The first race to the South Pole resulted in a split decision. The French were the first to sight Antarctica and make landing, while the Americans charted the greatest stretch of coast and established its continental dimensions. The British, meanwhile, who were the last on the scene, traveled the farthest and saw the most. James Ross’s extraordinary 1841 voyage blazed the trail for polar explorers of the later Heroic Age by whom he, Wilkes, and D’Urville have been unceremoniously eclipsed.
The Victorian explorers’ greatest legacy, however, lay not in national conquest, but in their shared commitment to scientific discovery. These were the first humans to properly encounter the seventh continent’s icy grandeur, and their mixed feelings of wonder and terror mirror our own growing awareness of an existential threat issuing from the polar south. Even as they struggled for survival in the icy seas—conditions for which they were suicidally ill-equipped—they doggedly mapped, recorded, sketched, and sampled all they met with, however confounding. Nearly two centuries later, the business of Antarctic data collection is an empire unto itself, a vast domain. Though the Victorians retreated in awe from the ice continent, stymied in their efforts to make landing and claim the pole, they are its true founders as an object of knowledge.
The Victorian discoverers live on, likewise, in a suite of place names increasingly familiar to our own age of polar obsession: the magnificent Ross Sea and Ice Shelf in West Antarctica; Wilkes Land and its Basin in the east. Dumont D’Urville’s name, unfortunately, is attached only to a French research station, a negligible island and peak off the Antarctic Peninsula and, on some maps, a patch of sea. But long-suffering Adélie D’Urville has her penguin, which, though now threatened by a deteriorating Antarctic habitat, is a proven climate-change survivor and might yet find a way to outlive us all.
In this era of rapid glacial melt at the poles, the bitter Anglo-American dispute in the 1840s and beyond over the exact contours of East Antarctic coastline can seem like a luxury. But to its Victorian discoverers, land was the prime currency of exploration. As emissaries of agricultural nations, ice was a “barrier” to their true object. Ross, D’Urville, and Wilkes peered across the vast white belt surrounding the mystery continent, desperate for dirt and terrain, for an ecology they could recognize. By these standards, for Charles Wilkes to mistake an ice shelf for mountainous coast was a cardinal error. But that is all changed now. The scientific descendants of the Victorian explorers mostly bypass the land except as a support infrastructure for trillions of tons of ice. Because it is the nature of Antarctica’s glaciers, not the land beneath them, that will determine the sorts of lives we, the global human community, will lead in the coming centuries.
In 2010, Leg 318 of the Integrated Ocean Drilling Program (IODP) set out to better understand the waxing and waning of the East Antarctic ice cap since its initial glaciation thirty-four million years ago. In particular, how had the ice cap responded to global warming episodes of the past—as in the Miocene and late Pliocene epochs, when Earth’s temperatures rose to levels we are now rapidly approaching in the twenty-first century? Given East Antarctica’s land elevation—it is the most mountainous territory on Earth—the prevailing assumption was its massive ice sheet was safe from anthropogenic warming. But with almost two hundred feet of potential sea-level rise locked in the East Antarctic ice sheet, it paid to be sure.
So, the IODP’s Glomar Challenger set sail from the New Zealand port of Wellington, bringing two supplementary passengers: a polar meteorologist and an ice watcher with deep Southern Ocean experience. Both were kept busy during the two-month voyage, as the Glomar Challenger traversed the treacherous seas first charted by D’Urville, Wilkes, and Ross one hundred eighty years ago. Their object was the still-unexplored continental margin, a dark undersea world of alternating troughs and ridges, transected by canyons, and with a precarious upward slope extending landward, beyond their reach, toward the recessive base of the ice shelf. Unlike the land-hungry Victorians, the terrain that mattered to the IODP scientists lay beneath the ocean floor, in marine fossil records of ice sheet fluctuation buried in a five-mile-deep sedimentary column. No one doubted the existence or importance of this submarine treasure trove; the challenge lay in retrieving it under the worst maritime conditions in the world.
