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An icy retreat

Filed under: — group @ 26 July 2010 - (Deutsch) (Español)

Guest Commentary by Dirk Notz, MPI Hamburg

It’s almost routine by now: Every summer, many of those interested in climate change check again and again the latest data on sea-ice evolution in the Arctic. Such data are for example available on a daily basis from the US National Snow and Ice Data Center. And again and again in early summer the question arises whether the most recent trend in sea-ice extent might lead to a new record minimum, with a sea-ice cover that will be smaller than that in the record summer of 2007.

However, before looking at the possible future evolution of Arctic sea ice in more detail, it might be a good idea to briefly re-capitulate some events of the previous winter, because some of those are quite relevant for the current state of the sea-ice cover. The winter 2009/2010 will be remembered by many people in Europe (and not only there) as particularly cold, with lots of snow and ice. Not least because of the sustained cold, some began to wonder if global warming indeed was real.

Such questioning of global warming based on a regional cold period of course neglects the crucial difference between weather and climate, with the former being the only thing that we as individuals will ever be able to experience first hand. A single regional cold spell has not a lot to do with climate – let alone with global climate. This becomes quite obvious if one instead considers the mean temperature of the entire globe during the last 12 months: this period was, according to the GISS data, the warmest 12-month period since the beginning of the records 130 years ago. Regarding sea ice, it was particularly important that temperatures in parts of the Arctic were well above average for most of the winter. This was directly experienced by some members of our working group during a field experiment at the West Coast of Greenland.


Fig. 1: Temperature anomaly at 1000 hPa during the first half of January 2010 with respect to the period 1968-1996. Warm anomalies in the Arctic and cold anomalies in Northern Europe and parts of North America are clearly visible.

The initial plan of this field experiment was to study the growth and decay of sea ice in great detail throughout an entire winter. In particular, we wanted to focus on the evolution of very young sea ice that had just formed from open water. Therefore, we wanted to start our measurements just before initial ice formation, which usually takes place in mid-November, at least according to past experience of the local Greenlandic population. Hence, we traveled to our measuring site close to the Greenlandic settlement of Upernavik in early November to put out our measuring buoys. We were hoping that ice formation would start shortly after we had put out the instruments such that they were protected from storms and waves. However, with temperatures that were often more than 10°C above the long-term mean, sea ice was nowhere to be seen. Even in January, there were days on end with above 0°C temperature and heavy rain fall. Finally, in February a stable ice cover formed, which of course remained relatively thin and which hence had melted completely by mid May.

The fact that it was sometimes warmer at our measurement site at the West Coast of Greenland than it was in Central Europe at the same time surprised us quite a bit. However, some recent studies indicate that such a distribution of relatively high temperature in parts of the Arctic and relatively low temperature in Northern and Central Europe and parts of the US might become somewhat more wide-spread in the future. While the Arctic has always shown large internal variability that lead to large-scale shifts in weather patterns, in the future the ongoing retreat of Arctic sea ice might cause those weather patterns to occur more often that allow for Northerly winds to bring cold air from the Arctic to the mid-latitudes. Hence, it is quite possible that because of the retreat of Arctic sea ice, some smaller parts of the Northern Hemisphere will experience pronounced cold spells during winter every now and then. The mean temperature of the Northern Hemisphere will nevertheless increase further, and the export of cold air from the Arctic of course leads to warm anomalies there.


Fig.2: Evolution of Arctic sea-ice extent from September 2009 until mid May 2010. The blue line denotes the mean extent from 1979 until 2000, while the shaded region denotes the variability during that time (± 2 standard deviations)

But let’s return to the evolution of Arctic sea ice. Because of relatively high temperatures, Arctic sea-ice extent remained well below the long-term mean for most of the preceding winter. However, in March temperatures suddenly dropped for a couple of weeks, in particular in parts of the Barents Sea and in parts of the Beaufort Sea. This in turn lead to the formation of a thin ice cover in these regions, which caused a marked increase in observed sea-ice extent. For the measurement of this extent, it doesn’t matter at all how thick the ice is: any ice, however thin, contributes to sea-ice extent. Therefore, only considering a possible “recovery” of just the extent of Arctic sea ice always remains somewhat superficial, since sea-ice extent contains no information on the thickness of the ice. A much more useful measure for the state of Arctic sea ice is therefore the total sea-ice volume. However, for its estimation one additionally requires information on the overall distribution of ice thickness, which we have not been able to measure routinely in the past. While this will hopefully change in the future because of the successful launch of the Cryosat 2 satellite a couple of weeks ago, at the moment we unfortunately must rely on judging the current state of the Arctic sea-ice cover mostly by its extent.


Fig.3: Evolution of Arctic sea-ice extent since April 2010 in comparison to 2007 and 2009. The blue line denotes the mean extent from 1979 until 2000, while the shaded region denotes the variability during that time (± 2 standard deviations)

Because of the very low thickness of much of the Arctic sea ice, it wasn’t too surprising that at the end of the winter, sea-ice extent decreased rapidly. This rapid loss lead up to the lowest June sea-ice extent since the beginning of reliable observations. After this rapid loss of the very thin ice that had formed late in winter, the retreat slowed down substantially but the ice extent remained well below the long-term mean. Currently, the ice covers an area that is slightly larger than the extent in late July of the record year 2007. However, this does not really allow for any reliable projections regarding the future evolution of Arctic sea ice in the weeks to come.

