> It doesn't need to happen in every area. It just needs to happen in enough areas that the carbon output is brought below a threshold that the environment can safely absorb.

That is actually a misconception. There is no such threshold, at least not for carbon dioxide (it's a bit more complicated for methane and some other greenhouse gases). It accumulates in the atmosphere.

There is some uptake of co2 by natural processes, but that's roughly relative to the amount you put in. If you put in more co2 the concentration of co2 in the atmosphere will keep growing.