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Warming, interrupted: Much ado about natural variability

Filed under: — raypierre @ 12 July 2009

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.


388 Responses to “Warming, interrupted: Much ado about natural variability”

  1. 301
    manacker says:

    Chris (284)

    The period 1910-1944 showed warming of 0.54°C, as observed by Hadley.

    While atmospheric CO2 figures for this period are based on estimates rather than hard empirical data, the CO2 increase over this period only “supports” a theoretical GH warming (at equilibrium) of 0.2°C (or 0.18°C as co2isnotevil has shown us in 286). Yet we saw an observed linear warming of 0.54°C over this period, or around three times that which could be explained at equilibrium by GH warming from CO2..

    This is what we are comparing here, Chris, not the net overall warming actually measured from 1850 to 1944 nor the theoretical GH warming we might have expected from 1750 to 1944.

    The solar explanation by co2isnotevil (286) may actually make more sense than trying to tie this all to human CO2 emissions.

    Max

  2. 302
    CTG says:

    Re 285
    “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.”

    Not true. Whilst the collapse of an ice sheet in itself does not alter the sea level, what it can do is to speed up the flow of the glacier that was feeding it, leading to more ice going into the sea, which will raise the sea level at some point.

    All this was quite extensively discussed on this site just a couple of months ago, so you obviously have not been paying attention, Max.

  3. 303
    Mark says:

    “As an engineer, I find it hard to see any climate change effect that would significantly accelerate this normal process.”

    Because as an engineer you will work with higher tensile strength materials.

    As a denier of AGW you will then transfer this knowledge in egineering into climate science and not see any problems.

    Ice will extend into the ocean. Where there is water. Water that isn’t frozen. Now this ice will try to MAKE that water frozen, but this takes energy and the ice will get warmer.

    As it gets warmer, its strength reduces somewhat and localised melting will occur.

    Now tell me an engineering scenario when you have to build something that will be in contact with a molten version of itself quite extensively and for a long time?

  4. 304
    Doug Bostrom says:

    manacker 17 Jul 2009 at 5:21 pm

    “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.

    These are primarily of interest as they may affect surface albedo, and in that respect thickness has no impact, but it is total sea ice extent (or area) in both the Arctic and Antarctic that counts.”

    Strawman.

    You’re inserting the old, tired “if an ice cube melts, it does not affect the level of the water in the glass” canard, hoping it’ll distract attention from other important characteristics of the ice.

    I’m sure you noticed that Bryan’s post mentioned nothing about sea level, but you’re apparently hoping others don’t pick up on that.

    As to the primary interest of the data Bryan cited, what it’s telling us is a message about the qualities of the ice. You’re apparently asserting something along the lines of “Hey, I’ve given you a glass of Thunderbird, why are you complaining that you ordered a vintage varietal?” Sure, the ice is white, the wine is red, but is that the point? No.

  5. 305

    For some reason I can’t get past the spam filter trying to respond to RS’s #260. RS, you are artificially ballooning the number of points and significance by using monthly data when the proper time scale for temperature is about 30 years. It’s like me taking the temperature here at one-minute intervals from 6 AM to 9 AM. That gives me 181 points, which I then use to show a significant upward trend in temperature, proving that the oceans will boil in two days.

  6. 306
    Steve E says:

    Speaking of emerging trends and the need for oceanic monitoring, is anyone trying to organize international forces to design a joint global ocean monitoring network, or are we still peppering the issue with a hail of little BB’s?

  7. 307
    BobFJ says:

    Raypierre, many thanks your response appended to my 290

    Response: Actually, temperature increase has been shown to have a very pronounced effect on the breakup of ice shelves. It is indeed mechanical fracture that does the job, but what warming does is to form massive melt ponds at the surface, which then cause hydraulic fracture. –raypierre]

    I’d like to learn more from you, as may too, other readers here.
    Are you able to point us to some references for quantification of “hydraulic fracture“.
    The reason I ask is that as a mechanical engineer, (as would I think some “rock engineers” = geologists), I find what you say to need some additional explanation and illustration.

