4.9.2.2Human activities that increase greenhouse gases
AQA GCSE Chemistry Foundation (8462), Foundation tier · Chemistry of the atmosphere › Carbon dioxide and methane as greenhouse gases
Practise Human activities that increase greenhouse gases. 8 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Which human activities add carbon dioxide and methane to the atmosphere, and how to judge the evidence that this is warming the Earth. Expect 'give two activities' recall questions, data on carbon dioxide levels, and questions asking you to evaluate evidence in a report and describe uncertainties.
Methane: cattle and other livestock farming; rice paddy fields; waste decaying in landfill
Deforestation: burning releases CO2 AND fewer trees remove CO2 by photosynthesis
Peer review = other experts check the work before it is published
Climate models are simplified because the climate system is very complex
Good evidence: peer reviewed, lots of data, not biased, conclusion supported by the data
Notes
Activities that increase carbon dioxide
Burning fossil fuels (coal, natural gas and fuels made from crude oil) for electricity, heating and transport. Combustion releases the carbon locked up in the fuels as carbon dioxide.
Deforestation: when forests are cut down and burned, carbon dioxide is released, and there are fewer trees left to remove carbon dioxide by photosynthesis.
Activities that increase methane
Farming cattle and other livestock: the animals release methane produced during digestion.
Rice paddy fields: rice grows in flooded fields, and decay in the waterlogged soil releases methane.
Landfill sites: waste decaying in landfill releases methane.
A growing world population needs more food and energy, so these activities are increasing.
The evidence and its uncertainties
diagram
Using peer-reviewed evidence, many scientists think that human activities will make the Earth's average surface temperature rise, and that this will lead to global climate change.
Measured carbon dioxide levels have risen every decade.
Peer review: other experts in the same field check the methods, data and conclusions before the work is published. This helps to catch mistakes and reduce bias.
The climate is a very complex system, so it is difficult to model. Scientists use simplified models, which give a range of predictions.
Uncertainties include incomplete data about past climates, natural changes (e.g. volcanic eruptions and changes in the Sun) and not knowing how much gas people will release in future.
Media reports may simplify, use only part of the evidence, or be biased. Check who produced a report, whether it was peer reviewed and how much data it is based on.
Scientists need to communicate results to a wide range of audiences (the public, politicians, businesses) clearly, so that people can make informed decisions.
How to answer each type of question
Give human activities that increase a greenhouse gas
Example. Give one human activity that increases the amount of carbon dioxide in the atmosphere and one human activity that increases the amount of methane.
For deforestation, add the second effect: fewer trees to photosynthesise.
Example. Explain how deforestation increases the amount of carbon dioxide in the atmosphere.
Show the model answerHide the model answer
Burning the trees releases carbon dioxide (1). There are fewer trees to remove carbon dioxide from the atmosphere by photosynthesis (1).
Don’t lose marks
Writing just 'pollution' or 'cars'. Say 'burning fossil fuels (e.g. petrol in cars)'.
Giving only one effect of deforestation in a 2-mark question. Also say that fewer trees are left to photosynthesise.
Mixing up the gases: livestock, rice paddy fields and landfill release methane; burning fuels and deforestation release carbon dioxide.
Saying scientists have 'proved' what will happen. Say the evidence suggests it, and that predictions are uncertain.
Bringing the ozone layer into a greenhouse gas answer.
More tips
Memory tricks
Carbon dioxide: 'Fuels and Forests'. Methane: 'Cows, Crops (rice) and Rubbish (landfill)'.
Deforestation is a double hit: carbon dioxide released AND less carbon dioxide removed.
Judging a report? Ask 'Who, how much, checked?': who produced it (bias), how much data, was it peer reviewed.
Exam technique
Read which gas the question asks about before listing activities.
In 'evaluate the evidence' questions, comment on sample size, how and where data were collected, peer review and possible bias, then give a conclusion.
When you describe a trend, quote values from the graph or table with units (e.g. ppm).
A correlation is not proof of a cause: say the rise in carbon dioxide matches the rise in fossil fuel use, not that it 'proves' it.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Give two activities that release carbon dioxideBurning fossil fuels and deforestation both increase the carbon dioxide in the atmosphere.
Grade 4
Give two activities that release methaneFarming cattle and other livestock, growing rice in paddy fields, and waste decaying in landfill sites.
Grade 5
Explain how deforestation increases carbon dioxideBurning the trees releases carbon dioxide, and fewer trees are left to remove it by photosynthesis.
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) Give two human activities that increase the amount of carbon dioxide in the atmosphere.[2]
(b) Give two human activities that increase the amount of methane in the atmosphere.[2]
Show the answer and mark scheme
(a)
burning fossil fuels (e.g. in power stations or vehicles)
deforestation / cutting down or burning forests
(b)
animal farming (e.g. cattle)
decomposition of rubbish in landfill sites
Question 2Medium5 marks
A newspaper article included this headline: ‘Coldest winter in our town for 20 years — so global warming is not happening!’
(a) Explain why the conclusion in the headline is not valid.[2]
(b) Explain why it is important that research about climate change is peer reviewed.[2]
(c) Suggest one reason why reports about climate change in the media may be misleading.[1]
Show the answer and mark scheme
(a)
one town / one winter is not representative of the whole Earth
climate change is about long-term trends in average global temperature (weather varies from year to year)
(b)
other (independent) scientists check the methods, data and conclusions
so errors or bias can be found and the findings are more likely to be valid
(c)
they may be based on only part of the evidence / may be simplified / may be biased / may present opinions or speculation as fact