by Rasmus Benestad, Eric Steig and Gavin Schmidt
In a recent paper in Science, Eric Rignot and Pannir Kanagaratnam present new satellite observations of the speed of glaciers of Greenland, and find that they are sliding towards the sea almost twice as fast as previously thought. Additionally, between 1996 and 2005, they detected a widespread glacier acceleration and consequently an increased rate of ice discharge from the Greenland ice sheet. However, previous papers have recently noted an increase in snow accumulation in the interior (i.e. Johannessen et al., 2005), so how do these different measurements fit into the larger picture of Greenland’s net mass balance?
The measurements by Rignot and Kanagartnam were made with interferometers which measure the movement of the surface horizontally, and so is complimentary to the altimeter data published previously (which measures the absolute height of the ice). Overall, they found widespread increases in glacier speeds, and increases of about 30% in ice discharge rates. (Note that the satellite image shows that the glaciers in the east tend to slide far into the sea whereas on the western coast that happens less).
The higher velocity of the ice is thought to be related to higher temperatures causing increased melt-water which can penetrate to the base of the glacier and hence reduce the ground friction. However, this accelerated movement is not necessarily tied to an increased rate of melting of the Greenland ice, although it can be related. Surges of ice streams from the ice sheet can also occur due to increased accumulation at the head of the glacier. However, when the increased ice velocity is matched to a decreasing thickness that can be sign of net mass loss. These ideas are consistent with observations of surface melting which had a record extent in 2005, and has been increasing steadily (though with significant interannual variability) since 1993. Using the analysis of Hanna et al (2005) (based on the reanalysis datasets) for the surface mass balance, Rignot & Kanagartnam estimate that Greenland is on balance losing mass, and over the period of their study the ice sheet mass deficit (the amount of ice lost to the sea) has doubled increasing from 90 to 220 km3/year (an increase of 0.23 to 0.57 mm/yr sea level equivalent – SLE).
In the earlier Science paper, Johanessen et al. found increased snow accumulation on the top of the interior Greenland ice sheet between 1992 and 2003. Above 1500m a.s.l in much of the interior Greenland they estimated an increase of 6.4 ± 0.2 cm/year and below 1500m they observed a decreasing trend of -2.0 ± 0.9 cm/year. Hence, growth in the interior parts and a thinning of the ice nearer the edges. However, Johanessen et al. were not able to measure all of the coastal ranges. Indeed, the thinning of the margins and growth in the interior Greenland is an expected response to increased temperatures and more precipitation in a warmer climate. These results present no contradiction to the accelerated sliding near the coasts, but both will affect the ice/snow (fresh water) mass estimate. Whereas the finding of Rignot and Kanagaratnam suggests a larger sink of the frozen Greenland fresh water budget (the ice is dumped into the sea), the snow deposition in Greenland interiors is a source term (increases the amount of frozen fresh water). It does not matter for the general sea level in which form the water exists (liguid or solid/frozen) when it is discharged into the sea: The same mass of liquid water and immersed ice affect the water level equally (Archimede’s principle).
A third relevant study is a recent paper in the Journal of Glaciology by Zwally et al. (2005) on the ice mass changes on Greenland and Antarctica. They use the same satellite obsevations (ERS 1 and 2) as Johanessen et al. and again find that the Greenland ice sheet is thinning at the margins (-42 ± 2 Gt/year = -46 ± 2 km3/year below the equilibrium-line altitude – ELA), but growing in the inland (+53 ± 2 Gt/year = 58 ± 2 km3/year). The mass estimates have been converted to volume estimates here, assuming the density of ice is 0.917 g/cm3 at 0°C, so that the mass of one Gt of ice is roughly equivalent to 1.1km3 ice*. This means that the Greenland ice has an overall mass gain by +11 ± 3 Gt/year (=10 ± 2.7 km3/year) which they estimated implied a -0.03 mm/year SLE over the period 1992-2002.
The critical point for Greenland is whether the increased rate of glacier motion more than compensates for the greater accumulation on the surface. While the broad picture of what is happening is consistent between these papers, the bottom-line value for Greenland’s mass balance is different in all three cases. Looking just at the dynamical changes observed by Rignot & Kanagaratnam, there is an increased discharge of about 0.28 mm/year SLE from 1996 to 2005, well outside the range of error bars. This is substantially more than the opposing changes in accumulation estimated by Johannessen et al and Zwally et al, and is unlikely to have been included in their assessments. Thus, the probability is that Greenland has been losing ice in the last decade. We should be careful to point out though that this is only for one decade, and doesn’t prove anything about the longer term. As many of the studies make clear, there is a significant degree of interannual variability (related to the North Atlantic Oscillation, or the response to the cooling associated with Mt. Pinatubo) such that discerning longer term trends is hard.
