Core: Global climate change and its impacts
Global climate change and its impacts
This core unit examines the climate system, the causes of recent warming and the uneven impacts of change. SL answers need to distinguish evidence, cause, impact, adaptation and mitigation.
Core rules
- Natural greenhouse effect keeps Earth habitable; the enhanced greenhouse effect results from added greenhouse gases, especially CO2 from fossil fuels, methane from agriculture and nitrous oxide.
- Radiative forcing is the change in energy balance; positive forcing warms. Feedbacks include ice-albedo (melting ice absorbs more heat), water vapour and permafrost carbon release.
- Evidence comes from instrumental records, ice cores, tree rings and satellite data. Atmospheric CO2 is now about 420 ppm, and global mean surface temperature is roughly 1.1–1.3°C above pre-industrial levels.
- Impacts include sea-level rise, heatwaves, changing rainfall, coral bleaching, crop stress, water scarcity and health risks. Vulnerability depends on exposure, sensitivity and adaptive capacity.
- Mitigation reduces emissions: renewables, energy efficiency, carbon pricing, afforestation. Adaptation reduces harm: sea walls, drought-resistant crops, early warning, managed retreat.
- Ocean acidification is a separate consequence of CO2 dissolving in seawater; pH has fallen by about 0.1 units since pre-industrial times.
Worked example
A low-lying island state faces sea-level rise. Reasoning: the cause is global emissions, but vulnerability is local: elevation, reef health, groundwater salinity and dependence on tourism. Mangrove restoration and raised infrastructure are adaptation; they cannot stop ocean warming. Mitigation is a global public good, so the island has little control over the main driver. A strong evaluation recognises limits to adaptation, such as the cost of relocation and loss of cultural heritage.
Traps
- Confusing climate change with ozone depletion.
- Treating a single storm as proof of climate change.
- Listing impacts without linking them to vulnerability.
- Treating adaptation and mitigation as interchangeable.