Arctic Ice 2009

[weather eater]

To add to that, over the last 30 years of ice data, there have been signs of recovery before, only to slip back, put it another way if we had two successive years of warming the cry would be, its to short a timescale to make a judgement. Think I'll wait and see a few more years before slapping anyone on the back.

[oldsnowywizard]

I'd just posted on the general thread and realised we may have needed that post here to. Seeing as ice extent only requires a 15% (or more) coverage the more open water we accrue over summer allows for a greater distortion in 'ice extent' as the remaining pack can spread out and so long as it covers 15% of the open water will appear as it had when there was 100% ice cover.

Maybe , once ICESAT is up , we need to look at measuring ice volume across the arctic so we can better get a feel for the losses and not become confused when the weather stretches out the ice to cover a larger extent with 15% cover?

GW if an area of ice shows 15% how does that relate to the ice concentration maps that show ice concetration of 60 to 100% as they have done in iced up areas through out the summer? i would have thought if a measurable area had 15% of sea ice it would be shown on the concentration maps of having a low % and likewise the other way round? i would have thought it would be extremely misleading for a 15% cover to be represented as a high percentage of concentration... making the charts null and void? sorry long winded query...

[laserguy]

Because the relative isn't bouncing up and down and singing, Stew. In the last two days the relative has regained partial consciousness, after nearly four previous weeks getting gradually more comatose (albeit with many up-and-down variations in consciousness within that). Is this the start of a full recovery? It's possible, and one passionately hopes so....but it would be unwise to get too excited yet.

I spent four weeks in a coma when a vital organ failed. It got to the stage where all the doctors gave up any hope of recovery and advised the missus and kid to prepare their goodbyes. Thankfully,they were wrong. Just offering a different analogy...

[BUSHY]

I'd just posted on the general thread and realised we may have needed that post here to. Seeing as ice extent only requires a 15% (or more) coverage the more open water we accrue over summer allows for a greater distortion in 'ice extent' as the remaining pack can spread out and so long as it covers 15% of the open water will appear as it had when there was 100% ice cover.

Maybe , once ICESAT is up , we need to look at measuring ice volume across the arctic so we can better get a feel for the losses and not become confused when the weather stretches out the ice to cover a larger extent with 15% cover?

This page http://pafc.arh.noaa.gov/ice.php shows that lower percentage ice is not counted. Compare to cryo maps.

[doctormog]

The bottom line is that it doesn't matter how it is measured as long as it is always measured the same way.

Basically an ice extent of x million sq km this year means the same as an extent of x million sq kn 30 years ago if the same criteria are applied for the measurements. It's a red herring (and unscientific) to suggest otherwise.

[Methuselah]

The bottom line is that it doesn't matter how it is measured as long as it is always measured the same way.

Basically an ice extent of x million sq km this year means the same as an extent of x million sq kn 30 years ago if the same criteria are applied for the measurements. It's a red herring (and unscientific) to suggest otherwise.

Precisely, Michael...100% agree with you!

[MR EXTREMES]

well after all the excitement of a slight recovery here come the media again.

http://news.bbc.co.uk/1/hi/sci/tech/8272357.stm

[Gray-Wolf]

If the smoke and mirrors that concentration vs extent doesn't exist then why do NSIDC choose to comment upon the 'spread' of ice or the compaction of ice in their monthly reviews of ice over the summer? I still think that areas that were traditionally 100% ice cover over summer (the Siberian side or behind Bering) can still be included in the extent when they are only 30-40% ice covered giving the impression of little change until ice levels drop below 15%.

If we look at the C.T. plots for the various areas it is easy to see the slow down this past Aug but is this less ice melting or wind blown ice propping up the 15% or more criteria?

Though I agree with keeping to the same measuring system when the measuring system itself is variable then cannot results can become a tad misleading?

[Duncan McAlister]

If the smoke and mirrors that concentration vs extent doesn't exist then why do NSIDC choose to comment upon the 'spread' of ice or the compaction of ice in their monthly reviews of ice over the summer? I still think that areas that were traditionally 100% ice cover over summer (the Siberian side or behind Bering) can still be included in the extent when they are only 30-40% ice covered giving the impression of little change until ice levels drop below 15%.

If we look at the C.T. plots for the various areas it is easy to see the slow down this past Aug but is this less ice melting or wind blown ice propping up the 15% or more criteria?

Though I agree with keeping to the same measuring system when the measuring system itself is variable then cannot results can become a tad misleading?

