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Peter Ellis

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Re: Ice free predictions and their uncertainty
« Reply #50 on: September 09, 2016, 12:57:17 PM »
*shrug* If that's the message you take, I can't stop you.

We're playing Russian Roulette with the world's climate, the gun is getting increasingly loaded with bullets, we have no idea when it will go off, and you want to piffle on about trying to predict whether we'll shoot ourselves on the first trigger pull or the tenth.  Understanding the science of how and what will happen is far more important than the random chance factor of exactly when the gun goes off.

pauldry600

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Re: Ice free predictions and their uncertainty
« Reply #51 on: September 09, 2016, 02:42:54 PM »
Yes looking at the IJIS average over the years since the 80s the average used to be 6m2 then 5.5 then 5 now its in the 4s. At best we have 25 years left till no ice ...peobably way less. So by 2040 theres bound to have been a number of ice free Summers.

Here in Ireland we had our warmest ever September NIGHT.
20c. Normal nighttime here is 8c. I feel its the ever warming oceans that are driving up these temperatures.

Why is Antarctic staying so cold though?

Archimid

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Re: Ice free predictions and their uncertainty
« Reply #52 on: September 09, 2016, 03:21:46 PM »
Understanding when it will happen is highly significant in two different ways scientifically and socially.
In scientific terms the earlier it happens the stronger the implied forcing. With more forcing the faster the global warming once the ice reserves are gone. In social terms, the earlier it happens the less time we have to prepare and adapt. We could also prevent it using geoengineering, but that takes time. Knowing when it will happen will give engineers the deadlines needed to complete  their tasks.


The problem is the uncertainties. Given the complexity of the system and the current rate of change no model could possibly predict when it will happen with the confidence required to take action. Meaningful action on something of this scale requires changes that nobody likes. What if they predict an ice free arctic by 2020 with 80% probability?  Can a decision maker make the decision to change the world based on an event whose probability is 80% and whose outcome ranges from extinction of humanity at worst to an utopia for northerners at best.

 They can't, specially with people scientifically asserting that there is nothing to worry. The only logical alternative is to classify the work, make assurances that government will keep functioning  and hope for the best. That's where we are right now. Wait and see.

I am an energy reservoir seemingly intent on lowering entropy for self preservation.

6roucho

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Re: Ice free predictions and their uncertainty
« Reply #53 on: September 09, 2016, 03:29:04 PM »
Yes looking at the IJIS average over the years since the 80s the average used to be 6m2 then 5.5 then 5 now its in the 4s. At best we have 25 years left till no ice ...peobably way less. So by 2040 theres bound to have been a number of ice free Summers.

Here in Ireland we had our warmest ever September NIGHT.
20c. Normal nighttime here is 8c. I feel its the ever warming oceans that are driving up these temperatures.

Why is Antarctic staying so cold though?
Antarctica may be gaining ice, but it's still warming faster than anywhere except the Arctic.

Iceismylife

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Re: Ice free predictions and their uncertainty
« Reply #54 on: September 09, 2016, 05:25:05 PM »
...
Why is Antarctic staying so cold though?
The short answer is Greenland's ice sheet and the sea ice, those reflect a lot of sunlight. And the sea ice keeps the heat in the water from getting at the environment.

JMP

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Re: Ice free predictions and their uncertainty
« Reply #55 on: September 09, 2016, 10:54:50 PM »
...
Why is Antarctic staying so cold though?
Aside from it being late winter there at the moment.
Since Carbon-dioxide and Methane seem to be remaining more concentrated in the Northern Hemisphere (where more are produced) and are not dispersing globally to uniform levels. I'm thinking that might obviously have something to do with the Southern Hemisphere not warming as fast, but cannot find that this has exactly been confirmed - precisely at the moment.     


NASA | A Year in the Life of Earth's CO2 (2006): https://youtu.be/x1SgmFa0r04

from The Copernicus Observatory:

« Last Edit: September 09, 2016, 11:02:16 PM by JMP »

crandles

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Re: Ice free predictions and their uncertainty
« Reply #56 on: September 09, 2016, 11:33:32 PM »
Why is Antarctic staying so cold though?

For Southern Hemisphere, I think standard answer is much more ocean in southern hemisphere causing large heat capacity so rate of warming is slower in southern hemisphere.

For Antactica:

http://www.nsstc.uah.edu/data/msu/v6.0beta/tlt/uahncdc_lt_6.0beta5.txt
report southern polar region not warming at all - trend -0.01C per decade.

Ozone and CFCs are greenhouse gases, not sure but think ozone hole has more effect so reduced ozone causes cooling (but possibly other knock on effects could be more important?).


https://en.wikipedia.org/wiki/Antarctica_cooling_controversy
reports
Quote
the data are extremely sparse
and
Antarctica seems to be both warming around the edges and cooling at the center at the same time. Thus it is not possible to say whether it is warming or cooling overall.

Other ozone hole effects such as moving atmospheric cell closer to pole may also be changing winds complicating matters.

Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #57 on: September 10, 2016, 05:45:51 AM »
Of course the consequences of an ice-free Arctic are interesting! The details of whether random variability means that it happens in 2020, 2025 or 2030... not so much.

Peter, I'm pretty sure I understood the point you were making all along.

However, I can also understand how easy it is to be misinterpreted, especially when, as in this instance, a phrase you employed was taken on its own - without your accompanying contextual setting.

Bill, I read your response to Peter Ellis' post several times now, and I must admit that I have no clue what you are talking about.

Specifically :
- Which exact point is it that you 'understood' that Peter Ellis was making ?
- Why do you state that Peter Ellis was "misinterpreted" ?
- Which "phrase" from him was "taken on its own" and who did that ?

It would be nice if you could answer these questions, because what I see is that Peter Ellis is trying to downplay the fact that IPCC changed the definition of "less than 1 M km^2" to the much more restrictive (and scientifically unsustained) definition of "less than 1 M km^2 for 5 consecutive years".
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Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #58 on: September 10, 2016, 05:56:02 AM »
Of course the consequences of an ice-free Arctic are interesting! The details of whether random variability means that it happens in 2020, 2025 or 2030... not so much.

The same argument holds no matter if we define "ice-free" for one year, or "ice-free" for 5 consecutive years, so there is NO scientific reason to change the definition.

