2.6 Climate change: Describe the causes and effects of global climate change.

2.6 Climate Change – Causes, Evidence, Impacts and Responses

1. What is Climate Change?

Climate change is a long‑term (decades to centuries) alteration in the average state of the atmosphere, oceans and land surface. It is expressed through changes in temperature, precipitation, wind patterns, sea‑level and the frequency/intensity of extreme weather.

2. Evidence that the Climate is Changing

• Instrumental records – Global mean surface temperature has risen by about 1.1 °C since the late 19th century (NASA GISS, 2023).
• Ice‑core data – Air bubbles from Antarctic and Greenland ice show CO₂ increasing from ~280 ppm pre‑industrial to > 420 ppm today, closely tracking temperature rise.
• Tree‑ring & sediment records – Provide a natural baseline for temperature and precipitation over the past 10 000 years.
• Sea‑level measurements – Tide‑gauge and satellite data indicate a global rise of about 3.3 mm yr⁻¹ since 1993.
• Glacier monitoring – > 90 % of the world’s glaciers have retreated since the 1960s.

3. 5.1 Causes of Global Climate Change

3.1 Natural (Geophysical) Causes

3.2 Human (Anthropogenic) Causes

*Values are global annual averages (UNFCCC, 2023). Rounded for IGCSE use.

3.3 International Policy Framework (Context)

• UNFCCC (1992) – Sets the global arena for climate negotiations.
• Kyoto Protocol (1997) – First legally binding emission‑reduction targets for developed nations.
• Paris Agreement (2015) – Goal to limit warming to “well below 2 °C” and pursue 1.5 °C; each country submits nationally determined contributions (NDCs).
• IPCC Assessment Reports – Provide the scientific basis for policy; the 2021‑2022 Sixth Assessment Report underpins the latest targets.

4. 5.2 Impacts of Climate Change

4.1 Physical Impacts (Observed)

4.2 Environmental Impacts

• Biodiversity loss – Species unable to shift ranges fast enough (e.g., alpine plants confined to mountaintops → “mountain‑top extinction”).
• Coral bleaching – 2020 global event affected ~ 75 % of surveyed reefs; driven by sea‑surface temperature rise and ocean acidification (pH ↓ 0.1 since pre‑industrial).
• Biome shifts – Desert expansion in the Sahel; boreal forest contraction northward.
• Ocean acidification – 30 % increase in dissolved CO₂, reducing calcification rates in shell‑forming organisms.

4.3 Socio‑economic Impacts

4.4 Future‑scenario Projections (RCP/SSP Pathways)

• RCP 4.5 (medium mitigation) – Projected global warming of ~ 1.8 °C by 2100; sea‑level rise 0.45‑0.60 m; moderate increase in extreme heat days.
• RCP 8.5 (high‑emission “business‑as‑usual”) – Warming of ~ 3.7 °C by 2100; sea‑level rise 0.74‑1.00 m; tropical cyclone intensity up 15‑20 % and frequent severe droughts in the Mediterranean.
• These scenarios help students discuss *predicted* impacts (e.g., loss of low‑lying islands, shifts in agricultural zones) alongside observed changes.

4.5 Case Study – The Arctic (Illustrative)

Observed change: Average annual temperature ↑ ≈ 2 °C since 1970; sea‑ice extent reduced by ~ 13 % per decade.

• Permafrost thaw releases CH₄ and CO₂ – a positive feedback loop.
• Traditional Inuit hunting routes disappearing – threatens food security and cultural heritage.
• Opening of the Northwest Passage creates new shipping routes – raises risk of oil spills and invasive species.

5. 5.3 Evaluation of Responses

5.1 Mitigation – Reducing Greenhouse‑Gas Emissions

• Renewable energy (solar, wind, hydro, tidal)
  • Pros: Low‑carbon, falling costs, job creation.
  • Cons: Intermittency, storage needs, land‑use or visual impacts.
• Energy efficiency
  • Pros: Immediate emission cuts, lower household bills.
  • Cons: Requires upfront investment and behavioural change.
• Reforestation / afforestation
  • Pros: Carbon sink, biodiversity, soil protection.
  • Cons: Long lag before sequestration realised; competition with food production for land.
• Carbon capture & storage (CCS)
  • Pros: Can capture emissions from hard‑to‑decarbonise sectors (e.g., cement, steel).
  • Cons: High capital cost, limited commercial deployment, risk of leakage.
• Policy instruments – Carbon taxes, emissions trading schemes, subsidies for low‑carbon technologies.

5.2 Adaptation – Coping with Inevitable Change

• Flood‑defence infrastructure (levees, sea walls)
  • Pros: Protects lives and property; can be engineered to specific risk levels.
  • Cons: Expensive; may give a false sense of security; can be overtopped by extreme events.
• Drought‑resistant crops & altered farming calendars
  • Pros: Maintains food production under water stress.
  • Cons: May reduce nutritional diversity; seed distribution and farmer training required.
• Coastal retreat & managed realignment
  • Pros: Reduces long‑term risk; creates new wetland habitats that act as carbon sinks.
  • Cons: Social disruption, loss of land value, political resistance.
• Public‑health preparedness
  • Pros: Saves lives during heat‑waves; reduces disease spread.
  • Cons: Requires sustained funding, public awareness and coordinated services.
• Early‑warning systems & climate‑smart planning – Use of satellite data and GIS to anticipate floods, landslides and heat‑waves.

5.3 Comparative Evaluation

Mitigation tackles the root cause of climate change and yields long‑term global benefits, but progress depends on international cooperation and rapid policy implementation (e.g., meeting Paris Agreement targets). Adaptation is essential for communities already experiencing impacts; it can be tailored locally but becomes increasingly costly as climate risks intensify. An effective climate‑policy mix therefore combines ambitious mitigation with equitable, well‑funded adaptation.

6. Geographical Skills – Using Data to Understand Climate Change

1. Interpreting a temperature‑time graph – Identify the trend line, calculate the rate of warming (°C per decade), and discuss outliers such as volcanic cooling years.
2. Reading a CO₂ concentration curve (ice‑core vs. instrumental) – Compare pre‑industrial levels with modern values; calculate the percentage increase.
3. Mapping climate impacts – Colour‑code a world map by dominant impact (sea‑level rise, desert expansion, cyclone intensity). Explain why latitude, ocean currents and topography influence these patterns.
4. Data‑handling exercise – Given a table of annual sea‑level rise for five coastal cities, calculate the average rise, identify the city at greatest risk, and suggest an appropriate adaptation measure.

7. Suggested Revision Diagram