“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 of a big sea-level rise from Antarctica.”
The New York Times
May 18, 2017
By Justin Gillis
Part 1: Miles of Ice Collapsing Into the Sea
The acceleration is making some scientists fear that Antarctica’s ice sheet may have entered the early stages of an unstoppable disintegration.
Because the collapse of vulnerable parts of the ice sheet could raise the sea level dramatically, the continued existence of the world’s great coastal cities — Miami, New York, Shanghai and many more — is tied to Antarctica’s fate.
Four New York Times journalists joined a Columbia University team in Antarctica late last year to fly across the world’s largest chunk of floating ice in an American military cargo plane loaded with the latest scientific gear.
Inside the cargo hold, an engineer with a shock of white hair directed younger scientists as they threw switches. Gravity meters jumped to life. Radar pulses and laser beams fired toward the ice below.
On computer screens inside the plane, in ghostly traces of data, the broad white surface of the Ross Ice Shelf began to yield the secrets hiding beneath.
“We are 9,000 miles from New York,” said the white-haired engineer, Nicholas Frearson of Columbia. “But we are connected by the ocean.”
A rapid disintegration 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 used to regard that scenario as fit only for Hollywood disaster scripts. But these days, they cannot rule it out with any great confidence.
Yet as they try to determine how serious the situation is, the scientists confront a frustrating lack of information.
Recent computer forecasts suggest that if greenhouse gas emissions continue at a high level, parts of Antarctica could break up rapidly, causing the ocean to rise six feet or more by the end of this century. That is double the maximum increase that an international climate panel projected only four years ago.
But those computer forecasts were described as crude even by the researchers who created them. “We could be decades too fast, or decades too slow,” said one of them, Robert M. DeConto of the University of Massachusetts, Amherst. “There are still some really big question marks about the trajectory of future climate around Antarctica.”
Alarmed by the warning signs that parts of the West Antarctic ice sheet are becoming unstable, American and British scientific agencies are joining forces to get better measurements in the main trouble spots. The effort could cost more than $25 million and might not produce clearer answers about the fate of the ice until the early 2020s.
For scientists working in Antarctica, the situation has become a race against time.
Even as the threat from global warming comes into sharper focus, these scientists understand that political leaders — and cities already feeling the effects of a rising sea — need clearer forecasts about the consequences of emissions. That urgent need for insight has led scientists from Columbia to spend the past two Antarctic summers flying over the Ross Ice Shelf, a floating chunk of ice larger than California.
The Ross shelf helps to slow the flow of land ice from Antarctica into the ocean. Compared with other parts of Antarctica, the shelf seems stable now, but computer forecasts suggest that it might be vulnerable to rapid collapse in the next few decades.
The project to map the structure and depth of the ice shelf in detail, funded by American 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.
“Our goal is to understand how to predict what’s going to happen to the ice sheets,” said Robin E. Bell, the lead Columbia scientist in charge of the effort. “We really don’t know right now.”
Remote as Antarctica may seem, every person in the world who gets into a car, eats a steak or boards an airplane is contributing to the emissions that put the frozen continent at risk. If those emissions continue 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 exactly what the trigger temperature might be, or whether the recent acceleration of the ice means that Earth has already reached it. The question confronting society, said Richard B. Alley, a climate scientist at Pennsylvania State University, is easier to ask than to answer:
“How hot is too hot?”
Part 2: Looming Floods, Threatened Cities
The risk is clear: Antarctica’s collapse has the potential to inundate coastal cities across the globe.
Over tens of millions of years, thin layers of snow falling on the continent — in many places, just a light dusting every year — were pressed into ice, burying mountain ranges and building an ice sheet more than two miles thick. Under its own weight, that ice flows downhill in slow-moving streams that eventually drop icebergs into the sea.
If that ice sheet were to disintegrate, it could raise the level of the sea by more than 160 feet — a potential apocalypse, depending on exactly how fast it happened. Recent research suggests that if society burns all the fossil fuels known to exist, the collapse of the ice sheet will become inevitable.
Improbable as such a large rise might sound, something similar may have already happened, and recently enough that it is still lodged in collective memory.
In the 19th century, ethnographers realized that virtually every old civilization had some kind of flood myth in its literature.
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 University of Maine glaciologist living in South Dakota. “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, mainly in the Northern Hemisphere. At the peak of the last ice age, about 50,000 years ago, the ice sheets grew so large and locked up so much of the world’s water that the sea level fell by an estimated 400 feet.
Beginning perhaps 25,000 years ago, after the orbit shifted again, 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 hundred miles.
Human civilization did not yet exist, but early societies of hunters and gatherers lived along most of the world’s shorelines, and they would have watched the inundation claim their lands.
Remnants of that ice age remain. A little bit 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, lone scientific voices 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.
Extensive satellite monitoring began in the 1990s and, within a decade, evidence emerged that the ice sheet was already starting to speed up, retreat and destabilize. Since then, the rate at which some of the glaciers are dumping ice into the ocean has tripled. More than 100 billion tons are lost every year.
In 2016, Robert M. DeConto of the University of Massachusetts, Amherst, and David Pollard of Pennsylvania State University published a study, based on a computer analysis of Antarctica, that raised alarms worldwide.
Incorporating recent advances in the understanding of how ice sheets might break apart, they found that both West Antarctica and some vulnerable parts of East Antarctica would go into an unstoppable collapse if the Earth continued to warm at a rapid pace.
