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Messages - DavidR

Pages: [1] 2 3 ... 15
1
Arctic sea ice / Re: The 2019 melting season
« on: September 19, 2019, 11:06:45 PM »
If you look at the daily data rather than Chartic, which is a running average, you'll see that 2019 is below both 2007 and 2016 minima.

Not according to my spreadsheet, which has 4.08 million km² for 2016 versus 4.1 this year.

A "statistical tie" I suppose, but am I in possession of some stale data?

I  had the same figure but  I  think NSIDC has updated the figures since then.  It certainly  not in  the current data. According to the current data the five day average (4.1532) is just slightly lower than 2007 (4.1544) and 2016 (4.1654).  Statistically  identical.

2
Arctic sea ice / Re: The 2019 melting season
« on: September 18, 2019, 11:28:30 PM »
Sorry, about 4th lowest?  I keep forgetting about 2007.
NSIDC
Yes. It seems wrong that NSIDC keeps 2019 above 2007. It doesn't match with what we see on ADS NIPR (JAXA), even that we know that NSIDC has less accuracy on their measurement.

If you look at the daily data rather than Chartic, which is a running average, you'll see that 2019 is below both 2007 and 2016 minima.
The NSIDC 5 day average is still 16K above the 2007 minimum and 6K above the 2016 minimum. It will take a day or two around 4.1M km^2 to drop 2019 below the other two years but  I expect that to happen based on the picture from worldview.

3
Unless something extraordinary happens it looks like more than 50% of the voters got this poll right. This applies even if extent drops another 250K.

4
Antarctica / Re: SH Polar Vortex
« on: September 09, 2019, 04:47:22 AM »
There is now a Sudden Stratospheric Warming event in place over the Antarctic. Judging by the effects these have in the northern hemisphere we will be seeing effects on the polar vortex and decreased ice extent over the coming months. These SSW's are very rare in the southern hemisphere but we are likely to be seeing more and more of them.

Here's a layman's explanation with a focus on the effect on Australia.
https://theconversation.com/the-air-above-antarctica-is-suddenly-getting-warmer-heres-what-it-means-for-australia-123080

The following comment is particularly relevant for the Antarctic "We also expect an enhanced decline in Antarctic sea ice between October and January, particularly in the eastern Ross Sea and western Amundsen Sea, as more warm water moves towards the poles due to the weaker westerly winds."

5
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: September 05, 2019, 03:01:34 PM »

Using only mark one eyeball I would bet a curve would be a much better fit than a straight line to either data set. 
Acceleration not a steady decline.
Someone from ASIF did ask tamino to look into this on his  blog post before last .
Warming also shows acceleration.

Acceleration Huh?
We have just been discussing

https://tamino.wordpress.com/2016/07/17/arctic-heat/

Acceleration and more recently deceleration appears to have been shown to be statistically significant.
We have to  remember that any graph is a two dimensional representation of a multi-dimensional issue. Any trend line or formula is a further reduction.  The change analysis is interesting but without identifying  a causal relationship is not telling us much.  The years 2005-2007were remarkably  warm in  the Arctic but  since then similar temperatures are not 'remarkable'.

There is a good reason why climate specialists look at  30 years of data, and anything  less than that  is just  noise. Fun to  discuss but  just  noise.   

6
Arctic sea ice / Re: The 2019 melting season
« on: September 03, 2019, 11:53:31 AM »
The NOAA-ESRL temperatures for August are out and show just  how warm the Arctic was over summer.
https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
The first  number is the ranking and the number in brackets the variation from the record. This shows air temperatures at  record levels in August and over summer (Jun-Aug). SST were near record in the same period.  Globally 2019 is running second or 3rd warmest. This does nothing to  explain the flatlining of extent  loss but  suggests that the melt  could continue over the next few weeks.

