2010-08-10 21:10:38Basic Rebuttal No.60: Has Arctic sea ice returned to normal? REVISION 4
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Arctic Sea Ice: Why Do Skeptics Think in Only Two Dimensions?

Argument No.60: Has Arctic sea ice returned to normal?

Discussions about the amount of sea ice in the Arctic often confuse two very different measures of how much ice there is. One measure is sea-ice extent which, as the name implies, is a measure of coverage of the ocean where ice covers 15% or more of the surface. It is a two-dimensional measurement; extent does not tell us how thick the ice is. The other measure of Arctic ice, using all three dimensions, is volume, the measure of how much ice there really is.

Sea-ice consists of first-year ice, which is thin, and older ice which has accumulated volume, called multi-year ice. Multi-year ice is very important because it comprises most of the volume of ice at the North Pole. Volume is also the important measure when it comes to climate change, because it is the volume of the ice – the sheer amount of the stuff – that science is concerned about, rather than how much of the sea is covered in a thin layer of ice*.

Over time, sea ice reflects the fast-changing circumstances of weather. It is driven principally by changes in surface temperature, forming and melting according to the seasons, the winds, cloud cover and ocean currents. In 2010, for example, sea ice extent recovered dramatically in March, only to melt again by May.

Sea-ice is subject to powerful short-term effects so while we can't conclude anything about the health of the ice from just a few years' data, an obvious trend emerges over the space of a decade or more, showing a decrease of about 5% of average sea-ice cover per decade.

 

Source: Rayner et.al, 2004, updated

Where has the thick ice gone?

When we consider the multi-year ice and look at the various measurements of it, we see a steep decline in this thick ice. As you might imagine, thick ice takes a lot more heat to melt, so the fact that it is disappearing so fast is of great concern.

 

Source: Polar Science Centre, University of Washington

It is clear from the various data sets, terrestrial and satellite, that both the sea ice extent and multi-year ice volume are reducing. Sea ice extent recovered slightly during the Arctic winters of 2008-09, but the full extent of annual ice reduction or gain is seen in September of each year, at the end of the Arctic summer. The volume of multi-year ice has not recovered at all, and is showing a steeply negative trend.

* Footnote: Although a thin layer of ice doesn’t tell us much about the overall state of ice loss at the Arctic, it does tell us a great deal about Albedo, the property of ice to reflect heat back into space. When the sea ice diminishes, more heat passes into the oceans. That heat melts the thick ice and speeds up the melting of thinner sea ice, which in turns allows more heat to accumulate in the oceans. This is an example of a positive feedback.

2010-08-10 22:53:16Different Graph
Robert Way

robert_way19@hotmail...
24.224.230.112

Hello All,
I was thinking perhaps you should plot up the data for september sea ice extent instead of the 1st graph. The data can be found here http://www.ncdc.noaa.gov/bams-state-of-the-climate/2009-time-series/?ts=arctic_seaice   by clicking on the name of the series.

It also would help make the graphs more readable.

2010-08-10 22:56:10Another Link
Robert Way

robert_way19@hotmail...
24.224.230.112
Here is the actual data for the longest data series used in that NOAA graph

http://www1.ncdc.noaa.gov/pub/data/cmb/bams-sotc/2009/global-data-sets/ARCTIC_SEAICE_hadisst.txt


2010-08-11 09:49:34Possible correction?
doug_bostrom

dbostrom@clearwire...
184.77.83.151

I may be wrong (it's been known to happen) but I believe sea ice extent and area measurements include both annual ice as well as multi-year ice.

A couple of suggested changes:

"New multi-year ice cannot accumulate unless some first-year (sea) ice survives through the Arctic summer, replacing ice lost through natural break-ups and calving, the icebergs drifting south before they melt."

-->

"New multi-year ice cannot remain stable in volume unless sufficient first-year (sea) ice survives through the Arctic summer, replacing ice lost through natural break-ups and and ice escaping South "

PIOMAS volume is not actually derived from GRACE data. Some Arctic geoid improvements have been performed w/GRACE in conjunction w/ICESat producing ice freeboard data but I don't think there's a longitudinal data product using that combination, or at least I can't find it if there is (and if it does not exist, why not?? A scandal!)


