Prague, 1 December 2005 (RFE/RL) – Scientists caution that it’s still too early to draw definitive conclusions.
But initial findings show that the strength of a key North Atlantic Ocean current between Africa and the east coast of America has slowed by 30 percent in just the past 12 years. And that could have a serious impact on Europe’s climate.
At present, much of the weather in coastal North America and northern Europe is kept mild thanks to the effects of a current known as the Gulf Stream, which originates in the Gulf of Mexico and travels all the way to northern Norway.
The Gulf Stream is just one part of what scientists call the "great ocean conveyor belt." This natural underwater phenomenon is also known as the "thermohaline" conveyor belt -- derived from the Greek words for heat and salt. It stretches all through the North and South Atlantic into the Indian and Pacific oceans -- maintaining a constant rapid flow of currents that have a moderating effect on the global climate.
These circular currents are driven by the salinity of the ocean water. According to Chris West, director of Oxford University’s Environmental Change Institute, if the ocean water becomes less saline for some reason, the currents slow down.
"This big global ocean circulation which brings warm water from the tropics up towards Europe is actually driven by water becoming very cold and sinking off Labrador and Greenland," West said. "And that getting very cold and sinking because of its density could be stopped if that water was very much less saline. So if a lot of fresh water was mixed with it, it would never get dense enough to sink and to drive this whole global process. So sometimes it's called a ‘thermohaline conveyor belt.’ It is driven by heat and the salt content of the water."
Researchers believe the salinity of the North Atlantic may be decreasing because of the melting of the polar ice caps caused by global warming. As the glaciers melt, especially off the coast of northern Canada and Greenland, millions of tons of freshwater get mixed in with the ocean water.
Scientists will have to make many more measurements in different locations to find out whether the great ocean conveyor belt is really slowing down and if it is, whether global warming is the main culprit.
But Stuart Cunningham, of Britain’s National Oceanography Center, which came up with the latest data, said there is reason for concern. "We were very surprised to see these changes since '92 -- so really in the last 12 years or so," he said. "The [overall] measurements go back to the late '50s. We don't really have enough information to know if it's part of the natural variability or if it's a long-term trend that could mean a really significant impact for European climate."
Cunningham illustrates just how significant the impact would be if the ocean conveyor belt were to stop suddenly: "We know there's good evidence in the paleoclimate records -- ice core records and so on -- that during the last Ice Age, this overturning circulation had in fact stopped. And we know that large parts of western Europe and North America were covered in glaciers and that really was a function of the lack of heat being brought northwards in the ocean."
Chris West at Oxford thinks that is unlikely. He doesn’t believe enough fresh water will be pumped into the ocean to cause such a catastrophe. "The obvious sources [of fresh water] are the rivers that flow from Asia and North America into the Arctic Ocean and it's possible the flow of those could increase," he said. "We know that Greenland is melting faster now than it has done for many thousands of years. But even together, those two sources of fresh water don't seem to be enough to switch off the circulation."
But both scientists say that right now, they still have more questions than answers. Nothing is ruled out and one thing appears certain: global climate change will have a more varied and unpredictable impact than anyone could have ever predicted.