Carbon sequestration is the storage of carbon dioxide (usually captured from the atmosphere) through biological, chemical or physical processes, for the mitigation of global warming. Most projects can be regarded as geoengineering. It has been proposed as a way to mitigate the accumulation of greenhouse gases in the atmosphere released by the burning of fossil fuels.
Where the CO2 is captured as a pure by-product in processes related to petroleum refining (upgrading), or from flue gases from power generation. CO2 sequestration can then be seen as being synonymous with the storage part of carbon capture and storage, a term which refers to the large-scale, permanent artificial capture and sequestration of industrially-produced CO2 using subsurface saline aquifers, reservoirs, ocean water, aging oil fields, or other sinks.
The first large-scale co2 sequestration project (1996) is called Sleipner, and is located in the North Sea where Norway's StatoilHydro strips carbon dioxide from natural gas with amine solvents and disposes of this carbon dioxide in a deep saline aquifer. In 2000, a coal-fueled Synthetic Natural Gas plant in Beulah, North Dakota, became the world's first coal using plant to capture and store carbon dioxide. "Weyburn-Midale CO2 Project, World’s first CO2 measuring, monitoring and verification initiative". Petroleum Technology Research Centre. http://www.ptrc.ca/weyburn_overview.php. Retrieved on 2009-04-09.
Biological processes have a huge effect on the Global carbon cycle. Major climatic fluctuations have been driven by these processes in the past, such as at the Azolla event which started the current Arctic climate. Fossil fuel formation is as a result of such processes, as is the formation of clathrate or limestone. By manipulating such techniques, geoengineers seek to enhance sequestration. Methods such as ocean iron fertilization are examples of such geoengineering techniques.
Ocean iron fertilization
Iron fertilization of the ocean to encourage plankton growth which removes carbon from the atmosphere on a temporary, or arguably permanent basis. This technique is controversial due to difficulties of predicting its effect on the marine ecosystem, and the potential for side effects or large deviations from expected efficacy. Such effects potentially include the release of nitrogen oxides and disruption to the nutrient balance in the ocean. Iron fertilization is a natural process and it is the enhancement of this process which is the geoengineering technique.
Ocean urea fertilisation
Proposed by Ian Jones with the purpose to fertilize the ocean with urea, a nitrogen rich substance, to encourage phytoplankton growth.
Australian company Ocean Nourishment Corporation (ONC) plans to sink hundreds of tonnes of urea into the ocean, in order to boost the growth of CO2-absorbing phytoplankton, as a way to combat climate change. In 2007, Sydney-based ONC completed an experiment involving 1 tonne of nitrogen in the Sulu Sea off the Philippines
Reforestation of marginal crop and pasture lands to transfer CO2 from the atmosphere to new biomass. It is essential to ensure that the carbon did not return to the atmosphere from burning or rotting when the trees died. To this end, it would be important to either manage such forests in perpetuity or use the wood from them for biochar, BECS (see below) or landfill. This technique can give 0.27W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of 1/6 of current levels of anthropogenic CO2 emissions. It is notable, however, that this CO2 levels will have risen by the time this could be achieved.
Peat bogs are a very important store of carbon. By creating new bogs, or enhancing existing ones, carbon sequestration can be achieved.
Encouraging various layers of the ocean to mix can move nutrients and dissolved gases around and thus act as a geoengineering approach. Placing large vertical pipes in the oceans to bring nutrient rich water to the surface, triggering algal blooms, which also store carbon when they die. - a mechanism somewhat similar to ocean iron fertilization. This technique may result in a short-term rise in CO2 in the atmosphere, which limits its attractiveness. Forced upwelling can give 0.28W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of 1/6th current levels of anthropogenic CO2 emissions. An alternative forced downwelling approach can give 0.16W/m2 of globally-averaged negative forcing, which is sufficient to reverse the warming effect of about 1/10th current levels of anthropogenic CO2 emissions. It is notable, however, that this CO2 levels will have risen by the time this could be achieved.
Biochar is charcoal created by pyrolysis of biomass. The resulting charcoal-like material is landfilled, or used as a soil improver to create terra preta. Biogenic carbon is recycled naturally in the carbon cycle. By pyrolysing it to biochar, it’s rendered inert and sequestered in soil. Further, the soil encourages bulking with new organic matter, which gives additional sequestration benefit.
The carbon contained in the soil is therefore unavailable for oxidation to CO2 and consequential atmospheric release. As a result, the radiative forcing potential of the avoided CO2 is removed from the planet’s energy balance. This technique is advocated by prominent scientist James Lovelock, creator of the Gaia hypothesis.It can give 0.52W/m² of globally-averaged negative forcing, which is sufficient to reverse the warming effect of about 1/3 current levels of anthropogenic CO2 emissions. It is notable, however, that CO2 levels will have risen by the time this could be achieved. According to Simon Shackley, "I would say people are talking more about something in the range of one to two billion tonnes a year."
The mechanisms related to the carbon sequestration properties of biochar, is referred to as bio-energy with carbon storage, BECS.
The term BECCS refers to Bio-energy with carbon capture and storage – Burning biomass in power stations and boilers which utilise carbon capture and storage. Using this technology with sustainably produced biomass would result in net-negative carbon emissions, as the carbon sequestered during the growth of the biomass would be captured and stored, thus removing carbon dioxide from the atmosphere.
This technology is sometimes referred to as bio-energy with carbon storage, BECS, though this term can also refer to the carbon sequestration potential in other technologies, such as biochar.
Burying biomass (such as trees) directly, thus sequestering the carbon in the ground rather than allowing it to escape, mimicking the natural processes that created fossil fuels. Landfill of trash also represents a physical method of sequestration.
Biomass ocean storage
The production of fossil fuels is a natural process which often involves the ocean burial of biomass in the ocean, often near river mouths which bring large quantities of nutrients and dead material into the ocean. Transporting material, such as crop waste, out to sea and allowing it to sink into deep ocean storage has been proposed as a means of sequestration of carbon.
Carbon Capture and Storage
CO2 can be injected into old oil wells and other geological features, or can be stored in pure form in the deep ocean.
CO2 has been used extensively in enhanced crude oil recovery operations in the United States beginning in 1972. There are in excess of 10,000 CO2 wells in the state of Texas alone. The gas comes in part from anthropogenic sources, but principally from large naturally-occurring geologic formations of CO2. It is transported to the oil-producing fields through a large network of over 5,000 kilometres (3,100 mi) of CO2 pipelines. The use of CO2 for Enhanced oil recovery (EOR) methods in heavy oil reservoirs in the Western Canadian Sedimentary Basin (WCSB)has also been proposed. However, cost of transport remains an important hurdle. A similar CO2 pipeline system to that of Texas does not yet exist in the WCSB that could connect most of the sources for CO2 in Canada associated with the mining and upgrading operations in the Athabasca oil sands, with the subsurface heavy oil reservoirs that could most benefit from CO2 injection hundreds of km to the south.