The largest contributions to sea level rise so far are estimated to have come from thermal expansion, with the melting of mountain glaciers and icecaps being of second order. Looking forward, the current (small) imbalance (whether positive or negative) of the Greenland ice sheet is not terribly important. What matters is if the melting were to increase significantly. Ongoing observations (most promisingly from the GRACE gravity measurements, Velicogna et al, 2005) will be useful in monitoring trends, but in order to have reasonable projections into the future, we would like to be able to rely on ice sheet models. Unfortunately, the physics of basal lubrication and the importance of ice dynamics highlighted in the Rignot & Kanagaratnam results are very poorly understood and not fully accounted for in current ice sheet models. Until those models include these effects, there is a danger that we may be under-appreciating the dynamic nature of the ice sheets.
References:
Hanna, E; Huybrechts, P; Janssens, I; Cappelen, J; Steffen, K; Stephens, A (2005) J. Geophys. Res.Vo. 110, D13108, doi:10.1029/2004JD005641
Johanessen, O.M; Khvorostovsky, K; Miles, M.W; Bobylev, L.P. (2005) ScienceVo. 310 no. 5750, pp 1013-1016
Ringnot, E; Kanagaratnam, P (2006) ScienceVo. 311 no. 5763, pp 986-990
Velicogna, I; Wahr, J; Hanna, E; Huybrechts, P. (2005) Geophys. Res. Lett.Vo. 32, L05501, doi:10.1029/2004GL021948
Zwally, H. Jay; Giovinetto, Mario B.; Li, Jun; Cornejo, Helen G.; Beckley, Matthew A.; Brenner, Anita C.; Saba, Jack L.; Yi, Donghui (2005), Journal of Glaciology, Volume 51, Number 175, December, pp. 509-527(19)
*Update: Correction for arithmetic error in orginal post in converting Gt to km3, see comments.
Re #99 —
Gerald, I am sure I could have phrased it better. Comment #91 points out that all the warming is AGW but also there is the gap between the predicted cooling during the Holocene and no cooling or warming at all. That gap is what I meant by more than 100%.
So I did get right into it. The marbles illustrate the point that we expect the future to be like the past. It is not. The globe should be cooling slightly. It is not. The highly confirmed cause is the increase in greenhouse gases. And we know what/who put those there, don’t we?
I don’t know how to reply to your last (and new) point: “we may have increased the temperatures in the last several decades — but what caused it?” Are you aware of the effects of greenhouse gases? If not, that is what caused it. If so, I do not understand your question.
Anyway, I hope I have clarified that I did do the calculation. It was so easy that climate scientists, who have other things to occupy themselves, couldn’t be bothered. In this comment I hope I have sufficiently explained why I said “more than 100%”.
Regarding the comment for 98 on the Friedlingstein et al and Cox et al studies regard positive feed back of land process:
How positive is the feedback between climate change and the carbon cycle? , a 2003 article.
If I read this correctly, the authors conclude about 180 ppm due to land feedback when the total co2 reaches 980. So a 600 ppm rise (from today) yields a 180 ppm feedback, starting from the current position, or 30%.
Hi David (#s 91 & 101). I understood where you were going with that. But I have a different question. Why were you 99% sure after the first 7 boxes?
This relates to a problem I have been having using the binomial expectation to calculate standard deviations for low proportions. It’s a frequentist thing to do, whereas a Bayesian approach is probably better (but I don’t know how to do it). In any case, to adjust for the limited sample size, and using your prior of 50%, I would have estimated the frequency of black marbles to be 7.5/8 = 94% (I added one marble with a 50% chance of it being black). That’s the proportion I would have used in the binomial formula for the purposes of determining my ‘certainty’.
So I guess I’m asking for an explanation of 99% and for some help in my own problem.
Re #103 —
For my argument in #91, 94% would work almost as well. I’m not sure that a Bayesian would approve of the fast method I used. I’ll work out the correct details tonight and post it tomorrow afternoon, PST.
Gerald, in case David’s clarification still wasn’t quite clear:
(numbers are hypothetical)
We have warmed 1oC recently, absent anthropogenic influences we should have cooled .2oC, therefore the percentage of the warming would be anthropogenic is 1.2/1 or 120%.
So it is not as ridiculous as you indicate.
Re #91,#101,#103,#104,#105.
You speak of calculation. You can throw any figures out(which you did) and calculate. But you have not scientifically measured. You make reference to thousands of years ago. Temperatures went up and down at that time. How would they have gone up without AGW – according to your theory? Was there AGW then? Likely close to zero. So I have a hard time accepting the more than 100 percent or anywhere near that amount. With those figures you are suggesting that without AGW we would be rapidly approaching an ice age.
My point still remains – If we went up One Degree – the percentage of that increase due to AGW has not been measured. It is being attributed(linked)by association to CO2 because the amount of CO2 has been measured as increasing
Estimates of the net change in land carbon since the glacial maximum seem to be converging betwen a
doubling and a
30 percent rise
But, from http://www.earthscape.org/r1/rel01/ ,”The Migrating Boreal Forest”, I notice that much of the Canadian boreal forests occured after the holocene epoch, and in previous glacial cycles, never would have appeared.
So, this is quite confusing to me, In previous glacial epochs the rapid melt would have exposed barren tundra soils in the Northern hemisphere causing a peak in co2 rise. In our epoch, the melt was gradual enough to allow migration of large forests north.
