Table 3: Overview of current operational cost estimates and potential side-effects for various RM measures.

MeasureAnnual potential in Wm−2Operational costs in B $US/Wm−2Main investment requirementsUncertaintiesSide-effectsSources

SRM surface measures

Modification of crop and forest albedo−1 No quantitative assessment available, but operational costs and investment requirements are expected to be relatively lowGenetic modifications; replacement of existing plantsIncreases effectiveness of afforestation; side-effects due to genetic modifications[6, 67]

SRM cloud measures

Modification of marine stratus clouds by injection of salt aerosols from Flettner ships−40.135R&D $US 27 M; Setting-up $US 30 M; ship fleet $US 1.7 B; additional logistic and maintenance costs (e.g., ports)Automatic operation of ships; replacement and maintenance requirements; Flettner rotorsSalt is nontoxic and residence time is low (<2 weeks); climatic side-effects [32, 33, 68, 69]

TRM cloud measures

Modification of cirrus clouds by injection of bismuth(III) iodid−1 to −4 No quantitative assessment available. Spreading is suggested to be done from airplanes on scheduled flights, implying cost in the order of magnitude or even lower as for modification of marine stratus clouds; otherwise, cost estimates from sulfur injection can be applied; understanding of cloud dynamics is low and in turn necessary spreading amounts are highly uncertainBismuth(III) iodide is nontoxic and residence time is low (<2 weeks); climatic side-effects [7072]

SRM stratospheric measures

Sulfur injection; existing airplanes (>18 km)Unlimited16–67Airplane fleet $US 18–56 B; base station $US 1 B per unitRecovery of ozone layer slows down; increase of anthropogenic sulfur emissions by 10 to 17 percent; ratio of diffuse irradiation to direct irradiation increases resulting in higher net primary production and lower solar power generation; perception of sky changes (less blue skies, more red sunsets); space observation affected; climatic side-effects [23, 24, 29, 31, 35, 7383]
Sulfur injection; newly designed airplanes (>18 km)Unlimited2–12Airplane fleet $US 6–36 B; base station $US 1 B per unitCoagulation between already existing and newly injected particles and therefore spreading amount; estimation of fuel costs; sulfur logistics; existing airships would only allow spreading height of 6 km
Sulfur injection; newly designed airships (>18 km)Unlimited5–18Airship fleet $US 19–66 B; base station $US1 B per unit
Injection of engineered nanoparticlesUnlimited No quantitative assessment available; prototypes do not exist; irrespective  of construction costs, spreading amount is estimated to be 0.1 Mt implying cost reductions up to the order of 200 in comparison to sulfur injectionResidence time of nanoparticles; climatic side-effects [81]

Comparison to existing abatement measures

Conventional emission control (450 to 550 ppm CO2 by 2100)−2 to −5200$US 940 B/year (2020–2035) $US 1280 B/year (2030–2035)Time period for comparison; based on annual share of GDP (0.5 to 1 percent); simulation resultsSide-effects associated with nuclear power, CCS, and biofuel production[2, 6]

Detailed derivation of estimates can be found in [25].