AQA GCSE Combined Science (8464), Higher tier · Chemistry › Chemistry of the atmosphere › Carbon dioxide and methane as greenhouse gases
Practise The carbon footprint and its reduction. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
What a carbon footprint is, how it can be reduced by cutting emissions of carbon dioxide and methane, and why these actions may be limited. Expect a definition, 'describe actions' and 'give reasons why actions may be limited' questions, and data questions that compare emissions.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Give one way to reduce carbon dioxide emissionsFor example, generate electricity from renewable resources instead of burning fossil fuels.
4
Define carbon footprintThe total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
5
Describe actions to reduce emissionsAlternative energy, energy conservation, carbon capture and storage, carbon taxes and licences, carbon off-setting and carbon neutrality.
6
Give reasons why actions may be limitedScientific disagreement, lack of public information and education, lifestyle changes, economic considerations and incomplete international cooperation.
6
Describe actions to reduce methane emissionsFor example, collect methane from landfill to use as a fuel, send less waste to landfill, and reduce livestock numbers.
7
Calculate and compare emissions from dataUse given data, e.g. grams of carbon dioxide per km × distance, and convert units correctly.
8
Evaluate ways to reduce a carbon footprintWeigh how much each action saves, its cost and its limitations to reach a justified judgement.
Notes
What a carbon footprint is
The carbon footprint is the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.
Full life cycle means every stage: getting the raw materials, manufacturing, transport, use and disposal.
A carbon footprint can be reduced by reducing emissions of carbon dioxide and methane.
Actions to reduce emissions
Alternative energy supplies: more use of renewable resources (such as wind, solar and hydroelectric power) and nuclear power instead of fossil fuels.
Energy conservation: using less energy, e.g. insulating buildings, using efficient appliances, and using public transport.
Carbon capture and storage: carbon dioxide from power stations or factories is captured and stored deep underground, e.g. in old oil and gas fields, instead of being released.
Carbon taxes and licences: making companies pay for the greenhouse gases they release, or allowing them to release only a limited amount, encourages them to emit less.
Carbon off-setting: balancing emissions by paying for actions that remove carbon dioxide, such as planting trees, which absorb carbon dioxide by photosynthesis.
Carbon neutrality: activities with zero net release of carbon dioxide, because any carbon dioxide released is balanced by the same amount removed or offset.
Reducing methane: collect methane from landfill sites and burn it as a fuel, send less waste to landfill, and farm fewer livestock (e.g. by people eating less meat).
Why actions may be limited
Scientific disagreement over the causes and consequences of global climate change.
Lack of public information and education, so people don't know what to do or why.
People may not want to make lifestyle changes, e.g. flying less or changing their diet.
Economic considerations: many actions are expensive, and some countries depend on fossil fuels for jobs, income and development.
Incomplete international cooperation: not every country agrees to cut emissions, and one country acting alone has a limited effect.
Cheatsheet
Carbon footprint = total CO2 and other greenhouse gases emitted over the full life cycle of a product, service or event
Full life cycle: raw materials → manufacture → transport → use → disposal
Reduce a footprint by cutting emissions of carbon dioxide and methane
Actions: alternative energy, energy conservation, carbon capture and storage, carbon taxes and licences, carbon off-setting (e.g. tree planting), carbon neutrality
Carbon neutral = zero net release of carbon dioxide
Limits: scientific disagreement, lack of public information and education, lifestyle changes, economic considerations, incomplete international cooperation
1 kg = 1000 g and 1 tonne = 1000 kg
How to answer each type of question
Define carbon footprint
2 marks4
Say it is the TOTAL amount of carbon dioxide and other greenhouse gases.
Say it is over the FULL LIFE CYCLE of a product, service or event.
Example. What is meant by the carbon footprint of a product?
Show the model answer
The total amount of carbon dioxide and other greenhouse gases emitted (1) over the full life cycle of the product (1).
Describe actions to reduce emissions
2 to 3 marks5
Give different actions, not the same idea twice.
For each one, say how it reduces emissions (e.g. 'so less fossil fuel is burned').
Example. A school wants to reduce the carbon footprint of its buildings. Describe three actions it could take.
Show the model answer
Any three from: fit solar panels, or buy electricity from renewable sources, so less fossil fuel is burned (1) insulate the buildings or use energy-efficient lighting, to conserve energy (1) plant trees to offset some of its carbon dioxide emissions (1) send less waste to landfill, e.g. by recycling or composting, to reduce methane emissions (1)
Give reasons why actions may be limited
2 marks6
Give barriers, not more actions.
Choose from: cost (economic considerations), lack of international cooperation, lifestyle changes, lack of public information and education, scientific disagreement.
Example. Many countries have agreed to reduce their greenhouse gas emissions, but global emissions are still high. Give two reasons why.
Show the model answer
Any two from: not all countries cooperate or agree to cut emissions (1) reducing emissions is expensive / some countries depend on fossil fuels for their economy (1) people are unwilling to change their lifestyles (1) there is a lack of public information and education (1) there is scientific disagreement about the causes and effects of climate change (1)
Calculate and compare emissions
2 to 4 marks7
Write down the rate and the amount, e.g. g per km and km.
Multiply, then convert units as the question asks (÷ 1000 for g to kg).
For a 'net saving', subtract any extra emissions from the amount saved.
