Greenland's ice sheets hold clues to global sea-level rise

Scientists are drilling deep into glaciers and using sophisticated equipment to better understand a critical piece of the climate puzzle.Sunday, October 21

By Kristen Pope
Climbers descend several hundred feet into an ice sheet in Greenland, where they hope to plumb the mysteries of global climate change.

Word spread fast at the Kangerlussuaq International Science Support facility in Greenland: one of the bridges along Greenland’s longest road was now under the raging Watson River.

A research team was almost stranded on the far side of the bridge by the roaring water, and when they returned they warned Rutgers professor Åsa Rennermalm and her team, who were just about to head out to set up their field camp at the end of the road. Rennermalm opted to wait until the next morning when the temperature—and glacially fed river—would be lower to venture out to her research site.

Rennermalm’s team was delayed on July 15, just two days before one of the Greenland Ice Sheet’s three 2018 meltwater peaks, which occurred on July 17, July 31, and August 9. Summer is Greenland’s 'melt season', and these three “significant melt events” encompassed around 193,000 square miles—around one-third of the Greenland Ice Sheet’s surface—according to the National Snow and Ice Data Centre. These melting events weren’t as severe as 2012’s extreme season, which led to a surface melt of over 97 percent of the ice sheet and washed out a major bridge along the same road, but researchers are concerned and many are investigating the ice sheet to see just how fast it’s disappearing.

If the Greenland Ice Sheet melts significantly, it will affect far more than a few bridges. It could cause significant sea-level rise, which could leave coastal communities throughout the world—and even entire island nations—underwater. To learn more about how quickly the ice sheet is expected to melt, scientists from all around the world, including Rennermalm, are conducting research at far-flung field locations to study different aspects of the ice sheet, track changes, and plan for the future.

Where does the water go?

Rennermalm has studied Greenland’s ice sheet and tundra for nearly a decade, and she is currently working on several projects, including one to determine how much meltwater actually leaves the ice sheet versus how much remains deep within. “You might think everything escapes, but our research points [otherwise],” Rennermalm says.

“We are studying what happens to water at higher elevations,” she says. “Instead of forming channels [that run off], it will infiltrate into the snow and ice [where it is stored].”

Rennermalm also studies surface hydrology, examining how water flows on the ice sheet using high-resolution satellite images and other techniques. Learning where meltwater goes, and how much stays within the glacier versus going out to sea, could greatly help scientists in predicting sea-level rise.

University at Buffalo professor Jason Briner’s team is also looking to learn how rapidly the Greenland Ice Sheet may be melting. His team hopes to see if warmer air, which typically carries more moisture, may end up depositing additional snow in the Arctic—a factor which could reduce the rate of ice sheet shrinkage.

His team is working to figure out whether precipitation, temperature, or a combination of the two is influencing melt rate. Knowing this will help scientists develop more accurate computer models.

“If the ice sheet gets more snowfall in warm times then we might want to know that in our computer model forecasts of ice-sheet shrinkage and sea-level rise,” he says.

These models will help answer key questions. “What we’re interested in figuring out is the sensitivity of the ice sheet to climate change,” Briner says, noting this will ultimately influence sea-level rise. “If there's an abrupt climate change versus a gradual climate change, does that affect the ice sheet differently?”

Drilling deep into ice

High on the windswept Arctic ice in North East Greenland, the East Greenland Ice-Core Project (EastGRIP) team spent a four-month field season this summer collecting an ice core from the North East Greenland Ice Stream—a moving mass of ice. Researchers are using this multi-year international collaboration to peek into the past and find useful clues for the future.

“Understanding previous warm climate periods like the Climatic Optimum 5,000 to 8,000 years ago and seeing that as an analogue to the warm period we have now is certainly also of very big interest,” says Dorthe Dahl-Jensen, chairman of the EastGRIP Steering Committee and professor at Niels Bohr Institute in Copenhagen, Denmark.

“The Greenland Ice Sheet is losing mass in two ways: one is by melt along the margin along the coast of Greenland and the second is by discharge of ice through these ice streams,” says Dahl-Jensen. “We know very little about these ice streams and they’re responsible for about half of the mass loss from the Greenland Ice Sheet.”

This is the first time a team has drilled so deeply to extract an ice core from an ice stream, according to Dahl-Jensen. Snow trenches under the surface house the main research, and a team of scientists, bundled up in parkas, winter hats, and other extreme weather gear, is drilling through the ice stream all the way to bedrock—a projected distance of 2,550 metres (about 8,400 feet). The remote field location is accessed via a snow runway or “skiway,” which allows the U.S. Air National Guard's 109th Airlift Wing to transport personnel and equipment.

In 2017, ice core drilling began, with scientists collecting 900 metres (3,000 feet) of core that year and 750 more metres (2,500 feet) in 2018. With 900 metres left to go, the team anticipates drilling to bedrock by 2019 or 2020. Ice core samples are analysed on site for electrical conductivity, stable water isotopes, and other measures, with sections flown to other research facilities for further analysis.

While the ice coring project focuses on what’s happening beneath the surface, University of Colorado professor Jim White and colleagues are also studying what happens in the air above EastGRIP by flying drones overhead to collect air samples at various heights in order to measure the isotopes in the vapour—another key part of the sea-level rise puzzle.

“What I think is really important to know from a human perspective, from a policy perspective, is how rapidly we’ll see the sea level rise,” White says. “That determines a lot of things like 'Where do I rebuild?' 'What can I expect from the value of homes along the coast, the insurance rates, infrastructure?' There's a whole bunch of things that have economic and socioeconomic impact that really depend more on how rapidly sea level rises than the fact that it is rising.”

Kristen Pope received logistical support from the National Science Foundation to report this story.