Arctic Sea Ice : Forum

Cryosphere => Arctic sea ice => Topic started by: crandles on August 28, 2016, 12:47:24 AM

Title: Ice free predictions and their uncertainty
Post by: crandles on August 28, 2016, 12:47:24 AM
https://www.carbonbrief.org/guest-post-predictable-first-ice-free-arctic-summer (https://www.carbonbrief.org/guest-post-predictable-first-ice-free-arctic-summer)
Quote
How predictable is the first ice-free Arctic summer?

In conclusion, our findings suggest that we cannot predict the timing of an ice-free Arctic summer with an uncertainty of less than about 25 years.

Hmm, possibly I suppose, but: If the central estimate is 10 years or less away then I wouldn't think that 25 years uncertainty would be needed. If the central estimate is over 50 years away then an uncertainty of more than 25 years might be needed?
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 28, 2016, 04:43:29 AM
Have someone ever read "How to Lie with Statistics" (https://www.amazon.com/How-Lie-Statistics-Darrell-Huff/dp/0393310728/ref=sr_1_1?s=books&ie=UTF8&qid=1472351896&sr=1-1&keywords=how+to+lie+with+statistics)? I read it long time ago, like 20+ years.

When I see this kind of articles, I said that the shortest answer is my signature.  ;)
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 28, 2016, 04:50:11 AM
75% of all statistics are made up on the spot.

25 years is too generous of an uncertainty. That much I know.
Title: Re: Ice free predictions and their uncertainty
Post by: longwalks1 on August 28, 2016, 05:19:01 AM
It appears to be based on the paper  doi:10.1002/2016GL070067

How predictable is the timing of a summer ice-free
Arctic?

Alexandra Jahn1, Jennifer E. Kay2, Marika M. Holland3, David M. Hall4

From conclusions,
Quote
Our results from the 40-member CESM LE and the 15-member CESM ME show that
due to internal variability alone, we can not predict the timing of a summer ice-free Arctic
with an uncertainty of less than 21 years. The much smaller ensembles (5–10 members)
from the CMIP5 archive show uncertainty ranges of 7–15 years due to internal variability,
which are consistent with the expectation for smaller ensembles from the bootstrapped
CESM LE. Past, present, and near future sea ice volume, trends, area, extent, and thickness
as well as global temperature metrics do not allow us to narrow the prediction
uncertainty due to internal variability within individual models.

I am puzzled about in the original source where they start talking about 5 and 10 year consecutive 1 x 10E6 ice extents. If I read it right, they are not using consecutive years, but they give the usage of consecutive years more ink than I believe it deserves. For a rugby or Canada-US football analogy it smacks of "moving the goal posts."   

Quote
Table 1. Range of years from CESM and CMIP5 ensembles when an ice free September in
the Arctic is first reached, based on different definitions of“ice-free” used in the literature. The
ensemble spread is given in parentheses after the year range and the ensemble size is given in
square parentheses after the model name
       

is found at the very end of the article with 5 and 10 year consecutive columns included.

One basis of the paper is doi:10.1175/BAMS-D-13-00255.1.

http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-13-00255.1 (http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-13-00255.1)

The Community Earth System Model (CESM) Large Ensemble Project: A Community Resource for Studying Climate Change in the Presence of Internal Climate Variability

More also about posted here at
https://forum.arctic-sea-ice.net/index.php/topic,1356.msg60085.html#msg60085 (https://forum.arctic-sea-ice.net/index.php/topic,1356.msg60085.html#msg60085)

In at least two places in the CESM  paper talks about a hiatus in global warming in the modelling.   

Quote
Off-shoot  experiments  have  already  started including  experiments  to  test  the  competing  hypotheses  for  hiatus  periods,  to  evaluate hurricanes in CESM1(CAM5) using high resolution time slice experiments, to force regional downscaling  simulations,  and  to  run  a  complementary  ensemble  under  RCP4.5  forcing  to assess  avoided  impacts.

This gives me pause, as I am not sure that there has been a hiatus in the Arctic.  I am not disputing that this form of modelling has value and use. I might be comparing apples and oranges. I wonder, however if CESM's value is larger outside of the Arctic. 

Quote
After initial condition memory is lost, which occurs within weeks in the atmosphere, each ensemble member evolves chaotically, affected by atmospheric circulation fluctuations characteristic of a random, stochastic process

Would using CESM have less use in an ocean environment with multi-year ice. 

A few years in the future however might convince me that I used too much ink on these studies. 

Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 28, 2016, 05:35:01 AM
It upsets me that the IPCC started to use the definition of 5 consecutive years. See the poll:
https://forum.arctic-sea-ice.net/index.php/topic,1559.0.html (https://forum.arctic-sea-ice.net/index.php/topic,1559.0.html)
Title: Re: Ice free predictions and their uncertainty
Post by: epiphyte on August 28, 2016, 07:31:58 AM
It upsets me that the IPCC started to use the definition of 5 consecutive years. See the poll:
https://forum.arctic-sea-ice.net/index.php/topic,1559.0.html (https://forum.arctic-sea-ice.net/index.php/topic,1559.0.html)

Quite seriously, I think that the most appropriate metric in this situation might be termed the "Gin and Tonic Test"...

I.E. When there's not enough ice to prevent it from tasting awful, there might as well not be any at all.
Title: Re: Ice free predictions and their uncertainty
Post by: mmghosh on August 28, 2016, 12:30:49 PM
From the IJIS poll thread
1980's Avg:   7.23
1990's Avg:   6.55
2000's Avg:   5.48
2003:   5.93
2004:   5.68
2005:   5.18
2006:   5.63
2007:   4.07
2008:   4.50
2009:   5.05
2010:   4.62
2011:   4.27
2012:   3.18
2013:   4.81
2014:   4.88
2015:   4.26

A straightforward linear extrapolation leads to the 2050s decade.  Isn't that bad enough?
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 28, 2016, 12:51:26 PM
From the IJIS poll thread
...
A straightforward linear extrapolation leads to the 2050s decade.  Isn't that bad enough?

It is not a linear trend. It has acceleration. And Extent is a good (and the fastest) measure to follow the status of the Arctic sea ice on a daily basis, but it should not be used to make any forecast (IMHO, NSIDC and IPCC are wrong using extent to make a forecast).

To make a forecast, you have to recognize that the Arctic sea ice is also loosing thickness. When you try to make any forecast with volume, recognizing that the melt has accelerated, then you can use a linear trend, but with less years.

Edit: Using extent and/or using the definition of "5 consecutive years" on a forecast, are ways to lie with statistics.

I like Wipneus forecasts:
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on August 28, 2016, 04:10:30 PM

It is not a linear trend. It has acceleration. And Extent is a good (and the fastest) measure to follow the status of the Arctic sea ice on a daily basis, but it should not be used to make any forecast (IMHO, NSIDC and IPCC are wrong using extent to make a forecast).

To make a forecast, you have to recognize that the Arctic sea ice is also loosing thickness.

What makes you so sure it isn't a case of 'It had acceleration' when thick MYI was being reduced significantlyand was largely no re-growing in winter, but now we are down to most being less than 2m thick, what is lost is largely regrown in the winter so it is decelerating as the models suggest will happen?
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 28, 2016, 04:52:05 PM
Too many feedback systems have kicked in at this point. For just one example, albedo on land, which is being lost earlier in the melt season. The last three years, the global temperatures have set records and made a huge jump from pre-industrial averages. Arctic amplification is making it worse for the Arctic.
Title: Re: Ice free predictions and their uncertainty
Post by: Richard Rathbone on August 28, 2016, 05:03:04 PM
The first ice free September will be predictable about 2 months before it happens.

