By Jillian Melero, Dec. 16, 2018 –
The Greenland ice sheet is more than three times the size of Texas, 2 miles deep at its thickest point. And it’s melting.
Not only is it melting, but it’s melting at a rate not seen in 400 years, according to a paper published in Geophysical Research Letters in April. The study involved taking short ice core samples and examining the surface layers of snow to find out how much melting had occurred.
In some places, it’s melting 250 percent faster – in others 575 percent faster than it has over the last 20 years compared to pre-industrial times, according to a study published in the international science journal Nature in early December.
If the Greenland ice sheet (GriS) melts away completely, it will raise sea levels by more than 20 feet, according to the National Snow- and Ice Data Center (NSIDC).
The Nature study, by researcher and lead author Luke Trusel, outlined the rapidly increasing melt rate of the GriS, as measured through similar ice core samples, and correlated that data using satellite observations and modeling. Trusel works at the Cryosphere &Climate Lab at Rowan University in New Jersey.
The study found that global temperature alone was not the only contributing factor to the rapid melt. Other factors that are symptoms of global warming, such as algae and soot traveling through the air and becoming trapped in the ice, have changed the color of the ice from white to a darker, more heat-absorbent shade, contributing to the rapid melting.
Geologists and researchers such as Trusel study the history of these ancient icy masses to try and gain key understanding of what has happened before and what is happening now so they can better predict what will happen in the coming years and how it impacts the places and ways that we live today.
The annual Comer Climate Conference gathers climate scientists, geologists and researchers from universities around the country to Wisconsin each fall. These experts spend two days reviewing the work they’ve done — studying the history of geological changes and climate impacts in the past to better understand the pressures these systems are under today, and how they might react in the future.
“We as a society are recognizing that one of the primary controls of the changes in water level of the ocean are the freshwater that is locked up in ice sheets – and the last great ice sheet came and went but that was responsible for something on the order of 85 meters of sea level change,” said Tom Lowell, professor of glacial and Quaternary geology (from approximately 2.6 million years ago to the present) at the University of Cincinnati. “[Sea level] went down and came back up in a rapid [pace] – it didn’t go in a symmetrical pattern. So the point is, how fast can sea level go up? And what are the sources of that?” he asked at the conference.
To find the answers to these questions, some researchers look into the history of the long gone ice sheets, such as the Laurentide, that once covered North America.
The Laurentide Ice Sheet (LIS) stretched across Canada and much of the northern United States more than 20,000 years ago. The motion and retreat of this massive glacier carved out the Great Lakes, as it slid across the continent, gouging out basins, that it would later fill as it melted.
The movement of the ice sheets or continental glaciers have formed the lands and waters that we live on today. And as these processes repeat or accelerate, they will also reshape the landscapes of our future.
Lowell presented his research on the Laurentide at the annual Comer Climate Conference in Wisconsin in October.
“I would argue that if you really want to understand how to kill off an ice sheet, you’d want to go to ice sheets that are no longer with us, and that is the basis for my long interest in the Laurentide ice sheet,” Lowell said. “I would also argue that our understanding of the Laurentide, which is the largest one of those puppies, is less well understood than it seems.”
Some of the mystery around the Laurentide can be seen in the varying pattern of seams visible within the ice sheet. At the end of the last glacial maximum (LGM) – when glaciers reached their furthest extent between 26,000 and 21,000 years ago – the Laurentide covered an area of more than 5 million square miles and was up to 2 miles thick in some places. When the Laurentide began to melt and recede, it’s estimated to have raised sea levels by approximately 85 meters, or more than 278 feet.
All that remains of the Laurentide today is a single ice cap the size of Delaware, the Barnes ice cap, in the Canadian Arctic.
Lowell’s presentation “Reorganizing Ice Sheets” examined the Laurentide and identified periods of separation and reformation of the ice sheet. Different sections of the ice slid in different directions at different times at different speeds before coming back together and solidifying again. But the causes of these drifts, the rate at which they occurred, and the reasons they took the directions they did are still unknown. But finding these answers can give us some insights as to how fast ice sheets can melt today as climate change accelerates global warming.
“The point that I really want to drive across here is Greenland, at its last glacial maximum was bigger than it is today, but Greenland will get lost in this [the Laurentide]. According to my modeling friends, the uncertainty of the Laurentide is the same sea level equivalent as Greenland,” Lowell said. “Think about that for a second. If you want to reconstruct former sea level rises, [what’s the uncertainty of the estimate of] this puppy we don’t know [points to the Laurentide] to the same volume as that guy [points to Greenland].”
Brenda Hall is a professor with the School of Earth and Climate Sciences and Climate Change Institute at the University of Maine. Her research focuses on the cause of ice ages, and of rapid climate change, as well as the stability of ice sheets to help predict where – and how fast – climate change can impact ice sheets today. Hall has research projects in the Antarctic, South America, and Greenland, and presented her research on the Antarctic ice sheet at the Comer Conference in October.
“I can divide the work I do between two main themes,” Hall said. “One being trying to understand abrupt climate change on a variety of different time scales, and then the other part of the work, which is really what I was presenting on today is how do we understand the stability of ice sheets that exist on Earth and their potential to cause changes in sea level.”
The Antarctic ice sheet has two main components. The larger East Antarctic ice sheet is a land-based ice sheet. If it were to melt, it could raise sea levels by 50-55 meters or 164 – 180 feet, but it’s thought to be relatively stable, Hall explained.
In contrast, the smaller West Antarctic ice sheet isconsidered less stable. It’s on land that is largely below sea level, and because of that, it’s thought to be susceptible to rapid collapse. If the West Antarctic ice sheet were to collapse, it would raise global sea levels by 4 meters, or more than 13 feet, inundating many islands and coastal cities. Because of its perceived instability, there is concern about this ice sheet, as well as portions of the East Antarctic ice sheet, Hall said.
“Glaciers that end in the ocean have a very different response to climate change, than glaciers that end on land. And we have suspicion that that is telling us something about the different mechanisms that are controlling the glaciers.” Hall said she will be returning to the Antarctic to continue her research within the next year. “This time we’re really taking a close look at behavior of marine-terminating glaciers versus the ones that are ending on land,” Hall said.
Ultimately, much of the research has led to more questions. Both Lowell and Hall said that one of the greatest misconceptions about their work is that things are “all figured out.” And sometimes these general misunderstandings can lead others to make to some risky conclusions.
“I think there sometimes is a misconception about changes in the past,” Hall said. “There are times in the past when it’s been warmer than today, there’s no doubt about that, but there’s sometimes a misconception that if there are warm times in the past, then somehow warming now isn’t bad.”
Hall’s concerned that this assumption can lead to complacency or to behaviors that could contribute to climate change and rapid ice sheet deterioration, such as what we’re now seeing in Greenland’s ice sheet. Melting ice sheets mean escalating sea level rise.
“There’s natural climate variability, but there’s also man-made climate variability which will be superimposed on whatever the natural climate cycle is. And, we don’t really understand the natural climate cycle, so we don’t even know if we’d have the potential to trigger something that we don’t know about,” Hall said. “So, that’s the biggest misconception is in the public is, yes there’s natural climate variability, and yes there are times when it’s been warmer in the past, but that doesn’t mean that it’s okay for it to get warm now because of what we might be doing.”
Photo at top: (L-R) Scott Braddock, Brenda Hall, Paul Koch, Rachel Brown, Audra Norvaisa, Jon Nye formed a research team working in the McMurdo Sound Region of Antarctica. (photo from University of Maine School of Earth and Climate Science)