    [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. Ian Joughlin has got some good slides on the subject (perhaps they are online somewhere?). - gavin]

  8. 308
    Jörg Schulze says:

    You make the point, that the recent cooling has no significance, as it is just a little bit of natural variability, but you give us a laughable short perspective from 1950 to today. If you would look at the climate variability starting at about 10000 years before today, You would see, that the whole so called” global warming” is well inside the natural variability. It was warmer than today during the roman optimum and the medieval optimum. If you would look into a time-scale of billions of years, You might well see, that a climate, that does not change, would be a very surprising oddity.

    [Response: You are mistaken if you think it is merely the fact that climate changes is the issue - it is not. The issue is why climate is changing and whether we can attribute changes to physical causes. You can't do it for periods that are too short because of the unforced variability, but you can for the long-term trends either recently (predominantly due to increasing GHGs), or over the Holocene (orbital forcing), or the whole Cenozoic (tectonically driven changes in circulation, weathering, outgassing etc.). - gavin]

  9. 309
    manacker says:

    Bob_FJ (290)

    There seems to be differences of opinion as to whether global climate changes have much to do with glacial calving. Here are just three references:

    “Little is known about the forces and mechanisms that lead to rift initiation and propagation – partly because we have very few measurements against which hypotheses can be tested.”
    http://geosci.uchicago.edu/research/glaciology_files/iceberg_calving_research.shtml

    “According to a study by scientists at the British Antarctic Survey (BAS) and University College London (UCL) using ESA’s ERS satellite data, a loss of 31-cubic km of ice from the WAIS’s interior from 1992 to 2001 was pinpointed to the Pine Island Glacier.

    The thinning caused the glacier to retreat by over 5 km inland, supporting the argument that small changes at the coast of the Antarctic continent – such as the effects of global warning – may be transmitted rapidly inland leading to an acceleration of sea level rise.

    Although these long-term regional changes are a cause for concern, the present iceberg calving event does not in itself signal a significant change in the WAIS. Over the last 15 years, the glacier front has advanced seawards at a rate of 3 km/year, so the calving of a 20 km-wide iceberg has simply shifted the glacier front back close to where it was after the last calving event in 2001.”
    http://www.sciencedaily.com/releases/2007/10/071019102619.htm

    “Nonclimatic behaviour of calving glaciers has been documented in a large number of locations, both in historical time and during the Late Glacial and Holocene. Interactions between calving dynamics, sedimentation and topographic geometry can partially decouple calving glaciers and marine ice sheets from climate, initiating independent advance/retreat cycles; it is therefore rarely possible to make reliable inferences about climate from their oscillations.”
    http://ppg.sagepub.com/cgi/content/abstract/16/3/253

    Max

  10. 310
    Martin Vermeer says:

    BobFJ #292: don’t sweat it… I won’t try to teach you anything against your will ;-)

  11. 311
    Hank Roberts says:

    Typo in that name; hat tip to Google’s suggesting the right spelling; here is some of the research Gavin refers to, for engineering study:

    http://scholar.google.com/scholar?hl=en&q=%22Ian+Joughin%22+ice+crack

    Images (including some at RC you could search — box at the top of the page):
    http://images.google.com/images?hl=en&q=%22Ian%20Joughin%22%20ice%20crack&sa=N&tab=si

  12. 312
    manacker says:

    CTG

    You wrote: “Whilst the collapse of an ice sheet in itself does not alter the sea level, what it can do is to speed up the flow of the glacier that was feeding it, leading to more ice going into the sea, which will raise the sea level at some point.”

    You are correct (all things being equal). But glacial calving is part of a natural dynamic process. If there is more snow, there will be an increase in glacial mass, resulting from more water leaving the sea, which will lower the sea level at some point. But more glacial mass may again lead to an acceleration of the glacial flow, etc.

    From what I have been able to read, there is no definitive link between global warming and glacial calving in the Antarctic. Maybe you have some links to other data.

