CO2 Storage, it's possible, but what about
It is possible and there are several demonstration projects running. In Europe, the carbfix project quotes a price of $24.8/ton for carbon sequestration. Geothermal power is used to pump the CO2 underground, so no energy from fossil fuel is required. 

There are concerns about the available capacity for storage using these mechanisms, and the pumping process does trigger seismic activity (e.g. wikipedia).

It is likely that carbon buried in geological formations will be sequestered more reliably and for longer that carbon which is simply absorbed by trees ... but there is no guarantee on that there will not be some leakage.

Because of these concerns, and because generating electricity from sustainable sources is cheaper than burning fossil fuels and then trying to manage the pollution, the main focus of dealing with global warming should be reduction of fossil fuel use to near zero.

There may well still be a significant role for carbon sequestration in dealing with some CO2 emissions which are difficult to avoid.