What Greenland’s Melting Ice Tells Us About the History and Future of Global Warming

“Ghost of the Future, I fear you more than any specter I have seen… Will you not speak to me?”
–­Charles Dickens, A Christmas Carol
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April 4, 2019, in Copenhagen was almost a T-­shirt day. Such warmth in early spring is unusual for Denmark. But this is a country where climate change has driven up average temperatures nearly 3°F since 1875. I, though, am decidedly not warm. Standing inside a walk-­in freezer bigger than many people’s homes, my teeth are chattering loudly enough that I am sure the dozen or so scientists near me can hear them. It’s well below zero as the fog from my breath slowly covers my beard in frost. Here, the temperature is always the same.

This glistening, windowless freezer was purpose built to store ice. Not the ice you use to cool drinks, although you could—­and some have done exactly that—­but long cores of ice extracted from the world’s great ice sheets and glaciers. Over more than six decades, teams of drillers and scientists living and working in some of the most challenging conditions on Earth—­places where bare skin freezes solid in minutes, where the sun never sets at the height of summer and doesn’t rise in the dead of winter—collected the ice stored here.

I am in a rest home for these ice cores: slender, mostly transparent cylinders now cut into sections a few feet long and only inches wide. Curators here treat ice cores like rare books—­with great care. They store them in meticulously catalogued boxes loaded four high on sturdy metal shelves. Laid out on the ground end to end, the ice in this freezer alone would stretch for miles—­until, of course, it melted into one long, linear puddle.

Today, we are not here for the ice cores, interesting as they are. Rather, we’ve come to see something far less common: cores of what lay beneath the ice—­brown lumps of frozen soil in vintage glass jars. If you laid these frost-­mantled cylinders of earth end to end, they wouldn’t even stretch the length of a car, and altogether they weigh sixty-­nine pounds. My Danish colleagues have asked me to fly across the Atlantic to see these samples because I have made a long career of dating old things, especially rocks and soil from the Arctic.

To understand the coming and going of ice sheets, I analyze samples of sand in a dustless clean room and use repurposed particle accelerators from the 1960s, machines that once charmed physicists who now need bigger and better equipment. I use these instruments to weigh atoms and then count them one by one. Using such data, I’ve deciphered landscapes around the world, including the rocky desert of Namibia, the humid Brazilian rainforest, the dry lands of Israel, and the folded Appalachian Mountains.

Yet Greenland and its ice hold a special place in my heart. During four trips and a dozen helicopter flights there, I’ve seen some amazing sights, but I had never seen anything like these cookie jars holding frozen sand from beneath the ice sheet with a dusting of gravel and a hint of silt. Over my desk, there’s now a photograph of that day. In it, I am holding a jar in my gloved hand, smiling.

Getting to Copenhagen, I crossed six times zones and earned four thousand, two hundred and thirty-­three frequent flier miles. As one passenger on a crowded series of flights from Vermont to Denmark, I added about a thousand pounds of carbon dioxide to the atmosphere. That’s unsettling, because I study when and how ice sheets, like the one covering Greenland, come and go over time as the climate warms and cools in sync with rising and falling concentrations of atmospheric carbon dioxide. Greenland’s ice sheet is now shrinking rapidly, and my flight, which passed over the southern tip of the island, just helped melt a little more ice.

The jars of frozen soil in our hands came from Camp Century, a U.S. Army base hidden entirely inside Greenland’s ice sheet. The camp was about 120 miles from the northwest coast of Greenland, and nearly a mile of ice separated the surface of the glacier from the rock and frozen soil below. You would not be wrong to say that Camp Century was in the middle of nowhere. In 1960, Army engineers started drilling straight down from inside the camp with the goal of collecting continuous samples of ice from the top to the bottom of the world’s second largest ice sheet. After half a decade of work, on July 2, 1966, they pulled out the last sample from a depth of 4,506 feet below the snowy surface surrounding the camp.

On that day, I was four years old, the Cold War was raging, and the moon would remain free of human footprints for another three years and eighteen days. Working in frigid snow tunnels, with no heat and no daylight, the Army engineers had just finished drilling the world’s first complete deep ice core. The drillers had not only sampled the entire thickness of the Greenland Ice Sheet, but had also brought up more than eleven feet of frozen soil from beneath the ice, a record that stands to this day. Nearly fifty-­three years later, that material filled the jars in the Copenhagen freezer. We didn’t know it then, but the soil that lay beneath the ice sheet was keeping far more interesting secrets than we ever could have imagined on that warm April morning.

