A guest commentary by Kyle Swanson – University of Wisconsin-Milwaukee
I am quite humbled by the interest that has been generated by our paper “Has the climate recently shifted?” (Swanson and Tsonis, 2009), and would like the thank the RealClimate editors for the opportunity to give my perspective on this piece.
Before delving into the paper itself, a few words about the place of our work in the global warming “debate” are in order. A quote from the early 20th century Viennese polymath Egon Friedell (which I ran across in the wonderful book Cultural Amnesia by Clive James) captures the situation better than any words I could ever weave;
Electricity and magnetism are those forces of nature by which people who know nothing about electricity and magnetism can explain everything.
Substitute the words “modes of natural climate variability” for “electricity and magnetism,” and well…, hopefully the point is made.
It first needs to be emphasized that natural variability and radiatively forced warming are not competing in some no-holds barred scientific smack down as explanations for the behavior of the global mean temperature over the past century. Both certainly played a role in the evolution of the temperature trajectory over the 20th century, and significant issues remain to be resolved about their relative importance. However, the salient point, one that is oftentimes not clear in arguments about variability in the climate system, is that all else being equal, climate variability and climate sensitivity are flip sides of the same coin. (see also the post Natural Variability and Climate Sensitivity)
A climate that is highly sensitive to radiative forcing (i.e., responds very strongly to increasing greenhouse gas forcing) by definition will be unable to quickly dissipate global mean temperature anomalies arising from either purely natural dynamical processes or stochastic radiative forcing, and hence will have significant internal variability. The opposite also holds. It’s painfully easy to paint oneself logically into a corner by arguing that either (i) vigorous natural variability caused 20th century climate change, but the climate is insensitive to radiative forcing by greenhouse gases; or (ii) the climate is very sensitive to greenhouse gases, but we still are able to attribute details of inter-decadal wiggles in the global mean temperature to a specific forcing cause. Of course, both could be wrong if the climate is not behaving as a linear forced (stochastic + GHG) system.
With that in mind, our paper is fundamentally about inter-decadal variability in the climate system and its role in the evolution of the 20th century climate trajectory, as well as in near-future climate change. The climate system has well known modes of variability, such as the El Niño/Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO), that are active on inter-annual time scales. We are interested in how this short time-scale (from the climate perspective!) variability impacts climate anomalies over multi-decadal time periods.
What we find is that when interannual modes of variability in the climate system have what I’ll refer to as an “episode,” shifts in the multi-decadal global mean temperature trend appear to occur. I’ll leave the details of these episodes to interested readers (here and here), as things get pretty technical. It’s sufficient to note that we have an objective criteria for what defines an episode; we aren’t just eyeballing curves. The climate system appears to have had three distinct “episodes” during the 20th century (during the 1910’s, 1940’s, and 1970’s), and all three marked shifts in the trend of the global mean temperature, along with changes in the qualitative character of ENSO variability. We have also found similar types of shifts in a number of model simulations (both forced and unforced) that were run in support of the IPCC AR4 report.
The contentious part of our paper is that the climate system appears to have had another “episode” around the turn of the 21st century, coinciding with the much discussed “halt” in global warming. Whether or not such a halt has really occurred is of course controversial (it appears quite marked in the HadCRUT3 data, less so in GISTEMP); only time will tell if it’s real. Regardless, it’s important to note that we are not talking about global cooling, just a pause in warming.
What’s our perspective on how the climate will behave in the near future? The HadCRUT3 global mean temperature to the right shows the post-1980 warming, along with the “plateau” in global mean temperature post-1998. Also shown is a linear trend using temperatures over the period 1979-1997 (no cherry picking here; pick any trend that doesn’t include the period 1998-2008). We hypothesize that the established pre-1998 trend is the true forced warming signal, and that the climate system effectively overshot this signal in response to the 1997/98 El Niño. This overshoot is in the process of radiatively dissipating, and the climate will return to its earlier defined, greenhouse gas-forced warming signal. If this hypothesis is correct, the era of consistent record-breaking global mean temperatures will not resume until roughly 2020. Of course, this contrasts sharply with other forecasts of the climate system; the purple line roughly indicates the model-based forecast of Smith et al. (2007) , suggesting with a warming of roughly 0.3 deg C over the 2005-2015 period.
Why would anyone in their right mind believe what I’ve just outlined? Everything hinges on the idea that something extraordinary happened to the climate system in response to the 1997/98 super-El Niño event (an idea that has its roots in the wavelet analysis by Park and Mann (2000)). The figure to the left shows the spatial mean temperature over all grid boxes in the HadCRUT3 data set that have continuous monthly coverage over the 1901-2008 period. While this provides a skewed view of the global mean, as it is heavily weighted toward North America, Europe and coastal areas, unlike the global mean temperature it has the cardinal virtue of being a consistent record with respect to time. The sole exclusion in the figure is the line connecting the 1997 and 1998 temperatures.
Now, anomalous behavior is always in the eye of the beholder. However, the jump in temperature between 1997 and 1998 in this record certainly appears to pass the “smell test” (better than 3 standard deviations of interannual variability) for something out of the ordinary. Nor is this behavior dependent on the underlying time interval chosen, as the same basic picture emerges for any starting time up until the 1980’s, provided you look at locations that have continuous coverage over your interval. Again, as the temperature anomaly associated with this jump dissipates, we hypothesize that the climate system will return to its signal as defined by its pre-1998 behavior in roughly 2020 and resume warming.
