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Notes from The Gathering #5: Arctic sea ice: is it tipped yet?

Filed under: — david @ 13 December 2007

The summer of 2007 was apocalyptic for Arctic sea ice. The coverage and thickness of sea ice in the Arctic has been declining steadily over the past few decades, but this year the ice lost an area about the size of Texas, reaching its minimum on about the 16th of September. Arctic sea ice seems to me the best and more imminent example of a tipping point in the climate system. A series of talks aimed to explain the reason for the meltdown.

Sea surface temperatures were warmer this past summer also; I forget how many standard deviations the temperature was off the trend, but it was definitely anomalous. The region of the meltback is just inside the Bering Strait, where warm water flows in from the Pacific, but in the analysis of Steele et al. this inflow of comparatively warm water was not particularly anomalous in 2007 relative to other years. It could be that the exposure of the sea surface to the atmosphere by the melting ice could have an impact, although the meltback is so late in the solar heating season (September) that this effect seems of limited explanatory value also. Bit of a chicken and egg problem here.

Melting ice can be seen from space, I believe as puddles sensed by the QuickSCAT satellite. The puddles are most abundant in mid-summer when the sunlight is strongest, and by mid-September when the ice meltback was the strongest, the melting season was largely over. Apparently the reason for the disappearance was an anomalous weather system which generated a strong jet of surface winds blowing straight over the pole southward toward the Atlantic ocean, a “Polar Express”. A research ship frozen into the ice in 2006 crossed the Arctic in about a year, about three times faster than the transit time of the Fram in the 1890’s. To summarize, the ice cubes in the freezer tray didn’t melt because the freezer is broken exactly, but because the ice cube tray fell out of the freezer onto the warm floor.

The disappearance of the ice was set up by warming surface waters and loss of the thicker multi-year ice in favor of thinner single-year ice. But the collapse of ice coverage this year was also something of a random event. This change was much more abrupt than the averaged results of the multiple IPCC AR4 models, but if you look at individual model runs, you can find sudden decreases in ice cover such as this. In the particular model run which looks most like 2007, the ice subsequently recovered somewhat, although never regaining the coverage before the meltback event.

So what is the implication of the meltback, the prognosis for the future? Has the tipping point tipped yet? When ice melts, it allows the surface ocean to begin absorbing sunlight, potentially locking in the ice-free condition. Instead of making his own prognosis, Overland allowed the audience to vote on it. The options were

  • A The meltback is permanent
  • B Ice coverage will partially recover but continue to decrease
  • C The ice would recover to 1980’s levels but then continue to decline over the coming century

Options A and B had significant audience support, while only one brave soul voted for the most conservative option C. No one remarked that the “skeptic” possibility, that Arctic sea ice is not melting back at all, was not even offered or asked for. Climate scientists have moved beyond that.


202 Responses to “Notes from The Gathering #5: Arctic sea ice: is it tipped yet?”

  1. 101
    Tilo Reber says:

    I have a couple of temperature charts that I would like you all to verify. One is an RSS temperature anomaly chart and the other a HadCRUT3 temperature anomaly chart. These would seem to be very important, but I don’t know if I can trust them, considering their source.

    http://www.junkscience.com/MSU_Temps/RSSglobe.html
    http://www.junkscience.com/MSU_Temps/HadCRUG.html

    If these can be verified, then it seems that we are in the same place – temperature anomaly wise – in Dec of 07 as we were in Dec of 79. How would that be possible with CO2 having gone from 340 PPM to 380 PPM and with the Arctic albedo having significantly decreased?

    Thanks for any information.

  2. 102
    Sonny says:

    #80

    You’re kidding, right? That’s the sort of pop science thinking plaguing the White House and congress, members of whom don’t appear to understand grade school science.

    As an aside, I’ll second the new epoch, ‘ohshitocene’. My eleven year old son nearly choked laughing…until he remembered that it was the epoch in which he’d be growing up.

  3. 103
    Tilo Reber says:

    “You’re kidding, right? That’s the sort of pop science thinking plaguing the White House and congress, members of whom don’t appear to understand grade school science.”

