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Geoengineering interventions are large-scale attempts to purposefully alter the climate system in order to offset the effects of global warming. Most geoengineering proposals can be divided into two types: solar radiation management (SRM) and carbon dioxide removal (CDR).

Solar radiation management involves increasing the Earth's reflectivity to reduce the energy absorbed by the earth from the sun. The two most popular proposals for this are to spray seawater into the air to increase the reflectivity of clouds (marine cloud whitening) and to increase the concentration of highly reflective sulphate aerosols in the upper atmosphere (stratospheric aerosol injection). While both these interventions promise to be extremely cost-effective in reducing or averting global warming, it is very difficult to predict other impacts such action will have on the Earth's climate, and these may cause damage to human life comparable to that of the climate change that would have happened otherwise. Furthermore, such interventions require maintained action, and should this be interrupted the results could be catastrophic. Thus, while such interventions might be highly cost-effective in averting the impacts of climate change, the difficulty in fully understanding their effects mean such an approach is risky, and we thus do not recommend donations to organisations focusing on solar radiation management.

Carbon dioxide removal involves the development and deployment of technologies capable of extracting and storing carbon dioxide from the atmosphere. While such interventions are far lower risk than SRM, current estimates give the cost of removing one tonne of carbon dioxide at about $500 [1], and this still far exceeds the cost of abating a single tonne of carbon dioxide through the methods described in the mitigation strategies section. It is uncertain how far down this cost can be brought with further research. In any case, we currently do not think carbon dioxide removal will be more cost-effective than carbon dioxide emission mitigation.

See our analysis of other climate change interventions.


  1. The American Physical Society, Direct Air Capture of CO2 with Chemicals: A Technology Assessment for the APS Panel on Public Affairs, 2011.