The energy is stored as "gas hydrates", huge amounts of methane gas trapped by water molecules at the superhigh pressures found on the deep ocean sea-bed. The United States, Japan and India are rushing to exploit this energy store, which has been known about for decades but whose potential has only recently been understood.
"There's the equivalent energy there of all the [fossil fuel] that has ever been used and will be used," Dr Ben Clennell, of the School of Earth Sciences at the Leeds University, told the conference. "But it's unstable: gas hydrates only form at a particular regime of high pressure, of more than 50 atmospheres, and temperatures below 25C. If the seas warmed or their level fell then the hydrates will melt to produce water and give off their gas."
The sea-bed methane has taken thousands of years to form, mostly produced by bacteria that have eaten organic matter dafter it fell to the sea- bed, Dr Clennell explained. The gas then becomes trapped within "cages" of water molecules to form ice-like crystals. One cubic centimetre of gas hydrate holds up to 60cc of methane.
But once released into the atmosphere, methane traps 10 times as much heat as the same volume of carbon dioxide - making it a dangerous source of global warming.
Other risks posed by sea-bed gas hydrates come from geological evidence. One example shows that about 7,000 years ago, so much gas was released by a landslip along 600 miles of the ocean floor north of Europe that it caused a tidal wave that washed over the Shetlands. There is also "a lot of circumstantial evidence" that the release of gas led to atmospheric warming at the same time, Dr Clennell said. "It's a fuel of the future, but there are other dangers," he said.
Extraction methods being investigated now by the US and Japan include drilling into the muddy sea-bed and sucking up the contents, which would release the gas.
The idea was condemned, however, by the environmental pressure group Greenpeace. "Our view is that we have already found more conventional fossil fuels than we can afford to burn," said its energy campaigner, Matthew Spencer. "The US's pursuit of this shows that its energy policy is heading in the opposite direction from its commitment at Kyoto to reduce fossil fuel emissions."
t The Gulf Stream - the warm water current that flows between the Gulf of Mexico and the north-eastern Atlantic - provides the UK and Europe with heating equivalent to 30,000 times more energy than the total output of all Britain's power stations, according to new measurements by the Southampton Oceanography Centre. A similar cool stream flows south from between the Shetlands and Faeroes. But it travels so slowly that it takes 30 years to reach Brazil, where the water is warmed again.