Explain how changes in the distribution of biomes due to climate change could reduce the ability of terrestrial ecosystems to act as carbon sinks.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Rising temperatures and altered precipitation patterns cause a poleward or upward shift in biome boundaries. Forests and other high‑biomass biomes at the trailing edge are replaced by lower‑biomass biomes such as shrubland, grassland or desert, which store less carbon in vegetation. Higher temperatures also increase rates of decomposition and soil respiration, releasing stored organic carbon as CO₂. Consequently, terrestrial ecosystems release more CO₂ than they absorb, turning from net carbon sinks into net carbon sources and amplifying the greenhouse effect.
Examiner tips
- Use the exact terms ‘biome boundaries’, ‘high‑biomass biomes’, ‘decomposition’, ‘soil respiration’, ‘net carbon sink/source’, and ‘positive feedback’.
- Show the causal chain: temperature/precipitation → biome shift → lower biomass → less carbon stored → increased decomposition → more CO₂ released → loss of sink capacity.
- Keep the answer concise – 4 marks allow a short paragraph, not an essay.
Mark scheme (4 marks)
- Rising temperatures and altered precipitation patterns cause a poleward or upward (altitudinal) shift in biome boundaries.
- Forest / high-biomass biomes at the trailing edge are replaced by lower-biomass biomes such as shrubland, grassland or desert, reducing overall carbon stored in vegetation.
- Higher temperatures increase rates of decomposition / soil respiration, releasing stored organic carbon as CO₂.
- As terrestrial ecosystems release more CO₂ than they absorb, they shift from net carbon sinks to net carbon sources, amplifying the greenhouse effect / creating a positive feedback.
Key terms in this question
Related
- All IB DP Biology Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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