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wili

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Arctic Sea Ice Loss--Reversible?
« on: April 29, 2015, 04:26:35 PM »
Arctic Sea Ice Loss Likely To Be Reversible
Scenarios of a sea ice tipping point leading to a permanently ice-free Arctic Ocean were based on oversimplified arguments


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They created a model that bridged the gap between the process models and the GCMs, and they used it to determine what caused sea ice tipping points to occur in some models but not in others.

“We found that two key physical processes, which were often overlooked in previous process models, were actually essential for accurately describing whether sea ice loss is reversible,” said Eisenman, a professor of climate dynamics at Scripps Oceanography. “One relates to how heat moves from the tropics to the poles and the other is associated with the seasonal cycle. None of the relevant previous process modeling studies had included both of these factors, which led them to spuriously identify a tipping point that did not correspond to the real world.”

“Our results show that the basis for a sea ice tipping point doesn’t hold up when these additional processes are considered,” said Wagner. “In other words, no tipping point is likely to devour what’s left of the Arctic summer sea ice. So if global warming does soon melt all the Arctic sea ice, at least we can expect to get it back if we somehow manage to cool the planet back down again.”

Discuss
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Nightvid Cole

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #1 on: April 29, 2015, 04:58:57 PM »
I don't know what to think, because models still have A LONG way to go to accurately capture the physical processes that occur in and over sea ice. Even seemingly simple things like melt ponds are only just beginning to be incorporated into state of the art models, and most use only a very crude version of the ponds with only a few shape parameters at best. The models also seem deficient on their optics  - which would impact their ability to estimate the albedo of inhomogeneous ice and snow. Finally, they use limited parameter sets for the mechanical strength of the ice and the distribution of weak points in a melting floe, and also the models fail to account for the action of waves and swells on the ice. As a result the mechanical breakup is not simulated well.

The models thus have quite a long way to go before they can really start telling us as much about "reality" as we'd like.


Jim Hunt

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #2 on: April 29, 2015, 05:44:00 PM »
Note that Wagner & Eisenman are not attempting to model the "real world":

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Here we derive the model used in this study, which is an idealized representation of sea ice and climate with seasonal and latitudinal variations in a global domain. The surface is an aquaplanet with an ocean mixed layer that includes sea ice when conditions are sufficiently cold. We consider only zonally-uniform climates.

The real world is much more complex than that!
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

Xulonn

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #3 on: April 29, 2015, 05:49:28 PM »
I wasn't aware that science was telling us that if the ice went away, it would never return, even if we mitigated AGW/CC and global average temps went back to their more suitable (for human habitability) recent historical levels.

I thought that the Arctic sea ice had melted and returned at the end of warm periods in the past, and I had no reason to believe that it wouldn't recover again if the current AGW/CC event was reversed.  (However, I don't see mitigation and a warming trend reversal as likely in the near future.   

As expected, the findings presented in this paper were quickly - and grossly - cherry-picked and misinterpreted by Anthony Watts at his WUWT denialist website.  His fraudulent gloating ignored the fact the the paper stated that mitigation and a reversal of the current warming trend was required for ice to recover.  However, his b.s. was joyously celebrated as true by his dumbed down denialist minions, and as expected, Sou at HotWhopper quickly demolished this latest WUWT idiocy.   

Although I have not read the paper, I don't really see significance or controversy here.

Nick_Naylor

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #4 on: April 29, 2015, 06:16:16 PM »
Although I have not read the paper, I don't really see significance or controversy here.

The significance seems to be that a particular tipping point that was so speculative that most of us have never heard of it is beginning to look less likely than previously.

We are still going to have ice-free Arctic summers soon that won't go away during our grandchildren's lifetimes pretty much no matter what we do - assuming we can avoid global thermonuclear war.

jdallen

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #5 on: April 29, 2015, 06:33:54 PM »
At a high level, what applies here are hysteresis and what is best described as "momentum" in the effect of accumulated heat on systemic behavior.

The climate as a system has "memory" of previous conditions which shapes how it responds to new inputs.  When that "memory" changes (e.g. Via ice free summers), the same inputs will produce much different results.

So, of course the current conditions could be reversed, but not without much different inputs into the system.
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Peter Ellis

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #6 on: April 29, 2015, 06:36:24 PM »
Not sure an aquaplanet (no land) is the most useful model to use, but the results here are still of importance for those predicting a tipping point - they'll need to explain how the presence of continents will prevent ice regrowth if the climate cools again.

In terms of actual forecasting... irrelevant.  The climate's not getting cool again, unless you have a Magic CO2 Hoover (tm).

seaicesailor

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #7 on: April 29, 2015, 06:39:44 PM »
Just from what I read above, this study does not exclude the possibility of a tipping point. The way I read it is that their model shows no evidence that it may exist (once effects previously neglected are included in the model).