Concentration looks pretty strong here G-W :lol:

http://arctic.atmos.uiuc.edu/cryosphere/NEWIMAGES/arctic.seaice.color.000.png

[Admiral_Bobski]

Concentration looks pretty strong here G-W

http://arctic.atmos....e.color.000.png

Further to that, although ice extent is lower, the concentration around midway through the month seems higher than that of the same date in 2005!

Here's a comparison between September 10th 2005 and September 10th 2009:

Unless I'm reading this concentration thingy wrong, the ice concentration is higher this year than it was back in 1985, too! Anyone know why this might be the case?

Is it possible that changing synoptics are conspiring to keep the ice pack confined to a smaller area, thereby apparently reducing the ice extent, but increasing the ice pack concentration?

CB

PS - In fact I have yet to find a year since 1979 where the ice concentration at this point was as high as it is this year. That's interesting...

Edited September 25, 2009 by Captain_Bobski

[Devonian]

Further to that, although ice extent is lower, the concentration around midway through the month seems higher than that of the same date in 2005!

Here's a comparison between September 10th 2005 and September 10th 2009:

Unless I'm reading this concentration thingy wrong, the ice concentration is higher this year than it was back in 1985, too! Anyone know why this might be the case?

Is it possible that changing synoptics are conspiring to keep the ice pack confined to a smaller area, thereby apparently reducing the ice extent, but increasing the ice pack concentration?

CB

PS - In fact I have yet to find a year since 1979 where the ice concentration at this point was as high as it is this year. That's interesting...

I would tentatively suggest two possibilities:

1. Temperatures in the area north of 80 degrees seem to have had one of those periodic warming spikes that seem to happen up there - new ice isn't being formed at the normal rates for the time of year, but old ice is consolidating?

2. Winds seem to have being blowing from the south or to be light across the seas North of Siberia (which also looks to be relatively warm for the time of year atm). Perhaps pushing the pack ice together or out down east Greenland?

I wouldn't be surprised to see ice anomalies rise in coming weeks.

Edited September 25, 2009 by Devonian

[BLAST FROM THE PAST]

CB

PS - In fact I have yet to find a year since 1979 where the ice concentration at this point was as high as it is this year. That's interesting...

Now that is fascinating, and eye opening too. I would like to hear explanations on this.

BFTP

[songster]

Now that is fascinating, and eye opening too. I would like to hear explanations on this.

BFTP

I'd be intrigued in the explanation too, because the original assertion is at best wishful thinking and at worst nonsense..

The monitoring sites generally use ice extent rather than area, because melt ponds on top of the ice can confound the data by looking like open water. Melt ponding is however extremely unlikely to drop the apparent coverage below 15%, so by using that as a threshold you get somewhat more stable results. However, area measurements (which adjust each pixel individually according to the measured concentration) are also available at Cryosphere Today. The graph is here.

http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg

As you can see, Arctic ice area (not extent) is currently having the third worst year since records began. Why someone would choose to spin that as "best concentration since 1979" is utterly beyond me, unless it's simply a case of looking at the bits where there is ice, and ignoring the bits where there isn't. I can play that game too by dropping an ice cube in the Pacific and saying "Look, this square centimetre is 100% covered in ice!"

As to why the concentration appears higher this year than others, it could be winds compacting the pack and closing up leads, or it could be melt ponds icing over. My understanding is that it's been a colder and cloudier summer than usual up there, so the latter seems at least plausible.

[Devonian]

... it could be winds compacting the pack and closing up leads, or it could be melt ponds icing over. ...

Sounds likely to me.

I think it's cold over any ice, but elsewhere a good deal relatively warmer - see here with new ice formation delayed slightly.

The JAXA graph is flatlining.

Edited September 26, 2009 by Devonian

[stewfox]

Take a set of numbers (if you can, think of it as a generic dataset rather than a dataset that has anything to do with AGW).

28, 27, 25, 22, 24, 22, 20, 21, 16, 17, 19

Would the increase in the last two digits mean that the dataset wasn't showing a steady downward trend overall?

This data set doesnt show a 'steady down ward trend over all'

It shows a very high start as 28 which quickly fell of to 22 and then now appears to average out.

On your assumption if the data did show a steady downward trend another increase next year would be a blip ?

Out of interest what does this show ?

