2018 sea ice area and extent data

[Daniel B.]

Magnamentis, thanks for your thoughts.  I think it necessary to comment on a couple of your statements in the interests of accuracy.  First, sea ice extent is just sea ice extent.   There seems to be nothing wrong with the AMSR 2 measurements  -- they simply are what they are, and nothing more.  Processing the measurements through two different  algorithms and getting similar results for extent is pretty persuasive evidence that all is well. 

To challenge these measurements just because we think there has been a lot of melting of the ice is rather like challenging an accurate measurement of a person's height just because we think they have lost some weight.  One is not directly linked to the other.   

Second, Galileo was not persecuted for suggesting the Earth was a sphere and not a disk.  He was supporting Copernicus' idea, aided by evidence he, Galileo, had gathered, that the Earth orbited the Sun.  This was theologically perilous because it meant the Earth was not the center of the Universe. 

BTW, there was ample evidence that the Earth was a sphere by Galileo's time, and it had been gathered and mathematically analyzed.  An ancient Greek, Eratosthenes, had made a pretty good calculation of the size of the Earth.  And about a hundred years before Galileo was put on trial, Columbus had set sail to the west to get to the East Indies, a journey that would be irrational, if not suicidal, on a flat Earth.   

Good points.  The extent is what it is, and allows for a good comparison to similar historical measurements.  Extent varies differently from area or volume, due to its different measurement. 

I would like to add that Galileo was prosecuted largely because he proclaimed that heliocentrism was not just a theory, but fact.  He knew he was right, but lacked the proof to counter the age old theories documented by Aristotles (which included spherism).  His arrogance got in the way, not to mention the envy of his astronomical peers.

[gerontocrat]

JAXA Extent 110,126,025 km2（June 17, 2018）

Wow.

I had to check if 11 or 10 was the correct one. I've been doing this for too long .

So have I - damn and blast

[gerontocrat]

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2

Total Area loss 101k, Central Seas 58 k Periphery 17k, Other Seas 26k.   

Another big loss.

Analysis of individual seas.

Pacific Side
- The Okhotsk Sea area is 16 k (It just will not die).
- The Bering Sea area is 2 k.
- Chukchi Sea -3 k,
- Beaufort Sea -6 k (Canadian (western) end?).
i.e. Pacific side slow...

Atlantic Side
- Total area loss of the Baffin, Greenland, and Barents Seas just 17 k, of which the Baffin was 11k
- The Laptev Sea area loss just 0 k (zero) .
- The Kara Sea area loss 13 k.

CAB
- The Central Arctic Sea gained 9k. Ice pushed in from CAA and ESS the last five days?
- The Canadian Archipelago loss 32 k (wow?).
- East Siberian Sea loss 13 k

Other seas
- St Lawrence area is still 2 k,
- Hudson Bay area loss 27k, but area still behind 2010's average area.

[Pagophilus]

JAXA Extent 110,126,025 km2（June 17, 2018)
[/quote]
NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2
[/quote]

Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

[magnamentis]

I think it necessary to comment on a couple of your statements in the interests of accuracy. 

thanks for the kind and useful feedback, agree to lack of accuracy and i'm glad that someone provided information that helps to see things more clearly and getting rid of a few mix-ups

at times i'm a bit sloppy when trying to say too much in too little time and rightly so it backfires, point taken :-)

my main issue with extent measurement is that once the area with between "not 100%" and 15% threshold was relatively small while the rest was a more or less coherent ice mass and nowadays that the ice is more fractured i somehow see this 15% threshold as not contemporary. the numbers IMO are nowadays farther from telling the whole story (the big picture) than they were 1-2 decades ago.

[oren]

JAXA Extent 10,126,025 km2（June 17, 2018)

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2

Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

A. You are mixing JAXA extent and NSIDC area.
B. The algorithms have different resolutions, so will produce diffetent results for the 15% rule.
C. The data comes from different satellites with different microwave wavelengths and all that stuff.
D. Different coastal masks and other minor issues.
Wipneus can explain in full, but even when you compare extents they will be very different.

[Pmt111500]

JAXA Extent 110,126,025 km2（June 17, 2018)

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2


Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

Yes. As for the reasons, they might be related to navigational hazards. Of course we here in ASIForum.would like to use most accurate data possible, but we'll have to do with any internally consistent data we get our hands into. If you have info on better sources of data, please make them publicly known. It's common knowledge some instances may withold these off public so release them as soon as is convenient. And the earth is nearly round, just to be sure.