                         August        Summer         YTD
Air 80N+           1 (+0.134)   1 (+0.482)     6 (-1.619)
SST 80N+         2 (-0.027)    1 (+0.007)     11 (-2.114)

Air 67N+           1 (+0.630)   1 (+0.229)    2 (-0.795)
SST 67N+         3 (-0.056)    1 (+0.277)    3 (-0.918)

Air Global          2 (-0.039)    2 (-0.032)     2 (-0.164)
SST Global        4 (-0.153)    2 (-0.113)     3 (-0.174)

7
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: August 30, 2019, 12:58:03 AM »
PIOMAS volume provides monthly data, soon... DMI does have a daily tracker. I searched the forum for any comments on its validity and didn't see anything concerning, feel free to correct me.

http://ocean.dmi.dk/arctic/icethickness/images/FullSize_CICE_combine_thick_SM_EN_20190828.png

I am waiting for this, will help tell us how much of the stall is due to dispersion vs a real stall in melting.
Biases in PIOMAS are discussed here:
http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/validation/

PIOMAS won't help a lot at this stage because it overstates the volume of thin ice. With more thin ice widely distributed the PIOMAS volume estimate may hold up despite a reality of less ice. The last few days appear to have spread the ice and lowered the concentration which will lead to an increase in the error in the PIOMAS estimate.

As the attached graph shows the over estimate of volume, on ice below 1m thick according to  submarine measurements, could be double what the submarines are seeing.

8
Arctic sea ice / Re: The 2019 melting season
« on: August 11, 2019, 02:48:17 PM »
NSIDC for the 10 th puts sea ice extent at 5.093 M km^2 a drop of 166K km^2. 

Lowest on record!!!  2012 was lowest for just 2 days!.

2012 has lost its big chance to pull away and now its going to be a nail biting ride to the finish.

9
Arctic sea ice / Re: Slater's thread
« on: August 06, 2019, 06:03:32 AM »
No, you cannot make "true claims about the future". There is no such thing. You can predict what you think will happen and then you can be proven right or wrong.

Erm, what? How is "the pencil will fall when i tip it over" not a "true claim about the future"?
Because I might grab it before it falls, or some other unlikely event may occur. The claim is highly likely by not certain!

10
3.75 - 4.25. It's been a long hot three months above 80N,  significantly warmer than 2012 and 2016.  I expect this to play out with a long melt and a late minimum keeping the September average below 2007.

11
I'm sticking with 3.25-3.75. We will be closer to the record than to the current second place holder. The temperatures above 80N+ have been significantly warmer than 2012 and 2019 for the past three months. I am expecting a late minimum because of it with plenty of melt potential in September.

12
Arctic sea ice / Re: The 2019 melting season
« on: August 04, 2019, 01:01:55 AM »
Something of a milestone in the high Arctic last month according to ESRL-NOAA.
https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries.pl?ntype=1&var=SST&level=2000&lat1=90&lat2=80&lon1=0&lon2=360&iseas=0&mon1=0&mon2=0&iarea=1&typeout=1&Submit=Create+Timeseries

For only the fourth time ever the average SST in the area 80N+ was above 0degC.

Air temperatures in the same area were a record high nearly 0.5 degrees above the previous record.

https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl

13
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 30, 2019, 05:18:34 AM »
Attached is a graph showing cumulative losses from August 1st to the minimum.

Despite starting with a lower extent each decade, the area lost is increasing each decade. 
    ....

This is quite significant. For volume, anomaly charts suggest the trend leans opposite. (I haven't scrutinized the data, which appear highly variable by year.) If so, the combination implies a shrinking but resistant end-of-season blob over time.
I think latitude counts for a lot as the pack has shrunk.  It is also pulled North which means that the angle of incidence changes more rapidly and dramatically during the melt.  In short, while peak insulation is high, the timeframe is short, and what can practically be captured is less.

Lower latitude ice has longer timeframes to capture heat, and that capture over time will be more consistent.

At high latitude my hunch is increases in loss will be driven more by net increases in system heat over time, primarily imported from elsewhere.
Some time ago there was a post  suggesting a mathematical formula relating area loss and volume loss.  These must reach zero at approximately the same time so linear trends are unhelpful. According to the formula the last few million Km^2 of extent disappeared very quickly  as the volume declined.

We may have seen the start of this process in 2012 and we may see the process come into effect again this year.  Global Oceans, including the Arctic, have been warming up over the past seven years. It seems probable that there is a lot more heat in the Arctic than 7 years ago, so a much  less extreme weather event will be required to drive area and extent down to 2012 levels.   2019 is far enough ahead of 2012 at the moment that even the GAC may not significantly seperate them by Aug 10th.  (Another century drop on JAXA today putting 2019 further ahead of 2012 with 2012 losing less than 50K a day for the next  4 days)

14
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 29, 2019, 09:35:55 AM »
Attached is a graph showing cumulative losses from August 1st to the minimum.

