Human activities which contribute to an increase in greenhouse gases in the atmosphere: Students should be able to recall two human activities that increase the amounts of each of the greenhouse gases carbon dioxide and methane.

The idea

Greenhouse gases trap infrared radiation, and human activity raises their atmospheric amounts. For carbon dioxide, burning fossil fuels such as coal, oil and natural gas in power stations, factories and vehicles releases CO₂, while deforestation removes trees that absorb CO₂ and burning cleared vegetation adds more. For methane, rearing livestock such as cattle and sheep produces methane from digestion, and landfill sites release methane as waste decomposes anaerobically; rice paddy fields and extracting fossil fuels also add methane. A strong answer names two distinct activities per gas and links each to the gas released, for example coal-fired electricity generation for CO₂ and cattle farming for CH₄.

What earns the marks

• Names a valid carbon dioxide activity such as burning fossil fuels in power stations, transport or industry, and links it to CO₂ release.
• Names a second distinct carbon dioxide activity such as deforestation or burning cleared forest, explaining reduced CO₂ absorption or extra CO₂ release.
• Names a valid methane activity such as livestock farming, landfill waste decomposition or rice paddy fields, and links it to CH₄ release.
• Names a second distinct methane activity such as anaerobic decomposition in landfill or fossil fuel extraction, and links it to CH₄ release.
• Uses correct gas names or formulae CO₂ and CH₄ rather than vague phrases such as 'pollution' or 'bad gases'.
• Keeps the two gases separate, so each activity is clearly assigned to the gas it increases.

Common mistakes and how to put them right

• Confusing the gases by assigning livestock farming to carbon dioxide.

  Put it right: Ruminant digestion and manure release methane, CH₄, while fossil fuel combustion releases carbon dioxide, CO₂.

• Giving only one activity per gas when two are required.

  Put it right: Prepare two named activities for each gas, such as coal combustion and deforestation for CO₂, and cattle farming and landfill for CH₄.

• Treating deforestation as only a loss of trees.

  Put it right: Also state that burning cleared vegetation releases CO₂, so deforestation both reduces absorption and adds CO₂.

• Writing 'cars' without saying what is burned.

  Put it right: Specify burning petrol or diesel, which are fossil fuels, releasing CO₂.

Exam tips

• Read the command word 'recall' and give named activities, not definitions of the greenhouse effect.
• Separate your answer into a CO₂ part and a CH₄ part so the examiner can see two activities for each gas.
• Use chemical formulae CO₂ and CH₄ accurately, including subscript numbers, to show precise scientific language.
• If a question gives a table, place each activity in the correct gas column rather than listing all activities together.