Greenland ice melt overestimated due to satellite data algorithm issue

This is an interesting admission:

The melt extent algorithm used by Greenland Ice Sheet Today has been overestimating the melt extent, and as a result, daily images posted on this site in February and March may have indicated melt where none occurred.

This makes you wonder what other kinds of issues remain undetected in the satellite data. NSIDC has had to issue corrections in the past, when it was pointed out that their data and reality didn’t match. – Anthony

From NSIDC: An early spring re-calibration for melt detection

The algorithm for the Greenland Ice Sheet Today daily melt extent has been revised to account for unusually warm winter snow layers and residual meltwater deep in the snow. Meltwater from last summer’s intense melt season did not completely re-freeze through at least mid December. The adjusted algorithm shows greatly reduced melt extent for early 2013. This much lower extent is more consistent with available weather and climate records.

Melt extent and distribution

Figure 1. These images show cumulative melt extent before the algorithm correction (left) and after the correction (right). A few areas indicating one to two days of melting in southeast Greenland remain in the revised map. The red dot shows the location of the Danish AWS. Credit: National Snow and Ice Data Center – Click for hires image

As shown in Figure 1, the adjustment to the algorithm resulted in fewer melt days than previously indicated. The revised image at right shows new surface melting in 2013 in a few small areas along the central southeastern Greenland coast, within the region of earlier spurious melt signals but greatly reduced.

Conditions in context

Figure 2. This image shows air temperature anomaly for Greenland for the period December 2012 to February 2013. Reds and oranges indicate higher than average air temperatures. The temperatures shown are at approximately 1,500 meters (5,000 feet) in altitude, appropriate for coastal Greenland regions. However, central Greenland is above this altitude, and values shown there do not represent the true surface conditions well. Credit: National Snow and Ice Data Center courtesy NOAA ESRL Physical Sciences Division

Temperatures in Greenland have been higher than average this winter, with air temperatures near the coast averaging 2.0 to 3.5 degrees Celsius (4 to 6 degrees Fahrenheit) warmer than the 1981 to 2010 average. This has in part been a result of the persistent circulation pattern for the Arctic this winter, characterized by a negative Arctic Oscillation (AO). The AO is a measure of the intensity of the general pattern of low pressure over the northern high latitudes. A negative AO indicates higher-than-average pressures near the North Pole, allowing more frequent southward cold air outbreaks, and more intrusions of warm air masses from higher temperature areas. Despite these anomalously high temperatures along the Greenland coast, temperatures were not high enough to result in melting.

Adjusted algorithm and melt images

Figure 3. This plot shows surface air temperature at a PROMICE on-ice Automated Weather Station (AWS) near the southeastern Greenland ice sheet edge for early 2013. Temperatures did not exceed freezing at this site. Data from PROMICE were provided by the Geological Survey of Denmark and Greenland (GEUS) and are freely available. Credit: National Snow and Ice Data Center and J. Box, Geological Survey of Denmark and Greenland

The melt extent algorithm used by Greenland Ice Sheet Today has been overestimating the melt extent, and as a result, daily images posted on this site in February and March may have indicated melt where none occurred. While the algorithm was indicating some coastal melt in February and early March, a comparison with weather data for Nuuk (the Greenland capital city, located along the southwest of the island) and data from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) suggested these might be spurious melt readings. The local Automated Weather Station (AWS) data from a glacier along the southeastern coast (the Mittivakkat glacier AWS, shown by a red dot in Figure 1; data in Figure 3) indicate that the air temperature did not rise to the melting point (0 degrees Celsius, or 32 degrees Fahrenheit) in February or early March.

Figure 4. A model of the snowpack conditions indicates residual liquid water in the deep snowpack in southeastern Greenland. Credit: National Snow and Ice Data Center and X. Fettweis, Université de Liège, Belgium

During this period, starting around mid-February in southeast Greenland, the brightness temperatures in the upper few meters of the snowpack were 2 to 10 degrees Celsius (4 to 18 degrees Fahrenheit) higher than those observed during any other year in the 34-year record (1979 to 2012). While surface melt is not unprecedented in Greenland near the coast in February and March, the totals posted prior to March 14 were a result of these unusual snow temperature conditions, and not ongoing surface melt. This winter has seen unusually warm snow at depth on the ice sheet, following the intense melting that occurred last summer.

