Short Splice, Long Splice

Guest Post by Willis Eschenbach

When I was a kid I had the great fortune to be taught to splice rope by a grandson of Richard Henry Dana. He taught me how to do a long splice and a short splice … but I never learned how to do either the long or short data splice. For that, I had to wait for climate science.

Anthony recently highlighted a paper about reconstructed Greenland temperatures called “Past 4000 Years of Greenland Temperatures“. I don’t really have a dog in the fight, but I was greatly amused by their description of what they call “in situ observations”.

Here’s the top panel of their Figure 1.

Figure 1. ORIGINAL CAPTION FROM THE PAPER (top) Reconstructed Greenland snow surface temperatures for the past 4000 years and air temperature over the past 170 years (1840–2010) from three records. The thick blue line and blue band represents the reconstructed Greenland temperature and 1s error, respectively (this study). The reconstruction was made by two different methods before and after 1950. The “gas method” is as described in section 2, and the “forward model” is described by Kobashi et al. [2010]. Thick and thin black lines are the inversion‐adjusted reconstructed Summit annual air temperatures and 10‐year moving average temperatures, respectively [Box et al., 2009]. Thin and thick red lines are the inversion adjusted annual and 10‐year moving average AWS temperature records, respectively [Stearns and Weidner, 1991; Shuman et al., 2001; Steffen and Box, 2001; Vaarby‐Laursen, 2010]

I thought “hmmm, data from the summit of the Greenland ice cap, didn’t know about that” … so I went to find out what their data consists of, the famous “thin red line” in the Figure 1 above. Here’s what they say about the “in situ observations”:

5.1. Present Greenland Temperature

To place the Greenland temperature proxy reconstruction into a historical context, we incorporate two additional Summit temperature records. One record is obtained from a compilation of Summit Automatic Weather Station ∼2 m surface air temperature (SAT) observations (hereafter AWS or in‐situ record) that spans 23 years (1987–2010). The AWS were situated within 20 km of the GISP 2 coring site and within 25 m elevation of the ice sheet topographical summit (Figure 1, top, red line).

The series begins in May 1987 with Automatic Weather Station data after Stearns and Weidner [1991].

Shuman et al. [2001] merge this record with data from the Greenland Climate Network (GC‐Net) AWS data [Steffen and Box, 2001] to produce the first 12 years of this compilation.

Gaps before June 1996 are in‐filled using daily passive microwave emission brightness temperatures.

GC‐Net data then comprise the period spanning June 1996 to December 2003 with gaps in‐filled by Danish Meteorological Institute (DMI) Summit AWS data [Vaarby‐Laursen, 2010].

The DMI data exclusively form this data series from January 2004 through December 2010.

Man, I thought, that is a curious provenance for the summit temperature data. First, 12 years of observations, with gaps in-filled using satellite microwave observations. Then from 1999 to 2003 the summit temperature was estimated using surrounding stations. Gaps in the surrounding station data are infilled from the DMI Summit station data. Then from 2004 on, we have DMI summit station data only.

So I looked a bit deeper. It gets better. Remember the Shuman et al. observations that form the “first 12 years of this compilation”? It turns out that it was not one station, but three stations … and there was no overlap between the stations to compare temperatures. The Shuman paper is here. Their Figure 2 shows those first 12 years of the record, from three AWS stations: CATHY, GISP2, and SUMMIT.

Figure 2. Automated Weather Station records near and at the Greenland Summit. 

Note the lack of overlap and the number of gaps, covering days, weeks, or months. Here’s Shuman’s description of what they did:

In order to complete a temperature record from the Greenland Summit (May 1987 to October 1999), it will be necessary to adjust the AWS Cathy temperature record to account for the difference in its location as well as to complete the AWS GISP2 and AWS Summit records across multiple periods of missing data .

The methods detailed in Shuman et al. (1996) or in Shuman et al. (1995), which rely on appropriately located and contemporaneous SSM/I brightness temperature data (Table 1), will be used to achieve a complete and consistent temperature record.

Inconveniently, SSM/I data are not available from 4 May 1987 to 10 July 1987 and are missing from 3 December 1987 to 13 January 1988 (Table 3). Smaller gaps in the SSM/I or AWS record of less than 5 days will be dealt with by interpolation.

