Daily changes in the graphs, maps and numbers assessing sea ice are entertaining to follow. The day-to-day discrepancies between output from different research teams get close scrutiny by those of us on the outside, trying to learn more about what’s happening to the ice. Seen from the step-back view of monthly averages, however, daily disagreements blur into substantial agreement. Figure 4 illustrates by plotting time series of September means for five main indices produced by the National Snow and Ice Data Center (NSIDC: website, data), the University of Bremen’s Institute of Environmental Physics (Uni Bremen: website, technical paper), IARC-JAXA Information Systems (IJIS: website, data) and the Polar Research Group at the University of Illinois (Cryosphere Today: website, data). So far as I know, Figure 4 is the first graphic to show these five September series together. Disagreements among the indexes appear minor; all five vary together around declining area or extent trends that steepen over the period of observation.
Figure 4
In some respects the agreement is not surprising; the indexes all are estimating the same physical reality, either the area (nominally, the area with 100% ice concentration) or extent (area with at least 15% concentration) of Northern Hemisphere sea ice. Moreover, there are some commonalities among their sources. Both Uni Bremen and IJIS, for example, base their estimates on observations from the Advanced Microwave Scanning Radiometer (AMSR-E) instrument designed by the National Space Development Agency of Japan (JAXA) and orbiting on NASA’s Aqua EOS satellite. The two teams start with different AMSR-E data products, however, which provide different spatial resolution (6.25 km Bremen, 12.5 km IJIS). They apply different algorithms (Bremen, IJIS) and land/ocean masks to process the data, and differ also in what they view as the time span for each “day” reported. The third extent index discussed here, from NSIDC, is based instead on passive-microwave observations that have a 25 km spatial resolution. NSIDC applies 5-day smoothing in its published graphs; IJIS employs 2-day smoothing, while Bremen shows 1-day values.
Notable differences in level and movement sometimes appear when the day-to-day values are compared, as widely (and often, informatively) done on this blog. Discrepancies are much reduced, though, when we step back to view monthly means. The separately-derived NSIDC and Uni Bremen extent values for September 2011, for example, differ by just 30,000 km2 — less than 1%.
NSIDC extent, 4.61 million km2
Uni Bremen extent, 4.58 million km2
IJIS extent, 4.71 million km2
NSIDC area, 3.20 million km2
Cryosphere Today area, 3.19 million km2
The falling September minimum has been most dramatic, but Arctic sea ice extent and area have declined significantly in every month of the year. This is illustrated in Figure 5, a cycle plot of the longest series, Uni Bremen extent (an earlier post showed similar cycle plots of NSIDC area and extent). Each squiggly line in Figure 5 depicts 39 or 40 years of data for that month. The squiggle at lower right in Figure 5 (September) is simply a miniature version of the Uni Bremen line in Figure 4. The 2011 values, emphasized in this plot, have been among the lowest recorded for each month.
Figure 5
In terms of the more volatile daily numbers, 2011 set new minimum records for Uni Bremen extent (Figure 6) and Cryosat Today area (Figure 7). In both cases, the 2011 values passed (by thin margins) the previous one-day records set in 2007. NSIDC called the 2011 daily minimum “a close second” to that to 2007, and IJIS ranked it second as well.
Figure 6
Figure 7
The exceptionally low ice area and extent that occurred in September 2007 resulted partly from winds that favored compaction and blew ice out through Fram Strait into the Atlantic, where it melted. Similar winds have no doubt blown many times before, but they had exceptional effects in 2007 because they were pushing around thinner, patchier and less extensive ice that had been reduced through decades of melting by warmer air above and warmer water below (Polyakov, Kwok & Walsh 2011). In 2011 ice area and extent reached levels comparable to 2007, but this time largely by melting in place without much help from the wind. This result, together with reports of thin ice encountered by icebreakers near the North Pole in 2011, detailed analysis of multiyear ice reductions, and other lines of evidence, suggests that the classic indexes of sea ice area or extent in Figures 4–7 might actually be understating how much ice has been lost.
Which brings up the next topic, past and possible future trends in Arctic sea ice volume.
Nice one Mr Hamilton.
In your first graph, the intriguingly numbered Fig 4, did you consider incorporating any of the other relevant measures, such as IJIS Area, Nansen Extent & Area or the DMI 30%?
I know it could get messy, but it would be interesting to see if any discrepancies between these look to be systemic, eg seasonal. Of course, this would be harder to detect with the DMI 30% extent, but it should always be between the 15%s and the area.
By coincidence, I had cause earlier today to raise the subject of ice loss at different times of the year. A poster on Tamino's Open Mind blog had recently "recommended" an article about Arctic Sea Ice over on the dark side (aka WUWT). Some of you may know of the original poster on said article, namely David Middleton.
At present I can't get a handle on formulating a suitable response to the OP - the writing was so woolly that I'm still trying to figure out how he reached the inevitable conclusion that nothing out of the ordinary is happening. (What a surprise, especially from a "geo-scientist from the evil oil & gas industry" - his words, not mine, I hasten to add.)
However, one misguided soul was gushing forth how the refreeze in winter was being ignored, and that talking about the September minimum was blatant cherry picking. It felt almost heartless to point out that (from the NSIDC data) the monthly trends in thousands of sq kilometres per annum were as follows...
Jan -49; Feb -46; Mar -43; Apr -39; May -33; Jun -44; Jul -68; Aug -72; Sep -85*; Oct -57; Nov -53; Dec -47
* As I did not have the Sep 2011 figure available at the time, I actually stated that the September decline was currently -81 thousand sq km/year, but would rise to about 84 - I underestimated it.
Posted by: BilltheillFrog | October 03, 2011 at 20:29
"did you consider incorporating any of the other relevant measures, such as IJIS Area, Nansen Extent & Area or the DMI 30%?"
I don't have those other datasets; Figure 4 just graphs everything I had on hand. I'm not sure you could add more series without overcluttering a graphic like Figure 4, but there are other possibilities.
Earlier this year I ran some comparisons between two daily extent series, UB and IJIS. I wrote a note about that somewhere on this blog, lost track of it now, but the answer was that yes there's a seasonal pattern in their differences.
Regarding ice loss in other months, Figure 5 tells that tale pretty clearly (also the earlier post mentioned, which shows cycle plots of 2 other datasets). When I write that "Arctic sea ice extent and area have declined significantly in every month of the year" you can take that literally -- I checked. The downward trends are statistically significant (simple linear or time series regression with AR(1) errors) for each month of the year and across at least 3 different datasets (NSIDC extent, NSIDC area, and UB extent as in Figure 5).
As for provocatively starting with something named "Figure 4" ... the reason is that this is part 2 of a 3 or maybe 4-part series, and I wanted to be able to refer back to earlier graphs. It's my textbook-author side coming out.
Posted by: L. Hamilton | October 03, 2011 at 20:56
PIOMAS September update, updates to my graphics;
Daily ice volume:
https://sites.google.com/site/arctischepinguin/home/piomas/piomas-trnd4.png
Monthly average ice volume with exponential trends (nothing visually changed)
https://sites.google.com/site/arctischepinguin/home/piomas/piomas-trnd2.png
Yearly minimum ice volume:
https://sites.google.com/site/arctischepinguin/home/piomas/piomas-trnd6.png
Posted by: Wipneus | October 03, 2011 at 21:49
If I wanted to do an area and an extent graph for the region called the central Arctic Basin, where would I go to get the September mean data?
