Cracking the Ice

On paper, Richard Alley cuts quite a figure. He's an Evan Pugh professor, holder of the highest academic rank that Penn State bestows. His contributions to ice science and the study of climate are widely cited around the world. He has been called one of the foremost glaciologists of all time. In person, Alley cuts a figure of a different sort. Something closer to the boy rockhound he was in the early 1970s: the kid who spent his days crawling through the caves around Worthington, Ohio, looking forward to meetings of the local geology club.

man in coat surrounded by ice

Most days, he pedals his bicycle to work: knees churning, head low over the handlebars, wind mashing his curly red beard as he flies across campus. ("I have never purchased a campus parking pass," he says proudly.) Seated in his office, he hangs one leg absently over the arm of his chair, sandaled foot bobbing as he launches into a quick lesson on how mountains form. He seems delighted to draw an analogy from Dr. Seuss.

He seems delighted, period. And eager to share. It's his relentless enthusiasm, in part, that makes Alley a popular teacher and speaker, in demand at the Smithsonian Institution as well as on National Public Radio and the BBC. But it's what he has to say about climate that draws attention at the White House and on Capitol Hill.

On rising global sea level from shrinking polar ice sheets: "No one expects Waterworld. But even a little change in that big a reservoir will be noticed."

On the possibility of rapid, catastrophic climate change in the not-too-distant future: "There's at least a slight chance that the world will reach out and bite us."

On the last half-million years of Earth's climate: "Where we live is just about the only boring piece of the whole story."

Much of what Alley knows about climate he has learned from studying a two-mile long column of ice, drilled from the frozen center of Greenland.

The Greenland core, extracted in the early 1990s, samples the layer-by-layer build-up of snow over tens of thousands of years: snow that is gradually packed down into ice by the accumulating weight of new layers. Unmelting, undisturbed, the ice traps dust, ash, and atmospheric gases, preserving these clues in the order received in what amounts to the richest record we have of Earth's climatic history.

Back in 1985, when the Greenland core was still in planning, Alley was a graduate student at the University of Wisconsin. His adviser there, Charles Bentley, "was one of the grand old men of glaciology," Alley remembers. "He was one of the guys who had done the heroic traversing of Antarctica back in the '60s, driving out across the screaming whiteness to see what was there." Through Bentley, Alley got involved in scouting for drilling sites for the new project. When the main coring started in 1989, Alley, by then an assistant professor at Penn State, signed on. For the next four years he spent his summers in central Greenland.

There, Alley was paired with Tony Gow, like Bentley a polar veteran, who with the Army Corps of Engineers had pioneered ice-core analysis in the 1950s. "We were supposed to be studying the physical properties of the ice," Alley remembers. "Density, the alignment of crystals. . . . We were looking for folds caused by flow," the accordioning of layers that results when moving ice flows over bumps in its bed. Where folds go undetected, a descending drill may penetrate the same layer of ice repeatedly, skewing measurements of age.

In the course of this work, Alley learned how to recognize the difference between a winter layer of ice and its summer counterpart. The latter, he explains, contains alternate layers of frost—"like the frost on your lawn on a cold morning, except better. In Greenland, you can get an inch of it—on the volleyball net, on the radio tower, and on the surface as well. But this only happens in summer. So summer snow contains intermittent layers—one inch of real dense snow, and one inch of poofy, low-density stuff. In winter it's all high-density."

Alley's distinction proved crucial in the struggle to attach accurate dates to the emerging core. "Once you can read layers this way, you have a system for counting the years, like tree-rings," he says. And once the core is reliably dated, "you're off to the races." From the thickness of each "ring," you can calculate annual snowfall. By its dirtiness, you can begin to determine levels of dust that were present in the air. From age and accumulation taken together, you can extrapolate temperature.

"This system is not perfect," Alley acknowledges. "But we can check ourselves against historical events." In 1783, for instance, a major volcanic eruption in neighboring Iceland floated large quantities of ash and sulfuric acid into the atmosphere. "We found and identified this particular residue in one of our samples," Alley says. The layer had already been assigned the year 1785.

The Greenland core—in hundreds of 20-foot segments, five inches in diameter— now rests in refrigerated splendor at the National Ice Core Laboratory in Denver, Colorado. "We can make sense of about 110,000 years of it," Alley says. What has emerged from this record is a portrait of Earth's climate history as a far bumpier ride than had previously been suspected.

two men lean over ice on a light

"Dramatic change can take place over very short periods," Alley says: "That's what jumps out." At the end of the last Ice Age, for example, according to the Greenland record, temperatures spiked 15 degrees F in just 10 years. "Snowfall doubled, and there was a five-to-ten-fold increase in the amount of dust in the air. Global wetland increased by 50 percent almost overnight. What that tells us is that there are switches as well as dials in the Earth system.