So for the 23 year record we have a long data splice as follows:

2 years of AWS CATHY data,

7 years of AWS GSIP2 data,

3 years of AWS SUMMIT data,

5 years of estimated data, and

6 years of AWS SUMMIT data.

All of this is “infilled” from a couple of sources.

Now, remember that this data is what they are using to calibrate their algorithm that converts ∂O18 data into temperature data …

The authors of the study cite Ellen Vaarby-Larson 2010, which is here. It shows the Summit temperature for the period 1998- Feb 2010:

Figure 3. Air temperature from the 04416 Summit AWS station. From Vaarby-Larson 2010.

Note that even in the modern period there are gaps of up to about a year in the record. (Also of note is that there are only about six three-hour periods in the record where it is above freezing, and that the summer/winter spread is about 60°C [108°F]. Yikes!) Here’s an example of why the record contains so many gaps and spaces:

Figure 4. Condition of the Summit station 04416 during the 2007 annual visit. From Vaarby-Larson 2010

Let me conclude by looking at some other problems endemic with AWS records. I cannot improve on the words of Ms. Vaarby-Larson, who said (op. cit.):

Recommendations

Generally, great care should be taken when using the observations from station 04416 Summit, since the observations are influenced by:

• Extreme climatic exposure of the station measurement equipment (the extreme cold causing e.g. low availability of wind observations during winter)

• Non static barometer elevation above sea level, due to the Greenland Ice sheet flow-patterns

• Non static height of measurements above ground, due to burial of the station by snow falling

None the less, the observations of temperature, humidity and wind (see Figure 10 – Figure 16 ) show no great, obvious shift in level or variance, at the individual station relocations in 2005, 2006, 2007 and 2009.

Any existing bias due to change in measuring height above ground, might be difficult to identify since:

• 04416 Summit only issues synop every three hours.

• There’s no direct measurement of the ongoing change in actual measuring height above ground, in-between station relocations.

• Change in weather conditions might produce the same signal in the observations

• Natural variability shows e.g. great temperature variance during winter compared to summer, please confer with the early attempt at investigation of temperature variance in Figure 17.

Hmmmm …

In a recent post called “A Modest Proposal—Forget About Tomorrow“, I discussed a paper that showed why even perfect “fitted” or “calibrated” models may not have predictive (or reconstructive) capabilities. In the current case, they are reconstructing the Greenland temperature based on a collage of actual observations, nearby observations, estimates, and satellite microwave brightness.

Let me be clear that there is nothing inherently wrong with putting together a pastiche composed of a variety of estimates and local observations and satellite data. There may even be something to learn from such a collation of disparate elements.

My point is that it doesn’t engender confidence when said pastiche is used to calibrate an algorithm designed to transform an ice core ∂O18 record into a temperature reconstruction. Even with the best of data, that’s a tough sell.

My conclusion? Only have one.

The confidence intervals in the original paper on historical Greenland temperatures are way too narrow.

w.

PS—Ya gotta love the Google Earth image of the Greenlad Summit temperature measuring site (Station ID# 04416), found here:

When I first looked that that I thought “They left out the satellite part of the image” … then I realized that they hadn’t left anything out. Anthony, I do believe we’ve actually finally found a truly rural temperature station …

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Jack Schieldge
November 12, 2011 8:01 am

Well we are overdue for an ice age. If AGW is as effective as said then maybe it’s a good thing.

Crispin in Waterloo
November 12, 2011 10:55 am

If the ice is only 161,000 years old at the bottom it means that the whole of Greenland was ice-free as recently as that. Does no one find this remarkable?
Surely natural variation sufficient to melt or reform all the current ice sheet is sufficient to explain anything now taking place on this planet! Claiming otherwise would be very difficult to prove. There is no doubt that the claims for AG warming are all based on very short time periods, with these same time periods refused by AGW proponents as proof of any stalled or cooling global temperatures.
These simple facts are sufficient to convince me the AGW case has not yet been proven, however technically plausible it may or may not be. Enthusiastic support does not make CAGW true any more than Flat Earth or Phlogiston.

