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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Brad, thank you for the info by the way. Always helpful to have as much info as possible. Wikipedia always makes me feel like I have been molested and unclean afterwards (if only due to William Connelly). Maybe it is just me. I am NOT a conspiracy theorist ( man DID walk on the Moon, 911 was NOT perpetrated by Americans, etc.) but the timing of this spill could not have been better for the alternative energy concerns. That is irrefutable.
Willis, do you offer a course in creative cursing? I confess I get tired of using and re-using the same dozen or so tired phrases each day when reading the political news. I might be interested in such a course. (Actually, if devoted to cursing, would it be more proper to call it a coarse?) Also, I highly recommend Sam Adams Boston Lager when you need a change from Corona; since you won’t need the limes, think of the savings!
Bulk density varies with temperature.
Mods! can someone help ‘Brad’ to an appropriate blog – he appears to be obsessing about blame for an oil leak in the Gulf – perhaps ‘Lawyers-R-Us’?
Well sure, but what time of day? It’s important.
Corona? Everyone knows that Negra Modelo is the best beer in Mexico! Although, I tend to choose an IPA or a stout, I do enjoy a Negra Modelo on a hot day.
And the hot wax thingie. I have it on good authority that hot wax is painful. It is best avoided.
Other than those two items, great post!
Regards,
Steamboat Jack
(Jon Jewett’s evil twin)
ok, so if true we now know where approximately 0.5 mm/yr of the 2 mm/yr sea level rise comes from. We already knew about the 2 mm/yr rise, so finding out what contributes to that is hardly alarming. Since the rest of the rise must come from either other ice melting or ocean thermal expansion, then if Greenland is melting more than we thought it follows that other ice isn’t or the oceans are not warming as much. So when do we see that story?
“Always” isn’t true. Many of us,probably most of us, favor some form of “no regrets” mitigation policies. E.g., moving toward nuclear, fusion research, encouraging increasing use of natural gas, encouraging better insulation, coal gasification, plasma incineration (see Prescription for the Planet), more hydropower, and a few others I can’t recall. What we’re opposed to is any forced march in that direction based on carbon-taxing or capping, which presumes falsely that wind, wave, and solar power (the classic “renewables”) are practical now or in the near future.
We also disbelieve that if “we” (the US, or the West) “do something,” that it will make a difference in the world’s co2 emissions. The rest of the world will not follow in our footsteps. The amount of money that it would take to get them to do so would bankrupt us. A saner course is adaptation, plus geo-engineering if necessary..
Anu says:
May 23, 2010 at 1:57 pm
Extrapolating this acceleration, we see every 9 years the mass loss will increase by a factor of 1.638. […] Since Greenland has only 2,850,000 cubic kilometers of ice, clearly it will all be gone way before 153 years from now – the three year average melting rate of 1,200,830 Gt/yr would melt it all in less than 3 years,
Well Anu, all I can say is if you ever hope to achieve your Greenland accelerating exponential extrapolation melt scheme, you first should have a long serious sit-down with ol’ Sol for he keeps assuring me lately he is just going to remain skeptical! 🙂
Jeez Willis… you had me all the way to Corona. I mean WT? I cannot for the life of me figure out why people drink that when there are perfectly good beers going untapped. If you have a hankering for Mexican beer then at least get something decent like a Negra Modello, or Bohemia … even Dos Equis.
Believe it or not, Aussies drink more Corona than any other import… it defies all logic I tells ya. Personally I am fond of Toohey’s Old, a fine winter drop if not served too cold.
As for the original topic I think Aesop summed this up some time back:
“We can easily represent things as we wish them to be.”
Smart chappie that…
You don’t need global warming to get a shrinking of Greenland. The ice might melt from the bottom due to geothermal heat insulated under the ice cap. And then the shrinking would come from the lack of new snow on the top.
I don’t say that Greenland is not shrinking because of global warming. What I say is they don’t make a proof of it because many variables can act on the ice thickness.
Is it just me, or do those two look too much like Douglas Adam’s Vogon Constructor Fleet ships from the TV series? Should I be concerned? Now that would be a catastrophe worth worrying about!