The only thing we know for SURE is that the latter definition will occur at least 5 years later than the first.
« Last Edit: September 10, 2016, 06:01:43 AM by Rob Dekker »
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oren

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Re: Ice free predictions and their uncertainty
« Reply #59 on: September 10, 2016, 02:53:15 PM »
Why is Antarctic staying so cold though?
Here's another try at the same question: Antarctic glaciers are melting, this causes a cold fresh layer to form in summer above the relatively warmer ocean below. And in the winter, this same layer freezes  easily and prevents the ocean from warming the atmosphere.

crandles

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Re: Ice free predictions and their uncertainty
« Reply #60 on: September 10, 2016, 03:40:51 PM »

Here's another try at the same question: Antarctic glaciers are melting, this causes a cold fresh layer to form in summer above the relatively warmer ocean below.

I may need a further try as well. Ho hum.

Not so sure about that, think it is too cold to be melting from air temps so it is warm upwelling deep water doing the melting, reducing buttressing and faster flow of glaciers thinning them and further reducing obstructions to faster flow. The deep water is probably salty but maybe when mixed with melt water the salty water sinks and you do get more of a fresh water layer?

Quote
And in the winter, this same layer freezes  easily and prevents the ocean from warming the atmosphere.

However the increased sea ice area seems likely to be important whether the cause is fresh water layer or more winds off the land.

The trends seem complex: centre probably cooling, edges of land and peninsular warming then ocean cooling. Then further away warming (Probably should have noted that south polar region trend of -0.1oC/decade breaks down to land +0.06oC/dec ocean -0.05oC/dec.)

Cooler, warmer, cooler, warmer pattern may sound like a strange pattern to arise.

Suggested main causes:
Centre: ozone loss causing cooling.
Stronger adiabatic winds moves cold from land out to sea so colder over ocean and had the air stayed over land longer it would have got colder so as that is no longer happening so much, it is warmer at edges of land.

Also, consequent effect of increased sea ice as it moves away from land more quickly results in more sea ice which can give a much colder surface skin temperature than ocean.

Further away GHG warming eventually becomes dominant.

JMP

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Re: Ice free predictions and their uncertainty
« Reply #61 on: September 11, 2016, 07:01:10 AM »

Here's another try at the same question: Antarctic glaciers are melting, this causes a cold fresh layer to form in summer above the relatively warmer ocean below.

I may need a further try as well. Ho hum.


And, me too.  *sigh*

Iirc there is a (somewhat-counterintuitive) positive feed-back, where the cold melt water, stirs up more warm water causing melting as well which agrees with what Crandles is saying.  But, the fresh layer of water causing increased sea ice is correct afaik.  I'm not certain about the ozone depletion.  I do know that Antarctica is one of the driest places on Earth and wonder if that lack of moisture might generally extend to the stratosphere? this despite the snow that falls?  Since water vapor is a strong greenhouse influence - could this be a significant difference as well?

I Know insolation is different for the SH - as we are further from the sun in the Antarctic winter and closer in the Antarctic summer, but the austral summer is also shorter.  The averaged difference is negligible but less insolation during winter might still be a significant factor in winter sea ice growth.  Antarctic sea Ice mostly melts during austral summer anyway - there's very little if any old sea ice.

It really is an Apples to Oranges comparison between the two poles, despite the obvious similarities, since there really are significant differences.  (instead of Apples to Oranges I want to say Apricots to Almonds because these two are the same genus etc. but that's probably best left for another forum -  not to mention there is even an Antarctica section of this forum ;) and an esteemed ASLR far more knowledgeable than I am surely) Still can't qualify the influence of concentrated CO2 and CH4 in the NH. 400 ppm CO2 has been recorded in Antarctica.  But, this article suggests that the onset of warming from CO2 is more rapid than I had previously realized so I'm not discounting the increased NH concentrations. http://phys.org/news/2015-06-greenhouse-gas-caused-felt-months.html

A Continent surrounded by vast Oceans is entirely different than an Ocean surrounded by vast Continents.  Antarctica gaining sea ice in winter when there's so little sun to reflect, doesn't mean much, especially when you consider it's usually melted by summer anyway.   The important ice in Antarctica is the land ice which is actually decreasing. 


 

   


Bill Fothergill

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Re: Ice free predictions and their uncertainty
« Reply #62 on: September 12, 2016, 07:52:42 PM »


Bill, I read your response to Peter Ellis' post several times now, and I must admit that I have no clue what you are talking about.

Specifically :
- Which exact point is it that you 'understood' that Peter Ellis was making ?
- Why do you state that Peter Ellis was "misinterpreted" ?
- Which "phrase" from him was "taken on its own" and who did that ?

It would be nice if you could answer these questions, because what I see is that Peter Ellis is trying to downplay the fact that IPCC changed the definition of "less than 1 M km^2" to the much more restrictive (and scientifically unsustained) definition of "less than 1 M km^2 for 5 consecutive years".

Rob,

Apologies for any confusion I caused. On Friday, I was rushing out to see the Queen Stage on the Tour of Britain. (That's a cycling race, for the uninitiated.) As a consequence, I failed to take enough care in my wording, and, in particular, failed to be adequately explicit.

I'll try to make my position clearer, but that comes at the cost of a much longer post than I would normally contemplate.

Anyway, addressing your 3 questions...

Q1: "Which exact point is it that you 'understood' that Peter Ellis was making ?"

First off, I'll choose to ignore the quotation marks, as in 'understood'.

In Reply #861 to your #860 on the "2016 sea ice area and extent" thread, Peter made the following statement...

"The motive seems quite clear to me - try to get people to pay attention to the 5-year mean rather than individual years.  The first individual year under 1 million will be definition be an outlier and is almost certain to be followed by a year above 1 million.  For something as important as this, there needs to be a definition where the deniers can't turn around 12 months later and pretend there's a recovery. ..."

Whilst I would have phrased the second sentence more along the lines of "... The first individual year under 1 million ... is likely to be followed by a year above 1 million", I do agree with the need to avoid the unwitting or unnecessary provision of ammunition. You remember as well as I do all the bollocks about a recovery after the 2007 - 2008 - 2009 minima. (I don't make any claim as regards my understanding, or otherwise, of the motivation underpinning said definition change.)

Later, in Reply #42 of this thread, Peter stated...

"... Not sure if your Google findings help - they both come from after the report, at which point any competent scientist will be referring back to the agreed text to define the consensus view, and then explaining based on that. He [Prof Ed Hawkins] is doing basically the same thing as we are in this thread - pointing out that an individual ice-free year will, by definition, come earlier than five consecutive ice-free years (or indeed an ice-free 5-year running mean). 