The reason for this is mostly that sea ice in the Arctic has become very thin. Hence, in contrast to the much thicker ice of past decades, the ice now reacts very quickly and very sensitively to the weather patterns that are predominant during a certain summer. This currently limits the predictability of sea-ice extent significantly. For example, in 2007 a relatively stable high-pressure system formed above the Beaufort sea, towards the north of North America, leading to rapid melting of sea ice there. If again such stable high pressure system forms in the Arctic throughout the coming weeks, we might well experience a sea-ice minimum that is below the record minimum as observed in 2007. However, if the summer should turn out to be colder than during the previous years, a sea-ice minimum similar to that observed in 2009 would not be too surprising. Hence, at the moment all that remains is to wait – and to check again and again the latest data of Arctic sea-ice extent.


Fig.4: Arctic sea-ice extent on June 28July 20, 2010. The orange line denotes the mean extent on June 28July 20 from 1979 until 2000.

Dirk Notz is head of the research group “Sea ice in the Earth System” at the Max-Planck-Institute for Meteorology in Hamburg.

The original version of this article was published in German at KlimaLounge

References:

Honda, M., J. Inoue, and S. Yamane (2009), Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters, Geophys. Res. Lett., 36, L08707, doi:10.1029/2008GL037079.

Notz, D. The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss. Proc. Nat. Ac. Sci. 106(49), 20590–20595, doi:10.1073/pnas.0902356106 (2009).

Polyakov, I. V., and M. A. Johnson (2000), Arctic decadal and interdecadal variability, Geophys. Res. Lett., 27(24), 4097–4100.

Credits:
Figure 1: NOAA ESRL Physics Science division

Figures 2-4: Data: NSIDC, Graphics: D. Notz.


175 Responses to “An icy retreat”

  1. 51
    Didactylos says:

    pete best asked: “As Arctic summer sea ice decline is a central prediction of AGW theory can it be claimed that the increased summer sea ice melt and possibly overall its thickness (volume) is in line with these predictions taking into account natural variability of course ?”

    Good question! And the answer is (surprisingly) no. Arctic ice is doing much worse than predicted in the last IPCC report. This is one of those errors that you don’t get to hear about so much.

    In fact, current Arctic sea ice extent is completely outside the range projected by the IPCC models. They didn’t forecast it being this low until 2050.

    Reference figure 13 in the Copenhagen Diagnosis.

  2. 52
    Chris Dudley says:

    Mauri (#6),

    The updates are not always daily for the Arctic Ice Volume calculated by the Polar Science Center. In fact it was about a month between the last update and the most current one with data through 7/17/2010.

    One should also be careful reading the graph. It is given as an anomaly relative to a 1979-2009 average and the average plot here: http://psc.apl.washington.edu/ArcticSeaiceVolume/images/PIOMAS_daily_mean.png which marks months at their midpoints rather than their beginnings. This may be what caused Joe Romm to incorrectly claim that the ice volume was below 10,000 km^3 on 6/27/2010 http://climateprogress.org/2010/06/27/arctic-sea-ice-extent-volume-record-nsidc-volume/ It does appear to be around 8,000 km^3 now though.

    Basically, the resolution of the graphs is daily but the updates may not be.

  3. 53
    Peter says:

    Just a question to all- what is, if there is one the lag time in CO2?

    Arctic ice is melting- we know this- but is this in result to the current 392ppm CO2 level- or from C02 levels of 20, 30 years ago.

    Dr. Hansen has said the ice at the poles will begin to melt when CO2 passes 350ppm.

  4. 54
    wilt says:

    #48 Didactylos said: We can easily discount the year-to-year variation

    If so, why then was the outcome in 2007 not ignored by the warmists? Instead, it was presented as a kind of final proof that Armageddon was about to start. In my view, your desire to ignore all data that do not fit with your theory, resembles the attitude that many warmists had with respect to the global temperatures of the last 15 years (you have probably noticed that by now even respected AGW proponents like S. Solomon use the term ‘flattening’ for the temperatures in recent years).

    [Response: Stop fighting against strawmen. 'Proof of armageddon'? Really? Please stick to substantive points that relate to things that scientists have actually said about this - for instance here, rather than someone's fevered imaginings. - gavin]

  5. 55

    45 (wilt),

    In view of the decisive effects of wind and ocean currents, would you agree that the minimum value of Arctic sea ice is more related to weather than to climate?

    No, I wouldn’t, because of the point I keep making, which I believe is a re-iteration of Dr. Notz position. A quote from the original post above:

    Therefore, only considering a possible “recovery” of just the extent of Arctic sea ice always remains somewhat superficial, since sea-ice extent contains no information on the thickness of the ice.

    Ice extent, as I’ve said, is a mere proxy for actual amount of ice. Changes in extent from one year to the next border on irrelevant, just as changes in global mean temperature from one year to the next tell you nothing of the long term trend.

    I would agree that with the current, grossly abnormal degree of Arctic summer ice melt, which is a clear result of AGW, because it has “loosened” the ice and so seemingly allows it to “move” more than in the past, then the measure of ice extent as a proxy for actual ice volume is very subject to weather patterns. The fact that currents and local weather have such a strong effect on overall extent is meaningless in the context of the true issue, which is whether or not increased temperatures are melting more Arctic ice year to year, and even that will be subject to some degree to variations in local Arctic temperature which are in turn a result of local Arctic weather.

