Greenhouse gases, climate change & carbon footprint – GCSE Chemistry exam questions with mark scheme

1Grade 4–53 marks

Carbon dioxide and methane are greenhouse gases.

Describe how greenhouse gases keep the Earth warm. [3]

(short wavelength) radiation from the Sun passes through the atmosphere / reaches the Earth's surface(1)
the Earth emits (long wavelength) infrared radiation(1)
greenhouse gases absorb (and re-emit) the infrared radiation (so energy is retained in the atmosphere); ignore 'trap heat'(1)
Answer: Sunlight reaches the surface; the Earth radiates infrared; greenhouse gases absorb and re-emit it, keeping the lower atmosphere warm.
Examiner tip: 'Traps heat' scores nothing — say greenhouse gases absorb infrared (long wavelength) radiation.

2Grade 4–54 marks

The graph shows the concentration of carbon dioxide in the atmosphere from 1960 to 2020.

(a) Calculate the percentage increase in carbon dioxide concentration from 1960 to 2020. Give your answer to 3 significant figures. [2]

(b) Give two human activities that have caused this increase. [2]

(a) readings 315 and 415 (ppm) used in (415 − 315) ÷ 315 × 100 allow readings ±1 ppm(1)
(a) 31.7 (%) allow 31.0–32.5 from readings within ±1 ppm, given to 3 s.f.(1)
(b) burning / combustion of fossil fuels (coal, oil, natural gas) allow named fossil fuel, burning fuels in power stations / vehicles(1)
(b) deforestation allow cutting down / burning forests; do not accept methane sources (livestock, landfill, rice paddies); two examples of burning fossil fuels score 1 mark only(1)
Answer: (a) 31.7% (b) burning fossil fuels; deforestation
Examiner tip: Percentage change = change ÷ original × 100 — dividing by 415 gives 24.1%, which scores 0 for the answer.

3Grade 6–7Higher5 marks

Methane burns completely in oxygen.

CH₄ + 2O₂ → CO₂ + 2H₂O

(a) Calculate the mass of carbon dioxide produced when 1.0 kg of methane burns. Give your answer in kg.

Relative formula masses (M_r): CH₄ = 16, CO₂ = 44 [3]

(b) Give two reasons why it is difficult for governments to reduce carbon footprints. [2]

(a) moles CH₄ = 1000 ÷ 16 = 62.5 alternative method: 16 g (kg) CH₄ gives 44 g (kg) CO₂(1)
(a) moles CO₂ = 62.5 (1 : 1 ratio) so mass = 62.5 × 44 = 2750 g alternative: 1.0 × 44 ÷ 16(1)
(a) 2.75 (kg) allow 2.8; allow 2750 g for 2 marks only (not converted to kg)(1)
(b) any one from: scientific disagreement / incomplete understanding; economic considerations (cost, effect on jobs or growth); lack of public information / education; people unwilling to change lifestyle; lack of international cooperation / agreement(1)
(b) a second, different reason from the list(1)
Answer: (a) 2.75 kg (b) e.g. cost / economic impact and lack of international agreement
Examiner tip: Watch the units — work in grams, then convert back to kg at the end.

4Grade 1–3Foundation5 marks

The Earth's atmosphere contains small amounts of greenhouse gases.

(a) Which two gases are greenhouse gases? Tick (✓) two boxes. [2]

argon
methane
nitrogen
oxygen
water vapour

(b) Some human activities increase the amount of methane in the atmosphere.

Give two of these activities. [2]

Give one way the country could generate electricity that releases less carbon dioxide. [1]

(a) methane ✓(1)
(a) water vapour ✓ if more than two boxes are ticked, deduct 1 mark for each extra tick(1)
(b) any one from: (keeping / rearing) livestock / cattle / cows / animal farming; (decomposition of) rubbish / waste in landfill (sites); (growing rice in) rice paddies; allow leaks from natural gas extraction / pipelines ignore 'farming' unqualified do not accept burning fossil fuels / deforestation (these increase CO₂)(1)
(b) a second, different activity from the list(1)
(c) any one from: use renewable energy resources, e.g. wind / solar / hydroelectric / tidal / geothermal; use nuclear power; fit carbon capture and storage (CCS) to the power station allow named renewable resource ignore 'use less electricity' / 'burn less fuel' (question asks how to generate electricity)(1)
Answer: (a) methane and water vapour; (b) e.g. livestock farming and landfill sites; (c) e.g. wind turbines / nuclear power
Examiner tip: Carbon dioxide is not in the list, so many students tick nitrogen or oxygen because they are the main gases in air — water vapour is the greenhouse gas students forget.