The melt detection method, based on passive microwave emissions, is primarily sensitive to near-surface conditions, but has some input from the snowpack down several meters (10 to 20 feet). Heavy snow fell during the relatively warm winter, burying and insulating deeper snow. This contributed to anomalously high temperatures for the uppermost layers of snow this winter. Additionally, models based on snowpack properties suggested that some 2012 meltwater remained unfrozen at 5 meters depth (approximately 16 feet) in mid-December. The model results are consistent with observations from JAXA’s AMSR-2 sensor.

The algorithm was adjusted by combining the trend of observed brightness temperatures with a model of the expected microwave emission in the channels used for melt detection (the SSM/I sensor’s 37 GHz Horizontal polarization channel). This adjustment is generally performed every year in March to calibrate the melt detection thresholds. However, because of the unusual condition of the snowpack, the adjustment needed to be made much earlier than ever before.

Further information

Fettweis, X., M. Tedesco, M. van den Broeke, and J. Ettema, 2011. Melting trends over the Greenland ice sheet (1958-2009) from spaceborne microwave data and regional climate models. The Cryosphere 5, 359-375, doi: 10.5194/tc-5-359-2011.

Programme for Monitoring of the Greenland Ice sheet (PROMICE)

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So the Ice that was melting in Feb, was really not melting, and in fact might have been increasing in mass… Our Bad.

I believe if you changed all the catastrophic man-made global warming rhetoric, to a reference of the worldwide economy, rather than a reference to worldwide climate, the alarmists would be 100 percent accurate.

Niff

So the images are…..photoshopped?

Lawrie Ayres

It would appear the knowledge that an increasingly large number of climateers outside the government paid circle are keeping a careful and expert eye on their “data” is having a very positive effect. Shoddy work erring on the side of the warmers is no longer acceptable and is quickly identified and, encouragingly, is now being corrected. Kudos to all you honest scientists.

Lank remembers

The Washington Post
“The Arctic Ocean is warming up, icebergs are growing scarcer and in some places the seals are finding the water too hot, according to a report to the Commerce Department yesterday from Consulafft, at Bergen, Norway
Reports from fishermen, seal hunters, and explorers all point to a radical change in climate conditions and hitherto unheard-of temperatures in the Arctic zone. Exploration expeditions report that scarcely any ice has been met as far north as 81 degrees 29 minutes.
Soundings to a depth of 3,100 meters showed the gulf stream still very warm. Great masses of ice have been replaced by moraines of earth and stones, the report continued, while at many points well known glaciers have entirely disappeared.
Very few seals and no white fish are found in the eastern Arctic, while vast shoals of herring and smelts which have never before ventured so far north, are being encountered in the old seal fishing grounds. Within a few years it is predicted that due to the ice melt the sea will rise and make most coastal cities uninhabitable.”
* * * * * * * * *
I apologize, I neglected to mention that this report was from November 2, 1922, as reported by the AP and published in The Washington Post – 90 years ago.
Yep – ice melt was a tad overestimated back then too – and without the help of satellites!!

Pingo

Now try to spot a watermelon saying what good news this is! More difficult than finding an unbroken hockey stick..

Village Idiot

Proof (if we needed it) that the “Unprecedented Greenland Ice Sheet Surface Melt” of 2012 didn’t really happen
http://www.nasa.gov/topics/earth/features/greenland-melt.html

tokyoboy

Algorithms and models, not the reality, are über alles in the so-called climate science.

tty

One wonders why they didn’t check the weather at Kulusuk instead. Kulusuk is right in the middle of the supposed snowmelt area while Nuuk 400 is miles away on the other side of the icecap (and weather is often very different on the east and west coasts).
Here is weather for Kulusuk airport:
http://www.tutiempo.net/en/Climate/Kulusuk_Lufthavn/02-2013/43610.htm
February: average temperature – 3,6, average maximum -1,1, average minimum -6,4, all Celsius.
Nine days with maximum above freezing, none with minimum above freezing, seventeen days with snowfall. Which means that there was certainly some daytime snowmelt, but that except for evaporation it refroze next night.

