Environmental Economics and Sustainable Development
Every economy runs on a planet. We pull resources out of it, and we push waste back into it. For most of history, economics treated nature as a free, infinite warehouse and a free, infinite dump. It is neither. This chapter is about what happens when the bill for using nature never appears on anyone's invoice — and how economists try to make that hidden bill visible. It is the field where economics, ethics, and physics collide.
Externalities: the cost nobody pays
Start with the single most important word in this chapter: externality.
- Externality
- A cost or benefit from a transaction that falls on a third party who had no say in the deal. If it's a cost (pollution), it's a negative externality. If it's a benefit (a vaccine that protects others, basic research everyone can use), it's a positive externality.
- Private cost
- What the person making a decision actually pays.
- Social cost
- The full cost to everybody — the private cost plus the spillover onto third parties.
The economist A.C. Pigou named this problem in his 1920 book The Economics of Welfare. His insight is simple but devastating: when a factory's private cost is lower than the true social cost, the market produces too much of the polluting thing. The price tag lies. It tells buyers the product is cheap when, counting the dirty air, it is expensive.
We can draw the gap. Let PMC = private marginal cost (what the firm pays per extra unit) and SMC = social marginal cost = PMC plus the marginal external cost (the harm dumped on others). The free market settles where the demand line meets PMC. The efficient point — the one good for society as a whole — is where demand meets SMC. The wedge between them is wasted welfare, called deadweight loss.
price | SMC = PMC + external cost | / | / PMC (what the firm pays) | / / | / / | *Eff/....... efficient quantity (SMC = demand) | /\ / | / X <- deadweight loss (over-pollution) | / /\ |/ / *Mkt market quantity (PMC = demand, too much) +-----------------------------> quantity Market overproduces by the distance Eff -> Mkt
Pigou's fix vs. Coase's challenge
Pigou's solution was elegant: tax the pollution. A Pigouvian tax is a per-unit tax set equal to the external cost. It forces the polluter to internalize the externality — to feel the full social cost in their own wallet. Pigou's own example was taxing alcohol to cover the costs heavy drinking imposes on society. Modern descendants are everywhere: carbon taxes, London's 2003 congestion charge, Singapore's 1975 road pricing, tobacco and sugar taxes, plastic-bag fees. The mirror image is the Pigouvian subsidy — paying people to do things with positive spillovers, like vaccines or solar panels.
Pigou ruled for forty years until Ronald Coase (1960, "The Problem of Social Cost"; Nobel 1991) offered a rival idea. The Coase theorem says: if property rights are crystal-clear and transaction costs are zero, the two sides will simply bargain their way to the efficient outcome — no tax needed — and it doesn't even matter who legally holds the right. A factory polluting a laundry next door? Whoever values clean air more will pay the other to get their way.
The tragedy of the commons
In 1968, biologist Garrett Hardin published "The Tragedy of the Commons" in Science. Picture herders sharing one open pasture. Each gains the full value of adding one more cow but bears only a fraction of the overgrazing damage. So every herder keeps adding cows until the grass is destroyed. Individually rational, collectively ruinous. The same logic explains collapsing fisheries, drained groundwater, and the atmosphere itself — climate change is sometimes called "the mother of all commons problems."
Hardin saw only two escapes: privatize the resource, or have the state coerce everyone ("mutual coercion mutually agreed upon"). Then Elinor Ostrom — first woman to win the Economics Nobel (2009) — showed in Governing the Commons (1990) that he had missed a third path. Studying Swiss alpine pastures, Japanese village forests, Spanish irrigation huertas, and Maine lobster fisheries, she found communities that govern shared resources sustainably for centuries — no privatization, no distant state. Her eight design principles include clear boundaries, locally tailored rules, monitoring, graduated sanctions (small punishments first), and built-in conflict resolution.
Putting a price on carbon
For climate, the practical question is: how do we make carbon expensive enough to reflect its real damage? Two main tools, both market-based.
| Carbon tax (price tool) | Cap-and-trade / ETS (quantity tool) | |
|---|---|---|
| Government fixes… | the price per ton | the total quantity (the cap) |
| Market decides… | how much gets emitted | the price (via traded allowances) |
| You're certain about… | the price | the emissions |
| You're uncertain about… | actual emissions | the price (can be volatile) |
| Bonus | simple; raises revenue | least-cost: cheap-to-clean firms sell permits to costly ones |
Note these are not opposing philosophies — both are simply ways to make polluters pay. The economist Martin Weitzman (1974, "Prices vs. Quantities") showed the right choice depends on the shapes of the cost and benefit curves under uncertainty.
