Guest Geological Perspective by David Middleton
Before we get to my geological perspective of the Greenland Ice Sheet (GrIS), let’s first have a look at the NASA perspective:
Greenland Ice Loss 2002-2016
The mass of the Greenland ice sheet has rapidly declined in the last several years due to surface melting and iceberg calving. Research based on observations from the NASA/German Aerospace Center’s twin Gravity Recovery and Climate Experiment (GRACE) satellites indicates that between 2002 and 2016, Greenland shed approximately 280 gigatons of ice per year, causing global sea level to rise by 0.03 inches (0.8 millimeters) per year. These images, created from GRACE data, show changes in Greenland ice mass since 2002. Orange and red shades indicate areas that lost ice mass, while light blue shades indicate areas that gained ice mass. White indicates areas where there has been very little or no change in ice mass since 2002. In general, higher-elevation areas near the center of Greenland experienced little to no change, while lower-elevation and coastal areas experienced up to 13.1 feet (4 meters) of ice mass loss (expressed in equivalent-water-height; dark red) over a 14-year period. The largest mass decreases of up to 11.8 inches (30 centimeters (equivalent-water-height) per year occurred along the West Greenland coast. The average flow lines (grey; created from satellite radar interferometry) of Greenland’s ice converge into the locations of prominent outlet glaciers, and coincide with areas of high mass loss.
Wow! The GrIS lost 3,748 gigatons of ice from 2002-2016. That’s 4,089 km3.
|Ice: tonne per cubic meter (t/m³)||0.9167|
It’s difficult to visualize just how big 4,089 km3 is. Maybe our friends at Skeptical Science can help.
They say that a cubic kilometer of ice could enclose the Empire State Building with room to spare.
How much ice is Greenland losing? This is monitored by satellites which have measured changes in gravity around the ice sheet over the last decade (Velicogna 2009). In 2002 to 2003, the Greenland ice sheet was losing mass at a rate of 137 gigatonnes per year.
However, the rate of ice loss has more than doubled in less than a decade. The rate of ice loss over the 2008 to 2009 period was 286 gigatonnes per year.
This is a vivid reminder that global warming isn’t a statistical abstraction cooked up in a climate lab. Greenland is just one example of the physical realities of climate change. On the other side of the planet, Antarctica is also losing ice at an accelerating rate. All over the globe, glaciers are retreating at an accelerating rate.
4,089 Empire State Building-enclosing ice cubes!!! That’s bigger than this:
I can’t even imagine how many Manhattan-sized icebergs that is.
Wait a second! Manhattan-sized icebergs don’t look very big compared to the GrIS. Did you ever wonder why melting ice and calving icebergs are always compared to Olympic-sized swimming pools, Empire State Building-enclosing ice cubes, Manhattan Islands and Grand Duchies of Luxembourg? Why aren’t these catastrophic events ever compared to the size of the GrIS itself? Could it be that they don’t appear very catastrophic, or even anomalous, when compared to the GrIS?
How Big is the Greenland Ice Sheet?
According to U.S. Geological Survey Professional Paper 1386–A (2012), the volume of the GrIS is 2,600,000 km3. The USGS cites a 1954 reference for this number and also cites Bamber et al., 2011, which puts the volume at 2,900,000 km3. Bamber has subsequently upped his estimate to 2,960,000 km3. This is funny. Either the GrIS added 360,000 km3 of ice from 1954-2013 at a time when NASA said the GrIS was losing 4,089 km3 or the uncertainty of the volume of the GrIS is about 1,000 times the annual ice loss that is asserted with such precision by Amazing GRACE.
How Does the Recent Ice Loss Compare to the Volume of the Greenland Ice Sheet?
|1900–1983||75.1 ± 29.4 gigatonnes per year|
|1983–2003||73.8 ± 40.5 gigatonnes per year|
|2003–2010||186.4 ± 18.9 gigatonnes per year|
Here’s a graphical depiction of this projected up to 2017:
For a little more perspective, let’s convert this to ice cubes.
That’s all well and good for the 20th and early 21st centuries; but it doesn’t provide much of a geological perspective.
A Geological Perspective of the Greenland Ice Sheet
How does all this compare to the evolution of the GrIS in the Late Pleistocene and Holocene? For this perspective, I relied on Tabone et al., 2017. They devised a model to simulate how the GrIS has evolved over the past 250,000 years.
To study how oceanic changes impact the evolution of the GrIS over the last glacial cycles, we performed a set of sensitivity tests by perturbing the two key parameters of the basal melting rate equation (Eq. 10): the estimated present-day submarine melting Bref and the heat-flux coefficient κ. For each experiment we ran an ensemble of simulations over the GrIS domain throughout the last 250 ka. In this study the model is initialised by the present-day Greenland topography (Bamber et al., 2013), the characteristic relaxation time for the lythosphere is set to 3 ka and the sea level is maintained constant in time at its present-day value.