    Thank you Sonny. I don’t mind the personal attack. But it would have been nice if you had answered my questions as well.

  4. 104
    James says:

    Re #87: [Speaking of Ellesmere Island, there are fossilized forrests on the island. This would tend to indicate much warmer weather there in the past.]

    Or perhaps, given that it was 50 million years ago, that Ellesmere Island was located somewhat further to the south?

    Continents do move around, you know. In connection with which, we might consider the formation of the Central American land bridge, which separated the Atlantic & Pacific oceans. It’s interesting to note that this happened only about 3 million years ago, IIRC about the same time that the current cycle of ice ages kicked off. Maybe some cause & effect?

  5. 105
    dhogaza says:

    f these can be verified, then it seems that we are in the same place – temperature anomaly wise – in Dec of 07 as we were in Dec of 79. How would that be possible with CO2 having gone from 340 PPM to 380 PPM…

    You can’t just compare two points as you seem to be doing with the RSS data, at least.

    Ask yourself: why has the junkmeister failed to plot a trend line on that graph?

    … and with the Arctic albedo having significantly decreased?

    Um, in December the Arctic is dark 24 hours a day, why would its albedo have any effect during this month?

  6. 106
    cce says:

    Re: 89

    Draw a straight line through their graphs, and you see undeniable warming surrounded by random noise (and a few unpredictable, yet significant factors such as El Nino and Volcanoes). The anomaly at any given moment depends on any number of things. We’ve seen warming of 0.4 to 0.5 degrees over the satellite era, which is just about the same as the magnitude of the noise from year to year. So you can take “cold” months from the last few years, and compare them to “warm” months 30 years ago, and then conclude that “there is no warming.” That is Cherry-Picking in the extreme.

    These is the temperature anomalies for GISS (instruments), Hadley (instruments), UAH (satellites), and RSS (satellites) since the beginning of the satellite era. The X axis is “months since Jan 1979.” The anomalies have been shifted upwards or downwards to give each trend a y intercept of 0.

    http://cce.000webhost.org/giss.jpg
    http://cce.000webhost.org/hadcrutv.jpg
    http://cce.000webhost.org/uah.jpg
    http://cce.000webhost.org/rss.jpg

    Tamino has a few posts on this subject:
    http://tamino.wordpress.com/2007/12/16/wiggles/
    http://tamino.wordpress.com/2007/08/31/garbage-is-forever/
    http://tamino.wordpress.com/2007/10/16/many-factors/

  7. 107
  8. 108
    Tim McDermott says:

    Polar bears may be the most visible potential victims of an ice-free actic, but the entire ecosystem may be in peril. Turns out that “Ice algae are a very important part of the marine food web, contributing on average 57% to the total Arctic marine primary production.”Krembs & Deming

    Worst case both the pelagic and benthic arctic ecosystems could collapse. So walrus, seals, and the acrtic cod are endangered.

    Tipping points indeed. Why, exactly, did we bother to save the baby harp seals?

    Tim

  9. 109
    Patrick Roche says:

    Just this last week December 13, 2007 RUSH Limbaugh bravely announced that artic ice coverage was recovering at a record rate. Well that IS a load off! (sarcasm) I can’t wait to find out what the man thinks about peak oil.

    Patrick

  10. 110
    Chris O\\\'Dell says:

    As another piece of the 2007 Arctic sea ice puzzle, my group at Colorado State just submitted a paper to GRL on the 2007 ice anomaly. We found that 2007 was quite anomalous in terms of cloud cover over parts of the Arctic, especially the western Arctic where much of the ice anomaly occurred. Amazingly, Fox covered the story at AGU – you can read about it here:
    http://www.foxnews.com/story/0,2933,316753,00.html

    The paper will not appear for a while, but the gist is that cloud cover in 2007, especially June and July, was 10-15% lower in the western Arctic, and this coupled with the especially thin sea ice probably played an important role in the massive ice melt. The extra sunshine was enough to melt roughly 0.3 m of ice directly, or warm the surrounding oceans by about 2.4 K.

