A-Level Geography: The Carbon Cycle and Climate

The carbon cycle is the second half of the compulsory 'water and carbon cycles' core theme in A level Geography. This material builds the chain of reasoning that questions on it demand: where carbon is stored, what moves it, how fast, and what happens when people change the balance.

You begin with stores and fluxes. By far the largest store is the lithosphere, in carbonate rocks and fossil fuels; the oceans hold far more than the atmosphere, soils or vegetation. The slow, geological cycle moves carbon over millions of years through chemical weathering by carbonic acid, the formation of calcium carbonate, sedimentation and volcanic outgassing. The fast, biological cycle moves it within years to centuries through photosynthesis, respiration, decomposition and combustion, including wildfire. In the oceans you meet the biological pump, which carries organic matter to the deep ocean, and the carbonate pump, which sinks shells and skeletons.

The quantitative questions treat the carbon cycle as a mass balance, as the specifications ask. You calculate how much of a year's emissions stays in the atmosphere once ocean and land sinks are subtracted, convert between gigatonnes of carbon and gigatonnes of carbon dioxide using the ratio 44/12, and work out how long a forest takes to recapture the carbon released by a fire. All the figures needed are given in each task.

The second half links carbon to water and climate. Transpiration and stomatal exchange couple the two cycles in a rainforest; decomposition rates explain why tundra and peat soils hold so much carbon; the water vapour feedback amplifies warming; and a possible Amazon dieback shows how a positive feedback could run. Finally you evaluate human interventions: tree planting as an offset, carbon capture and storage, and re-wetting drained peatland, weighing what each can and cannot do.

The material offers a quiz with worked explanations, flashcards for processes and feedbacks, a printable written sheet of explanations and short calculations, and an oral exam in which an examiner asks one question at a time and gives brief feedback at the end.

• Describe the main carbon stores and the processes that transfer carbon between them
• Distinguish the slow geological carbon cycle from the fast biological cycle
• Explain the biological and carbonate pumps in the oceans
• Calculate an annual carbon budget and convert between GtC and Gt of carbon dioxide
• Explain links and feedbacks between the carbon cycle, the water cycle and climate
• Evaluate afforestation, carbon capture and storage and peatland restoration

Practice material written by Zestly, based on the 'water and carbon cycles' core theme of the DfE GCE AS and A level subject content for geography (2014) and board specifications such as AQA A-level Geography 7037, sections 3.1.1.3–3.1.1.4, and Pearson Edexcel A level Geography 9GE0, Topic 6.