Rational Db8

@ Lank remembers says: March 21, 2013 at 11:20 pm
Great post! Thanks for reminding us.

Gary Hladik

As with other areas of science, the devil really is in the details. Kudos for catching this error, now find the remaining bugs (yes, there are more).

Rational Db8

If Greenland is loosing all this ice over the past 30+ years, I’d dearly love to know how they explain the Glacier Girl.
For those here who might be unfamiliar, it’s easy to find the story online, and it’s truly fascinating. Essentially back during WWII, a small squadron of fighter planes had to ditch on Greenland. On the glaciers. About 50 years later, they went back and dug down through about 268 feet of ice to get to one of the P-38 fighters. They took her apart down in the hole, lifted her out piece by piece, Then they moved her to a more conducive location, put her back together and flew her.
Soooooo, to the researchers and scientists who think there’s been so much global warming causing huge ice melts…. just how the heck did a plane on the surface wind up buried under 268 ft. of snow and ice accumulated over those 50 years, during which so much of this global warming occurred????!!

Here we go again. Greenland ice melt over stated. Another body blow to the warmist’s creed.

David, UK

O.T., but in other news, heavy snow has fallen overnight throughout much of the UK, and continues to fall – and fall FAST. It’s a winter wonderland outside my window right now – and we’re three weeks into March! But I know it must be an illusion, because these days children just don’t know what snow is, because it NEVER snows these days. Yep, I’ll be wearing my shorts and Hawaiian shirt as is befitting for these warmer times.

DavidS

Meanwhile in the UK spring of 2013, children still don’t know what snow looks like.
sarc

SØREN BUNDGAARD

Al Gore-rithm issue;)

richard verney

Yet another example of a data set not fit for purpose.
Once again, the ‘error’ operating in the AWG proponents’ favour.
Guess, no surprise there. I share the sentiments expressed by Lawrie Ayres (March 21, 2013 at 10:49 pm) that being held up to scrutiny on the web is having some positive effect.

JDN

I remember commenting on a WUWT story a few years ago that someone needs to do spot checks on sea ice “data” from overflights. Is that going on? I look at the variation in sea ice coverage between algorithms, and the difficulty of figuring out what is ice vs. not ice, and I wonder how long until we find out that the Barents sea isn’t quite as ice-free as sea ice satellites make them to be.
Speaking of seeing things, I ran across the Dogger Bank incident (http://en.wikipedia.org/wiki/Dogger_Bank_incident) where the Russian navy destroyed British fishing boats because they thought they were Japanese. There was also a line in there about the American navy being so spooked by torpedoes that they fired at “ocean swells, trains on land, and rocks along the coastline, believing them to be enemy torpedo boats”. Just saying, it doesn’t require a computer to see things that aren’t there or vice versa, but computers help.

WIth the talk of all our “unseasonable” snow in the UK, I observe that it was my stepdaughter’s 15th burthday on Tuesday of this week and it has now snowed on 13 out of her 15 birthdays. But I suppose the plural of anecdote is not data…

Louis Hooffstetter

On March 22, 2013, the third day of spring, it’s literally freezing in the Carolinas. Yet somehow Greenland is melting!
Climastrology does it again!

tobias

I just won a bet here in BC Canada “against” a warmer (50 lat) , Lived here for 40 years bet him snow at least twice before March 19 ( It snowed 4 times.) Where does this report fit in anyhow, “Greenland ice melt overstated”,… in February ??. What else is new from their corner of the “debate”.
They are in full retreat , only theirs is real in contrast to the glaciers on Greenland.

Ian W

One would have thought that there would be some automated validation of these satellite metrics. There are numerous automated ground observation stations even in the arctic ocean there are automated buoys reporting weather and temperature data. There could be a rigorous cross check between the sensors that would have shown up inaccuracies very rapidly. Similarly for ocean temperatures now there are ARGO floats reporting SST they should be cross checked against satellite SST. As it is these ‘climate scientists’ take weather reports and rush off ito their pet politicians to trigger more non-science policies.

