'Doomsday Glacier' the size of UK so unstable its collapse could swallow cities

A massive glacier the size of Great Britain could trigger a catastrophic rise in sea levels if it collapses putting cities across the world at risk of being completely flooded, scientists have warned.

Thwaites Glacier, located in West Antarctica, is one of the largest and most unstable glaciers in the world. It's around 75 miles wide, and covers an area of approximately 74,000 square miles, making it similar in size to the mainland UK, or the US state of Florida. Among climate experts, it's picked up the the ominous nickname of the "Doomsday Glacier" due to major risks it poses to human civilisation in the event of a collapse.

The impact would be enough to raise global sea levels by approximately 65cm, enough to flood large areas of major world cities such as London, New York, and Bangkok, and leave many low-lying countries completely uninhabitable. If neighbouring glaciers collapse too, the total sea level rise could exceed 10 feet over the centuries - totally wiping out many of the world's most populated urban centres.

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Fears are growing over the impact of warm ocean currents flowing with increasing intensity beneath the floating ice shelf of Thwaites glacier, which are causing it to become unstable and 'retreat' to a smaller area.

A recent study found that these 'hidden lakes' underneath the glacier are having a much greater destabilising effect than previously thought, with one sudden outflow in 2013 seeing a volume of water equivalent to Loch Ness rush into the sea.

Professor Noel Gourmelen, lead author of the study and member of the International Thwaites Glacier Collaboration group, said: “We expected that water draining from the underside of the ice sheet plays a role in modulating ocean melting, the sheer magnitude of this lake drainage gave us the opportunity to finally observe and quantify its impact.

“The lake outflow took place in a key sector impacting Thwaites’ stability, the drainage in effect momentarily turbo-charged Thwaites’ ocean-driven retreat."

Thwaites is now spilling ice at more than twice the rate recorded in the 1990s - and scientists worry it may not be able to recover any time soon. An exceptionally warm summer in the southern hemisphere earlier this year is believed to have accelerated the problem.

Dr Alastair Graham of the University of South Florida toldNews.com.au: "If Thwaites Glacier collapses it would cause a rise of around 65cm (25 inches) in sea level.

"This year is really different. It’s very difficult to recover from this in one season. The game has changed."

It's thought that within the next few years we could begin to see parts of the ice shelf break apart, likely speeding up the flow and causing more ice to fall into the ocean.

This could also have a knock-on effect on neighbouring glaciers in the Antarctic, setting in motion a mass collapse that would cause further sea levels rises over the decades and centuries ahead.

Scientists say how quickly it and other glaciers in the region collapse depends on how much the world is able to bring down greenhouse gas emissions and limit global warming.