be used to counteract an externality.
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11© 2014 by McGraw-Hill Education
Chapter 18
Externalities
2© 2014 by McGraw-Hill Education
• How external costs and benefits affect trade-
offs.
• What effects externalities have on market
price, quantity, and surplus.
• What private solutions to externalities exist.
• How taxes, subsidies, quantity regulations, and
tradable allowances can be used to counteract
an externality.
What will you learn in this chapter?
3© 2014 by McGraw-Hill Education
• When individuals make calculated decisions, they
weigh the costs and benefits of the action.
– Private benefit that accrues directly to the decision
maker.
– Private cost that falls directly on an economic decision
maker.
• Sometimes other people are affected by our
decisions or have a stake in the outcomes.
– External cost describes a cost imposed without
compensation on someone other than the person
who caused it.
– External benefit describes a benefit that accrues
without compensation to someone other than the
person who caused it.
What are externalities?
24© 2014 by McGraw-Hill Education
• The total cost of a decision, the social cost, includes
both private costs and external costs.
• The total benefit of a decision, the social benefit,
includes both private benefits and external benefits.
• External costs and external benefits are collectively
referred to as externalities.
– Negative externality: external costs.
– Positive externality: external benefits.
• A network externality is the effect that an additional
user of a good or participant in an activity has on the
value of that good or activity for others.
– Can be positive or negative.
External costs and benefits
5© 2014 by McGraw-Hill Education
How can drivers be forced to consider external costs, and thus operate
on the social demand curve?
• The most straightforward option is to implement a gasoline tax.
Negative externality from the demand side
Market with private costs only
0
Quantity of gasoline (billions of gals.)
Price ($/gal.)
3
20
Sprivate
Dprivate
0
3
20
Quantity of gasoline (billions of gals.)
Price ($/gal.)
Sprivate
Dprivate
Market with social costs
Tax
1
Dsocial
1. If drivers bear full social
costs, the social demand
curve is below the private
demand curve
2.5
15
2. and the equilibrium is
at a lower price and
quantity.
If drivers ignore the external cost of pollution,
they only consider the private costs and
benefits of driving.
When drivers bear the full social cost, the
externality is eliminated and they drive less.
6© 2014 by McGraw-Hill Education
X
Y
Producer surplus
B
A
Consumer surplus
A tax increases surplus when a negative externality is
present in the market.
Negative externality from the demand side
Quantity of gasoline (billions of gals.)
Surplus when a negative
externality is internalized
0
Quantity of gasoline (billions of gals.)
Price ($/gal.)
Sprivate
Dprivate
2.5
15
Dsocial
Surplus under a negative
externality
0
3
20
Price ($/gal.)
Sprivate
Dprivate
2
1 C
External cost
• Under a negative externality, the surplus lost to
those outside the market due to the external
cost is subtracted from consumer and producer
surplus, C.
• Area C is equal to $1 × 20B = $20B.
• If the externality is internalized, demand shifts
downward by the amount of the tax.
• CS and PS in the market are both lower.
• The external cost imposed on people is
eliminated.
37© 2014 by McGraw-Hill Education
X
Y
Producer surplus
B
A
Consumer surplus
Suppose that a $1 per unit tax can mitigate a negative externality. Using the following graphs:
• Calculate total surplus in the presence of a negative externality.
• Calculate total surplus when the negative externality is internalized.
Active Learning: Calculating the cost of
negative externalities
Quantity of gasoline (billions of gals.)
Surplus when a negative
externality is internalized
0
Quantity of gasoline (billions of gals.)
Price ($/gal.)
Sprivate
Dprivate
2.5
37.5
Dsocial
Surplus under a negative
externality
0
3
50
Price ($/gal.)
Sprivate
Dprivate
2
1 C
External cost
1
5
1
5
8© 2014 by McGraw-Hill Education
Gain in total surplus
when externality is
internalized.
Surplus lost by
consumers and
producers.
A negative externality always reduces surplus unless
it is internalized.
Negative externality from the demand side
0 20
Quantity of gasoline (billions of gals.)
Price ($/gal.)
S
private
D
private
D
social
2.5
15
Tax
1
Surplus gained
by pollution
sufferers.
3
2
• When the negative externality is
internalized by imposing a tax, the
demand curve shifts downward.
– Smaller quantity sold.
• CS and PS is lost from imposing a
tax.
• Surplus is gained by others in
society when they receive surplus
from tax revenue.
• Surplus gain is yellow area.
