How stable is the Gulf Stream? Could it stop suddenly? I'm not completely clear on what Western intensification means, but it looks like a pretty powerful (combination of) forces that presumably wouldn't be likely to change on a timescale of years (or even decades, centuries).

But I recall reading some time ago that global warming is already known to be causing a significant increase in the amount of fresh (as opposed to salt) water being introduced into the system at the European end. I assume that's "one-time-only" melting of glaciers and snow/ice in areas that were previously permafrost, but for all I know there could be much more simply arising from a (potential) massive increase in precipitation across north-western Europe.

I freely admit I don't know the relative importance of warm/cold salty/fresh water in the thermodynamics of the Gulf Stream system, which is probably relevant. But what I really want to know is...


  Do we understand the Gulf Stream well enough to answer the question posed in my title?
There's a pretty good rundown of this issue over at RealClimate, and a wikipedia article dedicated to the topic.

A summary of the main points from there:


The Gulf Stream is part of the Meridional Overturning Current (global ocean conveyor), which is primarily wind-driven, and secondarily thermohaline-driven. The Gulf Stream itself is also primarily wind-driven.
There has been some reduction of the thermohaline drivers in the north Atlantic, due to increased temperatures, and influxes of fresh water, largely from melting of the Siberian permafrost. This part of the system does fluctuate (as do most parts), but there does appear to be a trend.
These changes are not enough threaten the Gulf Stream, and there hasn't really been any observations of an over-all slow down that couldn't be otherwise explained by natural variation.
It is likely that the Gulf Stream will slow down over the next few centuries (slow downs appear in some of the IPCC models out to 2100).
A complete shut-down is possible (it has happened before, notably during the Younger Dryas), but it is hard to predict, as causes are not very well understood. But it seems unlikely to happen any time soon.