    Max

  13. 313
    Hank Roberts says:

    From the Wilkins collapse topic earlier, which you can find with the search, I remember posting some tidbits and pointers on the various forces known to affect sea ice, including tides and waves from very distant storms:
    http://www.realclimate.org/index.php/archives/2009/04/wilkins-ice-shelf-collapse/#comment-118731

  14. 314

    #308 Jörg Schulze

    I know you have already been answered but I thought I might add for simplicity.

    Making an argument outside of relevant context is, er, um, irrelevant.

    Gavin has properly simplified the argument. It’s not that climate was warmer during the Permian or Eocene optimum, it’s about why it is warmer or cooler.

    To bring in even more relevance, it’s about human infrastructure and needs that have been designed and built around a climate regime that is now changing due to human influence.

    To get a handle on this look at the UCAR/NCAR work:

    http://www.ossfoundation.us/projects/environment/global-warming/natural-variability

    Natural variability on a difference path is a realistic way to characterize the difference.

  15. 315
    Hank Roberts says:

    PS, Max’s third quote isn’t about today’s conditions.

    It can be hard for youngsters now to believe, but until a few years ago, scientists thought Antarctica wasn’t going to start changing quickly.

    This “make a claim, provide some link” trick betrays trust. It’s done often knowing many people don’t actually check the claimed sources. Max can’t be trusted.

    The third link is from 1992.

  16. 316
    Hank Roberts says:

    Oh, kids, double untrustworthy; check the -first- link Max posted against the bit he quoted from it. Read down past the “little is known” (note the date, 2002) to where they say they’re starting research.

    “we’ve been working with an international team of scientists to deploy global positioning system receivers (GPS) and seismometers around the tip of a propagating rift on the Amery Ice Shelf, East Antarctica. The field work has been done in conjunction with a program monitoring rift propagation using satellite imagery.”

    Use those terms to search in Scholar — you can find the results of the research — much more is now known!

    Isn’t science wonderful, if you look it up for yourself?
    Even people trying to fool you can lead you partway toward good information.

    Max can’t be trusted to provide good information.
    Always check.

  17. 317
    David B. Benson says:

    Fixing a mistake in my comment #289, the constant c in the system response
    k[t - c + transient]
    for a = 1, b = 1/30 and weights both 1/2 is c = 15.5. That’s quite a long delay once the transient has (almost) disappeared.

    Another route to estimate a, b and the weights is to consider Figure 1(a) in the Knutti et al. comment on a paper by Schwartz:
    http://www.iac.ethz.ch/people/knuttir/papers/knutti08jgr.pdf
    to closely reproduce the response to the step function beginning in year 300 of the simulation. (The text suggests three decaying exponentials is more realistic.) Other papers (which I can’t find just now) point out that the initial doubling of CO2 begins to diminish due to ocean uptake, so the forcing is not just the unit stip U(t) but rather U(t)exp(-ht) for some small constant h (as a reasonable approximation).

  18. 318
    Mark says:

    “All this was quite extensively discussed on this site just a couple of months ago, so you obviously have not been paying attention, Max.

    Comment by CTG”

    It’s more that they don’t even notice the response.

    If they read anything, it’s only bits that prove AGW wrong. Even if that means taking them out of context and leaving out important information. Like the date of the quote…

    This could well be because they are being mailed talking points and/or picking them up from others.

    They certainly have enough of the text to make a quote but when you read the source you too easily find where they get it wrong in the same text. If they had actually READ the text then they would not have used it because it’s too easy to counter from it.

    The only thing I can think of is that someone is mailing about to “a few good men” and these rumoured counters to AGW are used indiscriminately.

    Credulously if you like.

  19. 319
    Doug Bostrom says:

    manacker 18 Jul 2009 at 1:18 pm

    “From what I have been able to read, there is no definitive link between global warming and glacial calving in the Antarctic. Maybe you have some links to other data.”

    Before anybody bothers to look, it would be a good idea to stretch manacker’s personal definition of “definitive” across a board and then pound a nail through each end, thus ensuring you’re not shooting at a moving target. Otherwise I suspect manacker’s “definitive” is going to change length no matter what comes down the pike.

    Manacker, what do you consider to be “definitive” in this case?