2010-08-11 15:36:09Sea ice vs multi-year ice
John Cook

john@skepticalscience...
121.222.17.49

Is it right to distinguish between "sea ice" and "multi-year ice"? Aren't they both sea ice? Wouldn't it be more accurate to use the labels "first year ice" and "multi-year ice"?

It would be awesome if we could also replot the PIOMASS data so it's simpler - without the standard deviation shading (maybe that's just me, I like a completely uncluttered, simple graph with as little text as possible and a big, clear heading like "Arctic Sea Ice Volume Anomaly".

In fact, on that note, I hate the term Anomaly because it's meaningless to the average person. But when I use "Change in Arctic Sea Ice Volume", that confuses people too. At least it does in the case of the Greenland ice mass anomaly graph  because people think the positive values mean Greenland was gaining mass in the first half of the graph:

Change  in Greenland ice mass, 2002 to 2010

Is "Variation in Arctic Sea Ice Volume" better? Or do we just have to grit our teeth and go with anomaly?

2010-08-12 00:40:39
Robert Way

robert_way19@hotmail...
24.224.230.112
Hello All, Perhaps a graph like this would serve the purpose well for readability


I don't know if one like this one would be easily readable but it certainly is something I put together that has interesting information



2010-08-12 02:58:30Update
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Thanks chaps - good comments and constructive criticisms. I'll definitely sort out 'first year' & 'multi-year' and get rid of sea ice in this context - it is ALL sea ice as was said. I'll also sort out the Grace/Piomass conflation - sorry about that.

I don't really have a view about the graphs. I chose one that looked fairly simple, because I thought it best to keep the graphs to a minimum at this level. Personally, I like Robert's Arctic sea ice min graph - clearest of all of them.

This begs a question: John C - are you exercising some kind of editorial role in all this. Who decides on the final version, what goes in and what goes out. I'm all for flat management, but the credibility of the site is paramount and we can't afford to screw up too much, or miss the boat.

2010-08-12 16:51:27A question for Robert
gpwayne
Graham Wayne
graham@gpwayne...
81.132.177.33

Hi Robert,

Having said I liked the 'red' graph best, there is one question I think worth considering. The graph I first chose (and this is true of other rebuttals) employs graphs from a known and credible public source. Personally, I think there may be more implicit credibility if we use only third party graphics/graphs or whatever, simply so their provenance and accuracy can be checked independently.

What's your view on this? (or anyone else)

2010-08-12 22:46:50Hello again
Robert Way

robert_way19@hotmail...
24.224.230.112
Hello Gpwayne,
I agree with your commentary that it is necessary to use the most credible source as possible. I could try to plot of NSIDC data from somewhere but I elected to go with the data available at http://www.ncdc.noaa.gov/bams-state-of-the-climate/2009-time-series/?ts=arctic_seaice which is the website for all the data released in their State of the Climate Annual report. The sea ice extent data that you see in the graph comes from Hadley. I think considering that Hadley is the pre-eminent global temperature record that they could be considered credible. That being said I do understand what you mean. There are skeptics who would hop onto this immediately and ask why NSIDC wasn't used. My only reply would be to say this one extends further back and that the graph is meant for non-experts and if someone wants to really discuss it they can look at the intermediate or advanced level response. Nevertheless this is all conjecture. I will look around to see if I can find some readily available data from NSIDC to keep this from being an issue.
2010-08-12 23:09:46
Robert Way

robert_way19@hotmail...
24.224.230.112
2010-08-12 23:15:31To digress slightly (apologies)
John Cook

john@skepticalscience...
121.222.17.49

Robert, while I think the extent vs temperature graph is a little advanced for a Basic rebuttal, it is quite an interesting graph. I've always thought of sea ice extent being a very noisy signal, due to it being subject to weather causing year to year fluctuations. I have this sense that sea ice volume is less noisy - in the same sense that total heat content is less noisy than surface temperature. Would this be a fair assessment? If so, it would be interesting to plot sea ice volume vs temperature anomaly and compare it to the sea ice extent vs temperature anomaly. An idea for a blog post perhaps? :-)

Graham, re editorial control, the system I've proposed is a peer-review system where each rebuttal needs to get 3 or 5 "thumbs up" approvals from other authors. Then I give final approval and it goes live. There seems to be general approval of this system but I'm open to suggestions to improve this (take it to the peer-review thread).

