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Educerie · IB Diploma · Economics
Unit 4 The global economy · 4.7 Sustainable development
What you must be able to do
| You must be able to | Level | What it looks like in the exam |
|---|---|---|
| Define sustainable development, and say what each part of the definition claims | SL, HL | "Define sustainable development" (2 marks); "Explain what is meant by…" (4 marks) |
| Explain the tension between output now and the stock left behind | SL, HL | Paper 1 part (a); the analysis half of a part (b) |
| Explain why a market on its own produces an unsustainable outcome, using externalities and common pool resources | SL, HL | Paper 1 part (a), 10 marks, with a diagram borrowed from 2.8 |
| Outline what the Sustainable Development Goals are, and what they are for | SL, HL | Paper 2 short answer; a named real-world reference inside a part (b) |
| Explain the relationship between sustainability and poverty, in both directions | HL only | Paper 1 part (a), or a Paper 3 explanation |
Before you start
Two pieces of Unit 2 do the heavy lifting here. From 2.8, a negative externality is a cost that falls on somebody who is neither the buyer nor the seller, and a common pool resource is one that is rival in consumption but that nobody can be kept out of. From Unit 1, scarcity and opportunity cost: using a resource today has a cost, and part of that cost is not having it later. Sustainability is one of the nine key concepts, and this is the subtopic that says what it means.
1The idea in one paragraph
Output today is made out of something. Some of that something can be replaced and some of it cannot, and the part that can be replaced can still be used up faster than it comes back. Sustainable development is the idea that a rise in living standards only counts if the next generation inherits enough to raise theirs too. The economics behind it is not new: the future is a third party to every transaction made today, and a third party who cannot bid, vote or sue is exactly the situation that 2.8 called a negative externality.
2What sustainable development actually says
The standard definition comes from a United Nations commission that reported in 1987, and it is the one the guide uses:
Sustainable development is development that meets the needs of the present without reducing the ability of future generations to meet their own needs.
Students quote about half of it. Figure 1 takes it apart so you can see what the other half is doing.
Three claims, and each one is doing work.
The present counts. This is not a rule about going without. A country that keeps its forest by leaving its people hungry has not achieved sustainable development; it has failed the first half of the definition.
The future counts too. What is handed on has to be enough for the next generation to meet its own needs. That is a claim about a stock, not about a flow.
Needs, not wants. The test is basic needs — food, clean water, health, shelter, schooling, safe work. Without that word the definition becomes impossible, because wants have no ceiling.
Two more terms make the rest of the subtopic easier. Natural capital is the stock of natural resources and natural systems a country has: soil, forests, fish, fresh water, minerals, and the air and rivers that absorb waste. A renewable resource replaces itself over time; a non-renewable resource does not. Sustainable development is, in one line, development that does not run natural capital down.
Development itself is wider than the environment. It has an economic side, a social side and an environmental side, and the Sustainable Development Goals in section 5 are organised on exactly that basis. An answer that treats this subtopic as "the environment one" has already dropped two thirds of it.
3The tension: output now against the stock left behind
Say it plainly, because the exam rewards it. Growth today usually means using more resources today. Every tonne of fish landed this year is a tonne that cannot breed next year. That is the tension, and pretending it is not there is not evaluation.
The tension has a precise form for a renewable resource. A fish stock renews at some rate each year. Harvest at or below that rate and the stock holds for ever. Harvest above it and the stock falls, and once it falls past a certain point it can no longer rebuild at all. Figure 2 draws the two paths from the same starting stock.
Use a renewable resource no faster than it renews, and a sink no faster than it clears.
The same logic covers pollution. The atmosphere and a river are sinks: they absorb a certain amount of waste per year and clear it. Below that rate nothing accumulates. Above it, the waste builds up, and the stock of accumulated waste is the problem, not this year's flow.
Non-renewable resources need a different sentence, because any use at all reduces the stock. Sustainability here does not mean never touching them. It means turning the proceeds into something that lasts — infrastructure, skills, a broader industrial base, a substitute technology — so that when the stock is gone the country still has an income. A country that sells its copper and spends the money on current consumption has converted natural capital into nothing, and its children inherit the hole.
4Where the economics came from: 2.8, applied to people who are not here yet
Nothing in section 3 is a new market failure. It is the two failures you already met in 2.8, with the third party moved into the future.
The negative externality of production. A logging firm pays for wages, fuel and machinery. It does not pay for the soil erosion downstream, the flooding, the carbon released, or the timber its grandchildren will not have. Those are real costs and somebody bears them, so the firm's marginal private cost sits below the marginal social cost. Figure 3 is the 2.8 diagram with the third party named.
The market clears where MPC meets demand, at Q₁. The socially efficient quantity is Q\, where MSC meets marginal social benefit. Q₁ is larger than Q\, so the market over-produces, and the shaded triangle is the welfare loss: the amount by which social cost exceeds social benefit on every unit between Q\* and Q₁.
