But we don't have to wait centuries to see this unfold. In West Antarctica's Amundsen Sea, it's happening already. There, rapid ice loss to climate change has been declared "unstoppable". No one lives at this hostile place far below the South Pacific. There are no national bases built along its forbidding coast. No country even thought it worthwhile to claim the ice-covered land behind. Increasingly though, scientists are paying closer attention to this region, which is the size of Iraq. They probe its margins in summer, and pore over satellite images of a 417,000-square kilometre drainage basin of grounded ice. They have found the glaciers running out of it are picking up speed, as their ocean-facing fronts melt and break up.

The overall loss of ice from the Antarctic ice sheet is contested. A NASA report this month challenged the Intergovernmental Panel on Climate Change's conclusion that Antarctica is losing 147 billion tonnes a year, suggesting instead it may have slightly gained overall. Even so, NASA report author Jay Zwally​ says losses from the West Antarctic sheet will likely outweigh East Antarctic gains in a couple of decades. His colleague, Eric Rignot, says of the key Amundsen Sea sector: "The collapse of this sector of West Antarctica appears to be unstoppable ... At this point, the end of this sector appears to be inevitable." What's happened? As with an ice block in a glass of water, Antarctica's floating ice shelves don't increase sea level when they melt.

But just as extra ice blocks will make a glass overflow, as blocking ice shelves are lost the door is opened for the glaciers and ice sheets behind them to run into the sea. The loss of an ice shelf was starkly illustrated when what was known as the Larsen B shelf fell apart on the Antarctic Peninsula in 2002. Within a month, 3250 square kilometres of it was lost. Recent work by the Woods Hole Oceanographic Institution in the US projected the melting of the surface of Antarctica's ice shelves would double by 2050, increasing their instability. The runaway loss of the Amundsen Sea glaciers show us what can happen with these shelves gone. Rignot's study in the journal Geophysical Research Letters examined Amundsen Sea sector "grounding lines". These are the points where glaciers leave the land to float and melt. His team examined satellite radar observations from 1992 to 2011 using a technique called interferometry, which can measure the slightest shifts in the Earth's surface.

They looked for the telltale rise and fall of glaciers' surfaces, as tides pushed underneath and ebbed away. They found widespread rapid grounding line retreat in the Amundsen Sea's four main glacier systems. The ice was being eaten away from below. "The most spectacular retreat is a 34 to 37-kilometre migration at the centre of the Smith/Kohler glaciers," Rignot said. "A 500-square kilometre region ungrounded from the bed in 1992-2011." This means that, for two decades, sea water had been forcing itself further between the ground and the ice at an average pace of about five metres every day. A similar retreat of 31 kilometres was found at the centre of the larger Pine Island Glacier, while the Thwaites Glacier (below) fell back 18 kilometres.

To understand why this is happening, look to the sky. Under human-induced climate change, winds in West Antarctica and the Antarctic Peninsula have been strengthening, and shifting further south. The air has warmed and so has the region's sub-surface coastal waters, according to work by the University of New South Wales' Paul Spence. "Anthropogenically-induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines, and at the base of floating ice shelves around Antarctica," Spence concluded in a paper for Geophysical Research Letters. What does this mean for the Amundsen Sea?

People working in Antarctica deal all the time with the "A-Factor". This is the grim knowledge that, because of Antarctica's remoteness, great scale and hostility, when something goes wrong, it's always magnified. The Amundsen Sea glaciers' plight is the "A-Factor" writ large. Not only is the ocean there warming significantly, it's flooding ground that already lies mainly below sea level. NASA says the loss of all the land-bound ice in this basin would raise the sea level by 1.2 metres. British ice sheet modeller Stephen Cornford has computed forecast changes in the Amundsen Sea in dramatic detail, and found that over centuries every major ice stream would retreat hundreds of kilometres. Children born today will be alive in 2100, when under the worst of his projections, West Antarctic Ice Sheet melt alone would increase global sea level by 20 centimetres.