Back in the days when I was naive i.e before I started to investigate the historic claims of climate change scientists-I would have believed the Greenland ice melt (and many other climate related things) was because someone had actually physically OBSERVED it. It seems that most climate science these days comes from models and maths and the original observed quality raw data is missing.
Incidentally, the warmest two consecutive decades in Greeland remain the 1930’s and 1940’s. We will have to wait until 2020 to see if the current spell of warmer than average weather beats it
tonyb

Dr. John M. Ware

Last year March here in Virginia was very warm, though not quite a record as I recall. This year is very different–cold, occasionally snowy, dreary. Two days ago it got to 62 degrees F here, the first day in the 60s this March, and likely the last according to the local weatherfellas. Yesterday our Weatherbug said the high was 46, but that was at midnight; by dawn it was 30 degrees, and by 7 a.m. it was 26 and snowing briskly. Not much stuck because the ground was so warm, but the grass and cars did get a white coating for a while. The high for the actual daylight was 35 with a brisk wind, making garden work impossible. How I have wished for just enough global warming to get some work done! Seeds need planting, beds need cleaning, etc., etc. Not in the outlook–more snow likely by Monday morning.

johnmarshall

Those damn temperature anomalies actually tell you nothing. It may be 3Cwarmer than a, supposed, average but was that above or below freezing, 0C?
The satellites also have problems with the many melt ponds that form on sea ice and report these as clear water. They also have problems with broken ice which again is reported as clear water.
Perhaps scare reports about the disappearing sea ice are not as real as thought.

For johnmarshall: Nothing about the warmists scare reports is real by definition!

Ian

I think the conversion is incorrect re Celsius to Fahrenheit ..being Canadian, I recognized this immediately :
” During this period, starting around mid-February in southeast Greenland, the brightness temperatures in the upper few meters of the snowpack were 2 to 10 degrees Celsius (4 to 18 degrees Fahrenheit) higher than those observed during any other year in the 34-year record (1979 to 2012). ”
2 Degrees C = 35 F
10 degrees C = 50 degrees F
however, if they meant the other way around.
4 degrees F = minus 15 or ( -15 C)
18 degrees F = minus 7 C or ( -7 C )
so which did they mean….

Richard Day

Our algo was off but we’re still believers in the church of global warming. By the way, we need a 14% increase in our funding. Bonuses and such.

Jimbo

For newbies obsessed that something is wrong in Greenland please take a look at the following. It looks like natural cycles to me.

Abstract
….The record indicates that warmer temperatures were the norm in the earlier part of the past 4000 years, including century-long intervals nearly 1°C warmer than the present decade (2001–2010). Therefore, we conclude that the current decadal mean temperature in Greenland has not exceeded the envelope of natural variability over the past 4000 years, a period that seems to include part of the Holocene…..
[Takuro Kobashi et. al.]
——-
Abstract
An aerial view of 80 years of climate-related glacier fluctuations in southeast Greenland
…………the recent retreat was matched in its vigour during a period of warming in the 1930s with comparable increases in air temperature. We show that many land-terminating glaciers underwent a more rapid retreat in the 1930s than in the 2000s,……
[Anders A. Bjørk et. al.]
——-
Abstract
“…the rate of warming in 1920–1930 was about 50% higher than that in 1995–2005….”
[Petr Chylek et. al.]
——-
Abstract
“…The annual whole ice sheet 1919–32 warming trend is 33% greater in magnitude than the 1994–2007 warming….”
[Jason E. Box et. al.]
——-
Abstract
“…The warmest year in the extended Greenland temperature record is 1941, while the 1930s and 1940s are the warmest decades….”
[B. M. Vinther et. al.]
——-
Abstract
The State of the West Greenland Current up to 1944
“….It is found that warmer conditions existed during the decade of 1880, followed by a colder period up to about 1920, when the present warm period began. The peak of the present warm period appears to have been reached in the middle 1930’s,…..”
[M. J. Dunbar]

On last year’s ‘unprecedented’ melt it appears to have been caused by soot according to the Guardian. Though in happened in 1889.
Rediscovered photos reveal Greenland’s glacier history
Cache of historical Arctic sea ice maps discovered

jayhd

This may seem like a stupid question, but don’t these “scientists” and computer “experts” validate their satellite data, images and models by actually going to a sampling of sites and getting real data and photographs? Without validation, what these people are doing is not “science”, it’s computer games!
By the way, I’ve become real familiar with the errors occurring in the GISS maps used by county planners and the various on-line mapping services. Errors such as drainage ditches labeled as roads, large farm equipment labeled as barns or sheds or silos, and so on. The GISS people don’t do a good job of validating their programs either.

