Guest geological perspective by David Middleton
This is a sort of a spin-off of Rutgers University Global Snow Lab and “the Snows of Yesteryear” and A Geological Perspective of the Greenland Ice Sheet. And, yes, there are a lot more than five charts in this post… And, none of them were all that easy.
There is a general scientific consensus that the Greenland Ice Sheet (GrIS) has been losing ice mass since the Little Ice Age (LIA). This should come as no surprise, since the LIA was quite likely the coldest climatic episode of the Holocene Epoch. Although it does appear that the GrIS may have gained ice mass during the mid-20th century global cooling crisis.
According to Mouginot et al, 2019, the GrIS was gaining an average of +47 ± 21 Gt/y from 1972–1980, then began to lose ice mass after 1980:
- -51 ± 17 Gt/y from 1980–1990
- -41 ± 17 Gt/y from 1990–2000
- -187 ± 17 Gt/y from 2000–2010
- -286 ± 20 Gt/y from 2010–2018
The alleged ice mass loss was driven by:
- A sharp decrease in surface mass balance from 1995-2012
- An increase in iceberg calving and other ocean-contact discharge
The drop in SMB was so severe, that it may have been negative in 2007 and 2012. Most of the ice mass loss is due to the calving of icebergs. The “funny thing” is that, apart from a spike in iceberg activity in the 1990’s, it’s not really much different now than it was from 1900 to 1950.
International Ice Patrol’s Iceberg Counts
Donald L. Murphy
Each year, the International Ice Patrol (IIP) estimates the number of icebergs that pass south of 48° N, the latitude south of which icebergs are considered a menace to North Atlantic mariners. The dataset (Table 1) extends from 1900, 12 years before the sinking of RMS Titanic, to the present.
For several reasons, these iceberg counts do not constitute a rigorous, scientific data set and should be interpreted with great care. For example, IIP’s reconnaissance operations focus on the icebergs closest to the transatlantic shipping routes, and rarely does IIP conduct a comprehensive survey of the area south of 48° N. In addition, the methods of observation have changed radically over the years as new technologies became available to detect and track icebergs. The earliest data were obtained from visual observations from early 1900s sailing vessels, while the recent information is obtained from visual and radar observations from modern ships, aircraft, and satellites.
There is striking year-to-year variability evident in the 112-year record of IIP’s iceberg counts (See Figure 1 below and Table 1 (a PDF which will open in a new window)). The mean number of icebergs estimated to have passed south of 48° N is 474. The greatest number of icebergs (2202) occurred in 1984, while twice in IIP’s history (1966 and 2006) no icebergs were estimated to have passed south of 48° N. Five times in IIP’s history there has been at least one iceberg estimated to have passed south of 48° N during each of the months of the ice year: 1915, 1919 through 1921, and 1985. April and May are, by far, the months with the most icebergs entering the shipping lanes.US Coast Guard Navigation Center
I was able to find detailed data on iceberg sightings on the National Snow and Ice Data Center website and extended the Coast Guard plot through 2019.
Chart Number One: Icebergs
While there was a significant increase in the 5-yr running average in the 1990’s, since then, it’s been comparable to 1900-1950. You would think that with Greenland spitting out Manhattan-sized icebergs on what seems like a weekly basis and the discharge rate supposedly rising by 50% since 1995, you should see it in the iceberg count.
Maybe the “unprecedented” Arctic warming is melting the icebergs before they can get south of 48° N. Well, the Arctic has a few very long-term “thermometers”… Ice cores from Greenland. The Greenland temperature reconstruction, most often cited by skeptics, is from the GISP2 ice core (Alley, 2000).
In my previous post, I was accused of misleading people with this graph:
Regarding the first graph: so often we see the GISP2 data mislabelled and here is no exception.
That data series ends in 1855, NOT in 1950 as labelled.
This has been made clear on this site so often, since 2010 in fact, that it’s hard to believe people keep using it without knowing that to be the case.
Why mislead people if our argument is so strong?TheFinalNail
Anyone with at least a 5th grade reading comprehension can see that the x-axis is labeled “Years Before Present (1950 AD). Anyone with the slightest knowledge of radiometric dating knows that the P in BP is 1950. This is also the standard for most paleoclimate reconstructions. Unless a paper specifies that “present” is any year other than 1950, it’s safe to assume that it’s 1950. The most recent year in the Alley time series is 95 BP or 1855.