What makes the future version worse than the usual one is who the third party is. Neighbours can complain, organise, sue and vote. People who are not born yet can do none of those things. There is no mechanism at all by which their preferences reach the price.
The common pool resource. The second failure needs no externality. A resource that is rival (what one person takes, another cannot) but non-excludable (nobody can be kept out) will be over-used even when every single user is behaving reasonably. Figure 4 shows why.
Read the middle box carefully, because it is the whole argument. A skipper who lands one more tonne keeps the whole of that benefit. The cost — a smaller stock next year — is shared with every other skipper, and with everyone who fishes after them. Each skipper's private arithmetic says take the tonne. Everyone's arithmetic says the same. The stock empties, and no villain was required.
Do not confuse this with a public good. A public good is non-rival: my watching a lighthouse beam does not use it up. A common pool resource is rival, and that is exactly why it can be exhausted. The policy responses — taxes, tradable permits, quotas, assigned property rights, community agreements — belong to 2.8 and to later subtopics in this unit, so name the failure here and take the policy from there.
5The Sustainable Development Goals
The Sustainable Development Goals (SDGs) are 17 goals with 169 targets beneath them, agreed by United Nations member states in 2015 and running to 2030. They replaced the Millennium Development Goals, which ran from 2000 to 2015 and applied mainly to low-income countries. Figure 5 lays out the 17 under the five headings the 2030 Agenda itself uses.
Three things about them are worth an exam sentence each.
They are universal. Every country reports against them, not only the poorest. A high-income country with high emissions per person is failing goals 12 and 13 whatever its income.
They are multidimensional. Only a handful of the seventeen concern output. Poverty, hunger, health, schooling and equality come first, which is the definition in section 2 turned into a list.
They put the environment among the goals, not among the constraints. Goals 13, 14 and 15 are ends in their own right, not side conditions on growth.
Now evaluate them, because a part (b) will ask you to. They are not binding: no country can be forced to meet a target and none is penalised for missing one. Progress is measured by indicators that many countries cannot yet collect, so the reporting is uneven. And the goals can pull against each other — goal 8 asks for sustained economic growth while goals 13 to 15 ask for less pressure on the climate, the oceans and the land, and no goal says which wins when they meet. That last point is the tension from section 3, written into the framework itself.
For the exam, the SDGs are your ready-made real-world reference. "Goal 6 targets universal access to safe drinking water by 2030" is a named, checkable fact, and it is worth more than a generic sentence about how countries should develop sustainably.
6HLSustainability and poverty
SL readers can stop at section 5. HL students must be able to explain how sustainability and poverty are connected, and the answer runs in both directions. Give only one and you have written half an answer.
Poverty makes unsustainable use more likely. A household with no savings, no insurance and no reliable income cannot afford to think about next year, because it may not get through this one. The future is discounted heavily, and the choices follow: cut the trees for fuel or charcoal because there is no other fuel; plough steep or dry land because the good land is taken; land the small fish because the family eats tonight; skip the fallow year because there is no stored grain to live on. None of this is short-sightedness. It is what the arithmetic of poverty produces.
Unsustainable use makes poverty worse. Thin soil grows less, so the next harvest is smaller. An emptied inshore fishery removes the livelihood it used to support. A drained aquifer means longer walks for water, which usually means girls out of school. Degraded land is also more exposed to drought and flood, and a household with no savings and no insurance has nothing to absorb the shock with. So the household is poorer again, and the pressure to take more from the resource goes up.
The two arrows form a loop, and the reason it matters for policy is that a policy attacking only one arrow tends to fail. Fencing off a forest from people who depend on it for fuel raises poverty and shifts the pressure somewhere else. Raising incomes with no conservation at all can accelerate the depletion instead of easing it.
Now the half of the picture that keeps the answer honest, and earns the evaluation. Poverty is not what drives most global resource depletion. Resource use and emissions per person are far higher among high-income consumers than among the poorest, and a great deal of what is extracted in low-income countries is consumed somewhere else entirely. Blaming depletion on poverty gets the scale of the problem wrong.
That leaves a genuine tension, and saying it out loud is what a good answer does. Lifting the poorest out of poverty means more energy, more materials, more building and more food, at least at first. So the question is not whether poverty reduction can be sustainable in the abstract; it is whether the extra resource use it needs can be made up for elsewhere, and by whom.
7Where marks are lost
Quoting half the definition. "Meeting the needs of the present" on its own is not sustainable development, and neither is "not harming the future" on its own. Both halves, plus the word needs, or the definition mark does not come.
Treating it as an environmental topic. Sustainable development has an economic and a social side too. An answer that only ever mentions the environment is capped by its own narrowness.
Saying it means stopping growth. It does not. It means growth whose basis can be kept up. Non-renewable resources may still be used, provided what they earn is turned into something lasting.
Confusing a common pool resource with a public good. A public good is non-rival, so it cannot be used up. A common pool resource is rival, which is precisely why it can be. Get this the wrong way round and the whole explanation collapses.
Writing "sustainable growth" when the term is sustainable development. Growth is output. Development is wider. The guide's term is sustainable development, so use it.