Marcos

i’m confused. why are satellite sensor results being put into a computer model to come up with its ‘data’? shouldn’t the sensor data, oh i dont know, be the data?

PaulH

So “Greenland Is Melting! Melting!” was front page news. Will this correction appear on Page 1, or will it be buried somewhere in the classifieds?

starzmom

For another slightly OT anomalous weather update, here in eastern Kansas we are expecting 9-12 inches of snow for Palm Sunday. At this rate my easter dress will be heavy wool with boots. And the forsythia have yet to show themselves.

Owen in GA

Ian says:
March 22, 2013 at 3:55 am
I think the conversion is incorrect re Celsius to Fahrenheit ..being Canadian, I recognized this immediately… :

Ian, I think they are talking differences in temperature rather than absolute readings. If something is 2C warmer, it is 18/5 F warmer (3.6F). You interpreted it to say the snow was 2 to 10 degrees C which is an impossibility as it would have melted.

Scott

Jayhd says
march 22, 2013 at 4:59 am
… but don’t these “scientists” and computer “experts” validate their satellite data …
A couple things about validation, to be a good validator you have to be skeptical of everything and not afraid of finding something wrong and potentially embarrassing to your organization. So you really can’t be the same guy who designed the satellite or comes up with the data … you are too close and would have too much to lose. When you are a validator you take off your “team player” hat for a while. So I can see how that’s a problem for the global warming community.
But there is a way around this. I’ve had a few validation projects and we couldn’t get half the guys to leave their computers and get out in the plant and find something we didn’t already know. They wanted to validate everything from their computer rather than walking a quarter mile in the plant. Really frustrating. They avoid the tough part about validating by not really validating.
Guys like Anthony should be the validators, not the scientists or computer experts.

numerobis

“This may seem like a stupid question, but don’t these “scientists” and computer “experts” validate their satellite data, images and models by actually going to a sampling of sites and getting real data and photographs?”
Isn’t that what the story says they did? They noticed the model was wrong by checking measurements on the ground; so they fixed the model.

Jimbo says:
March 22, 2013 at 4:29 am
Cache of historical Arctic sea ice maps discovered
===============
The old nautical charts from England’s golden age of exploration show that sea levels have not risen anything like what is currently believed. These charts are still highly accurate even today, and most of the modern nautical charts are simply copies of these older charts, with corrections for wrecks, rocks missing in the original surveys, and datum adjustments for GPS.
Very few areas worldwide have ever been re-surveyed due to the high cost. Yet, almost universally, if a rock was shown on the charts as awash at low tide 200-300 years ago, it is still awash at low tide today. If sea levels were truly rising, these rocks should no longer be visible at low tide. Nowhere on the charts is a datum adjustment for “sea level rise”.
Which is very strange. These charts are vital to preventing loss of ships and lives. You would think that if sea level rise was real, these charts would have been updated to reflect this.
The reason they have not is quite simple. If the charts were adjusted to show sea levels rising when it has not, then this would result in water depths being reported as deeper than they really are. This would result in ships running aground when they thought they were safe, resulting in the loss of ships and lives.
Thus, nautical charts are one of the best sources of information on sea level rise over the past 2-3 hundred years, and why to this date they have not been used to calibrate sea level rise. Instead we see endless tidal gauges mounted on sand and mud, or sea shells or tea leaves used a proxies.

Admad

Am I missing something here? Why would something which is readily observable have to be “modelled”?

beng

The cold weather in Scandinavia has something to do w/the Greenland east coast. Easterly winds from there have been crossing the N Atlantic to hit Greenland. That air isn’t Arctic by that time — not even below freezing.
It’s called weather.