Might be worth checking with him, I suppose - but the larger point he's making is that the first single ice-free year is both completely unpredictable and largely irrelevant in scientific (rather than psychological) terms. Trying to forecast individual years is a mug's game."


From these two statements, my interpretation was (and is) that Peter meant by the time the 5-yr running mean gets below the 1 million mark, there will be little scope for deniers to write it off as a fluke event - as happened in both 2007 and 2012.

As it happens, I don't actually agree with Peter, as the various machinations of the climate change denial machine are simply jaw dropping. We've seen outright denial that Arctic sea ice was declining; we've seen claims that that the levels seen post-2007 are comparable to those seen in the 1950's; and we're now seeing the groundwork being set for the future by claims that the Arctic was seasonally ice-free back in the 1920's. Revisionism in all its ugly glory!


Your 2nd and 3rd questions were...

Q2- Why do you state that Peter Ellis was "misinterpreted" ?
Q3- Which "phrase" from him was "taken on its own" and who did that ?

If you read Replies #43 and #44, the answers to these questions should be self-evident.

Archmid is correct in stating that a very low amount of ice in the Arctic is scientifically interesting. In fact, living in the UK, it's frankly fucking terrifying. The behaviour of the jet-stream is largely unpredictable at the best of times - that's why the weather is so ubiquitous in everyday conversations over here. However, that wasn't the point Peter was making, and, one of his statements was taken out of context in #43. (Hence Peter's response in #44)

My Reply #46 was merely intended to inform Peter that I had not interpreted his words in the same way as Archmid.

However, I fully agree with Archmid's sentiments. Leaving aside the ice/albedo effect, as well as the impact of greatly reduced sea ice on the jet-stream, what really scares scares me is the impact on the Greenland Ice Sheet. The obvious factor is Sea Level Rise, but the real bummer (as far as winters in western Europe is concerned) would be if the AMOC reduces significantly. (Do I hear "Younger Dryas" anyone?)

In fact, I'm really horrified by the prospect that nothing, in terms of emissions control or CCS up-scaling/implementation, gets put in place until this ludicrously low value of 1 million sq kms gets surpassed. Long before we hit the 1 million mark, the planet will be experiencing conditions not felt since the Quaternary Glaciation took hold in the northern hemisphere. The very idea that 1.001 can be equated to business-as-usual, but 0.999 equates to some kind of wake-up call is a sad reflection on the whole sorry business.

That value represents the point at which the area is no longer described by 7 digits, as from then on, 6 digits would suffice. To the best of my, admittedly limited, knowledge, the only time the area in the Arctic Basin dropped below the 2 million mark was when it hit 1.8 in 2012. Therefore, setting an "ice free" definition at just 1 million sq kms for the entire Arctic, comes across as a carte blanche to the denialist industry for the next few years - at least.


Rob, as to your final point, any question you have regarding Peter's supposed attempts to "... to downplay the fact that IPCC changed the definition of "less than 1 M km^2" to the much more restrictive (and scientifically unsustained) definition of "less than 1 M km^2 for 5 consecutive years", I'm afraid you will have to direct toward the man himself.

For what it's worth, at no time have I garnered the impression that Peter was attempting what you suggest. In Reply #460 of the "sea ice area and extent" thread, Peter stated...

"... The "five consecutive years" seems to have spread by a comedy of errors.

First, there's a bungled attempt at clarification in the figure caption on page 21. The intent of the sentence is clear from the graph- it plots the 5-year mean and draws a dotted line to show where the 5-year mean falls below 1 million - but the caption erroneously says this means 5 consecutive years below 1 million. ...
"

As I've said above, my own view would be that the 1 million sq kms figure would be far better applied just to the Basin, not to the whole Arctic.

Ned W

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Re: Ice free predictions and their uncertainty
« Reply #63 on: September 12, 2016, 10:22:16 PM »
The first ice free Arctic in millions of years [...]
It seems likely that the Arctic Ocean was sporadically ice-free in summer during previous interglacials, so not "millions of years".  Cronin et al. 2015 finds evidence for this and it's not at all surprising given the much higher insolation at high latitudes and the loss of most of Greenland's land ice during MIS-11.  Greenland didn't lose as much land ice during the last interglacial, but that was mostly because it was too short in duration -- which isn't really a constraint on the loss of sea ice.  So it's probably no more than 120,000 years since the last time the Arctic Ocean was ice-free.

It's also possible that there were low-ice or ice-free episodes during the Early/Mid Holocene, ca. 8000 years ago (Stranne et al. 2014).

Archimid

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Re: Ice free predictions and their uncertainty
« Reply #64 on: September 13, 2016, 04:36:27 AM »
Thank you Ned.  You bring up very important points.
Quote
It seems likely that the Arctic Ocean was sporadically ice-free in summer during previous interglacials, so not "millions of years".  Cronin et al. 2015 finds evidence for this and it's not at all surprising given the much higher insolation at high latitudes and the loss of most of Greenland's land ice during MIS-11.  Greenland didn't lose as much land ice during the last interglacial, but that was mostly because it was too short in duration -- which isn't really a constraint on the loss of sea ice.  So it's probably no more than 120,000 years since the last time the Arctic Ocean was ice-free.

I happen to agree. As a matter of fact, it is my pet theory that the main difference  between the eemian and the holocene is that the eemian lost the arctic early in the interglacial while the holocene reached it's thermal maximum but was able to maintain an arctic.  The changed albedo and planetary dynamics  of having no ice in the north pole took the eemian to a much higher thermal maximum.

I say a millions because I was under the impression that the uncertainty behind arctic sea ice conditions during interglacial was very large. I’m not sure what paper you refer too since there are many, however i think you are referring to the one that uses sea shells as proxy for temperatures.  I thought it was good enough for me, but I also think that the uncertainty  is too large too make life and death decisions like actually finding out what happens to a planet with just one frozen pole.

I rather assume the worst. We know from fossil records that crocodiles roamed the arctic millions of years ago. So for sure, it has happened millions of years ago. At the time horses were the size of dogs. It was too hot for large mammals.

Quote

It's also possible that there were low-ice or ice-free episodes during the Early/Mid Holocene, ca. 8000 years ago (Stranne et al. 2014).


Thank you. This is a great lead for me and I didn't know about it.  After reading, I now think it is possible for the arctic to be ice free at the beginning of the holocene. So I retract my statement.  This is has very likely happened much earlier than millions of years.

