Environmental Sustainability

Syllabus: Economic Issues → Environmental sustainability.

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Ecologically sustainable development

Ecologically sustainable development is development that meets the needs of the present generation without compromising the ability of future generations to meet their own.

The definition comes from the Brundtland Report of 1987, and it carries the central economic idea inside it: a trade-off between generations rather than only between people alive at the same time.

Three principles hold it up. Intergenerational equity, meaning the present generation should not deplete the natural capital future generations will depend on. The precautionary principle, meaning that where there is a threat of serious or irreversible damage, incomplete scientific certainty is not a reason to postpone acting. And conservation of biodiversity and ecological integrity.

The reason this is an economic problem rather than only an environmental one is a measurement failure. GDP counts the income from using natural resources but not the depreciation of the resource stock. An economy can therefore appear to grow while running down the natural capital that makes future growth possible.

That diagram is the entire argument in one picture. Pursuing maximum output now shrinks the frontier available later, so present consumption is achieved at the direct cost of future productive capacity.

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Private and social costs and benefits

This is the analytical core of the topic, and the four terms need to be precise.

Private cost is what the producer or consumer of a good bears. Private benefit is what they receive. Social cost is private cost plus any external cost imposed on third parties. Social benefit is private benefit plus any external benefit conferred on them.

Social cost = private cost + external cost
Social benefit = private benefit + external benefit

The problem follows immediately. Markets allocate resources according to private costs and benefits. Where private and social diverge, the market outcome is not the socially efficient one, and that divergence is what an externality is.

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Externalities and market failure

An externality is a cost or benefit falling on a third party who is not part of the transaction, and which therefore never appears in the market price. Market failure is the resulting misallocation, where the market produces too much or too little relative to the social optimum.

Negative externalities

Costs imposed on third parties, with pollution the standard case. A factory's private costs are labour, materials and capital, while the social cost also includes the health and environmental damage from its emissions.

Because the private supply curve reflects only private costs, the market equilibrium quantity qm exceeds the socially optimal qs, and the price Pm sits below the socially efficient Ps. The good is over-produced and under-priced at once.

The policy implication is to internalise the externality: make the producer bear the external cost through a tax, a charge or a market-based mechanism, so private cost rises to meet social cost.

Positive externalities

Benefits conferred on third parties, with education, vaccination and research and development the standard cases. The private benefit to the individual is real, but society gains more than the individual does.

Social demand exceeds private demand by the value of the external benefit, so the market under-produces at qm relative to qs. The policy implication is a subsidy, or direct public provision.

One distinction students frequently get wrong: a production externality shifts the supply curve, while a consumption externality shifts the demand curve. Check which one the question describes before you draw anything.

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Public and private goods, and free riders

Two properties define the categories. Excludability asks whether non-payers can be prevented from consuming. Rivalry asks whether one person's consumption reduces what is available to everyone else.

A private good is both excludable and rival, such as a sandwich or a car, and markets supply these efficiently. A public good is neither, which covers national defence, street lighting, a lighthouse and, critically for this topic, a stable climate.

The free rider problem

Because a public good is non-excludable, someone who does not pay cannot be stopped from benefiting. Everyone therefore has an incentive to let others pay and consume for free.

If everyone reasons that way, nobody pays and the good is not provided at all, even though everyone would be better off if it were. That is a market failure, and it is the economic justification for government provision funded through taxation.

Why this is the key to climate policy

A stable climate is a global public good. Any country reducing emissions bears the full cost while the benefit is shared worldwide and cannot be withheld from countries that contributed nothing.

Every country therefore has an incentive to free ride on everyone else's abatement, which is exactly why climate change requires international agreements rather than national action alone, and exactly why those agreements are so hard to enforce.

The related concept is the tragedy of the commons, where a shared open-access resource such as a fishery, groundwater or the atmosphere gets over-exploited because each user captures the full benefit of their own use while the cost is spread across everyone.

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Environmental issues

Preservation of natural environments

The economic problem is that natural environments produce benefits markets do not price: biodiversity, ecosystem services such as water filtration and pollination, and existence and option value.

Because those benefits are unpriced, land converted to agriculture or development shows a market return while conservation shows none, so the market systematically under-provides preservation. The Great Barrier Reef, old-growth forests and the Murray-Darling Basin are the Australian examples.

Pollution and climate change

Pollution comes in several forms: air, water, soil, noise and waste.

Climate change is the largest externality in economic history, which is Nicholas Stern's formulation and worth quoting. Four features make it economically difficult. It is a global externality, so it needs international coordination. It is long-term, so costs fall on future generations who cannot participate in present decisions. It carries deep uncertainty and potential irreversibility. And its costs and benefits are unevenly distributed between countries.

Australia's position is specific and creates the central policy tension. Per-capita emissions are high by international standards, reflecting a fossil-fuel-intensive energy sector and a resource-based economy, while the aggregate share of global emissions is small. Unilateral abatement therefore imposes costs on a competitive export economy while making little difference to global outcomes unless others act too.

Depletion of renewable and non-renewable resources

Renewable resources replenish naturally: fish stocks, forests, fresh water, soil fertility. They are sustainable only while the rate of use stays below the rate of regeneration. Push past that, through overfishing, over-extraction of groundwater or soil salinity, and a renewable resource is effectively converted into a depleting one.

Non-renewable resources exist in fixed supply, so coal, iron ore, oil and gas, and every unit used permanently reduces what remains.

For a resource exporter like Australia the economic question is intergenerational. How much of the endowment should be extracted now, and should the proceeds be consumed or invested? Converting a non-renewable resource into consumption leaves nothing behind. Converting it into human or physical capital preserves the value for the generations who will not have the resource. Sovereign wealth funds exist for exactly that reason, and Norway's is the standard comparison.

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What the exam does with this

Environmental sustainability carried full extended responses in 2018, 2020 and 2023, and has not appeared in Section III or IV since. That makes it the most conspicuous gap in the recent record, which is not a prediction but is a reason not to deprioritise it.

Five things to get right.

Use the externality diagrams and label them. They convert an abstract argument into analysis and they take almost no time to draw.

Say market failure and then explain why, rather than describing environmental damage. The economics lives in the divergence between private and social costs.

Use the public good and free rider framework for anything on climate policy. It explains both why international agreements are needed and why they underdeliver, which is efficient.

Frame ESD as intergenerational equity, and bring in the production possibility frontier diagram.

Link to the other objectives. Environmental sustainability conflicts with growth in the short run, which is precisely what conflicting-objectives questions are looking for. See conflicts between economic objectives.

Related notes: Environmental management policies · Economic growth · The diagram guide