Despite starting with a lower extent each decade, the area lost is increasing each decade.  2012 shows up as a real outlier with the difference between 2nd placed 2016 (2.30M) and 2012 (2.90M) almost  matching the difference between 2016  and the 1980's average (1.58 M).

Note that  2008 lost 2.46M so 2016 is actually third, but I'd left  the noughties out  of the graph.

15
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 29, 2019, 06:04:38 AM »
[ADS NIPR VISHOP (JAXA)] Arctic Sea Ice Extent.

July 28th, 2019:
     6,190,083 km2, an almost century drop of -98,213 km2.
     2019 is the lowest on record.
     (2012 highlighted).
As can be seen from the graph, over the next  5 days 2012 had a relatively slow decline, about 150K below average. It  would not be surprising to see 2019 around 300K below 2012 by Aug 2nd when the GAC started to have an effect. The GAC period involved a loss of around 1 M Km^2 in 7 days.  I suspect 2019 can lose 700K in the same period to keep it in touch with 2012.

16
Arctic sea ice / Re: FireStorm in Siberia
« on: July 25, 2019, 03:14:02 PM »
The low was already predicted three days ago by ECMWF, see chart, weak low south of Kara. No way they predicted the fires, even I doubt they take into account all the physics needed to predict a fire-caused cyclone.
This is smoke caught by a normal atmospheric low. A lot of smoke yes, but it is not causing the low.
The fire and the cyclone were there at  least the day before that prediction so it's hard to say which  impacted which. The centre of the wind system has now moved much closer to the Arctic ocean and any  day now it should start  pushing  a lot of smoke over the Arctic. The system keeps on growing in diameter. Almost  big enough to  cover the Arctic Ocean now. The Arctic ocean with  a smoky blanket and a cyclonic wind pattern in early August is a scary thought.  If it gets there I  would be revising my minimum predictions down by about 500K km^2.

17
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 24, 2019, 08:05:47 AM »
Jaxa is up now and the figures for the last  three days are below.
6860793
6745450
6665411

Jaxa needs a 30K rise tomorrow to lose first place despite a 228K drop by 2012 tomorrow.  2011 and 2012 slow down a bit after tomorrow.

Jaxa needs a 78K drop per day to stay ahead until the end of the month.  Average decline over this period is 85K per day.

18
Arctic sea ice / Re: FireStorm in Siberia
« on: July 23, 2019, 11:08:01 PM »
We are seeing this quite regularly now across Siberia and Canada.

Here's another large one from three years ago

https://worldview.earthdata.nasa.gov/?p=arctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Graticule,Coastlines&t=2016-07-23-T00%3A00%3A00Z&z=3&v=-1431632.3581548978,-2481565.9215648486,6219686.631759871,6176537.860140877&r=124.774

And Canada August 2018

https://worldview.earthdata.nasa.gov/?p=arctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Graticule,Coastlines&t=2018-08-15-T00%3A00%3A00Z&z=3&v=-4848140.54029414,-4367989.641814728,-1849437.3807216217,-42882.6898112871&r=-72.8907
These are large smoke plumes l, but have not formed into the cyclonic wind pattern typical of a firestorm. The cyclonic pattern concentrates the heat and intensity of the fires. The cyclonic pattern has increased to almost 2000 km across, which in Australia, which is prone to large fires, would be equivalent to covering South Australia, NSW, Victoria and Tasmania. In the US it would be nearly a third of the country.

19
Arctic sea ice / Re: FireStorm in Siberia
« on: July 23, 2019, 04:31:55 AM »
If that  cloud was in Europe it  would cover the west coast of Norway to well east of Moscow and the North of Sweden to Warsaw.  That is a massive area.

20
Arctic sea ice / Re: The 2019 melting season
« on: July 23, 2019, 03:57:26 AM »

Slater's 50 Day Lead projects 2019 to be the new low by a good margin. Interesting how quickly things can change.

No it doesn't
In detail,  to be informative, rather than just contradictory, it is currently predicting 3.95 M km^2.

http://cires1.colorado.edu/~aslater/SEAICE/this_year_map.png

This would place 2019 second. However even Slater must treat August values probabalisticly and extreme results always have a low probability even this close to the end of the season.   

