Singapore's carbon tax is rising to S$45 per tonne of emissions in 2026, up from the much lower level at which it started. In syllabus terms it is a Pigouvian tax: a tax set to internalise the external cost of carbon emissions, raising firms' private cost of production towards the true social cost and reducing output towards the social optimum. On a diagram it shifts the supply curve, which reflects private cost, upward by the tax, raising price and lowering quantity. The sharp evaluation is that a unilateral local tax can cause carbon leakage, where firms relocate and the emissions are simply produced elsewhere, so global emissions may not fall; and that the higher cost feeds into energy prices, which is one reason alternatives such as cleaner generation, including nuclear, are worth weighing seriously.
Singapore's carbon tax is going up. As at June 2026, the rate is rising to S$45 per tonne of emissions, a long way from the modest level it started at, and the trajectory is set to keep climbing through the rest of the decade. The intention is plain enough: emissions cause harm that the firms doing the emitting do not pay for, so the tax makes them pay, and a price on carbon is meant to bend the whole economy towards producing less of it.
This is one of the cleanest real world examples of a topic that sits right at the centre of your syllabus, and it is worth getting straight, because it is the kind of context an exam loves to set. The headline economics is textbook. The interesting economics, the part that decides grades, is where the textbook stops and the judgement begins.
The economics: a Pigouvian tax on a negative externality
Start with why carbon is a problem the market does not solve on its own. When a firm burns fuel to produce, it imposes a cost on third parties who are not part of the transaction, through the warming those emissions contribute to. That is a negative externality of production: a divergence between private cost, what the firm pays, and social cost, what society as a whole bears. Because the firm only counts its private cost, it produces more than the socially optimal amount, and the gap is the market failure.
- Negative externality
- A cost of production or consumption that falls on third parties outside the transaction. Carbon emissions are the standard example: the harm from warming is borne by society, not the emitter.
- Pigouvian tax
- A tax set equal to the external cost at the socially optimal output, so the polluter pays for the harm it causes. A carbon tax is the textbook case.
- Internalising the externality
- Making the firm bear the external cost as a private cost, so its private incentive lines up with what is good for society, moving output towards the social optimum.
A carbon tax is the standard remedy for exactly this failure: a Pigouvian tax, named after the economist Arthur Pigou, set to put a price on the harm. By charging the firm for each tonne it emits, the tax turns part of the external cost into a private cost the firm now has to count. The firm's cost of production rises, it cuts output and emissions, and in principle output settles back at the level where social cost and social benefit meet, the social optimum. On a diagram, the tax shifts the supply curve, which represents private cost, upward by the amount of the tax, raising the price and lowering the quantity produced.
Read it off the figure. The original supply curve is private cost alone; the tax lifts it towards the true social cost. Price climbs, quantity falls, and the fall in output is the fall in emissions the policy is after. If the tax is set well, output lands near the social optimum and the market failure is corrected. That is the answer most students would write, and it is correct as far as it goes. It just does not go far enough to score at the top.
Mr Toh's take: the leakage the diagram hides
Here is what I want students to see, because it is the part that turns a competent answer into a sharp one. The first big idea is carbon leakage. Yes, raising the carbon tax raises a firm's cost of production. But a firm facing higher costs here can do something the simple diagram never shows: it can relocate to somewhere production is cheaper, and then the emissions still get produced, just somewhere else. The problem we are actually trying to solve is global emissions, not local ones, so a unilateral local carbon tax can end up shifting emissions abroad rather than reducing them globally.
The second thing worth saying out loud is what the tax does to prices. A higher cost of production feeds straight into energy prices, so electricity bills get more expensive. That is not a reason to do nothing, but it is a real cost, and it is one reason I think it is worth seriously weighing alternatives, including cleaner generation such as nuclear energy, rather than treating a tax as the whole answer. Good economics does not stop at, the policy works on the diagram. It asks who pays, whether the harm actually falls, and what else we could do instead.
When a question gives you a carbon tax, do not stop at the diagram. Draw the tax shifting the supply curve up by the external cost and explain that it internalises the externality and lowers output towards the social optimum, then evaluate properly. Lead your evaluation on carbon leakage: the externality is global, the tax is local, so firms can relocate and the emissions simply move abroad. Then weigh the cost push effect on energy prices and competitiveness, and compare the tax with alternatives such as tradable permits, subsidies for clean substitutes, or cleaner generation. A model sentence: "Although a carbon tax internalises the external cost and reduces domestic emissions, because the externality is global rather than local it risks carbon leakage, where production and its emissions relocate abroad, so the net effect on global emissions, and not just the diagrammatic fall in domestic output, is the proper test of the policy."
