How the Gulf Stream works
Britain is much warmer than other countries on the same latitude,
and this is partly due to the Gulf Stream - a current of warm water
that flows from the Gulf of Mexico past the shores of western Britain.
It is part of a larger system of ocean currents (with a hundred times
the flow of the Amazon) often called the 'conveyor belt'. The engine
that drives this conveyor is in the Arctic; surface sea water there is
cooled by bitter winds, becomes denser, sinks to the bottom of the
ocean and flows south - the return current of warm surface water is
the Gulf Stream. But this sinking process can be disrupted when fresh
water overlays the salty ocean water - fresh water from rain, rivers
or melting ice; an increase in fresh water could slow down or even
switch off the Gulf Stream. If it did, a 'what-if' experiment with the
Hadley Centre computer model shows that the UK would cool by up to 5
°C, and it could happen quickly - in a matter of a decade or two. If
it did happen, the disruption to society would be enormous. But will
What could happen?
The Gulf Stream has switched off before, at the end of the last ice
age about 13,000 years ago, when meltwater from a huge glacier in
Canada flowed into the North Atlantic and stopped the sinking
mechanism - Europe cooled by several degrees in only one or two
decades. Richard Wood and his team at the Hadley Centre used their
complex climate model to look at the effect on the Gulf Stream of
future climate change, caused by the greenhouse effect as carbon
dioxide is emitted in ever-increasing quantities. What they found was
that, yes, the Gulf Stream did slow down - by about 20% by the middle
of the century - but it didn't completely switch off. And the cooling
effect on Britain of the decreased flow was more than offset by the
How sure are we?
But don't relax completely yet; this might be the prediction from
the Hadley Centre's model (and from other climate models), but there
is an enormous amount we don't understand about the earth's climate
system, and the oceans in particular, so we need to make sure this
reassuring prediction is a robust one. And some recent measurements
from research ships in the Arctic seem to indicate that changes are
already taking place which could call the model predictions into
question. So research continues apace to gain a better understanding
of processes in the oceans that could affect the conveyor belt.
Scene from the Hollywood blockbuster, 'The Day After Tomorrow'
And the chances?
Although we estimate that the chances of a 'Big Chill' in the
next hundred years has a low probability, we don't know how low,
and if it happened it would have a very high impact. We need to
understand more about the vulnerability of the Gulf Stream, to
make sure that this climate disaster remains the fiction of a
Hollywood movie and doesn't become a reality.
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