  20. 320
    Hank Roberts says:

    And, lo! picking keywords, trying Google Scholar, just as examples of what’s out there to be read:

    http://scholar.google.com/scholar?hl=en&scoring=r&q=ice+shelf+rift+propagation&as_ylo=2008

    An investigation into the forces that drive ice-shelf rift propagation on the Amery Ice Shelf, …

    JN Bassis, HA Fricker, R Coleman, J Minster – Journal of Glaciology, 2008 – seismo.berkeley.edu

    … and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf …

    T Scambos, HA Fricker, CC Liu, J Bohlander, … – Earth and Planetary Science Letters, 2009

    … observations of glaciogenic ocean waves (micro-tsunamis) on icebergs and ice shelves

    DR MacAYEAL, A Emile, C Richard, NB … – Journal of Glaciology, 2009 – earth.northwestern.edu

    Seismic observations of sea swell on the floating Ross Ice Shelf, Antarctica

    LM Cathles IV, EA Okal, DR MacAyeal – J. Geophys. Res, 2009 – earth.northwestern.edu
    … rift trending from the southeast toward an actively propagating tip in the northwest (closest to the seismometer site) cuts vertically through the ice shelf …

    West Antarctic Ice Sheet collapse–the fall and rise of a paradigm
    DG Vaughan – Climatic Change, 2008 – Springer
    … of ice sheet into a deep rift beneath its … then the potential for changes to propagate inland …

    Flexural-gravity wave phenomena on ice shelves.
    OV Sergienko, DR MacAyeal, CL Hulbe, R … – American Geophysical Union, Fall Meeting 2008, …, 2008 – agu.org
    … of the ice shelf both influence the wave propagation) throughout the ice … stress distributions around features of interest (eg, ice-shelf rifts, ice rises, etc). …

    You know how to find this stuff. Don’t rely on some guy on a blog to point you to facts. Search for yourself. Ask at your local library for a reference librarian to help you.

  21. 321
    CTG says:

    Re 318 Mark

    Oh indeed, I am sure they are getting from somewhere. I have been having a debate with someone on another site who also seems to be getting fed “relevant” research. He claimed that the tree-ring divergence problem means that the instrumental record since the 1980s is wrong, and he had a paper that he said proved it. Five minutes on Google Scholar was enough to find a more recent paper by the same authors that found the divergence problem is much less of an issue than previously thought. Odd that he hadn’t taken the time to do the same research himself.

  22. 322
    CTG says:

    Re 312 Max

    “From what I have been able to read, there is no definitive link between global warming and glacial calving in the Antarctic. Maybe you have some links to other data.”

    Um, well perhaps you could start by reading the site that you are commenting on…

    http://www.realclimate.org/index.php/archives/2008/10/what-links-the-retreat-of-jakobshavn-isbrae-wilkins-ice-shelf-and-the-petermann-glacier/

    http://www.realclimate.org/index.php/archives/2006/03/catastrophic-sea-level-rise-more-evidence-from-the-ice-sheets/

    http://www.realclimate.org/index.php/archives/2006/06/ice-sheets-and-sea-level-rise-model-failure-is-the-key-issue/

    After reading those, think about your original claim and see if you still think it is so:

    “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.”

  23. 323
    G. Karst says:

    Re: Brian Dodge 17 Jul 2009 at #283

    Thank-you for the many citations regarding possible ice thinning.

    I have carefully checked your citations and could find no reference to actual total volumetric ice, anywhere. If you have those figures why didn’t you just state them? I would certainly interested in that data-set.

    Until better data arrives, I will just have to rely on delta area as being proportional to delta volume. Even with depth measurement coming on line, it will be sometime before sufficient data can be historically referenced. The declassification of Navy data may change this situation.