28,27,25,22,24,22,20,21,16,17,19,21

Edited September 26, 2009 by stewfox

[Admiral_Bobski]

I'd be intrigued in the explanation too, because the original assertion is at best wishful thinking and at worst nonsense..

The monitoring sites generally use ice extent rather than area, because melt ponds on top of the ice can confound the data by looking like open water. Melt ponding is however extremely unlikely to drop the apparent coverage below 15%, so by using that as a threshold you get somewhat more stable results. However, area measurements (which adjust each pixel individually according to the measured concentration) are also available at Cryosphere Today. The graph is here.

http://arctic.atmos....urrent.area.jpg

As you can see, Arctic ice area (not extent) is currently having the third worst year since records began. Why someone would choose to spin that as "best concentration since 1979" is utterly beyond me, unless it's simply a case of looking at the bits where there is ice, and ignoring the bits where there isn't. I can play that game too by dropping an ice cube in the Pacific and saying "Look, this square centimetre is 100% covered in ice!"

As to why the concentration appears higher this year than others, it could be winds compacting the pack and closing up leads, or it could be melt ponds icing over. My understanding is that it's been a colder and cloudier summer than usual up there, so the latter seems at least plausible.

First off I'd like to clarify that nobody is "spinning" anything here. I merely noticed, by direct visual comparison, that the concentration of ice is higher this september than any previous september. This is not spin - it is a statement of fact.

There's also the fact that ice area and ice extent are the same thing (assuming that both allow for a minimum concentration of 15%, which I think they do - please do set me right if that's not the case).

My point was that, although the ice extent is lower than any previous year except 2007 and 2008, the ice that is there is more tightly pushed together (which is what concentration is a measure of). What would the ice extent this year be if the concentration of that ice was lower? There'd be the same amount of ice, but it would be spread over a wider area.

Perhaps this year there is as much ice as there ever was, but it's concentrated into a smaller area (hence the ice concentration is higher). I acknowledged in my first post on this subject that this could be a result of synoptics (wind movements, ocean currents or whatever), with this comment:

Is it possible that changing synoptics are conspiring to keep the ice pack confined to a smaller area, thereby apparently reducing the ice extent, but increasing the ice pack concentration?

No spin - just curiosity.

CB

Edited September 26, 2009 by Captain_Bobski

[Admiral_Bobski]

For clarification, there is a subtle difference between ice area and ice extent which, as defined by arctic-roos.org is this:

Ice extent and ice area are calculated for a grid resolution of 25 km. The difference between area and extent for our data is always positive. This difference represent the area of the open water in the pixels partly covered by ice (i.e. ice concentration less than 100%). In other words, ice area takes into account that there is a fraction of open water in pixels with ice concentration above 15 % and below 100 %

I have not yet found out how they determine the fraction of open water - is it determined by actual ice concentrations, or is there a "one size fits all" formula they use? I shall see what I can find out.

CB

[J10]

It does appear that we have bottomed out for the year in terms of ice extent. My personal opinion is that there has been a recovery since the year of 2007, but no real sign of a long term recovery as by any measure the ice area, volume or extent, Arctic ice levels are significantly below 30 year averages.

The next data to await with interest is the ice volume and only if this is higher than 2007 and 2008, can we say that the levels of ice concentrations are higher than recent years.

This thread will close in about a week, allowing comments about this summers performance and an Autumn version of this thread will open in early October.

[Thundery wintry showers]

This data set doesnt show a 'steady down ward trend over all'

It shows a very high start as 28 which quickly fell of to 22 and then now appears to average out.

On your assumption if the data did show a steady downward trend another increase next year would be a blip ?

Out of interest what does this show ?

28,27,25,22,24,22,20,21,16,17,19,21

The data with the 21 on the end supports your conclusion "fell off to 22 and then now appears to average out", as it shows a fall from 22 to 16 and then a recovery.

However, the data stopping at 19 does not support that conclusion. A dataset that starts off at 22, goes down to 16 and goes back up to 19 does not average out, it shows a partial recovery towards the end.

OK let's turn it the other way, what does this data show?

16,17,19,22,20,22,24,23,28,27,25,23

An averaging out at about 20?

[J10]

Take a set of numbers (if you can, think of it as a generic dataset rather than a dataset that has anything to do with AGW).

28, 27, 25, 22, 24, 22, 20, 21, 16, 17, 19

Would the increase in the last two digits mean that the dataset wasn't showing a steady downward trend overall?

