(That's the
North Atlantic Thermohaline Conveyer, baby!)
It breaks down from
warm conditions. Increased polar ice melt dilutes the currents, which can not hold together if the salinity falls below a certain point. So the oceanic heat can't be mixed, meaning hotter tropical conditions and colder polar ones.
If it's breaking down
now, we can expect very odd weather this year, including an increase in drought conditions as well as more (and more intense) hurricanes, since the oceanic heat will accumulate toward the equator.
Then, next autumn, it will get colder earlier than normal in Europe, and the winter will probably be the most severe in a century or more. It will be a bad winter in North America, but the real blow will arrive in the following winter.
We could also expect to see very strange weather phenomena, especially very powerful thunderstorms in cold and Arctic regions, including "snow tornados", which the Western Inuit peoples called "Dancers". Such storms have only been seen on a handful of occasions; "thundersnow" is much more common, and Delaware got some thundersnow in the snowstorm last week.
Art Bell and Whitley Strieber wrote a semi-fictional book about this, called
The Coming Global Superstorm, which is being made into a disaster movie this summer,
The Day After Tomorrow. It's a shame that Bell and Strieber have so little scientific credibility, because the book is actually pretty good for popular scientific writing. Strieber's interwoven fiction is excellent, no matter how you feel about his UFO experiences.
It's also possible that the problem will go away soon, since these conditions were getting started back in the late 1950s, too. However, the current climate changes are far more intense than they were 40 years ago, and the Earth is now warmer than it's been in over 3 million years. I personally have been convinced
since 1978 that the next ice age is starting, mainly on the strength of the
early work done on the subject -- yes, it's that strong a case. The sad thing is that, even though it's a natural phenomenon we are powerless to change, we have accelerated its arrival by hundreds if not thousands of years.
Well, that's my quasi-scientific rant.
--bkl
Edited for movie link and cool picture of NYC on ice.