Guest Post by Willis Eschenbach
This topic is a particular peeve of mine, so I hope I will be forgiven if I wax wroth.
There is a most marvelous piece of technology called the GRACE satellites, which stands for the Gravity Recovery and Climate Experiment. It is composed of two satellites flying in formation. Measuring the distance between the two satellites to the nearest micron (a hundredth of the width of a hair) allows us to calculate the weight of things on the earth very accurately.
One of the things that the GRACE satellites have allowed us to calculate is the ice loss from the Greenland Ice Cap. There is a new article about the Greenland results called Weighing Greenland.
Figure 1. The two GRACE satellites flying in tandem, and constantly measuring the distance between them.
So, what’s not to like about the article?
Well, the article opens by saying:
Scott Luthcke weighs Greenland — every 10 days. And the island has been losing weight, an average of 183 gigatons (or 200 cubic kilometers) — in ice — annually during the past six years. That’s one third the volume of water in Lake Erie every year. Greenland’s shrinking ice sheet offers some of the most powerful evidence of global warming.
Now, that sounds pretty scary, it’s losing a third of the volume of Lake Erie every year. Can’t have that.
But what does that volume, a third of Lake Erie, really mean? We could also say that it’s 80 million Olympic swimming pools, or 400 times the volume of Sydney Harbor, or about the same volume as the known world oil reserves. Or we could say the ice loss is 550 times the weight of all humans on the Earth, or the weight of 31,000 Great Pyramids … but we’re getting no closer to understanding what that ice loss means.
To understand what it means, there is only one thing to which we should compare the ice loss, and that is the ice volume of the Greenland Ice Cap itself. So how many cubic kilometres of ice are sitting up there on Greenland?
My favorite reference for these kinds of questions is the Physics Factbook, because rather than give just one number, they give a variety of answers from different authors. In this case I went to the page on Polar Ice Caps. It gives the following answers:
Spaulding & Markowitz, Heath Earth Science. Heath, 1994: 195. says less than 5.1 million cubic kilometres (often written as “km^3”).
“Greenland.” World Book Encyclopedia. Chicago: World Book, 1999: 325 says 2.8 million km^3.
Satellite Image Atlas of Glaciers of the World. US Geological Survey (USGS) says 2.6 million km^3.
Schultz, Gwen. Ice Age Lost. 1974. 232, 75. also says 2.6 million km^3.
Denmark/Greenland. Greenland Tourism. Danish Tourist Board says less than 5.5 million km^3.
Which of these should we choose? Well, the two larger figures both say “less than”, so they are upper limits. The Physics Factbook says “From my research, I have found different values for the volume of the polar ice caps. … For Greenland, it is approximately 3,000,000 km^3.” Of course, we would have to say that there is an error in that figure, likely on the order of ± 0.4 million km^3 or so.
So now we have something to which we can compare our one-third of Lake Erie or 400 Sidney Harbors or 550 times the weight of the global population. And when we do so, we find that the annual loss is around 200 km^3 lost annually out of some 3,000,000 km^3 total. This means that Greenland is losing about 0.007% of its total mass every year … seven thousandths of one percent lost annually, be still, my beating heart …
And if that terrifying rate of loss continues unabated, of course, it will all be gone in a mere 15,000 years.
That’s my pet peeve, that numbers are being presented in the most frightening way possible. The loss of 200 km^3 of ice per year is not “some of the most powerful evidence of global warming”, that’s hyperbole. It is a trivial change in a huge block of ice.
And what about the errors in the measurements? We know that the error in the Greenland Ice Cap is on the order of 0.4 million km^3. How about the error in the GRACE measurements? This reference indicates that there is about a ± 10% error in the GRACE Greenland estimates. How does that affect our numbers?
Well, if we take the small estimate of ice cap volume, and the large estimate of loss, we get 220 km^3 lost annually / 2,600,000 km^3 total. This is an annual loss of 0.008%, and a time to total loss of 12,000 years.
Going the other way, we get 180 km^3 lost annually / 3,400,000 km^3 total. This is an annual loss of 0.005%, and a time to total loss of 19,000 years.
