Photo by Gary Comer
Icebergs break off and flow through Greenland’s coastal waters. The stunning ice armada comes at a potentially high cost to the island’s disappearing ice sheet.
Chasing Greenland’s melting ice in search of climate clues
by Gretchen Roecker
Oct 06, 2011
Photo by Philip Walsh
Greenland’s vast ice sheet covers 90 percent of the island, but is drawing back its margins to as warmer temperatures melt the frozen layer. Geologist George Denton and author Philip Conkling, who recently published "The Fate of Greenland," stand as specks on the barren bedrock.
Map courtesy of Thomas Lowell
The GRIP, GISP and Renland cores drilled through the Greenland ice sheet contain air bubbles that trap information about the planet’s past climate.
Photo courtesy of Thomas Lowell
Scientists Thomas Lowell, Brenda Hall and Meredith Kelly study west Greenland’s ice caps, the frozen domes perched on plateaus. Ice caps tower over the humans who hunt for climate clues at their edges, but are dwarfed by the vast ice sheet. Because of their relatively small size, ice caps offer more manageable research sites for scientists trying to learn about past and present climate changes.
Gretchen Roecker/MEDILL
Meredith Kelly, of Dartmouth College, presents her research on lakebeds near the west Greenland ice caps. Kelly uses radiocarbon dating techniques to find out how the ice caps – and the ice sheet – have grown and shrunk in response to changing conditions.
Photo courtesy of Thomas Lowell
Thomas Lowell scours ice cap margins for organic materials, such as leaves and wood, uncovered by the retreating glaciers.
“He recognized that even though this was a great adventure, it really meant the Arctic was changing very rapidly, and he wanted to do something about that,” said Philip Conkling, president of the Island Institute in Maine and Comer’s fellow seafarer.
That “something” was pouring energy and money into abrupt climate change research, starting in Greenland. Comer had sold his company, Lands’ End, to Sears in the early 1990s, and dedicated his fortune to supporting science, education and other causes.
“It is one of the premiere places to get histories of climate change,” said geologist Richard Alley of Pennsylvania State University. “There are just these huge wonderful climate records that we can pull out.”
Pulling out those records lets scientists fill in clues about current climate change. Alley’s work on ice cores extracted from the middle of the island has uncovered natural archives of temperature, measured from air pockets trapped far below the surface in these "time machines," as Alley calls them.
Similar ice cores in Antarctica link temperature rise with climbing carbon dioxide levels, which are today almost 25 percent higher than at any point in the past 650,000 years.
Greenland, the largest island on Earth, is almost entirely quilted in a sheet of ice more than 1,000 miles long, 600 miles wide and two miles thick, built up from millennia of snowfall. The bedrock beneath the frozen layers is secure in the North Atlantic, but according to NASA satellite data the ice sheet blanket is disappearing at a rate of at least 100 billion tons per year – equivalent to a billion blue whales’ worth of mass. That’s twice the rate measured in the mid-1990s.
“A lot of people are worried about changes in the Greenland ice sheet,” said Meredith Kelly, a Dartmouth College geoscientist and Comer fellow, because it holds enough fresh water to raise sea level worldwide by at least six meters, or about 20 feet, if it melts. “That would inundate a lot of people living along coastlines and cause a lot of massive changes for civilizations and for people to deal with.”
Following Comer’s alarmingly easy passage to the Arctic Ocean, Comer and Conkling connected with renowned geoscientist Wallace Broecker, of Columbia University’s Lamont-Doherty Earth Observatory. By 2002, the three men joined Alley, University of Maine geologist George Denton and a crew of climate scientists on Turmoil, bound for east Greenland.
Today, with support from the Comer Science and Education Foundation, some of those same scientists are scrambling to study clues revealed at the sheet margins as the ice melts in search of historical context for how and why Greenland’s ice sheet is slipping into the sea.
Why Greenland?
Long before Comer offered his ship as a research vessel, Broecker, Alley and other paleoclimatologists studied fingerprints of Earth’s climate history in Greenland’s frozen landscape. They looked for traces of how and why the planet has periodically fluctuated from warm to cool, wet to dry, inhabitable to habitable.