The research ship was not halfway to its first destination off the George V Coast when it ran into a low-pressure maelstrom delivering sixty-knot winds and forty-foot waves. When after three miserable days the storm lifted, the researchers saw their first penguins clipping the swell, and then icebergs en masse. The Leg 318 operation plan nominated seven drill sites, but the ice pack stopped them almost twenty miles short of the first, so they chose another to the northwest. Site 1355 was clear of ice, but technical problems plagued the drilling, and the cores drew only coarse sand and gravel. At the next site, they drilled a half mile deep to the Eocene-Oligocene boundary, only for an advancing storm to force them to abandon the hole.
With the northern drill sites exhausted, the Challenger had no choice but to turn south and risk the ice pack. For the next five weeks, at five separate sites, the drilling team dodged icebergs and whales, survived entrapment by the pack, rode out near-hurricane-force winds, and endured windchill temperatures of twenty below, which blanketed the decks and equipment in ice. On one occasion, a killer iceberg floated directly over a drill hole they barely had time to vacate. But it was all worth it. Sealed within their hard-won cores, and laid out in gnomic grandeur back on the dock at Hobart, was a vital message sent from deep time: a tale of Antarctic ice, stretching back fifty million years, from Hothouse to Icehouse.
The storm-battered Leg 318 mission of 2010 has produced a flood of breakthrough scientific papers: on Southern Ocean paleoclimate, glacial melt, sea-level rise, and the ever-changing relation between Antarctic land and ice. Charles Wilkes, were he alive, would have taken comfort in the bottom line: his fanciful 1840 map of the East Antarctic coast, or any map, was no more than a snapshot of a continent whose larger, dynamic existence over time is governed by tectonic plates, deep ocean currents, and Earth’s orbit around the sun, among other planetary forces humbling to contemplate. From the epic data dive of Leg 318 emerged one clear signal relevant to our present circumstances, and with it an ominous new catchphrase in the climate-change lexicon: “marine ice sheet instability.”
For analogies to our current era of global warming, the Leg 318 scientists looked beyond the world-chilling EOT, thirty-four million years ago (myr), to two more recent warm periods: the mid-Miocene (17–13 myr) and the mid-Pliocene (5–3 myr). Both warming episodes involved atmospheric carbon levels ranging between four hundred and six hundred parts per million, equivalent to our current levels and those predicted for 2100. By the mid-Miocene, the East Antarctic coastline bore no resemblance to the tropical diorama of the Early Eocene. Over the preceding twenty million years, its inland rivers had broadened into majestic fjords, like present-day Norway or Greenland, delivering seasonal ice to the cooling ocean. This peaceful rhythm was interrupted on occasion by dam-bursting ice-floods on a scale never seen in the human record. Then, as temperatures dropped further, the land became fully encased beneath its glacial canopy. The urgent question for Leg 318: how had elevated carbon levels in the past affected the great East Antarctic ice sheet? Was it immune to melting, as some models insisted, or had it been catastrophically undermined? Had an unstable Wilkes Land shed its frozen bulk, flooded the oceans, and redrawn the world’s coastlines, as it might yet do again?
Attention focused, in particular, on the so-called Achilles’ heel of East Antarctica, the glaciated coast fronting the Wilkes Subglacial Basin (WSB) that Lieutenant Joseph Underwood had been so eager to explore in the summer of 1840. The WSB is a massive, mile-deep crustal depression extending from the hinterland of the Transantarctic Mountains to the George V Coast, where its seaward outlet ranges a full four hundred miles in the neighborhood of the Ninnis and Mertz glacial tongues. While the majority of the East Antarctic ice cap drapes serenely over alpine ranges or plateaus—an unbreachable kingdom of ice—the glaciers of the WSB are grounded well below sea level, up to a half mile.
Emplaced so, the glaciers of this coast, like their counterparts in low-lying West Antarctica, are naturally vulnerable to changes in ocean temperature and circulation. But how vulnerable, and over what time frames? The WSB alone contains volumes of ice sufficient to raise global sea levels by thirty feet, enough to submerge the world’s great coastal cities and send millions of refugees scrambling for higher ground. During the Pliocene Climatic Optimum—when CO2 levels were last at the levels predicted for 2100—sea levels were seventy feet higher than today, implying significant ice sheet collapse in East Antarctica.
