G'day Dan,
It isn't all that easy to stop. It took a huge amount of fresh water to stop it for quite a limited period about 8,000 years ago and even then it seems that it was working again in about eight months. But it did have an impact on Europe for a while. I personally would not want to have been one of the tribes people that had gone to the trouble of having made summer clothes only to find we were stuck with basically very cold conditions for another century or so.
I don't think you can easily compare the records now being gathererd with pretty much anything. They can be compared with each successive year in the future if they keep it going long enough and I hope they do but core samples provide only limited information (and I'm a little confused here - sediment core samples or ice core samples - neither seems to be a good fit for temperature and salinity of the Atlantic in the area of the current recording over the last 100 years).
If the inter-ocean conveyor were to falter then I'd guess we'd have a reglaciation throughout the Northern Hemisphere. I'd be more worried if I lived in Canada or the US than Europe. The conditions in Europe, to some extent and set up to cope with snow and cold but that is not true for much of the US. I'm not sure you could get the conveyor to change in such a way that it stopped warming Europe but continued to work for the rest of the world and heat exchange is necessary somehow so I can't see it stopping. It does not stop during a glaciation or even during a reglaciation so it does not seem to be the trigger for a reglaciation. And I can't see how it could possibly work to cause a deglaciation.
The whole process smacks of "The Day After Tomorrow" and the science was a bit suspect in that movie. It made a good science fiction movie, emphasis on fiction. There is an explanation for the grass chewing woolly mammoth and the sudden extreme freezing that there does seem to be evidence for during the instability going into a reglaciation. It seems that jet streams are not only latitudinally unstable but can be altitudinally unstable during reglaciations. If a jet stream dipped to the point where it touched or gets very close to land, you get very fast air movement with incredibly cold air. Snap freeze! It seems that a jet stream, if it dipped towards the land would do so in the warmest area. That would be a lake. Thus you could get a jet stream ripping off the frozen skin of a lake, vacuuming up a large quantity of water into fine droplets, freezing these in the air and building up a block of ice that would snap freeze anything in its path.
While the hurricane in the South Atlantic is called a cold hurricane it does not act like a hurricane in several vital areas. It certainly does not produce the sinking of super cold air in its centre like they showed in the movie.
I'd be interested if you could explain what you meant by core samples, Dan. Personally I cannot see how they would determine climate in comparison to what this discussion is about. And using sediments or ice cores to determine world climate is a whole other topic.
Regards
Richard
