Miles of Antarctica's ice sheet collapsing into sea

Scientists fear disintegration caused by global warming could be unstoppable

(VichoT/iStock)

Engines droned as a military cargo plane sliced through the frigid air, making straight for the world’s largest chunk of floating ice.

In the belly of the plane, an engineer with a shock of white hair directed younger scientists as they threw switches. Gravity metres jumped to life. Radar pulses and laser beams fired toward the ice. On computer screens, in ghostly traces of data, the surface of the Ross Ice Shelf began to yield secrets hiding beneath.

Antarctica, an immense, frozen land, is hiding many of them. And some scientists are starting to think that nothing less than the fate of human civilization may hang on unravelling those mysteries.

Many people regard Antarctica as unchanging. But the ice moves from the land to the sea, billions of tonnes every year, and has done so for eons. Today the ice in parts of Antarctica seems to be accelerating. Some glaciers have been destabilised by warmer ocean waters. Scientists fear that parts of the ice sheet may be in the early stages of an unstoppable disintegration.

Because the breakup of parts of the ice sheet could raise the sea level by many feet, the continued existence of vulnerable cities near the world’s coastlines could depend on what happens here.

“We’re 9,000 miles from New York,” said the white-haired engineer, Nicholas Frearson, a leader of a Columbia University team that was studying Antarctica late last year. “But we are connected by the ocean.”

A rapid deterioration of Antarctica might, in the worst case, cause the sea to rise so fast that tens of millions of coastal refugees would have to flee inland, potentially straining societies to the breaking point. Climate scientists once regarded that scenario as fit only for disaster films. Now they cannot rule it out.

Yet as they try to determine how serious the situation is, they confront a frustrating lack of information.

Recent computer forecasts suggest that if greenhouse emissions continue at a high level, parts of Antarctica could break up rapidly, causing the sea to rise six feet or more by the end of this century — twice the maximum increase that an international climate panel projected four years ago. But the computer forecasts were deemed crude even by the researchers who created them. “We could be decades too fast, or decades too slow,” said one, Robert M. DeConto of the University of Massachusetts, Amherst.

Alarmed by signs that parts of the ice sheet are destabilising, the National Science Foundation in Washington and the Natural Environment Research Council in Britain 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.

It is a race against time to produce clearer forecasts about the consequences of emissions. Columbia scientists have spent the past two Antarctic summers flying over the Ross Ice Shelf, which helps to slow the flow of land ice into the sea. Computer forecasts suggest that it may be vulnerable to collapse in the next few decades. The project to map the shelf’s structure and depth, funded by taxpayers through the National Science Foundation, puts Columbia and its partner institutions on the front lines of one of the world’s most urgent scientific and political problems.

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 risk is clear: Even a partial collapse of the ice has the potential to inundate coastal cities across the globe.

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 2 miles 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 more than 160 feet — 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.

Improbable as such a large rise might sound, something similar may have already happened, and recently enough to be lodged in collective memory. In the 19th century, ethnographers realised that virtually every old civilization had some kind of flood myth.

In the Epic of Gilgamesh, waters so overwhelm the mortals that the gods grow frightened, too. 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 every living creature on his ark.

“I don’t think the biblical deluge is just a fairy tale,” said Terence J. Hughes, a retired glaciologist. “I think some kind of major flood happened all over the world, and it left an indelible imprint on the collective memory of mankind that got preserved in these stories.”

That flooding would have occurred at the end of the last ice age. Ice ages occur when wobbles in Earth’s orbit change the distribution of sunlight, allowing huge ice sheets to build up. At the peak of the last ice age, about 50,000 years ago, the ice sheets grew so large and locked up so much water that the sea level fell by an estimated 400 feet.

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 100 miles.

Human civilization did not yet exist, but early societies of hunters and gatherers living along the world’s shorelines would have watched the inundation claim their lands.

Remnants of that ice age remain. A little bit of ice still clings to mountains, but the main survivors are the two great ice sheets covering Greenland and Antarctica.

Scientists once thought that further destruction of those ice sheets was likely to take thousands of years. But, starting in the 1970s, some warned that the ice sheets could be vulnerable much sooner if greenhouse emissions were not checked. A scientist at Ohio State University, John H. Mercer, pointed in particular to the western part of Antarctica.