What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE, contrary to claims that others have made on our behalf. Nature (with hopefully some constructive input from humans) will decide the global warming question based upon climate sensitivity, net radiative forcing, and oceanic storage of heat, not on the type of multi-decadal time scale variability we are discussing here. However, this apparent impulsive behavior explicitly highlights the fact that humanity is poking a complex, nonlinear system with GHG forcing – and that there are no guarantees to how the climate may respond.
References:
Park, J. and M.E. Mann, 2000: Interannual Temperature Events and Shifts in Global Temperature: A Multiple Wavelet Correlation Approach. Earth Interactions, 4-001, 1-36.
Swanson, K.L. and A.A. Tsonis, 2009: Has the climate recently shifted? Geophysical Research Letters, 36, doi:10.1029/2008GL037022.
Gavin
You asked (328) if isotopious’ remark below (308) makes sense to anyone:
:
“Everything changes for a reason, and simply “averaging out” the short periods, then discussing whether or not the trend is statistical or not, is the same as playing Mozart with a Didgeridoo.”
(This was In response to your statement on 308 regarding short-term versus longer-term trends that cannot be compared: “you can’t do it for periods that are too short because of the unforced variability”).
Yes, Gavin, isotopious’ remark does make sense.
First of all, you have to be aware of the limitations of the “Didgeridoo” as a musical instrument (few outside Australia are). If you “average” out Mozart’s “Eine kleine Nachtmusik” sufficiently, you will eventually have a monotonal sound playable on a “Didgeridoo”, but it will no longer be “Eine kleine Nachtmusik”.
The short-term trends are being “averaged out” (or ignored) because they cannot be attributed to the assumed long-term climate forcing according to the theory but rather to “unforced variability” (which is not covered by the theory and has therefore not been assumed). It is sort of like modifying the observed physical data to match the assumed theory.
Isotopious’ point that “everything changes for a reason” is valid, even if this reason is “unforced variability”, which has not been assumed by the theory.
It could well be that unexplained forcing factors and “unforced variability” are actually driving our climate as much as or to an event greater extent than the forcing from the assumed theory, right? I have seen no conclusive empirical evidence to the contrary, so isotopious’ remark stands unless someone can bring this evidence.
Max
Hank Roberts 18 Jul 2009 at #326 “McMurdo Sound”
Doug Bostrom 18 Jul 2009 at #327 “Larsen Ice Shelf”
I assume you both have a scientific background, so I assume you both understand the scientific concept of representative sampling. So I find it somewhat curious that you cite isolated studies of small areas in the western Antarctic as being representative of total global ice mass (or even antarctic ice mass).
I am confident that reliable, trend(able), data will be available for analysis before too long. Then we will all be standing on firmer ground. Try preventing decent into mind-sets until then. All is not known and the future is coming at us at 3600 sec per hour, under foggy visibility.
Thanks for the conversation and interesting cites.
CTG
Back quickly to the LarsenB and Wilkins events.
These were already floating, so the breakup had no impact on sea level, as discussed earlier.
But let’s assume they had been grounded before breaking up (the ice was most likely once grounded ice before it became part of a floating ice shelf).
LarsenB had 3,250 km^2 of ice and Wilkins around 2,000. Assuming they were both 200 meters thick, this would be a total of 1,050 km^3 of ice, which would cause sea level to rise by 2.9 millimeters.
Estimated average annual snowfall in Antarctica is 5 cm (water equivalent), which equals 700 km^3 of water removed from the ocean or the equivalent of lowering sea level by 1.9 millimeters per year.
Some studies postulate that snowfall would increase in a warmer Antarctica, so that this number would increase. But who knows in actual fact?
It is obviously a dynamic situation.
Max
re #301.
manacker
I think we agree that your original assertions in post #266 are incorrect. There was substantial “human CO2” and this almost certainly did make a substantial contribution to warming not just during the period 1910-1944 (as your own calculation indicates) but to the entire period from the start of the 19th century..
Let’s look more closely at your new wriggle on this: You point out that the Hadley Centre Hadcrut analysis gives an extreme range of warming of 0.54 oC between 1910 and 1944. This is a highly cherrypicked time range (nice!) – and you like co2isnotevil’s suggestion that this warming could be due to sunspot numbers.
Let’s have a look.
The period from the early 1880’s to around 1910 in the Hadcrut analysis shows substantial cooling. This is likely the temperature response to the substantial negative forcings from volcanic aerosols arising from a particularly active period of volcanism (Galunggung, 1882, Krakatau, 1883, Colima 1890, Thompson Island 1896, Soufrieret 1902, Santa Maria 1902, Mount Pelee, 1902). This contributed to a reduction in temperature anomaly from around -0.3 around 1880 to around -0.5 around 1910.
So we expect a significant contribution from temperature recovery following wash out of atmospheric aerosols and relief from this negative volcanic forcing in the post 1910 warming. What we really need to explain is the warming of perhaps 0.25 – 0.3 oC left over.