  24. 324
    BobFJ says:

    Co2isnotevil, Reur 286
    You wrote an interesting post which in part said:

    Max, re 282
    Your calculation is incorrect as well. The proper calculation is to first determine the power flux in and out of the surface, which for an average surface temperature of 288K is 390.11 W/m^2 from Stefan-Boltzmann. The forcing power (using the IPCC heuristic) is,
    5.35 * (ln(310/280) – ln(297/280)) = 0.23 W/m^2

    However, and sorry Max for intruding, but could you please explain how your method of calculation using S-B on a complex grey “body” varying in emissivity and temperature, both temporally and spatially, is valid? For instance, when T to the fourth power, relating to HEAT loss from the surface via EMR is contemplated, how do you make a meaningful average of it? Also, don’t forget that there are believed to be greater heat losses from sources other than EMR, e.g. see image from NOAA

  25. 325
    David B. Benson says:

    “Solar Cycle Linked To Global Climate”:
    http://www.sciencedaily.com/releases/2009/07/090716113358.htm

    Unusually well-done!

  26. 326
    Hank Roberts says:

    Karst found no references to actual sea ice density.
    Here’s an early one (1963). There are many, many more available, follow citations.
    Short answer: it’s quite variable over time; Google Scholar is your friend.

    http://handle.dtic.mil/100.2/AD410182

    “… Average density and salinity values at the different depths for
    each age of ice are shown in Figures 2, 3, 4 and 5. The average
    salinity and density for the total ice thickness of each ice age
    during the summer season are shown in Figure 6. The data from
    which these values were obtained are listed in the Appendix…..”

  27. 327
    Doug Bostrom says:

    G. Karst 18 Jul 2009 at 4:20 pm

    “I have carefully checked your citations and could find no reference to actual total volumetric ice, anywhere.”

    From Brian’s first cite:

    “Satellite radar altimeter measurements show that between 1992 and 2001 the Larsen Ice Shelf lowered by up to 0.27 ± 0.11 meters per year.”

    Seems to me it’s no great feat to take the areal coverage of the ice, figure a volume for 1992 based on the shelf height that year, then another volume for 2001 using the reduced observed shelf height.

    That would yield reduced volume, unless the area of the ice has increased sufficiently to account for the loss of height. Was there a commensurate increase in coverage during those years?

  28. 328
    isotopious says:

    #308
    “You can’t do it for periods that are too short because of the unforced variability”

    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.

    [Response: Does this make any sense to anyone? - gavin]

  29. 329
    BobFJ says:

    ALL: Re mechanical hinging failure of ice shelves:
    Thanks for so much interest but I remain unconvinced by the arguments presented that global warming has a significant effect in accelerating the process.

    Hydrostatic pressure as a proposed means of extending mechanically caused cracks sounds nice, but the problem I have with the hypothesis is that I’m not aware of any non-intrusive test that can validate it. Furthermore, ice shelves can be up to around 1,000 metres thick, (of which most is underwater), and this is a huge “thermal mass”. Consequently, the temperature of air within any crack, as distinct from the air above must surely be below freezing, and any melt water can thus not penetrate significantly.

    In a similar fashion it has been shown somewhere, that the bottom layers of (some?) shelves comprise of frozen seawater.

    The hypothesis of massive melt ponds at the surfaceetc, also breaks down when considering the calving of icebergs, which again, is nothing new.
    For instance, icebergs were visible from shore around New Zealand about 100 years ago

    Hank Roberts Reur 320;
    That is an impressive list of titles you refer. How do you find the time to read all that stuff? Going by some of the titles, such as: Seismic observations of sea swell on the floating Ross Ice shelf, I would not have thought to read it WRT the above, but congratulations for finding a connection anyway.
    (Don’t know when I can find time)

  30. 330
    nigel jones says:

    Hasnt China increased particulate emissions significantly since about 1995? Would this explain the recent slight cooling trend?

  31. 331
    Brian Dodge says:

    “Was there a commensurate increase in coverage during those years?”

    Nope.

    “On average, Antarctic Peninsula (AP) ice shelves have retreated by ~300 km2 each year since 1980 (1). This gradual retreat has been punctuated by two catastrophic collapses, in January 1995 (2) and February 2002, when the remaining northern sections of the Larsen Ice Shelf (LIS) (Fig. 1) fragmented into icebergs. In contrast to the prolonged retreats, these 2000- and 3250-km2 ice-shelf sections—Larsen-A and Larsen-B— disintegrated over days or weeks.”