21
Arctic sea ice / FireStorm in Siberia
« on: July 22, 2019, 03:40:14 PM »

This may amount to nothing but there is quite a large cyclone being fueled by fires in Siberia at the moment. On my estimate its about 1000 kms across and drawing in a lot of heat and smoke from the surrounding areas. Rather like those pictures of what happens when you light  too many  candles on a birthday cake.

https://en.wikipedia.org/wiki/Firestorm

If it happened to drift north over the Arctic Ocean I  can't see it being anything but destructive either this year or, by dumping a great deal of soot, in later years.   

https://worldview.earthdata.nasa.gov/?p=arctic&l=MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Graticule,Coastlines&t=2019-07-22-T00%3A00%3A00Z&z=3&v=540709.4034312759,1297218.1613725103,4472869.403431276,3173186.1613725103

22
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 11, 2019, 05:08:11 AM »
According to my spreadsheet, that's the third highest daily drop for July in the 2005-2019 period. 2012 and 2018 had a double century break, both on 24 July.

I do wonder when it starts to level off...
There were however two larger breaks in August  and one in June.

2008-08-06  -183782

2012-08-08 -183330

There are few century  breaks after 8 August.


23
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 10, 2019, 02:14:53 PM »
Would sunlight reflecting off a solid ice pack warm the air more than sunlight being absorbed by the open water between fractured floes?
No. The surface absorbs the majority of sunlight that the Earth absorbs. Air absorbs little sunlight. Any condition where the air above is warmer than the surface mean warmer air has been imported from elsewhere. Why do you ask?
With very  high albedo. corresponding  to fairly solid pack, 90% of the solar radiation is reflected giving it the opportunity to warm the air a second time. With a fragmented pack, as we see now, less radiation is reflected so  the warming of the atmosphere is muted. As a consequence air temperatures with a solid pack may be warmer than with a fragmented pack.
This could explain why summers back in the 40's and 50s were seen as nearly as warm as now in the NOAA-ESRL record.

24
Arctic sea ice / Re: The 2019 melting season
« on: July 10, 2019, 01:54:09 PM »
Another massive drop in NSIDC (247K) and Jaxa  (181) extents today.  Extent is lowest by a big margin.  As Neven said, quoting  Celine Dijon, " Baby, this is serious!"

25
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: July 10, 2019, 05:54:49 AM »
… DMI shows it right on the line.  Still just a hair above most years it seems.

Note the 'average' line is for 1958-2002 when the Arctic was a different beast.  (Don't ask me how it was 'warmer' then.)  Looking through the archive, you'll see recent years have an occasional bump above the above-0ºC green line segment, but averaging between the zero and the green line.  For 2019's trace to be right on the green line is actually rather spectacular!

[...]

That's something I've wondered previously, as well. Why would the North Pole and nearby have been slightly warmer  in those earlier years, when the ice was thicker?

[...]

As I say, that's just speculation. It could well be another reason. Does anyone know?
IIRC, (no source handy right now unfortunately), because first-year ice is saltier than multi-year ice, it has a lower melting point and so it will begin absorbing heat for melt at a lower temperature than multi-year ice.
Would sunlight reflecting off a solid ice pack warm the air more than sunlight being absorbed by the open water between fractured floes?

26
sometimes i ask myself what is the purpose of a poll that can be changed, i mean to change the slot each time something happens makes it quite easy to get near the truth.

sometimes i miss a point, hence don't hesitate to enlighten me (nicely LOL)
The point is to allow people to vote early but adapt to the same data that  later voters can see.  Otherwise there would be an advantage to voting late, but this would lead to  some people missing out on the vote entirely.  Would our votes have changed if there had been a sudden spate of ice retention weather leading to  low melt  in early July rather than what  we have seen. Its the vote at the closing  date that is fixed.
Also allows people to  make a mistake and fix it. ;D

27
I've moved down to 3.25 - 3.75. I expect  the minimum to be closer to a record than second place.  A double century break on NSIDC today,  suggests that high melting rates are entrenched for now. And I  am reminded that 2016 plummeted late, after high June and July  temperatures across the Arctic. 2019 has been generally warmer than both 2012 and 2016 through May and June, and is also running hot in July.