Posted by: William Crump | October 03, 2011 at 22:46
Yes, record daily and monthly minimum for PIOMAS. Updated the bar chart for our graphs page,
http://img.photobucket.com/albums/v224/Chiloe/Climate/sea_ice_VOL_min_to_date.png
Posted by: L. Hamilton | October 03, 2011 at 22:49
And filling in the 4th of my April predictions, the PIOMAS one was most wrong:
NSIDC extent -- predicted 4.4, observed 4.6
UB extent -- predicted 4.6, observed 4.6
NSIDC area -- predicted 3.1, observed 3.2
PIOMAS volume -- predicted 5.2, observed 4.2
Posted by: L. Hamilton | October 03, 2011 at 22:52
Wipneus:
Nice graphs, do you believe what they imply?
The trend2 chart is for monthly average ice volume, which means no ice for the entire month if the line is at zero.
Based on the trend2 graph the Arctic will be "ice free" for three full months in 2016 and will be ice free for July through November by 2018.
Do the projections of an ice free Arctic by the scientists who assembled the PIOMAS model match the trend2 forecast lines?
If not, why should any significance be attached to the lines in these graphs?
Posted by: William Crump | October 03, 2011 at 23:09
Larry,
Does the fact that your PIOMAS estimate was the most off imply any physical trend or is it more likely noise in the data?
The other results were prety close to your estimates. If you make more forecasts right away you can always claim to be the first this year!
Posted by: michael sweet | October 03, 2011 at 23:32
Much as I disagree with William Crump, perhaps he does have a point about ice free for 3 months following a bit too rapidly.
The fit for exponential and gompertz is very similar but the extrapolations are different. This does beg the question of why choose one extrapolation rather than the other? I like the gompertz because the difference between extrapolating from volume fit and from area fit is reduced and the projected thicknesses from extrapolating both volume and area seems more plausible to me.
For an alarmist agenda, the exponential extrapolation works well. The gompertz might be a more sensible choice if you want to show that predicting seasonally ice free in near future does not necessarily involve predicting winter ice free in the short term as well.
I think showing both is going to make it too cluttered.
Posted by: crandles | October 03, 2011 at 23:38
William - If you look at minimum volume levels on the 'daily' graph you'll see that the Arctic has lost an average of 780 km3 per year since 2002. (From ~11,000 km3 to ~4,000 km3.)
If you look at the 4,000 km3 left at the bottom for this year then it would take only 5-6 more years to melt out the remaining ice if the historical rate of melt continues.
My question to you would be "Why might that ice not melt?".
Can you identify some physical reason for the melt trend to significantly change?
Remember, currently the rate of melt is accelerating. And temperatures are almost certain to continue to rise....
Posted by: Bob Wallace | October 03, 2011 at 23:46
Bob:
I can identify why the Arctic wide trend line is giving a false reading.
The ice is surely melting, but not all ice types are disappearing at the same rate and ice from different regions are melting at different rates. This makes a trend line based on Arctic wide data suspect. Remember the volume for 2008 and 2009 were higher than 2007 and the 2011 drop of 400 km3 is not as high the 780 km3 average number.
If the volume decline is more due to the decline in volume of older ice than it is to a decline in the volume of younger ice (ice that is under 4 years old) then using the average of the two types of ice to predict when the arctic will be ice free will give a false assessment.
My question back is why do you believe the volume decline is occurring at the same rate regardless of the age or the thickness of the ice and regardless of where the ice is located?
The ice age distribution chart provided in the October 4, 2011 NSIDC report appears to indicate that thicker ice older than three years is declining faster than younger ice.
http://nsidc.org/images/arcticseaicenews/20111004_Figure6.png
Per NSIDC:
"First- and second-year ice made up 80% of the ice cover in the Arctic Basin in March 2011, compared to 55% on average from 1980 to 2000. Over the past few summers, more first-year ice has survived than in 2007, replenishing the younger multi-year ice categories (2- to 3-year-old ice). This multi-year ice appears to have played a key role in preserving the tongue of ice extending from near the North Pole toward the East Siberian Sea. However, the oldest, thickest ice (five or more years old) has continued to decline, particularly in the Beaufort and Chukchi Seas. Continued loss of the oldest, thickest ice has prevented any significant recovery of the summer minimum extent. In essence, what was once a refuge for older ice has become a graveyard."
I think we need to do more than just look at the volume trend line for the Arctic as a whole. The dynamics of the volume decline may be more complex than what can be expressed in a single line. My concern is that older ice has contributed disproportionately to the recorded volume decline which would make extrapolating the trend line for the Arctic as a whole an invalid exercise. If the volume of younger ice and ice in the central Arctic Basin is declining at a slower rate than the rest of the Arctic, then it will take longer than 5-6 more years to melt out the remaining ice, but rest assured it will melt out some day.
When I look at the data for extent and area for the central Arctic basin I do not get a trend line that shows an "ice free" Arctic in the time frame of 5-6 years. Only if you assume a catastrophic collapse of the ice in the central Arctic Basin do you get an "ice free" Arctic. This region is colder and melts more slowly than lower latitudes; although its melt rate is probably increasing, I just do not see it melting as fast as the rest of the Arctic.
The scientists who work on the PIOMAS model are on record as supporting a slower melt-out than 5-6 years, so I will continue to hold on to the crazy idea that it will take longer than 5-6 years.
Posted by: William Crump | October 04, 2011 at 23:39
Bob:
What I do believe is that it is likely that the weakness of the ice will make it more susceptible to extreme weather events. My best guess is that we will see a year in which the weather causes a big drop in volume and extent followed by a rebound of ice volume in subsequent years(but not recovery). No matter what, the ice is not going to return to pre-2000 conditions.
Perhaps you will get an "ice free" year in this manner, but I do not see that the Arctic will become reliably ice free in the manner that these graphs indicate in the next 5-6 years. The Arctic will not be ice free from August 1 through October 30th in 5-6 years in the manner indicated by the trend lines.
Posted by: William Crump | October 04, 2011 at 23:52
Re "My question back is why do you believe the volume decline is occurring at the same rate regardless of the age or the thickness of the ice and regardless of where the ice is located?"
Gosh we agree on this. But the older ice is less saline through brine rejection so the melting point is nearer to 0C than -1.7C for first year ice.
Consequently multi-year ice is much harder to melt because the air and water has to get up close to 0 before melting can start so there is a shorter melting period for multi-year ice and temperatures which are not as far above the melting point will do less melting.
The long term trend is for the proportion of first year ice to increase so we are getting a longer melting season for ice that was multi-year ice but has now been replaced by first year ice. So a greater volume of ice should melt during the melting season.
You seem to have a mistaken belief that because multi-year ice has been replaced by first year ice that the first year ice must be tougher to melt. The reality is the reverse.
Posted by: crandles | October 05, 2011 at 00:20
"I can identify why the Arctic wide trend line is giving a false reading."
Ah, so you suspect the volume measurement to be incorrect? It could be, but my understanding is that it is validated by samples taken from different points in the ice.
"My question back is why do you believe the volume decline is occurring at the same rate regardless of the age or the thickness of the ice and regardless of where the ice is located?"
I don't think volume decline is necessarily taking place at the same rate everywhere at the same time. I look at the volume measurement as a simple measurement of volume overall. Clearly melting takes place in some parts of the Arctic faster/sooner than in others. Just look at the regional graphs.
It feels to me as if you regard the Arctic Basic Ice as 'something special', not subject to the same laws of physics as ice in the other areas.
I look at the AB ice as 'the center of the ice cube' or as I suggested elsewhere 'the part of the cake shoved up against the wall and most protected by chewing vermin'.
Compacting winds tend to pile up ice in the AB, up against the northern shore of Greenland and the islands to the west. And the land masses protect that ice from warmer, melting currents.
Clearly the AB is losing thickness. The 20' thick ice of yore is gone. The edges are protected by the ice that remains out to 85 degrees, but that ice is starting to disappear by the end of the melt season. As that ice melts out earlier and earlier (if things continue as they have) then the sun-warmed water will start eating away at the AB ice. And since thickness seems to continue to be lost, the warmer water and wave action will have its way with that ice as well.