We’ve already agreed that there was likely a substantial contribution from anthropogenic CO2 (your “human CO2”). That’s inescapable, since there’s no question that atmospheric CO2 concentrations increases substantially in the periods during and leading up to yout time range. co2isnotevil suggests a sunspot related effect. That’s an odd one since here was nothing particularly anomalous about the sunspots during this period:
http://en.wikipedia.org/wiki/File:Sunspot_Numbers.png
and recent estimates of solar contributions [*] to early 20th century warming gives us perhaps a contribution of 0.1 oC for your 1910-1944 period.
So the likely contributions to early 20th century warming in the period you specify are something like 0.2- 0.25 oC of recovery from negative volcanic forcing, 0.1-0.2 oC of anthropogenic greenhouse forcing, and around 0.1 oC of solar forcing. One shouldn’t make the mistake of assuming that there is only one contribution to any period of temperature variation!
[*] Lean JL, Rind DH (2008) How natural and anthropogenic influences alter global and regional surface temperatures: 1889 to 2006 Geophys. Res. Lett. 35 art # L18701
http://www.agu.org/pubs/crossref/2008/2008GL034864.shtml
re #349
O.K. Alex! I did wonder what you meant when you referred to Swanson and Tsonis’s theory of an underlying true forced warming signal from GHG emissions that began in 1850 and continues today. I hunted through their paper for evidence of that and assumed that you had read it elsewhere.
That’s why I referred to “your interpretation of Swanson and Tsonis theory…”
Nevertheless, there was likely a significant human contribution to warming from at least 1850 as the atmospheric greenhouse gas levels indicate.
And that, folks is why the Hadley Centre doesn’t include Artic measures.
People like G.Karst will use it to say “you have this minor thing maybe wrong, so therefore your whole thing must be wrong…”
“Can you please explain how exactly the ‘melt pond hypothesis’ breaks down?
Comment by Anne van der Bom”
Think Jim Carey: “It’s devastating to my case!”.
He isn’t wrong, therefore anything that could prove it must itself be wrong.
manacker 19 Jul 2009 at 9:47 am
“It could well be that unexplained forcing factors and “unforced variability” are actually driving our climate as much as or to an event greater extent than the forcing from the assumed theory, right? I have seen no conclusive empirical evidence to the contrary, so isotopious’ remark stands unless someone can bring this evidence.”
Your standards are so elastic.
On the one hand, we have an enormous body of scientific research with demonstrated though imperfect predictive capacity as well as an imperfect yet growing body of empirical data, both of which appear to be lending increasing confidence to the scientific foundations of climate research.
For you this is insufficient to the point of ridicule. And please, don’t say you have not found it ridiculous or we’ll all have to be treated to more manacker quotes, empirical evidence as it were.
As a response, you offer “unexplained forcing factors” as offering so massive a potential impact as to entirely counteract and contradict the sizable and growing body of research, theory and evidence explaining the behavior of our climate.
Your hypothesis is so vague as to appear as superstition, particularly the blind faith you invest in its power.
You then make the remarkable demand that somebody else provide empirical data to contradict your hypothesis, an impossible request as you have provided nothing to test, just vague mumbo-jumbo about “unexplained forcing factors”.
Not only elastic, but lazy. Surely you can do better.
G. Karst 19 Jul 2009 at 10:02 am
As you have not shown otherwise, I take it then that you concede the Larsen ice shelf lost a significant amount of volume during the period 1992-2001? We can add that to the body of “reliable, trend(able)” data?
If you do not make that concession, can you show why not, using data?
The tidal data from the San Francisco gauge shows a markedly similar pattern. The long run slope (year < 1997) is .0083 feet per year (p<0.0001). The slope between 1997 and 2009 is -0.0028 feet per year (p=.678). So clearly sea level rise has stalled as well. Which, according to the gauge data, it has 9 times since 1900. This clearly shows that global warming follows a punctuated equilibrium after periods of great change. Global climate change by jerks if you will.
For those who like the pictures with colored least squares lines can see them at: http://www.neilpelkey.net/UnrealClimate.pdf
For those who must play with the data themselves.
http://www.neilpelkey.net/tides.xlsx
P.S. please do not bother arguing that my statistical models or choice of data are probably suspect. That is, after all, my point.
So about the relaxation trajectory: is it fair to view the climate system’s response to the anthropogenic perturbation as a superposition of a steady-state response and a transient response?
Viewed this way, the Swanson and Tsonis paper is characterizing the transient response. The transient response can delay the arrival of the steady-state response, but the system must eventually achieve its equilibrium state. This is how I’ve been interpreting Karl’s conclusion: What do our results have to do with Global Warming, i.e., the century-scale response to greenhouse gas emissions? VERY LITTLE
BobFJ #337,
did you mean these SOHO MDI images?
http://soi.stanford.edu/production/int_dk_gifs.html
(Yeah, you have to be careful with digital imagery, the Kremlin never sleeps :-) )
Karst is just having fun attracting attention.
He says there’s no data.
I point to how to find it.
I give an example from decades ago, from which he could work forward to find all the subsequent research citing that paper.
He complains that paper is not “representative of total global ice mass.”
Clue: People will make an effort _for_a_while_ to help, on the chance you’re very young, or very new to the subject, or don’t know how to look things up.
After that you’re just setting up strawmen in the road in hopes to get more attention by suckering someone into attacking your dummies.