Mac the Knife
November 12, 2011 11:51 am

A very interesting analysis of this papier mache construction of a ‘modern age continuous temperature record’ from arbitrary (I’m being kind…) spliced temperature records and proxies, and using that soggy construction to try to establish a connection to the shaky-at-best oxygen/nitrogen isotope ratio temperature proxies from the Greenland icepack. As most engineers realize early on, after their first significant failure, “The devil is in the details!” Your analysis, Willis, shows the exceptional, undocumented, and probably calculation defying uncertainty embedded in those details, rendering their analysis and conclusions essentially bankrupt and useless. Analytically, their ‘constructions’ are even less palatable than the institutional grade ‘chop suey’ served in my old high school cafeteria was! Ugh….
Thank You, Willis!
And “Thanks!” to Malagaview, as well, for your cogent contributions!

Septic Matthew
November 12, 2011 12:53 pm

Delightful.

November 12, 2011 2:54 pm

G. Karst says: November 12, 2011 at 7:58 am
In tree rings, each line represents annual growth.
In ice snow, each line represents a snow event.

PRECISELY!
Rob R says: November 12, 2011 at 3:38 am
One of the ways they date the Greenland ice cores is by counting the individual annual layers.

The problem is that a “layer” can represent:
1) a snowing event,
2) a melting event
3) a freezing event
So you can count layers… but that is NOT years…
You can try to backtrack “dust” to a volcanic event…
But they only managed eight “hits” on that one…
The penultimate volcanic “dust” match is for Eldgja in 934 AD…
The it fizzles out in 79 AD with “dust” from Vesuvius…
At which point there are only about 500 meters down in the 3,030 meter core
Hardly convincing…. only another 159,379 years left to worry about!
Then we have the problem that the “core is deformed below 2,800 meters”.
Unsurprisingly this doesn’t ring any alarm bells with climate scientist.
To a rationale person this represents a residual ice cap.
A residual ice cap after numerous melting events…
A residual ice cap after numerous accumulation events…
Then we have the problem of the disappearing ice age…
Greenland was the focus of snow accumulation for the ice sheet that spread down over North America in the last ice age…
That is one heck of a lot of snow and ice…
And the average notional annual layer depth between 9,374 BP and 39,852 BP is just 24.38 millimetres!
Based upon a comparison with “recent” accumulations 90% of the ice age has disappeared…
And it gets worse as you dig deeper…
And we still don’t know if “bubbles” rise in 161,311 years…
And we still don’t know if “dust” settled in 161,311 years…
And we have to guess using a computer model how the ice has “flowed” for the last 161,311 years…
And how do they do this?
By supplying the snow fall and temperatures (and much more) for the last 161,311 years…
And if they know those parameters then they wouldn’t need to look at the ice core to begin with.
At this point they have lost an ice age and all credibility.
Willis Eschenbach says: November 12, 2011 at 11:23 am
AFAIK, the last time Greenland was largely ice-free was about three million years ago.

Sorry – but that is either a big “duck out” or just plain misdirection.

The Vikings arrived in Greenland from Iceland in 980 A.D. By 1000 A.D. around 5,000 people lived there in small farming communities. For several centuries the Viking civilization in Greenland maintained close ties to their European brethren through trade.
http://www.iupui.edu/~geni/documents/Vikings_in_Greenland-An_Overview.doc

Steve
November 12, 2011 4:46 pm

Well, the fjordlands were ice-free, as they are now, plus a little more, and it was warm enough to have a dairy-and-hunting economy. They still had to go to Markuland or further south for wood. So definitely warmer than today, but we are talking central to northern Norwegian climate, not the north of France or something.

u.k.(us)
November 12, 2011 5:06 pm

malagaview,
You were doing pretty well with your arguments about the science, I thought, but then you made the “misdirection” blunder.
BTW what is a “duck out”?

Anton Eagle
November 12, 2011 5:30 pm

Maybe I am incredibly dense or something… but when I look at image 3, I seen no warming whatsoever. So, where do they get they get the red line in image 1?

November 12, 2011 6:59 pm

Willis Eschenbach,
“Crispin, let me see if I can find an image to show why this is not true. Hang on … ok, try this one.”
Wikipedia has a nice picture of the bedrock below the Greenland ice:
http://en.wikipedia.org/wiki/File:Topographic_map_of_Greenland_bedrock.jpg
from
http://en.wikipedia.org/wiki/Greenland
Since central Greenland lengthwise is below sealevel and a number of areas of the surrounding mountains are very low, we end up with glacial flow rates varying radically even when not affected by geothermal sources. We also have the situation where most of the lower levels of the glacier that is not on the outside of the mountain range is NOT going ANYWHERE!!!