Obviously when melting is a gradual process some area has to be last to go. And the AB ice is the best protected of all areas. It will most certainly last the longest, but it will go.
This year the compacting winds seem to have taken a break. That could mean that a lot less ice has been stored in the AB and with next year's melt things could be nasty close to the Pole.
Posted by: Bob Wallace | October 05, 2011 at 01:06
Bob and Crandles:
I am not challenging the volume measurements made by the PIOMAS model, I am challenging the use of an Arctic wide data base to draw lines predicting future ice loss.
If the volume decline is not uniform for all regions of the Arctic, then the use of an average for the Arctic as a whole to predict future ice loss is not valid.
Bob appears to agree with this when he stated:
"Obviously when melting is a gradual process some area has to be last to go. And the AB ice is the best protected of all areas. It will most certainly last the longest, but it will go."
If you want to predict when the Arctic becomes "ice free" shouldn't the assessment be based on when the AB becomes "ice free" and not data from the Hudson Bay and other regions that are already ice free at the minimum?
Several commentators appear to be missing the point that I believe the Arctic will become "ice free". I also believe that the AB is losing thickness, but there does not appear to be any data on the rate of thickness reduction for first year, second year and third year ice in the AB that would support the rapid melt scenario. Find this data and I will abandon the view that ice will continue to exist in the AB during the month of September for the current decade.
I am challenging the rapid melt view that the AB will be continuously "ice free" for the month of September in seven years. My guess is that continuous "ice free" conditions for the entire month of September will not occur for a long time.
I do not have volume measurements from PIOMAS for the AB, but I do have area and extent data and they do not indicate a complete melt out will occur in the next 5-6 years. Volume is tricky as a .5 meter layer of ice only needs 500 km3 of ice volume to reach an extent of 1,000,000 km2.
The extent chart from MASIE shows 2011 as having a greater extent than 2007 and 2009 as of today. Yes, this is a bit of luck for me that 2011 is above 2009, but that is not necessary to support my view as the rate of decline of ice extent for the AB does not support an "ice free" in 6 years hypothesis.
ftp://sidads.colorado.edu/DATASETS/NOAA/G02186/plots/r11_Central_Arctic_ts.png
In looking at the MASIE extent charts for the period August 1 through the September minimum for 2007 through 2011, there does not appear to be a large reduction in extent that occurs in this period absent weather conditions like 2007. The minimal extent reduction in the AB during this period is another reason I am challenging the use of Arctic wide data which shows a steeper rate of decline during this period.
Cryosphere Today area graphs show a diminished AB compared to the 1979 to 2008 mean, but it only shows a decline of roughly 30% from the mean at the point of maximum melt (down 1 million km2 from the mean of 3.5 million km2). As of the beginning of August and the beginning of October, the area is only .5 million km2 down from the mean of 3.5 million km2, which is only a 15% decline. If the AB is going to become "ice free" for August through October by 2018 shouldn't we see a deeper reduction from the mean for this period?
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.1.html
Per Cryosphere Today the ice area is approximately 3 million km2 at September 30. Why should I believe a trend line based on Arctic wide volume data that says the AB will be ice free by 2018 for the month of October when it will likely be above 3.5 million km2 on October 30 of 2011?
Crandles:
As for which type of ice is tougher to melt, I do not think this matters as much as the data which show which ice is disappearing from the Arctic the fastest. The chart below from the NSIDC shows ice age percentages at the September minimum. It shows that ice older than 3 years is disappearing faster than ice that is younger - it has gone from being 50% of the ice to 10%. Ice that is less than 4 years old makes up 90% of the ice at the 2011 September minimum. Regardless of which ice is tougher to melt, it is clear young ice is surviving better than old ice.
http://nsidc.org/images/arcticseaicenews/20111004_Figure6.png
I am not trying to explain why this ice disappearance pattern is occurring, I am only pointing out that the use of Arctic wide data will produce a skewed result in predicting the future of the ice as the type of ice in the data base has not remained constant.
Thank you for reading my posts. We will have to wait a few years to see which view is a more accurate reflection of ice conditions.
Posted by: William Crump | October 05, 2011 at 17:58
Re "As for which type of ice is tougher to melt, I do not think this matters as much as the data which show which ice is disappearing from the Arctic the fastest. The chart below from the NSIDC shows ice age percentages at the September minimum. It shows that ice older than 3 years is disappearing faster than ice that is younger - it has gone from being 50% of the ice to 10%. Ice that is less than 4 years old makes up 90% of the ice at the 2011 September minimum. Regardless of which ice is tougher to melt, it is clear young ice is surviving better than old ice."
Sorry but this is nonsense. Look at the change from March 11 to September 11 in the maps on arctic sea ice news figure 6:
http://nsidc.org/images/arcticseaicenews/20111004_Figure6.png
I would say that 75% of the multi-year ice area survives while less than a third of the first year ice area survives.
The first year ice is more easily lost than multi-year ice due to salinity. On an annual basis, the first year ice is easily lost but because it is first year ice it makes a rapid recovery in winter to show little first year ice loss. Note also any mult-year ice melted in summer is generally replaced by first year ice which gives the appearance of first year ice recovery but is actually very bad news for the ice.
I accept that you are saying that it will all melt out eventually. But you do so by introducing ludicrous ideas like this first year ice is not melting out as much mult-year ice. I hope you can see that what you are saying on this is simply wrong.
Likewise with your exclude the surrounding seas argument. One way to roughly calculate the time to ice free is by taking remaining ice volume divided by typical annual ice volume loss. Lets for the moment set aside arguements about the shape of the decline whether linear or past trend of accelerating decline or a slowing rate of decline. The annual volume loss is determined by the heat budget. If less heat goes into the ice because there is less ice then temperatures will rise and the rate of loss will increase to compensate. OK this allow some extra heat to be lost through the atmosphere to space which is an argument for a declining rate of volume loss. But this hasn't shown up yet in the curve fitting exercises and there is little time left for it to show up.
Your exclude the seas around the arctic basin seens to want to do much sillier things to this calculation, excluding a significant amount of the annual loss as well as ignoring thickness reduction by looking at area/extent.
>"I am not trying to explain why this ice disappearance pattern is occurring, I am only pointing out that the use of Arctic wide data will produce a skewed result"
And we are trying to patiently explain why your method seems to us to be more skewed than ours. But when we point things out to you there seems no recognition of this.
Posted by: crandles | October 05, 2011 at 19:21
"If the volume decline is not uniform for all regions of the Arctic, then the use of an average for the Arctic as a whole to predict future ice loss is not valid."
If you've got your money spread across multiple banks and are spending mainly from one or only a few you can't use the lingering balance in the untouched ones to predict that it will take longer to go broke than what your average balance predicts.
Our hotter climate is "spending" our ice balance. It's melting the easiest to get to ice first. As the easiest ice gets melted earlier in the summer (or doesn't get replaced in the winter) more ofthat heat will be available to attack the AB ice.
And, as the ice melts, amplifying forces such as loss of albedo and increased heat absorption by open water increase. We're seeing that in the shape of the volume curves.
If the Arctic Basin was full of 3+ meter ice then we might anticipate a melt slowing as the protective edges were eaten away. But based on reports from ships cruising through the places where that thick ice might be found, it's gone.
Perhaps some new player will join the field and stop what is looking like a rout for team ice. Perhaps we'll see increased cloud cover earlier in the year blocking sunlight. But so far whatever that blocking agent is, it hasn't been spotted.
As for basing predictions on extent, I think that a very shaky endeavor. Extent says only that there are x number of grid square with some ice in them. There are times when the extent of the fish pond outside my window is 100%. A couple sunny days will melt that ice out as it has little thickness.
