Fortune magazine (no bastion of liberal thinking, mind you) weighs in on the question of abrupt climate change with a tidy little explanation of the potential for the thermohaline circulation to abruptly change:

Scientists still don’t know whether a climate disaster is on the way. But taken together, these changes appear strikingly similar to ones that preceded abrupt climate shifts in the past. Many researchers now believe the salient question about such change is not “Could it happen?” but “When?”

It’s important to note the language here. We’re really tallking about “global climate change”, not “warming”. Big and important difference.