  11. 111
    Russell says:

    Re #106
    Since AGW is contagious through-out our solar system, Mars should be melting its ice-cap any day now. That will release CO2 and water vapor, and all kinds of nasty GHG’s into the atmosphere. It will reach the tipping point, and make the planet habitable.
    It could be the perfect refuge for polar bears, walrus, and all manner of cold weather critters.

  12. 112
    Nick Barnes says:

    Any idea what has gone wrong with the charts over at Cryosphere Today?

  13. 113
    J.C.H. says:

    I will no longer be commenting on this blog as I’ve begun work on my first novel. It’s called “The Sea Ice Also Refreezes.”

  14. 114
    Hank Roberts says:

    Tim, thank you very much for this link, it’s answered a lot of questions I’ve had about how and when and where in the sea ice the algae grows. And _that_ answers what changes in the absence of sea ice. Repeating it:
    http://www.arctic.noaa.gov/essay_krembsdeming.html

    This is part of “primary productivity” — scary to see changes at this basic level.

  15. 115
    Ray Ladbury says:

    Re #111, Uh, Russell, do you have even a vague notion of what drives climate on Earth, let alone on the other planets? Venus is dominated by a runaway greenhouse effect. On Earth insolation and greenhouse gases are important. On Mars, insolatin and dust storms are the main drivers. By the time you get to Jupiter, insolation is less important–Jupiter gives off more energy than it receives from the Sun. Maybe you should listen to Mr. Twain: “What gets us into trouble is not what we don’t know. It’s what we know for sure that just ain’t so.”

  16. 116
    Steve Bloom says:

    Re #110: Chris, the decreased cloud cover had been mentioned as a major factor at the time of the minimum. I’ll look forward to reading the paper to see the details, but does it include (or do you have) any thoughts as to why there was such a large reduction or whether there’s any reason to expect more of the same in the near future? Also, I believe Maslowski’s results don’t assume a major trend in cloud cover (or at least that wasn’t mentioned in the abstract or press coverage), so I’d appreciate knowing your view as to what can be expected if cloud cover recovers.

  17. 117
    Dan Hughes says:

    re: #110. Chris, does this mean Arctic heat transfer processes are dominated by the direct radiative process and less so by convective heat transfer between the ice and the atmosphere? It would seem that during the long Arctic Winter radiative cooling dominates over convection from the tropics as ice is added during this period.

    How do the structural-dynamics causing breakup, and thus increasing the surface area-to-volume ratio between the liquid water and the solid ice, fit in? The surface area to volume ratio between the ice and the atmosphere also increases, but 90% of the ice is under water.

    In general I’m asking what are the dominant structural, hydrodynamic, and energy-balance related (radiative and convective heat transfer, for both the atmospheric and the ocean) phenomena and processes that govern the decreases and increases in Arctic ice volume?

    Thanks

  18. 118
    Chris O\'Dell says:

    Re #116 – Steve, we really do not know the ultimate reason for the decreased cloud cover this year. There was anomalously high Arctic SLP this year – so it could be related to the phase of the NOA or AO, but we’re really not sure at this point. We only conclude that thinner sea ice in the future will be more vulnerable to the variability in cloud cover. It could very well be that there is a feedback loop between sea ice and cloud cover, but that remains an open question and is beyond the scope of our paper. By the way, a rough time series of June+July cloud cover over the western Arctic from MODIS-Terra data for 2000-2007 is
    2000: .54
    2001: .65
    2002: .57
    2003: .63
    2004: .52
    2005: .46
    2006: .58
    2007: .40
    (70+ N latitude, 120-180W longitude)
    So you can see that 2007 was quite anomalous, but so was 2005 (which also had a very low ice amount). -Chris

  19. 119
    Chris O'Dell says:

    Re #117. Dan, I think I’ll have to defer this question to an expert on Arctic sea-ice modeling, which I am unfortunately not. I am more of an expert in the remote sensing of cloud properties using satellite instruments, which is my connection to the paper I referred to. I can only speculate that all the processes you mentioned are important, and that probably their relative level of importance changes from the arctic winter to the arctic summer. Certainly direct radiative processes are very important in both summer and winter, but then again I would guess that so are vertical (ocean-atmosphere) and horizontal (ocean-ocean) convective processes. -Chris

