Effects of climate change: ecosystems, food security, sea level

OCR J383 Paper 2 tests climate change effects with detailed case-study questions. You need to know specific places, statistics and the difference between physical effects (on ecosystems) and human effects (on food security, displacement). The 8-mark question often asks you to evaluate the seriousness of different effects.

Physical effects

1. Rising sea levels

Causes of sea-level rise:

• Thermal expansion: as oceans warm, water expands (responsible for ~50% of observed rise).
• Melting ice: glaciers and ice sheets (Greenland, Antarctica) add water to oceans.

Current rate: global mean sea level has risen ~20 cm since 1900; rising at ~3.6 mm/year (accelerating).

Consequences:

• Coastal flooding and erosion: low-lying coasts and deltas (Bangladesh, Maldives, Thames Estuary) increasingly at risk.
• Saltwater intrusion: freshwater aquifers contaminated by seawater; farm land rendered unproductive.
• Maldives threat: average height 1.5 m above sea level; president held an underwater cabinet meeting in 2009 to highlight the risk. Estimated to be uninhabitable by 2100 under high-emissions scenarios.
• Bangladesh: 17% of the country could be submerged with 1 m of sea-level rise; 20 million climate refugees projected.

2. Coral reef bleaching

• Ocean warming causes coral bleaching: corals expel the algae (zooxanthellae) that give them colour and nutrients.
• If temperatures exceed 1 degree C above average for 8+ weeks, bleaching occurs; sustained heat leads to coral death.
• Great Barrier Reef (Australia): 50% of corals bleached in 2016 and 2017 consecutive years — 30% died; 2022 saw a 6th mass bleaching event.
• Coral reefs support ~25% of all marine species — loss = catastrophic biodiversity impact.
• Ocean acidification (CO2 dissolving in seawater forms carbonic acid) weakens coral skeletons → reduced reef building.

3. Arctic and tundra changes

• Arctic sea ice extent has shrunk by ~30% since 1979; summer ice projected to disappear by 2050.
• Permafrost thaw: releases methane (CH4) — a powerful greenhouse gas — creating a positive feedback loop.
• Arctic amplification: Arctic warms 2–4x faster than global average.
• Polar bear habitat destroyed; indigenous communities (Inuit) losing traditional livelihoods (hunting, ice travel).
• Thawing permafrost destabilises buildings, roads and pipelines in northern Canada and Siberia.

Human effects

4. Food security

Climate change affects food production through:

• Shifting growing seasons: some high-latitude regions (Canada, Russia) gain arable land; tropical/subtropical regions lose it.
• Increased drought frequency: crop failures in sub-Saharan Africa (maize yields projected to fall 20–65% under 4 degrees C warming).
• Flooding: Bangladesh — growing season disrupted by riverine and coastal flooding.
• Pollinators: warming disrupts bee populations → reduced crop pollination.
• IPCC projection: by 2050, up to 600 million more people could be at risk of hunger if emissions remain high.

5. Human displacement (climate refugees)

• Low-lying island nations: Pacific nations (Tuvalu, Kiribati) already relocating populations.
• Bangladesh: 50–70 million people could be displaced from coastal and riverine areas.
• Sub-Saharan Africa: drought-driven crop failure forces migration to cities → megacity growth; conflict over water.
• No international legal status: "climate refugee" is not currently recognised under the 1951 Refugee Convention.

6. Extreme weather

• More intense tropical storms (higher intensity, as oceans warm).
• Heatwaves: European heatwave (2003) killed 35,000 people; UK 2022 reached 40.3 degrees C for first time on record.
• Flooding: more intense precipitation events as warmer air holds more moisture (7% more water vapour per 1 degree C of warming).

Evaluating effects

For 8-mark evaluate questions, consider:

• Immediacy: some effects are already happening (coral bleaching, sea-level rise); others are projected future risks.
• Distribution: effects are unequal — LICs/small island states disproportionately affected despite contributing least to emissions.
• Reversibility: coral reef death and permafrost methane release may be irreversible tipping points.

Common OCR exam mistakes

1. Forgetting to distinguish between thermal expansion and melting ice as the two causes of sea-level rise.
2. Describing bleaching without explaining the mechanism — zooxanthellae expulsion = loss of food source and colour.
3. Not including specific case-study places — "some islands" scores less than "the Maldives" or "Tuvalu."
4. Failing to evaluate which effect is most serious — always reach a justified conclusion for the 8-mark question.