What the fate of Greenland means for the rest of the Earth

by Elizabeth Kolbert

In the middle of the night in the middle of the summer in the middle of the Greenland ice sheet, I woke to find myself with a blinding headache. An anxious person living in anxious times, I’ve had plenty of headaches, but this one felt different, as if someone had taken a mallet to my sinuses. I’d flown up to the ice the previous afternoon, to a research station owned and operated by the National Science Foundation. The station, called Summit, sits 10,530 feet above sea level. The first person I’d met upon arriving was the resident doctor, who warned me and a few other newcomers to expect to experience altitude sickness. In most cases, he said, this would produce only passing, hangover-like symptoms; on occasion, though, it could result in brain swelling and death. Belatedly, I realized that I’d neglected to ask how to tell the difference.

NSF Summit Station—according to the agency’s many rules, this is how visiting journalists are required to refer to the place—was erected in the late 1980s. Initially, it was occupied only in the summer; now a small crew remains through the winter, when, at Summit’s latitude—72 degrees north—the sun never clears the horizon. The station’s main structure is known as the Big House. It resembles a double-wide trailer and teeters almost thirty feet above the ice, on metal pilings. Arrayed around it are a weather station, also elevated on pilings; a couple of very chilly outhouses; several tanks of jet fuel; and an emergency shelter that’s shaped like a watermelon and called the Tomato. Some of the station’s residents used to sleep in tents, but a few years ago a polar bear showed up, so the tents have been replaced by metal sheds.

The Greenland ice sheet has the shape of a dome, with Summit resting at the very top. The ice dome is so immense that it’s hard to picture, even if you’ve flown across it. It extends over more than 650,000 square miles—an area roughly the size of Alaska—and in the middle it is two miles tall. It is massive enough to depress the Earth’s crust and to exert a significant gravitational pull on the oceans. If all of Greenland’s ice were cut into one-inch cubes and these were piled one on top of another, the stack would reach Alpha Centauri. If it melted—a rather more plausible scenario—global sea levels would rise by twenty feet.

Until relatively recently, it was thought that Summit would be, if not unaffected by climate change, at least untroubled by it. Such is the ice sheet’s bulk that at its center it creates its own weather. But in the past few decades Greenland has changed in ways that have stunned scientists who spend their lives studying it. Since the 1970s, it has shed some six trillion tons of ice, and the rate of loss has been accelerating. Crevasses are appearing at higher elevations, glaciers are moving at non-glacial speeds, and large parts of the ice sheet appear to be twisting, like a writhing beast. In July 2012, surface melt was detected at Summit for the first time since modern measurements began. In 2019, the station experienced melt in mid-June and then again in late July. On August 14, 2021, it rained, an event so remarkable that it made news around the world. (“For the First Time on Record, Rain Fell at the Summit of Greenland,” ran the headline in the Sydney Morning Herald.) There was late-season melt at Summit in September 2022, and more melt in June 2023.

The story of climate change is generally told in terms of human action, and for good reason. The almost two trillion tons of CO2 that people have pumped into the atmosphere have changed the planet in ways that every day become more apparent. Last year, average global temperatures set a new record, and by a wide margin. Canada experienced record wildfires; the Caribbean saw record ocean temperatures, which devastated its coral reefs; and Libya was hit with record rainfall, which led to a dam collapse that killed more than 5,000 people. This year’s global temperatures will almost certainly surpass last year’s. Among the many climate-related disasters of 2024 so far have been a heat wave in Mecca that killed 1,300 pilgrims during the hajj and Hurricane Helene, which caused at least twenty billion dollars’ worth of damage. How people—or governments and corporations, run by people—respond to the mounting losses will have repercussions that will last, for all intents and purposes, forever. As no less an authority than the United Nations’ Intergovernmental Panel on Climate Change put it, upon releasing its latest scientific assessment, “The future is in our hands.”

20,000 years ago, an ice sheet stretched…from Greenland across Ellesmere and Baffin Islands and down over Canada and much of the northern United States. So much water was tied up in the ice that sea levels were 400 feet lower than they are today.

