Increased salinity and decreased temperature both result in the water becoming denser. The denser water sinks and flows south. What does this have to do with global warming? The melting of Arctic ice is adding fresh water to the North Atlantic. This means that the waters at northern latitudes are becoming less dense and therefore less prone to sinking. The result could be a decrease in the rate of flow of the currents. A reduced Gulf Stream flow would have less of a warming effect on western Europe. There have been some predictions that the thermohaline circulation could shut down suddenly, causing a temperature drop of about 8°C (14°F) in western Europe in a matter of a few decades. Most climatologists think this is very unlikely. However, there could be a slowing of the circulation resulting in some cooling effect. But since global temperature is rising, the net effect may be that western Europe stays the same, or gets just a bit warmer. Since climate is very complicated, it is difficult to make accurate predictions. Specific tendencies are known, but how they interact with each other is less certain.
What Can We Expect?
The world's climate system is complicated. It is difficult to make precise predictions. But the future trends are becoming increasingly clear: rising sea levels, more frequent and more intense storms, and increased drought in many already dry parts of the world.