I'm rather less sure about the first ice-free June. That might well require tipping to an equable climate state, and I don't think anyone has a handle on what precipitates that.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on August 28, 2016, 08:22:23 PM
Too many feedback systems have kicked in at this point. For just one example, albedo on land, which is being lost earlier in the melt season. The last three years, the global temperatures have set records and made a huge jump from pre-industrial averages. Arctic amplification is making it worse for the Arctic.

Hmm, you choose 'the last three years' period and with all these feedback systems kicking in as you put it, 2013, 14 and 15 were higher than each of 2010, 11 and 12. Certainly can be noise but does this make you pause to wonder if perhaps all these feedback systems that are kicking in may not be very strong?
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid on August 28, 2016, 10:58:05 PM
It upsets me that the IPCC started to use the definition of 5 consecutive years.

 That definition is perfectly designed to not lie about the risks while minimizing them. Within that statement is the veiled assumption that after the ice is gone for the first time it will come back. That is a huge assumption.

My layman opinion is that after the first ice free September, the freezing season will be delayed. Ice grows from the center out. If there is no ice in the North Pole then it will take sometime before the periphery gets cold enough to freeze the saltier arctic. Once the Pole is covered in ice, sea ice extent will grow rapidly (as the waves allow) and probably cover the whole arctic. But it will be very thin, not even first year ice. That ice will melt very quickly the following summer. Then the cycle begins again only with the arctic being ice free for the whole summer instead of just a few months, further delaying the freezing season. Rinse and repeat until is gone.




Title: Re: Ice free predictions and their uncertainty
Post by: Iceismylife on August 29, 2016, 12:05:05 AM
It upsets me that the IPCC started to use the definition of 5 consecutive years.

 That definition is perfectly designed to not lie about the risks while minimizing them. Within that statement is the veiled assumption that after the ice is gone for the first time it will come back. That is a huge assumption.

My layman opinion is that after the first ice free September, the freezing season will be delayed. Ice grows from the center out. If there is no ice in the North Pole then it will take sometime before the periphery gets cold enough to freeze the saltier arctic. Once the Pole is covered in ice, sea ice extent will grow rapidly (as the waves allow) and probably cover the whole arctic. But it will be very thin, not even first year ice. That ice will melt very quickly the following summer. Then the cycle begins again only with the arctic being ice free for the whole summer instead of just a few months, further delaying the freezing season. Rinse and repeat until is gone.
Ice forms everywhere that the surface water local air temp. gets cold enough.
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 29, 2016, 12:10:34 AM
Too many feedback systems have kicked in at this point. For just one example, albedo on land, which is being lost earlier in the melt season. The last three years, the global temperatures have set records and made a huge jump from pre-industrial averages. Arctic amplification is making it worse for the Arctic.

Hmm, you choose 'the last three years' period and with all these feedback systems kicking in as you put it, 2013, 14 and 15 were higher than each of 2010, 11 and 12. Certainly can be noise but does this make you pause to wonder if perhaps all these feedback systems that are kicking in may not be very strong?
Naw, I live in the real world, not happy land.
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid on August 29, 2016, 02:22:34 AM
Ice forms everywhere that the surface water local air temp. gets cold enough.

Yes of course. However take a look at the first few months of the melting seasons. Ice do not grow in random patches throughout the arctic. It grows from the ice mass out, from the arctic islands out and from the arctic periphery in.

Temperature is not the only factor in the formation of arctic sea ice. Salinity and waves also play  an important part. When there sea ice present then the water adjacent to the ice has a more favorable environment to form ice. The ice calms waves and creates its own micro-weather. When there is no sea ice present then things like waves and mixing prevent ice from forming.

In the case of sea ice less arctic then waves and salinity will prevent formation until ice is formed in around the arctic islands and it grows from the peripheral coasts in. Thus rapid ice formation will be delayed for months, after the first blue ocean event.
Title: Re: Ice free predictions and their uncertainty
Post by: Michael Hauber on August 29, 2016, 05:36:30 AM
Too many feedback systems have kicked in at this point. For just one example, albedo on land, which is being lost earlier in the melt season.

The feedbacks currently operating are mostly the same as have been operating for thousands of years.  In most cases they do not kick in and out, but amplify every change in climate to some extent.  Nearly all The same feedbacks were operating in the little ice age as the medieval warm period as will be operating in another hundred years of AGW.

As an example the land albedo feedback was certainly operating throughout the medieval warm period (less land snow), the little ice age (more snow) and is still operating, but is weaker than it has been at any stage in recorded history.  Modelling shows that the warmer the planet is, the less change in albedo for ice loss for every degree of warming.  Other feedbacks show different behaviours - for instance water vapour feedback gets gradually stronger as the world warms.
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 29, 2016, 06:14:52 AM
Argue with my big friend. His name is NOAA.

www.noaa.gov/arctic-set-for-record-breaking-melt (http://www.noaa.gov/arctic-set-for-record-breaking-melt)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 29, 2016, 06:33:59 PM

It is not a linear trend. It has acceleration. And Extent is a good (and the fastest) measure to follow the status of the Arctic sea ice on a daily basis, but it should not be used to make any forecast (IMHO, NSIDC and IPCC are wrong using extent to make a forecast).

To make a forecast, you have to recognize that the Arctic sea ice is also loosing thickness.

What makes you so sure it isn't a case of 'It had acceleration' when thick MYI was being reduced significantlyand was largely no re-growing in winter, but now we are down to most being less than 2m thick, what is lost is largely regrown in the winter so it is decelerating as the models suggest will happen?

Hi Crandles.

I can beleive that there could be a deceleration, but definitely I see the first year of an ice-free Arctic before 2035 (and I believe that I am being conservative with this forecast).

I could be wrong but in my opinion, the IPCC models could be intentionally wrong. We have been seeing different versions of this graph, long time ago. This one comes from the US National Climate Assessment 2014. What the graph means is that reality is worst worse than the Model simulations. In this graph, clearly says that "Extrapolation of the present observed trend suggests an essentially ice-free Arctic in summer before mid-century".

Suddenly, the IPCC changes the definition of ice-free Arctic and starts talking about 5 consecutive years. And then the models are alright. Isn´t this a way to try to avoid the subject of when we are going to have an ice-free Arctic? Can we accept the argument of "Several models agree that..." knowing that the models haven't described the reality? Or accept that because 2016 did not beat the 2012 record low, then everything seems to be delayed? Isn't 2016 bad enough? Can we forget that all this is based on extent trends, not taking into account the volume?

In my (not humble) opinion, what this article is trying to do is just misinform the general public. Climate change is real but no so bad. We are not sure when we will have an ice-free Arctic. Maybe 2100.
Title: Re: Ice free predictions and their uncertainty
Post by: Neven on August 29, 2016, 07:34:08 PM
Naw, I live in the real world, not happy land.

Argue with my big friend. His name is NOAA.

Could you try and leave the 'smart ass' home when making comments, please? Thanks.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on August 29, 2016, 08:37:20 PM
All models are wrong and it is quite possible for all models to be too slow in reducing the ice below 1m km2 without needing to invoke intentionally wrong models. Suggesting that seems disrespectful to hard working scientists. I think conspiracy theories are generally unlikely and particularly so amongst argumentative scientists - too much reputation to gain by blowing the whistle.