“Bulk density varies with temperature.” ~Enneagram
But they are using the GRACE data to try to find out what the densities are in the upper atmosphere:
http://lws-trt.gsfc.nasa.gov/trt04_Crowley.pdf
It’s just interesting that the drag and neutral density of the upper atmosphere, right where GRACE is (500-450 km), are under study. In that paper, they are examining the variability of the density of the thermosphere with Solar activity. (!!!)
Thanks Enneagram.
Is it possible that GRACE could get different drag rates in the thermosphere because of Solar activity, too?
Someone else mentioned that there might be lunar gravity effects on the satellites.
fredb says:
May 23, 2010 at 5:22 am
But yours is not even a slightly valid point.
(a) “Suggests drivers”. Drivers of what? SUV’s perhaps. The result is tiny, insignificant, and could as well be an error as a real measurement.
(b) ignoring the fact that (a) is ridiculous and unfounded, what indicates to you that this result is “the early portion of an accelerating process with local positive feedbacks”? There is no evidence of this, and no reason to suppose there should be.
Go back to church and learn the dogma correctly, my son. Clearly your faith is strong, but your understanding is weak!
Bulldust says:
May 23, 2010 at 5:47 pm
Try a mixture, 1/2 Bass Ale, 1/2 Guinness Extra Stout, mmm, mmm, good!
back on topic:
I like what Richard Lindzen has been saying lately: everything happening in climate now, including Greenland and Arctic ice, is within the range of normal.
“Willis Eschenbach says:
May 23, 2010 at 3:39 pm
….
I thought the magma was what was flowing, not the bedrock.”
Rock is ductile under favorable heat-pressure-time conditions. At depth, isostatic rebound will manifest as ductile strain (or flow), while at or near surface there can be brittle failure.
Willis
Oakgeo has it correct.
There are numerous papers in a variety of Geophysical and Geological journals on the processes involved in crustal; and mantle reactions to isostatic lowading and unloading by ice. This includes geodetic measurements on land, and numerous studies of sea level change, both in “near-field” and “far-field” situations.
Please note that deap-seated movement of rock associated with icesheet isostacy has nothing to do with magma. The deep rock is ductile but remains in the solid state. There are isostatic impacts on land surface elevation up to several thousands of km from the major transient icesheets (The Laurentide and Fennoscandian icesheets) as well as more localised effects due to ice in Patagonia and the Southern Alps (NZ), as well assubstantial effects from changes to the Antarctic Ice Sheet. Such effects have been studied using uplifted and tilted marine and lake beaches and coral reefs in areas that are known to be tectonically stable.
It is also worth noting that changes in the distribution of ice and water over the earth’s surface have an impact on the earth’s rate of rotation.
From the p.d.f by Zeke the Sneak,
Makes you wonder how the accelerometer(s) survived acceleration into orbit.
Dave Wendt says:
May 23, 2010 at 3:04 pm
This would seem to indicate that lack of replenishment is a more likely culprit for the decline in mass balance, than enhanced melting. It seems a little unreasonable to project those drought conditions to persist and worsen for 150 years.
I’m doing an unreasonable projection of a growing rate of melting for only 153 years.
Willis is doing an unreasonable projection of a constant rate of melting for 12,000 to 19,000 years.
Clearly, my extrapolation is 78.43 to 124.18 times more reasonable than his.
Willis! Dude!
A MOST excellent exposition!
Keep’em coming.
Now, about that beer. You ought try a Lagunitas IPA.
Good for the soul!
Beer speaks. People mumble.
Interesting read. I agree that sometimes we jump to conclusions based on limited data. As you said, we’ve only seen things through the GRACE satellite for 6 years
Brad says:
May 23, 2010 at 5:47 am
They’ve been predicting oil landfall “any day” now for weeks.
Sounds like one of my diets.
Willis and Anthony, do you think we have enough scare reports gleaned from respectable science publications to print our own Guiness Book of AGW Dire Prediction Records?