Because the West Antarctic ice sheet sits in a giant bowl, much of it below sea level, it is fundamentally unstable and vulnerable to ocean warming. Extensive satellite monitoring began in the 1990s and, within a decade, evidence emerged that the ice sheet was speeding up, retreating and destabilising. 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 DeConto of the University of Massachusetts and David Pollard of Pennsylvania State University raised alarms worldwide. Incorporating advances in the understanding of how ice sheets might break apart, they 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 as much as 6 feet by the end of this century, and that the pace could pick up dramatically in the 22nd century. They do not claim that this is a certainty — they acknowledge that their analysis is still rough — but they argue that the possibility should be taken seriously.

When the seas rushed inland thousands of years ago, human communities were small, primitive and presumably able to move with relative ease. Today, the world population is seven billion and growing, and hundreds of millions of people and trillions of dollars of property are within a few feet of sea level.

If the rise turns out to be as rapid as some project, it could lead to a catastrophe without parallel in the history of civilization.

Some scientists point out that during the last ice age, ice sheets similar to West Antarctica’s formed in other ocean basins. But as the ice age ended and the oceans warmed, all of them collapsed. These experts have started to think that West Antarctica, as a fragile holdover, is basically a disaster waiting to happen — and that if human-caused global warming has not already set the calamity in motion, it may soon do so.

“We could have a substantial retreat on a time scale of 10 years,” said Robert A. Bindschadler, a retired Nasa climate scientist who spent decades working in Antarctica. “It would not surprise me at all.”

From the air, the Ross Ice Shelf looks like a vast white plain extending to the horizon. Only at its edge does it become something more dramatic: a spectacular sheer cliff rising from the sea, with icebergs calving away.

Scientists are racing to understand what is happening to the 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, and to fathom how damaging warming seas and changing wind patterns might ultimately prove to be.

The answers carry profound implications. In the scientists’ worst-case computer 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 10-15 feet, though most scientists think that would take well over a century. They are worried about a possible rise of as much as six feet by the end of this century.

Whether these alarming 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. “What are the sort of hidden roads it can go on?” said Robin E. Bell, head of the Columbia University laboratory that surveyed the ice shelf late last year.

A different undersea topography — high ridges of rock, for example — might keep warmer water out, stabilising the ice sheet.

As they flew back and forth across the ice in December, the Columbia team used some of the world’s most sophisticated geophysical instruments to peer beneath the surface.

Kirsty J. Tinto, the scientist leading the field team, loved watching the measurements strip away the illusion that the ice was just a boring pancake. “You take a slice through it and you can see a thousand years of history, a hundred million years of history,” she said.

Though the shelf appears stable for now, satellite evidence suggests that other parts of West Antarctica are starting to deteriorate. Many scientists think that relatively warm ocean water is the culprit. “It’s kind of a blow torch on the underside of the ice shelf,” said Bindschadler, the retired Nasa scientist.

But the warmer water attacking the ice has not been linked to global warming — at least not directly. The winds around the continent seem to be strengthening, stirring the ocean and bringing up a layer of warmer water that has most likely been there for centuries.

Are those stronger winds tied to human-caused global warming?

“We’re not sure because we don’t have enough data, for long enough, to separate signal from noise,” said Eric J. Steig, a scientist at the University of Washington.

Though the role of global warming is unclear, it is likely to be a factor in the relatively near future. Many experts think that warmer air temperatures will start to weaken West Antarctica from above, even 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 parts of the continent, far from American and British research bases. Working together, the two countries plan to devote tens of millions of dollars to answering some of the urgent questions. For instance, scientists need to know a lot more about the ground beneath the glaciers. Is it slick mud that may allow the ice to flow much faster, or hard rock that could slow down the ice even in a warmer world?

“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 the research effort.

Also, gaining a better understanding of how Antarctica’s ice has waxed and waned in the past may offer a rough guide to the changes that human-caused global warming could wreak.

During a natural warm period about 120,000 years ago, for instance, the sea level rose 20-30 feet compared with today, implying that the ice sheets in both Greenland and Antarctica may be sensitive to slight global warming.

But some research suggests that a catastrophe might not yet be inevitable. In their study last year, DeConto and Pollard found that aggressive emission cuts might well stabilise Antarctica for centuries.

“There’s still a chance that all hell will break loose,” DeConto said. “But the model is suggesting there’s a way to reduce the risk.”

Copyright The New York Times