Topic 2 of 3Cambridge A Levels

Atmospheric Processes & Climate Change

Global circulation, weather systems, causes and effects of climate change

Global atmospheric circulation is driven by unequal heating of Earth's surface.

Three-cell model:

Hadley cell (0-30°): Hot air rises at equator → moves poleward → sinks at 30° (subtropical high pressure)

Ferrel cell (30-60°): Surface air moves poleward, meets polar air at polar front

Polar cell (60-90°): Cold dense air sinks at poles

Climate change evidence: Rising global temperatures (~1.1°C since pre-industrial). Ice cores, sea level data, glacier retreat, shifting seasons.

Causes:

Natural: Solar variation, volcanic eruptions, orbital changes (Milankovitch cycles)

Human (enhanced greenhouse effect): CO₂ (fossil fuels), methane (agriculture), deforestation reduces CO₂ absorption

Effects: Sea level rise, extreme weather events, coral bleaching, permafrost melting, crop yield changes, biodiversity loss.

Responses:

Mitigation: Reduce emissions (Paris Agreement, renewable energy, carbon tax)

Adaptation: Sea walls, drought-resistant crops, early warning systems

Key Points to Remember

1Three-cell model: Hadley, Ferrel, Polar
2Enhanced greenhouse effect from human CO₂ emissions
3Evidence: ice cores, sea level, glacier retreat
4Mitigation reduces causes; adaptation manages effects

Pakistan Example

Pakistan's Climate Vulnerability — Floods, Heatwaves, and Glacial Melt

Pakistan contributes <1% of global emissions but ranks among the most climate-vulnerable countries. The 2022 floods (one-third of country submerged) were linked to enhanced monsoon rainfall from warming oceans. Glacial melt in Gilgit-Baltistan threatens water supply for millions. Pakistan's NCCP (National Climate Change Policy) is an adaptation response.

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