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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ADD (Arithmetic Deficit Disorder) is certainly a widespread syndrome. Especially, it would seem, among the well educated.
Thanks for posting this. What I am amazed at is the effect of a satellite’s position in orbit by passing over Greenland. At first I found it incredulous that you could determine weight based on that method but then they mentioned another method that seems to confirm it. btw, Greenland wasn’t named Greenland as a wishful thought.
Does the grace data necissarily imply there is any unusual melting going on at all? If snowfall patterns aren’t what the were when the ice sheet was building, then one would expect ice loss as glaciers do what glaciers do, which is slide off into the sea. Since the ice loss is such a trivial amount, it could easily be explained by natural variability of precipitation rates.
Has anyone done a study to determine how much ice human activity is adding to the world? Since the advent of commercial refrigeration how many tonnes of ice are scattered over various campsites….in fish coolers…cooling the Corona? And then we have the residential refrigerators locking up tonnes of water. The puny loss at Greenland is well compensated for.
On the subject of AGW
Overcome your fear……have a beer. 15000 years is not tomorrow.
Schnurrp says:
“Greenland icecap melting at this rate yields sea level rise of about .59mm / year or just over 2″ by the turn of the century. I believe that’s the way to look at it, not how long it will take to disappear. Is my math right?”
It’s easy to make orders-of-magnitude errors with this sort of problem, but it seems about right.
200 cubic-km of water would cover 200,000 square-km to a depth of 1 metre, or 200,000,000 square-km to a depth of 1 millimetre. The total sea-surface area of the Earth is about 350,000,000 square-km, so 200 cubic-km of water per year would cover that surface by a little over 1/2 a millimetre per year, or about 5 centimetres (2 inches) by the end of the century. 200 cubic-km of ice would produce less than 200 cubic-km of water (since water is denser than ice), but that hardly affects the general outcome, which is that melting of Greenland ice at the present rate is not in itself cause for alarm.
Someone please write a letter to the National Geographic to put in perspective their June 2010 article on “Greenland, Ground Zero for Global Warming” by using Eschenbach’s numbers!
So Greenland is rising – how the heck can these satellites accurately measure the volume of its ice cap, if this factor is not taken into account?
Nobody seems to take into account precipitation patterns – this NOAA report indicates Greenland had below average precipitation for the years 1961-2001 (no subsequent data available). I suppose it is not too simplistic to assume that if the average precipitation falls in Iceland, then its glaciers will be seen to be melting as they are not having their normal annual recharge.
http://www.climate4you.com/Polar%20precipitation.htm#Arctic%20annual%20precipitation%20change%201901-2000
Whoops – Greenland, not Iceland.
“Paul Daniel Ash says:
[…]
And in “twenty years or so,” if the majority of the world’s scientists are drawing the correct conclusion from the data, we will be in that much worse of a pickle.”
Science is not about majorities, Paul. It’s about evidence. I think you’re confusing it with politics.
Willy Eschenbach says:
“tty, the measurement by the GRACE satellites is not measuring the height of the ice and estimating the ice loss from that. It is measuring the weight of the ice. As such, the isostatic rebound doesn’t affect the answer, because although the underlying rock moves vertically, the weight of it doesn’t change.”
It most definitely affects GRACE. As you say GRACE measures the gravity field. This is affected by the level of the ice and the level of the heavier underlying rocks. If you measured both the change of height of the ice surface and the gravity change (without any measurement errors), then you could eliminate the effect of the changes of the rock surface, but not by measuring only one of them.
I am not sure if anyone else has posted this here, but The Hockey Schtick has just posted a stidy that completely refutes what the Satellites are finding, the ice is growing at 5.4 cm/yr.
http://hockeyschtick.blogspot.com/2010/05/greenland-ice-sheet-growing-54-cmyr.html
Paul Daniel!
“And in “twenty years or so,” if the majority of the world’s scientists are drawing the correct conclusion from the data, we will be in that much worse of a pickle.
You guys always discount the downside risks. It would be an interesting intellectual exercise, except that you are gambling with huge stakes. Anyway, enjoy the beer.”
In 20 years I will be dead, which is the nature of things! I am totally unafraid of my demise!
In my lifetime at this time I am proud that I contributed scientifically and logically, as Willis and Anthony have done here!
I AM fearfull that I have $ encumbered my wonderful grandson with the debt that this obvious ‘folley’ of AGW is creating.
As a beleiver in human nature, and education, I would TRUST that my grandaughters and grandson, in this fabulous country of America will be able to solve this “AGW problem”, if it exists”, or DIE trying! I DO have confidence in them! I produced and educated them to QUESTION EVERYTHING!
No matter what, “Our Goose is Cooked” if AGW is right the world is doomed! Even if we roll back the clock to 1800 it won’t help!
Buck UP man! You drank the Kool-Aid that we can’t manage this as individuals! The “Collective” (minus emerging nations who are still starving) will solve this problem through Votes and $. WE ARE DOOMED! This article tells us that!
How about a Schlitz? The one with gusto
The question is why do they take trivial ice melt and blow it up to dramatic proportions? It’s because that’s how propaganda works. The science is a failure and so they have to resort to other means to drive their policy.
