When will the Arctic Go Ice Free?

[The Walrus]

Phoenix, deniers will always deny. No use guiding the conversation by seeking the side of least drama, although I understand your position perfectly.
About when will the Arctic go ice-free, this is a big unknown. There have been many threads about it in this section over past few years. So don't shout it from the rooftops until it actually happens, but don't think it can't happen either. Only time will tell, and by time I mean several years or a decade. It's a slow road.
OTOH, the ASI has crashed enough that anyone who can be alarmed is already alarmed. Those that close their ears will close their ears anyway.

I don't subscribe to the cynical view. Opinion polls show that climate is a rising issue in the US where I live. Yale conducts annual climate surveys. In my home state of Nevada, 93% of Democrats polled before the February caucus supported a Green New Deal. The % of Democrats who listed climate as the #1 issue increased by 3-4x from the 2016 primary to the 2020 primary. Climate caught health care as a leading issue for Democratic voters in 2020.

People are being converted through relentless messaging,  exposure to increasing and irrefutable evidence and peer pressure. The GOP is losing young voters.

ASIF as a whole is a great resource for climate science discussion. I value it. Thanks for your role in moderating.

I have not seen any recently, but I suspect polls toady will reflect a vastly different viewpoint on a number of issues. 

[JNap]

Last time I promise...

Year    Chance of that single year     Chance of at least one year since 2019
            going below 0.8K km3           having gone below 0.8 km3
2020          0%                                        0%
2021          0%                                        1%
2022          1%                                        1%
2023          1%                                        2%
2024         2%                                         4%
2025         3%                                         6%
2026         4%                                       10%
2027         6%                                       15%
2028         8%                                       22%
2029       12%                                       31%
2030       16%                                       42% 
2031       21%                                       55%  First BOE more likely than not by 2031
2032       28%                                       67%
2033       34%                                       78%
2034       42%                                       87%
2035       49%                                       94%
After 2035, each single year has >50% chance of BOE
...

Glen, thank you for the series of detailed analysis based on the linear trends.   I am not sure if linear is the best model or not (it seems that the Gompertz may be slightly better?), but regardless, it indicates that the 2030 - 2032 timeframe would seem to be the most likely for the initial BOE based on the data.

I also agree with your last point that once we have a BOE, the warming process would seem to have a self reinforcing, "positive" feedback loop, i.e. More open arctic ocean collecting more solar insolation for more and more days in September, then August, and so on.

Thank you again for your analysis.
 

[gerontocrat]

I also agree with your last point that once we have a BOE, the warming process would seem to have a self reinforcing, "positive" feedback loop, i.e. More open arctic ocean collecting more solar insolation for more and more days in September, then August, and so on.

"a self reinforcing, "positive" feedback loop"?  By September insolation is in rapid decline. At high latitudes the months that matter for AWP are the two months either side of the June solstice, i.e. starting now.

You can see from the attached AWP graph from NICO Sun how the late 2012 melt kept AWP below average until well after the solstice, and despite the record low minimum ended far below 2016 and 2019, two years in which melt started early.

In other words, 2016 and 2019 may have contributed far more to Arctic Amplification than did 2012, despite the outrageously low 2012 minimum. That early season melt by also allowing far greater warming of the Arctic ocean upper layers, might also help to delay the re-freeze significantly.

A BOE will certainly be a significant symbol, but the Arctic climate wreckage must surely come from longer periods of open water earlier in the year, as may be happening again this year ?

[S.Pansa]

New paper on the prospects of an ice-free Arctic based on CMIP6 projections.
Press info here. Some snippets:

"... If we reduce global emissions rapidly and substantially, and thus keep global warming below 2 °C relative to preindustrial levels, Arctic sea ice will nevertheless likely disappear occasionally in summer even before 2050. This really surprised us" said Dirk Notz, who leads the sea-ice research group at University of Hamburg, Germany. ...

Paper here
Abstract & Plain Language

Abstract

We examine CMIP6 simulations of Arctic sea‐ice area and volume. We find that CMIP6 models produce a wide spread of mean Arctic sea‐ice area, capturing the observational estimate within the multi‐model ensemble spread. The CMIP6 multi‐model ensemble mean provides a more realistic estimate of the sensitivity of September Arctic sea‐ice area to a given amount of anthropogenic CO2 emissions and to a given amount of global warming, compared with earlier CMIP experiments. Still, most CMIP6 models fail to simulate at the same time a plausible evolution of sea‐ice area and of global mean surface temperature. In the vast majority of the available CMIP6 simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area < 1 million km2) in September for the first time before the year 2050 in each of the four emission scenarios SSP1‐1.9, SSP1‐2.6, SSP2‐4.5 and SSP5‐8.5 examined here.

Plain Language Summary
We examine simulations of Arctic sea ice from the latest generation of global climate models. We find that the observed evolution of Arctic sea‐ice area lies within the spread of model simulations. In particular, the latest generation of models performs better than models from previous generations at simulating the sea‐ice loss for a given amount of CO2 emissions and for a given amount of global warming. In most simulations, the Arctic Ocean becomes practically sea‐ice free (sea‐ice area < 1 million km2) in September for the first time before the year 2050.