In her lab at the University of London, Leg 318 scientist Carys Cook scrutinized one marine core in particular, drawn off the Adélie Coast in Wilkes Land. Two hundred fifty feet in total length, the Site 1361 core offered a continuous geoclimatic history of the Pliocene, the intermittently warm epoch initiated five million years ago. What she found was something like Pharoah’s dream in the Bible, with its fat cows followed by lean cows, signifying rich harvests and poor. In the 1361 core, Cook identified eight diatom-rich layers of submarine clay interspersed with eight diatom-poor layers. The diatom-rich portions represented periods of reduced ice on the Wilkes Land coast, when warm, biologically productive seas bathed the Antarctic shore. The diatom-poor layers, conversely, signaled a return to impoverishing cold.
Sifting through the warm-climate sections of the core, Carys Cook came across microscopic grains of igneous rock dating from the Jurassic origins of the East Antarctic crust. These grains bore no relation to the surrounding sediment and could only have been imported. From this point, Cook’s chain of reasoning was simple and irresistible. The nearest igneous source lay hundreds of miles away in Victoria Land, deep within the Wilkes Subglacial Basin. The sole means by which these rock fragments could have been eroded was by relentless grinding at a glacial margin. Therefore, the Wilkes Land glaciers, which currently line the coast, or extrude tongue-like into the ocean, had retreated hundreds of miles from these maxima during the Pliocene, before rebounding and retreating again in a spectacular binge/purge cycle of glacial excess. The marine-based glaciers of Wilkes Land, like Ninnis and Mertz, were dangerously unstable and had in the past disappeared hundreds of miles inland under climate conditions similar to our own.
For an all-important second line of evidence to support this alarming conclusion, Cook turned to the results of an earlier IODP expedition, Leg 188, which hinted at a massive Pliocene ice-rafting episode in Prydz Bay, a thousand miles to the west of Wilkes Land. On the seafloor at Prydz Bay, scour marks a half mile deep record the transit of icebergs released from an epic ice sheet disintegration. The source of the ice-rafted debris at Prydz Bay could be nowhere else than the WSB, which had shrugged off its glacial cover in rising Pliocene temperatures like an unwanted blanket. An “iceberg armada,” deposited into the ocean at a rate up to nine times faster than in our current interglacial period, included bergs fifteen hundred feet thick, dwarfing their present-day counterparts. The “massive iceberg production event” discovered at Prydz Bay, concluded Cook, was the natural consequence of a Wilkes Land glacial regime highly sensitive to even modest changes in temperature.
The tipping point for East Antarctic sea surface temperatures, according to the Leg 318 cores, is 3°C. Today, the freezing waters of the Wilkes Land continental shelf continue to enjoy the protection of katabatic winds and a powerful cold stream at abyssal depths. The circumpolar current is warming, however, and will soon cross the threshold at which the glacial massifs begin their irreversible self-destruction. During the Pliocene Climatic Optimum four and a half million years ago, the dominant westerly winds of the Southern Ocean shifted southward, driving oxygenated water masses downward along the East Antarctic margin and eroding the glacial shelf. Other studies show that with circumpolar seas at 3°C, the Antarctic ice cap becomes susceptible to orbital drivers (mirroring ice age rhythms in the Northern Hemisphere) and to small but persistent increases in atmospheric CO2 and mean temperature—a world like our own, except with sea levels eighty feet higher than today. In short, we are currently charting a new course for humanity’s future, sailing headlong back to the Pliocene.
A 2014 paper in Nature narrowed the implications of Wilkes Land marine ice sheet instability to the starkest possible formula. Matthias Mengel and Anders Levermann, modelers from the Potsdam Institute for Climate Impact Research, concluded that the warm-water erosion of a relatively small barrier or “ice plug” at the coastal margin would unloose the pent-up Wilkes Land glaciers on an irreversible cascade. Though this extreme scenario is not due to unfold this century, for the human generations alive to bear witness, it will be the Pliocene iceberg armadas all over again. When that time arrives, all the maps of our world—not just Charles Wilkes’s—will be reduced to historical curiosities only.
Marine ice-sheet instability is a more immediate threat in low-lying West Antarctica, which contains ice mass equivalent to the entirety of Greenland. Changing global sea levels over the last several million years have been dominated by the advance and retreat of West Antarctic glaciers along their marine basins, suggesting the future will mirror the past.
