The record shows that CO2 concentration follow changes in temperature. So I would feel perfectly confident predicting that if temperatures keep falling in a few years CO2 will start to fall too.
Human output is about 7% of annual carbon cycle, ~30 gigatons. Still enough to see increase of about 2 ppm/year but may have slight drop from ocean uptake. Good point though.
The natural annual cycle is more or less balanced. The same CO2 that is absorbed by northern hemisphere vegetation in spring is released in the fall minus what is stored in woody mass and soil (relatively small considering how much forest we still chop down worldwide). The net effect is this:
The fluctuation is natural. The year over year rise is manmade.