For a detailed date range see the supporting information, especially table S4

[JNap]

I also agree with your last point that once we have a BOE, the warming process would seem to have a self reinforcing, "positive" feedback loop, i.e. More open arctic ocean collecting more solar insolation for more and more days in September, then August, and so on.

"a self reinforcing, "positive" feedback loop"?  By September insolation is in rapid decline. At high latitudes the months that matter for AWP are the two months either side of the June solstice, i.e. starting now.

A BOE will certainly be a significant symbol, but the Arctic climate wreckage must surely come from longer periods of open water earlier in the year, as may be happening again this year ?

Jim, I certainly agree that once we have the initial BOE, there will not be a sudden positive insolation feedback loop.   What I intended to convey is that as we get closer to a BOE, there will be an increasing amount of open ocean during earlier and earlier during the summer to get to a mid-September BOE.  It is those times earlier in the melting season that will start getting more of  the impact from the strong arctic insolation period, say from approximately May 1st to August 10th.

[The Walrus]

I also agree with your last point that once we have a BOE, the warming process would seem to have a self reinforcing, "positive" feedback loop, i.e. More open arctic ocean collecting more solar insolation for more and more days in September, then August, and so on.

"a self reinforcing, "positive" feedback loop"?  By September insolation is in rapid decline. At high latitudes the months that matter for AWP are the two months either side of the June solstice, i.e. starting now.

A BOE will certainly be a significant symbol, but the Arctic climate wreckage must surely come from longer periods of open water earlier in the year, as may be happening again this year ?

Agreed.  By late September, at the time of minimum sea ice expanse, the sun is already starting to recede below the horizon.  Insolation will likely be matched by latent heat loss.  Early season ice loss is much more influential with regards to increased solar insolation.

[JNap]

I also agree with your last point that once we have a BOE, the warming process would seem to have a self reinforcing, "positive" feedback loop, i.e. More open arctic ocean collecting more solar insolation for more and more days in September, then August, and so on.

"a self reinforcing, "positive" feedback loop"?  By September insolation is in rapid decline. At high latitudes the months that matter for AWP are the two months either side of the June solstice, i.e. starting now.

A BOE will certainly be a significant symbol, but the Arctic climate wreckage must surely come from longer periods of open water earlier in the year, as may be happening again this year ?

Early season ice loss is much more influential with regards to increased solar insolation.

Walrus, totally agree that the impact of solar insolation occurs in the period of 7 weeks prior and after the June solstice per the insolation graph in the above post.

[JNap]

Here is a possibly better way to view the overall declining trend of arctic ice.  It is the rolling 365 day PIOMAS volume just posted by gerontocrat on the PIOMAS thread. (Reply #3230)

This view shows a strong linear trend relationship.  And unlike the monthly September trend view where 2012 is an exceptional outlier, in this rolling year average view,  it is less so.  Also, the last few years show the trend continuing.

So although it is not intended to project the first BOE, it does support the overall continuing progression of ASI decline in the years since 2012.

2030 still seems like a good projection for the first BOE.

[Stephan]

It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The April value now includes 2020.
Volume and thickness for April 2020 lie well above the long term trend lines whereas area and extent dip slightly below it. The "BOE numbers" increased by averaged 1 year (thickness) and did not change (volume and extent) compared to April 2019.
The order (earlier → later BOE) generally is volume < thickness < area < extent.

Please note that this is not a forecast but a trend!
See attached table. stg = slope.

[Glen Koehler]

<snip>
This means SOLAR ALTITUDE just isn't high enough until the first week of June to overcome albedo.

This means we well have to see background temps warm likely another 2-4C around the ice in May and snow cover to vanish at least a week earlier than the current earliest before we see ice volume sustainably go lower than it already has.

This means a total melt out isn't likely until 2035-2040 or later

      I get the main point, even though the details within the reasoning are beyond my skill set.  And the basic point makes intuitive sense.  But I am truly asking, not arguing:
 
     Does your analysis fully account for the fact that the rules of ice melt are changing as thick MYI ice has been replaced by thinner saltier FYI, and even the FYI is getting thinner from year to year? 

     My gut (and linear regression of the Sept. volume trend, which I beat to death upthread) tells me that there is an exponential iterative process unfolding by which weaker ice begets more open water, lower albedo earlier in the season, warmer weather patterns, more storms, longer wind fetch, more ice mobility leading to export.  All of which leads to acceleration of ice loss. 

     Of course, my gut hunches aren't analysis, and are subject to overlooking major counter-arguments like the Chris Reynolds long slow decline scenario.  But I don't buy into that theory (no need to get sidetracked by why in this message).  I have a harder time discounting Notz and Stroeve 2018, who have PhDs in this stuff, swim in the data 365 days a year, and write deep articles about it that come up with the same 2035-2040 timeline as you stated or even later. 

     But I'm still wondering if the seasonal procession of solar angle (the one thing still operating normally in this topsy-turvy world) is enough to rule the system for a relatively incremental orderly dissembling of the ASI, when the stuff that the sun is shining on is changing so rapidly from year to year.  Rapid evolution in the receiving end of the solar energy <--> ice melt equation leads me to think that one or more abrupt, chaotic, or nonlinear qualitative process(es) will emerge and take over before many more years of weakening of the ice. 