Re graphs, if the data is available and I have the time, I always try to plot them myself. This enables me to format the graph exactly as I want it which is usually as simple as possible. I always assume my graphics are going to be used on other websites so I make sure they work well out of context, with a strong, clearly worded header devoid of technical jargon. Incidentally, I can always tell when other websites are using my version of a graph by the tell-tale Helvetica bold heading :-)

Peer-reviewed figures always try to cram in as much info as possible - I try to pare it down to the minimum amount of info required to tell the story you wish to communicate. So long as you cite your source, preferably a link direct to the source, this is sufficient - in fact, climate boffins appreciate the link to the original source so they can have a play with the data too. The fact that you've been hands on with the data doesn't hurt your own credibility either - getting down and dirty with the data does hold a certain cachet with skeptics :-)

So IMHO, the credibility doesn't come from whether the graph was plotted by a third-party or by yourself but the source of the original data. If someone is going to nitpick whether the data should be NSIDC or NOAA or JAXA or whatever, a good recourse is to plot all the different data in the one graph in the Intermediate or Advanced rebuttal. Give them the cliff notes version in the Basic version, drill down into the technical nitty gritty in higher levels.

2010-08-13 00:07:00response to john
Robert Way

robert_way19@hotmail...
24.224.230.112
Hello John,
I agree the extent versus temperature graph is a little advanced for a basic rebuttal it would be nice to have a simplified version that would just in some sort of manner show that as temperatures increase the resulting sea ice decrease is at least linear. Not so easy to figure out how to show for the average person but a graph showing that as temperatures rise, sea ice decreases goes a long way towards dispelling all the talk of other factors being dominant and so on. I would like to plot up the volume data data but I haven't been able to find it anywhere. (Maybe I just haven't looked hard enough). The polar science center doesn't seem to put up their raw volume data so it may be a little challenging. I'm not going to use Pips like Goddard because I don't trust his pixel counting method. It would be interesting to see though what the relationship looks like. I imagine it might not be as straight forward as you think. The polar science center graph doesn't show huge dips in years which had huge warming in the Northern Hemisphere so it could be that volume has a more direct relationship with a certain season's temperature rather than using annually resolved temperatures. All that being said, your volume graph will track the general temperature trend better than the actual surface temperature record because it is noisy. So your assumptions are probably correct.

But lets remember now, i'm not an expert on sea ice so I could be way off haha...

I think it is a really good idea to plot your own data to simplify it and make it more visually appealing. Plus you can avoid acronyms and such... I tried that with the comparison of the three data sources up above. That NOAA source I cited above is turning out to be a wealth of data for anyone interested.

Another suggestion I have John is that there should be links on skeptical science for all the easily accessible data. We could organize it into groups for example sea ice data or temperature and so on making it easier for amateurs to get a chance to handle the data themselves.
2010-08-13 00:12:04Another Digression
Robert Way

robert_way19@hotmail...
24.224.230.112
John, Do you by any chance know how to make box plots like the ones used for the multiple analysis of mass loss trends like at your link:

http://www.skepticalscience.com/Part-Three-Response-to-Goddard.html (at bottom)

I am interested in making a synthesis of the mass change measurements but I actually can't figure out how to make a plot like the ones they use here and I find these plots to be the best for this sort of thing.
2010-08-13 00:32:16Box plots
John Cook

john@skepticalscience...
121.222.17.49

BTW, love that Arctic sea ice graph with the 3 data sets. I love numerous datasets providing independent confirmation, that's my bread and butter. That's a blog post right there! :-)

The way I see it, your initial Red sea ice graph is a Basic level. All people need to know is the ice is declining. The graph with the three different data-sets is either an Intermediate or possibly even Advanced level. It delves into the technical aspects of measuring and validating the data.

