We are talking about something like 100 parts per million increase in C02 over the last century of burning fossil fuels... That 100 ppm sits on top the natural CO2 in the atmosphere and really only represents a few percent of what is there naturally. Yes it's up, but we are discussing a dynamic system that deals with CO2 naturally, and as you point out it's effectively dealing with the bulk of the extra we put out. One would *expect* the concentration to increase a lot more, given what we are pumping into the air. The system will achieve steady state again, likely with a higher CO2 concentration than we see in the past records, but not above what the Earth has survived before, even if we burned every last scrap of fossil fuels we could find in one day.
We are having an effect, but how much can an extra 100 parts per million actually do? It's seriously nearly nothing, both in the amount of carbon following though the cycle each year and the net affect it can possibly have. I know some folks are totally freaked out over this, but when you look at the grand scheme of things and realize the really small of a fraction this really is of our atmosphere and start looking at the scales on all those alarming graphs and charts with the red arrows going straight up, it's not really all that likely to be a problem. Certainly it's not a problem you can hobble your economy and national security in a vain effort to fix but I digress.