Deforestation is one human activity that contributes to climate change. Explain how large-scale deforestation leads to an increase in atmospheric carbon dioxide concentration and describe two consequences of this increase for the Earth's climate.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Vast areas of tropical forest are cleared every year for agriculture and urban development. Scientists have recorded a steady rise in atmospheric carbon dioxide levels over the last century, which has been linked to both fossil fuel combustion and deforestation.
Model answer (5 marks)
1. Trees absorb CO₂ during photosynthesis, fixing carbon in their biomass.
2. Removing trees reduces this uptake, so more CO₂ remains in the atmosphere.
3. When felled trees are burned or decompose, the stored carbon is released as CO₂.
4. CO₂ is a greenhouse gas that traps infrared radiation, increasing the Earth’s surface temperature.
5. Consequences: (a) global warming and (b) more frequent or severe extreme weather events such as storms, droughts or floods.
2. Removing trees reduces this uptake, so more CO₂ remains in the atmosphere.
3. When felled trees are burned or decompose, the stored carbon is released as CO₂.
4. CO₂ is a greenhouse gas that traps infrared radiation, increasing the Earth’s surface temperature.
5. Consequences: (a) global warming and (b) more frequent or severe extreme weather events such as storms, droughts or floods.
Examiner tips
- Use the exact phrases ‘photosynthesis’, ‘greenhouse gas’, and ‘infrared radiation’. Show the causal chain: removal → less uptake + release → higher CO₂ → warming. Mention two distinct climate effects, not just one.
- common_mistakes
- :
- Confusing CO₂ with other gases or omitting the release from burning/decay. Failing to name a second consequence or giving a non‑climate effect.
Mark scheme (5 marks)
- Trees absorb / fix carbon dioxide during photosynthesis, so removing trees reduces the uptake of carbon dioxide from the atmosphere.
- When felled trees are burned or decay / decompose, the carbon stored in them is released as carbon dioxide.
- Carbon dioxide is a greenhouse gas that absorbs / traps infrared radiation (heat) emitted by the Earth's surface.
- This leads to global warming / an increase in average global temperatures (first climate consequence).
- A second described consequence, e.g. more frequent / severe extreme weather events such as storms or droughts; OR melting of polar ice caps / glaciers causing sea level rise and flooding of low-lying land; OR changes in rainfall patterns causing habitat loss / desertification.
Key terms in this question
deforestation · carbon dioxide
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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