9© 2014 by McGraw-Hill Education
How can drivers be forced to consider external costs, and thus operate
on the social supply curve?
• The most straightforward option is to implement a gasoline tax.
Negative externality from the supply side
Market with private costs only
0
Quantity of gasoline (billions of gals.)
Price ($/gal.)
3
20
Sprivate
Dprivate
0
3
20
Quantity of gasoline (billions of gals.)
Price ($/gal.)
Sprivate
Dprivate
Market with social costs
Tax
1
1. If gasoline retailers bear
full social costs, the social
supply curve is above the
private supply curve
2. and the equilibrium is
at a higher price and
quantity.
If drivers ignore the external cost of pollution,
they only consider the private costs and
benefits of driving.
When drivers bear the full social cost, the
externality is eliminated and they drive less.
Ssocial
3.5
15
410© 2014 by McGraw-Hill Education
X
Y
Producer surplus
B
A
Consumer surplus
A tax increases surplus when a negative externality is
present in the market.
Negative externality from the supply side
Quantity of gasoline (billions of gals.)
Surplus when a negative
externality is internalized
0
Quantity of gasoline (billions of gals.)
Price ($/gal.)
Sprivate
Dprivate
Surplus under a negative
externality
0
3
20
Price ($/gal.)
Sprivate
Dprivate
External cost
• Under a negative externality, the surplus lost to
those outside the market due to the external
cost is subtracted from consumer and producer
surplus, C.
• This area equals $1 × 20B = $20B.
• If the externality is internalized, supply shifts
upward by the amount of the tax.
• CS and PS in the market are both lower.
• The external cost imposed on people is
eliminated.
4
1 C
Ssocial
3.5
15
11© 2014 by McGraw-Hill Education
Gain in total surplus
when externality is
internalized.
Surplus lost by
consumers and
producers.
A negative externality always reduces surplus unless
it is internalized.
Negative externality from the supply side
0 20
Quantity of gasoline (billions of gals.)
Price ($/gal.)
S
private
D
private
S
social
Tax
1
Surplus gained
by pollution
sufferers.
3
2
• When the negative externality is
internalized by imposing a tax, the
supply curve shifts upward.
– Smaller quantity sold.
• CS and PS is lost from imposing a
tax.
• Surplus is gained by others in
society when they receive surplus
from tax revenue.
• Surplus gain is yellow area.
2.5
15
12© 2014 by McGraw-Hill Education
• A positive externality also pushes quantity away from the efficient
equilibrium level, reducing total surplus.
• Internalizing a positive externality, the market reaches an equilibrium with a
higher quantity based on social costs and benefits.
Positive externalities from the demand side
3,000
0
Quantity of houses painted
Price ($)
Sprivate
Dprivate
1,500
300
Dsocial
3,500 1. When homeowners captureexternal benefits, the social
demand curve for house
paintings is above the private
demand curve, and
500
2. the equilibrium point
moves to a higher price
and quantity.
1,700
360
• Suppose a homeowner
painting a house provides
$500 in external benefit
to the neighborhood.
• If homeowners are able
to capture the external
benefits of painting a
house, demand shifts
upward.
– Larger quantity.
513© 2014 by McGraw-Hill Education
A
Consumer surplus
B
Producer surplus
The increase in total surplus can be calculated when
a positive externality is present.
Positive externalities from the demand side
• Internalizing the externality
– CS and PS increase; external
benefits disappear
• TS = X + Y = $540,000
Sprivate
X
Y
Dsocial
Dprivate
Surplus under a positive externality
0
3,000
3,500
300
Quantity of houses painted
Price ($)
Sprivate
Dsocial
Dprivate
Surplus when a positive externality is internalized
0
1,700
3,000
3,500
360
Quantity of houses painted
Price ($)
1,500
2,000
C
External benefit
• Area C is the amount of surplus gained by
those outside the market and is added to
consumer and producer surplus.
• This surplus equals $500 × 800 = $150K.
14© 2014 by McGraw-Hill Education
A
Consumer surplus
B
Producer surplus
Active Learning: Calculating positive
externalities
Sprivate
X
Y
Dsocial
Dprivate
Surplus under a positive externality
0
1,000
1,250
200
Quantity of houses painted
Price ($)
Sprivate
Dsocial
Dprivate
Surplus when a positive externality is internalized
0
291
1,000
1,250
256
Quantity of houses painted
Price ($)
250
500
C
External benefit
Suppose a negative externality exists and a $250 per unit subsidy resolves it.
