Sure, if you don't include the word "net". Natural processes account for the majority of CO2 introduced into the atmosphere. They also account for the majority of the CO2 removed from the atmosphere, because there's an equilibrium flow.

The important part is that anthropogenic sources are a significant contribution to the net imbalance of those flows, because it's all in one direction.

It's like arguing that your spending, because is a small fraction of the amount of money you move between your checkings and savings accounts, won't make you run out of money...