28
Moved down to  3.75 to 4.25.  It looks like a result below 2007 is now most likely with 80N+ temperatures still well above anything in the past 10 years.  If 2019 keeps pace with  2011-2013 over the next 4 days,  I will go  lower.

29
3.5 - 4.0. To  emphasize the probability that we will be below 2016, particularly because temperatures in May and June were generally higher than 2016 in both the Arctic and the high Arctic according to NOAA - ESRL.  Catching 2012 requires unusual weather in August  and September that  is possible but not probable.

https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl

30
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: June 19, 2019, 01:49:19 AM »
I think we all see the same thing here: The loss flatlines and even seems to drop. Which may very well be indicative of a real state change and not a statistical fluke. I think it may very well be the former, but the datapoints are too few to statistically validate any change in trends.

I think the  loss flatlines (in the case of the Arctic) because total winter extent vs loss is reaching a hard limit - zero - as to how much ice is left over at the end of the melting season.

We have seen a decline in melt season total loss of extent and volume, but that remaining volume is (1) harder to reach and increasingly (2) isn't replaced during the refreeze.

The sun reaches the 80N at the same time, and has the same effect, but there is less ice at lower latitudes.

My instinct now is to watch the winter numbers more closely than summer's, as that's were I think the real harbingers to our first BoE will show up.
Its worth reminding ourselves that "from the comparison with in situ observations  it appears that PIOMAS tends to overestimate thin ice and underestimates thick ice.  As the ice thins such systematic errors can affect the overall trend."

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/validation/

This suggests that  the apparent flattening of the trend over recent years may be an illusion that is created by the model biases.

31
Arctic sea ice / Re: Global sea ice area and extent data
« on: June 07, 2019, 04:44:19 PM »
Thanks to all for comments.

You seem to agree that on the stats regularly published on this site showing the decadal day to day changes, the figure is around 3% over 30 years from the satellite data.

But 7% or so when comparing maxima & minima.

Leaving aside all the snide comments, & responses to unasked questions- such as why the arctic decreases are quite large whereas the antarctic increases ( decadally) are also quite large - this still seems a small ( ish ) figure, without context of previous comparable measurements.

The comments that the picture has changed in the last 4 years seem remarkably silly. 4 years is no basis to measure such things. 30 years hardly seems very long..when there is no proper answer to the question.

Is a 3 or 7% variation unusual comparing several 30 year periods?

It also must seem suspicious that whenever a stat goes in the direction of a hypothesis ( the arctic ) the trend is real. But when it doesn't ( the antarctic ) special factors must be at play.
Roger you seem to want a simple answer to a complex question. We don’t know for certain that this decline is unusual however we do know that their is no evidence suggesting it is not unusual. We do know that global warming is a fact not an hypothesis, and that decline in sea ice is a likely consequence of AGW. But the decline in the sea ice does not prove that AGW is occurring and it is not an objective of this forum to prove anything about AGW. We want to know what is happening with the ice and identify short term and long term causes. What are you trying to observe? Or are you just trying to waste our time by refusing to consider the answers you are given?  A reasonable person seeing the changes in the sea ice would sky “why is it so”, and when given reasonable answers would accept them or dispute them with evidence. You don’t seem to have any evidence to refute the responses you are given.

32
Arctic sea ice / Re: Global sea ice area and extent data
« on: June 06, 2019, 04:06:54 AM »
The latest post showed:
1980's 24,033,325
2010's 23,331...

3%.

Of course this varies from day to day. Other stats show 2-3% decline.

My question simply follows the stats released on this forum.
Roger, When we look at  the trend we generally consider the decline in the maxima and minima for the year rather than day to day values. As you can see in the table below based on these figures the decline in Global Maxima and Minima are both 7%.  However you can also see that the Arctic decline is much  greater than this at 41% for the minima and the Antarctic trend is actually an increase.

What  a reasonable person who knew nothing about AGW would say to this is "Why is it so?". 

The answer for the NH is seems obvious once you check the temperature records and discover that  both the Arctic and the Globe are warming rapidly. Obviously the more heat the less ice.