It is always important to include the errors in the calculation, to see if they make a significant difference in the result. In this case they happen to not make much difference, but each case is different.
That’s what angrifies my blood mightily, meaningless numbers with no errors presented for maximum shock value. Looking at the real measure, we find that Greenland is losing around 0.005% — 0.008% of its ice annually, and if that rate continues, since this is May 23rd, 2010, the Greenland Ice Cap will disappear entirely somewhere between the year 14010 and the year 21010 … on May 23rd …
So the next time you read something that breathlessly says …
“If this activity in northwest Greenland continues and really accelerates some of the major glaciers in the area — like the Humboldt Glacier and the Peterman Glacier — Greenland’s total ice loss could easily be increased by an additional 50 to 100 cubic kilometers (12 to 24 cubic miles) within a few years”
… you can say “Well, if it does increase by the larger estimate of 100 cubic km per year, and that’s a big if since the scientists are just guessing, that would increase the loss from 0.007% per year to around 0.010% per year, meaning that the Greenland Ice Cap would only last until May 23rd, 12010.”
Finally, the original article that got my blood boiling finishes as follows:
The good news for Luthcke is that a separate team using an entirely different method has come up with measurements of Greenland’s melting ice that, he says, are almost identical to his GRACE data. The bad news, of course, is that both sets of measurements make it all the more certain that Greenland’s ice is melting faster than anyone expected.
Oh, please, spare me. As the article points out, we’ve only been measuring Greenland ice using the GRACE satellites for six years now. How could anyone have “expected” anything? What, were they expecting a loss of 0.003% or something? And how is a Greenland ice loss of seven thousandths of one percent per year “bad news”? Grrrr …
I’ll stop here, as I can feel my blood pressure rising again. And as this is a family blog, I don’t want to revert to being the un-reformed cowboy I was in my youth, because if I did I’d start needlessly but imaginatively and loudly speculating on the ancestry, personal habits, and sexual malpractices of the author of said article … instead, I’m going to go drink a Corona beer and reflect on the strange vagaries of human beings, who always seem to want to read “bad news”.
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I just can’t get worked up about Greenland. Primarily because 12, 000 years ago or so when ice was 2 or 3 miles thick down to Chicago, N. America was a very dry desert and life was very difficult. Water is good, ice is bad.
Toby:
From your link:
A few decades ago, any researcher claiming statistical significance with a 90% confidence interval would have been told, in no uncertain terms, to go back to school.
But, of course, we now live in the post-scientific era.
Suppose this is correct, there still remains one basic question:
Where is the proof that man is responsible?
Thanks
JK
Robust. Isn’t that a term I have heard in the past, while happening upon a cooking show?
Seems to me that it also had something to do with wine tasting.
Oh, very well, I’ll take the $3M in the bank that comes with the robust $200/mo. fee for storage.
Please hurry the check along, and tell Vanna I want to buy a vowel.
Willis, you explain things as clearly as Isaac Asimov. The best compliment I can bestow.
Thanks for the info, Willis. Well said.
0.005% — 0.008% ice loss per year, that could be stated as 50-80 ppm (parts per million), a unit well known in this field.
Slabadang says:
May 23, 2010 at 2:50 am
On dating of icecores, have you read through:
http://en.wikipedia.org/wiki/Ice_core ?
It describes the dating for recent years, and says there are several methods for going into the long past. You can start from there and look up the references.
Willis,
If you think one-third of Lake Erie is hype, how about trying 2 billion Hiroshima atomic bombs of heat being stored into the oceans based upon that Lyman paper in Nature:
http://news.yahoo.com/s/ap/20100519/ap_on_sc/us_sci_climate_reports
Of course, what is left out is that the Nature paper downgrades guru James Hansen’s 0.85W/m^2 to 0.64W/m^2 globally and annually averaged. So that 2 billion Hiroshima figure is 656 million less Hiroshima’s than before. This is about 0.2 milliseconds of solar output.