Listing the SDGs instead of using one. Naming all seventeen earns nothing. Naming one goal, saying what it targets, and applying it to the case in front of you earns the real-world mark.
Giving one direction of the poverty link (HL). Poverty pushes people towards unsustainable use, and unsustainable use deepens poverty. One arrow is half the marks.
8Write it right
There is no diagram the guide requires here, so the marks come from the wording. Every extended answer in this subtopic should carry all of the following.
- The full definition, all three claims, in the first two sentences.
- The word sustainability used by name, since it is the key concept the question is built on.
- A stock-and-flow sentence: not just "the resource is being damaged" but "it is being used faster than it renews".
- The market failure named — negative externality of production, or common pool resource — and a reason why the market misses the cost.
- A diagram where one helps. Figure 3 is the 2.8 externality diagram, and it earns marks here as long as MPC, MSC, Q₁, Q\* and the welfare loss are all labelled.
- One named real-world reference. An SDG with its number and its target is the cheapest one available.
- An evaluative sentence that says what the judgement depends on: the time period, who bears the cost, whether the resource is renewable, whether the country has an alternative.
9Try it
Marks in brackets. Answers and marker's notes are at the end. Do them before you look.
Q1. Define the term sustainable development. 2 marks
Q2. Explain, using the idea of a common pool resource, why a coastal fishery may be harvested faster than it can renew. 4 marks
Q3. Explain one reason why the Sustainable Development Goals may not be met by 2030. 4 marks
Q4 (HL). Explain the relationship between poverty and the unsustainable use of natural resources. 4 marks
10In one breath
Sustainable development means meeting the needs of the present without reducing the ability of future generations to meet theirs — present, future, and needs rather than wants. It has an economic, a social and an environmental side. The tension is real: output today uses resources today, and a renewable resource used faster than it renews eventually collapses, while a non-renewable one only counts as used sustainably if its proceeds are turned into something lasting. The economics is 2.8's: production externalities put MSC above MPC and the market over-produces at Q₁ instead of Q\*, and a common pool resource is emptied because it is rival but nobody can be excluded. The future is the third party that cannot bid or vote. The SDGs are 17 goals and 169 targets, agreed in 2015 for 2030, universal and multidimensional but unenforceable and sometimes in conflict with each other. HL: poverty pushes households into unsustainable use, unsustainable use pushes them further into poverty, and the largest footprints per person still sit with high-income consumers.
Answers
Q1. Sustainable development is development that meets the needs of the present without reducing the ability of future generations to meet their own needs. one mark for meeting present needs, one for not reducing the future's ability to meet its own. An answer that mentions only the environment, or only the future, scores 1. "Development that protects the planet" scores 0.
Q2. A fishery is a common pool resource: it is rival, because a tonne one boat lands is a tonne no other boat can land, and non-excludable, because no one can be kept out of open water. A skipper who takes one more tonne keeps the whole of the benefit, while the cost — a smaller stock next season — is spread across every other user and across everyone who fishes later. Each skipper's private calculation therefore says take the extra tonne even though the combined effect is a stock harvested faster than it renews. 1 for rival, 1 for non-excludable, 1 for the private benefit against the shared cost, 1 for reaching a harvest above the rate of renewal. An answer that says only "people are greedy" scores 0 — the point is that the outcome follows from reasonable individual behaviour.
Q3. The goals are not binding on any country. No government can be compelled to meet a target and none faces a penalty for missing one, so a country whose growth strategy conflicts with, say, goals 13 to 15 has no enforceable reason to change course. The goals can also pull against one another: goal 8 asks for sustained economic growth while goals 13, 14 and 15 ask for less pressure on the climate, the oceans and the land, and the framework does not say which takes priority. 1 for identifying a valid reason, 3 for developing it with a mechanism. Other valid reasons: gaps in the data needed to measure progress, financing shortfalls, or a shock that pushes progress backwards. A list of goals with no reason attached scores 0.
Q4 (HL). Poverty makes unsustainable use more likely: a household with no savings and no insurance cannot carry the risk of leaving a field fallow or leaving small fish in the water, so it takes what it needs today, cutting fuelwood, ploughing marginal land and fishing the stock down. Unsustainable use then deepens poverty: thinner soil produces smaller harvests, an emptied fishery removes the livelihood it supported, and a household with no reserves has nothing to absorb the loss, which raises the pressure to take still more. The two effects reinforce each other. That said, poverty is not the main driver of global depletion — resource use and emissions per person are far higher among high-income consumers. 1 for poverty leading to unsustainable use with a mechanism, 1 for a concrete example, 1 for unsustainable use leading back to poverty with a mechanism, 1 for recognising the loop or qualifying it with the high-income consumption point. An answer that gives only one direction is capped at 2.
Educerie · written from the published IB Diploma Programme Economics guide, first assessment 2022, section 4.7 Sustainable development. Original text, examples and questions. Diagrams drawn by Educerie. Last reviewed 10 September 2026.