Table 2: Overview of current operational cost estimates and potential side effects for various CDR measures.

MeasurePotentialOperational costs in $US/tCO2Main investment requirementsUncertaintiesSide-effectsSources

Biological-based carbon dioxide removal

Biochar production5 Gt CO2/year45
(15–76)
Bio-char production unitsNet carbon storage potential due to use as energy source; use as fertilizer may reduce costsUse as fertilizer increases net primary production; residuals from pyrolysis process might limit application for food production[3644]

Southern Ocean iron fertilization5 Gt CO2/year45
(8–82)
Iron sulfate production and treatment, ship fleet for spreading (20–500 ships)Necessary amount of iron sulfate; coagulation of iron sulfate; increase in export production; leakage (even though accounted for in the estimate for potential)Impacts on marine biogeochemistry, ecology, and biodiversity; increases nutrient supply for fish stocks, change in oxygen minimum zones, temporary acceleration of oceanic pH value (faster acidification) [2628, 4551]

Afforestation4 Gt CO2/year60
(19–101)
Measurement of carbon uptake and leakage varies between studies; unintended carbon release due to fire, storms; impact on albedoEcological  effects  and  implication for biodiversity; land requirements [6, 5254]

Chemical-based carbon dioxide removal

Spreading pulverized olivine4 Gt CO2/year42
(27–57)
Exploitation,  transport, pulverization,  and  spreading infrastructureAccess to target area (tropical catchment areas of large rivers) for spreadingIncrease in soil and oceanic pH value (reduced ocean acidification); ecological impacts (e.g. input of silicic acid into oceans) [5557]

Spreading pulverized calcium hydroxide1.5 Gt CO2/Gt CaCO350
(45–54)
Exploitation, transport, thermal treatment, storage for separated CO2, fleet for spreading (about 3000 ships)Exploitation and spreading logistics, uptake limited due to ocean circulation, storage of separated CO2CCS-related side-effects; increase in oceanic pH value (reduced ocean acidification) [5860]

Spreading pulverized lime0.3 Gt CO2/Gt CaCO365
(57–72)
Exploitation, transport, pulverization infrastructure, fleet for spreading (between 4000 and 6000 ships)Exploitation and spreading logistics, uptake limited due to ocean circulationIncrease in oceanic pH value (reduced ocean acidification)[59]

Air capture (sodium hydroxide)1.0–1.2 Mt CO2/unit/year250
(69–430)
$US 247–480 M/unitStorage of captured carbon, energy provisionCarbon-Capture-and-Storage- (CCS-) related side-effects [6166]

Comparison to existing abatement measures

Conventional emission control for limitation to 2°C increase by 205021 Gt CO2
(in 2035)
90–120
(in 2035)
$US 940 B/year (2020–2035) $US 1280 B/year (2030–2035)Simulation resultsSide-effects associated with nuclear power, CCS, and biofuel production [2]

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