Smoke does not stop at a border. Neither do fish, rivers or carbon dioxide. When the external cost created in one country lands in another, no single government can fix it, because the country doing the polluting has very little reason to act alone. That is why this last group of solutions looks so different from taxes and bans, and why it is so much harder to make work.
📘 What you need to know
Some externalities are global, so a national policy alone cannot reach the whole problem.
Tradable permits (a cap and trade scheme) fix the total quantity of pollution and let the market set the price of polluting.
Firms that pollute more must buy permits from firms that pollute less, so cutting emissions becomes a source of income.
International agreements are used for climate change, high seas fishing and the global trade in harmful goods.
Their biggest weakness is that there is usually no real penalty for a country that signs and then does not deliver.
Collective self-governance is the local version: the community that uses a resource writes and enforces its own rules.
The key evaluation idea is the free rider problem between countries: everyone gains if others cut emissions, and everyone gains most by not cutting their own.
Why national policy runs out of road
Imagine one country introduces a tough carbon tax on its heavy industry. Three things can happen, and only one of them is good.
Firms invest in cleaner technology and emissions fall. This is the outcome the policy is aiming for.
Firms move production to a country with no carbon tax. Global emissions barely change, and the first country has simply lost the jobs. This is often called carbon leakage.
Firms close, output shifts to foreign competitors who face no tax, and imports rise.
Notice that the atmosphere does not care which country the carbon came from. That is what makes climate change a global common pool problem: the benefit of cutting emissions is shared by everybody, while the cost of cutting them is paid by one country alone.
This is the free rider problem again, but with countries instead of people. Every country would prefer a world where emissions fall. Every country would also prefer that someone else does the falling. That tension is the reason climate negotiations are slow, and saying so clearly is worth real marks in an evaluation paragraph.
Tradable pollution permits
A cap and trade scheme works in two moves. First the government or a group of governments decides the total amount of pollution that will be allowed, and issues that many permits. One permit usually allows one tonne of emissions. Then firms are free to buy and sell those permits between themselves.
Supply is a vertical line because the total is fixed by the rules, not by cost. Demand comes from firms that want to emit. Tighten the cap and the same demand chases fewer permits, so the price of polluting goes up.
The result is a price on pollution that the government never has to calculate. A firm that can cut emissions cheaply will do so and sell its spare permits. A firm that would find it very expensive to cut will buy permits instead. Emissions get reduced wherever it is cheapest to reduce them, which is exactly what you want.
Tax or permits? A tax fixes the price of polluting and lets the quantity fall where it may. Permits fix the quantity and let the price fall where it may. If you care about hitting a specific emissions target, permits are the better tool. If you care about firms knowing their costs in advance, a tax is.
Tradable permits: advantages
Tradable permits: disadvantages
The total level of pollution is known and controlled, because it is set directly
Working out the right cap needs data on emissions that is difficult and expensive to collect
Cuts happen where they are cheapest, so a given target costs the economy less overall
If the cap is set too generously, permits are cheap and the scheme changes nothing
Firms that clean up can sell spare permits, which turns pollution control into profit
Large firms can afford to buy up permits, which squeezes smaller rivals out of the industry
The cap can be tightened over time, giving firms a predictable path to plan investment around
It is still a licence to pollute, and firms with inelastic demand pass the cost to consumers
International agreements
An international agreement is a deal between governments to limit an activity that crosses borders. In the syllabus they cover three sorts of problem:
Shared common pool resources, such as fish stocks in international waters, where countries agree annual catch limits.
Climate and environmental damage, where countries agree emissions targets and report progress against them.
Trade in harmful goods, where countries cooperate to disrupt cross-border trafficking.
International agreements: advantages
International agreements: disadvantages
The only realistic approach to a genuinely global externality
Almost never legally enforceable, so a country can simply fall short with no consequence
Reduces carbon leakage, because firms cannot escape by moving to a signatory country
A new government can withdraw or renegotiate, so long-term investment stays risky
Money, technology and expertise can be pooled and sent where they do most good
Richer countries built their wealth using dirty technology, and poorer countries argue it is unfair to be asked to skip that stage
Regular reporting creates public and political pressure to keep going
Negotiations take years, and the target usually ends up as whatever the most reluctant country will accept
If an essay asks whether international agreements work, resist the two easy extremes. They are not useless, because coordinated targets and reporting have genuinely shifted investment. They are not sufficient either, because signing is cheap and delivering is expensive. The honest answer is that they set the direction and national policies do the actual work.
Collective self-governance
Collective self-governance is what happens when the people who use a shared resource organise the rules themselves, without waiting for a government. Fishing communities agreeing seasons and gear limits. Farmers sharing an irrigation system on a rota. Villages managing a forest and deciding who may cut what.
It works better than outsiders often expect, for three reasons. Local users know the resource in detail, they can see immediately when someone breaks the rules, and they have to live with the neighbours they would be cheating. Rules people write for themselves get followed far more reliably than rules handed down from a capital city.
Collective self-governance: advantages
Collective self-governance: disadvantages
Users know the resource better than any distant regulator
Communities can disagree bitterly about what a fair share looks like
Monitoring is cheap, because members watch each other every day
It collapses if outsiders can still enter, since the group cannot exclude them
Builds a shared purpose and creates local jobs in managing the resource
Confronting well-funded or armed outsiders can be dangerous
Much more effective when the community is given formal ownership rights
Without legal backing, the agreement has no force against anyone who ignores it
WORKED EXAMPLE
A scheme issues 40,000 permits, each allowing one tonne of emissions. Firm A can cut a tonne for $18. Firm B would have to spend $65 a tonne. Permits currently trade at $30. Explain what each firm does. [4]
Step 1: Firm A compares its optionscutting costs $18, holding a permit costs $30Cutting is cheaper, so Firm A cuts emissions and sells the permit it no longer needs.Firm A gains $30 − $18 = $12 per tonneStep 2: Firm B compares its optionscutting costs $65, buying a permit costs $30Buying is cheaper, so Firm B buys the permit and keeps emitting for now.Firm B saves $65 − $30 = $35 per tonneStep 3: what happens overallTotal emissions stay at the cap, but the cutting is done by the firm that can do it cheapestTighten the cap and the permit price rises above $65, at which point even Firm B finds it cheaper to clean up.
💡 Exam tip
Start by saying why the problem is global. An answer that treats climate change like a local externality has missed the whole point of the question.
Use the free rider idea for countries. It is the sharpest single explanation of why agreements underdeliver.
Compare a tax with permits directly. Price certainty against quantity certainty is a clean, high-level comparison.
Bring in the development angle. Poorer countries face a real trade-off between growth today and emissions tomorrow.
Use the word enforcement. Almost every weakness in this section comes back to who checks and what happens next.
Do not write off any policy completely. Judgement means weighing, and a flat “this does not work” caps your marks.
⚠️ Common mix-up
Drawing permit supply as an upward sloping curve. The cap is fixed by rule, so the supply of permits is vertical.
Thinking permits let firms pollute more. The cap limits the total. What trading changes is which firm does the polluting.
Saying an agreement is legally binding. Most are not, and that is precisely the weakness examiners want you to spot.
Assuming collective self-governance is a soft option. It works best when it is backed by real property rights and real enforcement.
Ignoring carbon leakage. Emissions moving abroad is not the same as emissions falling, and strong answers say so.
Confusing the cap with the permit price. The government sets the cap. Demand from firms sets the price.
Up next: Public Goods and the Free Rider Problem, the market failure where the free market does not just supply too little, it supplies nothing at all.
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