IB DP Environmental Systems and Societies – HL lenses: environmental law, economics and ethics Study Guide

This study guide covers the three higher level lenses of IB Diploma Programme Environmental Systems and Societies (ESS). It is aligned to the International Baccalaureate Organization’s Diploma Programme Subject Brief, Environmental systems and societies, first assessment 2026, and covers HL.a Environmental law, HL.b Environmental and ecological economics and HL.c Environmental ethics. All three are HL only: SL students do not study them. It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions.

Once you know the ideas, condense them with the HL lenses revision notes and test yourself with the HL lenses practice questions. The IB DP ESS course hub and the printable ESS syllabus checklist show where this unit sits in the course.

What a “lens” is

The brief calls the lenses “conceptually more demanding” and says HL students must synthesize the core content, HL extension material and HL lenses. In practice, a lens is a set of questions you bring to an issue you already know from Topics 1–8:

• Law: Which rules apply to this issue? Who made them, who must obey them and how are they enforced?
• Economics: How is the issue valued? Who pays the costs and who takes the benefits? Which economic tools could change behaviour?
• Ethics: Who or what counts morally? Which principles justify one course of action over another?

The brief’s assessment objective 3 asks you to evaluate the “political, economic, ethical and sociocultural contexts of issues”. The lenses are the HL toolkit for doing that well.

What this unit covers

Lens (brief label)	Recommended hours (HL)	What to practise
HL.a Environmental law	5	Explain how laws at international, national and local level address an issue; evaluate why they succeed or fail
HL.b Environmental and ecological economics	7	Contrast the two economic schools; value ecosystems; explain taxes, permits and subsidies; interpret discounting
HL.c Environmental ethics	5	Apply ethical theories and positions on moral standing to an issue; judge competing claims, including justice between groups and generations

Only the hours come from the brief. The ESS syllabus guide and ESS subject guide set out the rest of the course structure.

HL.a Environmental law

Levels of law

• International law is made by agreement between states. A convention or treaty sets the framework; a protocol adds binding detail later. Examples: the Ramsar Convention on wetlands (1971), CITES on trade in endangered species (1973), the Montreal Protocol on ozone-depleting substances (1987) and the Paris Agreement on climate change (2015).
• National law is passed by a country’s legislature: for example, air-quality standards, species protection, or requiring an environmental impact assessment (EIA) before large projects.
• Local law includes by-laws and planning rules, such as city low-emission zones.

Hard and soft law

Hard law is legally binding and enforceable, for example a national pesticide ban. Soft law is guidance, declarations and voluntary targets, working through reputation and peer pressure rather than penalties. The Paris Agreement mixes the two: countries must submit and update climate pledges (nationally determined contributions), but there is no penalty for missing the targets in them.

Principles you should be able to name

• Precautionary principle: where there is a threat of serious harm, lack of full scientific certainty is not a reason to delay action.
• Polluter pays principle: whoever causes pollution should bear the cost of preventing or repairing it.
• Prevention principle: it is better to stop harm happening than to repair it afterwards.
• Intergenerational equity: today’s decisions must not leave future generations worse off. This links straight to the definition of sustainability in Topic 1.

Why international law is hard to enforce

States are sovereign: no world body can force a country to sign a treaty or obey one it has left. Monitoring is expensive. Free riders gain from others’ action while doing nothing. Laws succeed most when acting is cheap, substitutes exist and the science is clear. The Montreal Protocol is the standard success case: substitutes for CFCs were available, the ozone damage was measurable, and it is now ratified by every UN member state.

New directions

Some legal systems now give nature legal standing. Ecuador’s 2008 constitution recognises rights of nature, and in 2017 New Zealand gave the Whanganui River legal personhood. This is law shaped by ethics: an ecocentric view that nature has value apart from its use to people.

HL.b Environmental and ecological economics

Two schools

	Environmental economics	Ecological economics
Where the economy sits	The environment is one part of the economy	The economy is a subsystem inside the biosphere
Main problem	Market failure: prices leave out environmental costs	The economy’s physical scale is too large for Earth’s limits
Sustainability view	Weak: natural capital can be replaced by human-made capital	Strong: critical natural capital cannot be replaced
Typical solutions	Price the harm: taxes, permits, cost-benefit analysis	Set physical limits first; steady-state or “doughnut” models; circular economy

An externality is a cost (or benefit) felt by people outside a transaction. Air pollution from a power station is a negative externality: people downwind pay in ill health, but the electricity price ignores it. Correcting this is internalising the externality. Hardin’s tragedy of the commons (1968) describes a related failure: when a resource is open to all, each user gains from taking more, so the resource is overused.

Valuing nature: total economic value

Total economic value (TEV) adds up:

• Direct use value: products taken or used, such as fish, timber or recreation.
• Indirect use value: ecosystem services, such as flood protection or water purification.
• Option value: keeping the choice to use something in future.
• Non-use values: existence value (knowing it exists) and bequest value (leaving it for future generations).

Market prices only capture direct use. Other methods include contingent valuation (asking people their willingness to pay), the travel cost method and hedonic pricing (house prices near green space).

Worked example 1 — TEV (fictional data). A coastal mangrove is valued per year at: direct use USD 120,000, indirect use USD 340,000, option USD 30,000, existence USD 60,000, bequest USD 25,000.