Shame the PIOMAS data isn't available online. Would have to contact them direct, I guess. Don't know anyone at the PSC, I'm afraid.

Re box plots, no, never made such a plot. Be a bit of work, tracking down all that data from different sources.

Agree re linking to source data. If we group them, perhaps a blog post on each group. Then we can create a "synthesis blog post" that provides links to all the different groups.

 

2010-08-14 21:48:30Revision notes
gpwayne
Graham Wayne
graham@gpwayne...
81.152.239.255

Chaps - this one was a bit of a minefield for me - I tried to consider all the comments but in the end I used Robert's red graph for simplicity, and stayed with the PIOMAS graph, which I think looks simple enough (steep and downhill all the way!).

I changed the text, adding at the start something I missed that's important - extent v volume, that old chestnut. Now clarified, and elsewhere I removed some stuff I thought was over elaborate or a bit iffy.

Anyway, see what you make of it now.

2010-08-15 04:08:42Almost there!
doug_bostrom

dbostrom@clearwire...
184.77.83.151

This is looking really good.

I'm getting hung up on this sentence, though: " Its transience and reactivity means the scientific usefulness of sea ice data is limited, although the extent has trended downwards over the last few decades, losing about 5% per decade."

Maybe it would be better to say something along the lines of "Sea-ice is subject to powerful short-term effects so while we can't conclude anything about the health of the ice from just a few years' data, an obvious trend emerges over the space of a decade or more."

Main thing is, "scientific usefulness of sea ice data is limited" just doesn't quite tell the story.

2010-08-15 06:09:20Updated revision
gpwayne
Graham Wayne
graham@gpwayne...
81.152.239.255
Doug - your sentence is much better than the original, so I've used it instead. Thanks very much.
2010-08-15 07:12:36Good Post, one Note
Robert Way

robert_way19@hotmail...
142.162.181.139
Great Job on the post. One note though
You say Discussions about the amount of ice - Arctic and Antartic - often confuse two very different measures of how much ice there is. I think you should change the sentence to Discussions about the amount of Arctic Sea Ice often confuse...

My reason for the suggestion  is people often confuse the Arctic and Antarctic and often confuse sea ice with land ice (huge pet peeve of mine) so why bring antarctica into it, or talk about ice in general when were only talking about sea ice. I just think that there should be no way to confuse the types of ices or areas
2010-08-15 15:16:28Revision 3
gpwayne
Graham Wayne
graham@gpwayne...
81.152.239.255
Hi Robert - I take your point. I've removed the Antarctic reference accordingly.
2010-08-16 09:30:07Good to go
Robert Way

robert_way19@hotmail...
142.162.181.139
I think the post was good. Good Luck
2010-08-16 18:42:15Thumbs up from me
John Cook

john@skepticalscience...
121.222.17.49
Looks good, Graham. I assume the italic text at the end is not included, right? I can take or leave the source links too - am wondering if we should leave them for the intermediate level?
2010-08-16 20:17:52Footnote
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156

John - I intended the italic section to be included, as it's a footnote to a comment in paragraph 2 (hence the star *). I should add that I am trying to sneak in little bits of supplimentary information, since it is an opportunity to do so and every little bit helps, I feel. While I have the audience, I'm going to try to give them a richer diet than just mere subsistence nutrition, if you see what I mean

As for the source links, I don't think they hurt and I would included a small number personally, but I don't have a strong feeling either way. I do think, when the item is in a stand-alone form, a link is helpful because the intermediate version is more clicks away than the source material.