  20. 120
    Hank Roberts says:

    Who’s going to the Orlando meeting on the oceans and climate? March 2-7
    http://www.sgmeet.com/aslo/orlando2008/allsessions.asp

  21. 121
    Hans Vermeer says:

    552 billion tons of ice melted this summer from the Greenland ice sheet, according to preliminary satellite data to be released by NASA Wednesday. That’s 15 percent more than the annual average summer melt, beating 2005′s record.
    By SETH BORENSTEIN (quoting f.i. abdalati and serreze NSIDC)– 5 days ago / associated press
    Can anyone confirm this? Is this 552 km3 for real? That would be a pretty awkward melt-explosion.

  22. 122
    Tilo Reber says:

    re #104 “Or perhaps, given that it was 50 million years ago, that Ellesmere Island was located somewhat further to the south?”

    James, this is from a link that Gavin was kind enough to provide.

    “Paleolatitude studies suggest that the forest lay close to its present high-latitude position during the Eocene.”

  23. 123
    Tilo Reber says:

    re #108 “Turns out that “Ice algae are a very important part of the marine food web, contributing on average 57% to the total Arctic marine primary production.””

    Tim, it’s fascinating that there is enough energy inside the ice to allow these creatures to thrive. One thing did catch my eye in the article.

    “it provides a habitat for photosynthetic algae and nursery ground for invertebrates and fish during times when the water column does not support phytoplankton growth;”

    If the ice melted and the water was warmer, then would phytoplankton growth be supported? And would phytoplankton be a replacement microscopic food source? In Hudson bay, where it is melted 3 to 4 month a year, what is the microscopic food source that supports the food chain all the way up to seals and polar bears?

  24. 124
    Tilo Reber says:

    Re #107

    Phil – thanks I read the article. It was very informative. It also brought up some questions. Let me try them out on you.

    1. How do you select a timescale to determine if a trend is significant? Let’s say we throw out the El Nino year of 1998. Then we are saying that the slope established in the 22 years from 1975 to 1997 is significant, but the slope established in the 8 years from 1999 to 2007 is not. Somehow that doesn’t have a good intuitive feel to it.

    2. Let’s say that I accept that the slope from 1999 to 2007 is noise. Then comparing our current temperature chart to the hypothetical one created at your site, it would look like we are now at the very edge of the noise band. In fact, one might argue that the RSS data puts us over the band. This means that the temperature will have to start back up very soon or we will be out of the band and the data will become signal rather than noise. Guess we’ll have to do a wait and see for that one.

    3. The modeling experiment that we are talking about only tells us that the noise bands are just wide enough so that the temperatures that we have seen for the last 8 years could be noise. It doesn’t tell us that they are noise. That will be decided by the data that comes out in the next 2 to 3 years.

    4. I have a bit of a problem regarding anything in nature as noise in the same way that we generate computer noise. I don’t think that there is such a thing as noise in nature. We may identify major forcing trends and say that they represent the long term trend. And we may say that the noise represents a large number of minor and possibly unidentified forcing factors. But when you say that a forcing factor is and will remain the major forcing factor when you only have 22 years of data, and when the other forcing factors are neutalizing your dominant factor, even for 8 years, I think that is saying too much.

    5. The other thing that I wonder about is the modelers desire to use a 0.018 deg.C/yr CO2 forcing factor. And let’s say I accept that. But CO2 forcing is not linear. Supposedly the frequency band that CO2 is good at absorbing is already mostly absorbed by the current level of CO2. So more and more CO2 gives us less and less forcing. Can we know that there is enough residual forcing in CO2 to maintain a 0.018 deg.C/yr slope for any significant number of years?

  25. 125
    Phil. Felton says:

    Re #121

    552 km^2 is nothing compared with the additional 1.5 million km^2 of sea-ice that melted in the arctic in excess of the previous record.

  26. 126
    Steve Bloom says:

    Re #118: Thanks for the response, Chris. What’s most interesting is 2006 since it would have been another record low had it not been for an August cold snap (see NSIDC’s 2006 season report here). So perhaps Maslowski is right that it’s the warm water intrusion.

