Science: Greenland melted recently, shows high risk of sea level rise today
Long-lost ice core reveals that most of Greenland was green 416,000 years ago
IMAGE: A LARGE PORTION OF GREENLAND MELTED ABOUT 416,000 YEARS AGO—PERHAPS A BIT LIKE THE MODERN GREENLAND LANDSCAPE SHOWN IN THIS PHOTO—AND BECAME ICE-FREE TUNDRA, OR BOREAL FOREST, A NEW STUDY IN THE JOURNAL SCIENCE SHOWS. THE RESULTS HELP OVERTURN A PREVIOUS VIEW THAT MUCH OF THE GREENLAND ICE SHEET PERSISTED FOR MOST OF THE LAST TWO AND A HALF MILLION YEARS. INSTEAD, MODERATE WARMING, FROM 424,000 TO 374,000 YEARS AGO, LED TO DRAMATIC MELTING. THIS FINDING INDICATES THAT THE ICE SHEET ON GREENLAND MAY BE MORE SENSITIVE TO HUMAN-CAUSED CLIMATE CHANGE THAN PREVIOUSLY UNDERSTOOD—AND WILL BE VULNERABLE TO IRREVERSIBLE, RAPID MELTING IN COMING CENTURIES. view more
CREDIT: JOSHUA BROWN
Summary:
• A large portion of Greenland was an ice-free tundra landscape—perhaps covered by trees and roaming woolly mammoths—in the recent geologic past (about 416,000 years ago), a new study in the journal Science shows.
• The results help overturn a previous view that much of the Greenland ice sheet persisted for most of the last two and a half million years. Instead, moderate warming, from 424,000 to 374,000 years ago, led to dramatic melting.
• At that time, the melting of Greenland caused at least five feet of sea level rise, despite atmospheric levels of heat-trapping carbon dioxide being far lower than today (280 vs. 420 ppm). This indicates that the ice sheet on Greenland may be more sensitive to human-caused climate change than previously understood—and will be vulnerable to irreversible, rapid melting in coming centuries.
• The scientists—from the University of Vermont (UVM), Utah State University, and fourteen other institutions—used sediment from a long-lost ice core, collected at a secret U.S. Army base in the 1960s, to make the discovery. They applied advanced luminescence and isotope techniques to provide direct evidence of the timing and duration of the ice-free period.
A Green Land
During the Cold War, a secret U.S. Army mission, at Camp Century in northwestern Greenland, drilled down through 4560 feet of ice on the frozen island—and then kept drilling to pull out a twelve-foot-long tube of soil and rock from below the ice. Then this icy sediment was lost in a freezer for decades. It was accidentally rediscovered in 2017 and shown to hold not just sediment but also leaves and moss, remnants of an ice-free landscape, perhaps a boreal forest.
But how long ago were those plants growing—where today stands an ice sheet two miles thick and three times the size of Texas?
An international team of scientists was amazed to discover that Greenland was a green land only 416,000 years ago (with an error margin of about 38,000 years).
Their new study was published in the journal Science on July 21, 2023.
Bulletproof Evidence
Until recently, geologists believed that Greenland was a fortress of ice, mostly unmelted for millions of years. But, two years ago, using the rediscovered Camp Century ice core, this team of scientists showed that it likely melted less than one million years ago. Other scientists, working in central Greenland, gathered data showing the ice there melted at least once in the last 1.1 million years—but until this study, no one knew exactly when the ice was gone.
Now, using advanced luminescence technology and rare isotope analysis, the team has created a starker picture: large portions of Greenland’s ice sheet melted much more recently than a million years ago. The new study presents direct evidence that sediment just beneath the ice sheet was deposited by flowing water in an ice-free environment during a moderate warming period called Marine Isotope Stage 11, from 424,000 to 374,000 years ago. This melting caused at least five feet of sea level rise around the globe.
“It's really the first bulletproof evidence that much of the Greenland ice sheet vanished when it got warm,” says University of Vermont scientist Paul Bierman, who co-led the new study with lead author Drew Christ, a post-doctoral geoscientist who worked in Bierman’s lab, Professor Tammy Rittenour from Utah State University, and eighteen other scientists from around the world.