Posted by: Bob Wallace | October 05, 2011 at 20:47
Bremen saves the day:
and the tracking winter:
From BREMEN:
AMSR-E problems; maps not updated since Oct 4
The AMSR-E instrument has not produced data since Oct 4, 2011. Therefore, the sea ice maps cannot be updated. We are switching over to SSMIS data which might take a few days.
THey have already been saving these products for years.
Abstract
The PSI-SSMI level 2 product contains, for both north and south poles, polar sterographic 12.5 km resolution grids of sea ice concentration from the 85 GHz channel of SSM/I on DMSP, available since 1992. The daily maps are processed from the daily brightness temperature maps from NSIDC. The Artist Sea Ice (ASI) algorithm developped at University of Bremen (Germany) is used to processed daily sea ice concentration maps at 12.5 km resolution. The dataset covers the whole 85 GHz SSM/I mission. We are grateful to NSIDC (Boulder, Colorado) for the SSMI data.
That is the gist of it.
The SSMI is really no worse at this point than AMSRE, except weaker resolution. Since Jaxa was doing 25km grid res converted to 12.5km2 grid res for main products. Bremen having 12.5 grid res maybe converted to 6.25km for the winter with SSMI is great IMO.
Posted by: Chris Biscan | October 05, 2011 at 21:14
Notification service: There's an October 2011 Open Thread for all things off-topic.
Posted by: Neven | October 05, 2011 at 21:25
Thank you kind leader guy!
Posted by: Chris Biscan | October 05, 2011 at 22:04
Lacking a 'thickness' graph for Arctic ice I tried making one using annual PIOMAS minimum volumes and annual Breman minimum extents.
(Hopefully I didn't make any mistakes.)
It looks to me that during the last couple of years we ended up with about half the thickness of ten years back.
Since we don't have any information (with which I'm acquainted) that there's lots of thick ice stored somewhere in the Arctic it looks to me that we're headed toward a sudden melt out.
It might be interesting to try a graph with PIOMAS annual maximums and maximum extent. If someone can point me to the data....
Posted by: Bob Wallace | October 05, 2011 at 22:11
Two things.
Just look at the AVHRR pics north of Greenland. That is in no way a state to be called serious refreeze. The leads and cracks run everywhere. Within the limits of our reporting format (extent, area) it looks normal to speak of refreeze and feel relief when the 5 MKM² mark is reached again. But the format is delusive.
The second thing: one of us wondered why minimum volume 2011 would be that close to 2010 on PIOMASS, given the clearly worsened situatiion. I agree.
I muse on 2,8 MK x 1 m thickness and 1,5 MK x 0,4 m. I just cannot feel comfortable with the PIOMASS model, whether adjusted with real time data or not. I know some of you hold possible that it is too pessimistic, maybe even 1000 KM³ too low. My unpleasant feel is that it is at least 600 KM³ to optimistic...
To finish: during 2011 feedback was already so strong that 2007 is clearly history. We’re very close now to circumstances making a seasonally, practically ice free Arctic possible. There is no physical reason why the Central Pack would be more resistant. The only difference is that there was more ice to melt.
Posted by: Werther | October 05, 2011 at 22:44
Bob:
I appreciate your effort, but how much of the thickness decline is attributable to the loss of thick multi-year ice and how much is attributable to younger ice? Also is the thickness decline more severe at lower latitudes which have a higher heat input than higher latitudes?
These are the unanswered questions which make this data set unreliable IMO for extrapolation of future ice conditions.
The transition from nearly 2.3 meter ice to .9 meter ice may be occurring because of the massive loss of the oldest and thickest ice in the Arctic. I seriously doubt that first year ice declined in thickness from 2009 to 2010 by anything approaching the drop indicated in the chart or that first year ice is 40% (.9/2.3) of the thickness it used to be at the minimum.
Posted by: William Crump | October 05, 2011 at 22:59
William - If first year ice is more resistant to melt and the percentage of multi-year ice dropping shouldn't we be seeing the melt rate slowing rather than accelerating?
(Perhaps it is slowing the melt rate, but that effect is being overridden by positive amplifying factors.)
Posted by: Bob Wallace | October 05, 2011 at 23:15
"I just cannot feel comfortable with the PIOMASS model, whether adjusted with real time data or not."
I don't know whether to trust the PIOMAS model or not, but given that it is supposedly calibrated using collected data my leaning is to trust.
Sampling is a well established method of determining the state of things. We've got ways of looking at collected data and telling how likely it is representing the real world.
I'd assume that the folks running the PIOMAS numbers would be on top of their sampling procedures and if they are far off base they would be called out by other players in the field.
For example, during this year's Polarstern cruise we would have heard if they were finding ice much thicker or thinner than the PIOMAS model predicted. (Or we will hear when they release their report.)
Posted by: Bob Wallace | October 05, 2011 at 23:25
William says:
As has been pointed out to you in other comment sections, this is just wrong. Arctic insolation over the summer months is GREATER at higher latitudes, not less.
The central basin hasn't (in the past) had to deal with the more pronounced bottom melt found in the marginal ice zones, but the MIZs are growing in size and reaching further north. Likewise the effects of structural mechanics and kinematics are more and more coming into play as the ice thins and fractures. Looking solely at extent ignores these factors.
Your idea that trending the central basin is a better metric has been shown to be logically unsound. Rather than simply repeating the same arguments it may be time to pause, and critically rethink your assumptions.
For instance, how do ice shelves that were (just a few decades ago) dozens of meters thick, practically disintegrate when they are located in the most protected region of the arctic? Has the loss of these ice shelves decreased extent?
Posted by: Kevin O'Neill | October 05, 2011 at 23:50
On volume…
Bob, I was musing on questions raised by RuninCircles and Wayne Kernochian. I have no doubt the team of scientists maintaining the PIOMASS model are doing the best they can. The model prediction for September, 4000 km³, is alarming enough.
Kevin O’Neill pointed at the varying rate of volume loss, so it would be reasonable to have a relatively small volume decline 2010-2011 (still 10% - ouch).
You use the Polarstern report as illustration. I agree there. But they reported mostly 0,9 m thickness on their way from Svalbard right up to the pole. That’s the much debated Arctic Central Basin! What would you think 1,5 MK² slush puppy seas on the East Siberian Sea side would have had as an average? I’d be more ‘trusty’ if the PIOMASS team could present their sampling...
No matter what, the situation is fit for rapid collapse anyway. Being pessimist on that, I won’t be hairsplitting whether the volume loss was 10% or 23%.
Posted by: Werther | October 06, 2011 at 00:15
As I recall the Polarstern also reported hitting some thicker ~2 meter ice.
Extent seems like a terrible way to estimate volume as there is no differentiation between squares with 100% ice and 15% ice.
Some of the images that I looked at in the 'slush puppy' areas seemed to have ice sticking up more than a couple of inches above the surface. That's a very casual observation, not data. But based on those few glances volume might calculate out higher in those areas than what one might expect if they view 'slush puppy' as a layer of slush.
---
We have these basic questions which we can't seem to answer. I think it might be worth our while to recruit some gurus - perhaps a couple of advanced graduate students - who would be willing to answer a question now and then.
It might be good practice for someone destined to teach an undergrad course in their near future.... ;o)
Posted by: Bob Wallace | October 06, 2011 at 00:33
Kevin:
When you go to the beach in the Summer do you go to the North Pole or do you go to lower latitudes?
Ice shelf disintegration, this sounds like it reduces volume more than it reduces extent. The loss of the Canadian ice shelves is more disturbing than the 2011 volume model at PIOMAS.