      In other words, I see the "ice" hitting the fan by 2025-2030 with the next big warm anomaly and high Arctic storm activity year.  My scenario has 2035 beyond the far end of a plausible 1st BOE date, whereas the 2035-2040 estimate keeps it out of reach until at least 2035, and probably later.  I hope I'm wrong.

     Either way, at some point in the not too distant future, humanity will slap our foreheads in a collective Homer Simpson "D'oh" (as if we weren't warned and didn't see it coming).

[The Walrus]

I do not see it.  There is simply not enough incoming heat radiated into the Arctic to melt all that ice.  Since the beginning of the satellite era, June average ice extent has only decreased 14%, and shows no acceleration.  That is not an extremely large change in albedo.  I disagree with your exponential process, as those areas with open water have resulted in increased cloud cover, tempering the albedo effect.  Hence, albedo is less likely to rule the system.

https://www.nature.com/articles/s41598-019-44155-w

[Glen Koehler]

      Thanks, that's a good paper.   A lot to digest.  They focus on summer and early fall.  It seems like more open water in fall and winter would also lead to greater heat loss, thus functioning as a negative feedback.  But also that a higher cloud cover would work against that by reflecting more longwave radiation back down.  Lots of counterbalancing forces in a complex system. 

       Reminds me of my son describing the existence of "deterministically chaotic" systems today.  It seemed like a contradiction in terms to me, but as he explained it a system can be both deterministic AND chaotic, which means that it is unpredictable until you calculate each step between here and there.  Maybe the Arctic melt works like that.  We won't know until we get there!

[Hefaistos]

I do not see it. There is simply not enough incoming heat radiated into the Arctic to melt all that ice.  Since the beginning of the satellite era, June average ice extent has only decreased 14%, and shows no acceleration.  That is not an extremely large change in albedo.  I disagree with your exponential process, as those areas with open water have resulted in increased cloud cover, tempering the albedo effect.  Hence, albedo is less likely to rule the system.

https://www.nature.com/articles/s41598-019-44155-w

For a simulation of the role of solar angle, please have a look at the second simulation:

https://www.pveducation.org/pvcdrom/properties-of-sunlight/calculation-of-solar-insolation

If you have the tilt angle at 0 degrees, you emulate what's going on on the ground.
For high latitudes, above 70 degrees, only around half of incident power reaches ground (depending on latitude).
This is before any albedo effect.

"The graph shows the intensity of direct radiation in W/m² throughout the day. It is the amount of power that would be received by a tracking concentrator in the absence of cloud."

[Hefaistos]

Here's a more detailed page with some further explanations using the same simulation. I believe this has some relevance for the discussion about the actual effects reaching the ground in the Arctic.

"The Incident Power is the solar radiation perpendicular to the sun's rays and is what would be received by a module that perfectly tracks the sun. Power on Horizontal is the solar radiation striking the ground and is what would be received for a module lying flat on the ground. "

https://www.pveducation.org/pvcdrom/properties-of-sunlight/solar-radiation-on-a-tilted-surface

[The Walrus]

All of which makes the increased cloud cover over open water during the summer more relevant.

[oren]

A. Is there indeed a trend of increased cloud cover? Can this be supported by data?
B. 2016 nearly broke the 2012 area record, even with a cool and cloudy summer. So I wouldn't count on this to save the ice, even if such a trend emerges.

[Hefaistos]

A. Is there indeed a trend of increased cloud cover? Can this be supported by data?
B. 2016 nearly broke the 2012 area record, even with a cool and cloudy summer. So I wouldn't count on this to save the ice, even if such a trend emerges.

A. Not seemingly, all datasets show more or less constant levels since satellite data started in 1979

(the heading of the chart says it covers the period to 2000, but the x axis shows correctly the data until 2020)

[Phil.]

A. Is there indeed a trend of increased cloud cover? Can this be supported by data?
B. 2016 nearly broke the 2012 area record, even with a cool and cloudy summer. So I wouldn't count on this to save the ice, even if such a trend emerges.

A. Not seemingly, all datasets show more or less constant levels since satellite data started in 1979

(the heading of the chart says it covers the period to 2000, but the x axis shows correctly the data until 2020)

1979-2000 is the period that the anomaly is referenced to.

[The Walrus]

A. Is there indeed a trend of increased cloud cover? Can this be supported by data?
B. 2016 nearly broke the 2012 area record, even with a cool and cloudy summer. So I wouldn't count on this to save the ice, even if such a trend emerges.

I posted this earlier, and will re-post for your benefit:

https://www.nature.com/articles/s41598-019-44155-w

"Based on CALIPSO satellite observations of cloud properties, this study found that cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons in the past 10 years, while sea ice coverage varies significantly year-to-year."

and

"Overall, the geographic distribution of the covariance between clouds and sea ice confirms the response of clouds to the sea ice loss once again. The correlation coefficients between the sea ice anomaly and cloud anomaly are negative in most areas but positive in some areas. The region of negative correlation is more significant than the positive area. The nonuniform regional covariance reveals that the response maybe influenced by other factors such as atmospheric circulation. The significant but nonuniform response of clouds to the sea ice retreat may influence the albedo feedback."

Confirmed referring to this previous study:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009JD011773

Concerning the albedo:

"As the surface changes during the melt period from snow-covered sea ice to partially snow- melt pond-covered sea ice to totally open water, the albedo of this heterogenous surface will decrease. Because the cloud albedo lies between the albedo of snow and the albedo of dark open water, an increase in cloud cover due to loss of sea ice coverage is expected to partly compensate for the associated albedo decrease and tend to restore the TOA albedo during the sea ice melt period to the pre-melt value."