Sleepy

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #8 on: April 29, 2015, 06:56:09 PM »
I was looking at the paper here and wondered why noone linked to it.
http://www.tillwagner.me/

And then searched for this part.
Quote
It is worth emphasizing that the present model contains substantial nonlinearity, including the ice-albedo effect and factors associated with sea ice thickness changes. Such nonlinearity has been shown in SCMs to lead to both accelerating sea ice loss and bifurcations.

And found Sou.
http://blog.hotwhopper.com/2015/04/bombshell-dumb-denialism-from-anthony.html
Her final comment.
Quote
Given the way we're heading the findings offer small comfort. To stop Arctic sea ice from melting means stopping global warming.

Oyvind Johnsen

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #9 on: April 29, 2015, 07:16:00 PM »
I think this debate started after the great ice loss in 2007, but the theme is "tipping point" rather than "irreversibility". Here is an article refuting the tipping point in 2011:

http://nsidc.org/icelights/2011/03/09/arctic-sea-ice-and-the-tipping-point/

Ice loss is obviously reversible. The Arctic has seen ice-free conditions in the past, and now there is ice.

As I understand it, there are two questions related to tipping points/reversibility:

1) Are we already bound for (nearly) ice-free summers in the Arctic? (With a realistic view of emissions the next decades, and no unexpected cooling due to catastrophic supervolcanoes, meteorites or nuclear war.)

2) Once we have reached ice-free summers, will that mean that returning to the Arctic temperatures of the (e.g.) 1980s, will not be enough to return to the state of yearly ice fluctuations of the 1980s?

I don t know the answers to any of those questions, but my guess would be a "yes" to 1) and a "no" to 2).

Michael Hauber

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #10 on: April 29, 2015, 11:30:43 PM »
Tipping points are reversible.  However reversal may require additional cooling.  If there was a tipping point with an extra degree of warming to an ice free Arctic it may require three degrees (to pick a hypothetical) of cooling to get the ice back.

I suspect that a tipping point may have been passed with loss of multi-year ice, with the 'tip' occurring in 2007.  The consequence of this if true is that Arctic ice loss would slow once the tipping point is complete as the feedback would stop operating once there is no further multi-year ice to lose.  And although we have a small amount of multi-year ice left I believe it is beyond reach of the primary feedbacks resulting in loss of the significant ice pack - being weakening of the ice pack structure to allow faster movement - now the ice pack is weak enough that multi-year ice is limited by the time it takes ice to move from one side of the Arctic to the other under basically free movement of ice not limited by any significant multi-year ice jam.
Climate change:  Prepare for the worst, hope for the best, expect the middle.

Pmt111500

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #11 on: May 03, 2015, 05:06:30 AM »
“One relates to how heat moves from the tropics to the poles and the other is associated with the seasonal cycle. "

so they've previously forgotten the earth revolves around the sun at an angle, and missed an ef-ing 90% of the effect ghg's have ON EARTH, tripped in the 2nd law of thermodynamics and still got published. Not to say anything on arctic phytoplankton study or permafrost. WHAT HAVE they included. Stopping now before I lose it.

Peter Ellis

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #12 on: May 03, 2015, 11:13:44 AM »
I think you're missing the point.  This new model does include the seasonal cycle.  The "irreversible" (tipping point) effects only appear in simplified models that don't.  It's also worth pointing out that the much more sophisticated general circulation models also don't show tipping points (e.g Tietsche et al 2011).

Pmt111500

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #13 on: May 03, 2015, 04:28:01 PM »
now off hangover, I see your point...

Phil.

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #14 on: May 04, 2015, 01:58:18 PM »
Tipping points are reversible.  However reversal may require additional cooling.  If there was a tipping point with an extra degree of warming to an ice free Arctic it may require three degrees (to pick a hypothetical) of cooling to get the ice back.

The whole point of a 'tipping point' is that there is hysteresis in the change to an ice free state, i.e. once you've entered that state, it's more difficult to get back to the previous state.  For example, in an ice free state the temperature/salinity profile of the ocean will probably change.

jdallen

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #15 on: May 04, 2015, 05:37:47 PM »
Tipping points are reversible.  However reversal may require additional cooling.  If there was a tipping point with an extra degree of warming to an ice free Arctic it may require three degrees (to pick a hypothetical) of cooling to get the ice back.

The whole point of a 'tipping point' is that there is hysteresis in the change to an ice free state, i.e. once you've entered that state, it's more difficult to get back to the previous state.  For example, in an ice free state the temperature/salinity profile of the ocean will probably change.
I find a double (or triple or...) pendulum is a good metaphor to use when pondering this.  The ice, or lack thereof is one limb - one dimension - of it.  The end of the pendulum will have its path proscribed until that dimension changes.
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JER

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Re: Arctic Sea Ice Loss--Reversible?
« Reply #16 on: May 21, 2015, 04:14:37 AM »
Pardon me for asking what is probably a stupid question, but would it be possible to analyze the inner workings of what actually happens in Hudson Bay on an annual basis (it goes from being frozen to being completely ice-free and then freezes again) in order to figure out answers to the hysteresis questions for the Arctic Ocean as a whole?
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