Maybe you are correct about bottom melt- (can you show me any measurements of changes in thickness of Arctic Basin ice?), but I find the scenario of a melt out like a small pond changing from ice one day to no ice the next to be incredulous when applied on the scale of the Arctic.
Show me that the thickness of first year ice in the Arctic Basin is declining fast enough to create an ice free Arctic in 5 years and I will join the band wagon.
Until then, I will poke along with the area and extent data (2011 has just risen past 2009 on the MASIE chart and both CT and MASIE are over 3 million km2 and rising).
Since the precipitous wind driven drop in 2007 for the Arctic Basin to 2.1 million km2, the area measure at CT has been approximately 2.5 million km2 at the minimum for the last three years. There has never been two consecutive years in the satellite record where the Arctic Basin has dropped more than 200,000 km2. By the same token, I would never have predicted the magnitude of the single year drop in 2007; however the Arctic Basin has rebounded fairly well from this low.
While AGW is real, predicting an ice free Arctic within 5-6 years when the measured area and extent have been maintained for 5 years within a fairly narrow range (based on the above graphs) does not make much sense.
So please forgive me if I believe there is a flaw in the volume trend line analysis that indicates that we are in for 5 consecutive years of 500,000 km2 drops in area and extent for the Arctic Basin and that the Arctic will be ice free for the three months of August through October by 2018.
Posted by: William Crump | October 06, 2011 at 00:38
Well, William, I'm pretty used to your comments now. I almost like them as they open chanches for our group to critically address new approaches. But I have to say your statement 'the Arctic Basin has rebounded fairly well from this (2007) low' is nice for the comedy hour.
I guess our common interest is dangerous climate change, although we're concentrated on sea ice here. Looking back in, say, 10 years, it won't matter whether 'it' happened in 2014 or 2020. AGW will hit progressively harder and what's happening at the poles will contribute fiercely.
Posted by: Werther | October 06, 2011 at 01:09
William - "When you go to the beach in the Summer do you go to the North Pole or do you go to lower latitudes?" Is this an attempt to dispute the physics of solar insolation? The North Pole during summer months receives more solar insolation than the equator does over any similar period of time. That's just a physical fact.
Yes, the volume loss in the arctic basin (including ice shelves) has been substantial - yet extent is not affected. Looking at extent alone we would conclude nothing has changed, but it has, dramatically. But you didn't finish the the thought ... how do you explain the most protected area in the arctic basin losing this fast ice? Ice that has withstood thousands of summers?
"...the Arctic Basin has rebounded fairly well from this low." Really? So the ice is just as thick today as it was pre-2007? Or are you fixated solely on extent again?
Posted by: Kevin O'Neill | October 06, 2011 at 01:29
I should've been more careful when coming up with this term. I of course meant that some areas of the ice pack looked like slush puppie from far above (satellite images), not that there was literally thousands of square km filled with slush puppie. Slush puppie would be the miniature version of the real thing. I either have to explain this better next year or come up with a new term that describes ice that could flash melt under the right conditions.
Posted by: Neven | October 06, 2011 at 09:09
>"When you go to the beach in the Summer do you go to the North Pole or do you go to lower latitudes?"
Do you want to sunbathe for 6 hours or 24 hours per day? The answer to this changes where you should want to go, if you base it solely on solar insolation. How much nonsense do we have to rebut before you realise what nonsense you are spouting? Or are you deliberately spouting nonsense to try to provoke us?
Posted by: crandles | October 06, 2011 at 10:49
William Crump.
there is only one Arctic, one lot of ice to melt. dividing it into smaller areas is a convenience that is all.
have you not put any thought into this or are you just determined to defend the argument you have fabricated.
why on earth would you expect so see ANY significant drop in the central Arctic ice area before the lower latitudes melt out.
Have you not noticed the pattern that happens very year? for your demands to be met would require defying the laws of physics.
there is a temperature gradient from the lower latitudes to the north pole. for melting to take place in the high latitudes first would require the reverse which is clearly not going to happen is it? haver you also not noticed the ice flow patterns? ice from the Russian side gravitates towards the Greenland and Canadian coast. any ice tha does melt in the central Arctic gets topped up and will continue to do so until there is none left in these areas. Then and only then will there be large scale melting of the Central Arctic and you can expect to see that begin to happen within 5 years at the latest unless there is some unseen dramatic reversal. I can see no indication that a reversal is even potentially possible. Do you have some secret source of information that offers this possibility? If not then your argument is based no nothing.
Posted by: Philiponfire | October 06, 2011 at 16:18
Rather than slush puppy, how about punch bowl ice?
I'm not actually pushing that as an alternative, but it is closer to what is observed - chunks of ice bobbing around in the sea.
I think your 'slush puppy' was a work of minor genius. It refocused thinking away from solid sheets of ice. I suspect far too many people look at extent maps and assume that there is thick solid ice out to the edges, they need to be informed that inside the boundaries all is not well.
Posted by: Bob Wallace | October 06, 2011 at 19:08
I appreciate the interest in my comments, but I am not seeing much in the way of references to data that would change my position that extrapolation of Arctic wide data will result in a false reading of when the central Arctic Basin becomes "ice free".
I agree that the Arctic Basin has lost volume and that first year ice in the Arctic Basin has lost thickness, particularly at the minimum.
The issue is how fast is the first year layer losing thickness.
Every year this new ice is created in the winter and partially melts out by September. The data I want to use for a trend line of when the Arctic becomes "ice free" is the decline in the thickness of this first year ice. I am using area/extent data simply because there is no other source and the volume data appears suspect in terms of predicting the demise of first year ice.
The Arctic has become essentially "ice free" of ice that is more than 4 years old, but this pattern of decline is not being matched by younger ice. I conclude that first year ice is not declining as fast as multi-year ice.
I do not agree that first year ice is declining in thickness in the Arctic Basin at the same percentage rate as the volume trend line would indicate.
Can anyone provide an analysis of the data that refutes this?
Perhaps multi-year ice because it sits lower in the water is more susceptible to bottom melt and because it presents a larger profile both above and below the water line is more susceptible to transport out of the Arctic or to warmer zones of the Arctic (the graveyard) from winds and currents. Perhaps the difference is also a function of the resupply of first year ice with a new crop every year while multi-year ice is not being replenished so the existing batch is just being withered by global warming.
Whatever the mechanism, multi-year ice has disproportionately fueled the decline in volume being reported by PIOMAS. Using volume trend lines may accurately predict the demise of multi-year ice, but they will overstate when first year ice will disappear from the Arctic.
If the PIOMAS volume at the minimum declined from 12,000 km3 to 4,000 km3 does this mean that the thickness of first year ice at the minimum declined from 1 meter to .25 meters?
I think the answer is a resounding no as most of the loss is from the disappearance of the thick multi-year ice and areas which have gone from some ice cover to no ice cover. The remaining cover of first year ice (which grew from the zero starting point of the prior year minimum) is not declining in thickness as fast as the volume trend line and therefore the volume trend line can not be used to predict its demise.
The ICESAT data indicated that first year ice was growing to comparable levels of thickness at the winter maximum compared to prior years. I suspect it is suffering more annual melt than in the past because of the loss of surrounding thicker multi-year ice and general warming, but this loss of thickness is not as fast as the decline in the volume trend line.
This is not a matter of comparing how fast a thick ice cube melts v. a thinner ice cube or ice cubes with different salt levels. In the Arctic it is both a matter of melt and replenishment. The balance of melt and replenishment has shifted so that multi-year ice is becoming a smaller percentage of the ice that survives the minimum.
There has also been a higher rate of loss of ice area/extent in regions outside the Arctic Basin than inside the Arctic Basin. A point that none of the commentators has refuted. This would mean that the volume loss in the Arctic wide data is greater than the volume loss rate in the Arctic Basin.
