| If the ocean currents that transport warmth
up from the Gulf Stream were ever to slow down or to shut down
completely, the climate in Britain would be considerably colder
- similar in fact to that of Moscow, which is on the same latitude.
This event is known as Rapid Climate Change.
Scientists believe that Rapid Climate Change has happened
before, about 13,000 years ago. A period of warming caused
a massive ice sheet across the top of North America to melt
which flushed huge quantities of fresh water into the North
Atlantic Ocean. This flow of fresh water upset the process
of thermohaline circulation and the Gulf Stream current shut
down. Within 10 to 20 years of this happening, ocean temperatures
around Britain had dropped by an average of 10 degrees C.
Sea ice reached as far south as 45oN - which is well beyond
the UK's south coast. This mini-ice age lasted for 1200 years
and is called the Younger Dryas Cooling.
It is impossible to say whether our present period of warming
could cause the same thing to happen again. There isn't a
North American ice sheet to melt any more, but climate change
is causing ice caps to melt at both poles. The action of the
fresh water from these ice caps entering the North Atlantic
sea from Greenland and Russia could slow down the circulation
of the ocean currents. This is something Britain and Norway
are taking very seriously and carrying out a great deal of
research into.
Surface and deep currents in the ocean combine to form what
is known as the thermohaline circulation, more simply the
'great conveyor belt', which helps transport heat from the
equator towards the poles.
The sea between Greenland, Iceland and Northern Norway is
the main northern hemisphere region where surface water sinks
into the deep, completing the three dimensional loop of ocean
currents. The sinking is a result of relatively small changes
in the density of seawater, its salinity and its temperature.
Any changes to this delicate balance, for example an increase
of warmer 'fresher' water provided by river and ice melt,
could have the potential of changing the rate of flow and
direction of the Great Conveyor Belt. |