Evidence of sudden past temperature shifts in ice cores drilled in Greenland in the 1960s sparked Broecker’s seminal “conveyor belt” theory of thermohaline circulation in the ocean. The “conveyor belt” refers to the cycle where cold water heavy with salt sinks in the North Atlantic near Greenland and flows southward toward Antarctica, while warm Gulf Stream water moves northward along the surface, eventually cooling and sinking as it loses heat to the air. The flow brings climate signals between the poles.
“That blew my mind,” Broecker said. “Thinking about how those events happened got me onto the whole conveyor belt thing.”
Greenland’s unique features have been a gold mine for other researchers in the decades since Broecker’s brainstorm.
“It’s the big cold ice sheets” that make Greenland an excellent location for climate research, Alley said, because they provide a range of useful records not captured from smaller glaciers. “We can do a really good job of learning the history of atmospheric composition, we can learn the history of snowfall, we can learn the history of temperature.”
Ice cap canaries
While Alley’s ice cores show conditions at the center of the island, the edges of those “big cold ice sheets” intrigue climate scientists because they advance and retreat with even slight temperature shifts.
Geologists Brenda Hall of the University of Maine and Thomas Lowell of the University of Cincinnati have returned to Greenland five times since their first trip funded by Comer in 2002. Since that initial journey, they have fast-forwarded their focus to the Holocene, the current interglacial during which human civilizations have risen, fallen and spread across the continents.
Along with Kelly, Hall and Lowell are documenting how eastern Greenland’s ice has grown and shrunk over the 10,000-year period since the last major glacial period, when ice covered much of North America, Europe and Asia. Rather than studying the massive ice sheet that drapes most of the island, they focus on the smaller domed ice caps that dot Greenland’s plateaus.
“We’re working on the ice caps in part because they’re easier to work on, but our premise is that the ice caps are recording the same climate that the ice sheet is recording,” Hall said.
Using the small ice caps as proxies for the larger ice sheet provides information not available from other records about how the ice reacts to temperature shifts, Kelly said.
“The ice core records tell us a ton of information about what’s going on in the atmosphere,” Kelly said, “but they don’t tell us how the margin of the ice sheet is responding to warmings or coolings.”
In order to track those responses across thousands of years, Lowell, Hall and Kelly are chasing the retreating ice caps, which melt away to reveal evidence of life from earlier periods.
“Because these glaciers are in a retracted position,” Lowell said, “we see all kinds of weird things along the glacial margins.” Since 2005, Lowell has identified at least 16 species preserved by the ice, from sedges and trees to lemming droppings.
While Lowell collects organic samples preserved in the margins of the shrinking caps, Hall and Kelly drill into nearby lakebeds to suck out tubes of sediment. They analyze the layers and fish for seeds, leaves and insects trapped in the mud. They use radiocarbon dating methods to figure out approximately how long ago each sample was buried by the ice.
The retreating ice gives them unique access to information on glacial behavior, Hall said. Over the past five years their records have grown as the melting caps uncover more materials. But the unhealthy ice caps also signal rapid changes in the ice sheet whose impacts that could spill out across the globe.
“They’re the canaries,” Lowell said. Like the songbirds whose deaths once warned miners of toxic gases leaking below ground, the ice caps’ watery demises signal conditions that could be fatal for the larger ice sheet.
Lowell and Hall said they can’t predict how human actions ultimately will influence natural climate shifts, but that their records help others model what is likely to lie a few years or centuries ahead.
“Our work better documents how things looked in the past,” Lowell said, so that “the projections for the future are more refined.”
Projections aren’t necessary to see that Greenland’s ice is disappearing. Lowell, Hall and Kelly simply watch the ice caps shrinking away from year to year. Conkling, who recently helped Broecker, Alley and Denton write “The Fate of Greenland,” an account of their trips on Turmoil and their work on the island, said he and Comer witnessed the powerful melt.
“Every 10 minutes an enormous wall of ice would just go into the water,” Conkling said. “There were dying glaciers everywhere we went. You couldn’t say that climate change isn’t happening.”
