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Author Topic: The Slow Transition  (Read 87773 times)

sedziobs

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Re: The Slow Transition
« Reply #400 on: February 12, 2017, 08:48:55 PM »
Regarding freezing degree days: does 1 day at -51.8 C have the same effect as 50 days at -2.8 C?  The empirical ice growth models simply use total FDD with no knowledge of their temporal distribution over the winter.  Perhaps the difference is negligible, but I imagine the distribution of FDD must have some impact.

For reference, here is Chris Reynold's relevant post:
http://dosbat.blogspot.co.uk/2015/01/the-simplest-model-of-sea-ice-growth.html

Gray-Wolf

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Re: The Slow Transition
« Reply #401 on: February 12, 2017, 09:19:42 PM »
Regarding freezing degree days: does 1 day at -51.8 C have the same effect as 50 days at -2.8 C?  The empirical ice growth models simply use total FDD with no knowledge of their temporal distribution over the winter.  Perhaps the difference is negligible, but I imagine the distribution of FDD must have some impact.

For reference, here is Chris Reynold's relevant post:
http://dosbat.blogspot.co.uk/2015/01/the-simplest-model-of-sea-ice-growth.html


Intensity , and duration of cold would need to be taken into account? How long does it take the cold to penetrate through 2m of ice and bring it down toward the outside temps? In the same way you can wave your hand over a candle flame without harm fleeting warmth or cold cannot bring full impact?

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DrTskoul

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Re: The Slow Transition
« Reply #402 on: February 12, 2017, 09:23:45 PM »
Regarding freezing degree days: does 1 day at -51.8 C have the same effect as 50 days at -2.8 C?  The empirical ice growth models simply use total FDD with no knowledge of their temporal distribution over the winter.  Perhaps the difference is negligible, but I imagine the distribution of FDD must have some impact.

For reference, here is Chris Reynold's relevant post:
http://dosbat.blogspot.co.uk/2015/01/the-simplest-model-of-sea-ice-growth.html


Intensity , and duration of cold would need to be taken into account? How long does it take the cold to penetrate through 2m of ice and bring it down toward the outside temps? In the same way you can wave your hand over a candle flame without harm fleeting warmth or cold cannot bring full impact?


Those empirical equations have been defined taking into account the heat diffusion equations. Integral over time has been transformed to a sum of FDDs. The exponents and proportionality constants account for ice specific physical constants ( thermal diffusion, heat capacity, etc )
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oren

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Re: The Slow Transition
« Reply #403 on: February 12, 2017, 10:59:44 PM »
Regarding freezing degree days: does 1 day at -51.8 C have the same effect as 50 days at -2.8 C?  The empirical ice growth models simply use total FDD with no knowledge of their temporal distribution over the winter.  Perhaps the difference is negligible, but I imagine the distribution of FDD must have some impact.

For reference, here is Chris Reynold's relevant post:
http://dosbat.blogspot.co.uk/2015/01/the-simplest-model-of-sea-ice-growth.html

This is what I meant when I wrote about the differences between past winters and current winters. The formulas are empirical and have been developed under certain implicit assumptions, which no longer apply. Results could be higher or lower depending on the actual temp integral and the physics, but the empirical result is far less accurate than it used to be.

ktonine

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Re: The Slow Transition
« Reply #404 on: February 12, 2017, 11:18:38 PM »
... the empirical result is far less accurate than it used to be.

Based on what evidence?  The FDD implied thickness has matched other measures very well this winter.

oren

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Re: The Slow Transition
« Reply #405 on: February 12, 2017, 11:23:54 PM »
... the empirical result is far less accurate than it used to be.

Based on what evidence?  The FDD implied thickness has matched other measures very well this winter.
Admittedly, no evidence beyond layman's intuition.

crandles

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Re: The Slow Transition
« Reply #406 on: February 12, 2017, 11:45:20 PM »
... the empirical result is far less accurate than it used to be.

Based on what evidence?  The FDD implied thickness has matched other measures very well this winter.

I think that is true, the measurements are for a particular period and those measurement will do better at predicting the same period than a future period. This might not need to be a major deterioration. OTOH perhaps storminess increases upward heat flux in the ocean and could change relevant parameters that alter the derived values?

.