5Grade 4–54 marks

The diagram shows how radiation passes into and out of the Earth's atmosphere. Arrows A, B, C and D show radiation.

(a) Which arrow, A, B, C or D, shows short wavelength radiation from the Sun? [1]

(b) What type of radiation is emitted by the Earth's surface? [1]

Use arrows B, C and D to explain why this increases the mean temperature of the Earth's surface. [2]

(a) A(1)
(b) long wavelength (radiation) allow infrared / IR (radiation) do not accept short wavelength / ultraviolet(1)
(c) more (long wavelength / infrared) radiation is absorbed by greenhouse gas molecules (in the atmosphere) allow arrow C becomes bigger / arrow B becomes smaller / less radiation escapes to space ignore 'heat is trapped'(1)
(c) more (radiation / energy) is re-emitted back to the Earth's surface (arrow D) so more energy is kept in the atmosphere / at the surface allow arrow D becomes bigger(1)
Answer: (a) A; (b) long wavelength (infrared) radiation; (c) more long wavelength radiation absorbed by greenhouse gases (C up, B down) and more re-emitted back to the surface (D up), so more energy is retained
Examiner tip: 'Traps heat' or 'the ozone layer' earns nothing — say greenhouse gases absorb long wavelength radiation and re-emit it back towards the Earth.

6Grade 4–5Foundation5 marks

The bar chart shows the mass of methane released each year by different sources in one country.

(a) Which source released the most methane? [1]

(b) Calculate the percentage of the total mass of methane that was released from landfill.

Give your answer to 3 significant figures. [3]

(a) livestock(1)
(b) total = 1500 + 900 + 600 + 300 + 200 = 3500 (thousand tonnes)(1)
(b) $\dfrac{600}{3500} \times 100$ allow ECF from an incorrect total(1)
(b) 17.1 (%) allow 17.14… for 2 marks only (not given to 3 s.f.) a correct answer to 3 s.f. scores 3 marks(1)
(c) any one from: recycle / compost / reuse more waste; send less (food / organic) waste to landfill; collect / capture the methane (from landfill sites) and burn it (as a fuel / to generate electricity); use anaerobic digestion of food waste allow burn / incinerate waste instead of putting it in landfill ignore 'stop using landfill' unqualified(1)
Answer: (a) livestock; (b) 17.1%; (c) e.g. recycle or compost more waste / capture the methane and burn it as a fuel
Examiner tip: The axis is labelled every 200 but each gridline is 100 thousand tonnes, so the 1500, 900 and 300 bars end on unlabelled lines — one misread bar makes the total, and so the percentage, wrong.

7Grade 4–57 marks

The table shows typical carbon footprints of electricity generated in different ways.

Method of generating electricity	Carbon footprint in g of CO₂ equivalent per kWh
coal	820
natural gas	490
solar	48
nuclear	12
wind	11

(a) What is meant by the carbon footprint of a product? [2]

(b) Wind turbines do not burn any fuel.

Suggest why the carbon footprint of electricity from wind is not zero. [1]

Calculate the reduction in the household's carbon footprint, in kg, if its electricity is generated using wind instead of natural gas. [3]

(d) Some governments charge a carbon tax on electricity generated by burning fossil fuels.

Suggest how a carbon tax reduces carbon dioxide emissions. [1]

