I have no blessed idea - the sooner the better - or the sooner the
less terrible for us and the rest of life on the planet.
There is a lot of "momentum" in this; through feedback/amplifying effects, etc. If we completely stop all carbon output right now, we'd get another 0.5-1C rise (on top of the ~0.8C we have already had).
We probably have 5-8 years to turn things around - 10 years on the outside, if we want to avoid 3-4C rise; let alone 2-3C. If we go another 20-30 years without major carbon cuts, then we'll likely see 4-5C. If we hit ~6C then we get hydrogen sulphide; a deadly poisonous gas, coming out of the ocean. Go
here to read about what sorts of things happen at increasing temperatures.
If we speed past 450ppm, then all bets are off.