How many of you have watched the movie "The Day After" with Dennis Quaid? There were model scenarios that I studied years ago in college (pre computer) that indicated a possible return to an "ice age" IF the amount of fresh water exiting the eastern seaboard of Canada, in particular, the St. Lawrence Seaway, were to increase dramatically, it would likely cut off the cold, salty current (the "thermohaline current") that sinks to the bottom, returns to the equator, warms, rises, and generates the Gulf Stream. It would NOT happen as quickly in that movie (obviously) but between the St. Lawrence and Greenland, it is possible that the Gulf Stream could be broken.
Without the warmth the GS brings to the North Atlantic, Iceland would really become "ice land", Ireland, Scotland, the UK, and the Scandinavian countries would be more like Siberia.
It's like a clockwork mechanism - remove one gear and the minute and second hand will keep moving but the hour hand stops. Remove tw gears and the clock is likely to stop.