4.12.2Theme D — Continuity and change
Impact of Climate Change — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 16 of 18 Unit quiz
Part 1 of 5Physical Changes
Climate change affects the abiotic conditions that organisms depend upon.
Rising temperature
- Average land and sea temperatures increase, and heatwaves become more frequent and more intense.
Melting ice
- Glaciers and polar ice sheets shrink, which removes habitat for ice-dependent species such as polar bears.
Sea level rise
- Water expands as it warms and meltwater flows into the sea, threatening low-lying coasts and island habitats.
Extreme weather
- Changes in rainfall patterns bring more severe droughts, floods and storms in different regions.
| Impact | Ecological consequence |
|---|---|
| Warmer seas | Coral bleaching and loss of reef habitat |
| Ocean acidification | Shell formation harder for molluscs and corals |
| Drought | Reduced plant growth and increased fire risk |
| Altered ranges | Species move toward the poles or higher altitude |
Part 2 of 5Ocean Acidification
1
The oceans absorb part of the extra carbon dioxide from the atmosphere.
2
Dissolved carbon dioxide reacts with water: CO₂ + H₂O ⇌ H₂CO₃.
3
Carbonic acid dissociates, releasing hydrogen ions: H₂CO₃ ⇌ H⁺ + HCO₃⁻, so the pH of seawater falls.
4
Hydrogen ions react with carbonate ions, reducing the carbonate available for organisms to build shells and skeletons of calcium carbonate.
Part 3 of 5Ecological Responses
Ecological Responses
Range shifts
- Species move to cooler areas, and those that cannot move or adapt face local extinction.
Food webs
- Different species respond at different rates, which can break links between predators and prey.
Pests and disease
- Warmer climates allow disease vectors and pest insects to spread into new regions.
Biodiversity
- Habitat loss and rapid change increase extinction rates, especially in specialised species.
Part 4 of 5Worked Example
Question
- Ocean pH falls from 8.2 to 8.1.
- Since pH = −log₁₀[H⁺], calculate by what factor [H⁺] has increased.
- A fall of 0.1 pH units means [H⁺] is multiplied by 100.1.
- 100.1 = 1.259, an increase of about 26%.
Answer [H⁺] increases by a factor of about 1.26 (26%).
Part 5 of 5Exam Checklist & Tips
4.12.2 – Key Points for the Exam
- Ocean acidification Decrease in the pH of seawater due to absorption of carbon dioxide.
- Coral bleaching Loss of symbiotic algae from corals under heat stress.
- Range shift Change in the geographical area occupied by a species.
- Sea level rise Increase in ocean volume from thermal expansion and meltwater.
- Habitat loss Reduction of the area where a species can live.
Common Mistakes
- Saying that melting sea ice raises sea level;
- floating ice already displaces its own weight, but land ice raises it.
- Writing that ocean acidification makes the sea acidic with pH below 7; it remains slightly alkaline.
- Forgetting thermal expansion as a cause of sea level rise.
- Stating that all species will benefit from warmer weather.
Last updated:
\n