    This is not equivalent to saying “that the minimum value of Arctic sea ice is more related to weather than to climate,” and that statement is patently false.

    In other words, whatever the outcome this year, neither AGW-proponents nor their adversaries should claim it as a ‘victory’ for their point of view.

    First, I get so tired of positioning the AGW debate as a game, with points scored, and to be won or lost. This is particularly true because a denier will always choose to score points with short term events (such as this year’s summer ice minimum with respect to last, or 2008′s global mean temperature as compared with 1998) when these are not valid observations.

    Second, no one with any sense is going to claim “victory” based on such annual outcomes. Even a completely ice free Arctic is not a victory, but merely another piece of mounting evidence supporting the theory which is already pretty much proven beyond doubt.

    Third, it’s not a victory, it’s the most debilitating defeat the human race may suffer in its short history. Being proven right will not be a victory (or rather, it will be Pyrrhic).

    You cannot watch the globe on a day to day, month to month or year to year basis and use that as a measuring stick for whether or not the theory of GHG and climate change is correct, or proven.

    Fact: Global temperatures continue, as a long term trend, to rise.
    Fact: Arctic ice continues, as a long term trend, to retreat.
    Fact: Glaciers, Greenland and Antarctic ice masses, as a long term trend, continue to shrink.

    Playing a game of watching for which particular indicator supports your position this year or next is silly. This is sadly very true when I know that (a) all of the physics behind AGW is correct and (b) the evidence is most pronounced at the poles and so (c) sometime within the coming decades, during my own lifetime, I expect to see a summer completely devoid of Arctic ice.

    Only an unexpected and at this point increasingly unlikely negative feedback in the climate system will save us from (c), and I’m not very hopeful that one will arise.

    It doesn’t have to happen this year, or with a linear downward trend. That’s not the point. It is going to happen. Period.

    P.S. I don’t believe, from all you’ve said, that you’ve either completely read or understood Dr. Notz’s post. Please go back and read it, several times, from start to finish.

  6. 56
    Ray says:

    Good article. I was surprised at the skepticism about our current ice volume measurements since Polar Science Center modeling estimates seemed to verify well. It’s hard to imagine a heavy winter rain in Western Greenland.

  7. 57
    Ron R. says:

    In the context of retreating sea ice, I wonder if the term should be devolution rather than evolution.

  8. 58
    pete best says:

    Re #51, I thought as much myself.

  9. 59
    Kevin Stanley says:

    RE: wilt’s “If so, why then was the outcome in 2007 not ignored by the warmists?”

    Well, in addition to Gavin’s point about sticking with what has actually been said by serious people, and Bob’s (and others’) point about extent being an imperfect (potentially quite poor) proxy for the amount of ice present, there’s also this: No one had ever seen ice extent that low before. Remember that since extent is measured by looking at area with 15% or greater ice coverage, then while it is possible to have high extent with fairly little ice, it is impossible to have low extent with a large amount of ice (unless, as another poster suggested, it’s suddenly become incredibly thick where it does exist, and projects only down into the sea and not up where we might notice).

    So while summer 2007, in retrospect, probably wasn’t a huge departure from the ongoing trend in ice amount…it was the moment when rate of the ongoing ice loss became *glaringly obvious*.

    In other words the year-to-year variation in amount of ice between 2006-2007 really wasn’t all that important in the big picture. It’s just that weather conditions conspired to make it obvious from orbit, through the low extent.

    Make sense?

  10. 60
    Edward Greisch says:

    41 Bob (Sphaerica): The buoys move around so much it is hard to see how anybody can make anything consistent out of it.

  11. 61
    Septic Matthew says:

    It is an interesting intellectual/emotional experience to watch these processes evolve in real time while reflecting that the judgment as to overall warming and cooling depends on decades of measurements. I check “Cryosphere” and other similarly themed sites with reliable data at least a few times per week.

    Today, global ice extent is nearly average (across the past 3 decades) for this time of year:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg

    That’s only a single time series, but it certainly is not evidence for global “warming”. With hundreds dead from cold in the Andes this month, what we have now is one of the oscillations in which the NH is above average in temp, and the NH is below average in temp (I make no claim as to “exact balance”.)

    According to another site, the Arctic (above 80 degrees N) has below average temperatures for this time of year, and has had for a few weeks now, co-incident with a dramatic reduction in the rate of Arctic ice melt (Danish Meteorological Institute: http://ocean.dmi.dk/arctic/meant80n.uk.php) since the rapid melt of the previous 3 months.

    Inferences about long-term climate change based on events of the last 7 months are imaginary, though undoubtedly fun.

  12. 62
    Septic Matthew says:

    oops, I meant that the Sh is now below average in temp. I hope that’s obvious in “context”.

  13. 63
    Hank Roberts says:

    ‘wilt’ above starts from this mistaken idea:

    > an ice layer that is supposed to get thinner year after year.

    Where did you get that one, wilt? Why do you believe it?

