The carbon cycle

Question 1

Volcanic activity

Answer 1

Carbon stored within magma is released as CO2 during volcanic eruptions. Other gases such as sulphur dioxide are also released.
Sulphur dioxide creates sulphate aerosols that actually reflect the sun’s rays, so a common outcome of volcanic eruptions is cooling rather than warming, despite CO2 being a greenhouse gas.
Recent volcanic eruptions produce much less CO2 than human activities however a large eruption could disrupt the carbon cycle significantly.
Mount St Helens released 10 million tonnes of CO2 in 9 hours, whereas it currently takes humans just 2.5 hours to put out the same amount.

Question 2

Deforestation

Answer 2

Destruction of forests occurs for timber, agriculture, HEP generation, logging, developments or mineral exploitation.
Clearing forests removes a natural store of carbon, reduces soil carbon content and closes down photosynthesis. if the cleared forest is burned there is a rapid flow of carbon from the biosphere to the atmosphere.

Question 3

Afforestation

Answer 3

The planting of new forests and reforestation may increase absorption of CO2. This is one form of carbon offsetting scheme.

Question 4

Carbon off setting scheme

Answer 4

A deliberate scheme to reduce atmpospheric CO2 through absorption (tree planting) or reduced emissions (moving to green energy use).

Question 5

Farming practices

Answer 5

Animals release CO2 and methane when they respire and digest food.
Growing rice in paddies can produce a lot of methane.
As population increases, food production rises.
Increased demand for beef and pig produce is causing increases in animal gas emissions and mechanisation.

Question 6

Soils

Answer 6

Ploughing can release CO2 stored in soil.
Intensive use of artificial fertilisers and other farm chemicals can lead to soils becoming sterile because of loss of their organic content.

Question 7

Land use changes

Answer 7

increasing urbanisation means that vegetation cover reduces. urban areas consume more energy than traditional rural ones, so more fossil fuels are being burnt.
urban construction materials increase the demand for concrete.

Question 8

cement production

Answer 8

processing limestone into cement is one of the largest single sources of man-made carbon dioxide other than fossil fuel use.
CaCO3 is heated to produce limestone, releasing CO2 as a major by-product.
The fuel needed to reach the high processing temperatures adds to the release of CO2.

Question 9

burning of vegetation

Answer 9

this may be deliberate or accidental.

carbon is released in smoke and reduces future capacity to absorb CO2.

Question 10

fossil fuel extraction and use

Answer 10

the largest contribution the atmospheric CO2.
This effectively takes the slow carbon cycle that took millions of years to sequester and releases it into the fast cycle in quantities far higher than natural cycles can process.

Question 11

the carbon budget

Answer 11

the net change between inputs from a carbon source and outputs to a carbon sink. before an anthropogenic intervention, these were exchanges in the natural world.

Question 12

ocean-atmosphere exchange

Answer 12

ocean out-gassing represents the largest source of carbon dioxide in the atmosphere. dissolved CO2 in sea water is released, particularly from the surface of warm, tropical waters into the atmosphere. oceans absorb and release carbon, to and from the atmosphere.
as carbon moves from one store to another, it is said to be in flux.