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 geoengineering by all commentators, instead being described as mitigation.
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Carbon sequestration
A wide range of techniques for carbon sequestration exist. These range from ideas to remove CO2 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).
Chlorofluorocarbon photochemistry
Atmospheric chlorofluorocarbon (CFC) removal is an idea which suggests using lasers to break up CFCs, an important family of greenhouse gases, in the atmosphere.
Methane removal
Methane potentially poses major challenges for remediation. It is around 20 times as powerful a greenhouse gas as CO2. Large quantities may be outgassed from permafrost and clathrates as a result of global warming, notably in the Arctic.
There are existing climate engineering proposals. Methane is removed by several natural processes, which can be enhanced.