Sadly when I read it I get this:

Quote
 

When using a dynamic surface albedo parameterization the reduction becomes considerably larger. The sea ice cover then enters a regime with ice free summers between about 6000 and 11,700 years BP (Fig. 3b). The sudden transitions from a perennial to a seasonal ice cover at 11,700 years BP and from a seasonal to a perennial ice cover at 6000 years BP are related to the fact that there is no stable state in the model characterized by a brief ice free period in the summer; it is either perennial sea ice or ice free conditions for an extended period of time in the summer. As explained in detail in Björk et al. (2012), the ice thickness distribution will more and more lean towards a dominant ice thickness category as the climate gets warmer. As soon as the dominating ice thickness category melts completely there is no possibility to maintain an equilibrium cycle with just a few days of open water because when this large area fraction becomes ice free the albedo will be lowered significantly and this enhances the amount of solar radiation absorbed by the ocean. The dominating ice thickness category will then melt somewhat earlier in the following summer season which will further enhance the oceanic absorption and so on. The system has then to find a new equilibrium characterized by a quite long period of almost completely open water during summer (a few thick ridged ice categories will still survive the summer but these occupy only a very small area fraction).


So basically what I said. Once the Arctic sea ice is gone the world enters a different state. On the flip side, I thought that once the Arctic sea ice was gone the world's temperature would rise several degrees. Now, based on this new information and the holocene temperatures I think that it will only account for a degree of so.

Still. I would prefer not to find out, but I’m afraid we will very very soon. We have already exceeded early holocene temperatures or we are about to.
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Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #65 on: September 14, 2016, 09:41:52 AM »
Bill, thank you very much for your elaborate reply.
A few notes below :

...
Q1: "Which exact point is it that you 'understood' that Peter Ellis was making ?"
...
Whilst I would have phrased the second sentence more along the lines of "... The first individual year under 1 million ... is likely to be followed by a year above 1 million", I do agree with the need to avoid the unwitting or unnecessary provision of ammunition.

Exactly. But the point works the other way around :

If the IPCC declares (as they just did) that the Arctic is only considered "ice-free" when there are "five consecutive years" of less than 1 M km^2 of ice, then IPCC just provided the BEST ammunition ever for deniers to make their point :

Just image : After many years of decline, Arctic sea ice hits below 1 M km^2 for the first time at some year in the future. We say : "After a long decline of the Arctic, we did not do anything. Now that the Arctic now was nearly ice free this year, we REALLY need to curb our emissions".
Deniers reply : "You alarmist ! Even the scientists at the IPCC do not agree with you. They understand that this is a fluke event, and that for real ice-free Arctic there need to be 5 consecutive years of less than 1 M km^2."

You see ? That IPCC definition is the best ammunition we could possibly give to deniers.
That is why Peter Ellis' "point" is incorrect, opposite from the truth and thus almost hypocritical.

Quote
Might be worth checking with him, I suppose - but the larger point he's making is that the first single ice-free year is both completely unpredictable and largely irrelevant in scientific (rather than psychological) terms. Trying to forecast individual years is a mug's game.
The first single ice-free year is not any more or less predictable than the first consecutive 5 years of ice free Arctic. We only know that the latter definition will become reality at least 5 years (and likely much later) than the first.
So this point is moot. Why did he mention it any way ?

Quote
From these two statements, my interpretation was (and is) that Peter meant by the time the 5-yr running mean gets below the 1 million mark, there will be little scope for deniers to write it off as a fluke event - as happened in both 2007 and 2012.

As it happens, I don't actually agree with Peter, as the various machinations of the climate change denial machine are simply jaw dropping. We've seen outright denial that Arctic sea ice was declining; we've seen claims that that the levels seen post-2007 are comparable to those seen in the 1950's; and we're now seeing the groundwork being set for the future by claims that the Arctic was seasonally ice-free back in the 1920's. Revisionism in all its ugly glory!

Exactly. That is why deniers ALWAYS find something to hold on to, and this is EXACTLY why the IPCC should NOT give them ammunition by re-defining when the Arctic is "ice-free".

Incidentally, it appears that this re-definition by the IPCC of what "ice-free" means came about in a rather obscure (no record) and so far unexplained way. A bit more detail here :
http://forum.arctic-sea-ice.net/index.php/topic,1559.msg89500.html#msg89500
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Peter Ellis

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Re: Ice free predictions and their uncertainty
« Reply #66 on: September 14, 2016, 10:11:28 AM »
I certainly don't intend to defend the "five consecutive years" definition.  I am however saying that I do not believe the use of this definition in the report to be malicious, politically motivated, or any other such claptrap. It's evident on the face of it that it is an accidental mis-explanation of a five-year mean.

I agree with the IPCC that the five-year mean is a much better metric to use when trying to FORECAST when the Arctic will be ice free. Obviously when discussing actual reality, you use the actual data.

Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #67 on: September 14, 2016, 10:28:09 AM »
I certainly don't intend to defend the "five consecutive years" definition.  I am however saying that I do not believe the use of this definition in the report to be malicious, politically motivated, or any other such claptrap. It's evident on the face of it that it is an accidental mis-explanation of a five-year mean.

Peter, the issue I have with your reply is that you immediately assume that this is an "accidental mis-explanation".

Given the strict rules under which IPCC edits (especially in the SPM report) operate leaves very little room for "accidental mis-explanation". At least there should be a record of how it came about.
Now with the total absence of ANY record of when, why and who made this "5 consecutive years" change to the definition, should have triggered at least some curiosity with you.
Something like "Ah. that is strange that they just changed the definition. Let me investigate" would have been a much better reply.

Instead, you come up with arguments (ammunition for deniers) that actually work the exact opposite than you propose, arguments (like scientifically irrelevant) that work equally no matter what the definition, and excuses and assumptions that are easily debunked (since the IPCC operates under strict editing rules).

Quote
I agree with the IPCC that the five-year mean is a much better metric to use when trying to FORECAST when the Arctic will be ice free. Obviously when discussing actual reality, you use the actual data.

Here you go again. Now you advocate the 'middle' definition (the "five year mean"), but only for forecasts (without explaining why) and you fail to mention why the original definition (less than 1 M km^2) would have to be changed at all.
« Last Edit: September 14, 2016, 10:35:34 AM by Rob Dekker »
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Peter Ellis

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Re: Ice free predictions and their uncertainty
« Reply #68 on: September 14, 2016, 12:18:20 PM »
Peter, the issue I have with your reply is that you immediately assume that this is an "accidental mis-explanation".  [...]  Something like "Ah. that is strange that they just changed the definition. Let me investigate" would have been a much better reply.
... but we collectively did investigate! See here, and the preceding posts.
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89334.html#msg89334

We know what happened and in what order.  A graph was included that made a forecast for when the five year mean would go below 1 million.  Then in a later draft, bracketed text was added that said "consecutive years". As I outlined in my previous post, there are several reasons to conclude that this was intended as a clarification rather than a change of definition. It's bracketed, begins with "i.e.", and the original text and the actual scientific data (the forecast graph) is left unchanged.

