Global warming is defrosting the massive ice caps at Earth’s poles at an increasingly alarming rate. Water once safely anchored in glacial ice is now surging into the sea. The flow could become a deluge. Millions of people living near coastlines are in danger. Inundation could impact every nation on earth.
But scientists don’t yet know how fast this ice will melt, or how high our seas could rise. In an effort to find out, a team of renowned and quirky geologists takes a 4,000-mile road trip across Western Australia. They collect fossils and rocks from ancient shorelines and accumulate new evidence that ancient sea levels were frighteningly high during epochs when average global temperatures were barely higher than today.
In Deep Water, veteran environmental journalist, radio producer and documentary filmmaker Daniel Grossman explores the new and fascinating science — and scientists — of sea-level rise. His investigation turns up both startling and worrisome evidence that humans are upsetting a delicate natural equilibrium. If knocked off balance, it could hastily melt the planet’s ice and send sea level soaring.
Unless we Earthlings get on a low-carbon diet — radically reducing our appetite for fossil fuels — two of Earth’s three great ice sheets, the Greenland and the West Antarctic, will shrink dramatically. (Researchers think the third, the East Antarctic Ice Sheet, is less sensitive to extra heat, although this is still debated.) Evidence shows that these huge glaciers have already reacted to the 1.5 degrees Fahrenheit of warming we’ve had since 1880s. For instance, until sometime in the 1990s, Greenland’s ice seemed to be neither gaining nor losing mass. It was in “equilibrium,” as scientists say.
Then, suddenly, the Jakobshavn Glacier, which was already the fastest moving in the world, doubled its seaward pace across Greenland’s ice sheet — from four to nearly eight miles per year.
The amount of ice swept by the glacier from Greenland’s interior to the coast doubled as well. When I visited the Greenland community of Ilulissat in 2003, I saw colossal blocks of blue, crenulated ice — some the size of Central Park, and half a mile tall — that had snapped off the glacier and fallen into a fjord called the Ilulissat Isbrae.
A crenulated iceberg, most likely ejected from the Jakobshavn Glacier, floats just offshore of Ilulissat, Greenland. This block of ice could easily be as big as a battleship.
Another huge glacier in Greenland, called Kangerdlugssuaq, reacted similarly around the same time. It fitfully tossed out giant icebergs for several years, then calmed down in 2007. But ice loss continues overall. By some estimates, Greenland now loses around 24 cubic miles of ice — more than the volume of all the glaciers in the Swiss Alps — each year. In the past decade, almost enough water has drained from or broken off Greenland to fill up Lake Ontario. The West Antarctic Ice Sheet in the Southern Hemisphere is likewise reacting to Earth’s warming. Remote sensing satellites passing over Antarctica suggest that this ice sheet is also shedding in the neighborhood of 24 cubic miles of ice annually. The two ice sheets are now out of equilibrium.
If the total loss — nearly 50 cubic miles of melted ice — sloshed across the United States, it would cover the entire country with about an inch of water. The oceans, though, are huge, and have barely registered this giant outburst. All that extra water would only raise sea level by less than the width of a pencil lead. But Earth could warm anywhere from 4.5 to 11.5 degrees Fahrenheit by the end of this century — unless urgent action is taken, on a scale not yet seriously considered. As seen with the Jakobshavn and Kangerdlugssuaq Glaciers, the polar ice sheets will react to a mere 1.5-degree warming. An increase in temperature several times greater could be much worse.
For 30 years, Hearty has pondered how much and how fast these ice sheets will respond to more heat. Raymo won a long-term grant from the National Science Foundation in part to explore the issue. These scientists, and many others like them, assert that the response of the ice sheets to a couple more degrees Fahrenheit of heating might foretell the fortunes of every nation on Earth.
It’s hard to predict how ice sheets will handle the heat. If only an ice sheet behaved like an ice cube dropped out of a freezer tray on a summer day. Ice cubes melt from the outside inward. As the exterior dribbles off, the inner ice appears in an orderly fashion, like layers of an onion. To determine the rate of melt, you account for factors like the temperature of the room, the movement of air currents, and whether the melt water drains off or collects around the remaining ice. Researchers know how to do this for ice cubes, and also for glaciers and ice sheets. They’ve estimated, roughly, that if all the world’s glaciers melted like ice cubes, sea level would go up about 15 inches by the end of the century. The estimate also factors in the expansion of warmer ocean water and areas of increased snowfall.
But ice sheets, while behaving like ice cubes in certain ways, also waste away in a manner no ice cube ever will: from the inside out. Frozen streams convey an ice sheet’s bulk from the interior to the perimeter, sometimes hundreds of miles away. There, at the edge of the ice sheet, great blocks shear away — like the ones I saw at the Ilulissat Isbae. Only huge mountains of ice, like the Jakobshavn Glacier in Greenland, possess the mass to make the interior flow like a liquid rather than staying rigid. Jakobshavn, half a mile thick where it meets the sea, unloads about 5 cubic miles of those city-park-size icebergs into the sea every year. Scientists aren’t sure why ice streams speed up at times or why they taper off. They don’t know the limit of an ice stream’s speed. They have no idea how much ice these frozen rivers could cast into the sea, though many researchers believe the amount could dwarf the quantity that dribbles off from surface melting.