• Calculate total surplus in the presence of a positive externality.
• Calculate total surplus when the positive externality is internalized.
100 100
15© 2014 by McGraw-Hill Education
Gained from
extra trades.
• When the positive
externality is internalized by
imposing a subsidy, the
demand curve shifts
upward.
– Larger quantity sold.
• CS and PS is lost from
internalizing externality.
• Surplus is gained by market
participants receiving a
subsidy from tax revenue.
• Surplus gain is green area.
Positive externality from the demand side
Lost when
externality is
internalized.
Gained when
externality is
internalized.
Sprivate
Dprivate
3,000
0
Quantity of houses painted
Price ($)
300
1,500
2,000
3,500
Dsocial
360
A positive externality always reduces surplus unless
it is internalized.
616© 2014 by McGraw-Hill Education
• A positive externality also pushes quantity away from the efficient
equilibrium level, reducing total surplus.
• A subsidy corrects this market inefficiency, increasing surplus.
Positive externality from the supply side
Under a positive externality, the surplus by those
outside the market is added to consumer and
producer surplus, Area C.
• If the externality is internalized through a
subsidy, the supply curve shifts downward.
• CS and PS in the market are both higher.
• The external benefit is now internalized to only
market participants.
B
Producer surplus
A
Consumer surplus
Quantity of houses painted
Surplus under a positive
externality
300
Price ($)
Sprivate
Dprivate
C
$1500
$1000
$500
External benefit
$3000
X Ssocial
$1300
Y
Quantity of houses painted
Surplus under a positive
externality
0 360
Price ($)
Sprivate
Dprivate
$3000
17© 2014 by McGraw-Hill Education
Positive externality from the supply side
0 300
Quantity of houses painted
Price ($) Sprivate
Dprivate
Dsocial
360
$1000
$1500
Ssocial
Lost when
externality is
internalized.
Gained when
externality is
internalized.
$500
Gain in total surplus
when externality is
internalized.
A positive externality always reduces surplus unless
it is internalized.
• When the positive externality is
internalized by imposing a subsidy,
the supply curve shifts downward.
– Larger quantity sold.
• CS and PS is lost from internalizing
externality.
• Surplus is gained by market
participants receiving a subsidy
from tax revenue.
• Surplus gain is green area.
18© 2014 by McGraw-Hill Education
• External costs and benefits can be diffuse,
complex, and hard to control.
• Solutions must ensure that individuals experience
costs and benefits that are equal in value to the
true social costs and benefits of their choices.
– This may require coordinating across millions of
people.
• The Coase theorem states that if there are zero
transaction costs to negotiate and agreements are
enforceable, then an efficient equilibrium through
private trades can be reached, even in the
presence of an externality.
• Often, these two assumptions do not hold true.
Dealing with externalities
719© 2014 by McGraw-Hill Education
• Because of the cost and difficulty of coordinating
private solutions, people often turn to public
policy for solutions to externalities.
• A Pigovian tax counters the effects of a negative
externality.
• There are two main problems with this solution:
– Setting the tax at the right level.
– No guarantee that the government can or will do
anything to help people bearing the external cost.
Dealing with externalities
20© 2014 by McGraw-Hill Education
As previously analyzed, a tax can move the market
equilibrium to the social optimal equilibrium.
Dealing with externalities
0 15 20
1
2.5
3
4
5
S
Quantity of gasoline (billions of gals.)
Price $/(gal.)
Under a negative externality,
demand is above the optimal
level.
• Under a negative externality, the demand
curve is above the optimal demand curve by
the amount of the external cost.
• This causes quantity to be higher than the
efficient level.
(A) The effect of a negative externality
Dprivate
Dsocial
A Pigovian tax can move the
demand curve back to the
optimal level.
0 15 20
1
2.5
3
4
5
S
Quantity of gasoline (billions of gals.)
Price ($/gal.)
• A Pigovian tax counteracts a negative
externality.
• If the tax is set equal to the value of the
external cost:
• The externality cost is canceled.
• Quantity goes to the efficient level.
(B) The effect of a Pigovian tax
Dprivate
Dsocial
21© 2014 by McGraw-Hill Education
• Suppose government
estimates that painting
houses creates $500 worth
of external benefits for
neighbors.
• If this subsidy exactly
equals the external benefit
of painting houses,
equilibrium occurs at the
socially efficient outcome.
– Increased efficiency does
not imply increased
fairness.
– Troublesome to quantify
the externality.