"Most of the time," he explains, "when we think about how climate works we think about a dimmer dial. Put a little more CO2 into the system and the world will change a little. Change the sun a little, move the continents, and there's a little change in climate. The effect is corresponding.

"With a light switch, though, you push a little and nothing changes. A little more, and nothing changes. A little more, still nothing. Until one day you push hard enough, and everything changes. Right now. Sudden, major change."

The Ice Age cycle, with its waxing and waning epochs of frigidity, is "basically a dial," Alley says. Temperatures tail off gradually over a period of tens of thousands of years, then turn around and start climbing again. "This variation closely parallels measurements of CO2 in the atmosphere, which in turn is somehow tied to periodic wiggles in Earth's orbit." These "wiggles" alter the distribution of sunlight in the Northern and Southern hemispheres.

Incidents of rapid change dance to a different piper. "It's an independent process that seems to have to do with ocean circulation," Alley says.

In simple terms, the ocean circulation acts like a giant heat-exchange belt between the Northern and Southern hemispheres. In the Atlantic, warm surface water is carried north from the coast of Brazil all the way to Norway. As it reaches colder air, it loses heat, and—cold water being denser—sinks, returning south to be warmed again. This orderly flow plays a major role in determining regional climate.

Take a computer model of the circulation, however, and tweak it just a bit, and you can prevent those warm currents from flowing north. If you do, Alley says, the North Atlantic quickly freezes over—and as soon as that happens, the whole conveyor just shuts down. Temperatures drop across the entire Northern hemisphere, and the South grows continually warmer.

Things eventually right themselves. Salt levels in the Atlantic, rising with evaporation and no longer flushed by north-south currents, eventually build up and jump-start the circulation by making surface waters dense enough to sink into the deep ocean. But the re-start is abrupt, Alley says, and the upshot of it is rapid northern warming.

"This pattern shows up repeatedly in the ice record. It's like something superimposed on the Ice Age cycle, seesawing on top of it."

The models show that one good way to start the seesaw is to flood the North Atlantic with fresh water. And one way to do that, Alley says, is by raising global temperatures enough to make a melt of Greenland.

Melting glaciers are one potentially major impact of the current global warming. Already, temperatures in this century have nudged up enough to melt the glaciers scattered on the Earth's mountaintops. In less than 15 years, according to measurements by Ohio State glaciologist Lonnie Thompson, the snows of Kilimanjaro, Africa's highest peak, will be gone—and a similar fate awaits the tropical glaciers of the Andes. Even in the northern Alps, indications are that 90 percent of the volume of ice measured a century ago will be gone by 2025.

NASA studies show that Greenland's ice is thinning, too Ð three feet a year in some places. The sharply increased rate of recent melting noticed in all these glaciers is a clear indicator that humans have impacted global warming, Alley says. But in terms of raising sea level, the major concern is Antarctica, where 91 percent of Earth's glacial ice resides. If the giant West Antarctic ice sheet were to collapse and fall into the ocean, sea level could rise 20 feet in 100 years, swamping coastal areas and lowlands around the world.

multicolored mosaic

Alley has been studying the mechanics of flow on the West Antarctic sheet since he was a graduate student. "In most of Greenland and most of Antarctica," he explains, "ice flows in a sheet." Snow falls and piles up, compacting into ice, and—once it piles high and heavy enough—gravity carries the ice outward, "like pancake batter," toward the sea.

"But near the coast, especially in West Antarctica," Alley says, things work differently. "The sheet tends to break up—into fast-moving jets, or streams, separated by larger, slow-moving areas." How stable is the current balance between fast ice and slow? And what would happen if that balance were thrown off?

Working with seismologists who bounce sound waves through the ice, Alley has hypothesized that the fast-moving streams are seated on a soft layer of mud, which lubricates their passage. He and others are currently testing this model, hoping to learn, among other things, whether climate changes might cause fast-moving streams to expand.

"Will the West Antarctic ice sheet fall into the ocean in the next 100 years? I would say it's a low probability event," Alley says, " but not a zero possibility."

Even far less drastic changes, he stresses, will have real global impact. "If you melt the Antarctic ice by one percent, people living at the coast will either have to build walls or move. And if you're in some place like Bangladesh, where do you move? A small change will matter to a lot of people. What that means is we really have to understand the ice well Ð and we don't yet."

Which is not to say that great progress hasn't been made over the course of his career. "It's amazing how fast this field has come along," Alley says. But what really delights him, it seems, is that there's so much more to learn.

Richard B. Alley, Ph.D., is Evan Pugh professor of geosciences in the College of Earth and Mineral Sciences, 517 Deike Building, University Park, PA 16802; 814-863-1700; ralley@essc.psu.edu. Alley was awarded the Faculty Scholar Medal for the physical sciences in 1999. His most recent book, The Two-Mile Time Machine: Ice Cores, Abrupt Climate Change and Our Future, was published in 2000 by Princeton University Press.

Last Updated September 01, 2001