Confident that what is past is prologue, Hearty hoped to explore these issues by reading in-the-field “archives” of climate history, written in tropical stones. At his side, I learned how to read the rocks as well.
Hearty earned his doctorate in glacial geology from the University of Colorado in Boulder, yet he studies tropical and subtropical seashores. He never takes samples anywhere near an ice sheet. I once asked him why.
“Polar bears,” he said. In his first year as a Ph.D. student, Hearty joined his graduate adviser, Gifford Miller, and another student on a research trip to the high Arctic in northern Canada. He spent his days shoveling soil off weathered granite bedrock near the coast of Baffin Island. Then, before inspecting the exposed rock, he would rinse its surface clean. The researchers, however, carried very little fresh water. To conserve, Hearty would empty his coffee bloated bladder onto the granite.
At each sampling spot, Hearty bent close to the ground. He noted straight, parallel scratches, sometimes barely visible, in granite burnished by centuries of wind and rain. Thousands of years earlier, at the start of the last ice age, the great Laurentide Ice Sheet had advanced across Baffin Island, scoring the bedrock with flinty stones scooped up during its advance.
At one point the ice sheet covered nearly half of North America. The two-mile-thick glacier gouged the bedrock again when it retreated, thousands of years later. Hearty measured the orientations of both sets of scratches, what glaciologists call striations. He penciled the cardinal directions into a waterproof Rite in the Rain field notebook, bound with a hard, sunflower-yellow cover. The researchers would later map the glacier’s direction by plotting the bearings of the striations. Miller would grind up shells they’d collected, determine their age, and then pinpoint when the ice sheet had advanced and retreated.
By boat, the team navigated the entire length of Frobisher Bay, a deep recess in the rim of Baffin Island. It took most of a summer. Icebergs threatened to crush their two small vessels. Wicked currents stirred up by 30-foot tides strained the vessel’s sputtering outboards, sometimes pulling the team’s boats backward.
Polar bears unnerved Hearty most. In winter, the bears live atop sea ice that covers the Arctic Ocean. They hunt by reaching through holes and fissures, using their catcher’s-mitt paws and knife-sharp claws to grab ringed seals surfacing for air.
In summer, half of the region’s floating ice disappears. The planet’s frozen Arctic mantle shrinks like a white skullcap washed in hot water. The predators migrate to land, where a polar bear’s lumbering gait is no match for agile land prey such as a hare. Hearty says that on Baffin Island, polar bears in summer are “frustrated vegetarians.” They snack on pea-size berries. They long to catch well-fed, sluggish glaciologists — or so Hearty feared.
Several times each day, Hearty saw bears loping across tundra and stone ledges, usually heading toward him. Book learning had taught him nothing about handling bears. Miller, though, had experienced these fierce predators before. He told his colleagues what to do. While one researcher knelt and worked, the other two stood guard, fingering loaded .30-06 rifles. “I’m not cut out for the wilderness experience,” Hearty recalls thinking. Then, he had a comforting thought — “the epiphany,” he calls it. “I must study ice where it is melted.”
The next summer, in 1982, Hearty set up camp on the Mediterranean seacoast. He began a lifelong quest: a global survey of low-latitude coastlines — all polar bear free. As he worked, thousands of miles from the poles, the young scientist ruminated on troubling theories about the northern and southern ice sheets.
For about the last 3 million years, Earth has cycled in and out of ice ages, between periods of cold (glaciologists call them glacials) and intervening periods of warmth (interglacials). When it’s cold, millions of cubic miles of water freeze solid near Earth’s poles. When it’s warm, about two-thirds of the ice melts — most of it in the Northern Hemisphere — and drains into the oceans, elevating sea level by hundreds of feet.
Each cycle takes about 100,000 years to complete. The glacials and interglacials are unequal in length. It is hard to fathom now, because our civilization arose during the current interglacial, but coldness predominates.
During most of the previous 3 million years, either there was an ice age under way, or glaciers were slowly advancing or retreating. Through eons, the lowest sea levels have corresponded to glacials, periods when ice piled up on Earth’s poles. The highest sea levels have corresponded to interglacials, when ice sheets retreated and their ice dispersed through melting. The most recent ice age ended about 14,000 years ago. With spurts forward, pauses and rare, brief reverses, the sea rose between then and several thousand years ago, after which it remained virtually unchanged. If a new ice age were to come and the ice sheets to advance once more, the sea would retreat, as it has scores of times. But today’s ice sheets in the Antarctic and Greenland are doing the opposite. They’re melting, and the sea is rising at an accelerating rate.
Daniel Grossman is a veteran environmental journalist, radio producer and documentary filmmaker. He has written and produced stories for a wide range of national and international outlets including the New York Times, The Boston Globe, Discover, Scientific American, Public Radio International, NPR, BBC, and Germany’s Deutsche Welle, among other outlets. He has been awarded an Alicia Patterson Foundation Fellow and a Ted Scripps Fellowship in Environmental Journalism, and he frequently collaborates with the Pulitzer Center on Crisis Reporting. Grossman holds a Ph.D. in political science and a B.S. in physics, both from MIT, and is the co-author of A Scientist’s Guide to Talking with the Media: Practical Advice from the Union of Concerned Scientists (Rutgers University Press: 2006).