During the younger-dryas collapse, co2 levels were 40 ppm lower than previous cycles, and thanks to our experiment with co2 spiking, I conclude, some 12,000 years ago, a missing 60 gigatons of atmospheric carbon. The suspect is carbon sequestering in land biomass.
Gerald,
AGW theory does not say that all warming at all times must be anthropogenic. It only states that the current warming trend is dominated by human emissions of GHG’s. Other flucuations are the results of different combinations of different forcings. If they are unknown due to lack of adequate data, that does not mean they did not exist.
As for how much forcing comes from which factors, you might enjoy this link:
http://www.giss.nasa.gov/data/simodel/
BTW, my throw away figures were intended as a proof of concept only, because you had indicated you thought it a ridiculous notion on its face that we could cause more than 100% of a warming trend. I think they served their purpose.
The key issue about Greenland is the air which surrounds it, air is warmer so will be the surface of the ice sheet. Never mind about that + 1 C increase, it is at this time in many regions experience temperatures way above that number. I like to sympathise with those who believe that AGW is not happening, perhaps they have not felt regular +4 to +6 C monthly mean temperature anomalies, nor +30 C above daily average temperature warming, or 40 C SAT variations within a few days, all around Greenland, but I can’t. What does these temperature variations do to ice? We know what they do to mountain rock.
#68 – “Stick ourselves at glacial maximum in a chaotic system” and other posts about chaos.
Not a bad idea and also seems to be the only post with a constructive suggestion on how to use chaos as a decision making tool. Unfortunately we cannot stick ourselves anywhere until we have the power to manipulate climate. We won’t have that power for a long time (if ever) but we do have the power to change climate in an uncontrolled manner and we are forced by our infrastructure and lifestyle to use it.
Let’s for a minute disreagard predictions that have already been realised and pretend we don’t know anything about climate. To be able to manipulate climate we need a model of how it works, the chaos advocates tell us this is impossible in a climate system because chaotic influences will invalidate any prediction. So we are lead to belive models are not worth developing without chaos, and if they are developed with chaos then they are useless random predictions. In other words there is no point in mitigation or even analysing any of the data since conclusion are no better than “random predictions”.
The point of the models at a civilisation level is not to find the date of armmagedon or even Katrina-II, it is to put a number against a percived risk as best as is practicable (as any insurance company would do). Even if we accept that there are chaotic elements to climate change would it not be prudent to control our activities to reduce the unintended use of our power to change the current climate? And doesn’t chaos theory just increase the logic behind controlling those activities to reduce the percived risks?
The basic argument from the chaos advocates is that the climate is unpredictable so why bother changing our activities? If they look at the logical risk implications of chaos they may find an answer to their own question. Chaos theory implies the one thing we don’t want to change is climate, our climate changing activities can be changed and are negotiable via treaties and regulations but Peak Oil may make it a mute point in the next few decades.
Maybe I’m just too close to 50 but it seems to me the industrial revolution, like many well intended revolutions, is about to fail spectacularly. I just hope there are enough people left to start the next one.
Re # 108 – There is a related factor to CO2 – Increased condensation nucleii (which is not a GHG) which would cause increased cloud cover and consequently higher temperatures. I do not know if anyone is looking at it.
[Response: ??? Start here. This is one of the hottest current topics in climate – gavin]
Re Response in #111 – many studies cite aerosols as creating a cooling effect. However the point I was making was that some contributors spoke about the increase in cloud cover. My comment was addressing the reasons for the increase and a possible increase in temperature.
[Response: This is the ‘indirect affect’, and that is generally thought of as a cooling as well. However, there are a number of different processes involved which make the net impact rather uncertain (but it is almost certainly negative). – gavin]
Man is an intelligent squirrel, and tends to sequester carbon on land. We use oil because we have a land scarcity and need an efficient energy source to take ocean carbon and leave it on land. The atmosphere has been a transport system for us, moving ocean carbon to land, where we sequester the stuff.
So, we adapt to the scarcity of fossil fuel by engineering photosynthesis and gaining a 10 fold increase in solar efficiency. We engineer microbes to make cellulose a viable fuel source. Now, the atmosphere is a transport mechanism between underground carbon and land carbon. Photoshynthetic scientists are moving us through a major techological advance, as they alwas have done.
There is something innate in mammals, they collect carbon. In 300 years we will be facing an atmospheric carbon shortage. Maybe man’s destiny is to ultimately collect every bit of carbon from the oceans and from underground, bury it under a kilometer of ice while we huddle around our fusion fire at some oasis in on the equator.
Rasmus,
It’s as much your language as your climatolgy skills I’m drawing on here.
Wikipedia has been linked to many times here on RC presumably as a scource of reliable information. After viewing the Danish version under “Menneskeskabt drivhuseffekt” ( anthropogenic greenhouse effect)
I have the gravest misgivings!
http://da.wikipedia.org/wiki/Menneskeskabte_drivhuseffekt
Three quarters of the blurb highlights the reasons why sceptics believe the whole thing is invention or exaggeration, while there “is great uncertainty as to how large the anthropogenic effect is.”
