We’re already at 1 degree, and because of lags in the climate system we’ve already put enough CO2 in the atmosphere to bring us to 1.25 even if we stopped all emissions right now. If we were to turn around on a dime and emissions fell just as fast as they went up, that would mean we would be at the halfway point now, in terms of co2. Then the final value would be 540 ppm; almost one doubling. So, 2.75 degrees of warming or so.
Even that feels like a pretty optimistic scenario to me though. It’s more likely that it plateaus for a while before declining. So then we might end up 670ppm. That’s 1.25 doublings. That’s about 3.75 degrees.
I’d guess that we’ll land somewhere between those two, closer to the 3.75 degrees side.
Edit: corrected a math error