  14. 64
    wilt says:

    #55 Bob Spaerica wrote about “the current, grossly abnormal degree of Arctic summer ice melt”, and apperently he was referring to the rapid rate of melt in June.
    However, in my first contribution (#12) I discussed the July 2010 data. I wrote that in my view there is a discrepancy between the suggested sensitivity of this ‘very thin’ ice and the observation that in this July month the daily loss of sea ice is not higher but much lower than in the previous years.

    I agree with you that it would be silly to call an ice-free Arctic a victory for anyone.
    Furthermore, I have read and understood what Dirk Notz has written in his post. Basically, he argues that the sea ice in the Arctic has become very thin, and hence, in contrast to the much thicker ice of past decades, the ice now reacts very quickly and very sensitively to the weather patterns that are predominant during a certain summer.

    In view of those data, and also since the conditions at the Arctic this summer do not seem to be not completely different from those in 2008 or 2009, I remain sceptical about the concept that a large part of the remaining ice will melt soon. But we will see, by the end of summer.

  15. 65
    Doug Bostrom says:

    Septic Matthew says: 26 July 2010 at 3:29 PM

    Nice misunderstanding, SM. The graph you show of course includes -all- sea ice, both that in precipitous decline in the Artic as well as that surrounding the Antarctic. The seemingly counterintuitive increase of Antarctic sea ice of course helps to lessen (hide?) the decline visible in the graph. See this post at Skeptical Science for some background information on why Antarctic sea ice is behaving as it does. Others I’m sure will volunteer more corrections.

  16. 66
    dhogaza says:

    Septic Matthew:

    That’s only a single time series, but it certainly is not evidence for global “warming”.

    Ahem, it’s not evidence for uniform warming across the globe.

    However, it is evidence that science is on the right track. Scientists have, after all, been predicting that sea ice in the southern hemisphere would behave differently than sea ice in the arctic for many years. You’ve correctly pointed out that this is exactly what’s happening.

    What’s odd is that you think that when scientific predictions are supported by observations that somehow this undermines science.

    Why is that, SM?

  17. 67

    64 (wilt),

    …and apperently he [Bob] was referring to the rapid rate of melt in June…

    No, I was referring to the long term trend, in which the summer ice retreat for all recent years is between two and four standard deviations below the long term average. As I’ve said, month watching and year watching is pointless. Trends are what matter.

    Extent Measure 1 with standard deviation
    Extent Measure 2 with standard deviation

    and this:

    Northern Hemisphere Extent Anomalies 1980-2010

    Basically, he [Dr. Notz] argues that the sea ice in the Arctic has become very thin, and hence, in contrast to the much thicker ice of past decades, the ice now reacts very quickly and very sensitively to the weather patterns that are predominant during a certain summer.

    Yes. So weather very much affects extent from month to month and year to year, but the underlying problem is the temperature change and ongoing, increased melt due to abnormally high temperatures year round, including earlier and later melt seasons, not the wind and weather.

  18. 68

    61 (Septic Matthew),

    Today, global ice extent is nearly average (across the past 3 decades) for this time of year

    Except that this is always going to be the case, because while a nightless summer is happening on one pole, a sunless winter happens on the other. While ice cover shrinks here, it grows there, so the sum will always be about the same, even when ice completely vanishes from the Arctic in the summer.

    It’s like looking at a flat tire and pointing out that it’s only ever flat on the bottom, the other sides are always round, so it’s really not that big of a problem.

    And I rather doubt that global temperatures will ever reach the point where they are above freezing at the poles even in winter, so that the numbers you present would ever drop. It’s a frightening thought, though.

    So….

    Very nicely distracting misrepresentation of data and facts, though. You do the denial crowd proud. You should do guest posts over at WUWT.

  19. 69
    Didactylos says:

    wilt said “I remain sceptical about the concept that a large part of the remaining ice will melt soon.”

    You really aren’t paying enough attention, are you? Only a small part of the remaining ice has to melt to equal recent years, and what happens is entirely dependent on weather conditions over the next couple of months.

    I just can’t work out what you are trying to prove. Do you fondly imagine that Arctic ice has begun to turn around? There is no evidence for such an idea, and overwhelming evidence to the contrary. If you want to live in a pretend world where what you believe is always true, then fine. Just don’t come here seeking justification.

    Arctic sea ice area is today missing 1.3 million square kilometres, compared to the baseline average. That is slightly worse than both preceding years, and comparable with 2007, 2008 and 2009. No doubt last year and the year before you were sceptical that so much ice could melt by the end of the season, but despite varied weather, we set the 2nd and 3rd record lows.

    In just a couple of days, the ice area will drop below the baseline minimum, with weeks to go in the melt season. So, it’s game over. There is simply no way a miracle can occur and the minimum area be above average. All that remains to be seen is exactly how much below average it is.

    (Note: this post mostly discusses area, not extent. It applies to both, but numbers and dates may differ.)

    Why does 2007 get so much attention? Blame the media for the hype. For the scientific attention: why not? It was an unusual year, some claim unprecedented. If you go back and look, you will find much speculation about “tipping points”. But from the point of view of communicating climate change, record years provide volume, but not insight. As soon as the record isn’t immediately broken, the boring old “it’s stopped” arguments come crawling out. And I really wish they wouldn’t.