TEV     = 120,000 + 340,000 + 30,000 + 60,000 + 25,000 = USD 575,000
Use     = 120,000 + 340,000 + 30,000                   = USD 490,000
Non-use = 60,000 + 25,000                              = USD 85,000
Indirect share = 340,000 / 575,000 x 100               = 59.1%

Judged only on timber and fish (20.9% of TEV), clearing it for shrimp farms would look far better than it is.

Economic tools

• Pigouvian (environmental) tax: a tax per unit of pollution, such as a carbon tax.
• Cap-and-trade (tradable permits): a cap fixes total emissions, and firms buy and sell permits. The EU Emissions Trading System, which began in 2005, is an example.
• Subsidies: payments for cleaner behaviour. Costa Rica’s payments for ecosystem services reward landowners for keeping forest.
• Command and control: direct regulation (standards, bans), where economics meets law.

Worked example 2 — carbon tax. A factory emits 12,000 t of CO₂ a year. A tax of USD 40 per tonne is introduced. It can cut its first 5,000 t at USD 25 per tonne; further cuts cost USD 60 per tonne.

No abatement: 12,000 x 40               = USD 480,000 tax
Abate 5,000:  5,000 x 25 = USD 125,000 abatement
              7,000 x 40 = USD 280,000 tax
              total                     = USD 405,000
Saving = 480,000 - 405,000              = USD 75,000

The factory abates while a tonne costs less to cut than to tax (25 < 40) and stops when it costs more (60 > 40).

Worked example 3 — cap-and-trade. Two firms must cut 1,000 t between them. Firm A abates at USD 20 per tonne, firm B at USD 50 per tonne. An equal split costs 500 × 20 + 500 × 50 = USD 35,000. If B buys permits from A and A makes all 1,000 t of cuts, the cost is 1,000 × 20 = USD 20,000. The same cut is achieved for USD 15,000 less. The permit price settles between USD 20 and USD 50.

Discounting

Economists discount future costs and benefits: a sum received later is worth less today. Present value = future value ÷ (1 + r)ᵗ, where r is the discount rate and t the number of years.

Worked example 4. A climate policy avoids USD 1,000,000 of damage in 50 years.

r = 1%:  1,000,000 / 1.01^50 = USD 608,039
r = 3%:  1,000,000 / 1.03^50 = USD 228,107
r = 5%:  1,000,000 / 1.05^50 = 87,204 USD

A higher rate makes long-term harm look small. Choosing the rate is partly an ethical choice about how much future people matter, which links to HL.c.

HL.c Environmental ethics

Ethical theories

• Consequentialism (for example utilitarianism): the right action produces the best overall outcome. Cost-benefit analysis is a consequentialist tool.
• Deontology: some duties and rights hold whatever the outcome, for example a duty not to destroy a species or a right to clean water.
• Virtue ethics: asks what a good person would do, and stresses traits such as care, restraint and humility.

Who counts morally?

Position	Has moral standing	Link to Topic 1 value systems
Anthropocentric	Humans only; nature has instrumental value	Anthropocentrism, technocentrism
Sentientist	All beings that can feel pain (Peter Singer, 1975)	Between the two
Biocentric	Every living organism (Paul Taylor, 1986)	Ecocentrism
Ecocentric	Whole ecosystems, species and processes (Aldo Leopold’s land ethic, 1949; Arne Naess’s deep ecology, 1973)	Ecocentrism

Intrinsic value means valuable in itself; instrumental value means valuable for what it does for someone. Review the value systems in Topic 1: Foundations first.

Justice

• Distributive justice: who bears the costs and who gets the benefits.
• Procedural justice: who has a voice, for example whether indigenous communities are consulted.
• Intergenerational justice: duties to people not yet born. The same idea appears in law (intergenerational equity) and economics (the discount rate).
• Climate justice: those who contributed least to emissions often face the worst impacts.

Using all three lenses together

Take overfishing, from Topic 4. Through the law lens, coastal states control fishing in exclusive economic zones up to 200 nautical miles offshore under UNCLOS, but the high seas are much harder to police. Through the economics lens, an open-access fishery is a tragedy of the commons; tradable catch quotas turn a share of the catch into an asset worth protecting. Through the ethics lens, a utilitarian weighs jobs today against stocks tomorrow, an ecocentrist argues the marine ecosystem has intrinsic value, and a justice view asks whether small-scale fishers lose out when quotas are sold to large fleets.

A strong HL answer links the lenses: a law works only if the economics give people reason to obey it, and ethics decide what the law should aim for.

Common errors

• Describing a treaty without saying whether it is binding or how it is enforced.
• Calling any agreement a “law”. Declarations and voluntary targets are soft law.
• Confusing environmental economics (pricing within markets) with ecological economics (limits on scale).
• Treating a carbon tax and cap-and-trade as the same: a tax fixes the price and lets the quantity vary; a cap fixes the quantity and lets the price vary.
• Saying discounting is “wrong” without explaining what the rate does to long-term values.
• Labelling a stakeholder “ecocentric” with no evidence from the case.
• Treating the lenses as separate essays instead of linking them.

Where next

• Condense it: HL lenses revision notes
• Test it: HL lenses practice questions
• Exam format: ESS exam preparation and ESS assessment revision notes
• Core topics to apply the lenses to: Topic 2: Ecology

Official syllabus

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