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What is carbon sequestration?
Carbon sequestration is the storage of carbon dioxide (CO2) to prevent its release into the atmosphere where it contributes to global warming.
Although trees, plants and crops naturally sequester CO2 by converting the gas to biomass and soils, the term carbon sequestration generally refers to either the intentional creation of additional biomass for sequestration or for methods of storage that don't naturally occur.
The stores of CO2 are often referred to as carbon 'sinks'.
Is this the same as 'carbon capture and storage'?
Nearly - but not quite. Sequestration is effectively the storage part of carbon capture and storage.
What methods of carbon sequestration exist?
The main types of carbon sequestration include: increased storage in vegetation and soils, geological storage, ocean storage and mineral storage. Some methods are currently being used and others are propositions and have yet to be applied.
- Vegetation and soils
The most obvious means to significantly increase vegetation is through afforestation (planting trees where there were none previously) or reforestation (replanting trees in areas that have been deforested). Critics of this method claim that it is only effective when the vegetation is alive and that old trees emit more CO2 than they take up.
Altering farming practices to plant crop and grass species with extensive root systems can increase soil carbon content significantly. It is claimed that improving the soil carbon content by 0.5 per cent in the top 30 centimetres of just two per cent of Australia's agricultural land would sequester all of our annual CO2 emissions. This doesn't mean that it would be easy to achieve or that it could continue year on year, however.
Other related ways of sequestering carbon in vegetation include restoring natural carbon sinks, such as degraded wetlands.
- Geological storage
This method is also known as geo-sequestration. It involves locking CO2 below ground in geological formations such as oil fields, gas fields, aquifers and coal seams that cannot be mined. Typically the source of the CO2 is from major industrial and energy related sources like power stations.
Proponents of geo-sequestration claim that this method stores carbon indefinitely. They also point to the potential benefits it offers such as aiding the recovery of oil from ageing oil fields and releasing methane from coal beds that can be captured for use.
On the other hand, critics are concerned by the energy required for the process, the risk of CO2 leaks, and of course the fact that some of the supposed benefits include facilitating further harvesting of fossil fuels.