IB DP Environmental Systems and Societies – Atmosphere, climate change and stratospheric ozone 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 Topic 6 of IB Diploma Programme Environmental Systems and Societies, aligned to the International Baccalaureate Diploma Programme Subject Brief: Environmental systems and societies, first assessment 2026. It covers syllabus sections 6.1–6.4, and every question suits both SL and 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.

The brief gives Topic 6 Atmosphere and climate change 10 teaching hours at SL and 23 at HL. It does not list the subtopics or learning outcomes for this topic, so the numbered subtopics and outcomes on this page follow the syllabus numbering used in the printable ESS checklist, not the brief itself.

All data tables are fictional. Learn the content first in the study guide and the revision notes. The IB DP ESS course hub and the printable syllabus checklist show where this unit sits.

Questions

1. Distinguish between weather and climate. [2]

2. Outline how the natural greenhouse effect warms Earth’s surface. [3]

3. Table 1 shows annual mean CO₂ concentrations at a fictional monitoring station, Station K. Take the pre-industrial concentration as 280 ppm.

Year	1990	2000	2010	2020
CO₂ (ppm)	354.0	369.7	389.9	413.4

(a) Calculate the mean annual rate of increase from 1990 to 2020. [2] (b) Calculate the percentage by which the 2020 value exceeds the pre-industrial level. [2] (c) Use your answer to (a) to estimate the concentration in 2040, and explain whether this is likely to be an underestimate. [3]

4. Explain why air temperature rises with height in the stratosphere. [2]

5. A fictional dairy farm emits 800 t of CO₂, 20 t of CH₄ and 2 t of N₂O a year. Use GWPs of 28 for CH₄ and 265 for N₂O.

(a) Calculate the farm’s total annual emissions in t CO₂e. [3] (b) Calculate the percentage of the total that comes from methane. [1] (c) Suggest two measures the farm could take to reduce its emissions. [2]

6. Explain how the loss of Arctic sea ice acts as a positive feedback on global warming. [4]

7. This question is about stratospheric ozone.

(a) Write equations to show how ozone forms in the stratosphere. [2] (b) Explain why one chlorine atom can destroy many ozone molecules. [2] (c) Explain why ozone depletion is greatest over Antarctica in spring. [2]

8. Table 2 shows the lowest October total-ozone reading at a fictional Antarctic station, Station P.

Year	1980	1995	2010	2025
Ozone (DU)	290	105	120	150

(a) Calculate the percentage decrease from 1980 to 1995. [2] (b) Calculate the mean rate of recovery from 1995 to 2025. [1] (c) Assuming this rate continues, estimate the year when the reading first rises above 220 DU. [2] (d) Suggest why recovery is much slower than the decline. [2]

9. Classify each of the following as mitigation or adaptation, with a reason: (i) a carbon tax on petrol; (ii) planting drought-tolerant maize; (iii) restoring a peat bog; (iv) raising homes on stilts in a flood zone. [4]

10. Table 3 shows fictional data for three countries.

Country	Population (millions)	CO₂ emissions per person (t per year)
A	60	9.5
B	210	1.2
C	25	16.0

(a) Calculate the total annual CO₂ emissions of each country in Mt. [2] (b) Compare Country B’s share of the combined population with its share of the combined emissions. [2] (c) Discuss how a climate-justice perspective might shape what each country is expected to do under the Paris Agreement. [5]

11. To what extent has the Montreal Protocol been more successful than international agreements on climate change? [9]

Answers

1. Weather is the state of the atmosphere at a place over hours or days [1]; climate is the average of weather over a long period, usually 30 years or more [1]. [2] Examiner insight: “Distinguish” needs both terms defined with a clear contrast (short-term vs long-term); defining only one caps the answer at 1 mark.

2. Incoming short-wave solar radiation is absorbed by the surface, which warms [1]. The surface emits long-wave infrared radiation [1]. Greenhouse gases absorb some of this infrared and re-emit it in all directions, including back to the surface, keeping it warmer (about 15 °C instead of about −18 °C) [1]. [3] Examiner insight: An answer that says gases “trap UV” or “reflect heat” loses the absorption mark; the wavelength change from short-wave in to long-wave out is what earns it.

3. (a) (413.4 − 354.0) ÷ 30 [1] = 1.98 ppm per year [1] (b) (413.4 − 280) ÷ 280 × 100 [1] = 47.6% [1] (c) 413.4 + 1.98 × 20 = 453.0 ppm [1]. Likely an underestimate [1], because each decade’s rise is bigger than the last (15.7, 20.2, then 23.5 ppm), so the rate is accelerating and the 2010–2020 rate alone (2.35 ppm per year) would give about 460 ppm [1]. [7] Examiner insight: In (c) the mark for “underestimate” needs evidence quoted from the table; “emissions are increasing” with no figures earns only the judgement mark.

4. Ozone in the stratosphere absorbs ultraviolet radiation [1], and the absorbed energy heats the air, more so at higher levels where more UV is available [1]. [2] Examiner insight: Naming ozone without saying it absorbs UV earns nothing; both the gas and the process are needed.

5. (a) CH₄: 20 × 28 = 560 t CO₂e [1]; N₂O: 2 × 265 = 530 t CO₂e [1]; total = 800 + 560 + 530 = 1890 t CO₂e [1] (b) 560 ÷ 1890 × 100 = 29.6% [1] (c) For example, capture methane from manure in a biogas digester [1] and apply less nitrogen fertiliser, more precisely [1]. Feed changes that cut cattle methane, renewable farm energy or planting hedgerows also earn credit. [6] Examiner insight: Adding 800 + 20 + 2 = 822 t loses both conversion marks and the total; a correct total from wrong conversions can still earn follow-through in (b).

