IB DP Environmental Systems and Societies – HL lenses: environmental law, economics and ethics Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – the IB holds copyright in its own papers. Use these alongside the official past papers available through your school or the IB store.

This practice set 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 questions are HL. It follows the IB ESS subject brief for first assessment 2026 — the course examined in the May and November 2026, 2027 and 2028 sessions.

All places, firms and data below are fictional. Money is in US dollars (USD). Give calculated answers to 3 significant figures unless told otherwise. Points listed for extended questions are indicative; real exam essays may be judged holistically against IB criteria, which your teacher will share.

Learn the ideas first in the HL lenses study guide and the HL lenses revision notes. The IB DP ESS course hub and printable ESS syllabus checklist show where this unit sits.

Questions

1. (HL) Distinguish between hard law and soft law, giving one example of each. [3]

2. (HL) The table shows annual mean sulphur dioxide (SO₂) concentration in the fictional town of Kessel Bay. A law limiting sulphur in fuel began in January 2019.

Year	2016	2017	2018	2019	2020	2021
SO₂ (µg m⁻³)	64	62	60	48	39	36

(a) Calculate the percentage change in SO₂ concentration from 2018 to 2021. [2] (b) Calculate the mean concentration for 2016–2018 and for 2019–2021. [2] (c) Evaluate the claim that the data prove the law was effective. [4]

3. (HL) Explain two reasons why international environmental agreements are difficult to enforce. [4]

4. (HL) A coastal wetland restoration scheme is expected to avoid flood damage worth USD 2,400,000 in 40 years’ time.

(a) Calculate the present value of this benefit using discount rates of 2% and 6%. [3] (b) Explain what your answers suggest about how the discount rate affects decisions on long-term environmental projects. [2]

5. (HL) Data for a fictional fishery managed by a national quota:

Year	2020	2021	2022	2023	2024
Quota (t)	900	900	700	700	700
Reported catch (t)	1,040	1,010	720	690	700
Spawning-stock biomass (t)	5,200	4,600	4,400	4,700	5,100

(a) Calculate the percentage by which the catch exceeded the quota in 2020. [2] (b) Describe the change in spawning-stock biomass from 2020 to 2024, using data. [2] (c) Using the law and economics lenses, suggest reasons for the pattern shown. [4]

6. (HL) Two factories, X and Y, must cut their combined emissions by 600 t a year. Cutting one tonne costs USD 15 at X and USD 45 at Y.

(a) Calculate the total cost if each factory cuts 300 t. [1] (b) Calculate the lowest possible total cost of the 600 t cut, and the saving compared with (a). [2] (c) Explain why, under cap-and-trade, the permit price would lie between USD 15 and USD 45 per tonne. [2]

7. (HL) A cement works emits 20,000 t of CO₂ a year. A carbon tax of USD 50 per tonne is introduced. The works can cut its first 8,000 t at USD 30 per tonne; any further cuts cost USD 70 per tonne.

(a) Calculate the tax bill if the works makes no cuts. [1] (b) Determine how many tonnes the works will cut, and its total annual cost after doing so. [3] (c) Calculate the saving compared with making no cuts. [1]

8. (HL) A fictional wetland is valued per year (in thousands of USD) as: fish 210, water purification 380, flood control 450, option value 40, existence value 90, bequest value 30. A developer offers to drain it for farmland worth 600 per year.

(a) Calculate the total economic value. [1] (b) Calculate the non-use value as a percentage of TEV. [2] (c) Explain why judging the wetland only by its market value would be misleading. [2] (d) Evaluate contingent valuation as a way of estimating existence value. [3]

9. (HL) Compare and contrast how an anthropocentric and an ecocentric ethic would judge a proposal to build a hydroelectric dam that floods a forested valley. [4]

10. (HL) To what extent can environmental law alone reduce greenhouse gas emissions? Refer to the economics and ethics lenses in your answer. [9]

11. (HL) Discuss the ethical arguments for and against giving a river legal personhood. [7]

Answers

1. Hard law is legally binding and can be enforced with penalties [1]; soft law is non-binding guidance, declarations or voluntary targets [1]; valid examples, such as a national ban on a pesticide (hard) and a voluntary climate pledge (soft) [1] [3] Examiner insight: “Distinguish” needs the difference made explicit for both terms; two unrelated definitions with no contrast lose the comparison mark.

2. (a) (36 − 60)/60 × 100 [1]; −40.0% (a 40.0% decrease) [1] (b) 2016–18: (64 + 62 + 60)/3 = 62.0 µg m⁻³ [1]; 2019–21: (48 + 39 + 36)/3 = 41.0 µg m⁻³ [1] (c) Supports: the fall from 2019 (12 µg m⁻³ in the first year) is much faster than the decline before [1]; the timing matches the law [1]. Against: SO₂ was already falling before 2019 [1]; other causes such as a factory closure or weather are not ruled out, so “prove” is too strong [1] [8] Examiner insight: Describing the fall earns little; the marks come from questioning the claim, including the earlier downward trend.

3. States are sovereign, so no global body can force a country to comply [1]; a state can withdraw or miss targets with little penalty [1]. Free riders gain from others’ cuts without acting [1], which weakens others’ willingness to comply [1] [4] Examiner insight: “Explain” needs each reason developed with a consequence; a list of four reasons scores less than two developed ones.