Fast-­forward three months to the end of July 2019, in our laboratory at the University of Vermont. Yesterday, a van delivered two samples of the soil from below Camp Century, both still frozen solid after a several-­day trip from Denmark. Two other geologists, Drew Christ and Leah Williamson, were there with me. Between us, we’d processed thousands of samples. Yet nothing had prepared us for what was about to happen.

First, we let the samples, safely sealed in plastic bags, melt slowly. Then we separated the sand from the gravel and the mud. I was hot, tired, and staring mindlessly into a bin of murky water when I saw something small and dark floating on the surface. I tossed off my safety goggles and grabbed my glasses.

“Drew” I said, “you need to see this. I think these are plant parts.” From the look Drew gave me, it was clear he wasn’t buying it. We were both exhausted. I’d been teaching a summer high school environmental science program for almost a week, and he was just days away from defending his doctoral thesis. I grabbed a small plastic pipette, sucked up a few of the black bits, and placed them on a white Teflon tray the size and shape of a hollow ice-­hockey puck. I handed the tray to Drew. Quickly, he placed it under the microscope in the corner of the room, flipped on the glaring LED lights, and looked down the dual eyepiece. Silence. I remember best the expression of utter shock on Drew’s face when he stood up and turned toward me. He glanced at Leah, same expression. Astonishment.

We took turns looking into the scope and babbling. Between the sand grains, we could see leaves and twigs—­remnants of a frozen ecosystem, ancient Arctic tundra vegetation, perfectly preserved in nature’s deep freeze for who knows how long. In that moment, we knew that at least once before, Greenland’s ice had melted away, allowing plants to grow where today there is a mile-­thick glacier. Under the microscope, we saw irrefutable evidence that ice wasn’t a stable, permanent fixture on the island. Sometime in the past, Greenland’s massive glacier, which today covers an area the size of France, was far smaller. I’ve done science for forty years and this remains my only eureka moment.

The rest of the afternoon was a blur. I brought the high schoolers in for a look, and Drew explained that these plants once sat beneath an ice sheet and that they might be a million or more years old. “Cool,” they said. The Camp Century ice core was not only the first to reach the bottom of any ice sheet, but now, more than a half century later, it has a new honor—­it’s the first, and so far only, ice core chock full of bits and pieces of ancient plants, insects, and mosses. On that summer afternoon, two samples of brown, pebbly mud began rewriting the history of the Greenland Ice Sheet, one fossil and one sand grain at a time. The high school kids were right: this was cool, and it was only the beginning of what that frozen earth in those 1970 vintage glass jars was going to tell us. Soon, a couple of frozen lumps of soil would show the world, beset by a rapidly warming and changing climate, that Greenland’s ice sheet was fragile, far more fragile than most wanted to believe. We needed to find out when it had melted, and why.

This is a story about Greenland, its ice sheet, and climate change, both in the past and today. The protagonist is an ice core that radically changed our understanding of Earth, its climate, and their intertwined history. Below the ice sheet’s snowy surface is another, and arguably equally important, story—­one about unexpected outcomes and their consequences. No one expected climate change at the start of the Industrial Revolution. But, as the world burned greater and greater amounts of fossil fuels over the last two centuries, the impacts became increasingly clear. We know unambiguously now that warming and the loss of ice is a consequence of human actions.

When Edwin Drake struck oil in Pennsylvania in 1859, he didn’t imagine the outcome would be Greenland’s ice sheet melting, transferring what had been frozen water on land into the global ocean. None of the men who drilled the world’s first deep ice core knew in 1966 that their work would become so important decades later, after most of them were dead. Yet a few handfuls of frozen soil from nearly a mile below those drillers’ feet showed that Greenland’s ice sheet was unstable even in the absence of human meddling with Earth’s climate. We know now that 400,000 years ago, during an interglacial interval probably no warmer than today, tundra vegetation replaced ice without the assistance of fossil fuel-driven global warming.