However in the Antarctic the picture is quite different Although the trend in temperatures is up there was a period from 1988 to about 2010 where the trend was flat or even in decline. A reasonable person will then ask why does this contradict expectations. As our temperature measures are consistently measured it is unlikely inaccurate measures are the reason. 

The two explanations I have heard are that:
a. ice melt water off the land is decreasing the salinity  of the water causing more freezing because fresh water freezes at a higher temperature than salt water.
b. the ozone hole that  was created in the 20Cent has changed the wind patterns so that stronger winds are blowing the ice further of the coast causing a greater extent.
Both these explanations are supported by relevant measurements.  But they may not be the complete answer. 

What we have seen since the 2015/6 El Nino is that Antarctic extent has dropped to extremely low levels, where only one day since Sept 9th 2016 has been ranked at 11 or above in the 31 year record. Prior to 2017 every year had at least 25 days ranked 20 or above.  So we appear to  be seeing a significant change.

PS. While you might not like being called a denier suggesting the Global warming is anything but a well documented fact is a clear sign of denial or ignorance. You can check out the temperature record here: http://www.woodfortrees.org/plot/ if you  actually are unaware of global temperature trends but don't try and dispute them here as Neven sensibly doesn't allow the forum to be corrupted by people arguing nonsense.

33
3.75 to 4.25 (moved up one because this is the average)   Ice coverage looks a lot  like 2012 and 2016. Temperatures in the Arctic have been very  hot  over the past  two months. 

According to ESRL Air temps above 67N and 80N were hottest  on record for the last month and sea temps above 67N were also hottest on record.
https://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl

This suggests a lot of inbuilt  melting  as that heat attacks the ice.

34
The distribution of ice at this stage looks much more like 2012 and 2016 than any of the other years this decade so I predict a low outcome 3.5 - 4.0.

35
Arctic sea ice / Re: The 2019 melting season
« on: April 25, 2019, 02:21:24 AM »
Slightly off topic but yet another sign of arctic warming - the break up of ice on the Yukon yesterday was the second earliest ever recorded and only 8 hours behind  the earliest breakup on the same date in 2016
Technically this was indeed the second earliest break up, but while the indicator ( a post is placed out on the river ice connected to a clock, when the ice moves, the post pulls a pin from the clock, which stops and records the official time of break up) showed break up, in actual fact almost all the ice is still intact. Photos of the river condition are regularly posted on the site yukonriverbreakup.com. This morning's pic shows the open water at the top left, where the "tripod" was. We should have another pic in an hour or so!
Of course April 23rd this year was the 113th day of the year, while April 23rd 2016 was the 114th day of the year. But who is counting, its still early.

36
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: April 24, 2019, 11:42:42 PM »
According to NSIDC both Arctic and Antarctic Sea Ice extent are at record low levels today.
I wonder how long it is since this last occurred

On vishop https://ads.nipr.ac.jp/vishop/#/extent
on the right side, there is a possibility to check global values. There it is easy to see when the summ of both is at the lowest.Nov 2016 to Oct. 2017 had most of the time the lowest summ, 2018 was often close to that value. But your question is about both separately at the lowest. Daily data for Arctic can be downloaded lower on the page of the link, but I didn't search yet for Antartic data.
This happened quite a bit over the last three years, 12 times last year and over 60 times in 2016 and 2017.  It  only occurred once in the 9 years prior to that. Surprisingly not once in 2007 or 2012. This has more to do with Antarctic levels plummeting in the past 4 years than changes in the Arctic.

37
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: April 24, 2019, 03:13:55 PM »
According to NSIDC both Arctic and Antarctic Sea Ice extent are at record low levels today.
I wonder how long it is since this last occurred

38
Arctic sea ice / Re: "Stupid" Questions :o
« on: April 22, 2019, 03:12:07 PM »
It's been long enough now that I think we can safely say something happened in 2015.  I've been saying near the end of December, but from the looks of this it was more like the middle of the year. (Graph from https://sites.google.com/site/arctischepinguin/home/global-sea-ice)

My stupid question for the day is this:  What happened in 2015?
This graph shows the rankings for NSIDC global Extent since 2014. As you can see there was a major change in mid 2015 which agrees with your observation.  The global pattern closer resembles the Antarctic pattern.  My opinion is that  this was caused by the 2015-2016 El Nino which significantly increased Pacific water temperatures which have remained a lot warmer than average since then. This should have made it more difficult for ice to form in the southern hemisphere.   

