The cycling of water in the North Atlantic ocean has increased in the last decade, possible due to global warming. Kerr (2004) summarizes recent research showing that tropical waters are observed to be warmer and saltier due to increased evaporation, and water at high latitudes has become fresher (less salty). Continuation of this trend could slow or even stop the Gulf Stream's delivery of warm water to the North Atlantic, which would cause substantial cooling to Scandinavia.
Reference
Kerr, R. A., 2004: Sea change in the Atlantic. Science, 303, 35.