The externality is global. The tax is local. That gap is where the marks are.
None of this is an argument against pricing carbon. A price on emissions is a serious, defensible policy, and the case for it is strong. The point is that the evaluation, the leakage, the energy prices, the comparison with permits and cleaner generation, is not a bolt on at the end. It is the analysis. A student who can hold both halves, the clean diagram and the messy global reality, is doing exactly what an A grade essay asks for.
- A carbon tax is a Pigouvian tax on a negative externality: it makes the polluter pay for the harm, internalising the external cost of emissions.
- On the diagram it shifts supply up by the tax, raising price and lowering output from the free market level towards the social optimum.
- The figure to remember: Singapore's carbon tax is rising to S$45 a tonne in 2026, up sharply from where it began.
- The headline evaluation is carbon leakage. The externality is global but the tax is local, so firms can relocate and the emissions are produced elsewhere.
- Then weigh the cost push on energy prices and compare with alternatives such as tradable permits, clean subsidies and cleaner generation including nuclear.
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Frequently asked
What is Singapore's carbon tax?
Singapore's carbon tax is a tax on greenhouse gas emissions, charged per tonne emitted, designed to make the firms responsible for emissions pay for the harm they cause. As at June 2026 the rate is rising to S$45 per tonne, a sharp increase from the much lower level at which the tax began, and it is set on a rising path through the rest of the decade. In economic terms it is a Pigouvian tax on a negative externality of production: by putting a price on carbon, it turns part of the external cost into a private cost firms must count, encouraging them to cut emissions and shift towards cleaner production. Always check the latest official figure, since the rate is scheduled to keep changing.
Is a carbon tax effective?
It depends on what you measure it against. A carbon tax does what the diagram says: it raises the private cost of producing emissions, lowers domestic output towards the social optimum, and creates a standing incentive to cut emissions and invest in cleaner methods. The serious challenge is carbon leakage. Because the harm from emissions is global but the tax is local, firms facing higher costs can relocate production to where it is cheaper, and the emissions are simply produced elsewhere, so global emissions may not fall by as much as domestic ones do. A carbon tax also raises energy prices, which has real costs for households and competitiveness. So it can be effective, but its effectiveness is best judged on global emissions and weighed against alternatives, not on the domestic diagram alone.
What is carbon leakage?
Carbon leakage is when a policy that raises the cost of emitting in one place causes the emitting activity, and its emissions, to move somewhere with weaker policy, rather than disappear. A unilateral carbon tax raises a domestic firm's cost of production, so the firm may relocate to a country with a lower or no carbon price, where it carries on emitting. Domestic emissions fall, which looks like success, but global emissions, which are what actually matter for the climate, may barely change. This is the central evaluation point on any carbon tax question, because it shows that the externality is global while the tax is local, and a strong answer leads its evaluation here.
How do I use the carbon tax in an economics essay?
Treat it as a clean application of negative externalities and Pigouvian taxation, then evaluate hard. First, explain the market failure: carbon emissions are a negative externality of production, so private cost is below social cost and the free market overproduces. Second, show the carbon tax as a Pigouvian tax that shifts the supply curve up by the external cost, raising price and lowering output towards the social optimum, with a clear diagram. Third, evaluate: lead on carbon leakage (global externality, local tax), then weigh the effect on energy prices and competitiveness, the difficulty of valuing the external cost precisely, and a comparison with tradable permits, subsidies for clean substitutes, and cleaner generation. Anchoring it in Singapore's rate of S$45 a tonne in 2026 gives you a real, current context that examiners reward.
Why does a carbon tax raise electricity prices?
Because a carbon tax raises the cost of producing the things that emit carbon, and a great deal of electricity is generated by burning fuel. When generators have to pay for each tonne they emit, their cost of production rises, and that higher cost is passed through into the price of electricity, so household and business bills go up. This cost push effect is a genuine downside that belongs in any balanced evaluation, and it is one reason the debate extends to alternatives such as cleaner generation, including nuclear energy, that can lower emissions without leaning entirely on a tax that raises prices.
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