  20. 70
    Rattus Norvegicus says:

    John @50:

    Walt Meier has a couple of posts up about PIOMAS vs. the Navy models (he had a bit to do with developing the Navy model (PIO?). BTW, he is legit and works at NSIDC now. The posts are worth reading even if the comments aren’t :).

  21. 71
    Brian Dodge says:

    wilt — 26 July 2010 @ 8:38 AM “I don’t understand how this would be compatible with the ‘very thin ice’ suggested by Dirk Notz.”
    Bob (Sphaerica) — 26 July 2010 @ 11:08 AM “Wind matters, AMO matters, but it’s not nearly as important temperature, period, and the effect of local (Arctic) weather on temperature.”
    Greg Robie — 26 July 2010 @ 9:33 AM “Comparing what is being observed this year with 2007, it almost constitutes a sea change.”
    Walt Meier — 26 July 2010 @ 11:18 AM “I’m a little bit skeptical that the volume anomaly is so low.”

    “Now consider Fig. 2 B, which shows the impact of a much thinner ice-thickness distribution: Because here most of the ice has a thickness of around 1 m, the area that becomes ice-free during summer crucially depends on the amount of total melting: In the example shown here, 90% of the area remains ice covered for a total melt of 0.5 m during a relatively cool summer, whereas only 50% of the area remains ice covered for 1 m of total thinning during a warmer summer.”
    “Because of the nonlinear ice-thickness distribution, a gradual thinning of the ice cover can initially lead to an acceleration, and, at some point, a very rapid loss of ice-covered area during summer.”[1]

    “In the simulations, ice retreat accelerates as thinning increases the open water formation efficiency for a given melt rate…” [2]

    I downloaded data from IJIS, Normalized each years data to the maximum extent for that year, and plotted them aligned to start at the day of maximum extent [3]. Note the relatively low spread in extent of previous years near the midpoint of the melt. The divergent trajectories due to weather affect the final minimum, but even years with higher final extent (e.g. 2009) are integrating the effect of higher temperatures in loss of thickness and volume distribution.

    Its pretty clear to me that this year exhibited a “sea change” in the dynamics of ice melt at the start of the year. Wind, AMO, Temperature all matter, and affect the start, rate, and end point of the melt(extent), but the thickness of the ice(volume) has a strong effect too. The decreasing minimum extents of the last few years have been accompanied by decreasing thickness and volume, and the persistent ice has integrated that change. The graphs and pictures available to us lay people have obscured the change in volume until recently[4]; Ice that was 3 meters thick may now only be 2m, and 2m may now be only 1 m, but extent doesn’t show those changes. I would argue that the dramatic rate of early melt this year is indicative of a low volume anomaly; that the “very rapid loss of ice-covered area” at the beginning of the year is a seasonal analogue of changes modelled by Holland et. al. in 2006 and expanded on by Notz in 2009.

    [1] http://www.pnas.org/content/106/49/20590.full?sid=e07507fe-9f98-41fb-9054-eafdd9d49f2b The future of ice sheets and sea ice: Between reversible retreat and unstoppable loss Dirk Notz, PNAS November 2, 2009, doi: 10.1073/pnas.0902356106
    [2] http://www.agu.org/pubs/crossref/2006/2006GL028024.shtml Holland, M. M., C. M. Bitz, and B. Tremblay (2006), Future abrupt reductions in the summer Arctic sea ice, Geophys. Res. Lett., 33, L23503, doi:10.1029/2006GL028024.
    [3] http://www.imagenerd.com/uploads/2010icemelt-cM9fB.jpg
    [4] http://psc.apl.washington.edu/ArcticSeaiceVolume/IceVolume.php

  22. 72
    belazeebub says:

    I would suggest that people (re-)read:

    ‘Perennial pack ice in the southern Beaufort Sea was not as it appeared in the summer of 2009′
    David G. Barber et al
    http://www.agu.org/pubs/crossref/2009/2009GL041434.shtml

  23. 73
    noiv says:

    The usually high correlation between area and extent is going to vanish this year.

    http://arctic-roos.org/observations/satellite-data/sea-ice/observation_images/ssmi_ice.png

    In the real world the difference is open water between the floes. MODIS took a nice photo yesterday:

    http://ice-map.appspot.com/?map=Arc&sat=ter&lvl=7&lat=77&lon=180&yir=2010&day=207

    The NSIDC named it ‘diffuse ice’, isn’t ‘crushed ice’ more depicting? Also, it is strange that in September an extent of 6 million square kilometers with 50% ice concentration will not be called a record minimum.

    The Arctic is not only changing faster than the IPCC can model it, but also faster than we can adjust our ontology. Since 30 years the extent describes the arctic ice as a two dimensional object. Hopefully Cryosat will spend another dimension soon.

