Changes in the carbon cycle over time, to include natural variation…

The idea

The carbon cycle fluctuates over time through natural and anthropogenic drivers. Natural variations include volcanic activity, releasing lithospheric carbon dioxide, and wildfires, which rapidly transfer biospheric carbon to the atmosphere while reducing photosynthetic capacity. Human impacts significantly accelerate these changes. Hydrocarbon fuel extraction and burning shift vast quantities of fossilised carbon into the active cycle. Farming practices, such as cattle rearing and ploughing, release methane and oxidise soil carbon. Deforestation removes vital carbon sinks, and broader land use changes, like urbanisation, seal soils and alter natural fluxes, disrupting the long-term equilibrium of the global carbon cycle.

What earns the marks

• Explain how volcanic activity transfers carbon from the lithosphere to the atmosphere as carbon dioxide.
• Describe the dual impact of wildfires: immediate release of carbon dioxide and long-term reduction in the biosphere's capacity to sequester carbon.
• Analyse how hydrocarbon extraction and combustion move slow-cycle carbon into the fast cycle, creating an atmospheric surplus.
• Evaluate the impact of farming practices, such as methane emissions from livestock and carbon loss from soil ploughing.
• Assess how deforestation and land use changes (e.g., urbanisation) reduce biomass carbon storage and alter soil carbon fluxes.

Common mistakes and how to put them right

• Stating that volcanic eruptions are the primary cause of recent atmospheric carbon increases.

  Put it right: Clarify that human activities, particularly hydrocarbon burning, release significantly more carbon annually than volcanic activity.

• Confusing the greenhouse effect with ozone depletion when discussing hydrocarbon burning.

  Put it right: Explicitly link hydrocarbon combustion to the enhanced greenhouse effect and global warming, not the ozone hole.

• Treating deforestation and land use change as identical processes.

  Put it right: Distinguish deforestation (tree removal) from broader land use changes, which include urbanisation, afforestation, and agricultural conversion.

Exam tips

• Use specific data, such as gigatonnes of carbon (GtC), to compare the magnitude of natural versus human-induced carbon fluxes.
• When discussing wildfires, acknowledge that they can be both a natural variation and exacerbated by human-induced climate change.
• Structure essay answers by contrasting the timescales of natural variations (often geological) with the rapid pace of recent human impacts.