The data that does exist shows almost no change in the thickness of first year ice in winter. From 2004 to 2008 the ICESAT data showed dramatic declines in the thickness of multi-year ice and almost no change in the thickness of new ice in winter. The graph below shows that it is multi-year ice that is driving the thickness decline not first year ice.
http://www.nasa.gov/images/content/365869main_earth2-20090707-full.jpg
Although this data is old and only refers to winter sea ice thickness and covers a short period of time, it does support the view that first year ice is not declining as fast as multi-year ice. Perhaps Cryosat will provide a source to update this data and we will have a better read of how fast the thickness of first year ice is declining.
Does anyone know where I can find a similar chart for the change in thickness of first year ice for the minimum?
If the decline in thickness shown in this chart is combined with the NSIDC graphs that show that older thicker ice makes up a smaller percentage of the ice at the maximum and the minimum than it has in the past then the conclusion that the volume decline is being driven more by the loss of thick older ice than it is by a decrease in the volume of first year ice is inescapable.
I have not seen any data provided by the various commentators that has refuted this notion - and please lets use real data and not references to pencils or ice cubes.
Provide data showing a rate of decline of first year ice in the Arctic Basin sufficient to cause a melt out in five years and I will join your bandwagon.
Posted by: William Crump | October 06, 2011 at 19:37
First of all, William, please read this study:
"Influence of Initial Conditions and Climate Forcing on Predicting Arctic Sea Ice" by Blanchard-Wrigglesworth et al GRL 2011 So volume is actually predictable.
Secondly, in your prosecution of your narrative you state:
"The ICESAT data indicated that first year ice was growing to comparable levels of thickness at the winter maximum compared to prior years."
Yet that statement is at odds with this analysis by Tamino:Which shows that "every day this year has shown a lower volume than the same day for any previous year".
The Great Death Spiral yet lives; those that wish to live in the lands of green-coloured fire trucks are free to do so, of course...
Posted by: Daniel Bailey | October 06, 2011 at 20:00
If the Arctic Sea Ice could speak, I wonder what it would be saying...
...Perhaps this
Posted by: Daniel Bailey | October 06, 2011 at 20:08
William - How much more do you think volume will drop before we see the curve start to flatten, based on your analysis of things to come?
I think you said at one point that >3 year ice was now down to about 10% of total ice?
If that's the case shouldn't we be reaching the point at which melting older ice should be too small a piece of the pie to drive the volume curve downward at an accelerating rate?
Posted by: Bob Wallace | October 06, 2011 at 22:34
This is talking about 2003 to 2008 ice...
"Until recently, the majority of Arctic ice survived at least one summer and often several. That balance has now flipped.
Seasonal ice, or ice that melts and re-freezes every year, now comprises about 70 percent of the Arctic sea ice in wintertime, up from 40 to 50 percent in the 1980s and 1990s. Thicker ice surviving two or more years now comprises just 10 percent of ice cover, down from 30 to 40 percent in years past."
http://www.archive.org/details/SVS-3589
Minimum PIOMAS volume was 7.1 thousand km3 in 2008 and fell to 4.4 by 2010. That's a 38% loss of volume. Minimum Breman extent and CT area did not change appreciably over that three year period.
That would allow one to argue that multi-year ice has further disappeared and/or first year ice is now thinner. You can't take a smaller amount of ice and spread it over the same area without it being thinner.
A <10% of ~2 meter ice (vs. >90% 1 meter ice) is small potatoes when one is trying to explain a close to 40% drop in volume.
Posted by: Bob Wallace | October 06, 2011 at 23:14
William Crump (and anybody else);
First, if there is no multi-year ice in the arctic, then that is the same thing as an ice free arctic.
Second, multi-year ice used to make up a majority of the ice in the arctic (about 55%). However, it has been on a decline that appears to have accelerated since 2006. The following is a chart:
Multi-year ice is currently only about 20% of the arctic. Simple trend line was drawn using 3rd degree polynomial in Excel and cross zero around 2016. However, that assumes similar rate of decline as over last few years. Personally, I suspect rate will moderate somewhat, but difficult to foresee multi-year ice beyond 2020. Only possible chance would be major volcanic eruption.
Environmental activist are no match for economic forces.
Posted by: Andrew Xnn | October 07, 2011 at 03:32
William - you might want to read this 'casual' report from the Polarstern. They report a bit on ice thickness....
"In the central Arctic the proportion of old, thick sea ice has declined significantly. Instead, the ice cover now largely consists of thin, one-year-old floes. This is one of the results that scientists of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association brought back from the 26th Arctic expedition of the research vessel Polarstern.
---
Their conclusion is: at sites where the sea ice was mainly composed of old, thicker ice floes in the past decades there is now primarily one-year-old ice with an average thickness of 90 centimetres. Only in the Canadian Basin and near the Severnaya Zemlya island group in northern Siberia did the sea ice physicists encounter significant amounts of several-year-old ice. As a rule, this old ice is between two and five metres thick."
http://www.sciencedaily.com/releases/2011/10/111006102617.htm
I'm not clear on the naming of different regions of the Arctic, but isn't the Canadian Basin the western part of what CT labels the Arctic Basin?
Posted by: Bob Wallace | October 07, 2011 at 22:56
Hi Neven and William Crump,
I would like to suggest that it might be a good idea for William to write a guest post on any subject that he wishes to discuss.
Anybody else who is then interested in this subject - whatever it may be - could then address this concern at their own leisure?
Posted by: idunno | October 07, 2011 at 23:16
Chart from bouy data referred to by Neven in PIOMAS September 2011 (volume record lower still) an October 4, 2011 post.
Warning - this data is provisional.
2011C 2011D 2010H
Locate NP Mag. Cen Arc
Type FY FY MY
Initial 192 140 115
Maximum 214 160 240
Minimum 144 105 90
Change 70 55 150
%change 33% 34% 63%
Bottom 0 0 40
Top 40 55 110
Max 6/21 6/21 6/20
Min 8/20 7/20 8/20
measured in cm.
Data is provisional and spot locations are not sufficient coverage to extrapolate what is occurring to Arctic ice thickness, but this limited data indicates top melt is greater than bottom melt and First Year ice shows less change than Multi Year ice.
Does anyone know of additional data?
Posted by: William Crump | October 10, 2011 at 16:31
The Polarstern article includes the following:
"Compared to their measurements from 2007, when the extent of the sea ice had di-minished to a record minimum of 4.3 million square kilometres, the researchers have not yet found any differences, however."
Posted by: William Crump | October 10, 2011 at 17:09
Daniel Bailey:
I agree with Tamino's statement that volume is the most important metric for measuring what has happened to Arctic ice.
I believe this statement is intended as a refutation on anyone who says that no significant change has occurred since 2007 because no change in area/extent has occurred since 2007.
I do not contend that no significant change has occurred, quite the contrary. I am saying that the nature of the ice is very different today than the past and that extrapolations using historical data onto current conditions is not valid because of this change in the nature of the ice.
I believe that significant change has occurred as the character and quality of Arctic ice as the ice has shifted from thick multi-year ice to thin first year ice. My point is the first year ice is not showing signs it will be gone in 5 years.
What I do not see in Tamino's excellent post is an analysis of what changes have occurred in the thickness of first year ice in the rather large region known as the Central Arctic Basin (or any other region).
Do you have any articles that discuss the change in thickness of first year ice?
As for line drawing, if negative numbers are provided on the y-axis, then the volume extrapolations go negative - just like the line in Andrew's chart that shows negative 20% ice. How would "negative ice" occur?
Just provide data that shows the thickness of first year ice is declining fast enough to create an ice free arctic in 5 years and my position is DOA.