    Science 31 October 2003: Vol. 302. no. 5646, pp. 856 – 859
    DOI: 10.1126/science.1089768
    Larsen Ice Shelf Has Progressively Thinned
    Andrew Shepherd,1* Duncan Wingham,2 Tony Payne,3 Pedro Skvarca4
    (paywalled; I’m a subscriber)

  32. 332
    Rod B says:

    BobFJ (324), a minor correction: I believe all heat loss from the Earth system is only from radiation; or did I miss what you meant?

  33. 333
    barry says:

    I was intrigued by this line from the Swanson paper.

    “The top panel in Figure 1 shows that in a 74 statistically rigorous sense such synchronizations only occurred four times (1910-20; 1938- 75 45; 1956-60; and 1976-1981) during the 20th century, and three of those synchronizations 76 (all but 1956-1960) coincided with shifts in the climate state.”

    Might that suggest a fifth climate mode as yet undetected, that was not synchronized 1956 – 1960? And would it be possible to mathematically deduce a likely periodicity for such a mode using the above information?

  34. 334
    Doug Bostrom says:

    BobFJ 18 Jul 2009 at 7:42 pm:

    “Hydrostatic pressure as a proposed means of extending mechanically caused cracks sounds nice, but the problem I have with the hypothesis is that I’m not aware of any non-intrusive test that can validate it.”

    Sure, and by the same logic we know that destructive testing of all as-built structures is required to validate their design, yes? Materials science does not exist?

    “Furthermore, ice shelves can be up to around 1,000 metres thick, (of which most is underwater), and this is a huge “thermal mass”. Consequently, the temperature of air within any crack, as distinct from the air above must surely be below freezing, and any melt water can thus not penetrate significantly.”

    I believe you intended to say “water within any crack” but your conjecture still does not follow. What about a fracture originating below the ice, in water? Does it adhere to different rules? Does water entering such a fracture automatically freeze? If so, how is it that we observe any fractures either extending either from below or above? Would they not instantly be mended by frozen water?

    Phoning it in.

  35. 335
    Doug Bostrom says:

    Brian Dodge 18 Jul 2009 at 9:38 pm

    “‘Was there a commensurate increase in coverage during those years?’

    Nope.”

    Of course not. “Obtuse” or “recalcitrant”, we do not really know. Not enough data.

  36. 336
    BobFJ says:

    Rod B Reur 332,
    Sorry, I was talking about heat loss from THE SURFACE, the largest portion being via evapo-transpiration. The NOAA figure that I linked to shows it rather well

  37. 337
    BobFJ says:

    Martin Vermeer, you wrote in your 310:

    BobFJ #292: don’t sweat it… I won’t try to teach you anything against your will ;-)

    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?

  38. 338
    dhogaza says:

    Until better data arrives, I will just have to rely on delta area as being proportional to delta volume.

    First year ice thickness vs. older ice thickness is known (on average). We know that much more of the arctic winter extent is now first year ice. Therefore, the volume’s different.

    Your reliance isn’t based on logic or known data, but your political ideology. Pseudoscience, in other words.

  39. 339
    Hank Roberts says:

    > remain unconvinced
    Uh huh. And so you use logic instead of reading research.
    How many teeth does a horse have? Famous question.

    > How do you find the time
    Start young, persist for decades, and rely on librarians.
    Stay curious about everything, and never rely on logic or memory.
    Look things up, each time.

    If you can’t read the research, at least read the summaries. Paste the name of the paper into Scholar to find other papers citing it.

    Here, this is engineering material. Just a little snippet; and this is just one of many papers on various issues being looked at about what’s happening.

    Why rely on logic when the science is so rich and so available?
    Wonder how many teeth a horse has? go ’round to the stable.

    Transoceanic wave propagation links iceberg calving margins of
    Antarctica with storms in tropics and Northern Hemisphere
    GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L17502, doi:10.1029/2006GL027235, 2006

    “… Sea Swell: An Agent in Iceberg Calving and
    Break-Up?

