3.1.1.3 Changes in the carbon cycle over time, to include natural variation (including wild fires, volcanic activity) and human impact (including hydrocarbon fuel extraction and burning, farming practices, deforestation, land use changes).

What are the 2 ‘natural variation’ causes of change within the carbon cycle?

Wildfires

Volcanic activity

What are human causes which lead to changes in the carbon cycle?

Hydrocarbon fuel extraction and burning

Farming practices

Deforestation

Land use changes

How can wildfires change the magnitude of carbon stores [4 marks]

Wildfires transfer carbon from the biosphere to the atmosphere as CO₂ is released through burning. This burning can encourage the growth of plants in the long term; However, the immediate effect is that by destroying vegetation, less carbon is absorbed from the atmosphere by plants through photosynthesis. Wildfires can have a neutral effect on the amount of atmospheric carbon

How can volcanic activity change the magnitude of carbon stores [4 marks]

Carbon stored within the earth in magma is released during volcanic eruptions, most of it entering the atmosphere as CO₂. Volcanic activity contributes a relatively low proportion of CO₂ to the overall carbon cycle and recent eruptions have released less CO2 than human activities, but a very large one could affect the carbon cycle significantly.

How can extracting and burning/combusting hydrocarbons impact the carbon cycle [4 marks]

Extracting and burning hydrocarbons (coal, oil and natural gas) releases stored carbon and methane (a potent GHG) into the atmosphere, increasing atmospheric CO2 levels and contributing to global warming. According to the IPCC, about 90% of anthropogenic carbon comes from the combustion of fossil fuels, primarily coal, but also oil and natural gas, this leads to positive feedback loops amplifiying global climate change.

How can deforestation impact the carbon cycle [4 marks]

Deforestation (cutting of trees) is often used to clear land for agriculture, logging or to make way for developments. In the Amazon Rainforest, an estimated 1.98 million hectares (4.89 million acres) of forest were cleared in 2022. Deforestation is detrimental as trees store large amounts of carbon and deforestation releases this carbon into the atmosphere, contributing to global warming and climate change. Deforestation also leads to habitat loss.

This is a positive feedback loop as it takes the carbon cycle away from dynamic equilibrium.

How can land use changes impact the carbon cycle [4 marks]

The change to urban land use has led to vegetation being removed to make way for buildings, reducing carbon storage in the biosphere and contributing to the increased urban heat island effects and greenhouse gas emissions (methane) from transportation and energy use.

However, afforestation - Planting trees on deforested or degraded land can sequester carbon from the atmosphere, acting as a sink and mitigating climate change.

Carbon emissions can be attempted to be reduced by land use laws. For instance Brazilian Forest Code that says that landowners have to keep 50-80% of their land as forest.

How can farming practices impact the carbon cycle [4 marks]

Cattle ranching is now the biggest cause of deforestation in the Amazon, and nearly 80 per cent of deforested areas in Brazil are now used for cows, who release methane - a potent greenhouse gas. Cattle release CO2 and methane when they respire contributing to increased atmospheric CO2.

Ploughing can release CO₂ stored in soil.

Growing rice in rice paddies releases methane. 

Farm machinery such as tractors may release CO₂.

All examples of positive feedback