Across Antarctica, Shifting Ice and Rock
ABOVE THE ROSS SEA, Antarctica — Engines droned as a military cargo plane made straight for the world’s largest chunk of floating ice.
In the belly of the plane, scientists threw switches. Gravity meters jumped to life. Radar pulses and laser beams fired toward the ice. The surface of the Ross Ice Shelf began to yield secrets hiding beneath.
Antarctica, an immense, frozen land, is hiding many mysteries. Some scientists think the fate of civilization may hang on unraveling them.
Antarctica’s ice is not unchanging; it moves from the land to the sea, billions of tons every year, and has done so for eons. But parts of the ice sheet may be in the early stages of disintegration and could raise the sea level by two or more meters, threatening the existence of vulnerable cities near the world’s coastlines. The sea could rise so fast that tens of millions of coastal residents would have to flee inland, straining societies to the breaking point. Climate scientists once regarded that scenario as fit only for disaster films. Now they cannot rule it out.
In Antarctica, the National Science Foundation of the United States and Britain’s Natural Environment Research Council are joining forces to get better measurements in the main trouble spots. The effort could cost over $25 million and take years to yield clearer answers about the fate of the ice.
Remote as Antarctica may seem, everyone who gets in a car, eats a steak or boards a plane contributes to emissions that put the continent at risk. If those emissions go unchecked and the world is allowed to heat up enough, scientists have no doubt that large parts of Antarctica will melt into the sea.
But they do not know the trigger temperature, or whether the acceleration of the ice means that Earth has already reached it. The question, said Richard B. Alley, a scientist at Pennsylvania State University, is easier to ask than to answer: “How hot is too hot?”
More than 60 percent of the freshwater on Earth is locked up in Antarctica’s ice sheets. The ice has been building up for tens of millions of years. Thin layers of snow falling were gradually pressed into ice, burying mountain ranges and building an ice sheet more than three kilometers thick. Under its own weight, that ice flows downhill in slow-moving streams that eventually drop icebergs into the sea.
If the ice sheet were to disintegrate, it could raise the sea level by 50 meters — a potential apocalypse, depending on how fast it happened. Research suggests that if society burns all the fossil fuels known to exist, the collapse of the ice sheet will be inevitable.
Something similar may have already happened. In the 19th century, ethnographers realized that many civilizations had flood myths. In the Epic of Gilgamesh, waters so overwhelm the mortals that the gods grow frightened. In India’s version, Lord Vishnu warns a man to take refuge in a boat, carrying seeds. In the Bible, God orders Noah to carry two of each creature on his ark.
“I think some kind of major flood happened all over the world,” said Terence J. Hughes, a retired glaciologist, “and it left an indelible imprint on the collective memory of mankind that got preserved in these stories.”
That f looding would have occurred at the end of the last ice age. About 50,000 years ago, the ice sheets locked up so much water that the sea level fell by an estimated 120 meters. Perhaps 25,000 years ago, the ice sheets began to melt and the sea level began to rise. Over several thousand years, coastlines receded inland by as much as a 160 kilometers. Early societies living along the world’s shorelines would have watched the inundation.
Remnants of that ice age remain. A bit of ice still clings to mountains, but the main survivors are the two great ice sheets covering Greenland and Antarctica. Starting in the 1970s, some scientists warned that the ice sheets could be vulnerable much sooner than previously expected if greenhouse emissions were not checked.
Because the West Antarctic ice sheet sits in a giant bowl, much of it below sea level, it is vulnerable to ocean warming. Extensive satellite monitoring began in the 1990s and, within a decade, evidence emerged that the ice sheet was retreating and destabilizing. Since then, the rate at which some of the glaciers are dumping ice into the sea has tripled. Over 100 billion tons are lost every year.
A 2016 study by Dr. DeConto and David Pollard of Pennsylvania State University found that both West Antarctica and some parts of East Antarctica were vulnerable to continued global warming. They reported that the sea level could rise nearly two meters by the end of this century, and that the pace could pick up dramatically in the 22nd century.
If the rise turns out to be as rapid as some project, it could lead to a catastrophe without parallel, as hundreds of millions of people and trillions of dollars of property are within a meter of sea level.
Some scientists have started to think that West Antarctica, as a fragile holdover, is a disaster waiting to happen. “We could have a substantial retreat on a time scale of 10 years,” said Robert A. Bindschadler, a retired NASA climate scientist. “It would not surprise me at all.”
Scientists are racing to understand what is happening to the Ross Ice Shelf as the planet warms around it. They are also trying to measure the role of human- caused climate change in weakening other parts of the West Antarctic ice sheet.
In the worst-case simulations, continued global warming causes the Ross Ice Shelf to collapse starting as early as the middle of this century. The shelf works like a bottle-stopper that slows ice trying to flow from the land into the sea. If it disintegrates, the ice could flow into the ocean more rapidly. The most vulnerable parts of the ice sheet could raise the sea level by three to five meters, though most scientists think that would take over a century.
Whether forecasts prove right depends in part on whether the sea floor beneath the Ross Ice Shelf has deep channels that could allow warming ocean water to attack the ice from below. A different undersea topography — high ridges of rock, for example — might keep warmer water out.
Many experts think that warmer air temperatures will start to weaken West Antarctica from above as warmer ocean water attacks it from below. The warmer water seems to be doing the most damage to a series of glaciers that flow into a region called the Amundsen Sea. Satellites have identified the most rapid loss of ice there, raising a critical question: Has an unstoppable collapse already begun? The region is one of the remotest of the continent, far from American and British research bases.
“What we need to know is really the details of what is occurring where the ice, ocean and land all come together,” said Ted A. Scambos, a University of Colorado scientist who is helping to plan research efforts.
Gaining a better understanding of how Antarctica’s ice has waxed and waned in the past may offer a guide to the changes that warming could wreak. During a natural warm period about 120,000 years ago the sea level rose six to nine meters compared with today, implying that the ice sheets in both Greenland and Antarctica may be sensitive to slight warming.
But some research suggests that a catastrophe might not yet be inevitable. In their study last year, Dr. DeConto and Dr. Pollard found that aggressive emission cuts might well stabilize Antarctica for centuries.
“There’s still a chance that all hell will break loose,” Dr. DeConto said. “But the model is suggesting there’s a way to reduce the risk.”