  24. 74
    Louis Derry says:

    re #61 – This post is “imaginative”. First, actually *look* at the data. You can download the data and do some simple stats on it (or something more sophisticated f you like times series analysis), but you really don’t have to. The trend is clear to the naked eye. In both curves (ice area, ice area anomaly) there is a clear decline since, oh, the beginning of the last decade. And this doesn’t even include the thinning effect on regrown sea ice that Dirk discusses (see many other publications). The most pronounced negative area anomalies are *all* in the last few years. The deviation between the 1979-2008 mean becomes obvious in about 2002 – just look at the plot. The 3 or 5 year running means all deviate from the 30 year average in the last 7-10 years. Whaddya mean “nearly average”? There’s this thing about data – if you actually look at it, it will often tell you a lot. That’s what we scientists do for a living. The data you cite quite clearly tell the story. You must have not really looked at it. Go ahead and do some stats – same result. You get about a -1.3 million km2 average anomaly over the last few years, almost all of it due to changes in the Arctic. This is a no brainer. Go back to the uiuc site and look carefully at the other images *and* at the data used to create them. The only years on record with < 4 million km2 of Arctic ice are since 2002 (or 2006, depending on how you count uncertainties). There is an old trick – when you want to hide something, plot it on the scale you can find, and it will make the change seem trivial. The folks at uiuc weren't trying to hide anything, they just must think this is so clear they didn't need to worry about plotting with a large y-axis range. The global plot they give inadvertently makes the trend *appear* a bit less striking than their plot of the Arctic anomaly http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.arctic.png, but it actually doesn't change the numbers at all. I could go on and on – but if it's not obvious in both the global and Arctic data sets I can't help you. Cliff Notes version: the numbers on global ice area *clearly* indicate large declines in the last decade. One can argue about "why?" but there is simply no question about "what?"

  25. 75
    Jeff L. says:

    I guess I shouldn’t read RealClimate comments late at night. I thought that Bob (Sphaerica) said “Question: I recently discovered the North Pole Clam.” That really piqued my curiosity! It was only a few sentences later that I discovered my error . . .

  26. 76
    Leif says:

    With the Arctic showing more exposed sea and lower ice volume, it is not surprising to me to see a warmer Arctic but that would imply to me that the future coldest winter air masses will subsequently have to occur over the land masses with regularity. The average temperature of the earth must remain about average. With a large segment, Arctic, significantly warmer the cold has to go someplace. Land cools faster then water, So land it is. Recall the record cold in Mongolia this winter with ~4 million livestock frozen to death. With lots of ice the Arctic could retain the cold. Now the “Arctic” and “coldest” will not be synonymous.

  27. 77
    James McDonald says:

    Granted this is an article about the Arctic, but sea ice in the Antarctic seems to have been unusually large this year. Was this expected? Is there a simple explanation?

    A back-of-the-envelope calculation of 1 million km^2 excess at 1 meter thick (?) would give an excess of about 1000 km^3 of sea ice. Meanwhile, GRACE indicates perhaps 100 km^2 of ice sheet melting. Could these be connected?

    In particular, melting ice would create an area of lower salinity around Antarctica, but how big, how deep, and how quickly would it diffuse?

    And lower salinity would lead to faster ice formation, but to what extent, and would it matter if the initial ice was formed near shore, where it would be likely to form anyway?

    These are just random musings, but it would be nice if someone with expertise could shed some light.

    Thanks…

    [Response: The difference between Arctic and Antarctic sea ice response is explained on page 30/31 of the Copenhagen Diagnosis. It makes no sense to look at the sum of both, since they are affected by very different processes and their seasons are out of sync - when you look in northern summer, the Arctic is near its minimum and the Antarctic near its maximum, so the sum is simply dominated by the latter. -stefan]

  28. 78
    James McDonald says:

    P.S. Part of the reason I ask is that some denialist is sure to notice this at some point and argue that the missing Arctic ice is countered by excess Antarctic ice, so what is the problem?

    It would be nice to have a cogent answer.

  29. 79
    Rod B says:

    Didactylos (48), in reply to wilt, you say, “…Icesat and submarine data show beyond doubt that the ice is a lot thinner now than previously.” Dirk Notz says in this article, “…one additionally requires information on the overall distribution of ice thickness, which we have not been able to measure routinely in the past.” And goes on to hope that the launch of the Cryosat 2 satellite a couple of weeks ago will improve things. Which is it??

    How exactly do you prove that “ice extent has plummeted dramatically” by some (magical?) discounting of the gradual increase of the extent the past few most recent years?

  30. 80
    Rod B says:

    Gavin (54), In his reply to wilt regarding the loss of ice extent Didactylos’ words were, “… we are in big trouble.” Because that might not quite be armageddon is being pretty nit-picky in your criticism, me thinks.

  31. 81
    James McDonald says:

    For a rather simply computed measure of the state of the Arctic, has anyone compiled totals for the km’s of coastline with significant ice? This is not a measure likely to have any profound meaning, but it is easy to compute and somewhere along the way from historic ice conditions to an ice-free arctic, this number will go from a large value to zero, so it would convey some sense of where we are in that process. And there is also the possibility that unexpected patterns would jump out if it were computed…

  32. 82
    Edward Greisch says:

    John P. Reisman (OSS Foundation): I used your web site to advocate fee & dividend on
    http://dotearth.blogs.nytimes.com/2010/07/26/next-steps-on-climate-and-energy-2/
    today. You should make comments on
    http://dotearth.blogs.nytimes.com
    often as well because the NYT has a large circulation. Dotearth is a good place to direct people to RealClimate.

  33. 83
    Edward Greisch says:

    “The winter 2009/2010 will be remembered by many people in Europe (and not only there) as particularly cold”
    Not if they are my age [64] and have lived in the same place most of that time. Last winter was very short and rather almost hot regardless of what the short-timers thought.
    “Even in January, there were days on end with above 0°C temperature” In Greenland? Unimaginable. Over 42 adult years, the warming is very noticeable to a person in a snowy place.