However, I have what is a rather different quibble. We seem to be saying FDD is low this year which will result in thinner ice. However there is a serious problem of cause and effect. At the other extreme, we could say there is less volume ie thin ice so heat transfers from ocean to atmosphere faster and therefore the atmosphere is warmer. So the low FDD could be a consequence of low volume and as there is fast transfer of heat from ocean to atmosphere, the volume of ice could be catching up to where it normally is. It isn't going to be one extreme or the other but some combination. Is it possible that the low volume and increased storminess could this year have altered the balance between the two causes making it more a case of ocean warming atmosphere. Then would using low FDD as a reason for low volume be giving a false indication of particularly low volume? Perhaps Cryosat2 data shouldn't be dismissed in favour of PIOMAS quite so readily?


Iceismylife

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Re: The Slow Transition
« Reply #407 on: February 13, 2017, 12:35:28 AM »
https://forum.arctic-sea-ice.net/index.php/topic,230.msg96282.html#msg96282

Ice grows next to ice or land so if we have 1/4 the ice at the start of the freezing season and it takes two months to catch up we would be at 10,573,160km^2 sea ice extent now.  If the assumptions are correct.  But it would likely be warmer and stormier. So less ice formation.  It mint not grow at all.

Neven

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Re: The Slow Transition
« Reply #408 on: February 13, 2017, 12:49:22 AM »

However, I have what is a rather different quibble. We seem to be saying FDD is low this year which will result in thinner ice. However there is a serious problem of cause and effect. At the other extreme, we could say there is less volume ie thin ice so heat transfers from ocean to atmosphere faster and therefore the atmosphere is warmer. So the low FDD could be a consequence of low volume and as there is fast transfer of heat from ocean to atmosphere, the volume of ice could be catching up to where it normally is. It isn't going to be one extreme or the other but some combination. Is it possible that the low volume and increased storminess could this year have altered the balance between the two causes making it more a case of ocean warming atmosphere. Then would using low FDD as a reason for low volume be giving a false indication of particularly low volume? Perhaps Cryosat2 data shouldn't be dismissed in favour of PIOMAS quite so readily?

Food for thought, crandles. Thanks.
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Hyperion

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Re: The Slow Transition
« Reply #409 on: February 13, 2017, 03:03:23 AM »
There's probably not a heck of a lot of reliability in cryosat, piomass or any basic fdd based estimates. the rules of the game have been changing so fast. The ice quality is rubbish and is far less thermally conductive than it used to be, and lower in density. Meaning that freeboard measurements by satelite are almost certainly overstating the actual thickness when the models assume that the submerged thickness is simular to what it used to be. Porous rotten ice, interleaved, snow layers and ice crusts from flash surface melts and supercooled water hitting the surface and flash freezing as per standard ice storm scenarios will all cause massive conductivity reduction. And its pretty certain that theres been major reduction in the low salinity layers integrity over the whole arctic ocean. we would be foolish to put any faith in models like mercantor for halocline and temperature at depth profiles without extensive direct measurements to back them up. Even if there is still a distinct boundary between surface water  and warmer atlantic/ pacific water below, the effects of all the slosh and wave action now going on will be assisting a lot of heat to soak upward into the surface layer making serious increase in underice roughness, and therefore surface area that will make it all the more vunerable to rapid melt out later in the season. :(
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epiphyte

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Re: The Slow Transition
« Reply #410 on: February 13, 2017, 07:00:28 AM »

However, I have what is a rather different quibble. We seem to be saying FDD is low this year which will result in thinner ice. However there is a serious problem of cause and effect. At the other extreme, we could say there is less volume ie thin ice so heat transfers from ocean to atmosphere faster and therefore the atmosphere is warmer. So the low FDD could be a consequence of low volume and as there is fast transfer of heat from ocean to atmosphere, the volume of ice could be catching up to where it normally is. It isn't going to be one extreme or the other but some combination. Is it possible that the low volume and increased storminess could this year have altered the balance between the two causes making it more a case of ocean warming atmosphere. Then would using low FDD as a reason for low volume be giving a false indication of particularly low volume? Perhaps Cryosat2 data shouldn't be dismissed in favour of PIOMAS quite so readily?

Food for thought, crandles. Thanks.

I've been thinking about that too - but came to the conclusion that if the ocean is warming the atmosphere more than heretofore, it is symptomatic of something new - and none of the possibilities I can think of seem ultimately conducive to higher than expected volume. viz:

 - thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there.
 - less snow cover causing greater heat loss and more freezing? Yes, but it's been stormy, so why would there be less snow? Also, the storms would seem to imply greater mixing with the warmer southern latitudes.
 - halocline breakdown. Ouch.