Though Greenland’s ice sheet isn’t likely to collapse into the ocean abruptly, Alley said, warming temperatures will spur more melting – common estimates from recent studies indicate that Greenland could contribute to at least a three-foot increase in sea level this century. The thawing margins add fresh water to the ocean that directly raises sea levels and could alter ocean circulation, eventually impacting the southern hemisphere and factors from carbon dioxide levels to fish populations.
“It’s a tremendous player in climate future,” Alley said.
Keys to the future revealed in the past
Preliminary results show that Greenland’s ice has been a big climate player throughout time, with evidence for advances and retreats that might correspond to bumps in the relatively stable Holocene climate. Lowell’s samples suggest a rapid thawing at the end of the last glacial period about 11,000 years ago that left the area almost ice-free.
Hall’s lake records show that at least one ice cap was smaller than its present size in from about 10,000 to 1,000 years ago AD, through middle of the Medieval Warm Period, a few centuries marked by slightly higher average temperatures in the North Atlantic when Norse sailed from Europe to settle in Greenland. She also found evidence for an ice advance between 1000 and 1150 AD, marking the onset of the “Little Ice Age,” the common name for a cold period spurred by a small temperature drop in the north that might have contributed to the decline of those settlements.
“It’s important to understand natural variability because these natural climate changes in the Holocene are relatively small,” Hall said. Those relatively small ups and downs in precipitation and temperature can generate big changes in what the planet looks like.
The approximately 6 degrees Celsius (10.8 F) warming that ended the last major ice age and the much smaller changes that marked the Medieval Warming and Little Ice Age might seem like tiny temperature shifts. But Hall said the obvious impact of slight changes not only on ice caps but also on living populations underlies her research.
“History shows us the effect that 1 degree Celsius can actually have on civilizations,” Hall said. “We really need to have a better understanding of what causes these natural climate changes, in order to have an understanding of whether or not we might trigger one of these inadvertently in the future.”
Global temperatures are already rising rapidly compared to past, natural shifts. According to NASA, the planet has warmed about 1.5 F since the burst of fossil fuel-burning industrialization in the late 1880s. While human-induced warming in the Arctic isn’t yet extreme, that could change if heat-trapping carbon emissions aren’t significantly reduced: estimates for additional temperature rise through 2100 under a “business-as-usual” scenario range from about 3 to 15 F, according to Alley’s book, “Earth: The Operator’s Manual.”
Studying patterns in how ice in the northern hemisphere has responded to the Holocene’s temperature swings, Kelly said, provides information about how climate changes naturally – and how projected extra warming could amplify that process.
“It gives us a natural baseline for how climate has changed in the past,” Kelly said, “and it also enables us, when we put together these global records from Greenland to the Swiss Alps to New Zealand, to try to understand the mechanisms that cause climate change.”
For example, Kelly said, she and fellow scientists have observed that a cooling period caused glacial growth about 3,000 years ago in Greenland, Europe, Peru and New Zealand. That similarity could point to something influencing climate in both hemispheres, like a change in Broecker’s conveyor belt or in atmospheric circulation, she said.
Carrying on a legacy
The retreating small ice caps offer a “window of opportunity” to study climate history, Lowell said. And while those canaries of climate change could disappear without greatly affecting sea level or climate mechanisms, they act as heralds for much larger consequences of warming.
“The ice caps could melt and nobody would notice,” Hall said. “But they are very sensitive climate indicators, and the records we get from that can help us really understand the ice sheet, which is the big player.”
A decade after Comer’s sail through a strikingly ice-free Northwest Passage, members of his research crew still hold their positions as human players in Earth’s climate future. Comer’s daughter, Stephanie, who was on that legendary Turmoil voyage, and his son, Guy, are carrying on their father’s legacy by continuing to support climate researchers through his foundation.
Hall, Lowell and Kelly don’t know what lies in Earth’s future, but by tracing the hidden histories revealed by melting ice caps, they are revealing a sensitive, interconnected planet whose climate and conditions can hinge on a few degrees of warming or cooling.
