If the West Antarctic Ice Sheet (WAIS) collapsed, global sea level would likely rise between 11 and 16 feet. Such an enormous increase would cripple the planet, considering a 3-foot rise in ocean level is predicted to flood 861,000 square miles of land and affect 145 million people.

So, what are the chances that one of the world's largest ice sheets will buckle catastrophically? According to a new study in the journal Global Change Biology, they are better than scientists ever thought.

Using the distribution of tiny marine organisms called Bryozoans (shown to the left), scientists discovered evidence for a surprisingly recent collapse in the WAIS.

"We compared similarity of faunas expecting it to be highest between adjacent regions," explained David Barnes of the British Antarctic Survey. "We found this to be true with a big exception — a very strong similarity between the distant Weddell and Ross Seas."

Currently, the Weddell Sea and Ross Sea are around 1,500 miles apart and separated by a 2 kilometer (1.2 mile)-thick block of ice.

Barnes and his colleagues hypothesize that perhaps as recently as 125,000 years ago, when temperatures were warmer and sea level was around 16 feet higher than today, sections of this great wall of ice came crumbling down. A sea pathway opened up (as shown in the graphic below) between the two seas and now-separated marine species mingled freely.

Previous geological studies have demonstrated that the WAIS collapsed sometime in the past 1.1 million years. Thanks to this new biological data, Barnes and his team have narrowed that window, with grave implications for the future.

A relatively recent collapse implies that the WAIS is "less stable than previously thought and may be the least stable of the three major ice masses (Greenland and East Antarctic being the other two)," Barnes said. 

The next step involves determining where the past collapses occurred and how much ice loss was needed to render the ice sheet critically unstable. Barnes and his team suspect that a channel did not open up directly between the Ross and Weddell Seas. Instead, ice melted at different points that connect both seas with the more centrally located Amundsen Sea. 

As global temperatures rise and the world's glaciers continue to melt at unprecedented rates, time is of the essence when it comes to understanding the past. Especially since, as Barnes explained, "two glaciers (Pine Island and Thwaites) in the Amundsen Sea are the fastest thinning ice sheets in the world."

Images: British Antarctic Survey