Csnavywx

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Re: The Slow Transition
« Reply #411 on: February 13, 2017, 07:58:15 AM »
Cryosat shouldn't be tossed. It's an actual dataset. Keep in mind it routinely shows higher max volume and lower min volume than PIOMAS and I would tend to side (in any case) with an actual observational dataset. That doesn't mean PIOMAS is useless or anything, even if it underreports volume at max, the year-to-year trend is still important.

Cumulative FDD totals are pretty straightforward so I'm not sure what all of the fuss is about. Less FDD = thinner ice in nearly all real-world cases. The insulation effect is already baked into the equation for determining thickness. The only real wildcard is snowcover area and depth.

Neven

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Re: The Slow Transition
« Reply #412 on: February 13, 2017, 10:08:54 AM »
Let's continue this discussion in the PIOMAS vs CryoSat thread.
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Shared Humanity

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Re: The Slow Transition
« Reply #413 on: February 13, 2017, 03:17:29 PM »
Let's continue this discussion in the PIOMAS vs CryoSat thread.


Thanks again. Can't understand why these two comments landed here. The proper thread is active.

Steven

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Re: The Slow Transition
« Reply #414 on: March 15, 2017, 06:53:16 PM »
New paper by R. Bintanja and O. Andry:

Towards a rain-dominated Arctic


Abstract:
Climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, little is known about future changes in the distributions of rainfall and snowfall in the Arctic. Here we use 37 state-of-the-art climate models in standardized twenty-first-century (2006–2100) simulations to show a decrease in average annual Arctic snowfall (70°–90°N), despite the strong precipitation increase. Rain is projected to become the dominant form of precipitation in the Arctic region (2091–2100), as atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rainfall and snowfall will heavily impact Arctic hydrology (for example, river discharge, permafrost melt), climatology (for example,snow, sea-ice albedo and melt) and ecology (for example, water and food availability)



Jim Williams

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Re: The Slow Transition
« Reply #415 on: March 15, 2017, 08:03:02 PM »
New paper by R. Bintanja and O. Andry:

Towards a rain-dominated Arctic


Abstract:
Climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, little is known about future changes in the distributions of rainfall and snowfall in the Arctic. Here we use 37 state-of-the-art climate models in standardized twenty-first-century (2006–2100) simulations to show a decrease in average annual Arctic snowfall (70°–90°N), despite the strong precipitation increase. Rain is projected to become the dominant form of precipitation in the Arctic region (2091–2100), as atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rainfall and snowfall will heavily impact Arctic hydrology (for example, river discharge, permafrost melt), climatology (for example,snow, sea-ice albedo and melt) and ecology (for example, water and food availability)




Smells Post Hoc to me.

We are watching the Arctic melt therefore the models are tweaked to show the Arctic melting.

DaveHitz

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Re: The Slow Transition
« Reply #416 on: March 16, 2017, 08:07:45 AM »

Smells Post Hoc to me.

We are watching the Arctic melt therefore the models are tweaked to show the Arctic melting.

Isn't that exactly how you are supposed to make models better?

Compare a model to reality, and if the model doesn't match, then adjust it until it does. Then let some more time pass, see if it still matches reality, and if it doesn't, then adjust again.

Gray-Wolf

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Re: The Slow Transition
« Reply #417 on: March 16, 2017, 11:05:33 AM »
I think a lot of Climate science finds itself 'running to catch up' due to the advanced nature of change? I first saw this in 07' with the apparent surprise of Science over the Arctic losses that year?
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epiphyte

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Re: The Slow Transition
« Reply #418 on: March 16, 2017, 03:04:58 PM »
On a related note, IIRC there was a paper a year or two ago pointing out that thunderstorms, previously unheard of in the arctic, have started occurring and are now growing in frequency as far North as the CAA and Alaska/Beaufort. AFAIK the climate models weren't predicting that. So perhaps even more catching up to be done?

ktonine

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Re: The Slow Transition
« Reply #419 on: March 16, 2017, 03:17:48 PM »
AFAIK the climate models weren't predicting that. So perhaps even more catching up to be done?

Consider their grid resolution.  They weren't predicting that because they don't predict local thunderstorms.  C'mon, let's try to keep this somewhat real.

epiphyte

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Re: The Slow Transition
« Reply #420 on: March 16, 2017, 04:09:10 PM »
AFAIK the climate models weren't predicting that. So perhaps even more catching up to be done?

Consider their grid resolution.  They weren't predicting that because they don't predict local thunderstorms.  C'mon, let's try to keep this somewhat real.