Yes, the models were too slow in removing thick MYI. How much relevance does this have to rate of removal of ice which re-grows to similar thickness each winter? Maybe the models will be too slow again, but I don't think we can be sure of this and it could go either way. 3 or 4 years since 2012 isn't enough to tell. 2013-15 were surprising given the data to 2012 and that doesn't seem to encourage belief that models will be too slow again but there isn't enough data.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 29, 2016, 09:39:42 PM
All models are wrong and it is quite possible for all models to be too slow in reducing the ice below 1m km2 without needing to invoke intentionally wrong models. Suggesting that seems disrespectful to hard working scientists. I think conspiracy theories are generally unlikely and particularly so amongst argumentative scientists - too much reputation to gain by blowing the whistle.

Yes, the models were too slow in removing thick MYI. How much relevance does this have to rate of removal of ice which re-grows to similar thickness each winter? Maybe the models will be too slow again, but I don't think we can be sure of this and it could go either way. 3 or 4 years since 2012 isn't enough to tell. 2013-15 were surprising given the data to 2012 and that doesn't seem to encourage belief that models will be too slow again but there isn't enough data.

I am not trying to disqualify all models and certainly, I want to respect the honest scientists working on these projects. But IPCC comes from "Intergovernmental Panel on Climate Change" and they are more than 10,000 people. How many of them are real and honest scientists? So, from my point of view, some thousand(s) IPCC people are politicians and it could be another thousand coming from the fossil fuel industry.

If we have Exxon, Hunt and others paying to misinform the general public, can we be so naive to think that everything that it is happening inside the IPCC is well intentioned? Just a question, even that I am sure that there are also scientists doing their honest work. At this point, I also want to recognize that I use information coming from the IPCC and I find it reliable. But I am concerned that global warming is happening much faster than what the IPCC is recognizing.
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 29, 2016, 10:07:23 PM
Naw, I live in the real world, not happy land.

Argue with my big friend. His name is NOAA.

Could you try and leave the 'smart ass' home when making comments, please? Thanks.
Sorry,Neven. You know I am usually the last to do that. I just got the feeling these guys were trying to pick a row, and that they were saying things they did not believe themselves only for that effect. I can't believe anyone on this forum would really feel that way. I guess I could be wrong.
Oh, and I was actually sincere, because where I live the world has changed so much, and I have neighbors and friends suffering because of it. However, will say no more.
Title: Re: Ice free predictions and their uncertainty
Post by: budmantis on August 30, 2016, 07:19:52 AM
I can commiserate Tigertown. There have been times I've felt the same way. By the way, thanks for the tip about adding smileys. Don't know why, I just cant get it to work! When I click on the smiley, the cursor disappears.

Regards,

Bud
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 30, 2016, 08:04:37 AM
Juan C. Garcia,
" But I am concerned that global warming is happening much faster than what the IPCC is recognizing."
   Rightly so. Scientist recently discovered that many fats they thought were bad for you to consume  ( the ones in eggs, for example) are actually good for you. As a matter of fact, you can't properly absorb vitamins that your body needs without certain fats. Also, they discovered that some fats kill viruses and bacteria and fungi that cause other health problems.As a matter of fact, the right ones(mct's) kill the very bacteria that causes heart diseases previously blamed on fats. The problem is, however, they can't get other scientist or doctors to change what they always have believed and taught, because they had believed it  for so long. I think a similar thing is happening here with this issue. They believed for so long that they had the rate of warming figured out, that they can't adjust what they believe, though it is happening before their eyes.
Title: Re: Ice free predictions and their uncertainty
Post by: abbottisgone on August 30, 2016, 08:52:15 AM

It is not a linear trend. It has acceleration. And Extent is a good (and the fastest) measure to follow the status of the Arctic sea ice on a daily basis, but it should not be used to make any forecast (IMHO, NSIDC and IPCC are wrong using extent to make a forecast).

To make a forecast, you have to recognize that the Arctic sea ice is also loosing thickness.

What makes you so sure it isn't a case of 'It had acceleration' when thick MYI was being reduced significantlyand was largely no re-growing in winter, but now we are down to most being less than 2m thick, what is lost is largely regrown in the winter so it is decelerating as the models suggest will happen?
.. This is why my favourite graphs are of the MYI  ;)

IMHO they are the sole reason for why the internet exists !
Title: Re: Ice free predictions and their uncertainty
Post by: mmghosh on August 30, 2016, 10:13:03 AM
The thing is,  IJIS is a measurement,  however indirect.  PIOMAS is a model.

People will generally trust direct or indirect measurements more than models.
Title: Re: Ice free predictions and their uncertainty
Post by: Michael Hauber on August 30, 2016, 10:56:49 AM
Argue with my big friend. His name is NOAA.

www.noaa.gov/arctic-set-for-record-breaking-melt (http://www.noaa.gov/arctic-set-for-record-breaking-melt)

The opinions of a marine biologist, and a media officer.  But they work at NOAA so they must be experts on Arctic ice.  Is the article somehow relevant to the topic at hand?
Title: Re: Ice free predictions and their uncertainty
Post by: abbottisgone on August 30, 2016, 12:06:23 PM
Too many feedback systems have kicked in at this point. For just one example, albedo on land, which is being lost earlier in the melt season.

The feedbacks currently operating are mostly the same as have been operating for thousands of years.  In most cases they do not kick in and out, but amplify every change in climate to some extent.  Nearly all The same feedbacks were operating in the little ice age as the medieval warm period as will be operating in another hundred years of AGW.

As an example the land albedo feedback was certainly operating throughout the medieval warm period (less land snow), the little ice age (more snow) and is still operating, but is weaker than it has been at any stage in recorded history.  Modelling shows that the warmer the planet is, the less change in albedo for ice loss for every degree of warming.  Other feedbacks show different behaviours - for instance water vapour feedback gets gradually stronger as the world warms.
Simply wrong!

<snip>

<Slow down, aig. Don't start all over again; N.>
Title: Re: Ice free predictions and their uncertainty
Post by: Hans on August 30, 2016, 01:08:53 PM

I am not trying to disqualify all models and certainly, I want to respect the honest scientists working on these projects. But IPCC comes from "Intergovernmental Panel on Climate Change" and they are more than 10,000 people. How many of them are real and honest scientists? So, from my point of view, some thousand(s) IPCC people are politicians and it could be another thousand coming from the fossil fuel industry.

Please have a look at the IPCC website about their organization. IPCC is a very small group, but for there reports they invite scientist from all over the world.

From IPCC AR5, WGI, chapter 11.3.4.1 Sea Ice (page 995, published in 2013)
Quote
Though most of the CMIP5 models project a nearly ice-free Arctic (sea ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the end of summer by 2100 in the RCP8.5 scenario (see Section 12.4.6.1), some show large changes in the near term as well. Some previous models project an ice-free summer period in the Arctic Ocean by 2040 (Holland et al., 2006), and even as early as the late 2030s using a criterion of 80% sea ice area loss (e.g., Zhang, 2010). By scaling six CMIP3 models to recent observed September sea ice changes, a nearly ice-free Arctic in September is projected to occur by 2037, reaching the  rst quartile of the distribution for timing of September sea ice loss by 2028 (Wang and Overland, 2009).
The full chapter 11 was written by around 55 authors. (I assume not all were involved in the sea ice paragraph.) However the authors did not base their wording only on own publications but analysed a broad spectrum of the scientific literature. Before publication the report was reviewed by many others.

It is the final Synthesis Report and the "Summary for policymakers"  were the big (political) discussions about the wording starts. Not about text on page 995.