Putting a linear trendline onto these figures give a formula of y=-1.072x+28.34, where the -1.072 is the gradient down per year.

[Solar Cycles]

Putting a linear trendline onto these figures give a formula of y=-1.072x+28.34, where the -1.072 is the gradient down per year.

I try not to get involved in this thread much, but I have to say you have done a splendid job JACKONE. It as remained unbiased and informative throughout, thank you!

[andy_leics22]

Out of interest what does this show ?

28,27,25,22,24,22,20,21,16,17,19,21

The extended Lottery numbers?

[J10]

What is surprising me at the moment, is the consistent level of the falls, around the 20,000 mostly with the odd 40,000 over the past week.

On top of the 2005 figure above other figures of note are 5,312,656 (the 2003-08 average), 5,254,531 which would be 1m above 2007 and 5,207,813 which would be 500k above last year.

Given the rate of loss ranges from 95k (2004) to 363k (2007) with an average loss of 235k From 2nd Sept to minimum ice extent, then a figure of 5.15-5.20m is most likely but hopefully the ice will remain above the markers laid out.

Next update on Sunday, hopefully the first rise will happen before then.

Today's provisional figure is 5,452,031, and this years low point is all but confirmed at 5,249,844 on the 13th September. How does this compare to past years.

• 6,032,031 2003 -782,187
  
• 5,784,688 2004 -534,844
  
• 5,315,156 2005 -65,312
  
• 5,781,719 2006 -531,875
  
• 4,254,531 2007 995,313
  
• 4,707,813 2008 542,031
  
• 5,249,844 2009
  
• 5,312,656 03-08 -62,812
  

[songster]

There's also the fact that ice area and ice extent are the same thing (assuming that both allow for a minimum concentration of 15%, which I think they do - please do set me right if that's not the case).

That's not the case. The ice extent measurement treats any pixel with >15% ice concentration as being 100% covered with ice. The ice area measurement weights it according to the measured concentration. Let's illustrate it with a simple example data set. Say we have eight pixels in the data set, each one representing 100km^2. The concentrations for the eight pixels (sorted into order for convenience) are 10%, 10%, 20%, 50%, 80%, 85%, 90%, 95%.

Extent calculation: Two pixels below 15% - treat as zero. Six pixels above 15% - treat as 100%. Stated ice extent = 600 km^2

Area calculation: Two pixels below 15% - treat as zero. Weight the other 6 pixels by percentage. (20%+50%+80%+85%+90%+95%) * 100km^2 = 420 km^2

This is why ice area figures are always lower than ice extent figures. The ratio of area to extent is equal to the average concentration across the pack as a whole - I've never actually seen the figure worked out, but it might be a handy measure of the degree of compaction of the pack. You could say that the area gives a better impression of the overall ice pack health, however as I said above it's susceptible to interference from melt ponding. Those pixels at 80/85/90/95% could all actually be 95% pixels with varying amounts of surface melt. Using extent instead will get round this issue at the cost of obscuring the effects of ice fragmentation. As long as you're consistent which you use, and the degree of fragmentation / ponding is similar from year to year, the overall trends will be accurate. Really, it's all an artefact of the problem that we don't have infinite resolution cameras. There's no such thing as "50% ice" in reality - a given point of the ocean surface is either iced over or not.

My point was that, although the ice extent is lower than any previous year except 2007 and 2008, the ice that is there is more tightly pushed together (which is what concentration is a measure of). What would the ice extent this year be if the concentration of that ice was lower? There'd be the same amount of ice, but it would be spread over a wider area.

Thing is, that's already taken care of in the area calculation. If you take a mass of 100% ice and spread it out so you now have twice as much 50% ice, then the ice extent measure will double, but the ice area measure will stay the same. The correction's already been done. Yes, the pack is a bit more compact this year than others (or possibly the melt ponds have iced over quicker). No, it's not sufficient to conclude that there's plenty of ice and the ongoing trend is all down to compaction. When you do the correction (i.e. use area rather than extent), it's still the third worst on record by quite some margin. Eyeballing pictures really isn't a good guide, unfortunately.

[parmenides3]

Neatly explained, Songster.

http://polar.ncep.noaa.gov/seaice/Analyses.html

contains some good explanations (scroll down the page.

Bob Grumbine is also a good egg and has recently started blogging, to cover some of the enquiries he gets about science and GW: http://moregrumbinescience.blogspot.com/

if you have technical questions about the Arctic, he may well address them for you...

P