1.1 Most effective
The simplest measure for choosing a geoengineering method might be to choose the one with ‘the maximum achievable forcing’. Recall that of the six geoengineering methods you have studied, three could counter any amount of CO2 forcing, while the others are more limited.
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The rank order is:
- sulfate aerosols, marine cloud brightening, solar shield (all three could balance any CO2 forcing)
- BECCS (estimated two-thirds of a doubled CO2 forcing by 2100)
- iron fertilisation (estimated 8% of a doubled CO2 forcing by 2100)
- urban albedo (estimated 1.3% of a doubled CO2 forcing).
So if you were looking for methods which achieved the maximum forcing, then you might consider sulfate aerosols, marine cloud brightening and solar shields as your primary focus. However, that’s not the only consideration.