  34. 84
    villabolo says:

    26 July 2010 at 11:05 PM
    James McDonald says:

    “. . . missing Arctic ice is countered by excess Antarctic ice, so what is the problem?”

    James, tell them the problem is that, such Ying/Yang metaphysics will not ‘equalize’ the altered and detrimental weather conditions that an open Arctic Ocean would cause.

  35. 85
    Ray Ladbury says:

    Rod B. says, “How exactly do you prove that “ice extent has plummeted dramatically” by some (magical?) discounting of the gradual increase of the extent the past few most recent years?”

    OK, Rod, you win the pony award (after the kid who is presented with a dungpile and gets excited because it means there’s a pony somewhere). How you can look at these trends
    http://tamino.wordpress.com/2010/07/26/summer-ice/

    and conclude the trend is pisitive defies explanation–unless you’ve forgotten the defiinition of climate. Of course there has been an increase since 2007–that was a very deep anomaly in the trend. Good lord! Get serious.

  36. 86

    This post and comments have inspired me to update my ‘Models can be Wrong’ page

    http://www.ossfoundation.us/projects/environment/global-warming/myths/models-can-be-wrong

    I added the Arctic Ice and Sea Level Rise graphs


    A Climate Minute: The Natural CycleThe Greenhouse EffectHistory of Climate ScienceArctic Ice Melt

    ‘Fee & Dividend’ Our best chance for a better future – climatelobby.com
    Learn the Issue & Sign the Petition

  37. 87

    Rod B

    I had posted this in the Information Levels post

    http://www.realclimate.org/index.php/archives/2010/07/information-levels/comment-page-4/#comment-181881

    Figure you missed it though.

    Rod, while I was planning, and still hope to do a more critical analysis of the confidence levels in ice data, I was talking to an ice modeler just yesterday, and since I did not ask if I could quote him, I won’t, though I’m ‘confident’ he would not mind.

    I asked, let’s forget about the data for a minute and let me ask you a general lay question. How confident are you that we are losing the Arctic ice?

    His answer was simple:

    “I would say it’s a certainty that we are losing the ice.”

    I don’t know if that is the particular answer you were looking for but, from all the analysis, within the error bars, we are losing the Arctic. Even without the errors, we are losing the ice. It’s as simple as that.

    Maybe consider signing the petition now? Or is it still too soon for you.


    A Climate Minute: The Natural CycleThe Greenhouse EffectHistory of Climate ScienceArctic Ice Melt

    ‘Fee & Dividend’ Our best chance for a better future – climatelobby.com
    Learn the Issue & Sign the Petition

  38. 88

    “The average temperature of the earth must remain about average.”

    No, it must remain exactly average.

    At whatever numerical value.

  39. 89
    Dappled Water says:

    James MacDonald (77) – yup, as shown in some model simulations as far back as the 1980′s & 90′s.

    http://www.sciencemag.org/cgi/content/abstract/278/5340/1104

    Complicated by the ozone hole, however some discussion on a proposed mechanism here:

    http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf

  40. 90
    Chris Dudley says:

    Interestingly, a lack of sea ice in the West of Greenland is being blamed for the large recent retreat of the Jakonbshavn Glacier: http://www.msnbc.msn.com/id/38233438/ns/us_news-environment/

  41. 91
    Kevin Stanley says:

    @RodB
    read Walt Meier’s post at 38 and look at PIOMAS to help answer your question:

    “Didactylos (48), in reply to wilt, you say, “…Icesat and submarine data show beyond doubt that the ice is a lot thinner now than previously.” Dirk Notz says in this article, “…one additionally requires information on the overall distribution of ice thickness, which we have not been able to measure routinely in the past.” And goes on to hope that the launch of the Cryosat 2 satellite a couple of weeks ago will improve things. Which is it??”

    You imply that the two views are inconsistent, but they are not. They just approach the same facts from different vantage points. There does indeed seem to be enough data to conclude with confidence that arctic ice has been thinning, AND there have not been observations as regularly as Dr. Notz (and most everyone else, I imagine) would like in order to make a precise estimate in which we may have confidence.

    And as for your next post…first, if you think it’s be “nit-picky” to consider “we’re in big trouble” as substantially different than “final proof of Armageddon,” then you and I live in different semantic universes. But presumably you would agree that nit-picking distracts from substantive conversation? So let’s stop talking about Gavin’s reaction to the word “Armageddon” and just compare the points didactylos was making in 48 with the points wilt was making in 54. I’m pretty sure one of them was right and one of them was bloviating. In case it’s not obvious, I’ll give you a hint: I think the one who was making the argument that taking all the relevant data into account, it’s clear the ice is declining rapidly (no matter what the year-to-year extent numbers) was right, and the one who responded to that very comment by accusing the first of harboring a “desire to ignore all data that do not fit with your theory” was bloviating. What do you think?

  42. 92
    Didactylos says:

    Rod B asks “which is it?”

    Well, both. My statement is completely compatible with the article. Submarine data and data from Icesat put the matter beyond controversy. However, they do not provide a complete, continuous picture. Cryosat-2 will continue the Icesat record with only a small gap, but before we had satellite thickness data, we were limited to when and where a submarine happened to be.