Since 1980, warming waters in the faraway tropics have altered southern atmospheric circulation, channeling warm air over West Antarctica. These winds, in turn, have driven the circulation of so-called Circumpolar Deep Water (CDW) southward. The CDW is salty and warm, up to 4°C, and travels at depth along troughs in the seafloor. The CDW’s new frontier, the Amundsen and Bellingshausen Seas, present a suite of ice shelves vulnerable to warm-water infusion, most notably those fronting the giant marine-based Pine Island and Thwaites Glaciers.
Fig. P.1. The rapidly melting glaciers of the Amundsen Sea, West Antarctica.—NASA/GSFC/SVS.
In two decades after 1992, the Pine Island Glacier retreated thirty kilometers. Ocean heat influx to the shelf face spiked, and the flow speed of glacial ice toward the coast doubled, launching icebergs into the sea in a slow-motion frenzy. Because of the reverse slope beneath it, this accelerated melting produces a feedback loop. The glacier’s base now rests on a bed four hundred meters deeper beneath sea level than in 1992, exposing an ever greater area of its face to further erosion by the warming sea.
Pine Island’s near neighbor, Thwaites—dubbed “The Doomsday Glacier” by Rolling Stone—is more concerning still. The size of Florida, Thwaites alone contains two feet of potential sea-level rise, enough to submerge Miami and much else besides. The discovery in 2018 of a miles-wide cavity in the glacier, the source of fourteen billion tons of ice now loosed to the oceans, suggests Thwaites will collapse this century. A team of no fewer than sixty researchers has now descended on the Amundsen Sea to track its decline. The International Thwaites Glacier Collaboration is the largest single research venture in Antarctica in decades.
In a runaway melt scenario, loss of these glaciers would irreversibly undermine the entire West Antarctic ice sheet, exposing the keystone Ronne Ice Shelf in the Weddell Sea to the east and the Ross Ice Shelf to the west. Surface melt from above-freezing air temperatures creates fissures in the shelf, while the warmer ocean flow beneath chips away at the base. Over time, glacial streams expand and the entire sheet drains into the surrounding oceans. In the future, trans-Antarctic seaways connecting the Amundsen, Weddell, and Ross Seas, last open in the Pliocene, will make for far friendlier sailing opportunities than the explorers of 1840–41 enjoyed. There will be an open polar sea at last, as the Renaissance geographers dreamed of. At the Ross Shelf, seismic sensors drilled in the ice have recorded startling vibration changes as its surface softens and fractures open in the glacial interior. The Ross Ice Shelf is “singing” its own requiem.
Historical precedents for this Antarctic end game are clearly identifiable in the sedimentary record. In the Pliocene, when Earth’s climate conditions closely matched our own, the Ross Ice Shelf melted away, allowing the massive load of land ice behind it to drain away into the ocean, drowning coastlines worldwide. But the conclusion of the last ice age fourteen thousand years ago offers a much more recent example of the West Antarctic Ice Sheet’s susceptibility to warming temperatures. Coral records from Barbados and Tahiti indicate that global sea levels rose at the rate of five meters per century to a high point of twenty meters (sixty-five feet) in less than five hundred years. A significant portion of that rise can be traced to West Antarctica. According to one 2016 model, the present sheet, under increased stress from warming, is due for a repeat collapse by 2250.
When it comes to predicting sea-level rise for our century, the Antarctic ice sheets are the joker in the pack. Pegged to temperature increases, seas might rise three feet by 2100 or twice that much. Either way, the costs of rising seas will top a trillion dollars annually by midcentury. Millions of people from low-lying coastal cities—from New York to Alexandria, Shanghai to Mumbai—will be forced to pack up and leave, joining a global exodus of up to two hundred million climate refugees worldwide. The humanitarian disaster set in train by the collapse of the Antarctic ice sheet will dwarf all forced mass migrations of the past, including the epic trauma of the Middle Passage. As coastlines are redrawn, the human social contract will be hastily rewritten, under emergency conditions not friendly to democratic process or human rights.
Beyond 2100, sea-level rise will not abate but only accelerate as more Antarctica glaciers reach their tipping point and more urbanized coastlines are inundated. This is without the prodigious interior ice sheets of East Antarctica, at their frigid elevations, contributing a single drop to the rising tides. But the great eastern ice cap is not invulnerable. Burning all available fossil fuels still in the ground would raise global temperatures sufficient to melt it completely, ensuring an eventual rise in sea levels of over two hundred feet.