  27. 127
    dhogaza says:

    In Hudson bay, where it is melted 3 to 4 month a year, what is the microscopic food source that supports the food chain all the way up to seals and polar bears?

    The polar bears are on land, and eat very little if at all, during those months. Then when it freezes, off they go. Mmmmmm, fat juicy seal, smack-smack, chew-chew, tastes good after not eating for so long!

    Those who claim that polar bears will easily adapt to a more terrestrial lifestyle seem unaware that they’ve lost the habit (and perhaps the physiological adaptations, though I’m not sure) of foraging for food on land. Our other two bear species exist to a large extent on tubers and berries, meat forming a lesser portion of their diet. Much like people, which is one reason they love our garbage cans so much. We eat food that black bears and griz love.

    Polar bears are devoted to meat, fresh meat.

  28. 128
    Hank Roberts says:

    The warm water coming from the Bering Sea, I think?

    “The climate and ecosystem of the Bering Sea has changed over the previous fifty years. There are two shifts in climate associated with increased warm temperatures and other factors, the first in the late 1970s and again around 2000. There was a major ecosystem reorganization following the late-1970s shift. These changes represent a transition from primarily cold Arctic ecosystems earlier in the 20th century, dominated by sea ice, to sub-Arctic conditions…. a shift toward warmer temperature of 2 deg C around 2000. Of particular importance is that recent winter temperatures are above the freezing point, indicating no or little sea ice in the southeastern Bering Sea for the previous four years (Fig 2 (b))….”
    http://www.beringclimate.noaa.gov/bering_status_overview.html

  29. 129
    Pekka Kostamo says:

    Re 125: Phil: 552 cubic km vs. 1.5 million square km ??

    In my opinion the Arctic Ocean change is indeed passing a tipping point. A rough outline would be as follows:

    A climate system of two physical seasons (“winter” and “spring” only) is developing into a 4 seasons system.

    In the “old” process the WINTER season was very clear. Ice and snow covered sea surface, no solar energy input (heat transport by the winds from lower latitudes), radiative cooling from cold (like -20 degC) surfaces is determined by the greenhouse gases. Albedo is high but not relevant. Little evaporation. No wind driven mixing of sea water. Hard fresh water ice forming at times on the surface and gradually replacing older one.

    SPRING season with wet ice floes, little open water and some wet snow, high albedo. Solar energy input 24/24, heat transport to the area also by winds, Out-radiation from surfaces at 0 degC. Evaporation from water surface (predominantly fresh water). Little wind driven mixing of sea water, low wind traction to sea surface circulation.

    The new SUMMER season brings open water. Low albedo meets 24/24 solar input, outwards radiation from sea surface a few deg above 0 degC. Wind driven mixing of surface waters and strong wind traction to speed up the larger scale circulation. Higher evaporation rate, also start generating salt particles that act as condensation nuclei.

    The new AUTUMN season is likely to be short initially. Surface waters cool and new (softer) ice is formed from saline sea water. Energy input is initially from sea and air currents from lower latitudes as the solar input goes to zero. Wind driven mixing of surface waters helps cool the water top layer until ice forms.

    Where did the extra heat captured in 2007 go? Most of it still circulates in the Beaufort gyre, in the uppermost 50 meters of the ocean. It is not efficiently leaked out via the surface as there is a layer of heat insulation (ice and snow) above it. (Ice formed rather rapidly). There is little mixing so it moves downwards very slowly. How it will express itself next spring will be interesting to see.

  30. 130
    Elmar says:

    Re#125
    552 kubic, not square km. I don’t know if it’s true, but we’ll find out from the press release tomorrow.

  31. 131

    Chris posts:

    [[Steve, we really do not know the ultimate reason for the decreased cloud cover this year. ]]

    Could it have anything to do with ocean die-off, and maybe reduced production of DMS by algae? If anyone remembers that theory…

  32. 132

    Tilo posts:

    [[How do you select a timescale to determine if a trend is significant? Let’s say we throw out the El Nino year of 1998. Then we are saying that the slope established in the 22 years from 1975 to 1997 is significant, but the slope established in the 8 years from 1999 to 2007 is not. Somehow that doesn’t have a good intuitive feel to it.]]