They conclude:

"Previous studies already show that a warmer Arctic is cloudier and that the corresponding cloud forcing changes from warming the surface to cooling the surface in different seasons. The interactions between the clouds and the surface are complex and play an important role in the Arctic energy balance. This study presents the local character of the damping effect by the clouds in the Arctic climate system. The albedo feedback is one of the most pronounced positive feedback in the polar regions. Clouds can damp this positive feedback: cloud formation can partly compensate for the change in albedo due to the melting of sea ice."

The referenced previous study is here:

https://science.sciencemag.org/content/299/5613/1725

[gerontocrat]

Who am I to question the scientists, but here goes anyway.

cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons

The albedo feedback is one of the most pronounced positive feedback in the polar regions. Clouds can damp this positive feedback: cloud formation can partly compensate for the change in albedo due to the melting of sea ice.

Cloud cover surely also dampens down release of heat from the ocean? Last year the Bering Sea +ve SST anomalies were, to put it mildly, stunning. The freeze was late, which must have been due to the high sea temperatures until that heat was gone, at least from the surface. In other words cloud cover perhaps prolongs the melt season and / or delays the freezing season.

Which effect is more significant, dampening melt / ocean heat uptake, or delaying ocean heat loss and the re-freeze?
_____________________________________
ps: Historical Note. It seems that mariners from a hundred years & more ago referred to the Bering Sea as "The Smoky Sea". The sea was notorious for its frequent and erratic fogs and mist.
(Fog is very low cloud ?)

[oren]

A. Is there indeed a trend of increased cloud cover? Can this be supported by data?
B. 2016 nearly broke the 2012 area record, even with a cool and cloudy summer. So I wouldn't count on this to save the ice, even if such a trend emerges.

I posted this earlier, and will re-post for your benefit:

https://www.nature.com/articles/s41598-019-44155-w

"Based on CALIPSO satellite observations of cloud properties, this study found that cloud coverage in ice-free regions in the Arctic linearly increased with the area of ice-free water during the melt seasons in the past 10 years, while sea ice coverage varies significantly year-to-year."

Thank you. I missed this the first time around.
It is interesting though how the little details in the article are not a perfect fit for the summary quoted above.
By "the last 10 years" they mean 2006-2015, although this was published in 2019.
By  "the melt season" they mean:

Anomalies (in absolute units) of cloud fraction obtained from CALIPSO observations during the summer and fall seasons (July to October) and sea ice concentration. The anomalies are calculated by subtraction of the 10-year (2006–2015) average. The cloud fraction is the average between August 1 and October 15. Sea ice concentrations are based on the average of the period from July 1 to September 15, which covers melting season.

As most insolation occurs between mid-May and end-July, their finding is not as relevant as might seem at first glance.

[The Walrus]

Just because their observation period does not match the melt season, does not make it irrelevant to the melt season.  Since the Arctic is almost completely ice covered at the start of the melt season, there is no open water to generate clouds.  The time period was chosen to maximize observational data.  Their work complemented previous work, which drew similar conclusions.

[oren]

Concerning the albedo:

"As the surface changes during the melt period from snow-covered sea ice to partially snow- melt pond-covered sea ice to totally open water, the albedo of this heterogenous surface will decrease. Because the cloud albedo lies between the albedo of snow and the albedo of dark open water, an increase in cloud cover due to loss of sea ice coverage is expected to partly compensate for the associated albedo decrease and tend to restore the TOA albedo during the sea ice melt period to the pre-melt value."

They conclude:

"Previous studies already show that a warmer Arctic is cloudier and that the corresponding cloud forcing changes from warming the surface to cooling the surface in different seasons. The interactions between the clouds and the surface are complex and play an important role in the Arctic energy balance. This study presents the local character of the damping effect by the clouds in the Arctic climate system. The albedo feedback is one of the most pronounced positive feedback in the polar regions. Clouds can damp this positive feedback: cloud formation can partly compensate for the change in albedo due to the melting of sea ice."

Far be it from me to question established science, but one must use science along with the details it includes. Let me just say I am not convinced by the bolded part. If clouds appear a month after open water, and considering that open water is a much delayed reaction to insolation, and considering the shortness of the insolation period in the Arctic, then cloud feedback is very weak compared to the albedo feedback. What they measured - clouds forming in August-mid October as a reaction to ice loss in July-mid September simply cannot support the above conclusions. Albedo improvement should have been multiplied by insolation level to achieve meaningful results regarding the strength of the effect. This is especially true since the last part of their cloud window is after the freezing season begins, which is when I would expect clouds to make a significant effect, and not a good one as they would tend to insulate the water and slow heat loss to space.

I will also add that the common wisdom on the forum seems to be that cloudiness increased since 2013, while they only covered the period up to 2015, potentially missing this supposed trend. So maybe there IS a trend of increased clouding that IS relevant to the melting season and actual albedo-insolation feedback, I am just saying this study does not prove it.