These satellite readings are useless at measuring small changes in a place like Greenland. The reason being that Greenland experiences huge changes in elevation due to isostasy and that there are very few bedrock outcrops to calibrate off of. Ice mass in Greenland could just as easily be increasing.
http://cat.inist.fr/?aModele=afficheN&cpsidt=15598567
1 meter sea level rise scare? You must be easy to scare. 2 years ago, James Hansen visited Norway.He explained that the sea level was about to rise by 75 meters and that it was a guaranteed disaster:
Newspaper article (Norway’s biggest paper Aftenposten) April 2008
http://www.aftenposten.no/klima/article2353729.ece
Hansen was quoted as saying: “- Hvis vi holder oss på 450 ppm lenge nok, vil sannsynligvis all isen smelte – og det tilsvarer en økning i havnivåene på 75 meter. Det vi har funnet er at målet vi alle har satt oss, er en katastrofe – en garantert katastrofe, sier den anerkjente forskeren til The Guardian.”
If we google translate that back to english: “- If we stay at 450 ppm for long enough, it will probably melt all the ice – and it corresponds to a rise in sea levels of 75 meters. What we have found is that the goal we have set ourselves is a disaster – a guaranteed disaster, ” said the renowned scientist to The Guardian.”
It didn’t scare me, but instead it triggered my interest in finding out what exactly these people were up to.
Willis, somehow I missed the blue link to the very first article “Weighing Greenland.” Most of the points I made above are there within. Just disregard my contention, I now know you were already aware.
With an ocean area of 335,258,000 km^2, the 200 km^3 contributes 0.59 mm per year, or 5.9cm per century, or about 2.3 inches per century.
Another great essay, Willis!
GRACE is a really cool scientific tool… But the breathless claims of ice loss that have been based on its data totally ignore potential margin of error and the meaningful resolution of residual gravity anomalies.
I believe that Velicogna & Wahr (2006) was the first publication like this. They estimated that Antarctica had lost 153 km^3/yr from 2002-2005 – All of the ice loss was from the WAIS. Well, that 153 km^3/yr works out to 0.006%/yr of the WAIS (0.0006%/yr of the total Antarctic ice sheet). Gravity is a great geophysical tool, but measurements that are accurate to tens to hundreds of thousandths of 1%? I don’t think so,
Velicogna et al. also found that their PGR estimate was greater than the ice loss estimate…
The PGR uncertainty was more than half of their annual ice loss estimate!
Interestingly, their estimated ice loss corresponded to the IPCC’s “0.4 ± 0.2 mm/year of global sea-level rise” due to the melting of continental ice.
Well, if I look at Jerejeva et al’s (2008) sea level reconstruction since 1700, I find that there were decades in the 1700’s and 1800’s in which sea level rose far more rapidly than it has in any decades since 1950.
Here are the top ten decades of sea level rise (mm/yr) since 1700…
1804-1813 12.75
1803-1812 10.67
1728-1737 10.30
1789-1798 8.38
1842-1851 7.87
1858-1867 7.82
1788-1797 7.72
1861-1870 7.66
1808-1817 7.58
1785-1794 7.18
All of those periods occurred long before man started pumping CO2 into the atmosphere. One has to wonder what sort of ice loss GRACE would have indicated if it was flying from 1790-1815. (I suppose that some of the late 18th – early 19th century sea level variability could be the result of a larger margin of error in the older data).
Here are the top ten decades (mm/yr) from 1950-2002…
1989-1998 4.66
1990-1999 3.95
1991-2000 3.86
1956-1965 3.79
1986-1995 3.78
1974-1983 3.71
1952-1961 3.65
1993-2002 3.63
1988-1997 3.44
1975-1984 3.30
Far less decadal scale sea level rise than was the norm during the intitial warm up from the Little Ice Age. And none of the 10-yr periods since 1700 has come anywhere close to the 22 mm/yr sea level rise recently predicted by the National Academy of Sciences.
My understanding is that GRACE is located about 460 km above the Earth’s surface and the two sensors are separated by 220 km. At those distances how can NASA be sure the gravity anomaly is caused by water loss and not something deeper. At what depth do they attribute the Greenland water loss to?