Camp Century, the quirky, futuristic city that the U.S. Army carved into Greenland’s ice sheet in 1960, is a critically important supporting character without which the critical ice core wouldn’t exist. But, to figure out Camp Century’s place in both human and climate history, as well as to understand what the science done at the camp says about our collective future, we need to go deeper—­deeper into the history of Greenland and its ice sheet, deeper into the people who built the remote Arctic camp and made its ice core possible, and deeper into the Cold War that drove so much frenzied American activity in the fragile Arctic. Such context shows that the Camp Century ice core was far more than a feat of engineering: it was the beginning of a more nuanced understanding of the Arctic in general and the science of ice sheets in particular.

In the Western view of things, Greenland has always been about the outer limits of human endurance, people versus nature, and meeting the challenge of the unknown and seemingly unknowable—­be that by crossing the ice sheet for the first time, detecting Soviet missiles flying over the Arctic on a ballistic path to New York City, or drilling through nearly a mile of ice. A drive to know, and a certain stubbornness, kept Robert Peary and Mathew Henson, their men, and their dog teams pulling 200-­pound sledges toward the North Pole in 1909, in the same way that they motivated Army drillers and scientists to spend six years coring before they finally got the equipment and techniques right and reached the bottom of the ice sheet. Human persistence in the face of challenges, both personal and professional, is central to this story.

Most people think of science as equations and equipment. But science is people, and people are unpredictable. They freeze to death. They leave their jobs. They threaten to throw an irreplaceable ice core into Lake Erie, and they misplace things, like frozen soil collected from below nearly a mile of ice. But to understand people and their day-­to-­day lives is to understand why the American military and scientific occupation of the Arctic happened, why thousands of men spent parts of their lives away from their families, living inside an ice sheet only 800 miles from the North Pole, and why today 8 billion people are now barreling headlong into a global climate crisis. People are the reason that the frozen soil from beneath the ice sheet vanished and then, more than twenty years later, reappeared, safe and sound in a Danish ice-­core repository.

Earth is complicated. In forty-­plus years of studying our planet, I’ve learned that the hard way. Over my career, it’s become all the rage to consider Earth as a system with feedbacks that don’t respond simply and smoothly to pushes and pulls. The climate system is full of jumps, times and places where temperature and precipitation patterns change abruptly. Wally Broecker, one of the first and most outspoken scientists to decipher Earth’s climate system, said it well: “The Earth tends to over-­respond….the earth system has amplifiers and feedbacks that mushroom small impacts into large responses.” Greenland’s ice and the frozen soil beneath it preserve the memory of such erratic behavior. They give us climate scientists pause.

Greenland’s ice sheet is central to Earth’s climate system and its response to human-­induced climate change. When white ice and snow melt, they stop reflecting solar energy in the twenty-­four-­hour sunshine of the Arctic summer. Dark-­colored rocks and green tundra take their place, soaking up the sun’s energy and warming the planet. Water locked up for millennia in solid ice on land is suddenly freed and races to the ocean. People living by the coast 10,000 miles away from the Arctic then watch their homes go beneath the waves. Greenland has exceptionally long arms. They envelop our entire planet and its people in one way or another. Greenland’s future is our future.

The more we understand about Earth, the more likely we will be to treat it better going forward. Geologists use the present to explain the past and use the past as our guide to the future. Greenland’s massive ice sheet is an archive, and ice cores, like the ones from Camp Century, are frozen Rosetta stones. Once we learned how to decipher those cores, they revealed Earth’s climate history, and thus a glimpse into our collective future catalyzed by seeing the past more clearly. As we face the increasing heat of a rapidly changing global climate, ice cores are key to answering one of the most pressing scientific questions of our time: What will become of Greenland’s ice sheet as humans warm Earth?

Every December, for as long as I can remember, the radio station where I live has played the same recording. It’s of an older Vermonter with a thick New England accent reading Charles Dickens’s A Christmas Carol. This year, when I heard the story and noted that the grass on my front lawn was still green and bare of snow, I started to wonder if we, the people of this planet, are a collective Scrooge. If so, then the Camp Century ice core could be the Ghost of Christmas Past. But then I thought, what about the frozen plant fossils, so well preserved in the frozen soil beneath the ice? Although ancient, those bits of moss, twigs, and leaves could well be the Ghost of Christmas Yet to Come, a disturbing way for us to envision Greenland’s future. A future when the ice is gone, again.

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Excerpted from When the Ice Is Gone: What a Greenland Ice Core Reveals About Earth’s Tumultuous History and Perilous Future by Paul Bierman. Copyright © 2024 by Paul Bierman. Used with permission of the publisher, W. W. Norton & Company, Inc. All rights reserved.