A massive iceberg currently “hanging on by a thread” is poised to break away from the Antarctic shelf. Scientists says it will be one of the top 10 largest ever recorded when it floats off into the ocean off of West Antarctica. Last month a long-running rift in the Larsen C ice shelf suddenly grew without warning. Now just 20km of ice is all that is keeping the 5,000 sq km chunk of ice – a quarter of the size of Wales – from drifting away. BBC News reports that, at about 350m thick, Larsen C is the most northern major ice shelf in Antarctica – and currently holds back the flow of glaciers that feed into it. Now scientists fear all of it will be vulnerable to breaking-up in the future if this piece breaks off. While the iceberg itself will not raise sea levels there are real concerns that if the shelf breaks up further glaciers it is holding back will speed up their passage into the ocean – which would impact sea levels. Best estimates suggest that if all the ice the Larsen C shelf currently holds back was to enter the sea, global sea waters would rise by 10cm. There is an ensuing debate whether the rift is a result of global warming – and directly due to climate change. Researchers from the UK’s Project Midas based in Swansea have been tracking the Larsen C rift for a number of years – and warned last year that it had suddenly grown. It’s causing particular nervousness after scientists observed the collapse of Larsen A ice shelf in 1995 – and then in 2002 the subsequent sudden break-up of the Larsen B shelf which disintegrated spectacularly. Then last month the rift grew rapidly – growing by a whopping 18km in the space of just two weeks. The BBC reports that the massive iceberg “now hangs on to the shelf by a thread of just 20km”. Project leader Professor Adrian Luckman of Swansea University said, “If it doesn’t go in the next few months, I’ll be amazed. There hasn’t been enough cloud-free Landsat images but we’ve managed to combine a pair of Esa Sentinel-1 radar images to notice this extension, and it’s so close to calving that I think it’s inevitable.” Professor Luckman predicts a chunk of around 5,000 sq km will break off – placing it within the top 10 biggest icebergs to have ever been recorded. It’s unclear whether the event is related to climate change – with some experts claiming it must be and others arguing it is rather a geographical phenomenon. Professor Luckman said, “We are convinced, although others are not, that the remaining ice shelf will be less stable than the present one. We would expect in the ensuing months to years further calving events, and maybe an eventual collapse – but it’s a very hard thing to predict and our models say it will be less stable; not that it will immediately collapse or anything like that. The eventual consequences might be the ice shelf collapsing in years to decades. Even the sea level contribution of this area is not on anybody’s radar. It’s just a big geographical event that will change the landscape there.”