Why bother.
Re 350 Max
Somehow I just knew the words “conclusive” and “definitive” would appear in your rebuttal. Weasel words that allow you to pretend that this problem does not exist.
I haven’t seen you present any evidence – conclusive, definitive or otherwise – that melting of ice sheets does not influence sea levels. Any yet you quite categorically stated that ice sheet have “no substantial impact”.
I presented several reviews, which in turn referenced several published papers that show quite strong evidence that there is an impact, but you dismiss this out of hand. So where does this authoritative stand come from? Are you God? Or have you read some science that the rest of us have missed?
Or are you just mindlessly regurgitating what the oil industry wants you to believe?
” Surely you can do better.
Comment by Doug Bostrom ”
That would require work, though.
He’s paid by the word, not by the fact, you know…
Climate. 1. The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region.
from
http://www.answers.com/topic/climate
Web definition: the weather in some location averaged over some long period of time
from
http://www.google.com/search?hl=en&client=firefox-a&rls=org.mozilla:en-US:official&hs=nTz&defl=en&q=define:climate&ei=SpdjSsf3MI6asgOdxqBn&sa=X&oi=glossary_definition&ct=title
WMO specifies 30 years or longer.
Cool:
Hank Roberts Reur 339:
Yes, I remain unconvinced that there is any climatic effect that significantly accelerates the mechanical hinging failure of ice shelves and the calving of icebergs. (ongoing for millions of years) As I’ve stated, the influence of melt water penetrating the cracks may be intuitively significant, but on closer inspection it is doubtful, because of the huge “thermal mass” that should rapidly freeze any water entering the cracks
You quoted and linked to a GRL paper entitled “… Sea Swell: An Agent in Iceberg Calving and
Break-Up?
Yes, I agree, there are mechanical effects that result in fracturing of the ice and two prime ones are tidal, and wave action. Your reference does NOT discuss the issues on which I’m unconvinced by any of the arguments raised here.
Please refer to the following image of the Ross ice shelf, and you may notice that it terminates abruptly from mechanical shearing
http://www.eoearth.org/upload/thumb/1/10/Ross_edge_large.gif/250px-Ross_edge_large.gif
It is interesting to compare with the white Cliffs of Dover….. Got it?
http://upload.wikimedia.org/wikipedia/commons/thumb/7/7e/White_cliffs_of_dover_09_2004.jpg/350px-
You may also find the three papers linked to in Max’s 309 interesting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Max, Reur 309:(/b>
Thanks for the links…. Interesting stuff!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Doug Bostrom 334, Anne van der Bom 348:
Maybe the above helps?
Anne; I remain unaware of anything empirically quantifying the hypothesis of hydrostatic cracking, and believe that it is all intuitive chat. Neither have I seen anything to confirm my belief that liquid water cannot exist within the huge “Thermal mass” of ice shelves, that are anywhere between around 100 and 1,000 metres* thick. However, as an engineer, it remains to me, a very strong intuitive argument.
* about 330 to 3,300 feet thick
Martin Vermeer Reur 346, Do you remember my 337, where I was rather puzzled by what you had written earlier, and I responded as follows:
Now that has me more than puzzled. For example, are you suggesting that the SOHO MDI image of the sun of quality 151 KB, (or you can click for a 657 KB enhancement), is inferior to the 9.65 KB “depiction” in Wiki’, and that it does not show a difference?
Your latest post is also unhelpful, and you continue to evade answering a simple question.
Richard Steckis says: There is no such requirement for a 30 year time scale for temperature statistics. What you are referring to is an arbitrary time scale chosen by the WMO for a climate signal to emerge from noise.
For a nice description of why you need 30 years of data to infer a climate trend, see
Results on deciding trends.
With the apparent ongoing forcing of about 0.15C/decade is it not likely that the ‘pause’ in observed surface temperature rise is occasioned by an increase in the effectiveness of available thermal sinks?
We have increased wind velocity in the southern ocean, which will be exposing deeper and colder waters to the air, and hence increasing the depth of that sink at the expense of warming deeper waters.
We have increased fracturing and breakup of floating ice – with the smaller cakes presenting a higher surface area per mass of ice. This gives faster melt, and so faster uptake of heat from surface atmosphere.
We have increased fracturing of ice cap and ice sheet/shelf surfaces which increases the surface area exposed to the atmosphere.
We have increased intrusion of near-surface water into grounded ice masses including under West Antarctic, which also drops the local temperature as the ice melts.
All these sinks have finite capacity before they get to equilibrium. It is not unexpected that the water-ice mixture remains close to freezing until the last bit of ice is melted, nor will it be a surprise when warming recommences with a hiss and a roar when these sinks approach equilibrium with surface air temperatures.
Any ‘pause’ in the observed pattern of temperature rise is just a case of the monster gathering itself before it springs from its lair again, with renewed vigour!
Jim Galasyn (361) — Yes, it is most reasonale to view the response to a pertubation as consisting of a superposition of a steady-state response and a transient response. So your concluding paragraph is indeed correct.
BobFJ says: 19 Jul 2009 at 6:06 pm
“I remain unconvinced that there is any climatic effect that significantly accelerates the mechanical hinging failure of ice shelves and the calving of icebergs.”
