Climate change — evidence, causes, effects and responses

Climate change is arguably the most significant environmental challenge of the twenty-first century. CCEA examiners expect you to discuss the evidence for climate change, distinguish between natural and human causes, assess effects at different scales, and evaluate mitigation (reducing the problem) versus adaptation (adjusting to the consequences).

Evidence for climate change

Temperature records: global average temperatures have risen approximately 1.1°C above pre-industrial levels (as of 2023). The ten hottest years on record have all occurred since 2010.

Ice cores: bubbles of ancient air trapped in Antarctic and Greenland ice allow scientists to reconstruct past temperatures and CO₂ levels going back 800,000 years. These show a clear correlation between CO₂ concentration and temperature — and current CO₂ levels (over 420 ppm) are unprecedented in human history.

Sea level rise: global mean sea level has risen approximately 20 cm since 1900 and is accelerating (currently ~3.7 mm/year). Caused by thermal expansion of seawater and melting of glaciers and ice sheets.

Retreating glaciers: almost all glaciers worldwide are retreating. The Arctic sea ice extent in summer has declined by approximately 40% since 1979.

Extreme weather events: increasing frequency and intensity of heatwaves, droughts, wildfires and intense rainfall events.

Causes of climate change

Natural causes (have always operated):

• Variations in Earth's orbit (Milankovitch cycles) — cycles of thousands of years.
• Solar output variation — small and insufficient to explain current warming.
• Volcanic eruptions — release CO₂ but also aerosols that can cool the climate temporarily.

Human (anthropogenic) causes (dominant since industrialisation):

• Burning fossil fuels (coal, oil, gas): releases CO₂ and methane, the main greenhouse gases.
• Deforestation: removes trees that absorb CO₂ through photosynthesis; burning them releases stored carbon.
• Agriculture: cattle produce methane (belching and manure); rice paddies produce methane; synthetic fertilisers release nitrous oxide.
• Industry and cement production: major sources of CO₂.

The greenhouse effect: greenhouse gases (CO₂, methane, water vapour, N₂O) trap outgoing infrared radiation from Earth's surface, warming the lower atmosphere. This natural process is being intensified by human emissions.

Effects

Global: sea level rise (threatening low-lying states — Maldives, Bangladesh); melting permafrost releasing stored methane (positive feedback); bleaching of coral reefs (thermal stress); shifting climate zones affecting agriculture; increased extreme weather.

Northern Ireland: increased flooding frequency (more intense rainfall, wetter winters); longer growing seasons (mixed benefits — some crops, some pests); coastal erosion acceleration (higher sea levels + more intense storms); potential change to the landscape of NI's upland peat bogs (important carbon store).

Mitigation vs adaptation

Mitigation (reducing the causes):

• Switching to renewable energy (wind, solar, tidal — NI has significant wind energy capacity).
• Improving energy efficiency of buildings.
• Reducing deforestation; planting forests.
• Carbon capture and storage (CCS) technology.
• International agreements: Paris Agreement (2015) — limiting warming to well below 2°C.

Adaptation (adjusting to unavoidable change):

• Building flood defences in coastal cities.
• Changing agricultural practices and crops.
• Developing drought-resistant crops.
• Managed retreat of coastal communities.
• NI: Northern Ireland's Climate Change Act (2022) commits NI to net-zero emissions by 2050.