This is an extra page that I’ll use later, but since you’re here:The global circulation of water in the oceans is driven by what happens in the North Atlantic.  The warm-water current known as 

the “Gulf Stream” flows into the North Atlantic where it gradually sheds its heat.  As this salty water cools it becomes more dense so it drops toward the ocean floor.  This pushes cold water along the ocean bottom and creates a sort of vacuum at the top which pulls more warm surface water.  In the diagram the warm surface current is in red and the cold deep current is in blue.  This is often referred to as the “Ocean Conveyor”.

The Ocean Conveyor is slowing down.

Since 1984 the amount of water flowing through the northern part of the Gulf Stream loop has decreased by 20% and is now decreasing at a rate of 2% to 4% per year.

The reason for this is the salinity of the North Atlantic is decreasing.  Salt water is more dense than fresh water, consequently, the less salty the water, the less density it will have when it cools, so the less likely the water will sink when it cools.

The reason for decreased saltiness is fresh water.  Fresh water is coming from the shrinking North Polar Ice Pack and the Greenland Ice Sheet. 

The North Polar Ice Cap is 46% thinner than it was 20 years ago.

Until the 1970s the Greenland Ice Sheet remained unchanged, but now it is disappearing at the rate of 24 cubic miles per year.  This melting is dumping 98 billion tons of extra fresh water into the North Atlantic per year.

The net result of all this fresh water is that the cold-water sinking in the Greenland Sea which contributes to the Ocean Conveyor has stopped.

The prevailing winds in the northern latitudes are from the west, so the warm air above the Gulf Stream is blown onto western Europe.  The heat from the Gulf Stream provides the British Isles with 27,000 times the amount heat compared to all the power plants on those islands put together.  If the Ocean Conveyor stops, the climate of the British Isles and Northern Europe would be the same as Northern Canada and Siberia.  The average temperature in Europe will drop about 18 degrees.   Scientists give this a 50-50 chance of happening before the full heating effects of global warming kick in.

The last time the Conveyor stopped was around 6100 BC when the remnants of the North American glaciers melted into the Atlantic.  It took only  10 years of melting to stop the Conveyor.  This event continued for 100 years until the Conveyor started back up again and it took another 10 years to get everything back to normal.  During those 100 years, however, the average world temperature dropped 9 degrees.

The point to this is that it can take only about 10 years to have a significant global climate change, and it looks like we are in the beginnings of one of those significant changes.