The human inheritors of this disaster, centuries from now, will inhabit unrecognizable shrunken continents hosting devastated ecosystems. As for our imagining the lives our descendants will lead, perhaps the Patagonians D’Urville encountered in 1838 offer a clue. These resilient climate warriors in Tierra del Fuego mostly prospered during their long migration from the north but were trapped by slingshot climate change millennia ago: first by the so-called Antarctic Cold Reversal, then by melting glaciers. Their lives were nasty, brutish, and short; then they died out. Given these suggestive precedents, the current prospect of Antarctic melting sets the stage for an epic reversal in human fortunes.
In January 2017, my Antarctic touring ship sailed southwest past Cape Flying Fish, where William Walker almost came to grief in the pack in 1839, and into the remote Amundsen Sea. No ships of trade travel this route, nor is it popular among tourists. It is simply too far from anywhere. We approached Peter the First Island, a misty snow dome rising out of the pack, where fewer people have stood than on the Moon. But the surrounding ice was too dense for a landing.
The impregnable pack likewise kept us at a distance from the West Antarctic coast and its low-lying glaciers. But the dynamic changes underway along this vital coast were evident even to the passing polar tourist. One afternoon, under a gleaming blue sky, we fell among a flotilla of stadium-sized icebergs. Their perfect flat tops showed they had only recently been calved from the Pine Island and Thwaites Glaciers to the south. Iceberg production in these waters has increased 75 percent over recent decades, thanks to warmer sea and air temperatures. Iceberg armadas during the Pliocene deglaciation of Antarctica patrolled these coasts, when Terra Australis threw off its icy mantle and seas rose by hundreds of feet. Our ship felt suddenly tiny, as it literally dodged the bergs. We were like scouts sent to gauge the strength of an enemy—the frontline of a new iceberg armada.
A string of endless days later, we arrived at the eastern edge of the Ross Ice Shelf. Setting out in rubber dinghies, we explored the Bay of Whales, the southernmost waters on Earth, from where Roald Amundsen set out across the shelf on his sprint to the South Pole in 1912. He famously beat Scott, who, loyal to the memory of his Victorian predecessors, had launched his ill-fated bid from the other, less practical side of the Ross Shelf under the loom of the Erebus and Terror volcanoes.
For the Antarctic visitor, baffled by the scale and sameness of the alpine coast for mile after mile, the iconic Mount Erebus, with all its explorer legends, at least offers the sense of destination, of having arrived somewhere. Major scientific research stations—American, New Zealander, and Italian—are clustered nearby, human outposts on an inhuman terrain. Just as for Ross and his men in 1841, our sight of Erebus and the adjacent “Great Ice Barrier”—capturable within a single photo frame—inspired feelings of pilgrimage. The helicopters were revved up, and I squeezed in beside a Scottish doctor and a fireman from Seattle. Flying south over the snow-blown Ross Ice Shelf, flat as a Midwestern prairie, we were amazed to come to a channel of open water, sparkling in the sunshine. A giant slab of the seaward-fronting shelf, the size of a city, had separated itself from the main body and was floating out to sea. This glaciological wonder had not been visible from the ship. Antarctic ice shelves routinely calve their excess ice, responding to the pressure of the glacial flow behind them. But multiple times in the past, with temperatures only a few degrees warmer than today, the entire Ross Ice Shelf zooming by beneath us had broken up and drifted into the ocean, unloosing the vast reserves of land ice behind it.
Our pilot had a reputation as a cowboy, and he didn’t disappoint. We flew breath-catchingly low through the channel, almost skimming the pale blue water as the ice cliffs blurred past on either side. We whooped and grinned at each other. In the pure thrill of being on the polar ice, it was difficult to focus on the distant Pliocene or any message Antarctica might be sending. On a months-long tour of the most unwelcoming place on Earth, actual pleasure is hard to come by. So we made doubly sure to enjoy ourselves on this once-in-a-lifetime flight, hotdogging through cracks in an ice shelf—as if we hadn’t a care in the world.