That’s quite a leap. Let’s just leave aside concentration of hydrostatic forces acting on a crack apex (a crack and its apex is an engineer’s nightmare) for a moment and instead think of an ice sheet in beam terms. We can make a beam of ice and test it, or we can predict what might happen to already existing beams. No controversy there, right?
As the cross section of a beam is reduced, with all other factors remaining equal its resistance to bending decreases, yes?
The material properties of ice can be used to predict the competence of a beam made of ice, yes?
Ice is not made of magical materials so a beam made of ice of 1X thickness will be less resistant to bending and ultimate failure than a beam of 2X thickness, yes?
In the case of ice shelves where thickness has been reduced, we can thus expect an earlier onset of failure in response to a given deflecting force, yes?
By “climatic effect” we include warmer temperatures, including sea temperatures, yes?
In general we’d expect an ice shelf fed at a constant rate and afloat in warmer water to retain less mass at any given point compared to if it were fed at the same rate and afloat in cooler water, yes?
In losing mass we’d expect that ice shelf to become less thick, meaning less beam cross section, yes?
We’ve already established that ice is not magic and that a beam of ice becomes less competent against bending loads as it loses cross section, yes?
When a beam is deflected to levels causing excessive strain it may yield either plastically or by brittle failure, yes?
We see by existing examples that ice shelves apparently are in fact not very plastic and tend to yield in brittle failure, a process called “calving”, yes?
I find it genuinely astounding that you can find your way to a conclusion that the mechanical strength of ice shelves is immune to climate effects.
Cracks of any depth just make the outcome worse. I don’t know the material properties of ice well enough to say with complete confidence that it is incapable of complete structural healing via refreezing, but all the same that is so unusual a property that it would be surprising if true.
Meanwhile, your remarks on refreezing are hand-waving. You’re trying to contradict without doing any work. Saying “but on closer inspection it is doubtful, because of the huge “thermal mass” that should rapidly freeze any water entering the cracks” is not doing the work needed to support your hypothesis.
Martin Vermeer 362:
Please look again at my 191 to which I referred you.
The link therein is: http://sohowww.nascom.nasa.gov/data/realtime/mdi_igr/512/
Why do you yet again evade the very simple question in my 337, by making more obtuse statements such as asking if I meant some other link, when all you had to do is click on the link that I gave to see that it IS SOHO MDI?
Here is my question 337 again:
“For example, are you suggesting that the SOHO MDI image of the sun of quality 151 KB, (or you can click for a 657 KB enhancement), is inferior to the 9.65 KB “depiction” in Wiki’, and that it does not show a difference?
Please answer the question.
Bob, you ‘remain unconvinced’ because nobody’s trying to convince you.
Your understanding is about where the field was ten years ago, before all the recent research came in. That raised a great many questions that the researchers are describing and working on in a veritable flood of publications.
And the International Polar Year research is only now beginning to work its way through the journal process, so there’s far more to come.
All anyone’s trying to convince you to do is read the literature and remain interested in a field that’s fascinating to those who, well, like this kind of thing. Even people like me who cheer from the sidelines.
So if your point is that you’re not convinced, you could start a blog and explain to the world what it is you’re not convinced about, and maybe interest people in trying to convince you. But you won’t get satisfaction here doing it.
http://scholar.google.com/scholar?q=ice+shelf+fracture
Why not be interested instead? Join the uncertain folks who’re reading what the scientists are doing. It’s better than most other forms of entertainment.
Brian Dodge, Reur 342:
Thank you for your carefully considered and very detailed comments.
They deserve a carefully considered response from me.
However, I can only address quickies at the moment, but I’d like you to know that I’m not ignoring it, and I‘ll get back to you later.
For one thing, I’m distracted by “The Ashes” cricket series at Lords, (England versus Australia) game 2, with day 5 dawning.
#370 Jim Galasyn,
Thanks Jim. That is the closest anyone has come to scientifically justifying the 30 year period. I will look at it more closely. However, I do not know if it can be reconciled with short term perturbations that can have long term consequences.
As I described above (#156), I identified three putative breakpoints in the HadCRUt3 data from 1950 through to present. Each one may compound on the one before to produce the overall warming of that 59 year period. Therefore just looking at the long term dataset without determining shorter time scale influences can give an incorrect picture about overall climate change and its causes.
@ Hank Roberts 19 Jul 2009 at 2:56 pm “Why bother?” Well, I’m retired, widowed, childless, have a relatively high speed internet connection, and haven’t got a lot of other stuff to draw my interest. Eventually the deniers will give up and go away(I’m not under any illusion that I will change their minds) and I will have learned a little more about climatology, and have had the opportunity to make fun of the willfully ignorant with an occasional snarky comment.
@ manacker
“It could well be that unexplained forcing factors and “unforced variability” are actually driving our climate as much as or to an event greater extent than the forcing from the assumed theory, right? I have seen no conclusive empirical evidence to the contrary….”
So, you conclude that the absence of evidence that “unexplained” (invisible, magical?) factors aren’t there is evidence that they “could well be”? Absent conclusive empirical evidence, it could well be that pigs can fly and Hades has frozen over. Or, to put in in more familiar terms, absence of evidence is not evidence of absence.
