But you release it now and reabsorb it in a few years time. The net effect is an increase in the CO2 in the air. It is not carbon neutral.
Its the same with wind power, etc. It isn't carbon neutral.. it only saves CO2 when compared to other methods. Once all electricity is wind/wave/solar it will not /save/ any CO2.
The reality is that you can only save CO2 by not using the energy.
It will take a large scale move to actually removing CO2 before anything is actually carbon neutral.