Where does CO2 come from?

The Carbon Cycle is a natural process which describes the movement of all the carbon on earth between the geosphere, atmosphere, biosphere and oceans. It is an intricate balance between several storage pools of carbon, with some natural systems acting as carbon sources and some acting as carbon sinks or storage sites . Transferral rates between each source range from days to millions of years. It is a complex system. Here is a simplified version of the carbon cycle.

THE MOVEMENT OF CARBON

Carbon is transferred between through the geosphere, atmosphere, biosphere and oceans in a variety of different ways. Plants utilise atmospheric CO2 in photosynthesis and when they decompose, they lock carbon into the soil and sediments. Sediments interact with the geologic cycle and become involved in the processes of weathering, dissolution, subduction and volcanism. Sediments are eventually prone to weathering and release their carbon back into the cycle. The worlds oceans act as a massive CO2 sink and atmospheric CO2 dissolves in their waters. Animals and plants respire, which means that they expel CO2. Through all these processes and more, all the carbon on earth is recycled through the sources.

HUMAN INTERVENTION

Fossil fuels are produced when plants and algae have been buried under heavy layers of sediments and subjected to high heat and pressure over millions of years. When these fossil fuels form to make coal, oil and natural gas deposits, they effectively ‘lock away’ the CO2 that was used by the plants and animals to make them. The carbon within these fossil fuels is then considered to be 'fixed' out of the carbon cycle because it is not involved in the transferral between carbon reservoirs around the world anymore. However, when fossil fuels are burned to produce electricity, the carbon within them is released back into the carbon cycle as CO2. Emissions from anthropogenic (or man made) CO2 are at such a high level, that the Earth’s natural carbon cycle cannot accommodate it.