5.9.2.2Human activities which contribute to an increase in greenhouse gases in the atmosphere
AQA GCSE Combined Science (8464), Higher tier · Chemistry › Chemistry of the atmosphere › Carbon dioxide and methane as greenhouse gases
Practise Human activities which contribute to an increase in greenhouse gases in the atmosphere. 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.
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.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
Give two activities that release carbon dioxideBurning fossil fuels and deforestation both increase the carbon dioxide in the atmosphere.
4
Give two activities that release methaneFarming cattle and other livestock, growing rice in paddy fields, and waste decaying in landfill sites.
5
Explain how deforestation increases carbon dioxideBurning the trees releases carbon dioxide, and fewer trees are left to remove it by photosynthesis.
6
Explain why peer review mattersOther experts check the methods, data and conclusions before publication, which reduces errors and bias.
6
Describe trends in carbon dioxide dataQuote values from a graph or table and calculate changes, e.g. the increase or percentage increase over a period.
7
Describe uncertainties in climate evidenceThe climate is complex, so models are simplified, data about the past are incomplete and future emissions are unknown.
8
Evaluate the quality of a climate reportJudge the amount of data, how it was collected, peer review, possible bias and whether the conclusion fits the evidence.
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
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.
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.
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 answer
Burning the trees releases carbon dioxide (1). There are fewer trees to remove carbon dioxide from the atmosphere by photosynthesis (1).
Use data on carbon dioxide levels
2 to 4 marks6
Read the values carefully from the table or graph, with units.
Increase = later value − earlier value.
Percentage increase = increase ÷ earlier value × 100, rounded as asked.
Link the trend to a cause, such as more burning of fossil fuels.
Example. The table shows the mean concentration of carbon dioxide in the atmosphere, in parts per million (ppm), measured at one station. 1960: 317 ppm 1980: 339 ppm 2000: 370 ppm 2020: 414 ppm (a) Calculate the percentage increase in carbon dioxide concentration from 1960 to 2020. Give your answer to 2 significant figures. (b) Suggest one reason for the increase.
Show the model answer
(a) Increase = 414 − 317 = 97 ppm (1); 97 ÷ 317 × 100 = 30.6 (1); = 31% (to 2 significant figures) (1) (b) More fossil fuels were burned (e.g. for electricity and transport) / more deforestation (1)
Evaluate the evidence in a report
3 to 4 marks8
Comment on the amount of data and where and how it was collected.
Ask whether it is measured data or opinion, and whether it was peer reviewed.
Check whether the conclusion goes further than the data (e.g. 'proves' a cause).
Finish with a judgement about the quality of the evidence.
Example. A newspaper article says: 'We asked 20 people in one town, and most said summers feel hotter than they did 30 years ago. This proves that burning fossil fuels is causing climate change.' Evaluate the quality of the evidence in this article.
Show the model answer
Any four from: the sample is small (only 20 people) (1) it is from only one town, so it does not represent the whole Earth (1) it is based on opinions of how summers feel, not measured temperatures (1) it has not been peer reviewed (1) it gives no evidence linking the change to burning fossil fuels, so it cannot prove the cause (1) so the evidence is poor quality and does not support the claim (1)
Shortcuts and 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.
Where marks are lost
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.
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.
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
Question 3Hard6 marks
{table} shows the mean carbon dioxide concentration and the mean global temperature anomaly for four decades. The temperature anomaly is the difference from the mean temperature for 1951–1980.
[object Object]
(a) Describe the relationship between carbon dioxide concentration and temperature anomaly shown in {table}.[1]
(b) A student said: 'These data prove that carbon dioxide from human activities causes global warming.' Evaluate the student's statement.[3]
(c) Scientists use computer models to predict future climate. Suggest two reasons why the predictions are uncertain.[2]
Show the answer and mark scheme
(a)
as the carbon dioxide concentration increases the temperature anomaly / mean global temperature increases
(b)
the data show a correlation between carbon dioxide concentration and temperature
a correlation does not prove that one causes the other / other factors could affect temperature (e.g. changes in the Sun's output, volcanic eruptions)
the data do not show where the carbon dioxide came from (human or natural sources)
there is a known mechanism (greenhouse gases absorb long wavelength radiation) and peer-reviewed evidence that supports a causal link
(c)
the climate is a complex system with many interacting factors
models are simplified
future emissions depend on human activity, which cannot be predicted exactly
some data are limited / measurements have uncertainties