Global warming of +10C is ====>!!NOT!!<==== a reasonable expectation (erratum et apologia)

[GliderGuider]

38. The biggest unknown in all this is

What happens when we hit about +2 to +3 or so. Not to the weather - we know that's going to go to shit - but how we decide to respond. We don't have to wait for +4 or +6 for things to grab out attention, 2 or 3 will do that well enough. That will probably happen around 2040 or 2050. Unfortunately if we hit +2 we'll still have another 3 in the pipeline, that will only manifest in the following 30 years.

This is the problem - by the time we decide to react and stop all further fossil fuel use, we still have at least half the eventual warming still to come. Take out current situation: we have +0.8C visible, and everybody assumes there is another half-degree or so to come. But if we all stood still and held our breath right now, it will probably go up to +2 over the coming few decades. The hysteresis is the killer - it makes everything we do too late by a bunch of decades.