[oren]

"Overall, the geographic distribution of the covariance between clouds and sea ice confirms the response of clouds to the sea ice loss once again. The correlation coefficients between the sea ice anomaly and cloud anomaly are negative in most areas but positive in some areas. The region of negative correlation is more significant than the positive area. The nonuniform regional covariance reveals that the response maybe influenced by other factors such as atmospheric circulation. The significant but nonuniform response of clouds to the sea ice retreat may influence the albedo feedback."

Confirmed referring to this previous study:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2009JD011773

Having had a chance to take a look at this previous study, it is immediately apparent that the described cloud effect is not relevant to the melting season.

Abstract
[1] Recent declines in Arctic sea ice extent provide new opportunities to assess cloud influence on and response to seasonal sea ice loss. This study combines unique satellite observations with complementary data sets to document Arctic cloud and atmospheric structure during summer and early fall. The analysis focuses on 2006–2008, a period over which ice extent plummeted to record levels, substantial variability in atmospheric circulation patterns occurred, and spaceborne radar and lidar observations of vertical cloud structure became available. The observations show that large‐scale atmospheric circulation patterns, near‐surface static stability, and surface conditions control Arctic cloud cover during the melt season. While no summer cloud response to sea ice loss was found, low clouds did form over newly open water during early fall. This seasonal variation in the cloud response to sea ice loss can be explained by near‐surface static stability and air‐sea temperature gradients. During summer, temperature inversions and weak air‐sea temperature gradients limit atmosphere‐ocean coupling. In contrast, relatively low static stability and strong air‐sea gradients during early fall permit upward turbulent fluxes of moisture and heat and increased low cloud formation over newly open water. Because of their seasonal timing, cloud changes resulting from sea ice loss play a minor role in regulating ice‐albedo feedbacks during summer, but may contribute to a cloud‐ice feedback during early fall.

[FishOutofWater]

Melt ponds have similarities to open water so I am not surprised that a study found that there was not significant correlation of cloudiness with open water in the summer.

The scientists who have focused their careers on ice have a point. The amount of energy involved in melting multiyear sea ice and "Atlantifying" the Barents sea has been enormous. Change has taken place on a decadal basis as greenhouse gases have caused an increase in the enthalpy of the global oceans.

Note that the melting of massive amounts of Greenland's ice in 2010 and 2012 may have led to a strong cooling of the north Atlantic southeast of Greenland. This cooling may have reduced the amount of ocean heat transported into the Arctic through the Fram strait.

The slow down in sea ice extent loss since 2012 is likely related to the cooling in the far north Atlantic caused by the influx of cold fresh melt water. I don't think that changes in albedo caused by cloud cover have been beneficial to the ice because cloud cover has had the most impact in the fall when it's dark. The clouds have caused warming of the lower atmosphere in the fall and winter months - not good for ice building up in the cold months.

[binntho]

Note that the melting of massive amounts of Greenland's ice in 2010 and 2012 may have led to a strong cooling of the north Atlantic southeast of Greenland. This cooling may have reduced the amount of ocean heat transported into the Arctic through the Fram strait.

The slow down in sea ice extent loss since 2012 is likely related to the cooling in the far north Atlantic caused by the influx of cold fresh melt water.

This seems to me to be pure conjecture, and as for the "slow down", well that has been repeatedly discussed and I for one have not seen any convincing evidence of there being anything other than an ongoing linear reduction in sea ice with random annual fluctuations. Choosing the record year as the starting point of a hypothetical slow down tastes surprisingly like cherry picking.

The annual melt of the Greenland glacier goes mostly to the west, not the east, and is caught by the West Greenland current moving counter-clockwise around the Baffin Bay, to the north before heading south along the coast of Canada. Even if it is a significant amount of water that melts every year (2012 saw ice mass loss in the region of 1000 Gt), compared to the ocean currents it simply vanishes without a trace (the West Greenland at 3.8 Sverdrups moves that much water in less than 5 minutes, and the Norht Atlantic Current moves 1000 Gt every minute) and has not been shown to have any influence on the amount of heat carried by ocean currents into the Arctic (and given the amount and trajectory of the melt waters, it is difficult to see how that could happen).

So are there any scientific papers supporting the conjectured "slow down" and any cooling effect of the Greenland Ice melt on the Arctic ocean? I'd be interested to see them, I had a quick peek on Google but didn't find any.

[gerontocrat]

... as for the "slow down", well that has been repeatedly discussed and I for one have not seen any convincing evidence of there being anything other than an ongoing linear reduction in sea ice with random annual fluctuations. Choosing the record year as the starting point of a hypothetical slow down tastes surprisingly like cherry picking.

Discussed ad nauseam

[oren]

An interesting and relevant post from the melting season thread, copied here for posterity (thanks to uniquorn for the idea):

The 12z models and 00z EURO the 12z euro isn't out yet have backed off considerably with the dipole in the long range.

Instead of setting up a full or 3/4 dipole the models slide the Eurasian vortex over the pole/Atlantic side and merge it with the GIS vortex which won't budge.

This keeps the torching over the Pacific half.

It's not a good pattern by any means but it definitely is much better than the entire CAB getting the roast.

This kind of thing is what will keep 2020 from passing 2012 in the end.