P-maker explained in detail how the editing process worked, and that this sort of change to a figure caption is NOT discussed in detail and agreed by all countries, but can be made "in consultation with" the scientists. In the same post, he explains that changes made to the SPM are then automatically propagated back into the underlying documents.
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89322.html#msg89322

Note that a change to a figure caption made "in consultation with" scientists is not the same as it being made BY the scientists. I actually am a scientist, and have first-hand experience of how what seems to me to be a perfectly clear explanation can be misunderstood by a press office! 

Quote
I agree with the IPCC that the five-year mean is a much better metric to use when trying to FORECAST when the Arctic will be ice free. Obviously when discussing actual reality, you use the actual data.

Here you go again. Now you advocate the 'middle' definition (the "five year mean"), but only for forecasts (without explaining why) and you fail to mention why the original definition (less than 1 M km^2) would have to be changed at all.

Because forecasting the five-year mean has a small chance of actually being right. Trying to forecast individual years is a short cut to looking like a bloody idiot, as we ourselves prove over and over every damn year. In the blog linked in this thread, Ed Hawkins points to this paper which attempts to estimate the error range on forecasts. (The people arguing with me did go and read the actual posts and papers linked rather than just the headlines, right?)
http://onlinelibrary.wiley.com/doi/10.1002/2016GL070067/abstract

The paper finds that there is an 20-year variability in the outputs of any forecast model due to sensitive dependence on parameter choice, and that over and above that there's a further 5-year variability caused by uncertainty in the level of future GHG emissions.  Given that, I'm surprised they even tried to forecast the 5-year mean, but it's such an important factor that I guess they had to try their best.

oren

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Re: Ice free predictions and their uncertainty
« Reply #69 on: September 14, 2016, 01:23:11 PM »
5-year mean is a good measure for achieving near-certainty that the Arctic has flipped a state. 1-year number is good for rallying those who forgot to rally when the globe started overheating. Both are scientifically sound.
5-year consecutive is an outrageous definition. Since it gives so much ammunition to deniers now and in the future, IPCC should have corrected it or clarified somehow that it's a mistake.
Since they did not, their intentions don't really matter, the outcome is the same. But I side with the malice hypothesis (of someone in the report editing chain).

Peter Ellis

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Re: Ice free predictions and their uncertainty
« Reply #70 on: September 14, 2016, 01:27:04 PM »
5-year mean is a good measure for achieving near-certainty that the Arctic has flipped a state. 1-year number is good for rallying those who forgot to rally when the globe started overheating. Both are scientifically sound.
... when announcing to the world AFTER THE FACT that X has happened! The very first year that Arctic ice drops below 1 million, it will be vital to tell the world, get people up there doing research, etc.  Trying to FORECAST which precise year that will be is scientifically meaningless, and a significant distraction.

I don't know how better to put it.  Surely you can see the difference between examination of actual data, and attempts to predict it?

Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #71 on: September 15, 2016, 07:18:11 AM »
Peter, the issue I have with your reply is that you immediately assume that this is an "accidental mis-explanation".  [...]  Something like "Ah. that is strange that they just changed the definition. Let me investigate" would have been a much better reply.
... but we collectively did investigate! See here, and the preceding posts.
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89334.html#msg89334

We know what happened and in what order.  A graph was included that made a forecast for when the five year mean would go below 1 million.  Then in a later draft, bracketed text was added that said "consecutive years". As I outlined in my previous post, there are several reasons to conclude that this was intended as a clarification rather than a change of definition. It's bracketed, begins with "i.e.", and the original text and the actual scientific data (the forecast graph) is left unchanged.

Right. The investigation started much earlier in that thread. Like here :
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89167.html#msg89167
where I was still under the assumption that the addition of "five consecutive years" only applied to one caption of one figure. And based on that I drew the same conclusions as the ones you summarized above.

But then I realized that the change in definition (addition of "five consecutive years") was much more widely spread in IPCC reports :
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89173.html#msg89173
There are two references in the SPM alone, and another two more in the Technical Summary.
And they are pretty blunt.

Quote
P-maker explained in detail how the editing process worked, and that this sort of change to a figure caption is NOT discussed in detail and agreed by all countries, but can be made "in consultation with" the scientists. In the same post, he explains that changes made to the SPM are then automatically propagated back into the underlying documents.
https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89322.html#msg89322

If this change of definition was indeed run through the standard update procedure, then it SHOULD have shown up in this list (of updates between the SPM and the TS documents) from the Stockholm session :
http://www.ipcc.ch/meetings/session36/p36_doc4_changes_underlying_assessment.pdf

The change of definition does NOT show up in this list, so we KNOW that it did not come via the normal procedures.

So we know that it this change did NOT come about as misinterpretation that slipped though the process (which is what you seem to believe).

This change of definition in the TWO most important documents that the IPCC produces came about in a DIFFERENT way. A very blunt way, outside the IPCC editing procedures.

That's why I agree with oren, that this smells like malice.

I'm not sure why you do not see that.

Quote
Because forecasting the five-year mean has a small chance of actually being right. Trying to forecast individual years is a short cut to looking like a bloody idiot, as we ourselves prove over and over every damn year. In the blog linked in this thread, Ed Hawkins points to this paper which attempts to estimate the error range on forecasts. (The people arguing with me did go and read the actual posts and papers linked rather than just the headlines, right?)
http://onlinelibrary.wiley.com/doi/10.1002/2016GL070067/abstract

The paper finds that there is an 20-year variability in the outputs of any forecast model due to sensitive dependence on parameter choice, and that over and above that there's a further 5-year variability caused by uncertainty in the level of future GHG emissions.  Given that, I'm surprised they even tried to forecast the 5-year mean, but it's such an important factor that I guess they had to try their best.