PS: haven a look at the report: there is also something about "ice free in 2016" (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter11_FINAL.pdf (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter11_FINAL.pdf))
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on August 30, 2016, 01:29:45 PM

PS: haven a look at the report: there is also something about "ice free in 2016" (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter11_FINAL.pdf (http://www.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter11_FINAL.pdf))

seems worth quoting the section:

Quote
11.3.4.1 Sea Ice
Though most of the CMIP5 models project a nearly ice-free Arctic (sea
ice extent less than 1 × 106
 km2
 for at least 5 consecutive years) at the
end of summer by 2100 in the RCP8.5 scenario (see Section 12.4.6.1),
some show large changes in the near term as well. Some previous
models project an ice-free summer period in the Arctic Ocean by 2040
(Holland et al., 2006), and even as early as the late 2030s using a
criterion of 80% sea ice area loss (e.g., Zhang, 2010). By scaling six
CMIP3 models to recent observed September sea ice changes, a nearly
ice-free Arctic in September is projected to occur by 2037, reaching the
first quartile of the distribution for timing of September sea ice loss by
2028 (Wang and Overland, 2009). However, a number of models that
have fairly thick Arctic sea ice produce a slower near-term decrease in
sea ice extent compared to observations (Stroeve et al., 2007). Based
on a linear extrapolation into the future of the recent sea ice volume
trend from a hindcast simulation conducted with a regional model of
the Arctic sea ice–ocean system (Maslowski et al., 2012) projected that
it would take only until about 2016 to reach a nearly ice-free Arctic
Ocean in summer. However, such an approach not only neglects the
effect of year-to-year or longer-term variability (Overland and Wang,
2013) but also ignores the negative feedbacks that can occur when
the sea ice cover becomes thin (Notz, 2009). Mahlstein and Knutti
(2012) estimated the annual mean global surface warming threshold
for nearly ice-free Arctic conditions in September to be ~2°C above the
present derived from both CMIP3 models and observations.

So what I was saying has support in the scientific literature but some people feel I am saying such things without believing it only for that effect. Do we want to be an alarmist echo chamber or a place for sensible discussions?

I am trying not to react so I will just say thank you Neven for the moderation, hope a lot more isn't needed.
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid on August 30, 2016, 03:09:34 PM
11.3.4.1 Sea Ice
Though most of the CMIP5 models project a nearly ice-free Arctic (sea
ice extent less than 1 × 106 km2 for at least 5 consecutive years) at the
end of summer by 2100 in the RCP8.5 scenario (see Section 12.4.6.1),
some show large changes in the near term as well. Some previous
models project an ice-free summer period in the Arctic Ocean by 2040
(Holland et al., 2006), and even as early as the late 2030s using a
criterion of 80% sea ice area loss (e.g., Zhang, 2010). By scaling six
CMIP3 models to recent observed September sea ice changes, a nearly
ice-free Arctic in September is projected to occur by 2037, reaching the
first quartile of the distribution for timing of September sea ice loss by
2028 (Wang and Overland, 2009). However, a number of models that
have fairly thick Arctic sea ice produce a slower near-term decrease in
sea ice extent compared to observations (Stroeve et al., 2007). Based
on a linear extrapolation into the future of the recent sea ice volume
trend from a hindcast simulation conducted with a regional model of
the Arctic sea ice–ocean system (Maslowski et al., 2012) projected that
it would take only until about 2016 to reach a nearly ice-free Arctic
Ocean in summer. However, such an approach not only neglects the
effect of year-to-year or longer-term variability (Overland and Wang,
2013) but also ignores the negative feedbacks that can occur when
the sea ice cover becomes thin (Notz, 2009). Mahlstein and Knutti
(2012) estimated the annual mean global surface warming threshold
for nearly ice-free Arctic conditions in September to be ~2°C above the
present derived from both CMIP3 models and observations.


All those references are from before the 2012 summer and before the 2016 winter/summer. It is important to note that those numbers also represents downward adjustments. Before 2007 the arctic was projected to be gone by 2070. After 2007 happened they were corrected  to project ice free by mid century and after 2012 it was adjusted to project ice free before 2050 and constantly ice free by 2050.

I would imagine that after the 2016 winter, and the non recovery from 2007 and 2012, the models will be further adjusted down.

As a layman, seeing this streak of underestimations places a lot of doubt in the actual capacity of scientist to predict the outcome of the arctic. I don't think it is because they are stupid or lazy or evil. It's simply a matter of not having enough data. There is plenty of data on the 1979-2004 arctic, but the 2005-2016 melting arctic is a new thing of which scientist can only speculate.  The  constant downward adjustments to the projections and the sheer uncertainty of climate change  calls for much more caution and much less "don't worry, it will be alright".
Title: Re: Ice free predictions and their uncertainty
Post by: Tigertown on August 30, 2016, 03:11:18 PM
Argue with my big friend. His name is NOAA.

www.noaa.gov/arctic-set-for-record-breaking-melt (http://www.noaa.gov/arctic-set-for-record-breaking-melt)

The opinions of a marine biologist, and a media officer.  But they work at NOAA so they must be experts on Arctic ice.  Is the article somehow relevant to the topic at hand?
Could have been the local dog catcher or anybody else, if they know when the snow melted. You should not judge people by their livelihood by the way. That is only part of what a person is. If it melts earlier in the year, you catch more rays for the year. I used the term kicked in, which perhaps I should have said kicked in to another gear. If NOAA and NASA believe it getting warmer faster and that its amplified in the Arctic, and you don't believe them, I really don't know what else to say.
Title: Re: Ice free predictions and their uncertainty
Post by: Sterks on August 30, 2016, 06:41:32 PM
Could have been the local dog catcher or anybody else, if they know when the snow melted. You should not judge people by their livelihood by the way. That is only part of what a person is. If it melts earlier in the year, you catch more rays for the year. I used the term kicked in, which perhaps I should have said kicked in to another gear. If NOAA and NASA believe it getting warmer faster and that its amplified in the Arctic, and you don't believe them, I really don't know what else to say.
Tigertown,
I think no one spoke negatively against your concepts. They were just modulating your opinion. Nothing shows that there are new feedback mechanisms in only three years of sampling, not even that old ones have accelerated. But as far as I understand no one has denied that these mechanisms exist and that the warming is amplified in the Arctic.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 30, 2016, 10:01:45 PM
Juan C. Garcia,
" But I am concerned that global warming is happening much faster than what the IPCC is recognizing."
...
The problem is, however, they can't get other scientist or doctors to change what they always have believed and taught, because they had believed it  for so long. I think a similar thing is happening here with this issue. They believed for so long that they had the rate of warming figured out, that they can't adjust what they believe, though it is happening before their eyes.

They have to change and also we have to change our way of thinking. We can fool ourselves and of course, we can fool other people with less knowledge than us.

But we are not going to fool nature. Nature is going at its own pace. So we better don't fool others and don't fool ourselves: the consequences will be greater.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 30, 2016, 10:19:27 PM
The thing is,  IJIS is a measurement,  however indirect.  PIOMAS is a model.

People will generally trust direct or indirect measurements more than models.

It is true that extent is a measure, while PIOMAS volume is just a model. Nevertheless, volume is the real thing, area [or extent] is just part of it. Even that volume is hard to measure and instead of 77.6%, it could be 75% or 70%, volume will always show greater loss than extent and the forecast of ice-free will always be sooner.

