Once again, Antarctica’s in trouble. New research reveals that if our greenhouse gas emissions continue to escape into the atmosphere unchecked, the southern continent’s Totten Glacier will retreat inland at an accelerated rate, pushing up sea levels by around 2 meters (6.6 feet) in the next few centuries.

According to a new Nature study, should the front of the glacier retreat reach roughly 150 kilometers (93 miles) from its current position, it will enter an irreversible state wherein it will inexorably shrink up to a further 250 kilometers (155 miles) inland, causing a huge influx of meltwater into the ocean. The glacier, part of the East Antarctic Ice Sheet (EAIS), is colossal: It’s roughly the area of Spain, and if the entire thing melted, it would cause 3.9 meters (12.8 feet) of sea level rise.

“The evidence coming together is painting a picture of East Antarctica being much more vulnerable to a warming environment than we thought,” Professor Martin Siegert, co-author of the paper and a glaciologist at Imperial College London, said in a statement. “This is something we should worry about.”

^{The Totten Glacier. Esmee van Wijk/Australia Antarctic Division}

Rooted deep below sea level, much like the glaciers in West Antarctica, Totten is exposed to increasingly warm seawater, which has been undercutting its base for some time now. A previous study indicated that there is a 5-kilometer-wide (3.1-mile-wide) valley beneath it, which is providing corrosive seawater the perfect path to its freshly exposed base.

As is always the case, consistently warming sea surface temperatures will cause ice masses to retreat. However, the bedrock underneath the ice has a huge influence on how the ice collapses, with certain “unstable” configurations causing it to retreat faster by permitting warmer water to flood in, or by encouraging the glacial base to flow faster by dipping at a steep angle.

For this study, the international team of researchers decided to use airborne geophysical surveying techniques to peer through the ice and look at the sedimentary rocks hiding beneath the glacier. In order to see how the glacier will respond to climate change in the future, they wished to use its geological record to see how it behaved to fluctuating temperatures in the past.

By mapping out the erosion-encouraging zones of bedrock, the researchers could confidently say at what points Totten’s erosion would begin to accelerate. As it turns out, there is a dangerous sloping zone in the glacier’s current mid-region that, if reached, would force the glacier to suddenly retreat back to a more stable position further inland.

^{The glacier’s catchment area as seen from above. Australian Antarctic Division}

The last time Totten retreated further back from this point was during the Pliocene epoch, about 3.5 million years ago. Back then, atmospheric carbon dioxide levels were at 400 parts per million, which is about where they are now.

“The atmosphere [back then] was a couple of degrees warmer than it is now, which is in line with what we expect for the end of this century if we do nothing about it,” Siegert told BBC News. If man-made climate change continues unabated, “the Pliocene is where we're headed," and the point of no return for the glacier's retreat is getting closer every day.

Although it would take several centuries for this major retreat to occur, it all eventually adds up: By 2500, the continued melting of the Antarctic land ice will cause a remarkable 15 meters (49 feet) in global sea level rise, enough to engulf large coastal cities across the world.