Ouch. The condescension, it burns! Obviously climate models aren't weather models and they can't predict storms. However if they were on-base they  _would_ have reflected the increasing prevalence of atmospheric conditions conducive to stormy weather.

In other words they would reflect the observation that storms are "occurring and are now growing in frequency" If you read my earlier post a little more carefully you will see that that is what I actually said.

ktonine

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Re: The Slow Transition
« Reply #421 on: March 16, 2017, 04:22:51 PM »
Ouch. The condescension, it burns! Obviously climate models aren't weather models and they can't predict storms. However if they were on-base they  _would_ have reflected the increasing prevalence of atmospheric conditions conducive to stormy weather.

In other words they would reflect the observation that storms are "occurring and are now growing in frequency" If you read my earlier post a little more carefully you will see that that is what I actually said.

I assume you mean:
I've been thinking about that too - but came to the conclusion that if the ocean is warming the atmosphere more than heretofore, it is symptomatic of something new - and none of the possibilities I can think of seem ultimately conducive to higher than expected volume. viz:

 - thinner ice causing more ocean heat to be lost to the atmosphere. No volume increase there.
 - less snow cover causing greater heat loss and more freezing? Yes, but it's been stormy, so why would there be less snow? Also, the storms would seem to imply greater mixing with the warmer southern latitudes.
 - halocline breakdown. Ouch.

Which says nothing about models, is evidence/data free, and actually contradicts what *models* do predict.

epiphyte

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Re: The Slow Transition
« Reply #422 on: March 16, 2017, 04:51:13 PM »
No,I was talking about the post from today which you suggested I "get real" about.



ktonine

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Re: The Slow Transition
« Reply #423 on: March 16, 2017, 05:04:46 PM »
No,I was talking about the post from today which you suggested I "get real" about.

 Epiphyte - you wrote: "If you read my earlier post a little more carefully you will see that that is what I actually said."

I then quoted your earlier post.  That's what the "I assume" was referring to - I assumed this is the 'earlier post' to which you referred.  And that earlier post is what I then characterized as "says nothing about models, is evidence/data free, and actually contradicts what *models* do predict."

Condescending? No.  Just tired of reading random flotsam and jetsam with no bearing on data, reality, or basis in sound theory.

oren

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Re: The Slow Transition
« Reply #424 on: March 16, 2017, 05:32:43 PM »
Enough, please...

epiphyte

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Re: The Slow Transition
« Reply #425 on: March 16, 2017, 05:36:18 PM »

Condescending? No.  Just tired of reading random flotsam and jetsam with no bearing on data, reality, or basis in sound theory.

How deep do you want to dig? Here is the post which prompted you to opine that I should "get real" for suggesting that climate models ought to be able to predict the weather, in it's entirety:

"On a related note, IIRC there was a paper a year or two ago pointing out that thunderstorms, previously unheard of in the arctic, have started occurring and are now growing in frequency as far North as the CAA and Alaska/Beaufort. AFAIK the climate models weren't predicting that. So perhaps even more catching up to be done?"

Did I say, as you seem to think, that the models should have predicted the actual storms? No. I didn't. I posed a question as to whether they had predicted that storms would occur and increase in frequency. You just read it wrong, which is likely to happen if you start from the assumption that other people are stupid.

Neven

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Re: The Slow Transition
« Reply #426 on: March 16, 2017, 06:00:27 PM »
Let's get back on topic or get out of here.

The Forum has a PM (personal message) function, but please stay civil there as well.
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gerontocrat

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Re: The Slow Transition
« Reply #427 on: March 16, 2017, 06:41:19 PM »
Is not the question - whither the slow transition ? To continue, to accelerate, or a sudden collapse ?
I am content to wait and see, though I am betting on acceleration.

Jim Williams

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Re: The Slow Transition
« Reply #428 on: March 17, 2017, 01:53:04 AM »
<snip>
« Last Edit: March 17, 2017, 09:51:23 AM by Neven »

Darvince

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Re: The Slow Transition
« Reply #429 on: March 17, 2017, 09:54:45 AM »



What does the black line represent? Permafrost?

Steven

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Re: The Slow Transition
« Reply #430 on: March 17, 2017, 07:31:32 PM »
What does the black line represent? Permafrost?


The black line represents  "the model-mean −10°C isotherm"  for annual mean temperature.  Upthread I had cropped the image a bit.  But you can view the full text of the paper here or here.