It is the story of the blind men describing an elephant. We have no to make the effort to look to the whole picture.

https://www.youtube.com/watch?v=Vn9BUfUCL4I (https://www.youtube.com/watch?v=Vn9BUfUCL4I)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 31, 2016, 02:17:08 AM

Please have a look at the IPCC website about their organization. IPCC is a very small group, but for there reports they invite scientist from all over the world.


I was sure I read 12,000 people that participated in the report, even though most of them participated for free. But I checked and you are right. They are less:

Quote
More than 830 Authors and Review Editors from over 80 countries were selected to form the Author teams that produced the Fifth Assessment Report (AR5).They in turn drew on the work of over 1,000 Contributing Authors and about 2,000 expert reviewers who provided over 140,000 review comments.
 See the complete list of AR5 Authors and Review Editors. For statistics and regional coverage among the author teams see the AR5 page.
 For the Fourth Assessment Report (AR4) released in 2007, over 3,500 experts coming from more than 130 countries contributed to the report (+450 Lead Authors, +800 Contributing Authors, and +2,500 expert reviewers providing over 90,000 review comments).
http://www.ipcc.ch/organization/organization_structure.shtml (http://www.ipcc.ch/organization/organization_structure.shtml)
It is not a question of how many people participated. I still believe that it is a mistake to change the definition of ice-free Arctic to ask for 5 consecutive years. In my opinion, it is going to be bad if we start to have several years of less than 3 million km2 on extent on the period 2017-2030. So why is the IPCC talking about 5 consecutive years with ice below one million km2? Seems that they believe that ice on Greenland or permafrost melt will not be a problem until this condition is met.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García on August 31, 2016, 02:45:34 AM
Returning to the main question on this topic: "...we cannot predict the timing of an ice-free Arctic summer with an uncertainty of less than about 25 years" I believe that it is a lie.

2016+25=2041

Defining “ice-free” as "daily sea ice extent of less than one million square kilometres on one year", we can open a poll on this Forum and ask to see how many of us believe that they expect to have the ice-free Arctic, before and after 2041.

From my point of view, I believe that Wipneus forecast (based on volume) could be closer to the true, and we can talk about natural variability, but we will not have this help for 20 years.

Edit September 1st, 2016: I add "daily" to the definition of ice-free Arctic, just to avoid the use of NSIDC monthly average, because it is not formally (or statistically) an average.
Title: Re: Ice free predictions and their uncertainty
Post by: mmghosh on September 02, 2016, 03:37:25 AM
IMO when IJIS falls below 1 million on a single day in September will be when the public, and the media be finally convinced.

A dramatic number, a black swan event that will finally bust the public perception of the envelope.  Our quibbles here will become moot, well, they're probably moot anyway, but still.
Title: Re: Ice free predictions and their uncertainty
Post by: budmantis on September 02, 2016, 05:27:18 AM
IMO when IJIS falls below 1 million on a single day in September will be when the public, and the media be finally convinced.

A dramatic number, a black swan event that will finally bust the public perception of the envelope.  Our quibbles here will become moot, well, they're probably moot anyway, but still.

Reaching 1 million should get everyone's attention, but I doubt that it will. I think that a significant percentage of denier's, probably more than half are too entrenched in their views and/or don't see an ice-free arctic as a problem. They wont change their minds until the consequences of an ice-free arctic are staring them in the face.
Title: Re: Ice free predictions and their uncertainty
Post by: abbottisgone on September 02, 2016, 09:58:39 AM
Juan,

1 milion sq km would be an abomination: to ask that that condition be repeated three five ( :o :o :o)<headshake> times <!another headshake> before begging the world to do something would in my opinion amount to global genocide!

I know people in level 8 positions concerned about todays long term weather forecast!!!!



Title: Re: Ice free predictions and their uncertainty
Post by: S.Pansa on September 08, 2016, 06:45:28 PM
This post is an answer to Peter Ellis from a discussion (https://forum.arctic-sea-ice.net/index.php/topic,1457.msg89167.html#msg89167) we and others have about the IPCC- definition of an ice-free Arctic as "when sea ice extent is less than 10 6  km 2  for at least five consecutive years". I thought this discussion is more appropriate in this thread. Neven, if I was wrong, feel free to move this.

Well maybe - but I am not convinced, even more so as you, for some odd reason, keep mentioning a conspiracy here.
Alleging that changes are silently being made to IPCC reports for political reasons, coupled with comments like "I'm wondering about the IPCC integrity process" look, sound and smell like conspiracy theory to me. Call it what you will.

1) The figure caption reads as follows:

Quote
Figure SPM.7: ... (b) Northern Hemisphere September sea ice extent (5 year running mean) ...   The dashed line represents nearly ice-free conditions (i.e., when
sea ice extent is less than 10 6  km 2  for at least five consecutive years).  ... 

So first they say "5 year running mean" and 9 lines later (in the original caption) they all of a sudden change to "five consecutive years"?

Exactly my point.  The first draft said  "5 year running mean", and that's what the graph shows.  In the final draft, the bracketed part "(i.e. when sea ice extent is.... etc)" was added, without changing the graph or any of the other associated text.  It's bracketed, and starts with 'i.e.' - both signs that it is simply an attempt to clarify the foregoing text, not to alter its meaning.

Hi Peter,

after some sleep I think you might be right. But the fact remains, that the addition "for at least five consecutive years" does alter the meaning of the foregoing text "5 year running mean" and not clarify it. Or am I wrong on this?
And as, according to P-maker, figure captions "may be changed by the secretariat in consultation with the scientists afterwards" I find it weird that a Scientist involved in the IPCC process can't distinguish between a 5 year running mean and 5 consecutive years.

Anyhow. I asked aunt Google for help and - generous as she is - she came up with some infos that might shed some more light on the matter.

- First I found this article in Planet Earth from August 2015 (http://www.nerc.ac.uk/latest/publications/planetearth/aut15-ice-free/) about an ice-free summer in the Arctic by Prof. Ed Hawkins.

- Who is Dr. Ed Hawkings? He is "Climate scientist in the National Centre for Atmospheric Science (NCAS) at the University of Reading. IPCC AR5 Contributing Author." (from here (http://www.climate-lab-book.ac.uk/2016/predicting-an-ice-free-arctic-summer/) about an ice-free summer in the Arctic by Prof. Ed Hawkins.

As it turns out he has contributed to the TS of AR5, WGI. So my guess is he should know why they added "5 consecutive years" I might be wrong tough). On page 21 he writes:

Quote
The Intergovernmental Panel on Climate Change (IPCC) concluded it was likely that the Arctic would be reliably ice-free in September before 2050, assuming high future greenhouse-gas emissions (where ‘reliably ice-free’ means five consecutive years with less than a million square kilometres of sea ice). Individual years will be ice-free sometime earlier – in the 2020s, 2030s or 2040s – depending on both future greenhouse- gas emissions and the natural erratic fluctuations.

- Second: In a more recent article on Climate depot (http://www.climatedepot.com/2016/08/25/climate-experts-at-war-over-prediction-of-ice-free-arctic/) he is quoted(last paragraph):

Quote
Dr Hawkins said the Intergovernmental Panel on Climate Change, the UN’s climate science advisory body, had forecast that the Arctic would be “reliably ice-free”, meaning more than five consecutive years below one million sq km, by the mid-21st century.
Dr Hawkins said: “Putting a precise date on when we see the first days or weeks that are ‘ice-free’ is unwise because of the chaotic nature of the climate system and uncertainties in future greenhouse gas emissions.”