In India, NASA shows serious water loss in the north. They barely discuss the even greater water gain in the south (attributed to greater rainfall). This is attributed to denisty loss/gain from GRACE. But the water loss does not seem to correlate very well with population density, although human use is stated as the likely cause.
So my questions are “what is the depth sensitivity of GRACE and what are the real causes of the calculated density anomalies?”.
Evelyn says:
May 23, 2010 at 2:39 am
And if that is not enough, we’re told that Greenland is rising because the ice no longer holds it down as it’s melting away.
The logical next step is to consider if the land is rising, what is dropping? If the ocean floor is subsiding then are we in danger of lower sea levels?
“And how is a Greenland ice loss of seven thousandths of one percent per year “bad news”?”
—–
I’ll wildly speculate and state that surely this is within natural climate variation. In the past it’s been worse than we thought.
Somewhere along the line they seem to forget about the variability of sea temps. The North Sea varies by 12°C over 6 months, the med by some 15°C and the arctic by, well not as much, but when the land is at -40°C and the sea water is at -4°C that is a significant warming signal. Bozos, who funds them? Oh I forgot, it’s us bozos.
Toby,
I find some of the statements made in the article you referenced to be particularly interesting.
Link to the article:
http://www.nature.com/nature/journal/v465/n7296/abs/nature09043.html
“…but the underlying uncertainties in ocean warming are unclear, limiting our ability to assess closure of sea-level budgets4, 5, 6, 7, the global radiation imbalance8 and climate models5. For example, several teams have recently produced different multi-year estimates of the annually averaged global integral of upper-ocean heat content anomalies (hereafter OHCA curves) or, equivalently, the thermosteric sea-level rise…”
So this basically states that there is no “consensus” between various teams regarding heat budgets for upper oceans, if I’ve got it right?
And wasn’t there a post quite recently here on WUWT predicting that the SSTs were about to “plunge”?…
How much are we paying these folks? I want another refund…
JimB
My pet peeve as well. Exaggeration of numbers and their importance occur throught the literature and especially in the media. Another pet peeve is making measurements for the first time and then proclaiming whatever they observe is unprecedented. The earth has been changing for billions of years. How can anything really be unprecedented?
toby says:
May 23, 2010 at 1:39 am
Of course it is only six years of evidence, but taken with all the other peices of evidence, it IS bad news. Like this:
http://www.nature.com/nature/journal/v465/n7296/abs/nature09043.html
___________________________________________________________________________
Toby, Look at the middle graph. IT IS FLAT LINING.
I suggest you read about error bars and the IPCC/temp before you get your shorts in a twist. This type of lying with statistics and graphs
is exactly what Willis is talking about. Shouting about changes of tenths of a degree in data that has an accuracy of 0.5 to 4.0 degrees C is just plain lying.
Statistical error in temperature data
In fact, it’s so much, much worse than we thought 6,000 to 7,000 years ago.
rbateman: May 23, 2010 at 3:54 am
Robust. Isn’t that a term I have heard in the past, while happening upon a cooking show?
Or while watching a documentary on australopithecines.
They’re extinct, despite their robustnessosity. Or is it robustositiness?
Valid point — EXCEPT: it ignores issues of
a) the loss is monotonic and suggests a drivers as opposed to variability, and
b) if (a) is true, that current physical understanding would indicate this is the early portion of an accelerating process with local positive feedbacks.
I blogged last year about greenland in Dutch, http://www.vkblog.nl/bericht/268863/Over_Groenland
Are there any recent updates by Konrad Steffen and Russell Huff, their last update is from 2007. Their scary extremes were used by Pier Vellinga to scare the dutch about sea level rise.
http://cires.colorado.edu/science/groups/steffen/projects/
Well Willis, I get all wound up about things like this because the place was frickin’ green several hundred years ago. So what’s the big deal anyway? It’s just more alarmist horse manure!
Don’t get me wrong; I agree with you about putting things in their proper perspective and you did a nice job of it. However these alarmists or bozos, whichever they are, cause such a waste of time and energy because of their religion or stupidity.