There is a link to Svensmarks graph in all its glory:
http://www.dsri.dk/~hsv/html_Carls_solartikel.htm
Sigh! Do any of your colleagues at DMI feel a moral obligation to contribute?:
http://www.dmi.dk/dmi/index/
Can Wikipedia get hijacked by minority views?
Inductive logic the Bayesian way. This is the first of a two part post. This part contains useful references and an important idea due to I.J. Good which appears rather neglected.
E.T. Jaynes
“Probability theory: the logic of science”
Cambridge Univeristy PRess, 2004
is recommended in a review as the book on Bayesian reasoning which is the ‘most fun to read’.
J. Hawthorne, “Inductive Logic”, Stanford Encyclopedia of Philosophy, 2005.
[[http://plato.stanford.edu/entries/logic-inductive]]
quickly, but thoroughly, shows most aspects of how to use Bayesian reasoning in science. Jim also e-mailed to me a site where there is a free Bayesian network program one might care to use/try:
[[http://www.hugin.com/Products_Services/Products/Demo]]
In Bayesian reasoning, the important concept is the ‘odds on’ aka ‘likelihood ratio’ between competing hypotheses, given the data. With hypotheses H and K with data D,
L = p(H | D)/p(K | D)
is the measure of how much better or worse H is in comparison to K. But it is much better to take the base 10 logarithm with units of bans and even better to take units of a tenth of a ban, called a deciban and abbreviated db. (The name ‘ban’ is due to A. Turing, 1941.) Now I.J. Good suggests that “A deciban or a half-deciban is about the smallest change in weight of evidence that is directly perceptible to human intuition.” So if
10 log L < 0.5
there is no perceptible advantage of hypothesis H in comparison to hypothesis K.
[Response: Use ‘& l t ;’ for the less than sign. Otherwise it thinks it is html. – gavin]
Applying some Bayesian reasoning —
To keep the application simple, we are ignoring any background information and treating the situation as simply a sequence of
Bernoulli trials: opening boxes one after the other to discover whether the marble inside is black or white. We are certain that there is exactly one marble in each box and it is either black or white. As Bernoulli trials, there is a number, r, which is the probability of discovering a black marble. We then have the infinitude of hypotheses H(r) for r in [0,1]. Finally, as p=1 is special, write B=H(1). We will compare all the hypotheses H(r) to B.
The data, D, consists of opening the first 7 boxes, the wooden boxes, to discover a black marble in each one. Now clearly the probability of the data D given B is 1, p(D | B) = 1. It will be the odds on,
L(r) = p(D | B)/p(D | H(r))
that determines how much better the hypothesis of all black marbles is in comparison to the hypothesis of random fraction r are black. (This is the correct ratio, I said it backwards in #115.)
For example, consider H(0.5). In this case we have r^7 = (0.5)^7 = 0.0078125 = p(D | H(0.5)). Now computing the logarithm of 1/0.0078125 and multiplying by 10,
10 log L(0.5) is about 20 db.
This means that hypothesis B is vastly superior to the hypothesis H(0.5).
We now turn to those hypotheses H(r) which are indistinguishable from B under I.J. Good’s claim that a half-decibel is resolvable to the human intuition. It turns out that 98%, i.e., H(0.98), gives about 0.607 db but 99% gives about 0.294 db. So H(0.99) is neither better nor worse, under this criterion, than B. But H(0.98) is worse than B.
Summarizing this part, after opening the first seven boxes, those made of wood, we have only a small range of hypotheses left to consider, B and those very nearby. What happens when we open the jade box?
Under the hypothesis that all boxes have the same statistics, we are quite unlucky in finding a while marble. We had thought there was only about a 1% chance of this occuring. Another hypothesis is that the composition of the box makes a difference. In this case we specialize our previous hypotheses to apply only to wooden boxes, starting over for jade ones.
I claim that this is exactly what scientists will do in such a situation. Of course the actual background knowledge will make a difference here. Furthermore, I claim that the hypothesis that wooden boxes and jade boxes have different values for the proportion r of black boxes is highly confirmed by the weight of the evidence, in much the same way as has already been done just for the wooden boxes.
> 114: “Wikipedia has been linked to many times here on RC
> presumably as a scource of reliable information ….”
Was that meant to say “source” or “scourge”? (grin) Both happen.
Wikipedia often does get hijacked; over time, given attention, it should be self-correcting, and there’s a procedure for evaluating writers, something like current editors can vote to stop taking changes from particular IP numbers proven to be malicious or misinformative, I think — it’s been much in the news lately as US Congressional staffers were abusing the process.
RE: #113. I would not rule out that scenario. In fact, I tend to think it likely.
I sort of got into the bayesian debate, and it reminded me of a task I once performed for some government agency.
The correct procedure to determine if the temperature curve is related to greenhouse gases is:
Take your temperature measurements over, say 1000 years, and perform a spectral analysis to compute its linear model. Go out to some number of spectra, get the number of terms to make everyone feel happy. Then you have a linear model of temperature, and the variance of the residual white noise is the gaussian covariance of the frequency terms. (There is a reference for this somewhere).
Now, compute the expected temperature curve from your gas law, normalize for average temperature (go back 1,000 years, zero is valid). Compute its spectra.