Figure 2 shows the evolution of the grounded ice volume (a) and area (b) for the simulations obtained for different values of the reference melting rate Bref and κ = 0. In this experiment the maximum ice volume reached at glacial times ranges between 3.2-3.9 million km3, just 8-32 % higher than the observed present-day ice volume (Bamber et al., 2013), suggesting that under constant oceanic forcing, the GrIS is limited to a configuration close to that of nowadays. The highest glacial ice volume is reached by imposing a null basal melting to the GrIS margins (Bref = 0), which corresponds to a simulation forced solely by paleo atmospheric variations.
Using the maximum basal melting scenario (Bref = 40), I tacked the modern GrIS volume profile on to the model.
Notice something funny? The GrIS may have actually been smaller than it currently is from 35 ka to 15 ka. And, this actually might make sense. Of course, the lower basal melting scenarios would reverse this… And they would also make the modern ice loss even more geologically insignificant.
Greenland Ice Sheet Stratigraphy
The image below is a GPR (ground-penetrating radar) cross-section of the GrIS. It is literally a work of art. GPR is analalogous in many ways to the reflection seismic data that we use in oil & gas exploration. If you click on this link, you will see a full-size image of the cross-section. Note that most of the ice is above the 12 ka horizon. This is very close to the Pleistocene-Holocene boundary. It indicates that most of the ice was deposited since the end of the last Pleistocene glacial stage (ice age in layman’s terms).
Earlier in this post I took a swipe at NASA for having the wrong perspective of the GrIS. Maybe I was mistaken… Or maybe NASA is a science savant… Because this is from NASA:
Greenland Ice Sheet Stratigraphy
Visualizations by Cindy Starr Released on January 23, 2015
For nearly a century, scientists have been studying the form and flow of the Greenland Ice Sheet. They have measured the change in the elevation of the surface over time using satellites. They have drilled ice cores in the field to reveal a record of what the past climate was like. They have flown aircraft over the surface of the ice sheet laden with instruments to gleen information about the interior of the ice sheet and the bedrock below.
Now a new analysis of this data has revealed a three dimensional map of the age of the ice sheet. This visualization shows this new 3D age map of the Greenland Ice Sheet, explains how it was created and describes the three distinct periods of climate that are evident within the ice sheet.
More information is available here.
The airborne GPR coverage of the GrIS is quite impressive:
The GPR profiles are tied to ice cores in much the same manner that we tie seismic lines to wells:
One common feature is that the volume of Holocene ice appears to be as large or larger than the volume of Pleistocene ice.
It’s particularly notable that in Central Greenland there is still a significant remnant of Eemian ice. In much of Central Greenland about 12,000 years worth of Holocene ice is thicker than over 100,000 years of Pleistocene ice. This is due to the fact that glacial stages (AKA ice ages) are very cold and very dry. The snow accumulation rate during the Holocene has been much higher than that of the last Pleistocene glacial stage.
How Does the Recent Melting of the Greenland Ice Sheet Compare to the Early Holocene?
Short answer: Same as it ever was. Vinther et al., 2009 reconstructed the elevations of four ice core sites over the Holocene. There has been very little change in elevation of the two interior ice core sites (NGRIP and GRIP), while the two outboard sites (Camp Century and DYE3) have lost 546 and 342 m of ice respectively.
From this geological perspective, the Greenland Ice Sheet is not behaving badly.
Bamber, J. L., J. A. Griggs, R. T. W. L. Hurkmans, J. A. Dowdeswell, S. P. Gogineni, I. Howat, J. Mouginot, J. Paden, S. Palmer, E. Rignot, and D. Steinhag. A new bed elevation dataset for Greenland. The Cryosphere, 7, 499–510, 2013 http://www.the-cryosphere.net/7/499/2013/ doi:10.5194/tc-7-499-2013.
Kjeldsen, Kristian K., Niels J. Korsgaard, Anders A. Bjørk, Shfaqat A. Khan, Jason E. Box, Svend Funder, Nicolaj K. Larsen, Jonathan L. Bamber, William Colgan, Michiel van den Broeke, Marie-Louise Siggaard-Andersen, Christopher Nuth, Anders Schomacker, Camilla S. Andresen, Eske Willerslev & Kurt H. Kjær. Spatial and temporal distribution of mass loss from the Greenland Ice Sheet since AD 1900. Nature volume 528, pages 396–400 (17 December 2015) doi:10.1038/nature16183.
Sutterley, Tyler C., Isabella Velicogna, Beata Csatho, Michiel van den Broeke, Soroush Rezvan-Behbahani and Greg Babonis. Evaluating Greenland glacial isostatic adjustment corrections using GRACE, altimetry and surface mass balance data. Published 15 January 2014 • 2014 IOP Publishing Ltd. Environmental Research Letters, Volume 9, Number 1.
