The Atlantic current that gives western Europe its mild climate is dramatically slowing, and Britain, Ireland and parts of the European continent could be plunged into bitter winters a decade or so from now, scientists say.
The Atlantic current that gives western Europe its mild climate is dramatically slowing, and Britain, Ireland and parts of the European continent could be plunged into bitter winters a decade or so from now, scientists say.
A Changing Atlantic Current Might Put The Chills On Western Europe
by Richard Ingham
http://www.terradaily.com/news/oceans-05zd.html
The Atlantic current that gives western Europe its mild climate is dramatically slowing, and Britain, Ireland and parts of the European continent could be plunged into bitter winters a decade or so from now, scientists say.
Their research provides the first backing for fears that global warming may brake the conveyor belt of ocean heat that allows northwestern Europe to have a balmy, if wet, climate even though it lies on the same latitude as northeastern Canada.
The conveyor belt is a spur: it is the branch line from a current system that circulates clockwise around the central Atlantic.
The branch flows northeastwards towards Europe, delivering its heat to the atmosphere as it goes along.
Eventually, by the time the current reaches Norway, its waters have cooled so much that they start to sink. They are then conveyed southwards again, along the coast of the western Atlantic, and are brought back to the tropical system where they are warmed again.
Researchers at the National Oceanography Centre at Britain’s University of Southampton monitored the flow of the main circulatory system in the central Atlantic.
They took a survey ship and travelled along 24 degrees latitude north, a line from the Bahamas to tropical West Africa.
They halted every 50 kilometers (31 miles) to lower instruments to gauge salinity and temperature, which are key indicators to determine ocean flow.
Previous research was conducted along the same line, in 1957, 1981, 1992 and 1998.
What stunned the researchers was the discovery, extrapolated from this data, that the northern spur — Europe’s precious heat conveyor — has slumped by 30 percent in volume since 1998.
The suspected culprit: a massive inrush of freshwater into the northern Atlantic, caused by melting glaciers in Greenland and melting sea ice, and higher flow into the Arctic from Siberian rivers caused by greater rainfall.
All these events, well documented in previous research, are attributable to global warming.
Freshwater is less dense than seawater because it lacks salt. Its influx into the northern Atlantic has been so huge that the overall density of water there has decreased.
This means that the cooler water is less able to sink and return back south.
In other words, the brakes are being applied to the heat conveyor.
“If the conveyor belt continues to slow right down, a drop of 4 C (7.2 F) in the average annual temperature in northwestern Europe could happen,” says Meric Srokosz, a science coordinator at Britain’s Natural Environment Research Council (NERC), which oversaw the research.
“It won’t be an instant thing, like in [the 2004 Hollywood movie] ‘The Day After Tomorrow.’ We’re talking about in a decade or so. And we’re not talking Ice Age, we are talking about more regular, extreme colder weather in winter,” he said in an interview.
As a gauge of severity, Srokosz referred to a notorious winter that gripped much of Europe in 1963, the so-called “Big Freeze.”
He cautioned, though, that there were still many unknowns. Britain, Ireland, northern France, the Lowland countries and Scandinavia could be affected, but it was possible for the chilling effects to reach into Germany and beyond.
Also unclear is how long the braking effect on the conveyor belt would last. Some computer models suggests decades, while others, far more pessimistic, say it could be permanent.
The idea that global warming may cause a big chill may seem strange. On Tuesday, for instance, the European Environment Agency (EAA) said the continent faced higher temperatures and possible desertification in parts of its most southerly countries.
But scientists have long warned that an overall rise in global temperature will mask localised effects, creating hot spots that are higher than the planetary norm and, conversely, cold spots that are chillier than average because their source of warmth is shut down. These local phenomenona may take years to emerge.
The study, which appears in Nature, the British weekly science journal, is lead-authored by Harry Bryden.
It coincides with a meeting in Montreal on the Kyoto Protocol, the UN’s pact to combat man-made global warming caused mainly by the unbridled burning of oil, gas and coal.
These fuels contain carbon that has been buried safely under the Earth for millions of years. Burning releases the carbon into the atmosphere, trapping the Sun’s heat in a so-called greenhouse effect and disrupting the globe’s delicate climate system.
Slowing of the Atlantic meridional overturning circulation at 25° N
Harry L. Bryden, Hannah R. Longworth & Stuart A. Cunningham
http://www.nature.com/nature/journal/v438/n7068/full/nature04385.html
The Atlantic meridional overturning circulation carries warm upper waters into far-northern latitudes and returns cold deep waters southward across the Equator1. Its heat transport makes a substantial contribution to the moderate climate of maritime and continental Europe, and any slowdown in the overturning circulation would have profound implications for climate change. A transatlantic section along latitude 25° N has been used as a baseline for estimating the overturning circulation and associated heat transport2, 3, 4. Here we analyse a new 25° N transatlantic section and compare it with four previous sections taken over the past five decades. The comparison suggests that the Atlantic meridional overturning circulation has slowed by about 30 per cent between 1957 and 2004. Whereas the northward transport in the Gulf Stream across 25° N has remained nearly constant, the slowing is evident both in a 50 per cent larger southward-moving mid-ocean recirculation of thermocline waters, and also in a 50 per cent decrease in the southward transport of lower North Atlantic Deep Water between 3,000 and 5,000 m in depth. In 2004, more of the northward Gulf Stream flow was recirculating back southward in the thermocline within the subtropical gyre, and less was returning southward at depth.