    [8] Considering the long history of investigation into
    trans-oceanic propagation of long-period ocean waves
    [Munk et al., 1963; Snodgrass et al., 1966], it is not
    surprising that our observations have revealed examples of
    sea swell traveling half-way around the earth to shake
    icebergs and ice shelves along a broad swath of the
    Antarctic coastline. What is unique about the observations
    presented here is that they imply that giant icebergs and the
    calving margins of major ice shelves are mechanically
    influenced by meteorological conditions in the far field.
    Considering that iceberg calving is involved in the mainte-
    nance of Antarctica’s ice-mass budget [Jacobs et al., 1992],
    it is thus natural to consider whether climate conditions in
    the extra-tropical northern hemisphere and the tropics (e.g.,
    storm intensity or hurricane/typhoon frequency) could exert
    a control on the mass budget of the Antarctic Ice Sheet.
    [9] A leading hypothesis for how tabular icebergs are
    calved concerns swell-induced vibration that can fatigue
    and fracture ice at weak spots, producing rifts that become
    iceberg-detachment boundaries [Holdsworth and Glynn,
    1978; Kristensen et al., 1982; Zwally et al., 2002]. With
    this hypothesis in mind, we considered whether the arrival
    of swell from the Gulf of Alaska storm discussed above
    contributed to the spectacular break-up of B15A on October
    27 2005 (Figure 1a)….”

    http://www.earth.northwestern.edu/people/emile/PDF/EAO186.pdf

  40. 340
    Richard Steckis says:

    #305 Barton Paul Levenson,

    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. This has nothing to do with temperature analysis which can be done at shorter time scales as has often been done by scientists at this site as well as Tamino.

    I say it is an arbitrary figure because I have asked time and again for an empirical justification or a peer reviewed publication justifying this time scale and have been met with either stony silence or, in the case of one person, an improper and wrong comparison to the acceptance of the celsius scale as a standard in science.

  41. 341
    Richard Steckis says:

    #328 Isotopius then Gavin says:

    “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.

    [Response: Does this make any sense to anyone? - gavin]”

    As an Australian, I can identify with the statement quite easily. It is in fact a good analogy although it may be wrong in this context.

  42. 342
    Brian Dodge says:

    “Consequently, the temperature of air within any crack, as distinct from the air above must surely be below freezing, and any melt water can thus not penetrate significantly.”

    Consider the temperature a gram of ice would have to be below zero to freeze a gram of water. Also, consider the rate at which the heat would diffuse through the surrounding ice if water was poured into a crack. And then, consider the forces generated by the expansion of the water in a crack as it froze. Ponding of liquid water was observed on the surface of Larsen B prior to collapse, and liquid water can penetrate cracks & crevasses in ice sheets and shelves, otherwise moulins wouldn’t exist. Cracks are initiated by various stresses- tides, winds, flow gradients – and no doubt there are complex interactions of the various forces involved. For instance, as the ice warms from the energy transported into cracks by liquid and freezing water, its strength will decrease, and thermal expansion will create localized stresses. These new stresses will interact with tidal stress, and the changing stresses will cause strain and creep, which will in turn cause effects like crack propagation, new crack formation, and dimension changes in existing cracks that will pump water (and heat) around. A geophone(paggophone?) recording of an ice shelf collapse would probably sound very interesting.

  43. 343
    Richard Steckis says:

    #305 Barton Paul Levenson says:

    “It’s like me taking the temperature here at one-minute intervals from 6 AM to 9 AM. That gives me 181 points, which I then use to show a significant upward trend in temperature, proving that the oceans will boil in two days.”

    I astounds me how some people can argue that the more data points one has, the less reliable is the statistical analysis. The fact is the data points encompass nearly a decade not a single year. Your appeal to ridicule in you example is well…. Ridiculous.

  44. 344
    Mark says:

    [Response: Does this make any sense to anyone? - gavin]

    Yes, iso is confused because you aren’t saying he’s right (and he KNOWS he is, so anything that isn’t saying so must be wrong), so he wants to spread it about.

    After all, confusion shared is confusion doubled.