Understanding Greenland’s past is critical for predicting how its giant ice sheet will respond to climate warming in the future and how quickly it will melt. Since about twenty-three feet of sea-level rise is tied up in Greenland’s ice, every coastal region in the world is at risk. The new study provides strong and precise evidence that Greenland is more sensitive to climate change than previously understood—and at grave risk of irreversibly melting off.
“Greenland’s past, preserved in twelve feet of frozen soil, suggests a warm, wet, and largely ice-free future for planet Earth,” says Bierman, a geoscientist in UVM’s Rubenstein School of the Environment and Natural Resources and a fellow in the Gund Institute for Environment, “unless we can dramatically lower the concentration of carbon dioxide in the atmosphere.”
Into the Light
The team’s new study in Science, combined with their earlier work, is causing a major and worrisome rethinking of the history of Greenland’s ice sheet. “We had always assumed that the Greenland ice sheet formed about two and a half million years ago—and has just been there this whole time and that it’s very stable,” says Tammy Rittenour, a scientist at Utah State University and co-author on the new study. “Maybe the edges melted, or with more snowfall it got a bit fatter—but it doesn't go away and it doesn't dramatically melt back. But this paper shows that it did.”
At Rittenour’s lab, sediment from the Camp Century core was examined for what is called a “luminescence signal.” As bits of rock and sand are transported by wind or water, they can be exposed to sunlight—which, basically, zeros out any previous luminescence signal—and then re-buried under rock or ice. In the darkness, over time, minerals of quartz and feldspar in the sediment accumulate freed electrons in their crystals. In a specialized dark room, Rittenour’s team took pieces of the ice core sediment and exposed them to blue-green or infrared light, releasing the trapped electrons. With some advanced tools and measures, and many repeated tests, the number of released electrons forms a kind of clock, revealing with precision the last time these sediments were exposed to the sun. “And the only way to do that at Camp Century is to remove a mile of ice,” says Rittenour, “Plus, to have plants, you have to have light.”
These powerful new data were combined with insight from Bierman’s UVM lab. There, scientists study quartz from the Camp Century core. Inside this quartz, rare forms—called isotopes—of the elements beryllium and aluminum build up when the ground is exposed to the sky and can be hit by cosmic rays. Looking at ratios of beryllium and other isotopes gave the scientists a window onto how long rocks at the surface were exposed vs. buried under layers of ice. This data helped the scientists show that the Camp Century sediment was exposed to the sky less than 14,000 years before it was deposited under the ice, narrowing down the time window when that portion of Greenland must have been ice-free.
Under Ice
Camp Century was a military base hidden in tunnels under the Greenland ice sheet in the 1960s. One strategic purpose of the camp was a top-secret operation, called Project Iceworm, to hide hundreds of nuclear missiles under the ice near the Soviet Union. As cover, the Army claimed the camp was an Arctic science station.
The missile mission was a bust, but the science team did complete first-of-its-kind research, including drilling a nearly mile-deep ice core. The Camp Century scientists were focused on the ice itself—part of an effort to understand Earth’s past ice ages and warm periods, the interglacials. They took little interest in the twelve feet of sediment gathered from beneath their ice core. Then, in a bizarre story, the ice core was moved in the 1970s from a military freezer to the University at Buffalo—and then to another freezer in Denmark in the 1990s. There it was lost for decades—until it was found again when the cores were being moved to a new freezer. More about how the core was lost, rediscovered in some cookie jars, and then studied by an international team gathered at the University of Vermont’s Gund Institute for Environment can be read here: Secrets Under the Ice.
Sea Level
Camp Century is 138 miles inland from the coast and only 800 miles from the North Pole; the new Science study shows that the region entirely melted and was covered with vegetation during Marine Isotope Stage 11, a long interglacial with temperatures similar to or slightly warmer than today. With this information, the team’s models show that, during that period, the ice sheet melted enough to cause at least five feet, and perhaps as much as twenty feet, of sea-level rise. The research, supported by the U.S. National Science Foundation, lines up with findings from two other ice cores collected in 1990s from the center of Greenland. Sediment from these cores also suggest that the giant ice sheet melted in the recent geologic past. The combination of these earlier cores with the new insight from Camp Century reveal the fragile nature of the entire Greenland ice sheet—in the past (at 280 parts per million of atmospheric CO2 or less) and today (422ppm and rising).
