UK will be in a deep freeze if the current strays

An armada of robot submarines and marine sensors are to be deployed across the Atlantic, from Florida to the Canary Islands, to provide early warning that the Gulf Stream might be failing, an event that would trigger cataclysmic freezing in Britain for decades.

The £16m system, called Rapid Watch, will use the latest underwater monitoring techniques to check whether cold water pouring south from melting Arctic ice sheets is diverting the current's warm waters away from Britain.

Without the Gulf Stream, the UK would be as cold as Canada in winter. Ports could freeze over and snowstorms and blizzards would paralyse the country. An extreme version of this meteorological mayhem provided the film The Day After Tomorrow with its plotline.

'The Day After Tomorrow suggested the Gulf Stream could fail within a couple of days,' said Rapid Watch's co-ordinator, Meric Srokosz of the Southampton Oceanographic Centre. 'In reality, a collapse will take a lot longer, but could still occur in about 10 years.' Rapid Watch has been designed to discover if such weakening is already occurring or is about to begin.

The Gulf Stream starts in the Gulf of Mexico and follows the eastern US seaboard before crossing the Atlantic towards western Europe. The heat it brings across the Atlantic gives Britain its temperate climate. The former chief scientist, Sir Robert May, once calculated that the Gulf Stream delivered 27,000 times the warmth that all Britain's power stations are capable of supplying.

But scientists have recently warned that the current is threatened by meltwater from Greenland and the Arctic. As global warming takes a grip, glaciers and ice sheets are disappearing faster and faster. This could bring major cooling to western Europe. As the Intergovernmental Panel on Climate Change warned last year, the Gulf Stream is particularly warm and salty, and increasing amounts of fresh water pouring into it from the Arctic are likely to disrupt it.

These fears have been backed by studies involving research vessels that have zig-zagged across the Gulf Stream, measuring currents at various depths, data that indicated that the Gulf Stream was indeed beginning to switch off.

But in 2004, Dr Srokosz - with his Southampton colleagues Professor Harry Bryden and Dr Stuart Cunningham - set up Rapid, a temporary array of sensors fixed to the seabed that provided daily measurements of the Gulf Stream for the first time. The first results, which were published last year, revealed that the Gulf Stream fluctuates in a highly unpredictable fashion.

'The Gulf flows at an average rate of 20 million cubic metres per second,' added Srokosz. 'But this flow varies from as little as four million cubic metres to about 35 million. This means past isolated measurements could be highly misleading.'

As a result, Srokosz has designed Rapid Watch, which has just received £16m from the Natural Environment Research Council. 'Rapid was a proof of concept study,' he said. 'Rapid Watch is a full-scale detection system.' Rapid Watch, which will begin operations later this year, will monitor the Gulf Stream until 2014. Cables will moor monitoring devices to the seabed and measure current flow, temperature and other variables at depths down to 5,000 metres.

In addition, robot probes - called gliders - will study the current as they descend and ascend. 'Robot gliders can currently operate to depths of about 1,000 metres, but soon versions that can dive to 5,000 metres should be ready.

'Certainly, it is critical we now find out how the Gulf Stream is behaving,' added Srokosz. 'It has an immense influence on our climate - and our lives.'