So the idea was, he says, to find a measure of ‘reliably ice-free’, whatever that means. And, accroding to this at least, "5 consecutive years" seems to be meant literally and not as an explanation of a 5 year running mean (Or am I reading this wrong again?)

One thing is sure: By his own admission, this definition will change the date for an ice-free Arctic from the 20s, 30s to later decades.
But are "5 consecutive years" more reliable as a 5 year running mean or a single year? And what is the scientific basis of this definition? I have no clue - I hope others do. The best thing would probably be to ask Dr Hawkins himself.
Any native speaking volunteers out there?   :)

Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis on September 08, 2016, 09:37:48 PM
the fact remains, that the addition "for at least five consecutive years" does alter the meaning of the foregoing text "5 year running mean" and not clarify it. Or am I wrong on this?

I have no argument with that.

And as, according to P-maker, figure captions "may be changed by the secretariat in consultation with the scientists afterwards" I find it weird that a Scientist involved in the IPCC process can't distinguish between a 5 year running mean and 5 consecutive years.

I suspect (but may be being overly generous) that this was inserted by "the secretariat" misunderstanding what the scientist was saying. Consulting scientists doesn't mean correctly interpreting the results of that consultation, unfortunately.

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's doing basically the same thing as we are in this thread - pointing out that an individual ice-free year will be 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid on September 08, 2016, 10:13:26 PM
Quote
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.

To me that is a an extraordinary claim.  I honestly don't know what to say about it that could not be offensive. I mean, really? The first ice free Arctic in millions of years not scientifically interesting?

C'mon.
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis on September 09, 2016, 09:55:55 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.
Title: Re: Ice free predictions and their uncertainty
Post by: skanky on September 09, 2016, 11:39:40 AM
Ed Hawkins runs this blog, for those who may want to discuss it with him:

http://www.climate-lab-book.ac.uk/ (http://www.climate-lab-book.ac.uk/)

 :)
Title: Re: Ice free predictions and their uncertainty
Post by: Bill Fothergill on September 09, 2016, 11:52:50 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.
Title: Re: Ice free predictions and their uncertainty
Post by: 6roucho on September 09, 2016, 12:24:20 PM
Surely predictability hinges on the nature of the decline? Will the ice melt out in a linear fashion, or will it undergo a state change? If it's a state change, then we can't in principle predict the timing of the event by extrapolating trends, since a non-linear event is characterised by divergence from historical behaviours.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on September 09, 2016, 12:37:29 PM
Ed Hawkins runs this blog, for those who may want to discuss it with him:

http://www.climate-lab-book.ac.uk/ (http://www.climate-lab-book.ac.uk/)

 :)

http://www.climate-lab-book.ac.uk/2016/predicting-an-ice-free-arctic-summer/ (http://www.climate-lab-book.ac.uk/2016/predicting-an-ice-free-arctic-summer/)

seems an excellent place to ask the question. (Think I should let Juan C. García or someone who has done more of the work tracking down what happened a shot at it before someone like me barges in.)
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid on September 09, 2016, 12:41:12 PM
Out of context?  Not only is the right context, it is the exact reason why a 5 year ice free definition was chosen over a single year. To minimize the significance of one single year without ice. It's a brilliant strategy.

I get it you.  You assume once the arctic is gone the world's climate will not significantly change. The jet stream will remain the same. Atmospheric patterns will remain the same. The salty Atlantic water will not mix with the Arctic ocean. The changes in albedo from an ice covered ocean to a water covered ocean won't matter. Unknown unknowns be dammed.


  Honestly, diminishing the significance of the first ice free arctic in millions of years sounds like madness to me. That would be perfectly fine for some random internet troll, but when this is happening at the front line of defense against climate change, the IPCC, its really disheartening.

How many people would be digging for answers to the uncertainties of an ice free arctic if they knew it will happen within 10 years?  How many people would prepare for the real but hidden from view worst case scenarios of such event? How many people would change their lifestyle to a low carbon one if they knew the real risks they face in their lifetimes? No worries, no response, no change. We'll just sit here and wait for it to happen.

I'm very sadden to see this written here and not only go without rebuttal, but be seconded. My hope is dimming. We will have an ice free arctic, because it is an irrelevant event. I pray you are right, but everything I know about the scientific process, uncertainty, risk assessment and society tells me that you and the IPCC are tragically underestimating the significance of an ice free arctic.






Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis 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.
Title: Re: Ice free predictions and their uncertainty
Post by: pauldry600 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?
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid 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.

Title: Re: Ice free predictions and their uncertainty
Post by: 6roucho 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Iceismylife 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.
Title: Re: Ice free predictions and their uncertainty
Post by: JMP 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 (ftp://youtu.be/x1SgmFa0r04)

from The Copernicus Observatory:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fwww.gmes-atmosphere.eu%2Fd%2Fgetchart%2Fmacc%2Fgac%2Fnrt%2Fnrt_fields_ghg%21Methane%21Surface%2106%21Global%21macc%21od%21enfo%21nrt_fields_ghg%212016090800%21%21chart.gif&hash=3af65cfe97e9affb141a99b53d7e7893)
Title: Re: Ice free predictions and their uncertainty
Post by: crandles 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 (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 (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.
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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".
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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.
Title: Re: Ice free predictions and their uncertainty
Post by: oren 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.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles 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.
Title: Re: Ice free predictions and their uncertainty
Post by: JMP 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 (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. 


 

   

Title: Re: Ice free predictions and their uncertainty
Post by: Bill Fothergill 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Ned W 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).
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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 (http://forum.arctic-sea-ice.net/index.php/topic,1559.msg89500.html#msg89500)
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis 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 (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 (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 (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.
Title: Re: Ice free predictions and their uncertainty
Post by: oren 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).
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis 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?
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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 (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 (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 (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 (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 (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 (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.
Title: Re: Ice free predictions and their uncertainty
Post by: charles_oil 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 (https://www.ipcc.ch/pdf/ar5/ar5_authors_review_editors_updated.pdf)

Lists enough of them I believe.
Title: Re: Ice free predictions and their uncertainty
Post by: oren 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Archimid 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 (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.

Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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 (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.
Title: Re: Ice free predictions and their uncertainty
Post by: budmantis 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"!
Title: Re: Ice free predictions and their uncertainty
Post by: charles_oil 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 ?).
Title: Re: Ice free predictions and their uncertainty
Post by: charles_oil 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......
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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 (http://www.realclimate.org/index.php/archives/2016/09/unforced-variations-sep-2016/comment-page-4/#comment-660355)
 
Title: Re: Ice free predictions and their uncertainty
Post by: charles_oil on September 17, 2016, 09:41:07 AM
ok - nothing yet - will try some others if nothing via David.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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   
Title: Re: Ice free predictions and their uncertainty
Post by: Rob Dekker 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 (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 (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 (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.
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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/ (http://www.swansea.ac.uk/texas-showcase/showcasespeakers/tavimurray/)

Good video:
https://www.youtube.com/watch?v=opid81mxkkI (https://www.youtube.com/watch?v=opid81mxkkI)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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/ (https://www.bas.ac.uk/profile/dgv/)

Video: https://www.youtube.com/watch?v=cYbjwQcaInQ (https://www.youtube.com/watch?v=cYbjwQcaInQ)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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 (http://science.gsfc.nasa.gov/sed/bio/josefino.c.comiso)

Josefino Comiso Biography Video: https://www.youtube.com/watch?v=Pwfl7les9r8 (https://www.youtube.com/watch?v=Pwfl7les9r8)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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://www.australianoftheyear.org.au/honour-roll/?view=fullView&recipientID=1367)
http://acecrc.org.au/people/prof-ian-allison-ao-aam/ (http://acecrc.org.au/people/prof-ian-allison-ao-aam/)

video: https://www.youtube.com/watch?v=GzUTwHiuG0s (https://www.youtube.com/watch?v=GzUTwHiuG0s)
Title: Re: Ice free predictions and their uncertainty
Post by: Juan C. García 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/ (http://rkwok.jpl.nasa.gov/)

Video: https://www.youtube.com/watch?v=26l2iNw4iJ0 (https://www.youtube.com/watch?v=26l2iNw4iJ0)

Title: Re: Ice free predictions and their uncertainty
Post by: Tor Bejnar on September 23, 2016, 09:32:17 PM
Here is an "Ice Free Arctic" prediction from xkcd (http://xkcd.com/887/).  Is this from 2011? Excerpt attached.  Surrounding predictions suggest large degrees of uncertainty.
Title: Re: Ice free predictions and their uncertainty
Post by: RoxTheGeologist 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 (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.