Steve
November 12, 2011 9:28 pm

Malagaview;
There are several problems here. The Norse farming methods worked well for nearly 500 years. That isn’t bad.
The Norse got along well with the Dorset and intermarried with them as archeological evidence shows. They also traded with them all along the north-eastern Canadian arctic, also discovered by archeologists.
The Norse did not up and attack the skraelings of Wineland the Great. It was a kerfuffle, as the saga clearly describes.
The Inuit, called ‘Eskimo’ or ‘cannibal’ by their Algonquian neighbors were much more warlike than the Dorset, and as they moved East, they eliminated the Dorset and Thule and then came into conflict with the Norse.
However, the Black Death opened up significant tracts of farmland on Iceland, that Greenlendings had inheritance rights to, and at this point, with the cooling climate, it was much more attractive to leave Greenland and move to Iceland.
The West Colony had already been abandoned when Bristol fishermen after bad luck on the Grand Banks, seeking slaves, were sent to the west colony by the east colony people. From this event, reports came to Norway which led to the Knutson expedition, which may or may not have reached west-central Minnesota by water. These were not Vikings, they were high medieval Norse and Shetland islanders scarce a hundred years before Columbus.
There is no evidence for a taboo against eating fish among Christian peoples, let alone the Catholic Norse. Nor is there a social class structure tied to Christianity. Over all I have to give this paper a C at best, if undergraduate work.

Myrrh
November 13, 2011 2:44 am

kuhnkat says:
November 12, 2011 at 6:59 pm
Willis Eschenbach,
“Crispin, let me see if I can find an image to show why this is not true. Hang on … ok, try this one.”
Wikipedia has a nice picture of the bedrock below the Greenland ice:
http://en.wikipedia.org/wiki/File:Topographic_map_of_Greenland_bedrock.jpg
from
http://en.wikipedia.org/wiki/Greenland
Since central Greenland lengthwise is below sealevel and a number of areas of the surrounding mountains are very low, we end up with glacial flow rates varying radically even when not affected by geothermal sources. We also have the situation where most of the lower levels of the glacier that is not on the outside of the mountain range is NOT going ANYWHERE!!!

Good image, looked like it could be a huge caldera in the the centre, so perhaps the whole island in total an old volcano. And recalling that the interglacial previous to ours is said to be hotter, the 161,000 years ago bottoming out of the ice could be during that previous glacial around 100,000 years ago, in which case the age of the bottoming out could be more accurately adjusted to that time, or the time adjusted to the bottoming out. Britain was much warmer at this interglacial too, hotter than our present one, the South more like African savannah if I recall with hippos or something in the rivers. Anyway, exploring this volcano thing:
Volcanoes in Greenland – http://www.hobotraveler.com/na_2_volcanoes-in-greenland.php
These are all around the edges and could be just all that is left of one very large volcano which blew at some time, like Santorini, but in the centre so leaving the island shape intact.
More becoming known of the present volcanic activity:

http://www.medindia.net/news/Volcano-Deep-Down-Could-Be-Melting-Greenlands-Ice-30702-1.htm
“A thin spot in the Earth’s crust is enabling underground magma to melt Greenland’s ice, scientists at the Ohio State University feel.
According to them, the “hotspot” is located in the northeast corner of Greenland — just below a site where an ice stream was recently discovered.

I don’t know if this is a real hot spot, like the island forming hawaiian one with the island formed moving away from and becoming detached from it. NE corner would suggest then that the island is moving southwesterly, perhaps?. Part of the movement that has Scottish rocks in the US?
And even further warm periods found:

http://www.medindia.net/news/DNA-Sample-Suggests-Greenland-was-Much-Warmer-During-Last-Ice-Age-23187-1.htm
“Ancient DNA samples recovered from the bottom of a two-kilometre thick ice sheet in Greenland has shown that the island was much warmer at some point during the last Ice Age than previously believed.
The DNA came from the trees, plants and insects of a boreal forest estimated to be between 450,000 and 900,000 years old. Previously, the youngest evidence of a boreal forest in Greenland was from 2.4 million years ago.
‘These findings allow us to make a more accurate environmental reconstruction of the time period from which these samples were taken, and what we’ve learned is that this part of the world was significantly warmer than most people thought,’ said Martin Sharp, a glaciologist at the University of Alberta and a co-author of the paper appearing in the journal Science.”