Of course, 1855 was back during the LIA, long before Al Gore invented Gorebal Warming. Fortunately, there are a few GISP2 temperature reconstructions that extend up to 1993 (Kobashi et al., 2008, Kobashi et al., 2011 and Kobashi et al., 2017). Unlike Alley, who relied on δ18O depletion as a paleo-thermometer, Kobashi employed “high‐precision analyses of δ15N and δ40Ar in trapped air in ice cores”…
The estimated average Greenland snow temperature over the past 4000 years was −30.7°C with a standard deviation of 1.0°C and exhibited a long‐term decrease of roughly 1.5°C, which is consistent with earlier studies. The current decadal average surface temperature (2001–2010) at the GISP2 site is −29.9°C.Kobashi et al., 2011
The GISP2 ice core was drilled at the same location as Summit Station, Greenland.
According to Kobashi, the average temperature at Summit Station over the past 4,000 years has been −30.7 °C. The average temperature since 2008 has been about −30 °C.
Chart Number Two: GISP2 Ice Core
I downloaded the Kobashi et al., 2017 climate reconstruction from NOAA and plotted it to evaluate the context of recent climate change in central Greenalnd. Technically, this could be described as three charts… But, who’s counting?
The inescapable conclusion is that if there ever was a climate “crisis,” it was during the Little Ice Age… It was FRACKING cold back then!
What’s that? Central Greenland isn’t the Arctic? No schist Sherlock!
Chart Number Three: The Arctic
So, let’s look at the recent Arctic temperature reconstruction by McKay & Kaufman, 2014.
The inescapable conclusion is that if there ever was a climate “crisis,” it was during the Little Ice Age… It was FRACKING cold! And it got pretty cold again in the 1970’s!
But, but, what about all of the ice mass loss measured by satellites?
What about it?
Three Decades of Greenland Ice Sheet Change
Posted by ESA Greenland Ice Sheet Climate Change Initiative.
This week there has been significant melting over a large area of the Greenland ice sheet. Temperatures even reached over 0°C for the second time this year at the very top of the ice sheet 3285m above sea level at Summit station where DMI operates a weather station.
The high melt rates have been due to warmer air moving over the ice sheet, which in combination with low snowfall over most of the ice sheet during the winter period means quite large amounts of melt might be expected this year. A large melt event this early is unusual but it’s not unprecedented a similar event happened in 2012 for example.
Specific melt events of this kind are controlled by local weather conditions in the North Atlantic but when these events are averaged over many years, you get the local background climate. In a paper published by scientists in a large European collaboration led by ESA and including DMI, DTU and GEUS, observations from satellites stretching back to the 1990s, including many shown here on the polar portal, have been used to give a well-rounded picture of how climate changes in Greenland have been affecting the ice sheet.
We show for example, that since the early 2000s the ice sheet has become thinner almost everywhere. For an ice sheet in balance with the local climate we expect to see a small increase in surface height year on year in the centre and a decrease around the edges as more snow falls than melts at higher elevations and the reverse happens lower down. However, scientists show that the ice sheet is now getting thinner almost everywhere (blue areas in the top row). “It’s quite striking that we see such big changes when we compare the early 1990s to the last few years” said scientist Sebastian Simonsen from DTU.
The folks at Polar Portal were kind enough to feature this image:
I focused in on the top panel, elevation changes, because I can put those changes into geological context.
How does the recent melting compare to the rest of the 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
Vinther’s elevation reconstruction runs from 11,700 to 40 years before the year 2000. So the most recent year is 1960.
Based on the mass balance estimates from Mouginot, there was very little net change from 1960 to 1995, the starting year for Polar Portal’s elevation change maps. I enlarged the elevation change maps and posted the ice core locations on them.
The scale is in meters per year. Note that there has been very little change in ice elevation at these locations. Using my Mark I eyeball, I estimated the annual changes in elevation from 1995-2017.
Ice Surface Elevation Change (m/yr)
Using the 2009 elevations provided by Vinther, I calculated the elevations of the four locations from 11,700 years ago up to 2017.
Chart Number Four…”Same as it ever was!”
But, but, the Greenland ice sheet is still shrinking! When it all melts, sea level will rise by 7 meters!!!
Chart Number Five: The Isopach Map
I usually prefer to use the word “graph” instead of “chart”… But charts can be either graphs or maps.
We petroleum geologists are obsessed with calculating volumes of oil and gas reservoirs and we spend a lot of time making things called “isopach maps” and running “volumetrics“. Fortunately for me, Eric Gaba – Wikimedia Commons user: Sting made an isopach map of the Greenland ice sheet.
