The Gulf Stream has stopped before

One of the likely outcomes of global warming is that the Gulf Stream could stop, thereby dropping temperatures in Britain and Scandinavia. This thermohaline circulation would be shutdown by glaciers melting and thereby desalinating the ocean.

Researchers now claim that they have proof that when the glacial Lake Agassiz burst some 8000 years ago and dumped its fresh waters into the North Atlantic, the circulation of the Atlantic was shut down. Temperatures in Greenland fell by 8C at this time.