Again, these could be tied into the now known periods of interglacials in our current ice age, around every hundred thousand years.

Myrrh
November 13, 2011 3:00 am

OOPS – I’m not going there… 🙂

http://www.mantleplumes.org/GreenlandHot.html
“Again, we reiterate: the high-Mg olivines could not have survived millions of years at mantle temperatures without exsolving their high chromium contents into chromite. Why postulate an ancient high-temperature melting event in preference to a Paleocene event?”

No doubt they’ll let us know when they’ve sorted it out..

peter azlac
November 13, 2011 3:27 am

Willis re CET
Thanks Willis, I had not seen your previous post on CET but even after the explanation by Parker I remain sceptical of the reasons for the adjustments, especially since in 2004 they replaced Malvern with Pershore, a with a site with a different microclimate, and in 2007 deleted Ringway and went back to Stonyhurst. This gives two sites close to each other in Lancashire (Stonyhurst and Sqires Gate), one truly in central England (Pershore) and one in the SE – Rothamsted. Knowing all these sites I can say they have different climates – one can see that by the type of farming at each site: grass and cattle, fruit and cereals respectively. This is acknowledged by the Met Office from data at their regional climate site – so why claim that CET represents Central England when it does not?:
http://www.metoffice.gov.uk/climate/uk/regional/
http://www.metoffice.gov.uk/climate/uk/averages/ukmapavge.html
The two Lancashire sites will, like Armagh in N Ireland, be most affected by the North Atlantic Sea temperatures (http://www.arm.ac.uk/preprints/445.pdf ) and precipitation as they are close to the coast on the Irish Sea (that is why Lancashire is known for cotton spinning), whereas I can say from my time at nearby Cambridge, that Rothamsted is affected by weather coming off the North Sea from the direction of Russia. So CET is a mixture of apples, oranges and pears with the varieties changing with the need to keep the graph heading ever upwards, or so it seems.
This does, however, raise a serious question as to whether global temperature anomalies have any real value. Surely, apart from the politics and financial aspect, we are concernesd with how changes in climate impact supplies of food and water and this is a zonal and regional problem. Natural changes in climate over centuries are reflected in the well known climate zones that can be delineated by where crops grow – for example the growth of maize and grapes during recent warming has moved northwards by a hundred kilometres plus,reflecting the fact that apart from fertilisers, agro chemicals and plant breeding, crop growth is determined by soil temperature, water supply and heat units. This concept of regional analysis of temperature anomalies is the basis pf the Ruti project of Lanser who finds that coastal thermometers exhibit different trends to those inland, as do differences by elevation. http://hidethedecline.eu/pages/ruti.php
http://hidethedecline.eu/pages/ruti/coastal-temperature-stations.php
This goes a long way to explaining the problem with CET that mixes all three – Malvern is hill country, Squires Gate and Stonyhurst are close to the coast and backed by the Pennines and Rothamsted in on the plain.
It is important to sort CET out as it is used by some climatologists in place of Nuuk Greenland – (giving the relevance to your current paper) in determining the phase of the NAO, especially since the BEST project now claims to link changes in global temperature to those in the North Atlantic.
http://www.cgd.ucar.edu/cas/jhurrell/Docs/folland.summerNAO.jclim08.pdf
http://research.eeescience.utoledo.edu/lees/papers_PDF/Atkinson_2005_AFM.pdf
http://coast.gkss.de/staff/storch/pdf/vinther.pdf

November 13, 2011 3:35 am

Interesting topic, more interesting to me is how you ran across Dana the Younger, grandson of one of my very favorite authors..
He should write a book:
Master Sailing Ships in 2 Years the Dana Way

November 13, 2011 5:31 am

kuhnkat says: November 12, 2011 at 6:59 pm
Since central Greenland lengthwise is below sealevel and a number of areas of the surrounding mountains are very low, we end up with glacial flow rates varying radically even when not affected by geothermal sources. We also have the situation where most of the lower levels of the glacier that is not on the outside of the mountain range is NOT going ANYWHERE!!!