In their worst-case scenario, the sea level could rise by six feet by the end of this century, and the pace could pick up drastically in the 22nd century. Dr. DeConto and Dr. Pollard 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 still 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 the worst-case projections, it could lead to a catastrophe without parallel in the history of civilization.
The National Science Foundation in Washington and the Natural Environment Research Council in Britain have decided to make a huge push over the next few years to get the data needed to refine the forecasts and get ahead of the alarming changes already occurring in Antarctica.
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.”
https://www.nytimes.com/interactive/2017/05/18/climate/antarctica-ice-melt-climate-change-flood.html
Part 3: Racing to Find Answers in the Ice
From the air, the Ross Ice Shelf looks like a vast white plain extending to the horizon. The monochromatic landscape is relieved only occasionally by rocks poking through, or by deep crevasses in the ice itself.
Only at its edge does the ice shelf become something more dramatic: a spectacular sheer cliff rising 100 feet above the ocean and extending 900 feet below the surface. From that cliff edge, icebergs occasionally calve away, completing a thousand-year journey of the ice from land to sea.
Scientists are racing to understand what is happening to the Ross Ice Shelf — and the rest of Antarctica — as the planet warms around it. They are trying to map the thickness of the ice and the shape of the sea floor beneath it in an effort to gauge how vulnerable the shelf may be to collapse, and how soon that could happen.
Scientists are also trying to measure the role of human-caused climate change in weakening some parts of the West Antarctic ice sheet, and to fathom how damaging the seas around the continent might prove to be as they warm over time.
The answers carry profound implications for humanity. In the scientists’ worst-case computer simulations, continued global warming will cause the Ross Ice Shelf to weaken and collapse starting as early as the middle of this century.
Right now, the shelf works like a giant bottle-stopper that slows down ice trying to flow from the land into the sea. If it collapses, the ice could flow into the ocean more rapidly, an effect that has already happened on a much smaller scale in other areas of Antarctica.
The most vulnerable parts of the West Antarctic ice sheet could raise the sea level by 10 to 15 feet, inundating many of the world’s coastal cities, though most scientists think that would take well over a century, or perhaps longer. They are worried about a possible rise of as much as six feet by the end of this century.
Whether these alarming forecasts ultimately prove right depends in part on the shape of the sea floor beneath the ice shelf, and in particular on whether it has deep channels that can funnel warming ocean water under the ice shelf and attack the West Antarctic ice sheet from below. A different undersea topography — high ridges of rock, for example — may keep warmer water out, stabilizing the ice sheet, possibly for hundreds of years.
“We’re hoping to figure out how warm water can get to the edge of the ice sheet,” said Robin E. Bell, head of the Columbia University laboratory that sent a team to survey the Ross Ice Shelf late last year. “What are the sort of hidden roads it can go on?”
As they flew back and forth across the vast white landscape in December, the Columbia scientists used some of the world’s most sophisticated geophysical instruments to see into and beneath the ice. As the hours-long flights wore on, the scientists took turns napping, knitting or eating cold pizza, but at all times, somebody kept close watch on the instruments.
Kirsty J. Tinto, the scientist leading the field team, loved watching as the measurements stripped away the illusion that the ice was just a flat, 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.
The Ross Ice Shelf appears stable now, so the Columbia project will function somewhat like a doctor’s baseline X-ray — a starting point for comparison if the ice starts to deteriorate.
Satellite evidence suggests that this is already happening in other parts of West Antarctica, and many scientists believe that relatively warm ocean water is the culprit. “It’s kind of a blowtorch on the underside of the ice shelf,” said Robert A. Bindschadler, a retired NASA climate scientist.
But the story is not straightforward, and 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? Some scientists think so, but others say the case is unproven. “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 who has studied temperature trends in Antarctica.
Though the role of global warming is unclear now, it is likely to be a factor in the relatively near future. Many experts think warmer air temperatures could start to weaken the ice of 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 of West Antarctica called the Amundsen Sea. Satellites have identified the most rapid loss of ice there, raising a critical question: Has an unstoppable collapse of the ice sheet already begun?
The Amundsen Sea region is one of the remotest parts of the continent, far from American and British research bases. Working together, the two countries are planning to devote tens of millions of dollars to getting better measurements there, having decided that it is imperative to begin answering questions about the region’s potential collapse.
For instance, scientists need to know a lot more about the ground beneath the glaciers there. Is it slick mud that may allow the ice to flow much faster, or hard rock that may 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 joint research effort.
Unraveling the answers, and 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 in the future.
Already, scientists know enough to be concerned. About 120,000 years ago, before the last ice age, the planet went through a natural warm period, with temperatures similar to those expected in coming decades.
The sea level was 20 to 30 feet higher than it is today, implying that the ice sheets in both Greenland and Antarctica must have partly disintegrated, a warning of what could occur in the relatively near future if the heating of the planet continues unchecked.
But some research suggests that a catastrophe might not yet be inevitable. In a study last year, Robert M. DeConto of the University of Massachusetts, Amherst, and David Pollard of Pennsylvania State University used their computer model to predict what would happen if emissions were reduced sharply over the next few decades, in line with international climate goals.
Under the most ambitious scenarios, they found a strong likelihood that Antarctica would remain fairly stable.
“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 of a big sea-level rise from Antarctica.”