Almost all of the recent thinning is in the outboard areas of the ice sheet (“Same as it ever was”). I downloaded a high-resolution copy of the isopach map and digitized the contours using NeuraMap volumetric analysis software. The area and volume of the isopach map were inline with estimates in USGS Professional Paper 1386–A, Table 2, page A77.
- Area: 1,736,095 km2
- Volume: 2,600,000 km3
I used the 10 m contour as the 0 contour. The area of the 0 m contour was very close to the USGS area.
The volume was a little higher than the USGS estimate; but well within the range of other recent estimates. 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.
As can be seen, estimates for the volume of the Greenland ice sheet vary widely and the methods of volumetric calculation yield a pretty wide range of results… Yet modern climate “scientists” can detect 0.015% annual changes in its mass… Go figure!
This is what happens if I drop the 1,000 m contour by 10 m:
|Method||Lose 10 m|
99.93% of the Greenland ice sheet doesn’t melt and/or calve into the ocean. The USGS paper states that if the entire ice sheet were to melt, sea level would rise by 6.5 meters. In the highly unlikely scenario above, sea level would rise by a whopping 4.8 mm.
- 6.5 m * 0.07% = 0.00478 m
What happens if I drop the 1,000 m contour by 100 m?
|Method||Lose 100 m|
- 6.5 m * 0.82% = 0.0531m
That’s just over 2 inches of sea level rise.
There you have it… The insignificance of Greenland’s ice mass loss in five easy charts… And a lot of not so easy charts and tables.
Alley, R.B. 2000. “The Younger Dryas cold interval as viewed from central Greenland”. Quaternary Science Reviews 19:213-226.
Alley, R.B.. 2004. “GISP2 Ice Core Temperature and Accumulation Data”.
IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series #2004-013. NOAA/NGDC Paleoclimatology Program, Boulder CO, USA.
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 www.the-cryosphere.net/7/499/2013/ doi:10.5194/tc-7-499-2013.
Grosjean, Martin, Suter, Peter, Trachsel, Mathias & Wanner, Heinz. (2007). “Ice‐borne prehistoric finds in the Swiss Alps reflect Holocene glacier fluctuations”. Journal of Quaternary Science. 22. 203 – 207. 10.1002/jqs.1111.
Kobashi, T., J. P. Severinghaus, and K. Kawamura (2008a). “Argon and nitrogen isotopes of trapped air in the GISP2 ice core during the Holocene epoch (0–11,600 B.P.): Methodology and implications for gas loss processes”. Geochim. Cosmochim. Acta. 72, 4675– 4686, doi:10.1016/j.gca.2008.07.006.
Kobashi, T., Kawamura, K., Severinghaus, J. P., Barnola, J.‐M., Nakaegawa, T., Vinther, B. M., Johnsen, S. J., and Box, J. E. ( 2011). “High variability of Greenland surface temperature over the past 4000 years estimated from trapped air in an ice core”. Geophysical Research Letters. 38, L21501, doi:10.1029/2011GL049444.
Kobashi, T., Menviel, L., Jeltsch-Thömmes, A. et al. “Volcanic influence on centennial to millennial Holocene Greenland temperature change”. Scientific Reports 7, 1441 (2017). https://doi.org/10.1038/s41598-017-01451-7
McKay, N., Kaufman, D. “An extended Arctic proxy temperature database for the past 2,000 years”. Scientific Data 1. 140026 (2014). https://doi.org/10.1038/sdata.2014.26
Mouginot, Jeremie, E. Rignot, Anders Bjørk, Michiel Van den Broeke, Romain Millan, Mathieu Morlighem, Brice Noël, Bernd Scheuchl & Michael Wood. (2019). “Forty-six years of Greenland Ice Sheet mass balance from 1972 to 2018”. Proceedings of the National Academy of Sciences. 116. 10.1073/pnas.1904242116.
Van den Broeke, M., Box, J., Fettweis, X. et al. “Greenland Ice Sheet Surface Mass Loss: Recent Developments in Observation and Modeling”. Current Climate Change Reports. (2017) 3: 345. https://doi.org/10.1007/s40641-017-0084-8
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. 461. 385-8. 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”. Climate of the Past. 12, 171–188, 2016 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. (Also available at https://pubs.usgs.gov/pp/p1386a.) Glaciers.
Yau, Audrey M., Michael L. Bender, Alexander Robinson, Edward J. Brook. “Last interglacial in the GISP2 Greenland ice core”. Proceedings of the National Academy of Sciences. Aug 2016, 113 (35) 9710-9715; DOI: 10.1073/pnas.1524766113