Billy Liar

Can some genius at NSIDC please generate an outline of the 1500m contour on Greenland, place it on their anomaly map (Fig 2) and set the color inside the contour to white.
The anomaly map would then appear a tad more honest: showing fictitious anomalies below the surface of the ice is somewhat bizarre to say the least.

This case shows up the folly of overreliance on algorithms, statistics and computer models, and not paying enough attention to real world data.
This was illustrated well with the issue of GHCN temperature adjustments in Iceland. In 1965, Iceland underwent a drastic drop in temperatures. The cold spell lasted well into the 1970’s, and was so severe that agriculture and fishing suffered hugely, leading to mass unemployment and 50% currency devaluation. This time even had a name, “The Sea Ice Years”, and has been well researched by proper scientists.
Yet, the GHCN algorithm interpreted this as a data glitch and adjusted the drop in temperature out of existence. GHCN still refuse to accept their adjustments are faulty.
There’s more on the background to the Sea Ice Years here.
http://notalotofpeopleknowthat.wordpress.com/2012/10/30/ghcn-temperature-adjustments-in-icelanda-closer-look-at-stykkisholmurpart-ii/

Chris4692

Village Idiot says:
March 21, 2013 at 11:37 pm

Proof (if we needed it) that the “Unprecedented Greenland Ice Sheet Surface Melt” of 2012 didn’t really happen

(Others as well)
The article says no such thing. It applies to recalibrating 2013 data, not 2012. It even refers to the water from the ice melt of last summer remaining unfrozen under the surface.
Although there are reasons to think that last summers melt was not unprecedented, this article is not one of them.

ps: there is good reason to increase water depth on nautical charts if sea level rise is occurring. Increased water depth opens up new sea-lanes and can save millions in costs. It is not unusual for ships to travel in areas where the difference between a safe passage and running aground is less than the difference between high and low tide for that day.

Paul Homewood says:
March 22, 2013 at 6:53 am
Yet, the GHCN algorithm interpreted this as a data glitch and adjusted the drop in temperature out of existence. GHCN still refuse to accept their adjustments are faulty.
===========
Very interesting. This shows the problems in adjusting temperatures to try and improve signal quality. What the computer thinks is noise may well be signal, and what the computer this is signal may well be noise.
This is in some way similar to the famous hockey stick, where in an attempt to amplify the signal in tree rings via “calibration” what actually happened was an amplification of noise. Since this noise was random it gave the appearance that temperatures had not changed for 1000 years and we all got the shaft as a result.

John F. Hultquist

jayhd says:
March 22, 2013 at 4:59 am
“. . . actually going to a sampling of sites and getting real data . . .

Such real data was called ‘ground truth’ and getting such was called “ground truthing.”
I remember it well, much like a beer for 25¢.
http://en.wikipedia.org/wiki/Ground_truth

knr

How lucky do you have to be to find all the ‘mistakes’ work in favour of the ideas your pushing ?

RE: Paul Homewood. Thanks for the link. I like your site.

Darren Potter

Now where is Mr. CostCo who was defending NASA’s Greenland ice loss and sea level measurements via satellite (http://wattsupwiththat.com/2012/12/03/why-ice-loss-and-sea-level-measurements-via-satellite-and-the-new-shepard-et-al-paper-are-highly-uncertain-at-the-moment/)
doubting possible issues of unknown errors and unaccounted for drift with remarks like:
“I have technical knowledge in the satellite and instrument domains …”
Mr. CostCo: “Basically you’re insinuating that the glaciological community as a whole does not know how to assess errors and neither does Nature/Science etc”
Wonder what Mr. CostCo would deem failing to properly assess errors that allowed a hosed algorithm involved in measuring Greenland’s Ice Sheets to go undetected until after Shepherd et al paper was touted? Possibly the old ‘Nothing to See Here, Move Along’?

Steve from Rockwood

Now why didn’t I read this in my local paper? They carried the unprecedented melting story…

J. Gary Fox

Great story with details on “Glacier Girl” … above comment by Rational Db8 on WWII planes buried in Greenland.
http://www.damninteresting.com/exhuming-the-glacier-girl/
Do we know which glacier was it that the 8 planes landed on?
Is it one of the “fast melting” glaciers listed As Rational noted, if so, how did they get buried in 268 feet of accumulated snow in 50 years?