Then you can ask the gaussian question, what is the probability that the spectra of your computed gas law could have have been sampled from the linear temperature model driven by white noise.
Any other alternative hypothesis should wash out.
Someone did this, I think, for I saw it announced with great fanfare.
Thanks DB (#115, 116); I’ll have to read that again. I should probably just take some time and try to learn Bayesian methods. My only critique of what you produced is that you should probably have r^7 x 2(because it could just as easily have been all white marbles — or maybe you should have used r^6 because once the first marble’s colour is known, you are just seeing if the rest are the same colour). Hmm, now I’m having trouble with basic probability. In any case, the calculations also don’t consider temporal autocorrelation. I think we’re assuming that each box is independent….
Sorry to all who find this irrelevant. Perhaps this will make it up to some of you:
http://www.marksgeneticsoftware.net/rxc.htm
This is a simple little freeware tool to do contingency analyses. It will give results equivalent to Fisher’s exact test, but you can have several rows and columns. I used it to get a p-value for the hypothesis that marble colour is not contingent on box type. I got a p-value of 0.125 (i.e., fail to reject).
Re #120 —
I am sure I did the calculations correctly. There are seven wooden boxes. Assuming Bernoulli trials does indeed mean an assumption of independence of the trials. This means that the probability of seeing seven black marbles is precisely r^7, since the trials are assumed to be independent.
I am now going to do one more comparison of two hypotheses.
The first hypothesis is that all wooden boxes contain black marbles and jade boxes contain white marbles. Call this hyptotheis Y. The second hypothesis, N, is that all boxes are the same, Bernoulli trials, with r=7/8 for the probability of seeing a black marble. The data D consists of 7 black and 1 white marbles. The probability of seeing this data, given Y is p(D | Y) = 1. The probability p(D | N) = (7/8)^7*(1/8) = 0.0491
Thus
10 log(p(D | Y)/p(D | N)) is about 31 db.
This is a large value of decibans, confirming that the weight of the evidence strongly favors hypothesis Y over N as explaining the data D.
Translating this back to AGW, recall that boxes correspond to the last 8 times that methane concentrations were over 550 bbp as recorded in the Vostok icore core record. Black marbles refer to subsequent decrease in methane concentrations tracking orbital forcing. White marbles refer to increase in methane concentrations despite the lower global forcing. Wooden boxes are the first 7 in the record. The jade box is the Holocene. The hypothesis Y corresponds to increased methane due to human activity, essentially Ruddiman’s thesis. The hypothesis N corresponds to a probabilitistic statement that methane concentrations only track orbital forcing 0.875 of the cases. We see that Y is much the better explaination, this being AGW as opposed to ‘just happened’.
There are, of course, an infinitude of hypotheses which could be
compared against Y. But Ockham’s Razor encourages one not to unnecessarily add concepts. Hypothesis Y is a simple and as explainatory as can be — and I was surprised to see how much
more so when I computed the 31 decibans.
Re: #111, “There is a related factor to CO2 – Increased condensation nucleii (which is not a GHG) which would cause increased cloud cover and consequently higher temperatures. I do not know if anyone is looking at it.”
CO2 emissions alone do not create more condensation nucleii. Other industrial and transportation-related pollution may, but water vapour cannot condense on CO2 molecules.
What CO2 emissions do is heat up the atmosphere, which in turn heats up the oceans (at a lag and far less rapidly), which leads to greater evaporation. This causes the increase in cloud formation, which is the condensation of which you mention. This increase in cloud formation will increase the overall albedo of the planet, but also, will trap longwave radiation inside the troposphere.
This is theorised by the IPCC in their prediction that overnight minimum temperatures will be much warmer than previous and that minimum temperatures will rise at a greater rate than daytime maximum temperatures. The reason: increased cloud cover at night. This is also the reason for the much warmer-than-normal (and possibly record-setting) December and January temperatures for areas of North Dakota and Minnesota and over much of the Canadian Prairies.
Re #122 – What I meant by related was that combustion produces nucleii in addition to CO2. That would lead to the increased minimum temperatures with more cloud forming on the nucleii.
Re: #123, “What I meant by related was that combustion produces nucleii in addition to CO2. That would lead to the increased minimum temperatures with more cloud forming on the nucleii.”
Possibly, but what an increase in CO2 emissions will do is increase the quantity of water vapour in the atmosphere, increasing the humidity, which will make cloud formation more likely.
Temperatures will go up, but so will dew point temperatures. This also leads me to think that severe thunderstorms and tornadoes will likely occur, as higher Ts and Tds lend more convective energy into a system.
Re # 124 – In the first part – that is generally what I said. Re severe weather – Dr Madhav Khandekar of Environment Canada did a study on it and could not find conclusive evidence that severe weather would increase(in Canada). You may have more thnderstorms but to get severe ones you need dry and moist areas to form plus upper support. These synoptic conditions vary from year to year and would not necessarily increase in frequency.
re 27.