We'll see

Yep, we've seen this time and again in the last 8-9 years. It's a pattern and I think part of the reason for this strong +PV tendency has been due to a marked increase in low-level baroclinicity and eddy kinetic energy as the mid-high lats warm faster in summer than the basin proper. It is providing a transient negative feedback by preferentially favoring storms over the basin during the summer months (on the cold side of the jet). This retards melt and slows down the year-to-year summer progression. Of course, eventually the warming signal will overwhelm this, but it may take another 20 years to do so (the occasional year like 2016 nonwithstanding). Eventually, increasing warming over land will cause the warm conveyor belts on these storms to start doing enough damage to offset the shielding effect and destroy ice cover anyways. We may end up seeing a fairly long period of not much change -- followed by a quick transient period to sea-ice free, followed by decoupling of the troposphere from the stratosphere in the autumn and subsequent large hits to winter ice volume recoveries. Nakamura et. al's BoE experiments suggested as such a few years back.

And I suspect 2007 and whatever future year(s) this happens will be seen as the turning points.

If you're looking for ocean-driven signals as well, simply look at the trend of shoaling along the Atlantic-inflow stream and heat content storage coming from the Chukchi. They're pointing to the 2040s as well. Incidentally, this is around the same time aragonite undersaturation in the Arctic begins to show up, too (aragonite undersaturation starts in the 2030s around Antarctica). Full-on ecosystem disruption seems pretty ripe around that time.

[Stephan]

It is time for the monthly update of my extrapolation when the extent [Ausdehnung], volume [Volumen], thickness [Dicke] and area [Fläche] will reach zero. The extrapolation occured linearly and by a logarithmic function; the latter one almost constantly resulting in earlier times (valid for volume and thickness, not for extent and area in the winter months). The May value now includes 2020.
Volume and thickness for May 2020 lie well above the long term trend lines, extent is at the trend line whereas area dips below it. The "BOE numbers" increased by averaged 3 years (thickness) and 2 years (volume) and decreased by 4 years (extent) compared to May 2019.
The order (earlier → later BOE) generally is volume < thickness < area < extent.

Please note that this is not a forecast but a trend!
See attached table. stg = slope.

[JNap]

The period between 2028 – 2032 still seems to me to be the most likely timeframe for the first BOE event based on the linear regression of the data.

I would love to get perspectives regarding the MOST IMPORTANT FACTORS that will drive the sea ice decline to less than 1,000,000 Km2.  From my understanding of the ASIF posts over the years, the following seem the top driving factors – and some FEEDBACK LOOPS among them – toward an Ice-Free Arctic.

1)   “Mechanical:”  That is, the flow of ice out of the CAB, primarily through the Fram Strait.  This factor would seem to generally become more prominent going forward given earlier breakup of the ice back and detachment of fast ice allowing the freer flow of ice for a longer period.    Thus, less overall ice remaining in the CAB that needs to thermally melt.

2)  “Bottom Melt:”  The impact of Atlantification, and to a lesser extent Pacification,  are slowly and steadily are warming up the arctic ocean and increasing bottom melt.   

3)   Albedo / Surface Melt:   The increasing ice melt is a positive feedback loop that enable the sun to further warn the arctic sea.  The degree of melt ponds and melting momentum that Neven cited in 2012 is an example.  But is seems with the breakup / fracturing of the ice since 2012, there doesn’t seem to be the same ability to have the degree of melt ponds as occurred in 2012.  Instead, it seems that there are now more Polynyas which warms the ocean around the edges of an icepack vs. a ponding situation where it would warm directly on the icepack.   (I look at Tealight’s AWP graphs as an indicator of greater potential and try to learn from it.)

4)   Weather: Specifically, looking the following aspects.   
(i) A major or consistent dipole that focuses winds that drive the ice out the CAB and into the Atlantic.   
(ii) GAC or similarly strong storms that breaks up the ice mechanically and also churn up the ocean water layers and bring the heat content from the mid-depths up to the surface that drives bottom melt.
(iii)  Higher pressure, thus sunnier weather to drive the radiative melting and increase the heat content of the ocean.
(iv) Air temperature / WAA.  Given the relatively low heat content of air vs. water or ice, this one seems to somewhat less impactful overall than the three above weather factors.

Would love to hear others’ thoughts.

[The Walrus]

JNap,
You have listed mostly positive feedback loops, but no negative ones.  These would include more open water leads to more heat loss in the fall and winter, and evaporation leading to enhanced cloudiness, blocking incoming radiation during the summer.  Based on the linear regression, I do not see anything corresponding to your early dates.

[oren]

I think the main factors are declining winter volume (not listed but affected by Atlantification and Pacification and open water and heat content in September), Mechanical as listed, Albedo/Surface Melt as Listed, plus warming continents (part of Weather).

[JNap]

JNap,
Based on the linear regression, I do not see anything corresponding to your early dates.

Walrus,
As an example, here is a linear trend chart from Wipneus for Sea Ice Volume.   Per others on the thread, it seems that ~800 km³ is the threshold for a BOE. Per the chart this would occur in 2029. 


Another example chart example from Wipneus, this one a Gompertz curve, also indicates a 2029 date for sea ice volume dropping below 800 km³

I do agree that there are possible negative feedback looks such as deeper snow cover given more open water.   But (and I am happy to be wrong and learn more) it seems that the increased cloud cover occurs in the Fall and thus may not be a negative feedback.   Instead, that Fall could cover would serve more as insulation and retain the top later of ocean heat longer in the Fall / Winter.    (There was very discussion, ~with the past week, of this on another thread...maybe the 2020 melt season thread?) 

