The Gulf Stream is a warm surface ocean current which originates in the Gulf of Mexico and flows northeast across the Atlantic, driven by the prevailing southwest winds. It influences the climate of the UK and Northwest Europe by bringing with it humid mild air.
Sometimes, the term "Gulf Stream" is restricted to describe the ocean current that travels past the east coast of the United States towards Newfoundland. The North Atlantic Drift forms the extension to the Gulf Stream which flows past the south coast of Labrador towards the west coast of Europe.
Within the Gulf of Mexico, the Gulf Stream is very narrow, only 50 miles wide, and travels very fast at 3 mph, carrying water at about 25C. The North Atlantic Drift widens considerably to several hundred miles, slows to less than 1 mph and splits into several sub-currents.
The Gulf Stream is one of the strongest currents known anywhere in the world. Without the warm Gulf Stream, the UK and other places in Europe would be as cold as Canada, at the same latitude.
The warm waters of the Gulf Stream lose a lot of moisture through evaporation, making the sea particularly salty. In the North Atlantic, the heavy salt water becomes cold enough to sink, forming a deep ocean current called the North Atlantic Deep Water (NADW). The NADW acts as a pulling mechanism on the Gulf Stream, maintaining the direction and intensity of the ocean current, and keeping the climate of the UK and Northwest Europe mild. Scientists have shown that thousands of years ago the NADW shut down in response to subtle shifts in global climate. This slowed and diverted the course of the Gulf Stream to such as extent that the regional climate of the Northeast Atlantic became considerably cooler. It is now suspected that global warming may trigger a shutdown in the NADW, and a slowing or diversion of the Gulf Stream, which would ironically lead to colder climates throughout the UK and Northwest Europe.