Andrew:
No ice means no first year ice and no multi-year ice, not just no multi-year ice. Please look at the NSIDC chart of ice age in their October 4, 2011 news release.
Posted by: William Crump | October 10, 2011 at 17:48
When all the sea ice in the arctic melts someday, then the only ice that will be left is that which forms later during the fall and winter. This is 1st year ice. Hence, multi-year ice will be gone.
Posted by: Andrew Xnn | October 10, 2011 at 18:24
Yes, Andrew Xnn, it's true that if there is no ice at some point during the summer, there must be no multi-year ice. But I agree with William Crump that the reverse is not necessarily true. The one possibility that I have come up with is that whatever remains of first year ice is advected before its first birthday. (I don't think that this going to happen, just that it is neither a logical, nor even physical, impossibility.)
Now, consider William's main point, that we don't really know the thickness of first-year sea ice at the minimum (and especially how quickly it is decreasing). I've seen several attempts to refute this, but none so far seem entirely convincing at either answering his point within his assumptions of pointing out where is assumptions are clearly incorrect.
I'm a bit busy right now, but I hope to post a more detailed analysis *someday soon*.
Posted by: Bfraser | October 10, 2011 at 19:38
@Bfraser: I am resurfacing only to point out that you raise an interesting point.
First-year ice becomes second-year ice at minimum -- but at minimum area. Minimum volume typically happens a bit later, as very thin (new!) first-year ice is averaged in with the remaining (now second-year!) ice as it refreezes.
Also, keep in mind that no ice in the Arctic lasts forever, and that most ice in the Arctic at any time in the last tens of thousands of years is less than five years old. Multi-year ice doesn't keep getting thicker -- it's pushed by the currents to the edge of the pack and melts out.
Anyway, back to the question of first-year sea ice at the minimum. It's easy to guesstimate (if you want to bother) just how much ice is left as first-year transitions to second-year ice at minimum area. You could, for example, note that there was not much change in minimum area from 2010 to now, but a greater change in volume at minimum area (around 10%, I believe), and most of the ice at both times was 1st-to-2nd, so the thickness of 1st-to-2nd was clearly less in 2011. Comparisons of maximum volume to area figures in 2011 and before shows that maximum volume is coming down faster than maximum area, so maximum thickness is likewise decreasing for both new-1st and 1st-to-2nd year ice. So new-1st and new-2nd-year ice is thickening less in winter and melting faster in summer.
Finally, consider that average thickness at minimum area has gone from above 3 meters in 1980 to a little above 1 meter. Assume a "worst-case" scenario in which as much as possible of that represented getting melting of multi-year ice. Then in the old days, each year of age would add less than 2 meters (peaking at 3 years). However, the total increase in thickness to maximum area was more like 12 meters -- so at least 10 meters of melt of 1st-year ice (or of 2nd-year ice on top of the remaining 1st-year ice) was going on then.
Now fast forward to today. Less than 12 meters of increase in thickness of new 1st-year ice over the winter, and decreasing; more than 10 meters of melt the next summer, and increasing. Sooner or later, depending on the rate of increase/decrease, winter increase is less than summer decrease and all first-year ice melts out before minimum area.
Posted by: Wayne Kernochan | October 10, 2011 at 21:17
Re "I agree with Tamino's statement that volume is the most important metric for measuring what has happened to Arctic ice."
I suggest that the measure is actually heat energy which comprises both latent heat of melting and temperatures. There is not much change in temperatures so mass of ice might be nearly as good. Volume is a reasonable approximation for mass.
William Crump seems quite clear that he accepts that volume is declining. This implies there is a positive net heat budget.
I suggest there are two major changes to the heat budget as ice volume declines, albedo effect and more heat loss though thinner ice in winter. There is also a small net increment in the budget as greenhouse gasses increase.
I am unsure how much of this William accepts. His arguments assume the central region continues at similar rates of decline regardless of any surplus heat budget that has to go somewhere. I am not clear whether William thinks it reasonable to say such surplus heat is entirely lost to space once the ice in further out regions have melted out rather than being spread between lost to space, higher temperatures and faster melting of remaining ice.
Above changes the focus to heat as metric and to the heat budget. Alternately we could consider his favoured first year ice area metric:
This has two components of change: a decrease at the edges which he tends to downplay by excluding outer areas. The second is an increase in the first year ice area from multi-year ice being replaced with first year ice. This replacement of multi-year ice allows more ice volume to be melted each melt season.
If 2m multi-year ice is replaced by 1.5m first year ice. This is then much easier to melt because it is thinner and because it is first year ice. If the average thickness of first year ice is 1.3m, William looks at this as an increase in thickness which then helps him suggest that the first year ice is not thinning fast enough.
On the other change of loss of first year ice in the outer regions, these are either excluded, or if included, these are likely to be thin ice. Loss of 0.2m thick ice will tend to increase the average thickness of the first year ice.
For these reasons it is more sensible to look at energy or total ice volume than split it into first year area and first year ice thickness.
Posted by: crandles | October 10, 2011 at 21:35
Re "The one possibility that I have come up with is that whatever remains of first year ice is advected before its first birthday."
Advected where? Presumably somewhere and then it isn't ice free.
Presumably it is possible to have a region that starts to freeze early and a region that melts out late. If the early freezing starts before the melt completes then there could be no multi-year ice nor a time with no ice.
You could also have some multi-year ice for a short period every year despite a situation where all areas do melt out every year by the multi-year ice moving from an early freeze region to a late melt out region.
Posted by: crandles | October 10, 2011 at 21:58
Wayne K says:
"keep in mind that no ice in the Arctic lasts forever"
True, but the ice-shelves have lasted for thousands of years - not merely 5 years. Other large sections of the arctic used to regularly have sea ice thickness measured in the dozens of meters - categorized in older papers as 9+ years. Not true anymore.
Crandles says:
"I suggest there are two major changes to the heat budget as ice volume declines, albedo effect and more heat loss though thinner ice in winter."
As pointed out by Rampal et al, ice mechanics and kinematics may account for why the GCMs underestimated recent sea ice losses. The newly ice free seas also have dynamic effects. They literally change the weather.
Bfraser says:
"The one possibility that I have come up with is that whatever remains of first year ice is advected before its first birthday."
The volume of advection through Fram Strait has remained constant. Though a thinner ice-pack allows the ice to move more freely and faster, it is also (by definition) thinner. The two factors essentially cancel each other out and the volume of advection remains constant. This also means that the percentage of ice advected increases (since volume has been decreasing), though the absolute numbers remain the same.
William: From, Arctic sea-ice melt in 2008 and the role of solar heating, Perovich et al.
Bottom melt will generally have more effect in the MIZs -- i.e., the low concentration edges.
Posted by: Kevin O'Neill | October 10, 2011 at 23:40
If I understand correctly William is saying that the rate of ice loss will slow substantially when only the central basin ice is left. William has most climate scientists on his side here. Look at all of the models used in the IPCC report. They all have a sigmoid shape. This would be like the Gompertz S curve everybody has seen here. Every GCM used by the IPCC believes the rate of ice loss slows when we get to small values of ice left. I disagree with this finding of the GCM's but I do not have the data or a nice supercomputer model to back up what I think is going to happen. I don't think anybody here has sufficient data to disprove that the ice loss could slow in the future as only a small amount of ice near the north pole is left. I think that the trend right now shows that the ice loss rate is speeding up and I don't think this will slow before we have low levels of ice which I define as less than half of the ice we had this summer by all measurements extent , area, and volume. I think this happens this decade. But this is just trend analysis not a physical ice behavior ocean circulation model.
Posted by: RunInCircles | October 11, 2011 at 00:43
During the 2007 minimum, sea ice area was 3M km2 and volume was 6460km3. This works out to an average thickness of about 2.1 meters.