[Tom_Mazanec]

That is for a BOE being a normal event. Given unusual conditions the first one can be earlier in the decade.

[JNap]

Tom,
Totally agree.  In 2010, 2011, and 2012, the volume dropped significantly below the trend line given an alignment of the weather conditions, (e.g. GAC).   I was simply trying to use the data to estimate of the first BOE year given the trends.

[Phoenix]

The period between 2028 – 2032 still seems to me to be the most likely timeframe for the first BOE event based on the linear regression of the data.

Would love to hear others’ thoughts.

IMO, there is lots of evidence to suggest that this is not a continuing linear process.

From 1979-2011, sea ice volume declined from 17k to 4.5k km3 at a pretty steady clip. We are poised to end 2020 at a level similar to the 2011 level. 4k km3 average decline per decade for 3 decades and then a decade with no net decline doesn't seem very linear does it?

From 2002-2012, there were something like 7 new low minimum volume records. Since then, none.

The Central Arctic Basin holds most of the ice at the minimum now and presents different melting obstacles than the ice that was conguered in earlier decades. It's entirely possible that it will take much longer to melt out than another decade. The key will be the distribution of weather events.

I agree with Oren that declining winter volume (the signature impact of AGW is seen most heavily in winter) will be a primary factor in moving in the direction of a BOE. All of the other factors which cause ice to be lost are accentuated when there is less ice to begin the melting season with. This year was the beneficiary of a relatively strong freezing season which is helping to offset a strong melting season.

The AGW induced lengthening of the melt season as evidenced by the mid-May melting of this spring is also a bad omen for the ice.

So much depends upon the whims of the weather and the uncertainty of how humans are going to react. There are geo-engineering possibilities which may change the trajectory. 

[The Walrus]

JNap, the threshold is generally accepted as 1 million square km.  The two-dimensional decline more closely resembles a linear decline, and would not occur in the next two decades.  Three-dimensional decline is much less linear, as Phoenix stated.

[JNap]

I agree that the Central CAB and CAA and N. Greenland coasts where the remaining ices resides will likely have a different melting dynamic than the other central seas and peripheral sea have experienced for the past 4 decades.   

But I also don't want to take anomaly / outlier years such as 2012 and then proceed to the overall conclusion that the marco trend is no longer (mostly) valid.   IMHO, it reminds me too much of happen with global temps with the super el nino year in 1998.  It took several years before that outlier year was exceed.  But the marco AGW trend continued along a similar path. 

What is do see occurring as mechanism that could drive the melt of the remaining CAB is a stronger, positive feedback loop of increasing AWP.  Earlier melts of Central seas such as the Siberian side this year, expose the ocean to more and more of the peak solar insolation period from mid-May to early Aug. 

Below is a crude attempt to illustrate.   
The first chart is many years of the amount of sea ice melt in the Laptev sea with 2020 (thus far) in red. 

The second chart is the amount of solar insolation by latitude, with 90 degress in orange.

The last chart is an overlay of the two.   This is where it gets interesting for me.   The combination of earlier melts to expose open ocean to peak solar insolation changes the amount of energy that can enter into the system.   This is where I fully agree with your point about the impact of weather.   If there are a lot of clouds for long periods during this albedo potential window, then only a small impact.  However, if the weather happens to have a period of higher amount of sun during this window, then the albedo potential will be realized.

From what I have read from Wipneas (and again, happy to be further educated), each day in higher solar insolation period will melt approximately 5 - 6cm of ice.  So if we have one week of earlier melt AND have a strong, sunny period, then 30 - 40cm of extra ice melt could occur.   

Only a few of these periods would have to align in a given year to materially impact the ice.  The long term trend for earlier melts would provide the increasing odds for such as situation.  The it would be up the variances in the weather to align a series or two of High pressure, sunny weather to make it occur.

[KiwiGriff]

These would include more open water leads to more heat loss in the fall and winter,

Not all of that heat is radiated to space.
Some of it goes on to be accumulated in the surrounding land masses.
This tells us some of the energy is retained within the earth system and is available to come back and reduce the sea ice at a later date.
As we can clearly see in the unprecedented warmth  in Siberia this year and the long term trend in arctic temperatures.

Volume is more important than extent .
 How much ice is remaining to melt? not how spread out the remaining  ice is.

[binntho]

As for the mechanical effects, the more open water there is for longer, the bigger will the effect of waves be on the remaining ice. And it is well established that waves can cause severe damage deep into the ice pack.

The current state in the Arctic is that at most some 50% of the Arctic ocean itself is free of ice, for a very short time (this is a rough estimate based on some 10 m km2 in the Arctic in total, i'll see if I have time to look at the actual numbers later today).

As we get closer to the 1m km2 BOE definition, the Arctic gets closer to 90% open water - and there will be significant open water for longer periods.

Wave action is a very strong negative feedbac, it is not a significant factor at the moment, but will increase in importance and become a very strong effect as we get closer to BOE. And I'd guess that it would accelerate the trend downwards significantly once it kicks in.

[Tom_Mazanec]

And 1 million square kilometers is not when we start having problems. Hurricane Sandy hints that the 2012 level may be that threshold.

