By STEVE CONNOR
A cataclysmic change in the world's climate occurred when undersea volcanoes released stupendous amounts of greenhouse gases about 55 million years ago, scientists have found.
The researchers warn that the dramatic climate change during this period could be a model for a similar disaster in the coming centuries as a result of man-made global warming.
The earth 55 million years ago was already a warmer place than it is now when it suddenly became much warmer - by between 5C and 10C - for some unknown reason.
Henrik Svensen and his colleagues from the University of Oslo in Norway believe they have found the cause of the sudden release of greenhouse gases into the atmosphere which caused global surface temperatures to soar.
They have identified thousands of volcanic vents under the Atlantic Ocean which they believe erupted 55 million years ago and in the process disturbed massive amounts of methane gas buried under the sea.
In a study published in the journal Nature they say that the vents caused the melting of solid deposits of methane which released carbon dioxide into the atmosphere and caused a dramatic increase in the amount of solar heat trapped by the atmosphere.
It is known that vast quantities of methane are still trapped under the sea in the form of a semi-solid substance called gas hydrates. These are individual molecules of methane surrounded by a "cage" of water molecules which behave like ice.
Although these methane deposits represent a huge untapped reservoir of potential energy they are known to be highly unstable and their sudden melting could trigger a runaway greenhouse effect.
This is what happened 55 million years ago when the volcanic vents under the Atlantic Ocean released at least 1500 billion tonnes of carbon in a geological instant - triggering one of the hottest periods in the history of life on Earth.
Gerald Dickens, an earth scientist from Rice University in Houston, Texas, said that this past event should be studied more, given that it is estimated that man-made emissions of carbon over the coming centuries amount to between 3000 billion and 4000 billion tonnes.