In 1995, 10 argentine soldiers witnessed a cataclysm that no other humans have ever seen, one that has since altered our understanding of climate change.
The men were stationed at Matienzo Base, a dreary cluster of steel huts that sat atop a wedge of volcanic rock jutting from the sea, 50 kilometers off the coast of Antarctica. The island was surrounded by a plain of glacial ice covering 1,500 square kilometers—25 times the area of Manhattan. Although the ice shelf floated on the sea, it was 200 meters thick—as solid as bedrock. Yet Captain Juan Pedro Brückner sensed that something was wrong. Meltwater had formed ponds that dotted the ice. He could hear a gurgling sound as the water seeped down into a network of descending cracks. Day and night, Brückner's men heard deep convulsions that sounded like subway trains passing underneath their beds. The rumbles grew more and more frequent.
Then one day, while the crew ate lunch inside one of the huts, they were blasted by a boom—“calamitously loud, like a volcano blowing up,” Brückner recalls. They ran outside. The ice shelf bordering their little island was breaking apart. The upheaval was so violent they feared the fracturing ice would tear the island from its foundation and roll it like a log into the ocean. They placed instruments by their feet to warn them if the ground started to tip. After a few tense days the men were evacuated by helicopter to another station 200 kilometers north. The island held, but the map had changed for good.
Brückner and his colleagues had witnessed the collapse of the Larsen A ice shelf, a signature event. All told, as warm summers have reached farther down from the bottom of South America into the northernmost section of the Antarctic Peninsula, four ice shelves on the eastern side of the peninsula, including Larsen A, have collapsed in a striking pattern from the northern tip southward toward the Antarctic mainland.
Once a shelf disappears, towering glaciers that had piled up behind it in fjords along the sea's edge are free to slide into the ocean. And slide they do, adding substantial volume to the sea. Scientists still do not know what triggers the breakup of an ice shelf or when future ones will occur, so they struggle to estimate how quickly glaciers will dump their ice into the ocean and therefore how much sea level will rise. Although the landmark 2007 report by the Intergovernmental Panel on Climate Change (IPCC) estimated that sea level will rise by just 18 to 59 centimeters by 2100, glaciologists worry that increasingly quick climate change could accelerate glacier melt 10-fold, thus pushing sea level much higher than anticipated. The ice shelf breakups might just provide that feedback.
The Antarctic Peninsula holds only a small fraction of the continent's ice, but it is “a natural laboratory,” says Theodore Scambos, a glaciologist at the National Snow and Ice Data Center in Boulder, Colo. “It's the trailer for the movie that's going to unfold over the rest of Antarctica for the next 50 to 100 years.”
Understanding this natural experiment has become an urgent priority. Scientists need to know how fast the ice shelves are disintegrating and what is causing the demise so that they can better estimate future sea-level rise. “Time and again, the models are conservative, and they're underestimating the magnitude of change,” says Robert DeConto, an ice sheet modeler at the University of Massachusetts Amherst. “We're sitting on our hands waiting for data.” Researchers on recent expeditions to the frozen continent have planted instruments that are giving scientists the information they need, and the latest projections from those data are alarming.
A Hard Bounce Off Iceberg UK211
The first documented disappearance of an Antarctic ice shelf occurred around 25 years ago. The Larsen Inlet ice shelf, a 350-square-kilometer slab north of Larsen A, was present in a satellite photograph taken in 1986, but by the time another image was made in 1988, most of it was missing. No one had any sense of how it might have vanished.