But, like so many stories that get told, this one doesn’t tell the whole story. The future depends on how humanity reacts to global warming, and it also depends on how the Earth does. Owing to advances in everything from satellite altimetry to deep-sea drilling, a great deal has been learned in the past few decades about the planet’s history. Much of the new science suggests that the climate is, all on its own, unstable, prone to dramatic and sometimes sudden shifts.

The history of Greenland is a case in point. During what’s known as the Last Glacial Maximum, some 20,000 years ago, an ice sheet stretched more or less continuously from Greenland across Ellesmere and Baffin Islands and down over Canada and much of the northern United States. So much water was tied up in the ice that sea levels were 400 feet lower than they are today, and it was possible to walk not just from Siberia to Alaska but also from Australia to Tasmania and from England to France. When the ice began to recede, around 15,000 years ago, large swaths of the world experienced catastrophic flooding. During one particularly sodden period, known as meltwater pulse 1A, sea levels rose by more than a foot a decade.

Most scientists believe that ice ages—there have been at least ten of them over the past two and half million years—are initiated and terminated by periodic shifts in the Earth’s orbit, caused by, among other factors, the tug of Jupiter and Saturn. But orbital shifts produce only slight changes in the amount of sunlight that reaches different parts of the globe at different times of the year. Such slight variations are insufficient to explain the growth and subsequent retreat of massive ice sheets. Rather, it seems, the orbital shifts act like a trigger, setting off other processes—feedbacks—that greatly amplify their effect. One relatively straightforward feedback features albedo, from the Latin word for “whiteness.” Ice and especially snow have a high albedo. They reflect lots of sunlight back to space. Thus, as an ice sheet grows, the planet absorbs less energy. This has a cooling effect, which encourages the buildup of more snow and ice, which results in more reflectivity, and so on. Start to melt an ice sheet and the same cycle spins in reverse.

Today, feedbacks are, to put it mildly, a growing concern. A report published last year by more than 200 researchers from around the world noted that many of the systems that determine the climate exhibit nonlinear behavior. Such systems may “shift to a very different state, often abruptly or irreversibly, as a result of self-sustaining feedbacks.” The researchers identified two dozen potential “tipping systems,” among them the Greenland ice sheet.

At a certain point, the report warned, feedbacks could become so powerful that, even if CO2 emissions were cut dramatically and temperatures stabilized, the ice sheet would continue to shrink, possibly until it collapsed. The “best estimate” of when this critical threshold will be reached is when average global temperatures rise 1.5 degrees Celsius—roughly three degrees Fahrenheit—above preindustrial levels. Even after that line is crossed, it will take many centuries for the changes set in motion to play out. Still, as a practical matter, there will be no going back. When it comes to tipping systems, the future is in our hands until it isn’t.

Days at summit begin with a staff meeting held in a heated tent that’s outfitted with a treadmill, weights, and yoga mats. In front of the treadmill, people have taped scenes from more temperate climes—ones with trees and flowers. On my first morning at the station—I still had a headache, but no fatal brain swelling—the station’s supervisor opened the session with a request for volunteers to lug a pair of propane tanks up the stairs to the Big House. Summit’s cook announced that the latest shipment of food was short on lettuce. Someone pointed out that there were problems with the flags on the station’s runway, which is made entirely of snow. A fourth person promised to clean the outhouses. After the meeting, I got to launch the daily weather balloon, which was about three feet tall and dangled a cartridge of electronic instruments. The balloon, filled with helium, flew out of my hands. I tried to follow it as it sailed over the ice, but I soon lost sight of it.

The view from Summit in all directions is pretty much the same: white. The Norwegian explorer Fridtjof Nansen, who, in the 1880s, led the first team to cross Greenland on skis, recalled the ice sheet’s monotony—an “interminable flat desert of snow.” There was, he complained, “no break or change in our horizon, no object to rest the eye upon, and no point by which to direct the course.” Especially when it’s cloudy, the ice, free of shadows, appears as one enormous blank page.