@ G. Karst
“So I find it somewhat curious that you cite isolated studies of small areas in the western Antarctic as being representative of total global ice mass (or even antarctic ice mass).”
The small areas of Larsen A&B plus Wilkins that collapsed, because of their 200+ meter thickness, more than offset the growth in thin seasonal sea ice. You can’t just compare 7000+ km^2 of lost shelves with growth of 400,000 km^2 of sea ice.
Larsen A – 2000km^2
larsen B – 3250km^2
Wilkins – 2000km^2
total area 7250km^2=7.25e^9m^2 Thickness 200+ meters
Larsen + Wilkins lost volume 7.25e9*2e2=14.5e11m^3
Pine Island sector lost volume 114km^3=1.14e11m^3 [1] (per year,2005) or 3.42e11m^3 through 2008
Antarctic peninsula east coast 34km^3= 0.34e11m^3 [2] (per year,2005) 0r 1.02e11m^3 through 2008
grand total (14.5+3.42+1.02)e11m^3=1.89e12m^3 lost
sea ice gained (400,000 km^2 at 2 meter thickness, gained over 30 years; G. Karst, 17 Jul at 9:18 am)
4e5*1e6*2=8e11m^3/30 years or 2.67e10m^3 per year
18,9e11/8e11=2.36 times as much lost (not counting the 30 year sea ice gain to the various other time frames ratio. I’m doing the math in my head – if anyone wants to get picky, I’ll happily fire up a spreadsheet. The simplifications I’ve made are in favor of the hypothesis that sea ice gain of 400,000 km^2 gives “Remarkably stable total ice (volume) results.”, and it still loses)
from http://rsta.royalsocietypublishing.org/content/364/1844/1637.full This paper has about 70 references, many with links, some freely downloadable; the areas currently under scientific study are neither small nor isolated.
“The Pine Island Bay sector of West Antarctica exhibits the largest negative mass balance of all Antarctica.”
“The glaciers draining West Antarctica into Ronne Ice Shelf are close to a state of mass balance.”
“The glaciers draining into Ross Ice Shelf exhibit a positive mass budget ”
“The positive ice balance of Siple Coast is more than three times smaller than the negative ice balance of Pine Island Bay, so that overall West Antarctica is losing mass (Rignot & Thomas 2002).”
[1.]”In total, the mass loss from the Pine Island sector increased from 81±17km3/yr ice in 1996 to 114±18km3/yr ice in 2005.”
“In East Antarctica, most glaciers are closer to a state of mass balance than assumed in the past, but there are exceptions. ”
“Totten Glacier and Moscow University Ice Shelf are thinning rapidly, along with most glaciers in Wilkes Land, such as Mertz, Ninnis and Frost.”
“Several glaciers (e.g. Lambert, David, Shirase) await more precise grounding line thicknesses and mean accumulation values to improve confidence in the mass budget results.”
“Overall, with the available data and uncertainties in mean accumulation and thickness, it is difficult to determine even the sign of mass balance of East Antarctica.”
“The Antarctic Peninsula has experienced regional warming six times the global average over the last century (Vaughan et al. 2001). ”
“After the collapse of Larsen A in 1995….. Drygalski Glacier was flowing three times faster in 2000 than prior to the collapse (Rott et al. 2002). In 2005, I find that Drygalski Glacier flows another 25% higher compared to 2000 …”
“In 2002, Larsen B ice shelf collapsed in three weeks following more than 10,000 years of stability (Domack et al. 2005). Following the collapse, Hektoria/Green/Evans, Crane and Jorum accelerated eight and two times, respectively (Rignot et al. 2004b; Scambos et al. 2004). In 2005, I find that Crane accelerated by a factor of 2 compared to 2000 (figure 4b–d), and is now calving inland of its 1996 grounding line. Hektoria/Green/Evans slowed down 500m/yr, but are still 700% out of balance.”
“On the west coast of Graham Land, Fleming and other glaciers have been flowing steadily since 1992. … but recent data showed that the region is 80% out of balance and Fleming Glacier flows 50% faster than in 1974, 50km inland of the grounding line (Rignot et al. 2004b).”
[2.]”The glaciers draining the east coast from Drygalski to Leppard lost 27±9km^3/yr ice in 2002 (Rignot et al. 2004b) and 34±10km^3/yr ice in 2005.”
“In Palmer Land, snow accumulation has increased by 10–20%… The interior gain in mass may therefore compensate the loss of mass at the coast. ”
“Wilkins Ice Shelf is slowly[not anymore!-BD] disappearing. On the east coast, the mass balance of Larsen D and E glaciers is unknown. We know very little about ice flow changes in this part of the Antarctic Peninsula.” [No doubt this area is being studied intensively since the collapse of Wilkins. Given what happened with the glaciers feeding Larsen A & B, anyone care to make any bets on whether the glaciers here show positive or negative mass balance?-BD]
@ Doug Bostrom 18 Jul 2009 at 4:05 am
““Changes in floating sea ice (even including “dramatic” events, such as the collapse of Larsen B and Wilkins) have no substantial impact on sea levels.” being a strawman argument – it doesn’t really matter whether it’s intended as a strawman, it is demonstrably wrong; although the immediate effects of floating ice melt don’t affect sea level, the sequelae (glacial acceleration) already being observed are contributing to sea level rise. The adages “hoist on one’s own petard” and “shooting oneself in the foot” leap to mind.
