Get your woolly scarves and jumpers out, the warming Gulf Stream may be slowing down. New research suggests that the flow of cold deep water from the North Atlantic has decreased by 20 per cent, a change that could hold back the Gulf Stream and make things chilly for us.
A research team from the Faroese Fisheries Laboratory, the FRS Marine Laboratory in Aberdeen, and the Bjerknes Centre for Climate Research and Geophysical Institute in Bergen studied one of the key "overflow" routes taken by the returning water. The flow has been reduced by a fifth since 1950, the scientists report in the journal Nature.
The warm, salty waters of the Gulf Stream flow up from the Caribbean, bringing with them a supply of heat that helps moderate northwest Europe's climate.
This shallow stream gradually cools and sinks, descending in a complex network of ocean currents. These chill the water and then recycle it, sending it back in an "overflow" from the North Atlantic on a number of routes between Greenland and Norway.
One of the key pathways is the "Faroe Bank Channel," a kilometre-deep groove in the seabed between the Faroes and northern Scotland. This pathway handles about a third of all the cold returning waters that replace the Gulf Stream and other currents.
The scientists cited earlier work that showed this overflow had become warmer and less salty, factors that can disturb the depth and speed of ocean currents. They took direct measurements in the Faroe Bank Channel and compared these with historical hydrographical data.
The team calculated that the Faroe overflow was carrying 20 per cent less water than it did 40 years ago, adding that this estimate was most likely "conservative". This, they believe, means the North Atlantic "inflow" from the Gulf Stream must also be slowing unless other return routes are making up the difference. They point out that so far they have found "no evidence" the other routes are doing this.
"A reduced overflow can therefore be expected to lead to a reduced Atlantic inflow of a similar magnitude," the authors say. This does not augur well for the Gulf Stream, which could become backed-up with nowhere to go.
The researchers believe the finger of blame for the disruption points to global warming caused by the build-up of greenhouse gases in the atmosphere. Yet even as other places warm up because of global warming, our part of the world would probably cool down.
"The heat transported by the Atlantic inflow gives rise to the exceptionally mild climate of north-western Europe, and a reduction of the inflow will have a regional cooling effect that counteracts the global warming trend," the authors write.
Unfortunately we might not have long to wait before we see whether this theory holds water. "As yet, direct flux measurements of the Atlantic inflow are of too short duration to establish long-term trends," the authors write. "Reports of cooling and freshening in the Norwegian Sea and of decreasing air temperatures in some of the regions most affected by the inflow could perhaps be partly explained by a reduced inflow."