It's very possible that some of it just doesn't get absorbed. It's kinda like the same way of thinking that classifies a resource as non-renewable. Like fossil fuels are considered nonrenewable, although they are constantly being made. We say they are non-renewable because we are using it up faster than it's replenishing itself. The same works in the atmosphere. The trees are pulling a lot of CO2 out of the air, and the ocean is absorbing a lot too. But more is constantly being added. It isn't like the trees pull out ALL of the carbon dioxide, AND THEN we go and add more. It isn't a turn taking ordeal. So yes the rees an ocean are working, but at any given moment more is being added. So there probably is still a lot just floating around in the atmosphere.