1.3.2 Processes affecting the Carbon Cycle

Question 1

What are natural process which affect the carbon cycle?

Answer 1

• Wildfires
• Volcanic eruptions

Question 2

How do volcanic eruptions cause changes in the carbon cycle?

Answer 2

• Carbon stored within the Earth in magma is released during volcanic eruptions. The majority enters the atmosphere as CO2.
• Recent volcanic eruptions have released much less CO2 than human activities. However, there is the potential for a very large eruption to disrupt the carbon cycle significantly.

Question 3

How do wildfires cause changes in the carbon cycle?

Answer 3

• Wildfires rapidly transfer large quantities of carbon from biomass (or soil) to the atmosphere. Loss of vegetation decreases photosynthesis, so less carbon is removed from the atmosphere.
• In the longer term, however, fires can encourage the growth of new plants, which take in carbon from the atmosphere for photosynthesis. Depending on the amount and type of regrowth, fires can have a neutral effect on the amount of atmospheric carbon.

Question 4

How does human activity affect the carbon cycle?

Answer 4

Humans are causing carbon flows from the lithosphere and biosphere to the atmosphere to happen much faster than they would naturally.

Processes:

• Deforestation
• Fossil fuel extraction and use
• Land use change
• Farming practices

Question 5

[Human processes affecting the carbon cycle]

Deforestation

Answer 5

• Forests may be cleared for agriculture logging, or to make way for developments.
• Clearance reduces the size of the carbon store and, if the cleared forest in burned, there is a rapid flow of carbon from the biosphere to the atmosphere.

Question 6

[Human processes affecting the carbon cycle]

Fossil fuel extraction and use

Answer 6

• Extracting and burning (combustion) of fossil fuels releases CO2 into the atmosphere.
• Without human intervention, the carbon would remain sequestered in the lithosphere for thousands or millions of years to come.

Question 7

[Human processes affecting the carbon cycle]

Land use changes

Answer 7

• The change in land use from natural or agricultural to urban is a major source of carbon.
• Vegetation is removed to make way for buildings – this reduces carbon storage in the biosphere.
• Concrete production releases lots of CO2, and lots of concrete is used when urban areas expand.

Question 8

[Human processes affecting the carbon cycle]

Farming practices

Answer 8

• Agricultural activities release carbon into the atmosphere.
• Animals release CO2 and methane when they respire and digest food.
• Ploughing can release CO2 stored in soil.
• Growing rice in rice paddies releases a lot of methane.
• As the world’s population has risen, so has food production. As a result, carbon emissions from farming practices have increased. Mechanisation of farming has also increased CO2 emissions.

Question 9

What is the carbon budget?

Answer 9

The difference between the inputs of carbon into a subsystem and outputs of carbon from it.

Question 10

What is a carbon store?

Answer 10

Where the outputs of carbon outweighs the inputs, so it releases more carbon than it absorbs

Question 11

What are carbon sinks?

Answer 11

Where the inputs of carbon outweigh the outputs, so it absorbs more carbon than it releases.