Physical impacts
Big idea: Climate change is causing widespread physical changes: rising temperatures, melting ice, rising seas, and more extreme weather events.
Temperature and precipitation
- Rising global temperatures: ~1.1°C above pre-industrial average; Arctic warming 2–3x faster
- Changed precipitation patterns: Some regions getting wetter, others drier; more intense rainfall
- More extreme weather: Stronger hurricanes, more frequent heatwaves, prolonged droughts
- Shifting seasons: Earlier springs, longer summers, shorter winters in many regions
Ice and sea level
- Melting glaciers: Mountain glaciers retreating worldwide; affects water supply
- Arctic sea ice decline: Summer extent decreasing ~13% per decade
- Ice sheet loss: Greenland and Antarctic ice sheets losing mass
- Sea level rise: ~3.7 mm/year; caused by thermal expansion AND ice melt
- Permafrost thaw: Releases stored methane — a positive feedback
Sea level rises from two causes: thermal expansion (water expands as it warms) AND melting land ice. Melting sea ice does NOT raise sea level (already floating).
Exam tip: Be precise about which ice matters for sea level. Land ice raises sea level when it melts; sea ice does not.
Ecosystem impacts
Big idea: Ecosystems are being disrupted by climate change through habitat loss, species range shifts, phenological changes, and ocean acidification.
Terrestrial ecosystems
- Range shifts: Species moving poleward or to higher altitudes to track suitable temperatures
- Phenological changes: Earlier flowering, earlier migration, mismatched timing between species
- Habitat loss: Polar bears losing sea ice; alpine species running out of mountain
- Increased fire risk: Drier conditions, longer fire seasons
- Pest and disease spread: Warmer temperatures allow pests to expand range
Marine ecosystems
- Ocean acidification: CO₂ dissolves in seawater, forming carbonic acid; pH has dropped ~0.1
- Coral bleaching: Warm water causes corals to expel symbiotic algae; mass bleaching events
- Changing fish distributions: Species moving to cooler waters
- Disrupted food webs: Changes in plankton timing affect entire food chains
Ocean acidification is sometimes called the other CO₂ problem. It threatens shell-forming organisms because acid dissolves calcium carbonate.
Exam tip: Questions often ask for cause → effect chains. E.g., Rising temperature → coral bleaching → loss of reef habitat → decline in fish populations.
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IB-style question — climate impacts on a coral reef [3]
A tropical reef system is under stress as ocean temperatures rise. Explain how climate change could damage this natural ecosystem. [3]
How to answer it, step by step
- Warmer water harms the coral
• Heat stress makes coral expel its algae — coral bleaching
• Bleached coral loses its food source and can die - One change spreads through the system
• Lost coral removes habitat for reef fish and other species
• Biodiversity falls and the food web is disrupted
Final answer
Build a chain (warmer water → bleaching → habitat loss) — a list of separate harms with no links scores fewer marks.
IB-style question — species shifting range [2]
A study finds a mountain butterfly is now found 300 m higher up the slope than it was 40 years ago. Suggest two reasons why warming has caused this shift. [2]
How to answer it, step by step
- Link the move to temperature
• Lower slopes have become too warm for the butterfly
• It moves uphill to stay in its preferred cooler temperature range - Think about its food/habitat too
• Its food plants may also be shifting upslope as the climate warms
• Cooler higher ground now matches the conditions it needs
Final answer
Each reason must connect the shift to warming — 'it likes the mountain' with no temperature link gets nothing.
Practice questions: Impacts on natural systems (10)
Use cause-effect chains. For sea level: mention thermal expansion and melting land ice. For oceans: separate warming from acidification.
Questions
- 1) A low-lying island notices more coastal flooding during high tides. State two processes linked to climate change that can cause sea level rise. (2)
- 2) A mountain region depends on glacier meltwater for summer river flow. Explain why water availability may first increase and then decrease over time as glaciers retreat. (3)
- 3) A coral reef experiences unusually warm sea temperatures for several weeks. Explain how this can lead to coral bleaching and one consequence for reef biodiversity. (4)
- 4) A shellfish farmer reports thinner shells in oysters over several years. Suggest how increased atmospheric CO2 can cause this change in seawater chemistry. (3)
- 5) A species of butterfly is now found higher up a mountain than 30 years ago. Suggest why species ranges shift uphill or poleward as climate warms. (2)
- 6) A forest has longer and drier summers. Explain how this can increase wildfire risk and give one ecological impact of more frequent fires. (3)
- 7) A lake shows more frequent algal blooms during hotter summers. Suggest one reason warming can increase bloom risk and one possible effect on dissolved oxygen. (3)
- 8) Permafrost in a northern region begins to thaw. Explain how this can create a positive feedback to climate change. (3)
- 9) Arctic sea ice extent is reduced at the end of summer. Suggest one physical effect on regional temperature and one effect on an organism that uses sea ice as habitat. (3)
- 10) A student says: ‘Melting sea ice will greatly raise global sea levels.’ State whether this is correct and justify your answer. (2)
Quick answer check
- 1) Thermal expansion of seawater; melting of land ice (glaciers/ice sheets).
- 2) Early: increased melt adds more runoff; later: glacier volume shrinks so less meltwater remains in dry season.
- 3) Heat stress → corals expel symbiotic algae → loss of colour/energy; consequence: habitat loss reduces fish/invertebrate diversity (any clear biodiversity impact).
- 4) CO2 dissolves → carbonic acid forms → pH decreases; fewer carbonate ions available → harder to form calcium carbonate shells.
- 5) Moving to cooler conditions as temperatures rise; climate envelope shifts to higher altitude/latitude.
- 6) Drier fuels + heat increase ignition/spread; impacts: mortality, habitat change, soil erosion, altered succession (any one).
- 7) Warmer water can increase algal growth/metabolism; blooms increase respiration/decomposition → oxygen depletion (can lead to hypoxia).
- 8) Thaw releases CH4/CO2 from decomposing organic matter → more greenhouse gases → more warming → more thaw.
- 9) Lower albedo means more heat absorbed → regional warming; organism impact: reduced hunting/breeding platform, habitat loss (any relevant ice-dependent species).
- 10) Not correct; melting sea ice already floats so it does not significantly raise sea level, but melting land ice does.