Title: Re: Ice free predictions and their uncertainty
Post by: crandles 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis 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.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles 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
Title: Re: Ice free predictions and their uncertainty
Post by: liefde 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;
(https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/grf/nsidc_global_area_byyear_b.png)

Taking that into account, there's really no saying when it will happen. It could be July 2017 with a little (bad) luck.
Title: Re: Ice free predictions and their uncertainty
Post by: RoxTheGeologist 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.
Title: Re: Ice free predictions and their uncertainty
Post by: Jim Williams 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;
(https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/grf/nsidc_global_area_byyear_b.png)

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.
Title: Re: Ice free predictions and their uncertainty
Post by: kiwichick16 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?
Title: Re: Ice free predictions and their uncertainty
Post by: 6roucho 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.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles 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?  ;)
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on December 07, 2016, 09:38:53 PM
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.

@Peter Ellis, sorry rather than just repeating myself graphically, I should explain:

If the data show an acceleration in extent decline and an acceleration in emissions then one way to get a more straight line might well be to graph extent against cumulative emission, as has been done.

But do we expect this to continue?

If all the models (assuming BAU increases in emissions) show acceleration in extent decline but then at some point changing to a declining rate as zero ice is approached. Then does it make sense to assume continued linear relationship between ice extent and cumulative emissions?

Or a different exercise: imagine a hypothetical world where we suddenly reduce emissions to zero. We would expect world to continue heating up (thermal inertia of oceans) and ice extent to continue to decline but cumulative emissions would stop dead. This would appear to break the linear relationship being suggested.

Similarly you can imagine a world where human emissions are no longer tied to GHG levels because of natural emissions from soils/permafrost/hydrates etc. Is the ice going to care whether the GHG in the atmosphere are natural or human ff burning sourced?

For these reasons, I am not convinced the relationship is reliably linear.

Just seeing a straight line is not enough to assume it will continue to be straight, it is sensible to also apply some thought to whether it makes sense to assume it will continue to be linear.

Having said this, if you want to know how much sea ice is destroyed by burning a certain quantity of ff to create CO2 then the answer looks pretty reliable for the immediate past and quite possible the near term future. If it is useful, I have no problem with the relationship being looked at, discussed and used where appropriate.
Title: Re: Ice free predictions and their uncertainty
Post by: jdallen on December 07, 2016, 09:58:05 PM
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.

@Peter Ellis, sorry rather than just repeating myself graphically, I should explain:
<snip>
For these reasons, I am not convinced the relationship is reliably linear.

Just seeing a straight line is not enough to assume it will continue to be straight, it is sensible to also apply some thought to whether it makes sense to assume it will continue to be linear.
<snip>

Here's my metaphor for what's happening, and how things will or will not trend...

https://farm1.staticflickr.com/339/19361016472_83bb01214d_o.gif

I think one way to look at the potential for an ice free arctic is rather than see it as a specific end-state, to instead view it as a threshold - a point at which the energy available to the system is high enough that cyclical events can push it past where summer extent can exist.

So I think we are in fact talking about two different things.  The first, which I think *is* mostly linear, is the rate at which net enthalpy is increasing in the arctic.  The second, which is *not* linear, are the variable and cyclical forces which cause seasonal states to flirt with my aforementioned threshold.

Again, pretty clearly to me, Peter's graph represents increasing potential for that limit - conditions which will preserve seasonal ice - to be passed.  It may be events will cause our observations to proceed straight down that trend without much deviation.  If an event occurs where we *do* break out of that linear trend, I don't think that will mean we've made a final transition to a consistently ice-free summer.  Rather, I think it will mean for that specific event, all of the limbs on our pendulum lined up such that we jumped over it.

So many feedbacks - that's the other problem - the "limbs" of our "pendulum" are changing over time as well.  But I say - focus on the increase in enthalpy, view it as an indicator of the potential of a melt out any given year.
Title: Re: Ice free predictions and their uncertainty
Post by: Peter Ellis on December 07, 2016, 11:00:05 PM
Just seeing a straight line is not enough to assume it will continue to be straight, it is sensible to also apply some thought to whether it makes sense to assume it will continue to be linear.

Well yes, but my point was rather more fundamental than that. Once you know that ice is declining linearly (and over the last 60 years, a linear fit is "good enough") and that CO2 is also increasing linearly (and over the last 60 years, a linear fit is "good enough") then this graph tells you literally nothing more.

Having said this, if you want to know how much sea ice is destroyed by burning a certain quantity of ff to create CO2 then the answer looks pretty reliable for the immediate past and quite possible the near term future.
No.  No it doesn't.  The fact that you get a linear correlation between two things that are changing nearly-linearly is not "pretty reliable", it's just how numbers work. Both have a nearly-linear relationship to time, therefore they have a nearly-linear relationship to each other. You could get an equally convincing graph by correlating the summer ice minimum to the height of a slow-growing tree planted in 1950, or world beef production in tonnes per year, or the average life expectancy in Portugal.  You CANNOT infer causation like this, and you certainly can't use it to make predictions without some underlying model for how one variable relates to the other.
Title: Re: Ice free predictions and their uncertainty
Post by: dnem on December 07, 2016, 11:14:40 PM
I tend to agree with jdallen's view of the big picture.  We will either "trend" our way down to zero or several major drivers will align and we'll get there before the trend predicts.  I don't think that the alignment of multiple drivers is predictable.

What I don't have is a good handle of the hysteresis in the system.  Is one ice free summer enough of an "attractor" to switch the arctic to a new equilibrium (always ice free in the summer)?
Title: Re: Ice free predictions and their uncertainty
Post by: jdallen on December 08, 2016, 01:33:10 AM
What I don't have is a good handle of the hysteresis in the system.  Is one ice free summer enough of an "attractor" to switch the arctic to a new equilibrium (always ice free in the summer)?
Maybe.  An "ice-free" summer will change two primary "legs"of our pendulum:
- total summer solar uptake by the Arctic ocean
- total available moisture during the fall refreeze

Those two by themselves may be enough to knock the system into a completely different equilibrium; at the least, it would take significant heat loss out of the Arctic to shift back to the old balance.