In addition to the negative mass balances in the Antarctic, there are the observations of tropical glaciers. a good place to start is
http://www.nichols.edu/departments/glacier/global%20glacier%20mass%20balance.htm
There are about 15 links here to other studies.
For a picture worth a thousand words, see
http://www.nichols.edu/departments/glacier/cum%20bn.jpg
There is also the accelerating ice mass loss from Greenland to consider
from http://www.unep.org/geo/geo_ice/PDF/GEO_C6_A_LowRes.pdf
“Total loss from the ice sheet more than doubled, from a few tens of billions of tonnes per year in the early 1990s, to about 100 billion tonnes per year after 2000,
with perhaps a further doubling by 2005.” Future science will reveal what effect the decrease in summer albedo, caused by record Arctic ice melt, and the subsequent increase in Arctic ocean heat content, has on the weather, climate and the Greenland ice sheet.
In the meantime, the numbers “representative of total global ice mass” are indubitably declining. Air temperatures may be experiencing an episodic shift to a pause in global warming, but ice loss is not. (TaDaaa! back on topic &;>)
Mr. BobFJ writes:
“…the influence of melt water penetrating the cracks may be intuitively significant, but on closer inspection it is doubtful, because of the huge “thermal
mass” that should rapidly freeze any water entering the cracks…”
http://web.pdx.edu/~chulbe/science/Larsen/larsen2002.html
points out a study by Weertman from the 1960’s discussing this topic.
http://earthobservatory.nasa.gov/Features/WilkinsIceSheet/
discussed meltwater ponds on Wilkins.
Mr. BobFJ might, if he tried, find similar studies in Greenland. Perhaps he will.
BobFJ #369
Do you want me to rub it in? I linked you to SOHO MDI pictures of the Sun with their limb darkening intact. The one you showed, had it digitally removed, and you erroneously claimed that the Wikipedia picture is somehow inferior and “exaggerated”.
I have news for you mate. Limb darkening is real and strong and you are mistaken. All it takes is a sunny day, one tube of a pair of binoculars and a sheet of white paper.
You were wrong on an elementary radiation physics thing, while pontificating on radiation physics. That was my argument, and you’re the one doing the evading. Until I see you fairly admit it and save what is left of your credibility, nothing else is worth debating.
Richard Steckis writes:
But that wasn’t what I was arguing at all. I was saying that you artificially inflate the number of points by chopping up the data too finely. Temperature has a cha-rac-ter-is-tic time scale of 30 years. Using monthly data gives you 12 times as many points, but the increased number of points doesn’t mean anything. Thus my analogy of 1-minute intervals for morning temperatures.
A decade is too short to mean anything where global temperatures are concerned.
It has a serious point which apparently went over your head.
manacker writes:
Try here:
http://BartonPaulLevenson.com/Correlation.html
http://BartonPaulLevenson.com/Sun.html
Chris
You wrote (354): “Let’s look more closely at your new wriggle on this: You point out that the Hadley Centre Hadcrut analysis gives an extreme range of warming of 0.54 oC between 1910 and 1944. This is a highly cherrypicked time range (nice!) – and you like co2isnotevil’s suggestion that this warming could be due to sunspot numbers.”
Not “cherry-picked” by me, Chris.
This period has been cited, most notably by IPCC AR4 and in the study of Delworth and Knutson:
http://www.sciencemag.org/cgi/content/full/287/5461/2246?ck=nck
“Over the period 1910-1944 (which encompasses the warming of the 1920s and 1930s), there is a linear trend of 0.53 K per 35 years in observed global mean temperature.”
“If the simulated variability and model response to radiative forcing are realistic, our results demonstrate that the combination of GHG forcing, sulfate aerosols, and internal variability could have produced the early 20th century warming, although to do so would take an unusually large realization of internal variability. A more likely scenario for interpretation of the observed warming of the early 20th century might be a smaller (and therefore more likely) realization of internal variability coupled with additional external radiative forcings. Additional experiments with solar and volcanic forcing, as well as with improved estimates of the direct and indirect effects of sulfate aerosols, will help to further constrain the causes of the early 20th century warming. Our results demonstrate the fundamental need to perform ensembles of climate simulations in order to better delineate the uncertainties of climate change simulations associated with internal variability of the coupled ocean-atmosphere system.”
The study points toward co2isnotevil’s suggestion that this warming could be partially due to additional external radiative forcing from the high level of solar activity.
To this topic you wrote: “recent estimates of solar contributions to early 20th century warming gives us perhaps a contribution of 0.1 oC for your 1910-1944 period”
Actually, I believe there have been a few studies that have put the solar contribution somewhat higher, albeit over a longer time period. The average of about 8 studies I have seen have put the contribution from the unusually high level of 20th century solar activity at around 0.35°C over the entire 20th century (about half of the total observed warming). These studies point to a higher relative solar impact prior to around 1970 than afterward, but if your estimate has around one-third of the total value for around one-third of the time period that might make sense.
Your other possible explanations are plausible, as well. Suffice it to say that Delworth had a bit of a harder time attributing the warming over this period than you did. In any case anthropogenic CO2 caused only a relatively small part of the total warming over the early 20th century warming period (around one-third), so we are basically in agreement.
