원출처: Principles of Microeconomics, by Libby Rittenberg, Timothy Tregarthen
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The Measurement of Benefits and Costs
Benefits: The Demand for Emissions
(...) One approach to estimating the demand curve for pollution utilizes the fact that this demand occurs because pollution makes other activities cheaper. If we know how much the emission of one more unit of a pollutant saves, then we can infer how much consumers or firms would pay to dump it.
Suppose, for example, that there is no program to control automobile emissions—motorists face a price of zero for each unit of pollution their cars emit. Suppose that a particular motorist’s car emits an average of 10 pounds of carbon monoxide per week.
- Its owner could reduce emissions to 9 pounds per week at a cost of $1 per week. This $1 is the marginal cost of reducing emissions from 10 to 9 pounds per week.
- It is also the maximum price the motorist would pay to increase emissions from 9 to 10 pounds per week—it is the marginal benefit of the 10th pound of pollution. We say that it is the maximum price because if asked to pay more, the motorist would choose to reduce emissions at a cost of $1 instead.
Now suppose that emissions have been reduced to 9 pounds per week and that the motorist could reduce them to 8 at an additional cost of $2 per week.
- The marginal cost of reducing emissions from 9 to 8 pounds per week is $2.
- Alternatively, this is the maximum price the motorist would be willing to pay to increase emissions to 9 from 8 pounds; it is the marginal benefit of the 9th pound of pollution. Again, if asked to pay more than $2, the motorist would choose to reduce emissions to 8 pounds per week instead.
Figure 18.2. Abatement Costs and Demand
A car emits an average of 10 pounds of CO per week when no restrictions are imposed—when the price of emissions is zero. The marginal cost of abatement (MCA) is the cost of eliminating a unit of emissions; this is the interpretation of the curve when read from right to left. The same curve can be read from left to right as the marginal benefit of emissions (MBE).
We can thus think of the marginal benefit of an additional unit of pollution as the added cost of not emitting it. It is the saving a polluter enjoys by dumping additional pollution rather than paying the cost of preventing its emission. Figure 18.2, “Abatement Costs and Demand” shows this dual interpretation of cost and benefit. Initially, our motorist emits 10 pounds of carbon monoxide per week.
- Reading from right to left, the curve measures the marginal costs of pollution abatement (MCA). We see that the marginal cost of abatement rises as emissions are reduced. That makes sense; the first reductions in emissions will be achieved through relatively simple measures such as modifying one’s driving technique to minimize emissions (such as accelerating more slowly), or getting tune-ups more often. Further reductions, however, might require burning more expensive fuels or installing more expensive pollution-control equipment.
- Read from left to right, the curve in Figure 18.2, “Abatement Costs and Demand” shows the marginal benefit of additional emissions (MBE). Its negative slope suggests that the first units of pollution emitted have very high marginal benefits, because the cost of not emitting them would be very high. As more of a pollutant is emitted, however, its marginal benefit falls—the cost of preventing these units of pollution becomes quite low. (...)
The Marginal Cost of Emissions
(...) Like the marginal benefit curve for emissions, the marginal cost curve can be interpreted in two ways, as suggested in Figure 18.3, “The Marginal Cost of Emissions and the Marginal Benefit of Abatement”.
- When read from left to right, the curve measures the marginal cost of additional units of emissions (MCE). If increasing the motorists’ emissions from four pounds of carbon monoxide per week to five pounds of carbon monoxide per week imposes an external cost of $2, though, the marginal benefit of not being exposed to that unit of pollutant must be $2.
- The marginal cost curve can thus be read from right to left as a marginal benefit curve for abating emissions (MBA). This marginal benefit curve is, in effect, the demand curve for cleaner air.
Figure 18.3. The Marginal Cost of Emissions and the Marginal Benefit of Abatement
The marginal cost of the first few units of emissions is zero and then rises once emissions begin to harm people. That is the point at which the air becomes a scarce resource. Read from left to right the curve gives the marginal cost of emissions (MCE). Read from right to left, the curve gives the marginal benefit of abatement (MBA).
The Efficient Level of Emissions and Abatement
Whether economists measure the marginal benefits and marginal costs of emissions or, alternatively, the marginal benefits and marginal costs of abatement, the policy implications are the same from an economic perspective. As shown in Panel (a) of Figure 18.4, “The Efficient Level of Emissions and Pollution Abatement”, applying the marginal decision rule in the case of emissions suggests that the efficient level of pollution occurs at six pounds of CO emitted per week. At any lower level, the marginal benefits of the pollution would outweigh the marginal costs. At a higher level, the marginal costs of the pollution would outweigh the marginal benefits.
As shown in Panel (b) of Figure 18.4, “The Efficient Level of Emissions and Pollution Abatement”, application of the marginal decision rule suggests that the efficient level of abatement effort is to reduce pollution by 4 pounds of CO produced per week. That is, reduce the level of pollution from the 10 pounds per week that would occur at a zero price to 6 pounds per week. For any greater effort at abating the pollution, the marginal cost of the abatement efforts would exceed the marginal benefit.
Figure 18.4. The Efficient Level of Emissions and Pollution Abatement
- In Panel (a) we combine the marginal benefit of emissions (MBE) with the marginal cost of emissions (MCE). The efficient solution occurs at the intersection of the two curves. Here, the efficient quantity of emissions is six pounds of CO per week.
- In Panel (b), we have the same curves read from right to left. The marginal cost curve for emissions becomes the marginal benefit of abatement (MBA). The marginal benefit curve for emissions becomes the marginal cost of abatement (MCA). With no abatement program, emissions total ten pounds of CO per week. The efficient degree of abatement is to reduce emissions by four pounds of CO per week to six pounds per week.