    You wouldn’t throw out the 1998 point. It’s still a valid data point. You’d just start early enough to get a significantly large sample.

  33. 133

    Tilo also posts:

    [[The other thing that I wonder about is the modelers desire to use a 0.018 deg.C/yr CO2 forcing factor.]]

    They don’t “use” a forcing, forcing is one of the outputs of the run.

    [[ And let’s say I accept that. But CO2 forcing is not linear. Supposedly the frequency band that CO2 is good at absorbing is already mostly absorbed by the current level of CO2. So more and more CO2 gives us less and less forcing. Can we know that there is enough residual forcing in CO2 to maintain a 0.018 deg.C/yr slope for any significant number of years?]]

    Yes.

  34. 134
    Tilo Reber says:

    “The polar bears are on land, and eat very little if at all, during those months. Then when it freezes, off they go. Mmmmmm, fat juicy seal, smack-smack, chew-chew, tastes good after not eating for so long!”

    re #127 Hi dhogaza. I probably wasn’t clear with my question. Since Hudson bay is ice free 3 to 4 month a year, it’s eco system would undergo the same change with regards to microorganisms as the pole if it melted 3 to 4 month a year. Since Hudson bay has no problems supporting all the life forms required to create the food chain all the way up to the seal and the polar bear, then could the arctic also create such a food chain in the abscense of the microorganisms that live in the ice. Phytoplankton might be the right candiate for the bottom of that food chain.

    But concerning the polar bears, one of the bloggers in Churchill mentioned that the bears killed 11 seals there while waiting for the pack ice to form up this year. I’m sure that their hunting success goes way down without the ice, but it’s good to know that they’re not completely helpless. He also said that the bears left to go out on the ice on 17th Nov. this year. The norm in the past was around the 14th of Nov.

  35. 135
    Jim Cripwell says:

    Ref 124 Steve Bloom writes “That will be decided by the data that comes out in the next 2 to 3 years.” and
    “Can we know that there is enough residual forcing in CO2 to maintain a 0.018 deg.C/yr slope for any significant number of years?” Your analysis is absolutely right. Thanks to Bali, pretty well all nations of the world will follow their own ideas of what to do about ghgs. Which means that ghgs are going to continue to rise at the same rate, or even faster than they have done for the first part of the 21st century. We will carry out the “experiment” to see what happens with ever increasing quantities of CO2 in the air; at least until Copenhagen in 2009. How long it will be before we know whether temperatures are actually dropping is not known, but maybe if the amount of ice in the arctic is more in Sep 2008 than it was in Sep 2006, people may want to take a good look at what is happening to global temperatures. The latest data fron NCDC/NOAA for November 2007, shows that the trend towards lower temperatures which has persisted for the whole of 2007 is continuing. Year to date, 2007 is the 4th warmest on record. There is still no sign of rising world temperatures in the 21st century.

  36. 136
    Ray Ladbury says:

    Tilo, Nature does not deal with anecdotal success–e.g. 11 kills by a few polar bears at a particular time and place. What matters is whether food supply sustains a genetically viable population. If not, the species adapts or dies. Ecosystems have a remarkable way of persisting. The question is whether those ecosystems that survive are also conducive to human survival and to our aesthetic preferences as well. I suppose we’ll always have the cockroaches and the rats.

    [Response: And the bacteria. Don't forget the bacteria. After reading Andy Knoll's book on Early Earth ecosystems, I realized that we're all basically guests of the prokaryotes. --raypierre]

  37. 137
    Ray Ladbury says:

    So, Jim Cripwell, we are still waiting to hear what you would consider “evidence” for ghg as the cause of the current warming epoch. You seem to be putting a whole helluva lot of emphasis on how much ice we have in Sep. 2008. Would that be your proof? You also keep saying there’s no sign of warming in the 21st century. Aside from being an incorrect assertion, would a convincing warming trend after, say 2005 be your proof? If so, for how long?

