The perspective of direct air capture of atmospheric carbon dioxide

Removing CO2 from the atmosphere by DAC, and then geologically storing it, or recycling it to renewable hydrogen-based fuels, is here discussed. The energy inputs for the capture of the atmospheric CO2 at the present concentration is ~45 GJ t−1 of C, 4.28 times the energy produced by burning the best coal generating the captured CO2. Accounting for non-uniformities of atmospheric CO2 concentration and pointwise capture, the energy cost is larger, as the atmospheric CO2 concentration close to the DAC machines will reach values below the preindustrial level when the global average will be above. DAC as a way to control global concentrations of atmospheric CO2 is questionable, making this solution unattractive.