Deforestation is one human activity linked to climate change. Explain how large-scale deforestation contributes to an increase in atmospheric carbon dioxide levels, and describe two possible effects of this increase on the Earth's climate.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Billions of trees are cut down each year worldwide. Forests store vast amounts of carbon in their wood, roots and surrounding soil. When trees are removed, this carbon store is affected in several ways.
Model answer (5 marks)
Deforestation removes trees that normally absorb CO₂ during photosynthesis, so less CO₂ is taken out of the atmosphere.
When trees are cut down they are often burned or left to rot; the carbon stored in their biomass and in the soil is released as CO₂, adding to the atmospheric pool.
CO₂ is a greenhouse gas – it absorbs infrared radiation emitted by the Earth and traps heat, so the extra CO₂ enhances the greenhouse effect.
The enhanced greenhouse effect raises average global temperatures (global warming).
Higher temperatures melt polar ice, raising sea levels and increasing the frequency and intensity of extreme weather events such as heatwaves and storms.
When trees are cut down they are often burned or left to rot; the carbon stored in their biomass and in the soil is released as CO₂, adding to the atmospheric pool.
CO₂ is a greenhouse gas – it absorbs infrared radiation emitted by the Earth and traps heat, so the extra CO₂ enhances the greenhouse effect.
The enhanced greenhouse effect raises average global temperatures (global warming).
Higher temperatures melt polar ice, raising sea levels and increasing the frequency and intensity of extreme weather events such as heatwaves and storms.
Examiner tips
- Use the term ‘photosynthesis’ and ‘greenhouse gas’ explicitly; link burning/decomposition to CO₂ release; mention the greenhouse effect before stating warming; give a specific climate effect (sea‑level rise or extreme weather) with a brief description.
Common mistakes
- Confusing CO₂ with other gases; not linking deforestation to CO₂ release; giving a vague effect such as ‘more rain’ without naming a specific phenomenon; omitting the greenhouse effect step.
Mark scheme (5 marks)
- Trees/plants normally absorb/remove carbon dioxide from the atmosphere through photosynthesis
- When trees are burned or allowed to decompose after felling, the carbon stored in them is released as carbon dioxide
- Carbon dioxide is a greenhouse gas that absorbs/traps infrared radiation (heat) that would otherwise escape into space
- This leads to an enhanced greenhouse effect / global warming — an increase in average global temperatures
- A named, described effect of rising temperatures on climate, e.g. melting of polar ice caps causing sea levels to rise / more frequent or intense extreme weather events / changes in rainfall patterns / disruption to seasons
Key terms in this question
Related
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