IB DP Environmental Systems and Societies – HL lenses: environmental law, economics and ethics Revision Notes

For full explanations and worked examples, start with the HL lenses study guide. These notes are for recall in the final weeks.

They cover the three higher level lenses of IB Diploma Programme Environmental Systems and Societies (ESS), aligned to the International Baccalaureate Organization’s Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026: HL.a Environmental law, HL.b Environmental and ecological economics and HL.c Environmental ethics. All three are HL only. It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions.

Practise with the HL lenses practice questions. The IB DP ESS course hub and printable ESS syllabus checklist show the whole course.

The big idea in one paragraph

The brief lists three HL-only lenses (5, 7 and 5 recommended hours) and asks HL students to synthesize them with the core topics. A lens is not a new topic. It is a way of re-reading an issue you already know — overfishing, climate change, ozone depletion, urban air pollution, waste — by asking three questions. Law: what rules exist, and do they work? Economics: how is it valued, and what changes behaviour? Ethics: who counts, and what is right?

HL.a Environmental law — key terms

Term	Meaning
Convention / treaty	Agreement between states setting a framework
Protocol	Later agreement adding binding detail to a convention
Ratification	A state formally agreeing to be bound
Hard law	Legally binding, enforceable
Soft law	Guidance, declarations, voluntary targets; no penalties
Sovereignty	Each state controls its own territory and laws
EIA	Environmental impact assessment, often required by national law before large projects
Rights of nature	Legal standing for ecosystems (Ecuador 2008; Whanganui River, New Zealand, 2017)

Principles: precautionary (act despite uncertainty when harm could be serious); polluter pays; prevention (stop harm before it happens); intergenerational equity.

Examples to quote: Ramsar (wetlands, 1971); CITES (trade in endangered species, 1973); Montreal Protocol (ozone-depleting substances, 1987; ratified by every UN member state); Paris Agreement (climate, 2015; binding duty to submit pledges, no penalty for missing them); UNCLOS (exclusive economic zones to 200 nautical miles).

Method: evaluating a law in steps

1. Scale: international, national or local?
2. Force: hard or soft law?
3. Target: which specific pressure does it address (emissions, trade, habitat loss)?
4. Enforcement: who monitors, and what happens to a breach?
5. Evidence: has the indicator improved since the law began? Could anything else explain the change?
6. Judgement: effective, partly effective or ineffective — and why.

Why laws fail

• No global enforcer (sovereignty).
• Free riders.
• Costly monitoring (oceans, remote forests).
• Weak penalties, or corruption.
• Key polluters outside the agreement.

Why laws succeed

• Clear science.
• Cheap substitutes.
• Few producers to regulate.
• Trade or reputational pressure.
• Financial help for poorer countries.

HL.b Environmental and ecological economics — key terms

Term	Meaning
Externality	Cost or benefit to people outside a transaction
Market failure	Prices do not reflect the full environmental cost
Internalising	Making the polluter pay the external cost
Tragedy of the commons	Open access leads to overuse (Hardin, 1968)
Weak sustainability	Human-made capital can replace natural capital
Strong sustainability	Critical natural capital cannot be replaced
Steady-state economy	Stable throughput of materials and energy within ecological limits
Doughnut model	Stay above a social foundation and below an ecological ceiling
Circular economy	Keep materials in use; design out waste

Must-know distinction: the two schools

• Environmental economics: the environment sits inside the economy. Fix market failure by putting a price on harm. Uses cost-benefit analysis. Weak sustainability.
• Ecological economics: the economy sits inside the biosphere. Fix the scale of material throughput first. Strong sustainability.

Total economic value (TEV)

Component	Type	Example (wetland)
Direct use	Use	Fish, reeds, recreation
Indirect use	Use	Flood control, water purification
Option	Use (future)	Possible future medicines
Existence	Non-use	Knowing the wetland birds survive
Bequest	Non-use	Leaving the wetland to your grandchildren

Valuation methods: market prices; contingent valuation (willingness to pay, stated in a survey); travel cost; hedonic pricing.

Tools and formulas

Tool	Fixes	Lets vary	Calculation
Pollution tax	Price per unit	Quantity emitted	Tax bill = emissions × tax rate
Cap-and-trade	Total quantity	Permit price	Cost = tonnes abated × cost per tonne, summed across firms
Subsidy / payment for ecosystem services	—	—	Payment per hectare or per unit of good behaviour
Discounting	—	—	Present value = future value ÷ (1 + r)ᵗ

Method: will a firm cut emissions under a tax?

1. Compare the cost of cutting one tonne with the tax on one tonne.
2. Cut every tonne that is cheaper to abate than to tax.
3. Pay tax on the rest.
4. Total cost = abatement cost + tax on remaining emissions.

