I think it's more accurate to say that there is something close to a consensus that this is one of the reasonable/possible scenarios, especially since there is good evidence of just such a sudden and dramatic shift happening before.

I've been reading about this particular prospect for a few years now, having first been introduced to it by William Calvin in this 1998 piece from The Atlantic Magazine.

http://www.theatlantic.com/issues/98jan/climate.htm

It's an excellent introduction.

For those of you who want a lot of a little more, here is an outstanding page of related links from the folks at the Woods Hole Oceanographic Institution:

http://www.whoi.edu/institutes/occi/currenttopics/ct_abruptclimate.htm