From the dawn of time, people have suspected powerful forces lurking deep in the oceans ‚ from the Greeks' fearsome sea-god Neptune to John Wyndham's submarine aliens in his 1950s novel The Kraken Wakes
. But science is once again going one better than science fiction. Researchers are discovering that hidden 'rivers' run through the oceans, and these powerful currents hold the destiny of our planet's climate. The beneficial aspects of ocean currents have long been known. For countries on the east side of the Atlantic, winters are a balmy holiday compared with the same latitudes on the west: the frigid coasts of Newfoundland and Labrador. It's a reminder that "weather" is not just a matter of the Sun's heat affecting the Earth's atmosphere. The world's interconnected oceans can store up solar heat in one part of the globe in one season, and invisible rivers in the ocean can transport the warmth thousands of kilometres to another part of the globe and deliver it in another season. In the case of the North Atlantic, heat is carried northward and eastward by the Gulf Stream. This current warms the coast evenly through the year, in winter as well as summer. Averaged over a year, the Gulf Stream provides Western Europe with a third as much warmth as the Sun does. This ocean warmth is so important to Europe that climatologists are seriously concerned about the stability of the Gulf Stream. If it switched off, Europe would be plunged into a mini-Ice Age. And current studies suggest that the unseen river in the North Atlantic is dangerously fickle. The focus of today's worries is the problem of global warming - the way that human activities are changing the climate, as the world gets warmer through the build-up of so-called greenhouse gases, such as carbon dioxide. Climatologists think that global warming may put the brakes on the Gulf Stream. While the rest of the world comes to swelter in greenhouse conditions, Europe would freeze! This concern is based on a new understanding of how the great ocean currents are all interconnected. The Gulf Stream is part of a giant pattern of moving water that stretches right around the globe. The Ocean Conveyor Belt
The warm water that is so important to Europe actually comes from the other side of the world, in the Pacific Ocean. This tepid stream, flowing unseen through the oceans, is the longest river in the world.
It flows along the surface, both because it is warm (and warm water, like warm air, rises) and because it is less salty ‚ and so less dense - than the deeper water. The warm waters travel westward from the central Pacific, past the north coast of Australia and round the southern tip of Africa before moving up into the Atlantic.
This great ocean river becomes the Gulf Stream by the time it heads up through the North Atlantic. But as the current surges past Europe, its nature begins to change. It cools down significantly as it gives up its precious heat to the European seaboard. And, all along its long journey, the warmth of this invisible river has encouraged water to evaporate from its surface layer, so it becomes increasingly salty. Around the latitude of Iceland, the moving stream becomes so dense that it sinks into the depths. This stream now becomes a cold river, flowing back along the ocean floor. Rounding the south of Africa and Australia, it returns to the Pacific, where it is pushed to the surface and warms to complete the cycle. The whole effect is like a conveyor belt bringing Pacific warmth to the North Atlantic. The ocean conveyor belt has run more or less smoothly since the end of the last Ice Age. But global warming may now throw a spanner into its workings. The planet is undoubtedly warming up, even if people still argue about how much of this is due to human activities, and the extra heat is melting ice in the Arctic Ocean. The ice turns into fresh water, which flows into the salty North Atlantic. The danger is that this fresh water might dilutey current of the Gulf Stream so much that it stops sinking down into the ocean depths near Iceland. If the Gulf Stream does stop, there will be nothing pushing the deep cold river at the bottom of the North Atlantic. As the Atlantic portion of the ocean conveyor belt grinds to a halt, then Europe could indeed freeze ‚ ironically, as a direct result of global warming.