When a city or state government sets up a marketable permit program (e.g. cap-and-trade), it must start by determining the overall quantity of pollution it will allow as it tries to meet national pollution standards. Then, a number of permits allowing only this quantity of pollution are divided among the firms that emit that pollutant. These permits to pollute can be sold or given to firms free.
Now, add two more conditions. Imagine that these permits are designed to reduce total emissions over time. For example, a permit may allow emission of 10 units of pollution one year, but only nine units the next year, then eight units the year after that, and so on down to some lower level. In addition, imagine that these are marketable permits, meaning that firms can buy and sell them.
To see how marketable permits can work to reduce pollution, consider the four firms listed in this table. The table shows current emissions of lead from each firm. At the start of the marketable permit program, each firm receives permits to allow this level of pollution. However, these permits are shrinkable, and next year the permits allow the firms to emit only half as much pollution. Let’s say that in a year, Firm Gamma finds it easy and cheap to reduce emissions from 600 tons of lead to 200 tons, which means that it has permits that it is not using that allow emitting 100 tons of lead. Firm Beta reduces its lead pollution from 400 tons to 200 tons, so it does not need to buy any permits, and it does not have any extra permits to sell. However, although Firm Alpha can easily reduce pollution from 200 tons to 150 tons, it finds that it is cheaper to purchase permits from Gamma rather than to reduce its own emissions to 100. Meanwhile, Firm Delta did not even exist in the first period, so the only way it can start production is to purchase permits to emit 50 tons of lead.
The total quantity of pollution will decline. But the buying and selling of the marketable permits will determine exactly which firms reduce pollution and by how much. With a system of marketable permits, the firms that find it least expensive to do so will reduce pollution the most.
How Marketable Permits Work
|Firm Alpha||Firm Beta||Firm Gamma||Firm Delta|
|Current emissions—permits distributed free for this amount||200 tons||400 tons||600 tons||0 tons|
|How much pollution will these permits allow in one year?||100 tons||200 tons||300 tons||0 tons|
|Actual emissions one year in the future||150 tons||200 tons||200 tons||50 tons|
|Buyer or seller of marketable permit?||Buys permits for 50 tons||Doesn’t buy or sell permits||Sells permits for 100 tons||Buys permits for 50 tons|
Another application of marketable permits occurred when the Clean Air Act was amended in 1990. The revised law sought to reduce sulfur dioxide emissions from electric power plants to half of the 1980 levels out of concern that sulfur dioxide was causing acid rain, which harms forests as well as buildings. In this case, the marketable permits the federal government issued were free of charge (no pun intended) to electricity-generating plants across the country, especially those that were burning coal (which produces sulfur dioxide). These permits were of the “shrinkable” type; that is, the amount of pollution allowed by a given permit declined with time.