Sometimes you'll hear the claim that humans are responsible for only 4% of CO2 emissions into the atmosphere. You can get that number from the diagram by comparing human emissions (9 GtC/year) to all others: 9/(60+60+9+90)=0.04. Is this the correct way to think about it? No. 
Prior to human activity, natural sources of carbon to the atmosphere were balanced by natural sinks of carbon from the atmosphere (60+60+90-120-90=0). Since the industrial revolution, humans have introduced a new source of carbon to the atmosphere.
That new source has been partially compensated for by land and ocean uptake (3 GtC/year on land and 2 GtC/year into the ocean). But what's leftover stays in the atmosphere and accumulates year and year after year.
Because the human source is not fully compensated for by land and ocean sinks, humans are responsible for well over 100% of the increase in atmospheric carbon since the industrial revolution. This becomes obvious when you look at how atm CO2 concentrations spiked since the 1800s.