Example. A family car emits 150 g of carbon dioxide per km. The family drives 12 000 km per year. (a) Calculate the mass of carbon dioxide the car emits per year, in kg. (b) By taking the bus for some journeys, the family would drive 2500 km less per year. Their share of the bus's emissions for these journeys is 50 kg of carbon dioxide per year. Calculate the net saving of carbon dioxide per year, in kg.
Show the model answer
(a) 150 × 12 000 = 1 800 000 g (1); ÷ 1000 = 1800 kg (1) (b) Saving from the car = 150 × 2500 = 375 000 g = 375 kg (1); net saving = 375 − 50 = 325 kg (1)
Evaluate a way of reducing a carbon footprint
3 to 6 marks8
Say how the action reduces greenhouse gases.
Give its limitations, e.g. time, cost, whether it really reduces emissions.
Use any data given, and finish with a justified judgement.
Example. An airline offers passengers the chance to pay for trees to be planted to offset the carbon dioxide released by their flight. Evaluate this as a way of reducing the effect of the flight on the atmosphere.
Show the model answer
Any three from: trees absorb carbon dioxide by photosynthesis, so they can balance the carbon dioxide from the flight (1) but the trees take many years to grow and absorb that much carbon dioxide, whereas the flight releases it straight away (1) the trees must not be cut down or burned later, or the carbon dioxide is released again (1) offsetting does not reduce the flight's own emissions; flying less would (1)
Shortcuts and memory tricks
Carbon footprint = 'cradle to grave': count every stage, from raw materials to disposal.
Six actions: 'All Countries Could Try Offsetting Now': Alternative energy, Conservation, Capture and storage, Taxes and licences, Off-setting, Neutrality.
Five limits: 'Some People Like Eating Ice cream': Scientific disagreement, Public information lacking, Lifestyle changes, Economic considerations, International cooperation incomplete.
Unit check: g → kg ÷ 1000, kg → tonnes ÷ 1000.
Where marks are lost
Defining carbon footprint as 'the carbon dioxide from burning fuel'. It includes other greenhouse gases and the whole life cycle.
Writing 'be more eco-friendly' or 'recycle' without saying how it reduces emissions.
Thinking that planting trees cancels emissions straight away. Trees take years to absorb the carbon dioxide.
Saying carbon neutral means 'releases no carbon dioxide'. It means zero NET release.
Giving more actions when the question asks why actions may be limited.
Exam technique
A definition of carbon footprint needs three ideas: total, carbon dioxide and other greenhouse gases, full life cycle.
'Give reasons why actions may be limited' wants barriers such as cost, cooperation, lifestyle, information and disagreement.
In 'evaluate' questions, use data from the question, compare the options and finish with a justified judgement.
Show each step of a calculation with its unit.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) What is meant by the carbon footprint of a product?[1]
(b) Give two ways of reducing emissions of carbon dioxide.[2]
(c) Which action would reduce emissions of methane? Tick (✓) one box.[1]
Building more landfill sites
Driving electric cars
Eating less meat from cattle
Using more fertiliser
Show the answer and mark scheme
(a)
the total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of the product
(b)
use alternative energy sources (e.g. wind, solar, nuclear)
energy conservation (e.g. insulating homes)
carbon capture and storage
carbon taxes / licences
carbon off-setting (e.g. planting trees)
(c)Answer: Eating less meat from cattle
Question 2Medium6 marks
A government plans to reduce its country's carbon footprint by building wind farms and introducing a carbon tax.
(a) Explain how a carbon tax could reduce emissions of carbon dioxide.[2]
(b) Explain how building wind farms could reduce the country's carbon footprint.[1]
(c) Give three reasons why actions to reduce a country's carbon footprint may be limited.[3]
Show the answer and mark scheme
(a)
companies / people pay tax for the carbon dioxide they emit (or for fossil fuels they use)
so they are encouraged to use less fossil fuel / switch to low-carbon energy sources
(b)
electricity is generated without burning fossil fuels, so less carbon dioxide is emitted
(c)
scientific disagreement over the causes and consequences of global climate change
lack of public information and education
people are unwilling to change their lifestyles
economic considerations / cost (e.g. of new technology, effects on jobs)
incomplete international cooperation (other countries may not reduce their emissions)
Question 3Hard6 marks
A gas-fired power station emits 2.0 million tonnes of carbon dioxide each year. The company plans to capture 90% of the carbon dioxide and store it underground (carbon capture and storage). The company will off-set the remaining emissions by planting a forest. Each hectare of the forest will absorb 10 tonnes of carbon dioxide each year.
(a) Calculate the mass of carbon dioxide that will still be emitted each year after carbon capture and storage.[1]
(b) Calculate the area of forest needed to off-set these remaining emissions.[1]
(c) The company claims that the power station will be 'carbon neutral'. Evaluate this claim.[4]
Show the answer and mark scheme
(a)Answer: 200 000 tonnes
200 000 (tonnes) / 0.2 million (tonnes)
(b)Answer: 20 000 hectares
20 000 (hectares)
(c)
carbon neutral means no net release of carbon dioxide / emissions are balanced by removal
the plan could balance the emissions from the power station itself
young trees absorb less carbon dioxide, so it will be many years before the forest absorbs 10 tonnes per hectare
the forest could be cut down or burn, releasing the carbon dioxide again
carbon capture uses energy, so more gas must be burned
stored carbon dioxide might leak / extracting and transporting the gas also releases greenhouse gases (e.g. methane leaks)