Discounting the future: an ethical fight in disguise
Here is the deepest puzzle. Suppose climate damage in the year 2125 will cost the equivalent of $1. How much is preventing that worth to us today? We answer with a discount rate — the exchange rate between future dollars and present dollars. A high rate says the distant future barely counts; a low rate says it counts almost as much as today.
The standard tool is the Ramsey formula: r = ρ + η·g, where ρ is "pure time preference" (how much we discount the future just for being later), η is how much we care about inequality, and g is expected growth. Tiny changes in these knobs swing the answer enormously.
| Stern Review (2006) | Nordhaus / DICE model | |
|---|---|---|
| Pure time preference (ρ) | ~0.1% — future people matter almost equally | higher, to match observed markets |
| Overall discount rate | ~1.4% (low) | ~4–4.5% (market-based) |
| Implied urgency | act hard, now | gradual "policy ramp" |
| Social cost of carbon | ~$85+/ton (high for its time) | under $20/ton |
The punchline is breathtaking. Plug Stern's low rate into Nordhaus's own model and the social cost of carbon jumps to roughly $159/ton — about ten times higher. Same physics. Same model. A tenfold difference, purely from the ethics of how much we owe future generations. William Nordhaus won the 2018 Nobel and argues a near-zero rate isn't grounded in how people actually save and invest. Stern argues that discounting future humans is an ethical choice, not a market fact.
This isn't academic. The Social Cost of Carbon (SCC) — the official dollar damage of one extra ton of CO₂ — drives US regulation. It was about $51/ton under Obama (3% rate); in November 2023 the EPA raised it to roughly $190/ton using a 2.0% rate and updated damage models. That number is politically fragile and central to every deregulation fight.
Sustainable development and the growth question
The phrase sustainable development comes from the 1987 UN Brundtland Report: "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Its heart is intergenerational equity — fairness across time. That lineage runs through the 1992 Rio Earth Summit to the UN's 17 Sustainable Development Goals (2015).
Does protecting the planet require sacrificing growth? One hopeful idea is the Environmental Kuznets Curve (EKC): an inverted-U where pollution rises during early industrialization, then falls once a country gets rich enough to afford cleanup.
This fuels the live green growth vs. degrowth debate. Green-growth bodies (OECD, IEA, World Bank) bet on decoupling — cutting emissions while GDP rises, through clean tech. Critics (notably Jason Hickel) argue truly global, fast-enough decoupling hasn't been demonstrated. A fair nuance: the UK and EU have cut emissions while growing — but partly by offshoring dirty factories abroad, so "consumption-based" emissions look worse than "territorial" ones.
Why is climate uniquely hard? It is (1) global — no world government, so countries free-ride (which is why Kyoto and Paris are voluntary); (2) long-term — hence the discounting fight; (3) uncertain and irreversible — tipping points may be catastrophic ("fat tails," in Weitzman's phrase); and (4) a pure commons. No single tool can fix all four, which is why real policy stacks carbon pricing + subsidies + standards + research.
Key Takeaways
- An externality is a cost or benefit dumped on bystanders; pollution is a pricing failure that makes markets overproduce dirty things.
- A Pigouvian tax forces polluters to feel the full social cost; Coase showed bargaining could work too — but only when transaction costs are near zero, which for climate they never are.
- The tragedy of the commons isn't inevitable: Ostrom proved communities can self-govern shared resources with the right rules.
- Carbon taxes fix the price; cap-and-trade fixes the quantity — both are market-based, and the SO₂ acid-rain program proved cap-and-trade works cheaply.
- The discount rate is an ethical choice, not a calculation; it alone can swing the cost of carbon roughly tenfold.
- Sustainable development means fairness to future generations; "grow first, clean later" works for local smog but not for CO₂.
- Climate is a uniquely hard externality — global, long-term, uncertain, and commons-based — so it needs a stack of policies, not one silver bullet.