In ice from 1,502 feet down, there was snow that fell when Nero was emperor; at 2,350 feet, snow from the reign of Tutankhamun. At the very bottom was snow that fell before the start of the last glaciation.

In fact, the ice sheet is packed with information, like a giant encyclopedia. Among the first to recognize this was Ernst Sorge, a German glaciologist. “I’m looking at a landscape whose vast simplicity is nowhere to be surpassed on earth, and which yet conceals a thousand secrets,” he wrote.

Sorge was part of a famous—infamous, really—expedition that set off from Copenhagen in the spring of 1930. The expedition’s leader was another German scientist, Alfred Wegener, who’s best known for having come up with the theory of continental drift. One of Wegener’s goals was to establish a camp at a site dubbed Eismitte, or “ice middle,” about a hundred miles south of where Summit now sits. Sorge and a colleague were supposed to overwinter at the site and take meteorological measurements. Owing to a series of unfortunate events, a third man, who was suffering from frostbite, ended up stuck at the camp as well and had to have his toes amputated with a penknife. Meanwhile, Wegener died as he was trying to fight his way back to the coast, eating his sled dogs along the way. His body is still buried somewhere in the ice.

From the surface, the camp at Eismitte looked like a snow fort with a round turret. Beneath the surface were chambers—a living room, an instrument room, and a storeroom—that had been dug out of the snow. Fascinated by the subglacial world, Sorge kept on digging until, at the far end of the camp, he had sunk a shaft more than 50 feet deep. Studying the walls of the shaft by lamplight, he discovered that he could tell the difference between snow that had fallen on Eismitte in the summer and snow that had fallen in the winter. By counting backward through the seasonal layers, he calculated that his shaft extended through 21 years’ worth of accumulation.

In the decades that followed, researchers delved deeper and deeper, using increasingly sophisticated drills. The farther the drills descended, the denser the layers of old snow became, until they were compressed into ice. But even in the icy depths the difference between summer and winter precipitation could be discerned. This made it possible to date each layer back through the centuries.

Meanwhile, scientists found that they could tease out a wealth of data from every annual increment. By analyzing the ice with a mass spectrometer, they could calculate what the average temperature on Greenland had been in any given year. And by extracting the gases contained in tiny bubbles of trapped air they could reconstruct changes in the atmosphere.

In the 1990s, a team of American researchers working at Summit succeeded in drilling all the way from the top of the ice sheet to the bedrock. In the process, they pulled up thousands of long, skinny cylinders of ice—two miles’ worth. In ice from 1,502 feet down, there was snow that fell when Nero was emperor; at 2,350 feet, snow from the reign of Tutankhamun. At the very bottom was snow that fell before the start of the last glaciation.

Analysis of the core showed, in extraordinary detail, how temperatures in central Greenland had varied during the last ice age, which in the US is called the Wisconsin. As would be expected, there was a steep drop in temperatures at the start of the Wisconsin, around a hundred thousand years ago, and a steep rise toward the end of it. But the analysis also revealed something disconcerting. In addition to the long-term oscillations, the ice recorded dozens of shorter, wilder swings. During the Wisconsin, Greenland was often unimaginably cold, with temperatures nearly 30 degrees lower than they are now. Then temperatures would shoot up, in some instances by as much as 20 degrees in a couple of decades, only to drop again, somewhat more gradually. Finally, about 12,000 years ago, the roller coaster came to a halt. Temperatures settled down, and a time of relative climate tranquility began. This is the period that includes all of recorded history, a coincidence that, presumably, is no coincidence.

Richard Alley, a glaciologist at Penn State and the author of a book about the ice-coring project, summed up the findings as follows: “For most of the last 100,000 years, a crazily jumping climate has been the rule, not the exception.”

Photo: Disko Island, Greenland, June 30, 2024. Courtesy: Naja Bertolt Jensen. Unsplash+

This article appears in the 2025-26 Berlin Journal (39). It is excerpted from “When the Arctic Melts: What the fate of Greenland means for the rest of the Earth,” which originally ran in the October 14, 2024 issue of the New Yorker.