Max
CTG
In your 364 you stated:
“I haven’t seen you present any evidence – conclusive, definitive or otherwise – that melting of ice sheets does not influence sea levels. Any yet you quite categorically stated that ice sheet have ‘no substantial impact’.”
There is no question that a significant shrinking of grounded ice either in the AIS, the GIS or non-polar mountain glaciers would result in an increase in sea level.
So far, the latter has been the more important factor (of the three).
Both the AIS and GIS were studied over a longer-term period 1992-2003, using millions of continuous satellite altimetry readings over the entire period. In both cases a slight increase in the size of the ice sheets was found.
GIS increased from April 1992 to October 2002 (truncating one entire winter season) by 11 Gt/year mass gain, equivalent to an insignificant lowering of the sea level by 0.3 mm over the period.
http://www.sciencemag.org/cgi/content/full/310/5750/1013
“Averaged over the study area, the increase is 5.4 ± 0.2 cm/year, or ~60 cm over 11 years, or ~54 cm when corrected for isostatic uplift. Winter elevation changes are shown to be linked to the North Atlantic Oscillation.”
http://www.ingentaconnect.com/content/igsoc/jog/2005/00000051/00000175/art00001
“The Greenland ice sheet is thinning at the margins (−42 ± 2 Gt a−1 below the equilibrium-line altitude (ELA)) and growing inland (+53 ± 2 Gt a−1 above the ELA) with a small overall mass gain (+11 ± 3 Gt a−1).”
AIS increased from April 1992 to April 2003 by 27 Gt/year mass gain, equivalent to an insignificant lowering of the sea level by 0.7 mm over the period.
http://rsta.royalsocietypublishing.org/content/364/1844/1627.full
“Our best estimate of the overall mass trend — growth of 27±29 Gt/yr−1— is based on an assessment of the expected snowfall variability. Mass gains from accumulating snow, particularly on the Antarctic Peninsula and within East Antarctica, exceed the ice dynamic mass loss from West Antarctica.”
More recent shorter-term studies have shown a reversal of the growth in the GIS and a possible reversal of growth of the AIS, but in any case the contributions to sea level are relatively minor.
http://www.sciencemag.org/cgi/content/abstract/315/5818/1529
“Our best estimate of their combined imbalance is about 125 gigatons per year of ice, enough to raise sea level by 0.35 millimeters per year. This is only a modest contribution to the present rate of sea-level rise of 3.0 millimeters per year. However, much of the loss from Antarctica and Greenland is the result of the flow of ice to the ocean from ice streams and glaciers, which has accelerated over the past decade. In both continents, there are suspected triggers for the accelerated ice discharge—surface and ocean warming, respectively—and, over the course of the 21st century, these processes could rapidly counteract the snowfall gains predicted by present coupled climate models.”
So the amount of sea level change attributable to mass reductions of the GIS/AIS are relatively minor to date, as I indicated earlier. Whether or not either becomes a significant factor in the future depends very much (as the studies have indicated) on whether or not the predicted accelerated ice discharge will counteract the predicted snowfall gains over the course of the 21st century. And the jury is still out on that question.
Max
re: 307
“[Response: If melt water pools on the surface and finds a crack in the ice, there is a strong pressure at the bottom of the crack since the water is denser than the ice. Thus there is a strong pressure gradient that (as long as the water doesn’t freeze) will work to further deepen the fracture.”
Why must the water be denser than the ice for there to be a strong pressure at the bottom of the crack? And what is a strong pressure gradient?
The pressure gradient in a column of liquid water is, to an excellent approximation, constant.
Isn’t it likely that when the water freezes that the volumetric expansion causes additional lateral strains.
[Response: In a melt pond the level of the water is at the same height as the ice. Since the water is denser than ice (by about 10%), there is more water mass above the bottom of the crack than there is immediately to the side in the ice. Freezing might also play a role, but I’m not sure that would be relevant in some of the catastrophic melt-lake failures that people have observed in Greenland (I hear that multi-sq km lakes can sometimes drain in an hour or so). – gavin]
I have a question regarding paleoclimatology. Since land use studies have shown that the increased evaporation from irrigated land causes regional warming would this not also apply to the land irrigated by melting glaciers. As the glaciers disappear this land would return to a more normal state and the evaporation would decrease causing regional cooling. This would be a considerable factor when there is a lot of ice melting on land and much less so once the land ice has disappeared.
BobFJ
19 Jul 2009 at 6:06 pm
How do you know
this is ‘intuitive chat’. You must have read it. What does it say?
The cracks take time to develop. As soon as a small crack appears, melt water water seeps into that crack, partly enlarging it and at the same time creating a deflection at the surface that attracts more melt water further away from the crack. As such a mechanism develops that can harvest solar energy at the surface over a large area and deliver it very localized inside the crack.
Secondly, the cracks to not have to go all the way down to the bottom for the ice sheet to break up. Just deep enough to weaken it so mechanical stress can finish the job.
Then there is also the seeping in of brine to consider, which will not freeze as easily.
Sorry for my layman’s explanation, but that is the way I think it works.
Steve, I don’t know about your question, but soil chemistry does change immediately after a glacier recedes: When glaciers disappear, the bugs move in: