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The unnoticed melt

Filed under: — group @ 9 September 2011

Guest commentary from Dirk Notz, MPI Hamburg

“Well, it’s not really good timing to write about global warming when the summer feels cold and rainy”, a journalist told me last week. Hence, at least here in Germany, there hasn’t been much reporting about the recent evolution of Arctic sea ice – despite the fact that Arctic sea ice extent in July, for example, was the lowest ever recorded for that month throughout the entire satellite record. Sea-ice extent in August was also extremely low, second only to August 2007 (Fig. 1). Whether or not we’re in for a new September record, the next weeks will show.

Figure 1: Evolution of Arctic sea-ice extent in July and August from 1979 until 2011. (NSIDC)

A rainy summer might be one reason for an apparent lack of public attention with respect to the ongoing sea-ice loss. Another reason, however, is possibly the fact that we scientists have failed to make sufficiently clear that a major loss of sea ice during the early summer months is climatologically more important than a record minimum in September. This importance of sea-ice evolution during the early summer months is directly related to the role of sea ice as an efficient cooling machine: Because of its high albedo (reflectivity), sea ice reflects most of the incoming sunlight and helps to keep the Arctic cold throughout summer. The relative importance of this cooling is largest when days are long and the input of solar radiation is at its maximum, which happens at the beginning of summer. If, like this year, sea-ice extent becomes very low already at that time, solar radiation is efficiently absorbed throughout all summer by the unusually large areas of open water within the Arctic Ocean. Hence, rather than being reflected by the sea ice that used to cover these areas, the solar radiation warms the ocean there and thus provides a heat source that can efficiently melt the remaining sea ice from below. In turn, additional areas of open water are formed that lead to even more absorption of solar radiation. This feedback loop, which is often referred to as the ice-albedo feedback, also delays the formation of new sea ice in autumn because of the accompanying surplus in oceanic heat storage.

Measurements from ice buoys show that indeed melting at the bottom of the sea ice has increased significantly in recent years. While field experiments that were carried out in the 20th century showed unambiguously that surface melting used to be the dominant mechanism for the thinning of Arctic sea ice, now in larger and larger areas melting at the underside of the ice is almost equally important. Such melting from below is particularly efficient since the temperature at the ice-ocean interface is fixed by the phase equilibrium that must be maintained there. Hence, any heat provided by the ocean to this interface will lead to thinning of the ice in summer and to slower ice growth in winter. At the surface, the ice temperature is not fixed as long as the ice isn’t melting, and heat input from the atmosphere can in part be compensated for by a change in surface temperature and an accompanying change in outgoing long-wave radiation at the ice surface.

In addition to these climatological reasons, there is another reason for why a public focus on just the September sea-ice extent is possibly misleading: Such focus might give the impression that sea-ice extent is stable in other seasons but summer. That this is not the case becomes obvious from the graphical distribution of extreme sea-ice extent for each individual month that is shown in Figure 2. The figure shows in red the years with the five lowest values of sea-ice extent for a certain month and in blue the years with the five highest values. A retreat of sea ice throughout the entire year is obvious. In fact, the sea-ice extent for every month since June 2010 has been among the five lowest values ever recorded by satellites.

Figure 2: Distribution of record minima and record maxima of Arctic sea-ice extent (NSIDC). The years with the five lowest values of sea ice extent for a certain month are marked in red, those with the five highest values of sea-ice extent are marked in blue. The darkness of the color indicates the ranking: the darkest red marks the lowest value, the darkest blue the highest.

Such widespread loss of Arctic sea ice has sometimes given rise to the concern that the total loss of Arctic sea ice at least during summer time can no longer be avoided. In this context, usually the ice-albedo feedback is mentioned, since it provides a mechanism that can in principle lead to a so-called “tipping point” beyond which the loss of the remaining sea ice becomes unstoppable. However, recent research shows that this scenario is too pessimistic. For example, in a paper published in Geophysical Research Letters in January 2011, Tietsche et al. [1] used climate model simulations to examine the evolution of Arctic sea ice after an extreme loss event. In their model simulations, they artificially removed all Arctic sea ice at the beginning of June for selected years and examined if the ice would recover from such extreme event.

Their main result is shown in Fig. 3: It took only about two years after each complete sea-ice removal until the ice had recovered to roughly the extent it had before the removal. Hence, sea ice extent is primarily defined by the prevailing climate conditions; the ice-albedo feedback mechanism is, in isolation, too weak to stabilize a very low sea-ice cover. In examining the mechanisms behind this finding, Tietsche et al. found that unusually large amounts of heat indeed accumulate in the ocean during the ice-free summer. However, this heat is efficiently released to the cold atmosphere already during the following autumn and winter. Once that heat release has cooled the ocean to its freezing temperature, sea ice forms again. Because this ice is initially very thin, the efficient release of heat from the ocean continues for some time, causing a rapid growth of the new sea ice. Much of this ice then survives the following summer, and sea-ice conditions can quickly return to those before the artificial perturbation.

Figure 3: Evolution of September sea-ice extent in coupled climate model simulations. The blue curve shows the evolution of the unperturbed sea-ice extent for the A1B scenario, with the gray shading showing the ensemble spread of three model runs. For the red curves, sea ice was artificially removed at the beginning of June in 1980, 2000, 2020, 2040 and 2060 within the climate model simulations. For all these perturbations, sea-ice extent recovered rapidly to the unperturbed extent. A similar result was found for sea-ice volume.

The finding that the long-term evolution of Arctic sea ice is primarily governed by the prevailing climate conditions implies that the loss of Arctic sea ice can still be slowed down and eventually stopped if an efficient reduction of CO2 emissions were to become reality soon. Last week, however, it became obvious once more how unlikely such scenario is: On 30th August, Exxon announced a deal with Rosneft, the Russian state oil company. As part of this deal, Exxon will invest more than US$2 billion to support Rosneft in the exploitation of oil reserves in the Kara Sea, which is part of the Arctic Ocean north of Siberia. One requirement for the success of this deal: a further retreat of Arctic sea ice. Given that climate model simulations indeed all project such further retreat of Arctic sea ice, it seems that at least to some degree, managers of big oil companies have started to make business decisions based on climate-model simulations. That may be good news. Or not.

This article is in part based on a German article that was published at Klimalounge.


  1. S. Tietsche, D. Notz, J.H. Jungclaus, and J. Marotzke, "Recovery mechanisms of Arctic summer sea ice", Geophysical Research Letters, vol. 38, pp. n/a-n/a, 2011.

172 Responses to “The unnoticed melt”

  1. 151
    ldavidcooke says:

    Hey Alistair,

    Now you have confused me, if the obliquity changes from roughly 24 to 21 deg. over roughly 26ky, then how does the total range of the Arctic circle get larger?

    Given any sphere, regardless its axis of rotation, the angle of incidence from a point source does not change. The only real difference is the duration of exposure of a given point may change. Hence, if we are considering a min. of tilt approaching (currently decreasing towards 21 deg.) Then the duration for a fixed insolative exposure for any given point is decreasing. Yet as to it’s influence over the area of the Arctic Circle, in relation to GW has not changed. At best the 3 deg. change in the fixed tilt angle mainly involves a change in the location of the albedo enhancing surface and a possible difference in heating or warming/cooling inertia as land-sea exposures change.

    If the axis were to move towards a 90 deg. Obliquity or tidal locked condition would the character of change become less zonal (in relation to the solar plane)? With the primary difference being rather then roughly 1/6th of the planets surface having to endour a semi- annual day that it would change to 1/2 of the planet having a permenant day. If so how much of the incoming insolation on the Sol side would be distributed by the atmosphere? In short, I could see there being a marked effect with a fixed low angle of obliquity and/or diminished rotational velocity (Venus…?); but 3 deg.?


  2. 152
    ldavidcooke says:

    Hey All,

    The reason I do not regard obliquity very high is a roughly 4 degree variation should suggest a roughly 1.5% variation in rotational velocity (If my math is any good it would suggest, to me, with the current Eular estimated angular velocity of 1040mph at the equator, a 3 deg. difference in angular velocity should be approx. 15 mph, with the current value being roughly 10 mph slower then the fastest rotational rate, (21 deg. obliquity). If you have a value significantly different I am interested in discussing it.

    Dave Cooke

  3. 153

    #151,2–I feel a tad confused myself.

    Dave, surely if we were to approach 90 degree obliquity, the Arctic Circle (per Alastair’s definition) would converge toward the Equator–which would definitely count as an expansion!

  4. 154
    ldavidcooke says:


    Hey Kevin,

    Sorry, I was talking in relation to the current global definition of the Arctic Circle. As to a change in direct insolation, over time for a specific location, yes, you and Alistair are correct. The global area receiving direct sunlight over a period of a day would be lower as the angle of obliquity increased. Even though the equtorial rotational velocity and the silloutte does not change.

    Alistair was helpful in letting me discover for myself the error of my thought. I appreciate the chance you are offering to clear that up,( without looking like I was desparately beating a dead horse). I think the point I was exploring was obliquity as a contributor to GW. Based on my rough estimate of the effect of 3 deg. I do not see obliquity a main contributor to Climate Change or Arctic warming.

    As a layman I would not be comfortable trying to calculate Euler rotational velocities and the difference that 3 deg. would make. But, my porportional est. of 1.5% may not be terribly accurate; however, as a factor contributing to CC I believe could at most vary temperature seasonality by roughly 2 weeks. Suggesting obliquity may slightly increase a more rapid seasonal temperature swing, I just do not see it likely to change the annual amount of temperature swing.

    Dave Cooke

  5. 155
    ldavidcooke says:

    Re: 153

    Hey Kevin,

    Pardon the brain burp, the last post was accurate for the Solstice in a solar orbit with the rotational axis pointing towards the sun, at the equinox with the current equator facing the sun, with a 90 deg. obliquity, the distribution area of insolation would not be much different then if obliquity were 0 deg. The only time it would matter is in a tidal locked condition where there were no rotation or if the axis pointed parallel to an orbital tangent. Sorry, heady subject and I lost my logic track.

    Dave Cooke

  6. 156
    Dani says:

    I had a friend who didn’t believe in global warming until she worked in Alaska and saw the melt first hand. She also saw the breeding of grizzlies and polar bears that never used to share the same territory but are forced to because of melting ice.

  7. 157
    ccpo says:

    Why is David Cooke’s rambling mess of denial allowed to be posted here?
    “David Cooke said… Well, there are many links between the bogus science of global warming and the bogus science of psychology.

    Both of these cons depend on weasel words, appeal to authority, misleading statistics and plain simple bluff. And both make ad hominem attacks on their critics.
    November 19, 2010 8:39 AM ”

    Note to David: Calling someone out for being dishonest is not an ad hominem attack. Your clear bias, as opposed to the feigned collegiality here, is betrayed by the quote above in which you say climate science is “bogus” a “con” and liken climate science discussion to weasel words, etc.

    I see no reason why the scientists here should allow posts from someone with such great disrespect for your work and who is inherently dishonest in his communication.

  8. 158
    ldavidcooke says:


    Hey ccpo,

    Likely because your “quote” was not mine.

    If you are really interested and am concerned over the basis of my bias, try researching ldavidcooke such as a moderator for climate and earth sciences at UK Weather World. That Dr. Schmidt and company has been gracious to allow me to share my observations and questions here has been very welcome. As of yet it is clear there is a lot of work ahead and attacking folks without trying to understand or point out errors in their thoughts is unproductive, IMHO.

    If you disagree with the observations I make or can clear up where I have posed questions you are welcome to post at the UKww climate forums; however, as this conversation began here, it would be more appropriate to either continue this discussion here, or to take it off line. Either way is fine…

    Dave Cooke

  9. 159
    ccpo says:

    I’m fairly confident you are one and the same, but it doesn’t really matter. You question here basic elements of climate science and it is time to stop coddling such either inept understanding or intentional obfuscation. Well past time. I don’t care what flavor of denial you employ; I identified them all years ago and have watched the various waves of repackaged denial break on the shores of science.

    I addressed your issues some time back. I see no need to do so again. It’s not the sun, and that is conclusive. It’s not anything (the primary driver, i.e) than GHGs. Period. This is obvious and unambiguous, so your pretense at polite “Gosh!”-ism does not impress.

    Anywho… I should have put this in Variations, so will drop it now.

  10. 160
    ldavidcooke says:

    Hey ccpo,

    Clearly you have made another error in I also did not say that the sun or input at the Top of the Atmosphere is the issue. What I did say was that changes within the lower atmosphere are changing both the average wideband insolation and weather patterns.

    It is likely these changes that are driving an increase in surface daily high air temperatures. In addition, there appears to be a reduction in surface relative humidity. This reduction in RH nor soil moisture are directly related to a increase in GHG radiant energy. Though I clearly agree that natural variation can be pushed by GHG.

    At issue in my lack of understanding is how can an increase of 135ppm of CO2 fully mixed at an average altitude of 500mb demonstrate an effect that is only visable in the paleo or fossil records at about a 1500 or 1250ppm above the current CO2 level? It is unlikely that by its self the influence of 135ppm of CO2 is as dramatic as the changes of recent note.

    Now if you are intetested in exploring or are interested in teaching I believe we might be able to have a wondeful conversation. If not then fine, though it makes me wonder at your purpose here.

    Dave Cooke

  11. 161
    Hank Roberts says:

    Well == is pretty definitely opinionated about whether CO2 can have any effect, he thinks it not likely.
    Would that be the same guy?

  12. 162
    ldavidcooke says:


    Hey Hank,

    Yes, this is the same person and the ideas posted pretty much matched my understanding of the Science at the time. As was the person on the Yahoo Climate Discussion Boards that refuted that the influence of GHGs on the GAT between 2000 and 2005 that was the claimed to be 3.5 deg. F. As is currently a moderator at UKww for Climate and Earth Sciences.

    As to the value of influence of GHGs on the GAT, I believe I am aware of the work to date wrt TSI and the radiational imbalance. As to the influence, Dr. Hansen and company did an excellent job of estimating the added input in watts that can be assocated with the retention of the 15um energy. It s not much different then a little more then 1/2 the value of the change in watts of the full spectrum between the solar min.-max. Though the solar max. Variation is distributed between 80-90% of the sillouette of the Earth whereas CO2 covers about 90% of the globe all the time and not just every 11 yrs.

    To me this would suggest that the influence of GHGs alone should be a little bit more then Sol at Max. Suggesting that weather anomolies observed during the solar maximum, pre-1950, would become the new normal, with the solar max. nearly doubling that influence.

    Dave Cooke

  13. 163
    ccpo says:

    David, you are talking nonsense.

    “At issue in my lack of understanding is how can an increase of 135ppm of CO2 fully mixed at an average altitude of 500mb demonstrate an effect that is only visable in the paleo or fossil records at about a 1500 or 1250ppm above the current CO2 level?”

    Assuming your framing is correct, go read the literature and you’ll know. Hint: it’s not JUST CO2. I already told you this has been covered here at RC, so you don’t have to go far to find the answers.

  14. 164
    ldavidcooke says:

    Hey ccpo,

    Thanks, though I am aware of the participants in the AR4. The confidence in some were low and of late I have not seen any measures that have improved their values. Of course I am limited to popular periodicals such as the NASA News, “Science Daily” and “Science News”. Oh and the critical reviews here.

    I believe there was a big push a couple of years ago in relation to some modeling work that Dr. Schmidt and the team were working on with NCAR though I have not seen anything further. I suspect the committiees and contributors are still waiting on the next report before unveiling the latest advancements. About the biggest change over the last three years was a reference that Hank made in relation to or a study of how the AR4 participants are being manifest or incorporated into the weather patterns and circulations, atmospherically speaking.

    Are you aware of recent any recent advances you can point out? It certainly helps me get things straight when the logic and information fit together. Otherwise I am left to my own devices and we see where that takes me.

    (Oh, btw a quick question where do you get the impression I am trying to add something new, when it is clear that is unlikely as I have neither the resources or capabilities? I am only reguratating what is present in the popular press and looking at how the data ties into my understanding of it.)

    Dave Cooke

  15. 165
    Hank Roberts says:

    There are plenty of websites that encourage regurgitating what is in the popular press, and the Open Thread at RC collects that stuff too.

    — this isn’t that —-

    Let’s talk about science — articles in published science journals, eh?

    Here’s a new article relevant to THIS topic
    The authors’ names will be familiar:

    Influence of initial conditions and climate forcing on predicting Arctic sea ice

    Blanchard-Wrigglesworth, E., C. M. Bitz, and M. M. Holland
    Geophys. Res. Lett., 38, L18503, doi:10.1029/2011GL048807
    Publication Date: 21 September 2011
    5 pages, 3 figures, 1 table

    Did you read it?

  16. 166
    ldavidcooke says:

    Hey Hank,

    Concur, each of the following are backed by science and none, to my knowledge, by obvious deniers.

    At best your link discusses the durability of ice based on volume, latent heat and energy added. The question seems to keep returning to the added energy coefficient. Changes in natural variations seem to adjust around environmental changes to a degree. Currently, we are just discovering the biologic response to environmental changes. We continue to discover the systemic thermodynamic responses to environmental changes. Where do you want to take the discussion next?


  17. 167
    Hank Roberts says:

    Dr. Notz wrote in the main post above:

    “… we scientists have failed to make sufficiently clear that a major loss of sea ice during the early summer months is climatologically more important than a record minimum in September….”

    And the increasingly early change from ice to open water changes almost everything else, not just the albedo:

    results include these titles:

    Climate change and the phytoplankton spring bloom: warming and overwintering zooplankton have similar effects on phytoplankton
    U Sommer… – Global Change Biology, 2011 – Wiley Online Library

    Competitive dynamics in two species of marine phytoplankton under non-equilibrium conditions P Cermeño, JB Lee, K Wyman, O Schofield… – Mar Ecol Prog, 2011

    Stoichiometric effects of warming on herbivore growth: experimental test with plankters
    W Makino, Q Gong… – Ecosphere, 2011 – Eco Soc America
    although the onset of the spring phytoplankton bloom occurs earlier along with warming, it is documented that … Water temperature and stratification depth independently shift cardinal events during plankton spring succession. Global Change Biology 16:1954–1965 …

    So as with other areas, there’s a physical change and a direct forcing, and then there’s feedbacks

  18. 168
    ldavidcooke says:

    Hey Hank,

    The degrees of freedom wrt gross population differences based on starting populations appear broad, then again it depends on the conditions specifed in the referenced docs. Following the chain may be useful or it may be a wild goose.

    Personally, it would be nice if a synoposis of initial state, change of state and terminal state would be useful to non-professionals in that specific field; but, that is not the way of most papers. Hence, without several days jogging it will be hard to determine the energy spectrum and intensity, dissolved O2/CO2/NO/SO/FeO/Ca/NaCl/…or initial conditions, as it is, the end or change in conditions did not appear either, hence it would appear difficult to duplicate the experiment.


  19. 169
    ccpo says:

    @266 Why post a bunch of links to an issue completely unrelated to melting Arctic Sea Ice?

    Rhetorical question.

    At best your link discusses the durability of ice based on volume, latent heat and energy added.

    Discusses the issues. How absurd!

    The question seems to keep returning to the added energy coefficient.

    Uh, the amount of energy added is the point. How keen of you.

    Changes in natural variations seem to adjust around environmental changes to a degree.

    Changes are affected by changes. What would we do without you, David?

    Currently, we are just discovering the biologic response to environmental changes.

    “Just?” Yeah… we haven’t known that changing ecosystems affect the biota in those ecosystems… just figuring that out. Yup. Let’s not do anything!

    We continue to discover the systemic thermodynamic responses to environmental changes.

    Yup. Good thing we understand them so well already that we can actually make educated models of what is coming.

    Where do you want to take the discussion next?

    With you? Nowhere. It’s pointless. You are not looking for answers, you are propagandizing.

  20. 170
    L. David Cooke says:

    Hey cppo,

    Actually, we are attempting to advance the store of knowledge and you…

    Dave Cooke

  21. 171
    ccpo says:

    No, David, you aren’t. You have argued points as if contentious that are not. You have presented ideas already scientifically invalidated as valid. You have claimed chicanery where none exists while failing to address the chicanery perpetrated by people spouting the same falsehoods you do, already well documented.

    To claim goodness is not to be good. To be good, one must do good. You are not doing good.

  22. 172

    The adiabatic nature of current arctic air is quite strong, the onset of
    dominant inversion driven lower atmosphere appears quite delayed. I credit the wider open seas for this. The re-freeze seems weakened or sluggish What I expect is any big wind will show this, current forecast for Fram strait calls for strong winds. We shall see how consolidated the pack is soon.