During the 2011 minimum, sea ice area was also 3M km2 but volume was 4001km3. This works out to an average thickness of about 1.3 meters.
Posted by: Andrew Xnn | October 11, 2011 at 01:11
@William Crump
I stumbled across this bit of first year ice thickness...
"One of the key aspects of the expedition were large-scale sea ice thickness measurements in the inner Arctic, in which researchers of the Alfred Wegener Institute and the University of Alberta cooperated closely. For this purpose they used a four metre long electromagnetic ice thickness sensor, called EM Bird. The Polar 5 towed the sensor on an 80 metre long rope at a height of 15 metres above the ice surface for the surveys.
A preliminary evaluation of the measurement results shows that one-year-old sea ice in the Beaufort Sea (north of Canada/Alaska) is about 20-30 centimetres thinner this year than in the two previous years. In 2009 the ice thickness was 1.7 metres on average, in 2010 1.6 metres and in 2011 around 1.4 metres. “I expect that this thin one-year-old sea ice will not survive the melting period in summer,” Dr. Stefan Hendricks assesses the situation."
http://www.sciencedaily.com/releases/2011/05/110516102253.htm
This is an 18% loss over two years.
Posted by: Bob Wallace | October 11, 2011 at 22:04
Thanks Bob Wallace.
That was the report that I vaguely remembered and was hoping to post here.
A naive estimate from that report would be 9 years (if 18% requires 2 years, then the remaining 82% would require 9 years).
Although that is not quite in the range of the curve fitters, it is not terribly far off, either....
Posted by: Bfraser | October 12, 2011 at 09:30
It seems to me that once a threshold of 'thinness' is hit forces other than top and bottom melt combine to cut that 9 years short.
Thin ice, early in the year, is likely to get broken into smaller pieces and churned by ocean forces as well as flushed into warmer waters.
What might be worth monitoring is the date when ice begins flowing through the Fram.
I ran across this video a couple of days ago. (Neven might have already posted it, don't know.)
http://www.climatewatch.noaa.gov/video/2011/old-ice-becoming-rare-in-arctic
It does a good job of showing how the ice flushes. It would seem like someone might be monitoring date/amount and could make a statement about whether flushing is happening earlier in the season.
Posted by: Bob Wallace | October 12, 2011 at 17:26
Thanks for the info Bob.
I think these measurements were for first year ice at the end of April or early May based on the comments in the article.
Bfraser:
While a straight line extrapolation may get you to an ice free Beaufort Sea in 9 years at the winter maximum, I would not put much faith in using just three data points. Based on the dynamics of the winter ice freeze-up, I would not expect the Beaufort Sea to be ice free in the time frame of 9 years.
As far as the "ice free" state of the Beaufort Sea, I would say that it is already "ice free" at the minimum as it looks like it was under 50,000km2 out of its maximum amount of 500,000 km2 per Cryosphere Today. This region went below 100,000 km2 at the beginning of August and is now climbing back up to 100,000 km2. This looks to be less than half of what it was at the same time last year, but I can not tell if this change is due to long term warming forces or just some sort of short term weather pattern that might not repeat next year.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.11.html
The article refers to measuring ice thickness inside the Arctic Circle which starts at 66.5 degrees north. The Beaufort Sea occupies the latitudes 76 north to 70 north, so it is below the region above 80 degrees that I am hyper-focused on.
The Arctic Basin is at 3.4 million km2 and rising, which is about 100,000 km2 below where it was at this point last year, so at that rate, only 34 years left, but I would not put any faith in a two data point extrapolation.
I expect that the Arctic Basin will get back to its maximum figure of 4.25 million km2 in early December.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.1.html
It will not be ice free in November by 2017, which is what the volume trend line extrapolations indicated.
Posted by: William Crump | October 12, 2011 at 18:14
Are you moving the goalposts William?
We've been talking about the first year we'll see the Arctic (essentially) melt out and now you seem to be shifting to "will not be ice free in November by 2017".
You previously said that data which showed new ice thinner would damage/destroy your argument. Are you willing to argue that even though the ice is thinning in part of the Arctic new ice in the Arctic Basin isn't?
Posted by: Bob Wallace | October 12, 2011 at 19:35
I am realizing that I posted my previous comment too quickly (because I'm really supposed to be working....).
I did not notice that it wasn't Central Arctic that was being measured.
Sorry for adding unnecessary confusion to the discussion.
Posted by: Bfraser | October 12, 2011 at 20:59
Here is the CCSM3 sea ice extent model from the Wang and Overland paper.
What they did was pick the six best models for sea ice. Dark red are observations up to 2007. The dark blue and magenta are 2 different CO2 emission scenarios. Grey is without any human CO2 emissions.
I did one better than Wang and Overland and picked the best of the best models:
Looks like a compertz curve of sorts; but slower to reach near zero than us curve fitters find.
Of course, who is to say that the best of the best models upto 2007 have properly taken sea ice mechanics and export into account?
Posted by: Andrew Xnn | October 13, 2011 at 03:46
Bob Wallace:
Sorry for the delay in responding.
The Beaufort sea is not the same as the Central Arctic Basin. The measurements you cite are also from peak ice periods, not the September minimum as it appears the Beaufort Sea is already ice free at the minimum.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.11.html
The Central arctic is showing some unusual flattening in its rise to the maximum. Looks like it is taking longer to reach 3.5 million than it has in prior years. Is this an unusual weather flux this year or is it indicative of global warming? I suspect it is a bit of both.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.1.html
Still waiting for a trend line analysis on first year ice thickness in the central Arctic Basin at the minimum that shows ice free conditions are likely in next decade.
I never said that first year ice in the Arctic Basin was not thinning.
My position is that it is not thinning fast enough to be ice free in the time anticipated by the trend lines drawn using Arctic wide data. The volume trend line drawers have the Arctic ice free for three months by 2017 and I think it was 5 months by 2019. That ain't going to happen.
Looks like a flattening of the curve is the prediction made by scientists in Andrew Xnn's post.
I will try to post next week.
Posted by: William Crump | October 20, 2011 at 20:17
William, it seems to me that if we are interested in whether first year ice thickness is declining over years then we want to look at peak ice, not end of melt season ice.
Now I realize that the Beaufort is not the Central Basin. But they are immediate neighbors. I'm comfortable with assuming that if peak season first year ice is thinner in the Beaufort then it's likely thinner next door as well. I can think of no reason why first ice would be not be similarly thinning in the Central Basin. Can you?
You seem to hold the Central Basin somehow harmless when it comes to physical forces. Overall volume continues to fall, including CB volume. The melt season heat input continues strong and promises to increase. Multiple accelerating factors have been identified and almost no decelerating factors suggested. IMO the CB is waiting for its turn to get a hair cut. Its turn is coming soon.
Now I won't be surprised to see some of the monthly curves begin to flatten as they fall further. At some point they will intersect the winter refreeze curve. But I'm concentrating on what we have been speculating on up until you started sliding the goal from when we first see a melt-out to when we see extended months of an ice free Arctic.
Posted by: Bob Wallace | October 20, 2011 at 21:32
Bob:
The extended months of an ice free Arctic is what the volume trend lines "predict". If you do not believe the trend lines for July, August, October, and November are correct, why should we place any faith in the September trend line?
The CB is likely to be thinning regardless of what season you want to measure, although data is difficult to get, but it is not thinning as fast Beaufort.
CB is above 3.5 million km2 of area per CT
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.1.html
Per NSIDC/MASIE chart, 2007 through 2011 appear to all be above 3.1 million km2 and within a narrow band of 100,000 km2 as they are all below 3.2million km2.
Where is the indication of a big melt in this data?
Posted by: William Crump | October 28, 2011 at 20:45