My response to his wondering is as follows :
There are a number of things one could do to impact on the concentration of CO2 in the atmosphere.
One is to couple carbon capture and storage (CCS) technology with biomass. This enables you to remove CO2 from the air (using a plant) and capture CO2 (by burning the plant in a CCS ... er ... plant). This has been discussed. It requires you to be able to produce, in a sustainable manner, a lot of biomass.
Cquestrate have a rather novel method, which doesn't act on the atmosphere directly, but rather on the ocean. You can contribute to the development of this idea, since it is open source.
Cquestrate and AFS both require one to be able to generate a very large amount of energy in a way that does not emit large amounts of CO2.