“If we melt just portions of the Greenland ice sheet, the sea level rises dramatically,” says Utah’s Tammy Rittenour. “Forward modeling the rates of melt, and the response to high carbon dioxide, we are looking at meters of sea level rise, probably tens of meters. And then look at the elevation of New York City, Boston, Miami, Amsterdam. Look at India and Africa—most global population centers are near sea level.”
“Four-hundred-thousand years ago there were no cities on the coast,” says UVM’s Paul Bierman, “and now there are cities on the coast.”
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Additional information:
- Original study in Science (available after embargo lifts): “Deglaciation of northwestern Greenland during Marine Isotope Stage 11.”
- Website with resources for media: Camp Century: below the ice
- One-minute video about the new study: https://www.youtube.com/watch?v=CYfSphNHOm8
- The University of Vermont’s National Science Foundation Cosmogenic Facility
- Utah State University’s Luminescence Lab
JOURNAL
Science
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Deglaciation of northwestern Greenland during Marine Isotope Stage 11
ARTICLE PUBLICATION DATE
21-Jul-2023
Greenland has greener history than previously thought, says USU Geoscientist
Tammy Rittenour and colleagues report much of the Artic island's ice melted as recently as 416,000 years ago, which has implications for sea-level rise
IMAGE: IN THE UTAH STATE UNIVERSITY LUMINESCENCE LAB, GRADUATE STUDENT HAWKE WOZNICK USES SIEVES TO PREPARE SEDIMENT SAMPLES FROM GREENLAND'S CAMP CENTURY FOR OSL DATING. USU GEOSCIENCES PROFESSOR TAMMY RITTENOUR AND COLLEAGUES REPORTED FINDINGS ABOUT THE SAMPLES IN THE JULY 20, 2023, ISSUE OF THE JOURNAL 'SCIENCE.' view more
CREDIT: USU/LEVI SIM
LOGAN, UTAH, USA -- New analysis of samples collected from underneath Greenland’s ice sheet reveal the Arctic island was much greener as recently as 416,000 years ago. The findings overturn previous views that Greenland’s continental glacier, which covers about 80 percent of the 836,3000-square-mile land mass, has persisted for the last two and a half million years.
“We’re discovering the ice sheet is much more sensitive to climate change than we previously thought,” says Utah State University geoscientist Tammy Rittenour. “This is a foreboding wake-up call.”
Rittenour, with colleagues from the University of Vermont and fourteen other institutions, reports findings in the July 20, 2023, issue of the journal Science. Their research is supported by the National Science Foundation.
A greener Greenland means the island’s formidable-appearing ice sheet – nearly two miles thick in places – is not as stable as it appears.
“We had always assumed the ice sheet has remained about the same for nearly 2.5 million years,” says Rittenour, professor in USU’s Department of Geosciences. “But our investigation indicates it melted enough to allow the growth of moss, shrubs and buzzing insects during an interglacial period called Marine Isotope Stage 11, between 424,000 to 374,000 years ago.”
The melting caused at least five feet of sea-level rise around the globe, she says. “Some of our model scenarios suggest sea levels up to 20 feet higher than today.”
“It was an unusually long period of warming with moderately elevated levels of carbon dioxide – CO2 – in the atmosphere,” Rittenour says. “What’s alarming about this finding is today’s CO2 levels are 1.5 times higher.”
Even if humans abruptly stopped activities that contribute to greenhouse gas emissions, she says, “we’d still have inflated CO2 levels for hundreds, maybe even thousands, of years to come.”
That’s an uneasy realization, she says, with current rates at which Greenland’s ice sheet is thawing.
“And that’s not taking Antarctica and other glacial areas into consideration,” Rittenour says. “The deglaciation has implications for the entire globe and is especially sobering for our coastal mega-cities, where so much of the world’s population resides.”
The team’s analysis is a continuation of research started several years ago, when the scientists happened upon samples collected from an extraordinary, Cold War-era military project.
“In 1960, the U.S. Army launched a top-secret effort called Project Iceworm in northwestern Greenland to build a network of mobile nuclear launch sites under the ice sheet,” Rittenour says. “As part of that project, they also invited scientists and engineers to conduct experiments in a highly publicized ‘cover’ project, known as Camp Century, to study the feasibility of working and carrying out military missions under ice and in extreme-cold conditions.”