    That’s enough to say that ice is a lot thinner now than it used to be, but with such poor coverage, it is hard to estimate exactly how much thickness has been lost, and from where.

    As for your waffle about “discounting of the gradual increase of the extent the past few most recent years” – you know you are talking nonsense. You are by no means stupid, so please don’t insult us.

  43. 93
    NeilT says:

    I see the constant wuwt assertion that it doesn’t matter where the ice is so long as the global measurement is the same as ever.

    Obviously it’s garbage but people who don’t have a clue just look at the headline numbers bend a braincell or two (not consumed by the TV shows), to the problem and then consign climate science to the junk pile.

    However, if this document
    http://www.arcus.org/files/search/sea-ice-outlook/2010/06/pdf/pan-arctic/wilsonjuneoutlook.pdf
    is correct in it’s claims (and I’d guess it would not have made it into the search outlook if it was wildly inaccurate); then in the next 2-20 years (according to DR Barber in his IPY webcast), when we are ice free during the summer in the Arctic, we run a 12.5% chance of a shutdown in the North Atlantic Drift.

    The document then states that a consequence of this shutdown would be 300mph winds and deaths in the northern hemisphere (including the US).

    Now what I’d like to know of the denialists is whether they would take an 8 cylinder pistol, put a round in it and take the 12.5% chance that it won’t blow their heads off when they play Russian Roluette (deliberate misspelling to avoid being identified as spam) with it.

    Because, to me, the game being played by those who deny all the scientific evidence is Russian Roluette, not with their lives but with millions of others who have no choice whatsoever . However, the refreshing thing (OK I’m weird), about this document is that it won’t be anonymous 3rd world folk (and many western people have 3rd world disaster fatigue), who die but Americans, Canadians, Russians and Scandinavians.

    Personally, I would have thought that any Sensible, Reasoning, person; would want to avoid this scenario like the plague. Even if it had a 1 in 100 chance of coming to pass!

  44. 94
    tamino says:

    For those who don’t seem to get it: global warming is about climate (the long-term trend), not weather (the short-term variations).

    Likewise, the decline of arctic sea ice extent is about the long-term trend, not the short-term variations.

    Anyone who suggest “the gradual increase of the extent the past few most recent years” as evidence against a significant long-term declining trend, just can’t be taken seriously.

  45. 95
    Didactylos says:

    NeilT:

    I do not believe any filtering was done on the SEARCH estimates. Charles Wilson’s submission is just a wild guess from an interested amateur. It does not inspire me with confidence, and I have to wonder whether it was planted by the deniers solely for the purpose of being wrong. Either way, I think SEARCH made a gross error in including it without any caveats.

  46. 96

    The legend below Fig. 4 reads “Arctic sea-ice extent on June 28, 2010.”

    But the legend on the top of the image says “20 July 2010.”

    Does the July 20 date refer to when the image was generated (based on data from June 28), or is something else going on?

    Hunter

    [Response: Well spotted, thanks. We updated the figure from the original KlimaLounge article, but forgot to update the caption. -stefan]

  47. 97
    Hank Roberts says:

    Good catch by Hunter Cutting above re Fig. 4
    Look at the original German version–the picture is different:
    http://www.wissenslogs.de/wblogs/gallery/16/Fig4.png

  48. 98

    Tank sie Dirk!

    Ok there are a couple of misconceptions with respect to this years melt especially with contrarian sites.
    First off, now there is has been dominating low pressure over the Arctic Ocean, which has stopped compressing the ice over the Beaufort sea, and also decreased surface temperatures by more clouds. But this has not stopped a massive melt from going on, since its largely melting from under water, and near the pole water as shown itself
    above and cracking through, meaning the remaining ice is not thick. On satellite pictures we can literally see
    extremely broken and wet conditions, everywhere I look its weak emaciated icescape. Weather wise, what I have seen is quite extraordinary, there was/is a bunch of circumpolar Arctic High pressures surrounding and forcing a low pressure at the pole:

    http://www.esrl.noaa.gov/psd/map/images/rnl/slp_30b.rnl.html

    In Each of these high’s have likely given all time high temperature records or persistent hot and dry weather making the news.
    So I read again with amazement the quick draw mc-Graw contrarian press shooting blanks and people are buying the end of global warming for the nth time fooled by masters of drama certainly not climate or weather.

  49. 99
    Doug Bostrom says:

    Didactylos says: 27 July 2010 at 10:26 AM

    Might help to note, SEARCH extended an entirely open invitation for predictions to all comers, regardless of affiliation or qualifications. A bold policy, perhaps inspired by recent demands for inclusion by “citizen auditors” and their allies. Personally I was surprised that only one conspicuous “outlier” (to put it kindly) attached itself to the collection. Possibly SEARCH expected the supporting methods documentation to speak for itself? Reasonable people would look at that and form a charitable conclusion, those with agendas would of course jump on it with both feet.

  50. 100
    crandles says:

    Peter #53

    It would seem likely that there is relatively little lag.

    Ref: Impact of instantaneous sea ice removal in a coupled general circulation model (GRL, VOL. 34, L14502, 5 PP., 2007 doi:10.1029/2007GL030253

    “Sensitivity experiments show an almost complete recovery from total removal or strong increase of sea ice after four years.”


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