Impact Of Climate Warming On Polar Ice Sheets Confirmed
http://www.terradaily.com/reports/Impact_Of_Climate_Warming_On_Polar_Ice_Sheets_Confirmed.html
Re #126 – That is outdated. It covers to 2002 and does not take into account the Zwally study of 2005 quoted at the top of this post.
re 127 126
The survey was published this week in the Journal of Glaciology.
http://www.igsoc.org/news/pressreleases/200603a.html
This link has nice photos by NASA/SVS.
http://www.nasa.gov/vision/earth/environment/ice_sheets.html
Re #127: Actually Zwally 2005 just covered data through 2002 and it’s the recent R+K paper in Science that discusses the rapid glacier flow of the last few years. There’s no conflict between the studies as they were measuring different things. See the original post, which places all of these studies in context, and Jay Zwally’s comment 5. (What is confusing is why Zwally 2005 is just being published now. Maybe that journal makes papers available electronically for a while before paper publication.)
For an average person who tries to follow this subject, I don’t know what to make of the data. A couple of weeks ago, there was another alarmist article about the Antarctic losing 36 cubic miles of ice per year. Yet the Antarctic is composed of over several million cubic miles of ice, is it not? In that context, how significant is the loss of 36 cubic miles of ice?
The melting in Greenland likewise appears to be very minor compared to the total overall mass of ice. Yet articles state that Greenland’s ice could possibly melt in several hundred years. Is this good science reporting when the current data supports no such conclusion? And why are scientists themselves fostering such misconceptions?
Paul, how much calculus do you have? The rate of change is changing, and the question is — how fast is the change in the rate of change.
That’s — for those like me who stopped just past algebra — not easy, and I agree the science journalists aren’t doing a very good job. Your posting makes clear that what your read didn’t convey the info.
Let me try the simple summary and then let the scientists correct me (“the way to get good information on the Internet is to post what you know and await correction”).
Snow falls and slowly gets packed down making ice. Ice builds up until it begins to flow slowly (pressure from above and warmth from the earth below). That makes a glacier, if the terrain lets it move.
Glaciers flow, slowly at the edges, faster at the middle.
Glaciers that flow out over cold water build up layers of ice (ice shelves).
Ice shelves ‘push back’ and keep some limit on how fast the glacier flows out from the land.
The ice shelves are floating on ocean water.
Ocean water is getting warmer.
The top of the ice caps is getting warmer, and water lakes form on top of the glaciers, water flows down through crevasses to the earth below, and makes a lubricating layer.
Ice shelves break up and float away (happening in Antarctica, quite unexpectedly, in the last few years).
Glaciers start to speed up. Until last November, only a few were speeding up. Now several more are speeding up, and so we have a pattern rather than a few exceptions. The pattern is that the speed of glaciers is changing.
We don’t know how fast the change is changing — will the glaciers be moving faster next year? Will more of them be moving faster? But this was a surprise.
Once a glacier gets moving — and it’s moving into warmer ocean water so it doesn’t make ice shelves, in fact it melts faster so there’s less ice to push back.
The concern is that we didn’t think the ice caps and glacial ice was going to change its motion, especially not so early in the warming period we know is happening, and the ice — both in Greenland and Antarctica, both ends of the planet — has started moving faster in many places, not just a few.
Okay, one of the glaciologists, please correct me (grin). (And please note your credentials, there are a lot of opinions but few informed ones)
Whoa, Paul. In the space of eight sentences, you’ve gone from “an average person who tries to follow” to an accusation of scientists fostering misconceptions without supporting data. And you did that by reading journalism on a brand new finding. That is fostering misconception without supporting data.
As for the finding in the Antarctic, it is still early and yes the numbers are not that large (but you should think of it in terms of sea level equivalent, not relative to the millons of km^3 total ice). It is new however. Greenland is much more significant and it is not just the amount of mass loss it is the acceleration. So your linear extrapolation to “why worry” is not very sound. Ice sheets are complicated and not well modeled but historical sea level rises suggest once things start to move, they can move quickly.
Realistically, if this is a long term warming (and not a simple cycle in periodicity) Greenland’s ice will mostly likely take a few thousand years to completely melt away. Were that to happen, long before that point was reached, sea level would rise noticeably. But how long is long? Probably about 1000 years, realistically. Worst case scenarios are rarely realized in fact.
[Response: Curious. You appear to be quite suspicious of very well established physics of the greenhouse effect (for instance, as implemented in GCMs), and yet completely confident about the much more poorly understood mechanisms and rates of ice sheet melting. Hmmm…. -gavin]
Thank you for your comments.
Comment #131
Hank, I can appreciate that the rate of change is changing, but that still does not address the issue. In the case of the Antarctic, we have recently been informed that 36 cubic miles of ice has melted. Out of how many million cubic miles of ice? To a layperson (me), that appears completely insignificant.
Comment #132
Coby, some scientists have been fostering misconceptions. The rate of increase in the ice melt in Greenland is a concern, yes, but there is no good data for some scientists to contend that Greenland’s ice could be gone in a few hundred years.
re 134.