[The Walrus]

Volume is more important than extent .
 How much ice is remaining to melt? not how spread out the remaining  ice is.

I would not be too sure about that.  If you read the recent posts, most effects are based on open water, which is a measure of extent (or area).  The albedo effect, energy loss, wave action, etc. 

[Tom_Mazanec]

Volume is probably better for estimating when the ice will disappear. Are or extant is probably better for estimating when the shrinkage will cause trouble.

[The Walrus]

Volume is probably better for estimating when the ice will disappear. Are or extant is probably better for estimating when the shrinkage will cause trouble.

Possibly.  However, volume will always decrease faster than area or extent (unless thickness is increasing), such that trying to use linear interpolation for both leads to errors.  Volume will naturally taper off as it approaches zero, such that both area and volume (and thickness) reach zero simultaneously.  Hence, a Gompertz (or other second order) curve would more aptly represent the trend in Arctic sea ice.  Others have mentioned that the inclusion of the peripheral seas distorts the trend, and a plot of just the CAA and CAB would be better at estimated a true BOE.

[oren]

Volume will naturally taper off as it approaches zero, such that both area and volume (and thickness) reach zero simultaneously.

Why would volume naturally taper off as it approaches zero? Just to give area a respite?
It is the opposite. At a certain volume threshold the Arctic becomes practically ice-free. Once the typical thickness of CAB ice is melted during a melting season, area will crash, while some volume may be retained in very thick ice floes (pressure ridges and very old MYI).
As the freezing season becomes shorter and less powerful, and the melting season longer and more powerful, not forgetting the contribution of increased mobility and export, this inflection point is not too far off, probably a decade into the future.

[P-maker]

Tom and Walrus,

It's mighty fine that the two of you try to get a pseudo discussion going, and Oren chipping in with minor details from obscure Arctic coastal stations.

Please relax and let the melting proceed as projected.

I were even considering opening a new thread under the title: "The Final Round".

It should delve into the details about how the final free-floating floe in the Arctic Ocean will demise.

Is there a thread already, or is it premature?

[The Walrus]

Volume will naturally taper off as it approaches zero, such that both area and volume (and thickness) reach zero simultaneously.

Why would volume naturally taper off as it approaches zero? Just to give area a respite?
It is the opposite. At a certain volume threshold the Arctic becomes practically ice-free. Once the typical thickness of CAB ice is melted during a melting season, area will crash, while some volume may be retained in very thick ice floes (pressure ridges and very old MYI).
As the freezing season becomes shorter and less powerful, and the melting season longer and more powerful, not forgetting the contribution of increased mobility and export, this inflection point is not too far off, probably a decade into the future.

That will likely happen as we approach zero, and the last vestiges of ice disappear.  Prior to that, volume losses will decrease as the surface area exposed to the elements decreases.  As less surface is exposed, less volume can melt.  Hence, as area continues to decrease, volumetric losses will slow.  Arctic melting is basically two-dimensional, from above and below.  Very little contribution occurs via side melting.

[oren]

So a small patch of ice in the middle of the ocean will melt at the same rate as when the whole ocean is filled up?
I should think higher air temperatures can easily attack the ice in such a case, while OTOH when it is surrounded by other ice it is much more protected. Besides, any movement of the lone patch of ice to a nearby open water region will result in its quick demise. Waves are also an important factor. Thus Arctic melting is not two-dimensional at all, and a lot depends on what goes on in adjacent regions of the Arctic ocean.

[The Walrus]

So a small patch of ice in the middle of the ocean will melt at the same rate as when the whole ocean is filled up?

Absolutely not!  That small patch has more surface area exposed to melting action than a similar patch surrounded by ice.  However, a large patch of 5 million sq. km has more surface area exposed than a large patch of 4 million sq. km.  I believe that you are overestimated the contribution by wave action at current.  This will come into play to a much greater extent when sea ice declines further and becomes more dispersed.

[gerontocrat]

Volume will naturally taper off as it approaches zero, such that both area and volume (and thickness) reach zero simultaneously.

Why would volume naturally taper off as it approaches zero? Just to give area a respite?
It is the opposite. At a certain volume threshold the Arctic becomes practically ice-free. Once the typical thickness of CAB ice is melted during a melting season, area will crash, while some volume may be retained in very thick ice floes (pressure ridges and very old MYI).
As the freezing season becomes shorter and less powerful, and the melting season longer and more powerful, not forgetting the contribution of increased mobility and export, this inflection point is not too far off, probably a decade into the future.

That will likely happen as we approach zero, and the last vestiges of ice disappear.  Prior to that, volume losses will decrease as the surface area exposed to the elements decreases.  As less surface is exposed, less volume can melt.  Hence, as area continues to decrease, volumetric losses will slow.  Arctic melting is basically two-dimensional, from above and below.  Very little contribution occurs via side melting.

When you smash ice to bits and shake it around melt will happen far faster than a sheet of ice.
Hence the cocktail shaker.

My guess is the conventional wisdom of the two-dimensional model only really applies when the ice is pretty much a continuous sheet, not so much when it is a broken up load of rubble at the mercy of wind and currents.

I am reminded of PolaStern's search last October for a halfway respectable flow with decent structural integrity, and how the Mosaic project was plagued by continuous leads, pressure ridges and general instability of the ice all through the winter.