The geography of Greenland is very intriguing… what precisely is buried beneath the ice remains to be seen… and the dynamics of the flowing ice may be more complex (than suspected) at depth … the “domed” nature of an ice cap (higher in the middle) drives the downward radial flow… while the underlying natural rock “dish” (higher at the edges) provides resistance to this radial flow at depth. So we have two forces in opposition… the containment of the rock “dish” versus a dynamic ice “dome” which varies over time. Given the massive accumulation if ice over Greenland during the last ice age it is fairly safe to assume that the balance of these forces (at depth) was very different from today.
So now we come the “chicken and the egg” question.
Why is much central Greenland is below sea level?
Obviously, this could be the natural geography of Greenland before the ice cap arrived… or perhaps the weight of the ice age “dome” compressed the underlying rock layers to form the retaining “dish”… or perhaps the flowing ice “gouged out” a depression in central Greenland during the last ice age… who knows… and who knows how to generate a realistic computer model of ice flows over the last 161,313 years.
The other side of this geographic mystery is that there is no Lake Greenland under the ice cap.
Given the natural “dish” shape of central Greenland I would expect geothermal heat to help generate a lake beneath the ice cap… after all there are 140 known subglacial lakes in Antarctica of which Lake Vostok is the largest… even the Greenland ice flow computer models have an input parameter that represents the estimated annual melting rate at the base of the ice core. http://en.wikipedia.org/wiki/Lake_Vostok
So where has the Greenland melt water gone? Evidently it is not in a lake… therefore, it seems safe to assume that the natural “dish” in central Greenland is not watertight… the ice is melting at the bottom of the ice cap and the water is somehow “running off” Greenland into the sea… quite where and how this run off is achieved is probably buried beneath ice and / or sea level.
Given:
1) the lack of a Lake Greenland
2) the Greenland ice core deformation below 2,800 meters
3) the lack of an ice age accumulation signature in ice core
i.e. at least 90% of the “ice age” ice has disappeared
4) the known history of human settlement in Greenland
5) the increased concentration of “dirty” ice at depth
Then
It is very likely that the settled science based upon the Greenland Ice Cores is misleading (to say the least).
It seems far more likely that there have been numerous epochs where the ice cap has advanced and retreated – natural variation… the core deformation and settlement history indicate that the ice cap has been far smaller (than today) in recent history… and in all likelihood the ice cap has retreated (perhaps on several occasions) into the mountains where a very dirty “residual ice core” has been retained… through melting and ablation the residual ice core retains “dust” artefacts from bygone accumulation epochs… but the ice and the air “bubbles” from the melting epochs have long since disappeared.
In essence:
The physical continuity of an ice core does NOT guarantee the temporal continuity of the ice cap in that location… this is especially applicable in Greenland.
u.k.(us) says: November 12, 2011 at 5:06 pm
You were doing pretty well with your arguments about the science, I thought, but then you made the “misdirection” blunder.

My perspective is that we are all left blundering around in the dark when we unquestioningly accept settled science… so we can all benefit from “nudges” that challenge us to “dig” into the settled science… sometimes the “nudges” are ignored… sometimes they work… sometimes they backfire… sometimes you have to take risks if you want to move the conversation forward… and sometimes I am just perceived as a unpleasant little man… such is life… that is why I usually restrict my “nudges” [comments] to ridicule and sarcasm… trying to pursue an open minded inquiry into settled science is not a straight forward adventure – there are so many twists, turns and inconvenient bumps in the road… that is why so many “advocates” prefer to establish an extensive uninterrupted narrative that is difficult to critically address.
BTW what is a “duck out”?

Another phrase that doesn’t well… a connected phrase is “ducking out”… but that doesn’t travel well either according to an “urban dictionary… what I meant was: to avoid the issues, to ignore the issues.
Steve says: November 12, 2011 at 9:28 pm
The Norse farming methods worked well for nearly 500 years. That isn’t bad.

In this context that is the only point I was trying to establish… it is a random quote [via a Google search] from the multitude of examples that support this view of history.