Hampered by brutal blizzards and unstable ice conditions, Project Iceworm’s cavernous underground bunker and tunnels were abandoned in 1966. But sediment samples collected at the bottom of a more than 4,000-foot-long ice core extracted from the site have yielded the surprising information about Greenland’s not-so-distant geologic past.
The frozen soil samples from the base of the Camp Century ice core were forgotten in a freezer for decades, until recently re-discovered.
“We have very few samples from below the Greenland ice sheet, because most drilling missions stop when they reach the base of the ice,” Rittenour says. “These re-discovered Camp Century sediments represent a unique, unspoiled time capsule of past conditions.”
While the frozen soil sat in a freezer for more than 60 years, science technology advanced. Rittenour, who is director of the USU Luminescence Laboratory, was invited to help date the sediment.
“Because the samples remained frozen and largely untouched, I was able to use luminescence dating to determine the last time they were exposed to sunlight,” she says. “If researchers had examined the sediments in the past, we couldn’t have run any of the analyses we did for this paper.”
Rittenour says today’s investigative technologies enable researchers to distill a good record of what’s happened in Greenland and other parts of the world.
“These once lost, Cold War relics from a top-secret nuclear military base carved within the ice are continuing to tell their secrets, and forewarn us of the sensitivity of Earth’s climate,” she says. “If we can lose the far northwest portion of the Greenland ice sheet under natural conditions, then we’re treading dangerous waters given current elevated greenhouse gas conditions.”
Utah State University Geosciences Professor Tammy Rittenour, pictured in July 2023 at Iceland’s Langjökull ice cap, studies the paleoclimatology of extreme environments throughout the globe.
CREDIT
USU/Tammy Rittenour
JOURNAL
Science
METHOD OF RESEARCH
Data/statistical analysis
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Deglaciation of northwestern Greenland during Marine Isotope Stage 11
ARTICLE PUBLICATION DATE
20-Jul-2023
Northwestern Greenland was ice-free 400,000 years ago, according to Camp Century sediments
Summary author: Walter Beckwith
Peer-Reviewed PublicationSediments recovered from the base of the Camp Century ice core show that northwestern Greenland was ice-free during a period of history known to have exhibited some of the lowest global ice volumes -- the Marine Isotope Stage (MIS) 11 interglacial period. The absence of ice at that location means that the Greenland Ice Sheet must have contributed more 1.4 meters of sea-level equivalent to global sea level during the interglacial – a period in which average global air temperature was similar to what we’ll soon experience, given human-caused climate warming. The climate conditions of past interglacials – periods during Earth’s climatic history characterized by warmer global temperatures and reduced global ice coverage – provide opportunities to better understand how Earth’s cryosphere will respond to our warming climate and contribute to sea level rise. However, well-dated sedimentary records from areas formally ice-free during interglacial periods are rare or difficult to obtain due to present-day ice cover. One notable exception is the Camp Century ice core from northwestern Greenland, which contained rare frozen subglacial sediments suggesting that the region was ice-free at some point during the Pleistocene. Using luminescence dating and cosmogenic nuclide data, Andrew Christ and colleagues analyzed the sediments and found they were deposited by flowing water in an ice-free tundra environment during the MIS 11 interglacial (~416 thousand years ago) after first being exposed at the surface and to sunlight less than 16,000 years earlier. Then, to better understand the deglaciation of Greenland during MIS 11, Christ et al. used an ensemble of ice sheet models and found that for the Camp Century location to be ice-free, melting of the ice sheet would have contributed to at least 1.4 meters of sea-level equivalent to the global mean sea level of the interglacial, which was between 6 and 13 meters higher than present. “If moderate warmth for 29 [thousand years] during MIS 11 resulted in significant ice loss from Greenland, then rapid, prolonged, and considerable anthropogenic Arctic warming will likely cause melting of the [Greenland Ice Sheet], raise sea level, and trigger additional climate feedbacks in the coming centuries,” write Christ et al.
JOURNAL
Science
ARTICLE TITLE
Deglaciation of northwestern Greenland during Marine Isotope Stage 11
ARTICLE PUBLICATION DATE
21-Jul-2023
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