Deforestation is carried out on a large scale in many parts of the world. Explain how deforestation contributes to an increase in the concentration of carbon dioxide in the atmosphere.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Millions of hectares of forest are cut down each year. Trees are often burned after felling, or left to decay. This has significant consequences for the carbon cycle and global climate.
Model answer (5 marks)
1. Trees absorb CO₂ during photosynthesis, storing carbon in their biomass.
2. When forests are cut, the number of trees that can take up CO₂ falls, reducing the natural sink.
3. Burning the felled timber immediately releases the stored carbon back into the atmosphere as CO₂.
4. If the wood is left to decay, microbial decomposition also emits CO₂ (and CH₄).
5. Consequently, the net atmospheric CO₂ concentration rises, enhancing the greenhouse effect and global warming.
2. When forests are cut, the number of trees that can take up CO₂ falls, reducing the natural sink.
3. Burning the felled timber immediately releases the stored carbon back into the atmosphere as CO₂.
4. If the wood is left to decay, microbial decomposition also emits CO₂ (and CH₄).
5. Consequently, the net atmospheric CO₂ concentration rises, enhancing the greenhouse effect and global warming.
Examiner tips
- Use the exact terms – photosynthesis, carbon sink, decomposition; link each point to CO₂ release.
- Show the causal chain: removal of trees → less uptake, plus combustion/decomposition → added CO₂.
- Keep each point brief but complete; 5 points total.
Mark scheme (5 marks)
- Trees/plants absorb carbon dioxide during photosynthesis
- Fewer trees means less carbon dioxide is removed from the atmosphere
- Burning trees/wood releases carbon dioxide
- Decay/decomposition of dead trees/plant material releases carbon dioxide
- The overall effect is that carbon dioxide levels in the atmosphere increase, contributing to the enhanced greenhouse effect/global warming
Key terms in this question
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