I am a great one for conquest of the planets, but I am uncertain that you could release enough CO2 on Mars to have the desired effect. I have seen proposals for other, better greenhouse gases, but even if it could be done, who in his right mind would want to colonise Mars? Does anyone suggest that its crust is 50% iridium? As a place to support itself it is the wrong size and in the wrong direction.
The sensible planets to colonise are Mercury and Venus, in that order, which are energy rich and probably mineral rich as well, with excellent agricultural prospects (Well, Venus anyway; Mercury is agriculturally a bit challenging, though there are in fact better options there than anything Mars could offer!) Possibly one could do something useful out in space as well, but before we look into that we have a lot of development to do.