Good post –
That study was up till 2003, i.e. before the Grace Satellites, so there is a direct contradiction after 2003?
Here’s a “back of the envelope” calculation for you. Supposedly, if all of Greenland were to melt, sea level would rise 20 feet. So .007% is .0014 feet annually, .14 feet per century. Not exactly worth getting excited about. In order to get so much as a foot out of that, you’d need the rate to increase more than seven-fold.
Peter Miller
“So Greenland is rising – how the heck can these satellites accurately measure the volume of its ice cap, if this factor is not taken into account?”
This factor is taken into account, see Khan et al. 2010, for example. There are many locations which have Differential GPS on the bedrock of the GIS (Greenland Ice Sheet) which help scientists measure this. So before you speak, get your facts straight if you’re not an expert in the field. Secondly the volume of the ice cap is also measured using radar interferometry, climate modelling, radar altimetry and laser altimetry so we do have a decent clue.
Willis, you’re getting steamed about an article you read in Grist? Isn’t that like getting worked up about something you read in National Enquirer? I’d say save your bile for when (not if!) something very similar gets published in Nature or Science (but in the meantime, enjoy that Corona).
I’m a little surprised that no one else noticed or commented on this (alth. I’m short on time & just skimmed the comments – apologies if anyone did).
The issue of context & perspective is something I’ve been harping on to my nervous family & friends for years. Just last week I devised a little Dick & Jane story problem comparing worst-case scenario of the current gulf spill to the total volume of ocean waters in the photic (life-supporting) zone, re: those scare stories making the rounds of the enviro blogs: It’s a Global Catastrophe!!! It’s gonna kill every living thing in the oceans!!! I provided links to the data, and questions designed to encourage perspective-based conclusions. It’s really amazing how much more convincing & eye-opening that approach is than trying to force-feed conclusions.
So, thanks for the data, Willis. This post & comments is one of the best I’ve seen in a while. I’m gonna give it a few more days until it starts to peter out, and then copy/paste the whole thing into my Climate\Context_Historical Perspectives folder.
all the 5 year old kids know that the artic is melting and all the polar bears are going to drown there teachers told them, it must be true . HOW DO WE GET THE RIGHT MESSAGE THROUGH TO THEM ?
OT – sortof. Today we learn from Felisa Smith, et al, that the extinction of the mammoths triggered climate cooling 11,500 years ago – the Younger Dryas. (USA Today: http://tinyurl.com/3xjy755 references Nature: http://tinyurl.com/2bdgrle ) “coincident with the first large-scale migrations of humans into the Americas.”
Mammoth guts produce methane. No megafauna, less methane, less global warming.
The paper concludes with “We are not the first to suggest that human-mediated activities influenced the planet prior to the industrial age. Although still controversial, the megafaunal extinction is the earliest catastrophic event attributed to human activities.”
Oh puleeze! When will the asininity stop? So much for “peer-reviewed” literature.
Great analysis! I weigh 165 pounds and am trying to lose 13 pounds due to heart disease. Let me see…. If I lose this excess weight at the same rate as the Greenland icecap, it will only take me about 1,150 years to lose one pound. Truly a worthy goal and a cause for celebration. Mark it on your calendar and check back with me then.
Robert says on May 23, 2010 at 10:35 am said
I think we know who hasn’t got a clue.
Bill Illis says:
May 23, 2010 at 8:58 am:
“… pretty soon, there will be an acceleration in sea level rise.”
Yes, that’s how it looks. But 2.99 mm/year = ≈3 cm/decade = 30 cm/century. A little less than a foot.
Isn’t that lower than the Holocene average?
The big number bias is common. It’s a means to robustify reported results.
As a kid growing up in Michigan back in the days when US automakers were profitable I would read about the UAW complaints in the paper. The unions claimed auto workers already bloated wages weren’t high enough because GM made a $2 billion profit! Whatever the profit, it was never reported as a % margin, just a big number. Today politicians do the same thing with oil company profits. They only report the big number without respect for the actual % of the total because the profit margin for “big oil” is not at all impressive compared to Coke or Pepsi.
Warmists, and Al Gore in particular, always speak of mankind’s CO2 emissions in terms of tons of CO2. This sounds scary but is meaningless without the context of how many tons of CO2 is already in the atmosphere or better still, how many “tons” of atmosphere exist. Small fractional percentages and ppm just don’t grab the attention like a big number of tons.
BTW…what exactly is the tons to Lake Erie conversion?
There are two sides, two weather systems now:
One yellow, and hot, on the NA east cost and a purple, and cold, on the Asian east coast:
http://weather.unisys.com/surface/sst_anom.html
Following GMF:
http://weather.unisys.com/surface/sst_anom.html
Why, is it forbidden to ponder the following:
http://www.xearththeory.com/introdis_earth_electromagnetic_coil_transformers_step_up_down.html
Paul Daniel Ash says on May 23, 2010 at 6:59 am said:
So, please tell us what the downside risks are and what the stakes are and how large they actually are.