  38. 138
    J.C.H. says:

    NASA’s Goddard Institute for Space Studies (GISS) predicted yesterday that 2007 will be Earth’s second-warmest year on record. – http://sciencenow.sciencemag.org/cgi/content/full/2007/1211/3

  39. 139
    Chris O'Dell says:

    Re #126. Steve, can you point me to the Maslowski reference you’re referring to?

  40. 140
    Dylan says:

    Would someone be able to give me a simple layman’s explanation of why the rate of ice melt and glacial retreat in Greenland (and elsewhere in the Arctic) does not exactly match the temperature record? That is, the hottest years in Greenland seemed to be around 2002-2004, but the fastest race of ice melt appears to be a several years later (this is using the GISTEMP data along with the GRACE observations). I can think of various possible explanations, but I’d prefer to have an expert confirm the correct one.

  41. 141
    Tilo Reber says:

    “Nature does not deal with anecdotal success–e.g. 11 kills by a few polar bears at a particular time and place. What matters is whether food supply sustains a genetically viable population.”

    I’m with you Ray. I don’t wish to suggest that the PB can survive without ice. I certainly don’t believe that they can. I was simply surprised to hear that they can do some level of hunting without ice. But in the long run, I’m convinced that they would die off without the ice. It appears that the annual iceless interval through which a population can sustain itself is around 3 to 4 month.

  42. 142
    Steve Bloom says:

    Re #139: Maslowki et al’s AGU presentation was U33B-04 and had a somewhat uninformative abstract, but this BBC article summed things up nicely. Also, this AP article has several interesting quotes from some senior scientists. See also this article regarding session U33B-01 on warm water intrusion.

  43. 143
    Steve Bloom says:

    Plus they had a second presentation on validating their model:

    (C22A-06) “Understanding Recent Variability in the Arctic Sea Ice Thickness and Volume – Synthesis of Model Results and Observations

    “We examine the diminishing sea ice thickness trend in the Arctic Ocean using results from the NPS 1/12-degree pan-Arctic coupled ice-ocean model. While many previous studies have analyzed changes in ice extent and concentration, this research focuses on ice thickness as it gives a better indication of ice volume variability. The skill of the model is evaluated by comparing its ice thickness output to actual sea ice thickness data gathered during the last three decades. This includes the model comparison against the most recently released collection of Arctic ice draft measurements conducted by U.S. Navy submarines between 1979 and 2000. Our model indicates an accelerated thinning trend in Arctic sea ice during the last decade. This trend is robust and independent of timescales for surface temperature and salinity relaxation. The validation of model output with submarine upward-looking sonar data supports this result. This lends credence to the postulation that the Arctic is likely to be ice-free during the summer in the near future.”

    While I’m at it here’s the abstract from the first session:

    (U33B-04) “On the Relative Importance of Freshwater Fluxes and Variability From the Arctic Ocean into the North Atlantic

    “We use a high resolution coupled ice-ocean model of the Pan-Arctic region forced with realistic atmospheric data to investigate the variability of freshwater content within the Arctic Ocean as well as sea ice and liquid freshwater fluxes into the North Atlantic during 1979-2004. Modeled fluxes are validated against recently published estimates. Results are analyzed to compare the relative contribution of the total combined liquid and solid freshwater flux through the two main pathways: Fram-Denmark Strait (FDS) and the Canadian Arctic Archipelago- Davis-Hudson Strait (CAADHS). Our results suggest the relative importance of the freshwater flux through CAADHS into the Labrador Sea. This implies the need for ocean models to adequately represent mass and property fluxes through the narrow and shallow passages of the Canadian Archipelago and Davis and Hudson Straits. We argue that this requirement must be satisfied to advance studies of the Atlantic Meridional Overturning Circulation (MOC) and especially its variability. Given the recent record sea ice melt in the Arctic Ocean, it is critical that global ocean and climate models improve their skill in simulating and predicting effects of changing exports from the Arctic Ocean into the North Atlantic.”

    It’s maslowsk[at]nps.edu, BTW.

  44. 144
    Phil. Felton says:

    Re#129
    Pekka Kostamo Says:
    18 December 2007 at 4:44
    “Re 125: Phil: 552 cubic km vs. 1.5 million square km ??”