Tabone, Ilaria, Javier Blasco, Alexander Robinson, Jorge Alvarez-Solas, and Marisa Montoya. The sensitivity of the Greenland ice sheet to glacial-interglacial
oceanic forcing. Clim. Past Discuss., https://doi.org/10.5194/cp-2017-127. Manuscript under review for journal Clim. Past. Discussion started: 8 November 2017.
Vinther, B.M., S.L. Buchardt, H.B. Clausen, D. Dahl-Jensen, S.J. Johnsen, D.A. Fisher, R.M. Koerner, D. Raynaud, V. Lipenkov, K.K. Andersen, T. Blunier, S.O. Rasmussen, J.P. Steffensen, and A.M. Svensson. 2009. Holocene thinning of the Greenland ice sheet. Nature, Vol. 461, pp. 385-388, 17 September 2009. doi:10.1038/nature08355.
Weißbach, S., A. Wegner, T. Opel, H. Oerter, B. M. Vinther and S. Kipfstuhl. Spatial and temporal oxygen isotope variability in northern Greenland – implications for a new climate record over the past millennium. Clim. Past, 12, 171–188, 2016 http://www.clim-past.net/12/171/2016/ doi:10.5194/cp-12-171-2016.
Williams, R.S., Jr., and Ferrigno, J.G., eds., 2012, State of the Earth’s cryosphere at the beginning of the 21st century–Glaciers, global snow cover, floating ice, and permafrost and periglacial environments: U.S. Geological Survey Professional Paper 1386–A, 546 p.
The Cold War connections to some of the ice core sites is really cool! The DYE-2 and DYE-3 ice core locations were once part of the DEW Line.
DYE-2 – a relic from a not so distant past
The dart is still in the dartboard and the beer is still on the counter in the bar. So untouched is DYE-2. Slowly, the weather and wind have encroached and in a few years it will probably be difficult to get in and see this unique, American cold war relic on the ice sheet in Greenland.
Text: Toke Brødsgaard, greenland today July 2015
There is an air of mystery when you move around the now abandoned DYE-2 radar station which is located quite a long way out on the ice cap in Greenland. The site remains so untouched that it is as if everyone left the place at the same time when it was abandoned in October 1988.
Moving around the build-ing, you can see rooms, bars and workshops in the same state in which they were left. The only evidence that time has passed, is that the weather has broken some windows and the snow has sneaked in and disturbed the peace.
The Distant Early Warning Line
DYE-2 was a major undertaking. At its most active, there were 60 men at the station. The fact that the building was able to accommodate such a large staff during periods when it was impossible to go outside because of cold and storms says a lot about its size.
Strategically, DYE-2 was in an important position, since it was a part of the Distant Early Warning (DEW) radar line. It was established to warn of any Soviet air attacks against the USA during the cold war. The DEW Line consisted in Greenland of DYE-1, which is located just outside Sisimiut, DYE-2 and DYE-3, which are located further to the east on the Greenland ice sheet and DYE-4 which is located not far from Kulusuk in East Greenland.
DEW was a chain of a total of 60 radar stations stretching over a 5,800km long line along the 69th parallel north from Alaska over Canada via Greenland to Iceland. The actual radar chain was active from July 31st 1957 until the end of the 1980s.
Camp Century is the pièce de résistance of irony.
Mysterious, ice-buried Cold War military base may be unearthed by climate change
By Julia Rosen Aug. 4, 2016 , 11:00 AM
It sounds like something out of a James Bond movie: a secret military operation hidden beneath the Greenland Ice Sheet. But that’s exactly what transpired at Camp Century during the Cold War.
In 1959, the U.S. Army Corps of Engineers built the subterranean city under the guise of conducting polar research—and scientists there did drill the first ice core ever used to study climate. But deep inside the frozen tunnels, the corps also explored the feasibility of Project Iceworm, a plan to store and launch hundreds of ballistic missiles from inside the ice.
The military ultimately rejected the project, and the corps abandoned Camp Century in 1967. Engineers anticipated that the ice—already a dozen meters thick—would continue to accumulate in northwestern Greenland, permanently entombing what they left behind.
Now, climate change has upended that assumption. New research suggests that as early as 2090, rates of ice loss at the site could exceed gains from new snowfall. And within a century after that, melting could begin to release waste stored at the camp, including sewage, diesel fuel, persistent organic pollutants like PCBs, and radiological waste from the camp’s nuclear generator, which was removed during decommissioning.
If these predictions come to pass, the researchers… [blah, blah, blah]…
If these predictions come to pass…
Bell et al., 2014 discuss in more detail what Data is laughing at.