You are correct that it is already too late to prevent global warming. It's been happening to some degree since we started farming rice. OTOH, a mild global warming has been advantageous. Without it we'd be entering an ice age. The ramped-up-on-steroids global warming that we've been pushing since the start of the industrial revolution, however, is something else again. We don't know just how bad it's going to get, but I do know that the actual projections have had the higher ends trimmed to avoid political repercussions. (Were the lower ends also trimmed? If so I haven't heard so.) Some of the model results that were excluded actually DO have Antarctica melting, and not just around the edges. Well, that's a lot worse than the mean projections, but the mean projection is that its going to be more than the 2 degrees Celsius that people talk about, probably closer to 4 degrees. That's nearly 8 degrees Fahrenheit. And that's going to mean LOTS of ice melting, and lots of deserts where there used to be farmland. It means that Canada will probably become good farmland...if it can get enough water. Oh, yes. It also means that the temperatures are going to get so high that we can't rely on any of the current models, because wind and ocean currents will shift too much. So we can't be sure where it's going to be wet, where it's going to be dry, or how wet or how dry.
My personal expectation (I'm no specialist, and a bit of a pessimist) is that we'll see over a meter sea level rise before the end of the century. Please note that this is not more extreme than some of the models predict, as some of them talk about 10's of meters, though I'm not sure of the timeline for that. I'm sort of expecting the Tethy's sea to form again for the first time since the Jurassic, but it would be a pretty shallow sea, I'm guessing less than a meter deep in most places...but how deep, of course, depends on the actual rise in sea levels. Maybe some genetic engineer will recreate the pleasiasaur to swim in it.