November 13, 2011 8:58 am

The NASA Earth Observatory has some interesting insights:
http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/
Their temperature profile diagram explains the sudden uptick in temperatures at 1,500 meters…
This is apparently caused by “warming from bedrock” just as we arrive at the “ice age”
http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/Images/borehole_profile_rt.gif
From this I conclude that the ice core is morphing / flowing due to both pressure and temperature gradients… so I guess this introduces many challenges when analysing the ice core chemistry – let alone the ice flow dynamics… but luckily the Scientists have resolved these problems…

Scientists can confirm these chemistry-based temperature measurements by observing the temperature of the ice sheet directly. The ice sheet’s thickness makes its temperature much more resistant to change than the six inches of snow that might fall on your driveway during a winter snowstorm. As Alley explained to the Earth Observatory, the ice sheet can be compared to a frozen roast that is put directly into the oven. The outside heats up quickly, but the center remains cold, close to the temperature of the freezer, for a long time. Similarly, the ice sheet has warmed somewhat since the Ice Age, but not completely. The top has warmed as global temperatures have warmed, while the bottom has been warmed by heat flow from deep inside the Earth. But in the middle of an ice sheet, the ice remains close to the Ice Age temperatures at which it formed. “Because we understand how heat moves in ice, [and] we know how cold the ice is today, we can calculate how cold the ice was during the Ice Age,” says Alley.

However, I am still left wondering how we can be certain that the original “bubbles” and “dust” embedded in the ice has remained fixed in-situ when most of the original ice has simply flowed away – about 90% of the original ice has disappeared at 1,500 meters.
The following ice core images highlight how the concentration of “dust” increases with depth so that “the bottom of a core (lower: 3,050 meters), rocks, sand, and silt discolor the ice”.
http://earthobservatory.nasa.gov/Features/Paleoclimatology_IceCores/Images/cores.jpg
I am left wondering whether the rocks, sand, and silt at the bottom of the ice core indicates that the ice cores from central Greenland could have been formed above a fresh water lake or a sea water lagoon… I will continue my searches… perhaps there are organic remains from the bottom of the ice core that confirm [or confound] the assumption that the last time Greenland was largely ice-free was about three million years ago.

November 13, 2011 9:45 am

More ice cores… more dirt… more surprises….
More support for the concept of a residual ice sheet….

DNA reveals Greenland’s lush past
Armies of insects once crawled through lush forests in a region of Greenland now covered by more than 2,000m of ice.
DNA extracted from ice cores shows that moths and butterflies were living in forests of spruce and pine in the area between 450,000 and 800,000 years ago.
Researchers writing in Science magazine say the specimens could represent the oldest pure DNA samples ever obtained.
The ice cores also suggest that the ice sheet is more resistant to warming than previously thought, the scientists say.
http://news.bbc.co.uk/2/hi/6276576.stm

Digging deeper we find:

Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland
Approximately 31% of the sequences from the John Evans Glacier silty sample were assigned to plant taxa passing the authentication and identification criteria. These belong to the Rosales (an order of flowering plants, including nine families such as the rose family Rosaceae), the Salicaceae (willow) family, and the genus Saxifraga (Table 1). This result is consistent with the John Evans Glacier forming no more than a few thousand years ago in a high Arctic environment (18).

In contrast to the John Evans Glacier silty sample, the 45% of the Dye 3 DNA sequences that could be assigned to taxa reveal a community very different from that of Greenland today. The taxa identified include trees such as alder (genus Alnus), spruce (genus Picea), pine (genus Pinus), and members of the yew family (Taxaceae) (Table 1). Their presence indicates a northern boreal forest ecosystem rather than today’s Arctic environment.

Allowing for full recovery of the isostatic depression that is produced by two-kilometers of ice, Dye 3 would have been about a thousand meters above sea level. In combination, these factors suggest that a high altitude boreal forest at Dye 3 may date back to a period considerably warmer than present.

Interestingly, the plant taxa suggest that this period had average July temperatures that exceeded 10°C and winter temperatures not colder than −17°C

In conclusion, our results reveal that ancient biomolecules from basal ice offer a novel means for environmental reconstruction from ice covered areas and can yield new insights into the climate and the ecology of communities from the distant past.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2694912/

G. Karst
November 13, 2011 10:21 am

malagaview:
You have done well and have added much to the conversation regarding Greenland’s enigmatic nature. Willis does a lot of article posts and therefore receives a lot of spurious criticism. I am sure you can understand his sensitivity to wayward remarks. Stick around. GK