The atmosphere is becoming more humid, increasing condensation. The significance of latent heat for snowmelt has been described by Dunne and Leopold (1978):
â??If water from moist air condenses on a snowpack, 590 calories of heat are released by each gram of condensate. This is enough energy to melt approximately 7.5 gm of ice, which when added to the condensate yields a total of 8.5 gm of potential runoffâ??.
Dunne, T., Leopold, L.B. (1978) Water in Environmental Planning.
http://www.mnforsustain.org/climate_snowmelt_dewpoints_minnesota_neuman.htm
Added heat from condensation applies to ice fields, glaciers, sea ice and seasonal snow depths in mid-high latitudes. Snow melts quicker with higher dewpoints, increasing runoff and flooding in the Upper Midwest and other areas.
RE #135 – Your study applied to a limited area(Minnesota).You state “Added heat from condensation applies to ice fields, glaciers, sea ice and seasonal snow deplths in mid-hogh latitudes” If you are now looking at the global picture you have to account for the latent energy used in melting and evaporation of the ice (670 cal/gram) to get that heat of condensation. If you mean that moisture is increasing globally, it had to use up the latent heat to get there.
Paul, ’til someone who actually studies the area answers, my pointers just as a regular reader.
The ice that’s melting is melting from underneath — what disappears is the bottom of floating ice shelves, because the ocean water is warmer. Eventually the ice shelf becomes unstable and breaks apart.
http://wdcgc.spri.cam.ac.uk/news/larseniceshelf/
Possibly there is a level of CO2 that toggles the polar ice — either growing — or melting:
http://www.nature.com/nature/journal/v421/n6920/abs/nature01290.html
Much of the Antarctic ice is displacing ocean water, because the solid land surface is well below current sea level.
Compare the topography — see how little solid land is above sea level (compare this to any contemporary picture of Antarctica showing the extent of the ice cap:
http://www.nature.com/nature/journal/v421/n6920/images/nature01290-f1.0.jpg
Oh, and (forgive me RC hosts for drifting further from the Greenland thread — I realize this is going way off topic)
From the bottom of the first link I posted, this:
http://nsidc.org/data/iceshelves_images/
gives a picture of the current ice extent, with links to detail on all the ice shelves in the Antarctic.
Re: #136, “If you are now looking at the global picture you have to account for the latent energy used in melting and evaporation of the ice (670 cal/gram) to get that heat of condensation. If you mean that moisture is increasing globally, it had to use up the latent heat to get there.”
Yes. This is true. However, with the latent heat energy exhausted by the evaporation of water and melting of ice, the global atmospheric temperature continues to rise at an increasing rate. This means an accelerating rate of evaporation and melting is likely as temperature and latent heat continue to rise. There is an imbalance there, and these environments are equilibrium-seekers, so one rate will accelerate to meet the other.
re 136.
On February 23, 2006, Luna Leopold died at the age of 90. Luna was a vital force, a man of extraordinary creativity and originality, whose passion about science and the natural world permeated all he did.
http://eps.berkeley.edu/people/lunaleopold/
The different blogs tend to converge so I thought I would blog here : I hope you dont mind.
1. The first reference is to a report on carbon levels over the poles which is worrying to say the least.
http://www.guardian.co.uk/climatechange/story/0,,1729256,00.html
2. There was a reference by Mr Benson to Scottish research on “adaptation” for farmers. Does he have any references for this please? I was talking to my daughter last night who farms with her family in South West France and is also one of the few remaining white farmers in Zimbabwe and we were discussing the impact of climate change on farming, world trade in agricultural products and the security of food supplies. I didnt know of any work done on “adaptation” and wonder if others may be able to add to Mr Benson’s comments.
3. Just to cheer everyone up the following reference is to a letter in The Guardian
http://www.guardian.co.uk/climatechange/story/0,,1728721,00.html
You will note that it is signed by 8 MPs. What were the other 600 odd doing then?
Great website. Keep going and don’t weaken.
Hosts — the forum software here isn’t recognizing the double comma in those Guardian URLs Eachran posted above. Meanwhile, for working links see:
http://www.guardian.co.uk/climatechange/
The Mount Zeppelin station is the northernmost settlement and measures a lot of gases; they are reporting increasing rates of change for CO2 and methane.
It seems Hank is the only one still focussing on the actual post. As a glaciologist who has worked on Jakobshavns Glacier and Pine Island Glacier, it is evident why one has an ice shelf and the other does not. Ice shelves exist only in areas where ablation is small and an accumulation zone extends to the edge of the glacier system. Ice shelves do not survive once surface melting and an ablation zone develops. The Larsen Ice Shelf was thinning already, as noted in the links of comment 137, however, I agree with the first comment after the paper on the link page, and that is thinning did not lead to the loss of the ice shelf alone. The more important component was the first noted development of substantial melting on the surface of the ice shelf. Ice shelves do not endure simply by ice flowing from feeder glaciers and spreading out over a portion of the ocean, they need an accumulating snowpack to survive the summer season on their surface.
Re #130, #134 — Paul asks if it is responsible for a scientist to state that the Greenland ice gap “could possibly” melt in a few centuries. This question deserves an answer. I will try, although I am no expert in any aspect of climatology.
