London could be among the "first cities to go" if global warming causes the planet's ice to melt, the UK government's chief scientific adviser has warned.
Increasing carbon dioxide levels could cause floods
The Guardian quotes Sir David King as saying the levels of the greenhouse gas carbon dioxide are higher now than they have been for many millions of years.
He said ice was melting faster and, if the trend continued, floods could wipe out London, New York and New Orleans.
Sir David has previously called for flood defences to be fortified.
His latest warning came at the launch of a scientific expedition to Cape Farewell in the Arctic, which is aimed at raising student awareness of climate change.
The expedition will also examine ocean currents, in particular the Gulf Stream, which may be affected by excess fresh water from melting ice.
"You might think it not wise, since we are currently melting ice so fast, to have built our big cities on the edge of the sea where it is now obvious they cannot remain," he said.
"On current trends, cities like London, New York and New Orleans will be among the first to go."
Sir David said the sea would rise six or seven metres if the Greenland ice cap melted and a further 110 metres if Antarctica melted.
He said ice fields on Mount Kilimanjaro in Tanzania were now expected to melt within the next three to four decades, despite having existed for hundreds of thousands of years.
Samples taken from Antarctic ice cores, he said, had shown carbon dioxide levels in the atmosphere during glacial periods were approximately 200 parts per million (ppm) and increased to about 270ppm in warm periods.
Now levels have reached 379ppm and are increasing at a rate of 2ppm a year.
Sir David said these levels were probably not much lower than they were 55 million years ago, when there was no ice on the planet.
Sir David's comments have been supported by Friends of the Earth campaigns director Mike Childs.
"Sir David King's warning should be a wake-up call to governments across the globe to stop prevaricating on climate change and instead take action to achieve year on year cuts in the amount of greenhouse gas pollution we are releasing," he said.
"Cuts of around 3% a year are needed and possible, but sadly we have seen no real cuts in carbon dioxide emissions since Tony Blair became prime minister in 1997."
Environment Secretary Margaret Beckett also called for increased international action, at the Green Alliance on Tuesday.
"Above all, we also need to demonstrate that countries do not have to choose between their environmental and economic aspirations, to forfeit one or the other, but that these aspirations can not only be compatible but mutually reinforcing."
Sir David has recently been in Moscow where he was encouraging the Russians to ratify the Kyoto Protocol.
He will also be visiting China and Japan.