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black figures are estimates of the natural stores and fluxes

red figures indicate the anthropogenic effects after 1750 (start of the Industrial Revolution)

The IPCC (Intergovernmental Panel on Climate Change estimates that 90% of carbon is from the anthropogenic combustion of fossil fuels (coal, plus oil and natural gas)

The remaining 10% is from land use changes (deforestation, land drainage and agricultural practices)

Half of the carbon is equally absorbed by oceans and vegetation.......the rest by the atmosphere (hence global climate change)

1. Hydrocarbon fuel extraction and burning

Hydrocarbons - or fossil fuels - are natural sources of energy formed from the remains of living organisms

When extracted from the ground (from 70-100 million year old rocks), and then burned (combustion), the stored carbon is released primarily as carbon dioxide

This leads to what is known as the "enhanced greenhouse effect" - ie. the increase in emissions of CO2 speeds up the natural greenhouse effect process

2. Changing farming practices

Population growth, and changes in diet and increase in wealth have all led to increase in agricultural production

Arable farming:

  • releases carbon in to the atmosphere when the soil is ploughed, as humus is an organic carbon store
  • "...on a world-wide basis, from the time agriculture began, almost 80 million tons of carbon have been released from the soil. Up until the late 1950s, ploughing released more carbon dioxide into the atmosphere than all the burning of oil and coal in history" (Hofstrand, 2007)
  • the increase in pastoral farming has had a further impact on arable farming as the animals are fed grain to increase their fat and energy stores

Increased demand:

  • leads to deforestation of land as more space is required, which causes a reduction in carbon storage and releases it into the atmosphere
  • has led to mechanisation for more efficient and less time consuming production
  • means more transportation, refrigeration and packaging of products, which all use energy, and therefore more carbon is combusted

3. Deforestation

Deforestation results in a permanent loss of forest cover and a large release of carbon dioxide (CO2) into the atmosphere.

It occurs primarily in tropical countries where forests are permanently cleared and converted to agriculture and urban settlement, and is therefore responsible for about 20 percent of global CO2 emissions.

See case study on the Amazon rainforest

4. Land use changes - urbanisation

Extra reading:

http://urbaneco.washington.edu/wp/urban-landscape-patterns-and-ecosystem-function/carbon-and-urbanization/

units are in Petagrammes of Carbon per year

Changes in the carbon cycle: human causes of change / human impacts on it

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