Peter, nobody is trying to forecast individual years.
Even IPCC states that ice-free condition may occur "before mid-century".
You are just burning a straw-man with that argument.
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charles_oil

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Re: Ice free predictions and their uncertainty
« Reply #72 on: September 15, 2016, 09:59:28 AM »
Surely best way to resolve this would be to ask the secretariat - or the authors themselves ?

https://www.ipcc.ch/pdf/ar5/ar5_authors_review_editors_updated.pdf

Lists enough of them I believe.

oren

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Re: Ice free predictions and their uncertainty
« Reply #73 on: September 15, 2016, 03:46:44 PM »
5-year mean is a good measure for achieving near-certainty that the Arctic has flipped a state. 1-year number is good for rallying those who forgot to rally when the globe started overheating. Both are scientifically sound.
... when announcing to the world AFTER THE FACT that X has happened! The very first year that Arctic ice drops below 1 million, it will be vital to tell the world, get people up there doing research, etc.  Trying to FORECAST which precise year that will be is scientifically meaningless, and a significant distraction.

I don't know how better to put it.  Surely you can see the difference between examination of actual data, and attempts to predict it?
Of course Peter. I fully understand your point, but I still think this mistake in explanation from mean to consecutive (if mistake it is), and the unclear definition of what the criterion is used for (prediction vs. announcement after the fact), will cause a lot of headache in years to come.

Archimid

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Re: Ice free predictions and their uncertainty
« Reply #74 on: September 15, 2016, 05:18:38 PM »
I get it that predicting exactly what year it will happen is next to impossible with current science, but there must be more accurate ways to represent the uncertainties. One way I have seen used is giving an earliest possible date for it to happen, with a probability attached to it. For example:

https://www.theguardian.com/environment/earth-insight/2013/dec/09/us-navy-arctic-sea-ice-2016-melt

Quote
"Given the estimated trend and the volume estimate for October–November of 2007 at less than 9,000 km3, one can project that at this rate it would take only 9 more years or until 2016 ± 3 years to reach a nearly ice-free Arctic Ocean in summer. Regardless of high uncertainty associated with such an estimate, it does provide a lower bound of the time range for projections of seasonal sea ice cover."


They didn't say "The Arctic will be ice free in 2016". They say it could be.  It didn't go this year but , they have 3 more years before that prediction is invalidated. Using the same analysis as they used and taking account the outcomes since then, that number is pushed back a bit, to about 2020.  Will it happen in 2020? Who knows!! Could it happen? The data is clearly indicating it could.

There are much more accurate ways to showing the uncertainty around an ice free arctic than normalizing the event by lumping it all together with other ice free years and pushing the boundaries into the future. When we talk about an event that might very well be irreversible and have the potential for catastrophic consequences for all of humanity, a lower bound is a better metric than an average of those events, at least from a security of mankind point of view.

Besides, to climate change deniers it does not matter how accurate the models are. Look at the temperature models. I don't think there is a data set more vetted and referenced in all of science. I mean NASA, JAXA, MET, NOAA, you name it, it agrees, yet the presidential candidate for the US thinks is a hoax. So does forty some percent of all Americans. What good are safe 100% guaranteed to be right predictions if you have teams of professional liars convincing people other wise?

The IPCC is supposed to be a scientific document. It should say matters as they are without pulling punches. Is the outcome too harsh? That's not science's problem, that's the politicians problem. The uncertainty too great? then you say it. "We don't know". Not knowing is an integral part of science. Pretending you know to avoid drama? That's highly unscientific.

« Last Edit: September 15, 2016, 06:42:53 PM by Archimid »
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Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #75 on: September 16, 2016, 07:21:13 AM »
Surely best way to resolve this would be to ask the secretariat - or the authors themselves ?

https://www.ipcc.ch/pdf/ar5/ar5_authors_review_editors_updated.pdf

Lists enough of them I believe.

Thanks Charles, for that list.
I do not know any of these scientists personally, but if you have email addresses, then I will drop them a request by email.

Meanwhile, I dropped a comment at RealClimate.org with request for more information on how this IPCC re-definition of "ice-free" came about in the AR5 Summary for Policy Makers and the underlying Technical Summary.
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budmantis

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Re: Ice free predictions and their uncertainty
« Reply #76 on: September 16, 2016, 07:33:49 AM »
I've been following this discussion with interest. I have little knowledge of how determinations for an ice free arctic are arrived at. From a purely common sense point of view, the first year the Arctic is ice free will be the second most important news we will hear. The most important will be the second consecutive year of an ice free arctic. To me that is when most of us, even some deniers will come to the realization that we are in the words of George H.W. Bush; "in deep doo-doo"!

charles_oil

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Re: Ice free predictions and their uncertainty
« Reply #77 on: September 16, 2016, 08:02:53 AM »
Rob -

The list just came up on a simple google search - so afraid I have no associated emails.  But as its publically available I imagine they could be found.  Not sure what the colour coding means (team leaders / substitutes ?).

charles_oil

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Re: Ice free predictions and their uncertainty
« Reply #78 on: September 16, 2016, 08:25:48 AM »
So - I have taken my own advice and emailed David Vaughan of the British Antarctic Survey with the request to elaborate for us! 

He is shown as one of the Chairmen (I think that's probably Chair Lead Author = CLA) for the Cryosphere section 4......

Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #79 on: September 17, 2016, 09:20:44 AM »
Thank you Charles, for sending an email to David Vaughan.
Please let us know of any response from him.

Meanwhile, no response on RealClimate.org yet other than one which ignores the question and instead attempts to downplay the change in definition.
http://www.realclimate.org/index.php/archives/2016/09/unforced-variations-sep-2016/comment-page-4/#comment-660355
 
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charles_oil

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Re: Ice free predictions and their uncertainty
« Reply #80 on: September 17, 2016, 09:41:07 AM »
ok - nothing yet - will try some others if nothing via David.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #81 on: September 19, 2016, 04:11:21 AM »
Thank for trying to contact the authors of IPCC Chapter 4 Cryosphere.
I will make a list of the authors, with mail and phone, to contact them.
It will be interesting if some of us try to contact a couple of authors, to know why and how the "5 consecutive years" was incorporated on the definition of ice-free Arctic.
We should make public our findings on this topic, if that is ok with Neven and Crandles.

Thanks again for your help!

Comiso, Josefino (Joey) - NASA Cryospheric Sciences Branch
      USA, josefino.c.comiso@nasa.gov, ph. 301 614 5708
Vaughan, David - British Antarctic Survey
      UK, dgv@bas.ac.uk (not sure), ph. 44 (0)1223 221400 (BAS)
Allison, Ian - Antarctic Climate and Ecosystems Cooperative Research Centre
      Australia, ian.allison@utas.edu.au, ph. 61 (0)3 6226 7888 (ACE-CRC)
Kaser, Georg - University of Innsbruck
      Austria, georg.kaser@uibk.ac.at, ph. 43 512 507 54457
Kwok, Ronald - NASA Jet Propulsion Laboratory
      USA, ron.kwok@jpl.nasa.gov   
« Last Edit: September 19, 2016, 04:16:26 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Rob Dekker

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Re: Ice free predictions and their uncertainty
« Reply #82 on: September 19, 2016, 07:37:26 AM »
Juan,

Thanks for posting the contact info for these IPCC scientists.

