In the northern region of the North Atlantic the water cools and sinks, deep water is formed, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into the North Pacific. Density differences between seawater determine the 'strength' of the 'conveyor belt' circulation. A change in these density differences as a result of climate change could lead to a 'weakening' or even a stagnation of this ocean current. Stagnation would result in a climate in northwestern Europe such as that of Labrador and Siberia, with more than 6 months of snow cover every year.
Climate models indicate an increase of precipitation at higher latitudes.
As a result of such a freshwater injection the conveyor could stop within100 to 300 years from now. The total shutdown of the conveyor will probably take less then 10 years after 100 to 300 years from now. Ice core records indicate that past cessation in the conveyor belt resulted in a drop of 7 degrees Celsius. Since Broecker's 1996, work, a number of modelling groups have indeed found a decrease in the strength of the conveyor circulation with greenhouse gas forcing, resulting in a cooling of the North Atlantic Ocean. This sinking at higher latitudes diminishes and the strength of the conveyor circulation could decrease.