39
Arctic sea ice / Re: The 2019 melting season
« on: April 22, 2019, 02:01:40 AM »
Yikes!
What is a Yike  ;D and how does it relate to that image? I  presume you  are expecting  something dramatic but have no idea what it is.  :o

40
Arctic sea ice / Re: 2019 sea ice area and extent data
« on: March 31, 2019, 06:07:18 AM »
A JAXA extent loss of -165712 km^2 today drops the extent over {150K corrected} 137K below the previous record for the day. This is the lowest March value since at least 2002. It is also the second largest single day loss for March.  Yesterdays drop of 113K was the 6th largest drop.
 

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Arctic sea ice / Re: The 2019 Melting Season
« on: March 02, 2019, 08:31:26 AM »
JAXA is currently  285 K below the maximum.  About 6 years have seen increases above 250K after this date. 2018 increased over 280K between March 7th and maximum on Mar 17th after dropping 150K in the previous week. 

So we probably have seen the maximum but the winds and the weather could easily flip that.  I  agree with an earlier commentator that  Mar 1st  is a sensible day to start this thread rather than waiting until we are absolutely certain that  the max has passed.

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Antarctica / Re: Sea Ice Extent around Antarctica
« on: December 30, 2018, 08:34:46 AM »
"There is one question for which I have not seen a good answer. Why has this sudden loss of Antarctic Sea ice over the last 3 years happened?"

I think it's the wind's fault

Maybe ocean stored heat reaching the area via underwater currents, which have also attacked the glacial ice there.
The change really started in 2015 as the El Nino  built. The attached graph shows the NSIDC daily rankings for extent since the beginning of 2014. As can be seen the daily ranking was only less than 26th on three occasions before the beginning of August 2105. The rankings then plummet  to well below 2014 until the end of the year.  Rankings jumped around between 5 and 25 for most of 2016 until they dropped quickly below 10 at the end of August  2016 and remained below 10 ever since.

In my view this is not because the ice has a 'memory' of earlier conditions. It is because global sea and Air temperatures have been at  record highs since 2014. As the ice expands during winter it is butting up against warmer waters in the Atlantic, Pacific and Indian oceans which limits growth and makes melt easier.

NASA has also observed that  the ozone hole is in decline. https://www.nasa.gov/feature/goddard/2018/nasa-study-first-direct-proof-of-ozone-hole-recovery-due-to-chemicals-ban The Ozone hole has previously  been implicated in distributing the ice and increasing extent.

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Arctic sea ice / Re: 2018 sea ice area and extent data
« on: October 20, 2018, 08:27:13 AM »
Its not often you need a gain of 143,000 Km^2 in a day to not drop from 3rd lowest to lowest, and a gain of 240,000 to stay at third. We'll have to see what tomorrow brings.

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Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: October 10, 2018, 09:36:38 AM »
Quote
volume will always show a faster rate of decline than either area or thickness, but will slow down as the other parameters catch up.
I'm not sure this is always true, but I'm not a thermodynamics anything (not an expert nor even particularly knowledgeable).  If a significant cause of ice melt is bottom melt (which will likely increase as thickness decreases, as solar input into this process increases with ice thinness), then declining thickness will accelerate as zero volume approaches, while area remains fairly unchanged.  If area decreases 'at all', it might be a 'fact' that volume will decrease at a lower rate than does thickness (although faster than the area decline).  But I think this doesn't require volume declines to actually "slow down".

It is a case of simple mathematics.  The current minimum sea ice extent is ~60% of the extent measured in 1980.  The minimum volume is ~30% of 1980.  The thickness is ~50% of 1980.  Volume is just a product of these two; and since both are decreasing, the volume must decrease faster.  As extent and thickness decrease, the volume loss will slow because there is less volume to lose. 

This is different from the typical ice cube in a glass experiment, whereby all sides melt equally.  The large disproportionate dimensions leads to a difference in the physical melting properties.  The larger extent (or area) dominates the melting characteristic. 

If one were to assume that volume is the key parameter, and volume continues to decrease at its current rate, then the decline in thickness would need to double and the decline in extent more than triple, so that all three parameters reach zero simultaneously.  That is not what we are experiencing currently.
The key  point  you  are missing is that the thickness is an average measure over the entire ice cap.  The area that is less than 20cm thick at maximum is 20 - 30  times greater than the are that is 2 m thick for the same volume. The simple formula V=A*T  only  works for a single cell.