2010-08-17 15:07:33Sorry!
doug_bostrom

dbostrom@clearwire...
184.77.83.151
Thought I already voted on this, sorry...
2010-08-17 23:34:04First post - take it with a grain of salt
Brendon

bpywell@iinet.net...
124.170.202.139

Hi Guys,

I've just joined up tonight and getting to find my way around. I thought I'd test the water and make sure I'm understanding the purpose here. If my my comments are misdirected please correct me. ;)

I've read the first post (I assume this is edited with each revision) and the one thing that immediately struck me was that it didn't seem much shorter than the intermediate level.

With that in mind I did a bit more editing and the following is a few suggestions on how some sentences might be modified.

Discussions about the amount of sea-ice in the Arctic often confuse two very different measures of how much ice there is. One measure is sea-ice extent which tells us how much area the ice covers. It is a two-dimensional measurement; extent does not tell us how thick the ice is. The other measure of Arctic ice is volume, the 3d measurement of how much ice mass exists.

Sea-ice consists of thin first-year ice, and older multi-year ice which has accumulated greater volume and is thicker. Sea-ice volume is the more important measure, because mass is a better indicator of how much heat has been exchanged.

Seasonally, sea-ice responds to the fast-changing circumstances of weather, forming and melting according to the seasons, the winds, cloud cover and ocean currents. In 2010, sea-ice extent recovered dramatically in March, but because it was thin, it also quickly melted again by May.

Sea-ice is subject to powerful short-term effects so while we can't conclude anything about the health of the ice from just a few years' data, an obvious trend emerges over a decade or more, showing a decrease of about 5% per decade.

2010-08-18 02:29:34On length
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156

Hi Brendan,

There are differing opinions about the length issue. My personal feeling is that these basic rebuttals are about density and technicality of information. The length issue belies what we try to do - no point in it being short if that means we don't elaborate fully, don't present all the facts, or create context for the rebuttal. I have not attempted to make my contributions artificially short, but readable enough to take the reader from beginning to end in a pleasant fashion. The criteria of length alone is not, in my view, sufficient basis for criticism (although redunancy always should be).

2010-08-18 07:51:31
Brendon

bpywell@iinet.net...
124.170.75.247
Thanks for the clarification. In that case, all's good.
2010-08-18 08:53:55
Andy S

skucea@telus...
66.183.162.8

This is very good. I have only two small suggestions 

1) In the fourth paragraph, I suggest you add the bolded word, as follows: In 2010, for example, sea ice extent recovered dramatically in March, only to melt again by May. 

 2) You might want a sentence explaining how the area and volume figures are derived. A skeptic is sure to pop up and say that the volumes are "only" models and it is not clear to a first-timer that area measurements are used because they can be easily determined from satellite images on a daily basis, whereas volumes require a more difficult and uncertain calculation.

2010-08-18 15:27:51Changes
gpwayne
Graham Wayne
graham@gpwayne...
86.156.59.156

Hi Andy, and thanks for the comments. Your first point is well made - I've changed the text accordingly (italicised rather than emboldened). On the second point, I think your concerns are entirely valid, but it can't be done in a sentence. To start with, there are issues about pixel counts on extent, and volume is, as you say, a bit more esoteric in the way it is calculated and that needs to be explained as well as the method validated. I suspect it's a can of worms where I end up equivocating all over the place and trying in advance to defend the measurements against an attack that is inevitable no matter what I write. Personally, I think that's one for the intermediate rebuttal.

2010-08-23 22:57:28Published with 1 change
John Cook

john@skepticalscience...
124.178.185.124
I hope you don't mind, Graham but I replaced 'deniers' with 'skeptics' in the heading. I personally avoid the term 'deniers' solely for the reason that it allows us to focus the discussion on science, not labels. I agree with the sentiment that denier is more accurate but I make the concession so we can talk about stuff that really matters.
2010-08-25 02:17:24Style issue
gpwayne
Graham Wayne
graham@gpwayne...
217.44.86.17
John - that's fine. I'll avoid 'deniers' in future and stick with skeptics. On the subject of the post, you do seem to have swapped out my entire text for something else, however...