The disclosure relates to an activated carbon scrubber apparatus 300 and a method of its operation for carbon dioxide (CO2) removal from a controlled environment. The scrubber apparatus is configured to switch between: an adsorption configuration in which it is configured to provide CO2-rich gas from the controlled environment to a sorbent bed 302 comprising activated carbon for CO2 adsorption, and to return the treated gas to the controlled environment; and a regeneration configuration in which it is configured to provide a regenerating gas from outside of the controlled environment to the sorbent bed to desorb CO2 and regenerate the activated carbon, and to discharge CO2-rich gas outside of the controlled environment. The method comprises alternately operating the scrubber apparatus in the adsorption configuration and the regeneration configuration over a plurality of cycles, wherein the scrubber apparatus is operated at a cycle frequency of between 4 and 30 cycles per hour. A heater 303 is controlled to heat the sorbent bed in the regeneration configuration.