So the Gulf Stream conveyor could stop in a few years after the arctic ice and greenland glaciers melt?  Evidently yes, as this recently retrieved Greenland ice core data shows.

A global thermostat?  To counteract warming..

What about the southern ocean conveyors?  Around antarctica?  Would that throw the southern pacific rim into a glacial state as well?  Evidently yes, as this recenty realized historical data shows.

So why worry about human caused GHG?  Because these changes will be too fast for most of humanity and many other species to adapt to.  The ice is melting a lot faster than previously thought, repeating the rapidity of these worst case warming events. 

What could be a more catastrophic weather condition than massive flooding and storm surge followed by glacial conditions overtaking large population centers like NYC?