In either case human made GHG are emitted with the potential to induce a run-away effect, which would magnify any natural trend to global warming.
Energyspin I think that this is slightly misleading, yes it is possible based on models that positive feedback could result in the runaway effects you speak of......what is somewhat irksome is that no one seems to be willing to address the potential for negative feedback which could result in the exact opposite effect....global cooling (eg. melting glaciers creates additional water vapor creates clouds blocks sunlight cools earth). We have to remember that the so-called butterfly effect can make systems change in either direction.
Point being the whole feedback argument is based on extremely poorly constrained models....if you can't define parameters for each and every one of the variables then it is pretty hard to predict with any certainty what will happen.
And again your facts on CO2 are incorrect....yes overall CO2 levels have increased by the percentage you mention. However anthropogenic CO2 accounts for only ~3% of the overall CO2 in the atmosphere (and overall CO2 accounts for only ~3% of greenhouse gases).....something else is going on as well to elevate these levels.