4.11.2Theme D — Continuity and change
Impact of Climate Change — IB Biology SL Revision Notes & Topical Questions
5 min read 4 parts Lesson 14 of 14 Unit quiz
Part 1 of 4Forests, Poles and Currents
Climate change affects ecosystems on land, at the poles and in the oceans, often through changes to temperature and water availability.
Boreal forests
- Drought, browning and fire may turn these large carbon sinks into sources, a tipping point that adds to warming.
Polar habitats
- Sea ice forms later and melts earlier, shortening breeding time for emperor penguins and reducing resting platforms for walruses.
Ocean currents
- Currents move heat and nutrients, and changes in them alter regional climate and the upwelling that supports fisheries.
El Niño
- Warm surface water stops nutrient upwelling off South America, reducing primary production and altering weather worldwide.
Part 2 of 4Range Shifts
Rising temperatures push species beyond their tolerance limits, so they must move, adapt or die out.
1
Each species can only survive where conditions lie within its tolerance limits.
2
As temperatures rise, suitable habitat moves towards the poles or up mountain slopes.
3
In Papua New Guinea, many montane birds on Mt Karimui shifted their upper limits upslope by more than 100 m over 50 years.
4
North American tree species show northward spread at their northern limits and contraction of some ranges.
5
Species that cannot move or adapt fast enough face local or global extinction.
| Shift | Direction | Example |
|---|---|---|
| Poleward | Towards higher latitude | North American trees |
| Upslope | Towards higher altitude | Montane birds in Papua New Guinea |
Part 3 of 4Coral Reefs
CO₂(aq) + H₂O(l) ⇌ H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃⁻(aq), and extra H⁺ combines with carbonate: H⁺(aq) + CO₃²⁻(aq) → HCO₃⁻(aq).
Coral Reefs
Reef structure
- Reef-building coral polyps secrete calcium carbonate and live with algae that supply them with carbon compounds.
Bleaching
- High water temperature makes polyps expel their algae, so the coral loses colour and may starve and die.
Acidification
- Carbon dioxide dissolving in seawater forms carbonic acid, raising hydrogen ion concentration and lowering carbonate availability.
Ecosystem loss
- About a quarter of marine fish species depend on reefs, so reef decline reduces biodiversity and food chains.
Part 4 of 4Exam Checklist & Tips
4.11.2 – Key Points for the Exam
- Tipping point A threshold beyond which a system changes rapidly to a new state.
- Range shift A change in the geographic area in which a species lives.
- Coral bleaching Loss of colour when coral expels its symbiotic algae.
- Ocean acidification A fall in ocean pH caused by absorption of atmospheric carbon dioxide.
- Upwelling The rising of cold, nutrient-rich deep water to the surface.
Common Mistakes
- Saying the oceans have become acidic; they remain slightly alkaline but their pH is falling.
- Treating ocean acidification as a direct result of warming rather than of dissolved carbon dioxide.
- Forgetting that bleaching is caused by loss of algae, not by coral dying instantly.
- Stating that every species moves; some stay or move downslope.
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