Meanwhile, back at the RealClimate.org, I posted this comment on the matter (currently in 'moderation') :

Quote
@mike: thanks for your note, but I think I was just misunderstood by all three commenters :

@wili, @hank @digby: Thanks for your reply.
All three of you are coming up with creative ideas on WHY the IPCC added “for five consecutive years” to the definition of (nearly) “ice free”.
But that was not what my question was about.

From a scientific point of view it does not matter how you define “ice free” or “nearly ice free”.
Either way the Arctic will decide what to do.

As an analogy, a drinker in the bar may claim that his glass is not empty yet since he defines “empty” or “nearly empty” only after 5 glasses.
That is scientifically a fine definition of an “empty glass” (since is changes nothing about what happened in reality), while it just postponed his own feeling of when it is time to be heading home….

Same thing with the definition of (nearly) “ice free”. By redefinition “ice free” from “1 M km^2” to “1 M km^2 for 5 consecutive years” IPCC simply postponed their own feeling of when there is no more ice left in the Arctic.

Note that this is a non-scientific re-definition. And note that its ONLY effect is that now the denier have the IPCC on their side long after the first time that the Arctic hits 1 M km^2.

Since the change in definition is not scientific, yet it shows up in two places in the Summary for Policy Makers and another 2 places in the WG1 Technical Summary (arguably the two most important documents that the IPCC produces), I wanted to know how this change came about.

We know this change happened during the 36th session of the IPCC in Stockholm, because the addition “after 5 consecutive years” is NOT present in the June 7 ‘final draft SPM’ as prepared by WG1 :
https://www.ipcc.ch/pdf/assessment-report/ar5/wg1/drafts/WG1AR5-SPM_FD_Final.pdf
and it IS present in the ‘approved SPM’ after the September 23-26 session :
http://www.ipcc.ch/meetings/session36/p36_doc3_approved_spm.pdf

And there seems to be no record of this change in the “differences” document that IPCC member countries signed off on during the Stockholm session :

http://www.ipcc.ch/meetings/session36/p36_doc4_changes_underlying_assessment.pdf

So the point I was trying to make, and the question that comes with it is :
WHEN exactly was this change in definition made, WHO changed it, under WHICH IPCC procedure, and WHY does it not show up in the “changes” document from the Stockholm session ?

Feel free to steal references and text from this.
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Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #83 on: September 20, 2016, 02:26:50 AM »
List of IPCC Cryosphere Authors (Continued, 2nd. part):

Mote, Philip - Oregon State University
     USA, pmote@coas.oregonstate.edu, ph: (541) 737-5694, (541) 737-5705
Murray, Tavi - Swansea University
      UK, t.murray@swansea.ac.uk, ph: 44 (0)1792 205678
Paul, Frank - University of Zurich
      Switzerland, frank.paul@geo.uzh.ch, ph: 044 63 55175
Ren, Jiawen - Chinese Academy of Sciences
      China, jwren@lzb.ac.cn, ph: 0931-4967384
Rignot, Eric - University of California - Irvine
       USA, erignot@uci.edu, ph: (949) 824-3739
Steffen, Konrad (Koni?) -    Cooperative Institute for Research in Envrironmental Sciences (CIRES)
       USA, konrad.steffen@colorado.edu
Zhang, Tingjun - Cooperative Institute for Research in Envrironmental Sciences (CIRES)
       USA, tzhang@nsidc.org
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #84 on: September 20, 2016, 02:35:47 AM »
Knowing the IPCC Authors:

Professor Tavi Murray is professor of glaciology, head of Swansea's Glaciology Group, and a deputy Pro Vice Chancellor at Swansea University.

http://www.swansea.ac.uk/texas-showcase/showcasespeakers/tavimurray/

Good video:
« Last Edit: September 20, 2016, 03:03:27 AM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #85 on: September 20, 2016, 02:44:30 AM »
Knowing the IPCC Authors:

David Vaughan - Director of Science - British Antarctic Survey

Professor David Vaughan is the Director of Science with responsibility for the strategic development and excellence in scientific output of the Science teams employed by the British Antarctic Survey.

https://www.bas.ac.uk/profile/dgv/

Video:
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #86 on: September 20, 2016, 03:00:44 AM »
Knowing the IPCC Cryosphere authors:

Dr. Josefino C Comiso

Josefino Comiso is a senior research scientist at the Cryospheric Sciences Laboratory of the Goddard Space Flight Center.  ...  At Goddard, his research led to new insights into many important processes in the polar regions including: (a) deep ocean convection and the influence of polynyas and Odden on bottom water formation; (b) phytoplankton blooms and relationships with the sea ice cover and (c) climate change signals as revealed by the changing sea ice cover and accelerated warming in the Arctic region. He was the chief scientist in many NASA aircraft missions in the Arctic and Antarctic that included a flight over a nuclear submarine near the North Pole that demonstrated the feasibility of measuring sea ice thickness from space. He has been a member of satellite sensor teams and has developed algorithms for the retrieval of sea ice concentration, surface temperature, and clouds.

http://science.gsfc.nasa.gov/sed/bio/josefino.c.comiso

Josefino Comiso Biography Video:
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #87 on: September 20, 2016, 03:24:24 AM »
Knowing IPCC Authors:

Professor Ian Allison AO AAM

Glaciologist

A pioneer of Australia's glaciological research program since the 1960s, Professor Ian Allison is acclaimed internationally as a glaciologist, making a significant contribution to climate science. An outstanding contributor to the Intergovernmental Panel on Climate Change (IPCC) Assessment Reports on Climate Change, Ian has worked tirelessly to synthesise global research results. He spent many years with the Australian Antarctic Division, ultimately leading the Ice, Oceans, Atmosphere and Climate program. As co-chair of the International Polar Year in 2007-08, Ian drove a coordinated, intense period of observational research activity in the Polar Regions. Ian’s enduring contribution to Antarctic affairs and the Antarctic community has been recognised with awards and accolades, such as the naming of Allison Glacier on Heard Island. Ian’s legacy also includes the work of the many PhD students he has supervised who have, themselves, made significant contributions to science. Ian’s community-mindedness and willingness to push ahead with fresh ideas has helped Australia build an internationally-respected scientific community.

http://www.australianoftheyear.org.au/honour-roll/?view=fullView&recipientID=1367
http://acecrc.org.au/people/prof-ian-allison-ao-aam/

video:
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Ice free predictions and their uncertainty
« Reply #88 on: September 20, 2016, 04:15:13 AM »
Knowing the IPCC Authors:

Ron Kwok [Ronald Kwok] is a Senior Research Scientist at the Jet Propulsion Laboratory, California Institute of Technology.