I do think the key really is total enthalpy in the ocean itself.  The last few years of dropping summer extent I think is an accelerating feedback to that, along with the massive inputs of heat coming in mostly on the Atlantic side via currents.
Title: Re: Ice free predictions and their uncertainty
Post by: be cause on December 08, 2016, 01:43:55 AM
The dmi 80'N anomaly is rising again and the 850 mb anomalies are going redder with every run , it looks like the rest of the year will be as anomalous as last Christmas . With the Fram pump primed and loaded with our thickest ice , the situation to our North is going critical . Unless something changes quickly Arctic ice is fast heading out of the atlas and into the history book ..
Title: Re: Ice free predictions and their uncertainty
Post by: Jim Williams on December 08, 2016, 02:30:18 AM
I do think the key really is total enthalpy in the ocean itself.  The last few years of dropping summer extent I think is an accelerating feedback to that, along with the massive inputs of heat coming in mostly on the Atlantic side via currents.

The problem is that you have to take the total ocean, not just the Arctic portion of the ocean.  What really counts here is how much further north the "Atlantic" and the "Pacific" have to get before the Arctic becomes a bay or sound, rather than an ice capped desert.  Hard to guess, but I think the evidence is for December 27th 2015 -- and it is just a matter of time before the residual ice is gone.
Title: Re: Ice free predictions and their uncertainty
Post by: magnamentis on December 08, 2016, 02:50:38 AM
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;
(https://sites.google.com/site/arctischepinguin/home/sea-ice-extent-area/grf/nsidc_global_area_byyear_b.png)

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.

predicting would have been to bold a statement but considering the possibility was indeed posted if one just would read back some posts in september and october this year.
Title: Re: Ice free predictions and their uncertainty
Post by: jdallen on December 08, 2016, 02:52:55 AM
I do think the key really is total enthalpy in the ocean itself.  The last few years of dropping summer extent I think is an accelerating feedback to that, along with the massive inputs of heat coming in mostly on the Atlantic side via currents.

The problem is that you have to take the total ocean, not just the Arctic portion of the ocean.  What really counts here is how much further north the "Atlantic" and the "Pacific" have to get before the Arctic becomes a bay or sound, rather than an ice capped desert.  Hard to guess, but I think the evidence is for December 27th 2015 -- and it is just a matter of time before the residual ice is gone.
I'll quibble with you here - not all ocean.  The Arctic is mostly isolated behind continents and continental shelves - there isn't as much opportunity for heat exchange via physical transfer as there is in a more open system - such as the boundaries between the Antarctic ocean and the Indian, South Atlantic and South Pacific.  As such, it forms its own mostly isolated heat sink/source.  At a qualitative level you can see that, if you compare ice coverage down to 70N on the Pacific side of the basin as compared to the Atlantic.  The Atlantic side is far more open, and is open right up to Svalbard and FJL.  On the Pacific side, screened from inflow, we have full coverage save for portions of the Chukchi.

Now, this is not to say increased heat in other places isn't factor - it is - but that's not my point.  My point is the primary reservoir of heat which will determine whether we have ice in the summer is the Arctic itself, not the adjacent oceans.
Title: Re: Ice free predictions and their uncertainty
Post by: Jim Williams on December 08, 2016, 01:56:16 PM
I do think the key really is total enthalpy in the ocean itself.  The last few years of dropping summer extent I think is an accelerating feedback to that, along with the massive inputs of heat coming in mostly on the Atlantic side via currents.

The problem is that you have to take the total ocean, not just the Arctic portion of the ocean.  What really counts here is how much further north the "Atlantic" and the "Pacific" have to get before the Arctic becomes a bay or sound, rather than an ice capped desert.  Hard to guess, but I think the evidence is for December 27th 2015 -- and it is just a matter of time before the residual ice is gone.
I'll quibble with you here - not all ocean.  The Arctic is mostly isolated behind continents and continental shelves - there isn't as much opportunity for heat exchange via physical transfer as there is in a more open system - such as the boundaries between the Antarctic ocean and the Indian, South Atlantic and South Pacific.  As such, it forms its own mostly isolated heat sink/source.  At a qualitative level you can see that, if you compare ice coverage down to 70N on the Pacific side of the basin as compared to the Atlantic.  The Atlantic side is far more open, and is open right up to Svalbard and FJL.  On the Pacific side, screened from inflow, we have full coverage save for portions of the Chukchi.

Now, this is not to say increased heat in other places isn't factor - it is - but that's not my point.  My point is the primary reservoir of heat which will determine whether we have ice in the summer is the Arctic itself, not the adjacent oceans.

If Siberia really does become the climatic North Pole; which it seems to be trying very hard to do, I think it will have a whole lot to say about your analysis.  The arctic is not where are nearly closed as you think.
Title: Re: Ice free predictions and their uncertainty
Post by: RoxTheGeologist on December 08, 2016, 08:33:21 PM
[
Well yes, but my point was rather more fundamental than that. Once you know that ice is declining linearly (and over the last 60 years, a linear fit is "good enough") and that CO2 is also increasing linearly (and over the last 60 years, a linear fit is "good enough") then this graph tells you literally nothing more.

This is true; I think that there was a study preformed by the cigarette companies a long time ago, with a similar argument about the correlation between lung cancer and cigarettes, and their analogy was that statistics show that people who eat blancmange have more road accidents.

I don't think we will ever come up with a complete model to show the real complexities of our global system, how exactly CO2 emissions cause or do not cause ice loss. We have to use surrogates models where we can. We could be debating the intricacies for the next 50 years, saying we can't be sure, and in the mean time the ice caps will disappear.

As a scientist I understand your argument; As someone who wants to change a mindset it is an excellent graph. Greenhouse gases have been emitted at this rate, and look how it has effected ice: Wip's graph is a great example of this. The systems that control the ice in the hemispheres are very different, but adding the total ice extent together produced a viral image. The earth is getting hotter and the ice caps are disappearing. We smoked cigarettes and it gave us lung cancer. We emitted CO2 and it caused the Arctic ice cap to shrink.


Title: Re: Ice free predictions and their uncertainty
Post by: andy_t_roo on December 08, 2016, 09:17:40 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

One thing to remember is that co2 is the forcing agent, and as such the amount of it in the atmosphere relates to the rate of change, as the equilibrium point gets further away. If we stopped emitting today, that graph would go straight down for a while.
Title: Re: Ice free predictions and their uncertainty
Post by: crandles on December 08, 2016, 09:30:35 PM


Having said this, if you want to know how much sea ice is destroyed by burning a certain quantity of ff to create CO2 then the answer looks pretty reliable for the immediate past and quite possible the near term future.
No.  No it doesn't.  The fact that you get a linear correlation between two things that are changing nearly-linearly is not "pretty reliable", it's just how numbers work. Both have a nearly-linear relationship to time, therefore they have a nearly-linear relationship to each other. You could get an equally convincing graph by correlating the summer ice minimum to the height of a slow-growing tree planted in 1950, or world beef production in tonnes per year, or the average life expectancy in Portugal.  You CANNOT infer causation like this, and you certainly can't use it to make predictions without some underlying model for how one variable relates to the other.

Agreed you cannot infer causation from the graph alone. I was trying to add something to say that because I don't think the relationship is reliably linear, that doesn't mean I think the paper is rubbish and shouldn't have been published. Maybe I worded it sloppily.

The graph alone doesn't allow you to infer causation, but we don't have the graph alone we have a whole host of IPCC reports and lots of scientific papers that indicates emissions increase greenhouse gas levels, greenhouse gases warm the world and especially Arctic areas in winter and a warmer Arctic winter is going to mean thinner ice that is easier to melt out. Also that the natural effects have been pretty small. Given such available extra evidence, then I don't see a lot wrong with saying
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if you want to know how much sea ice is destroyed by burning a certain quantity of ff to create CO2 then the answer looks pretty reliable for the immediate past and quite possible the near term future