    The original quote was 552 billion tons or ~552×10^9 m^3 if we estimate the average thickness of the ice melted this year as 1m (very conservative) then 1.5 million sq. km is 1.5×10^12 m^3

  45. 145
    Tilo Reber says:

    Re#135

    Jim, most people on this forum will disagree with me, but I’m glad that we get to extend the experiment for a couple of years. Here is my reasoning (or lack thereof). We are currently at or near a solar minimum. Solar cycle 24 has been delayed by at least a year, and it may be delayed longer. We have had low solar activity for much of this year, and it will probably contiue for a while longer. There are split opinions on cycle 24, but many people believe it will be a weak cycle. If it is a weak cycle, then we will get a chance to gather some evidence about the relative strength of solar forcing vs CO2 forcing. If CO2 forcing dominates solar forcing, then we should continue to have temperature go up during this time. If it doesn’t, then we may actually turn around and go down for some period of time – even with the current levels of CO2. I believe that the IPCC position is that CO2 is the driving factor for global warming and solar forcing is too weak to reverse it. There are a few people who disagree with that. I’m anxious to have the empirical evidence, and the next couple of years just may provide some of it.

  46. 146
    David B. Benson says:

    Here is a form of ‘tipping’ which simply is not publized enough:

    http://blogs.nature.com/climatefeedback/2007/12/coral_reefs_are_on_the_ropes.html

  47. 147
    Hank Roberts says:

    > if CO2 forcing dominates solar forcing, then we
    > should continue to have temperature go up during
    > this time.

    Well, you’re leaving out other factors and other predictions for the same time span, aren’t you?

    This, I think, takes the range of likely solar influence into account, and they think it’s minor:

    http://inel.wordpress.com/2007/08/09/hadley-centre-decadal-climate-prediction-system/

  48. 148
    Tilo Reber says:

    Re #147. “Well, you’re leaving out other factors and other predictions for the same time span, aren’t you?”

    Yes I am. But CO2 and solar forcing seem to be one major place where opinions diverge.

    “This, I think, takes the range of likely solar influence into account, and they think it’s minor:”

    It will be interesting to see if the new model works. Obviously how well they estimate the different forcing factors will play into that.

    From one of the referenced articles:

    “The climate projection, published today in the journal Science, suggests that a natural cooling trend in eastern and southern Pacific ocean waters has kept a lid on warming in recent years.

    And it will continue to do so, scientists say, but not for long.”

    I wonder what “a natural cooling trend” is?

  49. 149
    Nick Barnes says:

    Phil Felton @ 144: yes, the volume of sea ice melt is much greater than the Greenland mass imbalance. But many millions of square kilometres of sea ice melt every year (typically about 7 million), and the thickness of the ice which does not melt also varies with the seasons. In terms of volume, several tens of percent of the total sea ice melts – and refreezes – every year. It’s a very dynamic system, so it doesn’t need to be thrown very far out of balance to fall off a cliff: losing all the sea ice is only a factor of two or three away from the normal dynamic range.

    In comparison, the Greenland ice sheet is approximately balanced. It has a total of 2-3 million cubic kilometres of ice (a hundred or so times the total sea ice volume), and yet annual variations are usually only in the tens of cubic kilometres (because it’s in a deep freeze, the main ice mass processes are snowfall and glacier flow, not melt and freeze): much less than one percent of the total.

    The “552 billion tons” number is important because it is considerably outside past records, showing that the usual balance of the GIS has become an imbalance. The mechanisms are a combination of surface melt and accelerated ice flow.

    If the ice sheet pessimists are right – and they have some good arguments and models on their side – this number is a portent of serious ice loss to come.

    So the difference is this: we are losing sea ice right now (in ten years or less it may be all gone) whereas the GIS is still with us (the fear is that in ten or twenty years we might be seeing thousands or tens of thousands of cubic kilometres of annual loss). Personally I’m filing the GRACE numbers away as a benchmark, something to which to compare future ice imbalance numbers, as the ice flow accelerates.

  50. 150
    David B. Benson says:

    Tilo Reber (148) — I’ll hazard the amateur opinion that the ‘natural cooling trend’ is related to the upwelling of cold bottom water off the west coast of South America.


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