4. (a) PV = 2,400,000 ÷ (1 + r)⁴⁰ [1]; at 2%: USD 1,090,000 [1]; at 6%: USD 233,000 [1] (b) The higher rate makes the future benefit worth under a quarter as much today [1], so high discount rates make long-term projects look less worthwhile and favour short-term gains, which is unfair to future generations [1] [5] Examiner insight: Round only at the end; rounding 1.02⁴⁰ early spoils the 3 s.f. answer.

5. (a) (1,040 − 900)/900 × 100 [1]; 15.6% [1] (b) Biomass fell from 5,200 t to 4,400 t by 2022 (a 15.4% fall) [1], then recovered to 5,100 t by 2024, close to the 2020 level [1] (c) Law: in 2020–21 the quota was too high and not enforced, since catch exceeded it [1]; the cut to 700 t and closer compliance let the stock recover [1]. Economics: a tragedy of the commons, as each boat gains from extra catch while the cost is shared [1]; stronger monitoring or fines raised the cost of cheating [1] [8] Examiner insight: Trend descriptions need data with units and years; “it went down then up” without figures is not enough.

6. (a) 300 × 15 + 300 × 45 = USD 18,000 [1] (b) X cuts all 600 t: 600 × 15 = USD 9,000 [1]; saving USD 9,000 [1] (c) X will sell permits only if paid more than its cutting cost of USD 15 per tonne [1], and Y will buy only if the price is below its own cutting cost of USD 45 per tonne [1] [5] Examiner insight: Part (c) needs both sides of the trade; explaining only the buyer’s limit gets half the marks.

7. (a) 20,000 × 50 = USD 1,000,000 [1] (b) Cuts 8,000 t, because USD 30 < USD 50 but further cuts cost USD 70 > USD 50 [1]; abatement 8,000 × 30 = 240,000 and tax on 12,000 t = 600,000 [1]; total USD 840,000 [1] (c) 1,000,000 − 840,000 = USD 160,000 [1] [5] Examiner insight: A common slip is taxing all 20,000 t after the cuts; only the remaining emissions are taxed.

8. (a) 210 + 380 + 450 + 40 + 90 + 30 = 1,200 thousand USD per year [1] (b) (90 + 30)/1,200 × 100 [1]; 10.0% [1] (c) Fish alone (210) is worth less than farmland (600), so draining looks better [1]; but TEV (1,200) is double the farmland value, as services like flood control have no market price [1] (d) Strength: one of few ways to value non-use benefits, which have no market [1]. Limitations: stated willingness to pay may differ from real payment [1]; results depend on question wording and income [1] [8] Examiner insight: In (c), use the numbers from (a); “nature is priceless” earns no credit.

9. Similarity: both weigh the dam’s effects on the valley [1]. Anthropocentric: values the forest instrumentally, weighing electricity and jobs against lost timber and tourism [1]. Ecocentric: values the ecosystem intrinsically, so flooding it is a harm in itself [1]; likely to reject the dam even if human benefits are large [1] [4] Examiner insight: “Compare and contrast” needs at least one similarity as well as differences; two separate descriptions do not score the full marks.

10. Indicative points: law sets binding limits, such as emission caps or vehicle standards [1]; treaties coordinate action, but sovereignty and weak enforcement limit them [1]; non-signatories and free riders reduce the effect [1]. Economics: carbon taxes or cap-and-trade make cutting emissions pay [1]; without a price signal, laws are costly to monitor and evaded [1]; subsidies for renewables cut the cost of complying [1]. Ethics: climate justice asks high emitters to cut more [1]; intergenerational equity and precaution justify acting now [1]. Judgement: law is necessary but not sufficient without economic incentives and public support [1] [9] Examiner insight: “To what extent” needs a clear, reasoned conclusion; balanced points with no final judgement cap the response.

11. Indicative points. For: ecocentrism gives the river intrinsic value, so it deserves protection in its own right [1]; guardians can sue without proving harm to a human [1]; it respects indigenous worldviews that see the river as a living being [1]; it protects the river for future generations [1]. Against: anthropocentrism holds that only humans have interests [1]; it may restrict water use by poor communities, a distributive justice concern [1]. A weighed conclusion, for example that it is justified where guardians represent both river and local people [1] [7] Examiner insight: “Discuss” needs both sides linked to named ethical positions; bare opinion is not ethical reasoning.

Where marks are usually lost

• Taxing all emissions after abatement in carbon-tax calculations.
• Calling a law effective because an indicator improved, without checking the earlier trend or other causes.
• Putting ecosystem services under direct use value instead of indirect use value.
• Listing ethical labels without linking them to a stakeholder or decision.
• Writing the three lenses as separate blocks with no link between them.
• Missing a final judgement on “evaluate”, “discuss” and “to what extent” questions.

Next steps

• HL lenses revision notes
• HL lenses study guide
• Topic 1: Foundations practice and Topic 2: Ecology practice
• ESS exam preparation
• IB DP ESS course hub
• Printable ESS syllabus checklist
• All free 10-minute diagnostics
• Book a free trial class

Official syllabus

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