  45. 345
    Mark says:

    “Hydrostatic pressure as a proposed means of extending mechanically caused cracks sounds nice, but the problem I have with the hypothesis is that I’m not aware of any non-intrusive test that can validate it. ”

    Then you have a problem with intrusive testing too?

    Do you have a proposition that this would NOT happen?

    After all, aero engineers knew that the bumble bee couldn’t fly, but it didn’t do the maths and flew anyway. Then after some long time, the invention of sophisticated equipment meant taht the reason for it could be tested.

    It seems like bumble bees CAN fly.

    Now your complaint sounds a lot like “where’s the empirical evidence for it” seen so often in denial circles. Apparently it doesn’t work if you test a theory in isolation so you can control the variables and factor them out because it isn’t a trillion-ton block of ice on a remote island…

  46. 346
    Martin Vermeer says:

    BobFJ: “(Don’t know when I can find time)”

    Still you find time for posting…

  47. 347
    stevec says:

    “Response: Does this make any sense to anyone? – gavin”

    It makes sense to me, should I be scared? He is simply saying there is no true noise in the system since there are physical reasons behind any such noise. I doubt the importance of being able to identify the source of the noise in each and every instance but that is his point from how I read it.

  48. 348
    Anne van der Bom says:

    BobFJ
    18 Jul 2009 at 7:42 pm

    Consequently, the temperature of air within any crack, as distinct from the air above must surely be below freezing, and any melt water can thus not penetrate significantly.

    What do you mean by this? That any water flowing into a crack will immedately freeze and consequently not penetrate very deep? Do you have any observations to confirm this?

    The hypothesis of massive melt ponds at the surfaceetc, also breaks down when considering the calving of icebergs, which again, is nothing new.

    Can you please explain how exactly the ‘melt pond hypothesis’ breaks down? This remark leaves a bit too much to my imagination. You’re essentially asking me to take your word for it.

  49. 349
    Alex Harvey says:

    Chris @ 17 Jul 2009 at 9:18 am:

    I believe I have found the answer to my original question myself; I had misread the graph! The graph is too fine on my screen and it looked like an ’1850′ at the bottom left. However I have now seen the same graph reproduced at James Annan’s blog, larger, and I realised that it begins at 1950. Thus it appears to me that Dr. Swanson meant, the true trend one beginning 1950, not 1850. That’s good; it takes us further from the LIA. I don’t need to mention that there doesn’t seem to be any warming at all in IPCC2007 SPM Fig. 1. My apologies for the misunderstanding. Puzzling that no one corrected me! :)

  50. 350
    manacker says:

    CTG

    Thanks for your 322 with RC references on ice sheets, glacial calving etc.

    These were very interesting (I had actually read one of the three previously).

    That marine outlet glaciers detach from their beds and then start floating and calving seems like a normal process, as is the inland snowfall that provides the ice mass of the glaciers in the first place. Since glaciers are simply rivers of frozen water this is obviously very much an ongoing dynamic process.

    The mountain glaciers in Switzerland (where I live) have been retreating since around 1850, when they apparently reached their greatest extent of the past 10,000 years. As they retreat today, signs of earlier civilizations and vegetation during warmer periods (MWP, Roman Optimum, for example) are often found, indicating that these glaciers react to global temperature swings, periods of reduced local winter snowfall, etc.

    The example is given of the Petermann Glacier (Greenland), a large portion of which is already afloat and apparently calves 60 km^3 per year of ice.

    Paleoclimate studies show that sea levels were 3-4 m higher when the AIS was much smaller than today. Speculations of future sea level rise (perhaps some unspecified day in the future maybe) are interesting but hardly conclusive.

    The studies on the GIS and AIS are also interesting. While not mentioned in the RC write-ups, both GIS and AIS were shown to have grown in relatively long-term studies from 1992 to 2003 (Zwally/Johannessen and Wingham), but the GIS appears to be shrinking today based on more recent shorter-term studies.

    All-in-all your references did not provide any conclusive evidence that there is a definitive link between global warming and glacial calving today. It also did not convince me that this process (even major events such as Wilkins or Larson B) is contributing significantly to sea level rise today.

    But thanks for some interesting links, anyway.

    Max


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