Greenhouse gas removal
Greenhouse gas removal projects are a type of climate engineering that seek to remove greenhouse gases from the atmosphere, and thus they tackle the root cause of global warming. These techniques either directly remove greenhouse gases, or alternatively seek to influence natural processes to remove greenhouse gases indirectly. The discipline overlaps with carbon capture and storage and carbon sequestration, and some projects listed may not be considered to be climate engineering by all commentators, instead being described as mitigation.
A wide range of techniques for carbon sequestration exist. These range from ideas to remove CO
2 from the atmosphere (carbon dioxide air capture), flue gases (carbon capture and storage) and by preventing carbon in biomass from re-entering the atmosphere, such as with Bio-energy with carbon capture and storage (BECCS).
Pyrogenic carbon capture and storage
Pyrogenic carbon capture and storage is discussed as a promising technology of greenhouse gas removal. Pyrolysis is described by Werner et al. (2018) as "the thermal treatment of biomass at 350 °C–900 °C in an oxygen-deficient atmosphere. Three main carbonaceous products are generated during this process, which can be stored subsequently in different ways to produce [negative emissions]: a solid biochar as soil amendment, a pyrolytic liquid (bio-oil) pumped into depleted fossil oil repositories, and permanent-pyrogas (dominated by the combustible gases CO, H2 and CH4) that may be transferred as CO2 to geological storages after combustion."
A different procedure has been proposed by Esrafilzadeh et al. (2019) that makes it possible to create bio char under room temperature, using liquid metal electrocatalysts.
Methane potentially poses major challenges for remediation. It is around 20 times as powerful a greenhouse gas as CO
2. Large quantities may be outgassed from permafrost and clathrates as a result of global warming, notably in the Arctic.
- Chemical decomposition — reaction with hydroxyl radicals produced from photochemical decomposition of ozone in the stratosphere.
- Biological decomposition — by methanotrophs in soils and water.
In 2018, the Mercator Research Institute on Global Commons and Climate Change published a report on the costs, potentials and side effects of 7 greenhouse gas removal techniques It revealed that the costs differ between the techniques, but are in the order of 100 to 300 USD per eliminated tonne of CO2.
- Carbon negative fuel
- Solar radiation management
- Climate change mitigation
- Avoiding dangerous climate change
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- Negative emissions—Part 2: Costs, potentials and side effects