JD
it seems quite plausible that the new complex GCM that the author (and chris) believes are more accurate, that bifurcation is an artifact and that a rapid collapse will not occur...
Interesting discussion on the ‘model’. From an ‘engineer’s’ perspective (i.e. from one with a little practical sense combined with just enough scientific knowledge to be opinionated and annoying) I am reminded that there are many systems which can flick from mellow to Boolean (on/off, good / bad , +5 volts / -5 volts) even tho the components are not obviously inclined to such abrupt outcomes.
If one has detected a number of quasi-cyclic functions (variance in insolation, inclination of the planet’s orbit, the North Atlantic Oscillation, the Chinese share market [an important determinant of global GHG and particulates], sand storms from the Sahara et al) then as you throw those into the model pot you could see the output representing an oscilloscope chart of noise from a student party, until you throw in the last function and the whole thing goes straight-line high or low on you and you say ‘Wow how did that happen?!’.
Likewise, if you have found something like a square wave (we have ice/ we have no ice) you need to remember that situation can be readily derived from a mess of cyclic functions, which you can only detect by the meticulous (indeed the omniscient) deconstruction of the inputs.
In climate modelling we have a swarm of functions including the usual Knowns, Known Unknowns and of course the Unknown Unknowns. It is/ will be very hard to guess whether the function which could tip the output from one state to another is going to be the rhythmic chest-thumping of the gorilla in the room, the faintest flappering of one of Jim Hansen’s Monarch butterflies, or a 'Honk!' from a black swan.
My point is that you can mess with models in the most well-intentioned ways, but still be hopelessly wide of the truth. I know of many models which usually give plausible answers while using internal methods which are just plain wrong. And likewise I am sure there are models which are very correct in their internal functions which never get near the ‘truth’ in their outputs because they lack some key ingredient which is required to turn warm winds and gentle waves into catastrophe.
In particular I do not think that it is at all 'safe' to say '...bifurcation is an artefact and that a rapid collapse will not occur..' when in fact the complexity of your model is such that the potential end result of the sum of all the driving elements diverges exponentially from any cursory target by the power of the number of variables.
But keep up the good work, take care, and don’t take it all too seriously!