6. Sea ice has a high albedo, reflecting much sunlight, while open ocean has a low albedo [1]. As warming melts sea ice, more dark ocean is exposed and absorbs more solar radiation [1]. The ocean and air warm further [1], which melts more ice, so the original change is amplified — a positive feedback loop [1]. [4] Examiner insight: The final mark needs the loop closed (warming → more melting); stopping at “the ocean absorbs more heat” leaves the feedback unexplained.

7. (a) O₂ + UV → O + O [1]; O + O₂ → O₃ [1] (b) Chlorine reacts with ozone (Cl + O₃ → ClO + O₂), and then ClO reacts with an oxygen atom to release the chlorine again (ClO + O → Cl + O₂) [1]. Chlorine is not used up; it acts as a catalyst and repeats the cycle many thousands of times [1]. (c) In the dark polar winter, very cold polar stratospheric clouds form, and reactions on them convert chlorine to forms that are easily broken down [1]. When sunlight returns in spring, UV releases reactive chlorine, which destroys ozone rapidly [1]. [6] Examiner insight: In (b) the word “catalyst” alone is not enough; the mark needs the chlorine to be shown as regenerated.

8. (a) (290 − 105) ÷ 290 × 100 [1] = 63.8% [1] (b) (150 − 105) ÷ 30 = 1.5 DU per year [1] (c) (220 − 150) ÷ 1.5 = 46.7 years [1]; 2025 + 46.7 → about 2072 [1] (d) Ozone-depleting substances remain in the atmosphere for decades, so chlorine keeps reaching the stratosphere long after production stopped [1]; old stocks in equipment such as refrigerators and foams continue to leak [1]. [7] Examiner insight: In (a) dividing by the final value (105) gives 176%, which loses the accuracy mark; percentage change always uses the starting value.

9. (i) Mitigation — it discourages burning fuel, reducing CO₂ emissions [1]. (ii) Adaptation — it reduces crop losses from drought without cutting emissions [1]. (iii) Mitigation — peat stores carbon, so restoring it creates a carbon sink [1]. (iv) Adaptation — it reduces flood damage [1]. [4] Examiner insight: Each mark needs both the label and a reason; a correct label with no reason does not earn the mark.

10. (a) A: 60 × 9.5 = 570 Mt; B: 210 × 1.2 = 252 Mt; C: 25 × 16.0 = 400 Mt. Method shown [1]; all three correct [1] (b) B has 210 ÷ 295 = 71.2% of the population [1] but 252 ÷ 1222 = 20.6% of the emissions, so its share of emissions is far smaller than its share of population [1] (c) Indicative points, one mark each up to 5:

• Climate justice holds that those who emit most, per person and historically, should cut most and pay most [1].
• Country C, at 16.0 t per person, would be expected to make the deepest cuts [1].
• Country A has the largest total emissions, so its cuts matter most for the global total [1].
• Country B may argue for the right to develop and for finance and technology from richer countries, since its per-person emissions are low [1].
• Under the Paris Agreement targets are set nationally (NDCs), so these expectations depend on each country’s choices and on international pressure; a balanced judgement recognises that B’s large population means its future emissions still matter [1]. [9] Examiner insight: In (c) marks come from linking each claim to the table; a general account of climate justice with no reference to the three countries earns at most 1–2 marks.

11. Indicative points, one mark each up to 9. Real essays are marked holistically, so treat these as a guide.

• Montreal set binding phase-out timetables, and every UN member state has ratified it [1].
• Evidence of success: ODS levels are falling, and ozone is expected to recover around the 2060s in Antarctica [1].
• Reasons: few producers of CFCs and affordable substitutes [1]; a direct, easily understood health harm (skin cancer) [1]; the Multilateral Fund paid poorer countries’ costs [1].
• Climate agreements face harder conditions: fossil fuels underpin almost every economy and have many sources [1].
• Kyoto bound only industrialised countries; Paris relies on voluntary NDCs, and current pledges are not on track for 1.5 °C [1].
• Counterpoint: Montreal’s substitutes (HFCs) created a new warming problem, only addressed by the Kigali Amendment, so its success was partly traded against climate [1].
• Judgement: Montreal has been more successful on its own goal, largely because its problem was simpler; the comparison is uneven, and Paris has at least brought every country into a shared framework [1]. [9] Examiner insight: “To what extent” needs a stated judgement backed by the points above; a one-sided account of Montreal’s success with no comparison to climate agreements cannot reach the top marks.

Where marks are usually lost

• Confusing ozone depletion with global warming, or saying the ozone hole lets heat in.
• Saying greenhouse gases absorb UV or reflect heat, rather than absorbing and re-emitting infrared.
• Adding masses of different gases without multiplying by GWP.
• Using the final value as the base for a percentage change.
• Leaving out units (ppm, DU, t CO₂e, Mt) in calculated answers.
• Describing a feedback without closing the loop back to the original change.
• Classifying strategies without a reason, or calling a sea wall mitigation.
• Quoting a data trend with no figures from the table.
• Essays that list facts about one agreement without comparing or reaching a judgement.

Next steps

• Revision notes for this unit
• Study guide for this unit
• IB DP ESS course hub
• Printable syllabus checklist
• ESS exam preparation guide
• Topic 2 Ecology practice questions
• 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. The brief lists subtopics for Topic 1 only; the subtopic numbering on this page follows the printable ESS checklist.