(a) the total amount of carbon dioxide and other greenhouse gases (emitted) allow the total amount of CO₂ / greenhouse gases(1)
(a) (emitted) over the full life cycle of the product allow from making it to disposing of it / during its manufacture, use and disposal ignore 'during its use' alone(1)
(b) (fossil) fuels are burned / CO₂ is emitted when the turbine is made / transported / built / maintained / dismantled allow making the steel / concrete for the turbine releases CO₂(1)
(c) difference = 490 − 11 = 479 (g per kWh) allow 490 × 3200 = 1 568 000 (g) and 11 × 3200 = 35 200 (g)(1)
(c) 479 × 3200 = 1 532 800 (g) allow 1 568 000 − 35 200(1)
(c) 1533 (kg) allow 1532.8 / 1530 / 1500 (kg) allow 1 532 800 g for 2 marks (not converted to kg) a correct answer scores 3 marks(1)
(d) it makes electricity from fossil fuels more expensive (so) companies switch to renewable / nuclear / low-carbon methods allow encourages companies / people to use less fossil-fuel electricity ignore 'the money is used to plant trees'(1)
Answer: (a) total CO₂ and other greenhouse gases emitted over the full life cycle; (b) CO₂ released making/transporting/building the turbine; (c) 1533 kg (1530 kg); (d) makes fossil-fuel electricity more expensive, so companies switch to low-carbon sources
Examiner tip: The carbon footprint covers the whole life cycle — so 'it does not burn fuel' never means zero — and remember 1000 g = 1 kg at the end of (c).

8Grade 6–7Higher7 marks

The table shows the concentration of carbon dioxide in the atmosphere and the global temperature anomaly for some years. The temperature anomaly is the difference between the mean global temperature that year and the mean for 1951–1980.

Year	Carbon dioxide concentration in parts per million (ppm)	Temperature anomaly in °C
1900	296	−0.08
1920	303	−0.27
1940	311	+0.13
1960	317	−0.03
1980	339	+0.26
2000	370	+0.39
2020	414	+1.01

(a) Describe the relationship between the carbon dioxide concentration and the temperature anomaly. [2]

(b) Calculate the mean rate of increase in carbon dioxide concentration between 1960 and 2020.

Give your answer in ppm per year to 2 significant figures. [2]

Give two reasons why the data in the table alone do not prove this. [2]

(d) Scientists' research on climate change is peer reviewed before it is published.

Explain why. [1]

(a) as the carbon dioxide concentration increases the temperature anomaly (generally) increases allow positive correlation(1)
(a) but the pattern is not consistent / temperature anomaly fell while CO₂ rose between 1900 and 1920 or between 1940 and 1960 allow the biggest increase in temperature is after 1980 / 2000 when CO₂ rises fastest(1)
(b) $\dfrac{414 - 317}{2020 - 1960}$ allow 97 ÷ 60(1)
(b) 1.6 (ppm per year) allow 1.616…/1.62 for 1 mark only (not 2 s.f.) a correct answer to 2 s.f. scores 2 marks(1)
(c) any one from: a correlation does not show that one variable causes the other; other factors could affect the temperature (e.g. changes in the Sun's activity / volcanic eruptions / natural variation); temperature fell at times when CO₂ concentration increased (e.g. 1940–1960); only a few data points / years / one value every 20 years; older values are estimates / less accurate (e.g. from ice cores / fewer measuring stations) ignore 'not enough data' unqualified(1)
(c) a second, different reason(1)
(d) other scientists / experts check the work / method / data / conclusions (to check it is valid / to find errors / bias) allow to make sure the findings are reliable / valid before they are published ignore 'to check it is true'(1)
Answer: (a) as CO₂ increases, temperature anomaly generally increases but not consistently; (b) 1.6 ppm per year; (c) correlation is not causation / other factors; few data points / temperature fell 1940–1960; (d) other scientists check the method and conclusions
Examiner tip: A correlation in data is not proof of cause — the examiner wants you to spot where the pattern breaks (1940–1960) and name another possible factor.

9Grade 6–76 marks

Burning fossil fuels and farming livestock increase the concentrations of greenhouse gases in the atmosphere.

Explain how these activities could lead to global climate change, and describe the possible effects of global climate change on people and the environment. [6]

burning fossil fuels (e.g. coal, oil, natural gas) releases carbon dioxide(1)
livestock (cattle) release methane (from digestion / manure)(1)
carbon dioxide and methane are greenhouse gases(1)
the Sun's short wavelength radiation passes through the atmosphere and warms the Earth's surface(1)
the Earth's surface emits long wavelength (infrared) radiation(1)
greenhouse gases absorb long wavelength radiation and re-emit it, some back towards the Earth(1)
higher concentrations of greenhouse gases mean more energy is retained, so the global average temperature increases(1)
an increase in global average temperature causes climate change(1)
effect: sea levels rise (melting ice caps / glaciers and expansion of water), causing flooding and coastal erosion(1)
effect: more frequent and / or more severe storms(1)
effect: changes in the amount, timing and distribution of rainfall (droughts in some places, floods in others)(1)
effect: temperature and water stress for humans and wildlife(1)
effect: changes in food-producing capacity of some regions (crop failure / lower yields)(1)
effect: changes to the distribution of wildlife species / some species may become extinct(1)
scale / risk: effects vary between regions; people in low-lying coastal areas or poorer countries may be at greatest risk(1)