I’m going to treat this as a matter of sea stand. I will treat the melting of the Greenland ice gap as the equivalent of an increase in sea stand of 5 meters. (Experts please correct if this is badly wrong!) So the question might be posed as asking if it is responsible of a scientist to state that the sea stand could possibly rise 5 meters in a few hundred years.
One way to determine this is to look at periods in the past records when sea stands have risen by 5 meters or more within a few centuries. Looking at Figure 6.1 on page 98 of F. Oldfield’s “Enviromental change: key issues and alternative approaches” we discover a record of sea stand versus time from 26,000 to 10,000 years ago. From 14,500 to 14,000 years ago occured an event marked MPW-1A. During this interval the sea stand rose about 25 meters. From this same graph, after the end of the Younger Dryas 11,500 years ago, the sea stand rose at least 10 meters in about 500 years.
Given this has happened in the past, is a statement of “could possibly” a responsible statement? Note this is not a statement with a probability attached. The statement simply says that such an event, rise of sea stand of 5 meters in a few hundred years is not impossible. Given the historical facts listed above, what would you say?
144. I think that you are correct.
The problem is being the party pooper whether politician or scientist. You can imagine the excuse :
Well I know that I have been plugging growth as the panancea….but….anyone can make a mistake….cant they?
or
There is a 95% chance of everything being OK. OK?…OK maybe?
I dont like the odds or the timescale either and as a non-expert I am impressed by people like Mr Hansen (and the people who run this blog) who alert us all to the possibility of catastrophic collapse – of ice sheets but also of civilisation.
What to do? Well I cant say that I am impressed by 8 MPs in the UK asking us all to be a bit more attentive to climate change but I am impressed by scientists who try doggedly to get to the “truth”.
I am curious to know if the the added carbon in the atmosphere at the North Pole implies a faster melting of the Greenland sheet. Just so I know how long I have to build my Ark in the back garden.
Having read the IPCC WG2 and 3 I am curious also to know the up-date : I suspect it will make ugly reading.
The carbon in the recent story is carbon dioxide and methane; the high levels are local (not yet averaged out by mixing worldwide) around that far north sampling site because it’s wintertime (not much photosynthesis using it up as it’s released). Where it’s coming from and how fast in that local area is the issue (is there more coming out of peat bogs for example).
The report — I haven’t found anything besides press stories — is from the same lab that gave us the report of increased gas from peat and permafrost five years or so ago, if I recall correctly.
They’re sampling at the far north extreme of human settlement — as far from local human sources as possible.
Re #145 – **I am curious to know if the the added carbon in the atmosphere at the North Pole implies a faster melting of the Greenland sheet. Just so I know how long I have to build my Ark in the back garden.**
If you read the introduction at the top of this post, you will see studies that discuss accelerating of the glacier, increased melting at the leading edges, and increased accumulation in the middle of Greenland. They are having a problem calculating which is faster – melting the glacier at the leading edges or actually causing it to accumulate faster in the middle. Do not worry about the ark – it will take too long to melt. But I would be more concerned about pollutants in the air if they do not clean up industry.
Re #146: There was an “exclusive” story a few months ago in the Independent (UK) that claimed the Mauna Loa (Kea? – I can’t keep this straight) CO2 readings for 2005 (not yet officially released, which is interesting) had jumped considerably. If I recall right the article speculated that the cause might have been a big increase in peat burning in Indonesia. Maybe, and maybe there’s a local explantion for what’s going on in the Arctic, but OTOH the combination of the two reports causes one to wonder.
Re #147: While it’s true that the dynamic melting is unlikely to proceed quickly enough to have a big effect on coastal regions of the First World during the next 20 to 30 years, Gerald’s response seems to assume that we can discount to zero impacts on future generations. I find that morally objectionable.
On the science, IMHO Gerald misinterprets the post. While the exact current balance of ice loss vs. snow accumulation is interesting, the concern with Greenland is that as things continue to warm the rapid growth of the ice loss will quickly overwhelm the snow accumulation such that the rate of ice loss will increase vastly. Exactly how quickly the collapse could really occur has yet to be established, but the signs (the recent speed-up of glaciers in southern Greenland and the apparent progress of this speed-up into the north, plus the equally rapid growth in the surface melt zone) are very bad.
The much greater size of the Antarctic makes it less vilnerable to these effects in the short term, but the fact that the Greenland-sized West Antarctic ice sheet is largely grounded below sea level and has a clearer route to the sea than Greenland potentially makes it prone to collapse in a similar time frame.
I have yet to hear a scientist working on these issues say, e.g., we can categorically exclude the possibility that Greenland amd/or the WAIS might substantially collapse within a century or so. That makes me very nervous indeed since while we night hope to adapt reasonably to such melting on a scale of centuries, I doubt that would be true if it happened more quickly. A glance at topographic coastal maps to see the effect of a 10-15 meter sea level rise makes that point very clear.
Re #143: I wanted to take the opportunity to thank Mauri and the other scientists, climate amd non-climate, who participate in the comments on this site. It takes part of the load off the RC authors, which I know they appreciate since this is a volunteer effort, and adds further valuable perspective.