The powerful ocean current that bathes Britain and northern
Europe in warm waters from the tropics has weakened dramatically in recent years, a consequence of global warming that could
trigger more severe winters and cooler summers across the region, scientists warn today. Researchers on a scientific expedition
in the Atlantic Ocean measured
the strength of the current between Africa and the east coast of America and found
that the circulation has slowed by 30% since a previous expedition 12 years ago.
which drives the Gulf Stream, delivers the equivalent of 1m power stations-worth of energy to
northern Europe, propping up temperatures by 10C in some regions. The researchers found that the circulation
has weakened by 6m tonnes of water a second. Previous expeditions to check the current flow in 1957, 1981 and 1992 found only
minor changes in its strength, although a slowing was picked up in a further expedition in 1998. The decline prompted the
scientists to set up a £4.8m network of moored instruments in the Atlantic to monitor changes in the
current continuously. The network should also answer the pressing question of whether the significant weakening of the current
is a short-term variation, or part of a more devastating long-term slowing of the flow.
If the current
remains as weak as it is, temperatures in Britain are likely
to drop by an average of 1C in the next decade, according to Harry Bryden at the National Oceanography Centre in Southampton who led
the study. "Models show that if it shuts down completely, 20 years later, the temperature is 4C to 6C degrees cooler over
the UK and north-western Europe," Dr Bryden
said. Although climate records suggest that the current has ground to a halt
in the distant past, the prospect of it shutting down entirely within the century are extremely low, according to climate
is essentially a huge oceanic conveyor belt that transports heat from equatorial regions towards the Arctic circle. Warm surface
water coming up from the tropics gives off heat as it moves north until eventually, it cools so much in northern waters that
it sinks and circulates back to the south. There it warms again, rises and heads back north. The constant sinking in the north
and rising in the south drives the conveyor. Global warming weakens the circulation
because increased meltwater from Greenland and the Arctic icesheets along with greater river run-off
from Russia pour into the northern Atlantic and make
it less saline which in turn makes it harder for the cooler water to sink, in effect slowing down the engine that drives the
measured the strength of the current at a latitude of 25 degrees N and found that the volume of cold, deep water returning
south had dropped by 30%. At the same time, they measured a 30% increase in the amount of surface water peeling off early
from the main northward current, suggesting far less was continuing up to Britain and the
rest of Europe. The report appears in the journal Nature today.
of the conveyor-belt current was the basis of the film The Day After Tomorrow, which depicted a world thrown into chaos by
a sudden and dramatic drop in temperatures. That scenario was dismissed by researchers as fantasy, because climate models
suggest that the current is unlikely to slow so suddenly.
of the National Oceanographic Centre said: "The most realistic part of the film is where the climatologists are talking to
the politicians and the politicians are saying 'we can't do anything about it'."
director of the UK climate impacts programme at Oxford University's centre
for the environment, said: "The only way computer models have managed to simulate an entire shutdown of the current is to
magic into existence millions of tonnes of fresh water and dump it in the Atlantic. It's not
clear where that water could ever come from, even taking into account increased Greenland melting."
in climate change models mean that the overall impact on Britain of a slowing
down in the current are hard to pin down. "We know that if the current slows down, it will lead to a drop in temperatures
in Britain and northern Europe of a few
degrees, but the effect isn't even over the seasons. Most of the cooling would be in the winter, so the biggest impact would
be much colder winters," said Tim Osborn, of the University of East Anglia climatic
research unit. The final impact of any cooling effect will depend on whether it outweighs the global warming that, paradoxically,
is driving it. According to climate modellers, the drop in temperature caused by a slowing of the Atlantic current will, in
the long term, be swamped by a more general warming of the atmosphere. "If this
was happening in the absence of generally increasing temperatures, I would be concerned," said Dr Smith. Any cooling driven
by a weakening of the Atlantic current would probably only slow warming rather than cancel it out all together. Even if a
slowdown in the current put the brakes on warming over Britain and parts
of Europe, the impact would be felt more extremely elsewhere, he said.