Dealing with externalities
0 300
3,000
1,500
Dprivate
Sprivate
Price ($)
Quantity of houses painted
Dsocial
3,500
500
1.A $500 subsidy creates a
new demand curve, above
the old one
360
1,700
2. if the subsidy exactly equals
the positive externality, equilibrium
occurs at the socially efficient
outcome.
As previously analyzed, a subsidy can move the market
equilibrium to the socially optimal equilibrium.
822© 2014 by McGraw-Hill Education
Rover
Gallons of gasoline Gallons of gasoline
(B) Gasoline consumption under a tax
Net benefit to driver
1. Marginal
benefit equals
the tax level
Tax level1
2. but marginal
benefit is different.
0 60
1.2
2
Prius
Range
(A) Gasoline consumption under a quota
Net benefit to driver
0 60
1.2
2
Prius
Range
Rover
1. Quantity is
the same
20
1.33
0.8
Quota
2. and
quantity
varies
accordingly.
10 30
• One solution is to regulate quantity to be socially optimal.
• This does not make the market efficient if individuals make decisions
based on net benefit (marginal benefit – marginal cost = 0).
Dealing with externalities
• Under a quota, both drivers buy 20 gallons
regardless of the difference in their net
marginal benefits.
• Under a $1 tax, both drivers buy different
amounts of gas.
• Neither is left wanting to buy more.
• Total gallons consumed remain 40.
23© 2014 by McGraw-Hill Education
Prius surplus
Tax revenue
Prius
Range
Rover
Marginal benefit to driver
Gallons of gasoline
Surplus under a tax
0 10 30 40 60
1
1.2
2
Prius
Range
Rover
Quota
0 20 60
1.2
1.33
0.8
2
Gallons of gasoline
Marginal benefit to driver
Surplus under a quota
Tax level
34 + 20 = 54
20
34 40 + 1 + 15 = 56
15
1
10 + 30 = 40
Ranger Rover surplus
• Total surplus is higher under the tax than under the quota.
• The quota brings the two drivers to the same combined
quantity of gas consumption as the tax does, but does it
inefficiently (smaller total surplus).
Dealing with externalities
At 20 gallon quota, total surplus is $54. Under a $1 tax, total surplus is $56.
24© 2014 by McGraw-Hill Education
• Using a quota to deal with externalities can be
extended by permitting the buying and selling
of quota allowances, a tradable allowance.
– Market quantity is socially optimal (efficient).
– Total surplus is maximized.
– Tradable allowance does not create any
government revenue, because no taxes are
imposed.
Dealing with externalities
925© 2014 by McGraw-Hill Education
• Because of the difficulty of measuring externalities
directly, many policies target individual goods and
processes.
• The downside of targeting individual activities is that it
risks misaligning the incentives that consumers and
producers face with the goal of minimizing the
externality.
• A policy that directly taxes or subsidizes the
externalities encourages the development of
technology and processes.
– Consumers and producers have an incentive to find new
ways of doing things that don’t generate externalities.
– This allows them to avoid having to pay for a tax or the
rights to an allowance, aligning their incentives with the
end goal of the policy.
Dealing with externalities
26© 2014 by McGraw-Hill Education
• Any cost that is imposed without
compensation on someone other than the
person who caused it is an external cost.
• A benefit that accrues without compensation
to someone other than the person who caused
it is called an external benefit.
• External costs and benefits are collectively
referred to as externalities.
• The total cost of the decision, including any
externalities, is referred to as the social cost.
Summary
27© 2014 by McGraw-Hill Education
• A negative externality causes the individuals
who bear only the private cost to demand or
supply an inefficiently high quantity at any
given price.
• A positive externality causes individuals who
enjoy only the private benefit to demand or
supply an inefficiently low quantity at any
given price.
• In the presence of externalities, markets fail to
maximize total surplus.
Summary
10
28© 2014 by McGraw-Hill Education
• If agreements are enforceable and transaction
costs are small, the Coase theorem states that
individuals reach an efficient equilibrium
through private trades.
• A Pigovian tax counterbalances the effects of a
negative externality.
• A subsidy counterbalances the effect of a
positive externality.
Summary
29© 2014 by McGraw-Hill Education
• Setting a quota to counteract inefficiently high
consumption due to a negative externality can
lower quantity to the socially optimal efficient
level, but it does not maximize surplus.
• A tradable allowance is a production or
consumption quota that can be bought and
sold.
– Efficient quantity.
– Total surplus is maximized.
Summary