Worked reminder. Tax USD 40 per tonne; cuts cost USD 25 per tonne for the first 5,000 t, then USD 60. Cut 5,000 t (25 < 40), stop there (60 > 40).

Discounting reminder

A higher discount rate r shrinks future values more. Damage worth USD 1,000,000 in 50 years has a present value of about 608,000 USD at 1% but only about 87,000 USD at 5%. So high rates favour short-term gains over long-term protection. The rate is a value judgement, not only a technical number.

HL.c Environmental ethics — key terms

Term	Meaning
Intrinsic value	Valuable in itself
Instrumental value	Valuable for its use to someone
Moral standing	Being owed moral consideration
Consequentialism	Judge actions by outcomes (utilitarianism: greatest good for the greatest number)
Deontology	Judge actions by duties and rights, whatever the outcome
Virtue ethics	Ask what a person of good character would do

Must-know distinction: who counts?

• Anthropocentric: humans only.
• Sentientist: beings that can suffer (Singer, 1975).
• Biocentric: every living organism (Taylor, 1986).
• Ecocentric: ecosystems, species and processes as wholes (Leopold’s land ethic, 1949; Naess’s deep ecology, 1973).

Match these to the Topic 1 value systems: technocentric and anthropocentric views give nature instrumental value; ecocentric views give it intrinsic value. See Topic 1: Foundations revision notes.

Justice

• Distributive: who gets costs and benefits.
• Procedural: who has a say.
• Intergenerational: duties to future people.
• Climate justice: low emitters often suffer most.

Linking the lenses (memorise one chain)

Ozone depletion: law — Montreal Protocol, binding phase-out. Economics — substitutes were affordable, so compliance was cheap; the damage to health and crops made the benefits large. Ethics — precaution and intergenerational equity justified acting before every uncertainty was resolved. Each lens explains part of why this agreement worked.

Quick self-test

1. Define soft law and give one example.
2. State the polluter pays principle.
3. Give two reasons international environmental law is hard to enforce.
4. Distinguish weak and strong sustainability.
5. Classify flood protection by a mangrove within TEV.
6. A survey finds a mean willingness to pay of USD 18 per household per year to protect a lake. There are 25,000 households in the catchment. Estimate the annual value.
7. A firm emits 8,000 t of CO₂ and faces a tax of USD 30 per tonne. It makes no cuts. Calculate its tax bill.
8. Calculate the present value of USD 500,000 received in 30 years at a discount rate of 4%. Give your answer to 3 significant figures.
9. State one difference between a carbon tax and cap-and-trade.
10. Distinguish intrinsic and instrumental value.
11. Identify the ethical position that gives moral standing to all living organisms.
12. Explain how the choice of discount rate is an ethical issue.

Answers

1. Non-binding guidance or targets with no penalty for breach; for example, voluntary national climate pledges or a declaration of principles.
2. Whoever causes pollution should pay the cost of preventing or repairing it.
3. Any two: state sovereignty; no global enforcer; free riders; costly monitoring; key polluters outside the agreement.
4. Weak: natural capital can be replaced by human-made capital. Strong: critical natural capital cannot be replaced, so it must be conserved.
5. Indirect use value.
6. 18 × 25,000 = USD 450,000 per year.
7. 8,000 × 30 = USD 240,000.
8. 500,000 ÷ 1.04³⁰ = USD 154,000 (3 s.f.).
9. A tax fixes the price and lets quantity vary; a cap fixes quantity and lets the permit price vary.
10. Intrinsic: valuable in itself. Instrumental: valuable for what it provides to someone.
11. Biocentrism.
12. A high rate gives less weight to costs and benefits felt by future generations, so choosing it is a judgement about how much future people matter.

Where marks are usually lost

• Naming a treaty but not its date, scale, legal force or target pollutant.
• Claiming a law “solved” a problem with no indicator data to support it.
• Ignoring other explanations for improvement (recession, new technology, a factory closure).
• Mixing up the two economic schools, or saying ecological economics “rejects valuation” outright; it puts physical limits first.
• Putting an ecosystem service such as pollination under direct use rather than indirect use.
• In tax calculations, taxing all emissions even after the firm has abated some.
• Saying cap-and-trade lets firms “pollute as much as they like”: the cap limits the total.
• Using ethical labels without applying them to a named stakeholder in the case.
• Writing three separate lens sections with no link between them.
• Giving a one-sided “to what extent” answer with no final weighed judgement.

Related pages

• ESS exam preparation
• ESS assessment revision notes
• Topic 2: Ecology revision notes
• ESS syllabus guide

Official syllabus

International Baccalaureate Organization, Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026. These notes cover the HL lenses HL.a Environmental law, HL.b Environmental and ecological economics and HL.c Environmental ethics.