Some phenomenon would have to trigger it, though. For example, if the mass of ice that covers Greenland were to begin melting away, yes, it is plausible that the resulting desalinization of the water in that area of the atlantic could inhibit if not outright halt the heat transfer system that runs through it, thus causing a reversal of the warming trend. Such an event would directly act upon climatic trends worldwide. What you're saying is not necessarily untrue, Xenon, but such a shift in direction would not happen on its own. Furthermore, the event or chain of events that causes the next trend shift could have consequences just as troublesome as the warming trend now in progress, QED. Whatever is happening with this planet, we need to prepare for it. We may even have to take matters into our own hands more frequently than the environmental protection hippies would like.
On a side note, perhaps the ice caps act as a sort of climatic buffer viz melts acting upon the heat transfer system. Has anyone given much thought to this notion?