Over the entire cap the  AverageThickness = sum(( T  * N ) / Total(N))  for all thicknesses where N is the number of cells of a given thickness.  As the ice melts the ratios between the various N's doesn't change much  so the average thickness doesn't change either.

Simple example; there are 100 cells at thickness 0.1m and 10 at  thickness 1m;  after massive melting the number of cells has reduced to 10 at 0.1m and 1 at 1m.  The ratio hasn't changed and the average thickness hasn't changed despite area declining by 90%. 


45
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: October 08, 2018, 09:35:47 AM »
You are convinced that a BOE will occur when the ice gets very thin, the perhaps you should choose thickness as the measure to be looked at if you want to extrapolate.  The only reason that the two-dimensional measures give too high a value, is you think it should be lower.  I think that is a rather biased reason.  But, to each his own.
That's an odd argument if you ask me. The thickness is estimated by dividing area or extent by  volume. There is a lot of thin ice at the start of the season and a little bit of thick ice regardless of the overall extent.  As volume and extent decline the average thickness doesn't vary much. Thickness is probably a worse indicator than extent or area.  Volume seems a much more likely  measure because it measures the amount of ice lost each year.

Volume declines based on the difference between the ice formed in the freezing  season and the ice melting in the melting season. This has meant an average loss of about about 320 km^3 per year since 1988 but about 500 Km^3 per year since 2000 this appears to  be increasing exponentially  as warmer waters move into the Arctic.  With only  5000 Km^3 at minimum this year it seems highly likely  that within 10 years we will see a BOE in September. Extrapolating from extent,  thickness or area gives a much later date.

46
Arctic sea ice / Re: NSIDC 2018 Arctic SIE September average: August Poll
« on: September 30, 2018, 03:19:49 PM »
With just  one day to  go Extent seems to  be increasing at the end of the month as slowly  as it decreased at the start  of the month.  The average will be below 4.75 M as it  needs to  jump  by around 1M km^2 tomorrow to push the September average above 4,75 M .

40 of the 76  voters got it right.

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Arctic sea ice / Re: Accuracy of poll predictions
« on: September 24, 2018, 06:43:23 AM »
We are just following an established technique for identifying an answer when better data is not available:  https://en.wikipedia.org/wiki/Wisdom_of_the_crowd

Until we can predict the late summer weather this is about good as we can expect.  SIPN uses a similar approach: https://www.arcus.org/sipn.

Most of their contributers went low in August:

https://www.arcus.org/sipn/sea-ice-outlook/2018/august

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Arctic sea ice / Re: Accuracy of poll predictions
« on: September 23, 2018, 02:00:38 PM »
So there may be a kind of "educative" training in the next years, when those members which were wrong in their predictions on the far too low side will vote for higher, more realistic bins in the future?!?
We are in an environment where there is a high probability that the result will be midrange amongst  other recent years and a low probability that it will be exceptionally low. If the extent is one bin higher than out estimate nine times out of ten and 9 bins lower once out of ten then we are actually quite realistic. 

As a group we are concerned that extent is declining and therefore as a group we have a bias towards greater losses. We are not betting our children's inheritance on this,  just the worlds inheritance.

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The forum / Re: Poll predictions are stupid
« on: September 23, 2018, 09:03:38 AM »
Also NO.
It encourages us to think about why we are making our predictions and documents our predictions so that we can address what we predicted and why. Thus learning more about our own thinking.

Of course the variation in August and September is so dependent on the weather that even the August predictions have a massive confidence range covering most of the available options. Virtually the only outcome that was improbable on August 1 was a new record, anything else was still possible.  Perhaps we should have a "What happened?" thread where we discuss why we feel our predictions were wrong.

50
Arctic sea ice / Re: The 2018 melting season
« on: September 22, 2018, 03:52:44 PM »
The CAB and the Beaufort are striving to end the melt season, with rises over the past week. These recalcitrants have been the main reason the extent was not as low as some, like me, originally predicted. This was probably due to the cold winter in Alaska and Canada. How will the arctic will cope when Canada has a warm winter?

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