His research interests include the mass and energy balance of the Arctic and Southern Ocean ice cover and the role of the sea ice in global climate. His current focus is on the analysis of thickness, small-scale sea ice kinematics, time varying gravity from various spaceborne and airborne remote sensing instruments.

He is a member of NASA’s ICESat-1&2 science teams and ESA’s CryoSat-2 Calibration/Validation team. Dr. Kwok received the NASA Exceptional Achievement Medal (2003), the NASA Exceptional Scientific Achievement Medal (2008), and JPL’s Ed Stone Award for outstanding research publication (2003, 2005) for his work on understanding the Arctic Ocean sea ice cover.

http://rkwok.jpl.nasa.gov/

Video:

Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Tor Bejnar

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Re: Ice free predictions and their uncertainty
« Reply #89 on: September 23, 2016, 09:32:17 PM »
Here is an "Ice Free Arctic" prediction from xkcd.  Is this from 2011? Excerpt attached.  Surrounding predictions suggest large degrees of uncertainty.
Arctic ice is healthy for children and other living things.

RoxTheGeologist

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Re: Ice free predictions and their uncertainty
« Reply #90 on: December 06, 2016, 11:20:06 PM »

The correlation between CO2 and ice loss is interesting, the graph is published on the NSIDC page, and linked to the article.

http://ncaor.gov.in/files/Science_News/Arctic%20news-0811-16.pdf

We currently emit about 31 Giga Tons (Gt) of carbon Dioxide per year. On this chart we need to emit about another 1000 Gt of Carbon dioxide to become 'ice fee' so around 32 years at the current rate assuming the linear fit is a good model.

The data points from the last decade seem to have more variability and are largely below the linear fit. It would seem from those points that the linear fit does not hold for the current global changes we are witnessing and 32 years is overly optimistic.



crandles

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Re: Ice free predictions and their uncertainty
« Reply #91 on: December 06, 2016, 11:30:28 PM »

The data points from the last decade seem to have more variability and are largely below the linear fit. It would seem from those points that the linear fit does not hold for the current global changes we are witnessing and 32 years is overly optimistic.

7 below 2 above could occur by chance but I would tend to muse more about that linear model. The rate of decline has been fast as we reduced thick MYI down to a minimal level. That MYI takes a long time to grow but now we are removing mainly FYI which largely grows back in a normal winter the rate of decline could be slower. There again perhaps we won't get normal polar vortexs' in winter.

Peter Ellis

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Re: Ice free predictions and their uncertainty
« Reply #92 on: December 07, 2016, 01:54:19 AM »
Eh, that graph only shows that there's a strong trend in both measurements, which is close-enough-to-linear not to worry about any bendiness.  You'd get an equally good correlation with anything that has a more-or-less linear trend over the same time period.

crandles

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Re: Ice free predictions and their uncertainty
« Reply #93 on: December 07, 2016, 12:33:44 PM »
The line drawn looks to be very good but does it really extend to first and last 15 years well?

I don't think you can rule out the following sort of relationship

liefde

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Re: Ice free predictions and their uncertainty
« Reply #94 on: December 07, 2016, 01:15:11 PM »
The first ice free September will be predictable about 2 months before it happens.
Really? Nobody in early September 2016 would have predicted the absurd low appearing in November globally;


Taking that into account, there's really no saying when it will happen. It could be July 2017 with a little (bad) luck.

RoxTheGeologist

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Re: Ice free predictions and their uncertainty
« Reply #95 on: December 07, 2016, 04:55:02 PM »

It's an interesting correlation, maybe not wihout some merit in terms of building a model. An analogy might be that we are looking at the interior of an irregular pan of ice on a stove. We are watching the currents and eddies of the earth, modelling the convection cells and the material absorption, but the simply fact is the longer the pan is on the stove, the more ice will melt.

Jim Williams

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Re: Ice free predictions and their uncertainty
« Reply #96 on: December 07, 2016, 05:40:08 PM »
The first ice free September will be predictable about 2 months before it happens.
Really? Nobody in early September 2016 would have predicted the absurd low appearing in November globally;


Taking that into account, there's really no saying when it will happen. It could be July 2017 with a little (bad) luck.

What people don't seem to realize is that it could just as well be November 2017 as July.

kiwichick16

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Re: Ice free predictions and their uncertainty
« Reply #97 on: December 07, 2016, 08:25:09 PM »
what would Trump's reaction be if he was told Wipneus's  graph was actually US retail sales , for example?

or the number of people booking into his hotels?

6roucho

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Re: Ice free predictions and their uncertainty
« Reply #98 on: December 07, 2016, 09:03:32 PM »

It's an interesting correlation, maybe not wihout some merit in terms of building a model. An analogy might be that we are looking at the interior of an irregular pan of ice on a stove. We are watching the currents and eddies of the earth, modelling the convection cells and the material absorption, but the simply fact is the longer the pan is on the stove, the more ice will melt.

This could be a job for additive noise model testing.

One of the cornerstones of rationalism is that correlation doesn't imply causation (although it depends on what we mean by imply: correlated events are more likely to exhibit causation than those that aren't, so it encourages us to investigate physically to see whether causation is involved). What correlation doesn't imply is the direction of causation.

But there's some interesting maths around noise contamination that allows us to test this without experimentation. If noise from x causes noise in y, but noise from y does not cause noise in x, then we can prove that x causes y. So if warming causes noise in the melt data, but melt doesn't cause noise in the temperature data, then warming causes melt.

Of course we *know* that warming causes melt. The interesting question is whether the concurrent melting events at both poles is noise, or evidence of something substantive.

crandles

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Re: Ice free predictions and their uncertainty
« Reply #99 on: December 07, 2016, 09:07:04 PM »
what would Trump's reaction be if he was told Wipneus's  graph was actually US retail sales , for example?

or the number of people booking into his hotels?

Twitter rant demanding a recount?  ;)