Level	Marks	What it looks like
Level 3	5–6	A detailed, coherent explanation that links the release of named greenhouse gases to absorption and re-emission of long wavelength radiation and a rise in global temperature, then describes at least three effects of climate change on people and/or the environment, with clear cause-and-effect reasoning throughout.
Level 2	3–4	A clear explanation that identifies the greenhouse gas(es) released and links them to warming, with some reference to radiation or energy being retained, and describes at least two effects of climate change. Some steps in the reasoning may be missing or imprecise.
Level 1	1–2	Simple statements, e.g. that the activities release carbon dioxide or methane, that the Earth gets warmer, or one or more effects of climate change, with little or no linking between them.
No relevant content	0	Nothing worthy of credit.

Answer: Full answer links: CO₂ from combustion of fossil fuels and CH₄ from livestock → greenhouse gases absorb and re-emit long wavelength radiation → more energy retained → global average temperature rises → climate change → effects such as sea-level rise (flooding, erosion), more severe storms, changed rainfall, water stress, reduced food production, changes in species distribution.
Examiner tip: Top-band answers form a linked chain (gas → radiation absorbed → temperature rise → climate change → effect); a list of effects with no mechanism stays in Level 2.

10Grade 8–9Higher8 marks

A family drives 350 km on holiday. The car uses 6.0 kg of petrol for every 100 km travelled.

Petrol can be represented as octane, C₈H₁₈. The equation for the complete combustion of octane is:

$$2\text{C}_8\text{H}_{18} + 25\text{O}_2 \rightarrow 16\text{CO}_2 + 18\text{H}_2\text{O}$$

Relative formula masses ($M_r$): C₈H₁₈ = 114 CO₂ = 44

(a) Calculate the mass of carbon dioxide, in kg, released by the car during the journey. [4]

(b) One tree absorbs about 22 kg of carbon dioxide each year.

Calculate the minimum number of trees needed to absorb the carbon dioxide from the journey in one year. [2]

Give two reasons why. [2]

(a) mass of petrol = 350 ÷ 100 × 6.0 = 21 (kg) allow 21 000 g(1)
(a) moles of octane = 21 000 ÷ 114 = 184(.2) (mol) allow mass-ratio method: 2 × 114 = 228 (g) of octane forms 16 × 44 = 704 (g) of CO₂ for this mark(1)
(a) moles of CO₂ = 184.2 × 8 = 1474 (mol) allow 21 × 704 ÷ 228 for this mark in the mass-ratio method allow ECF from incorrect moles of octane(1)
(a) 64.8 (kg) allow 64.84… / 65 (kg) allow 64 842 g for 3 marks (not converted to kg) a correct answer scores 4 marks(1)
(b) 64.8 ÷ 22 = 2.9(5) allow ECF from (a)(1)
(b) 3 (trees) – rounded up to a whole number allow ECF: the next whole number above their value from (a) ÷ 22 do not accept 2 / 2.95(1)
(c) any one from: CO₂ / greenhouse gases are released extracting / refining / transporting the petrol; manufacturing the car (and its parts / materials); maintaining / disposing of the car; other greenhouse gases (e.g. methane / nitrous oxide) are released, not only CO₂ ignore 'incomplete combustion' / 'traffic jams' unqualified / 'petrol is not pure octane' (a modelling point, not part of the carbon footprint)(1)
(c) a second, different reason(1)
Answer: (a) 64.8 kg; (b) 3 trees; (c) e.g. CO₂ from extracting, refining and transporting the fuel; CO₂ from manufacturing the car
Examiner tip: Use the 2 : 16 (= 1 : 8) mole ratio from the equation, and in (b) round the number of trees up — 2 trees would not absorb all the CO₂.

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