Don't give up so quickly. Where there's a will there's a way. I am not saying that it is likely going to be pleasant (as indicated above), but I don't think it's the right thing to just call this unsolvable. It's certainly a huge project, maybe the biggest mankind ever faced, but still we need to tackle it, right?

Having said that, I believe you are right that reducing CO2 output is most likely not going to cut it anymore (if that is even possible at all). But there might be other ways to slowly reduce the carbon levels in the atmosphere.

Whether it's possible to do something short term (effective within decades), yes, I also highly doubt that.