[Neven]

When extent goes up by 43K, and area drops by 145K, Compactness drops by almost 2%:

[gerontocrat]

JAXA Extent 110,126,025 km2（June 17, 2018) Error by Gerontocrat - 10,126,025 km2

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2


Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

Extent is measured by saying if ice cover estimate for each pixel greater than 15% then ice cover = 100%
Area is measured by saying if ice cover estimate for each pixel equals, say, 50%, then ice cover = 50%.

Area estimate is, therefore, always less than extent, whether using NSIDC or JAXA measurements.
My posts use JAXA for extent, NSIDC for area as NSIDC produce area data for each sea daily easily uploaded from NSIDC (https://nsidc.org/arcticseaicenews/sea-ice-tools/). If JAXA produced the same data I would use JAXA data in the interests of consistency.

I try to avoid mixing NSIDC and JAXA extent data as they are always a bit different.

The graph below shows the difference between NSIDC area and NSIDC extent monthly averages for May

Hope that helps.

[Pagophilus]

Thank you so much, gerontocrat, for being so patient and kind.  Your reply also provides me with much new learning.

And I REALLY have to learn to read.  I completely missed the words 'area' versus 'extent' and hence my error.  I thought, no, I assumed they were both extent.  A sadder but a wiser man. 

I am just off to put on my dunce cap and stand in the corner for a while...

JAXA Extent 110,126,025 km2（June 17, 2018) Error by Gerontocrat - 10,126,025 km2

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2


Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

Extent is measured by saying if ice cover estimate for each pixel greater than 15% then ice cover = 100%
Area is measured by saying if ice cover estimate for each pixel equals, say, 50%, then ice cover = 50%.

Area estimate is, therefore, always less than extent, whether using NSIDC or JAXA measurements.
My posts use JAXA for extent, NSIDC for area as NSIDC produce area data for each sea daily easily uploaded from NSIDC (https://nsidc.org/arcticseaicenews/sea-ice-tools/). If JAXA produced the same data I would use JAXA data in the interests of consistency.

I try to avoid mixing NSIDC and JAXA extent data as they are always a bit different.

The graph below shows the difference between NSIDC area and NSIDC extent monthly averages for May

Hope that helps.

[Juan C. García]

[ADS-NIPR-JAXA] ASI Extent.

June 18^th, 2018: 10,130,433 km², a small increase of 4,408 km². 
2018 is the seventh lowest on record.

[jdallen]

[ADS-NIPR-JAXA] ASI Extent.

June 18^th, 2018: 10,130,433 km², a small increase of 4,408 km². 
2018 is the seventh lowest on record.

I'll point out here, what separates us from 2016 (current #1) is 3-4 days of decent melt, or a week of middling.I'll add that area took a very big hit while extent rose (-140K in fact per Neven).

While "7th" , things are closer than that number might seem to indicate.

[oren]

OTOH, while 2018 was 2nd in extent a while back, its area was relatively high to begin with as shown by Neven's compactness graph, so it's a mixed case.
The jury is still out IMHO.

[Wherestheice]

The trends are showing we might not be headed for a record low this year.... Gonna need some rapid melting here soon for that to happen.

[DavidR]

[ADS-NIPR-JAXA] ASI Extent.

June 18^th, 2018: 10,130,433 km², a small increase of 4,408 km². 
2018 is the seventh lowest on record.

I'll point out here, what separates us from 2016 (current #1) is 3-4 days of decent melt, or a week of middling.I'll add that area took a very big hit while extent rose (-140K in fact per Neven).

While "7th" , things are closer than that number might seem to indicate.

Since 2003 there has only been 5 daily increases in the JAXA record between June 1st and August 21st. All of these occurred since 2013 with two this year and one in 2013, 2015 and 2016. Most  of the declines less than 10000 km^2 also occurred in these recent years. This suggests a change in the pattern of the melting behavior since the very low extent and volume of 2012.  Perhaps due to easier dispersion of the thinner ice.

[gerontocrat]

JAXA Extent 10,130,433 km2（June 18, 2018）

Again,just to add to Juan's post :
Extent loss for the melting season to date is, at 3.76 million km2, 380k below the average for the last 10 years. That is a significant amount. See the graph on how consistently slower than or average daily melt has been for some time.

Extent is now just 22k (0.2%) above the average for 2010-2017.

On average 42% of the melting is done for this season - still a long way to go, on average 86 days.

Excluding 2012 from the 10 year average remaining extent loss. The outcome for the minimum then comes in at 4.43 million km2 as opposed to 4.31 million km2. The range of outcomes from the last 10 years remaining melt is 3.33 to 4.72 million km2, (The average September minimum of the last 10 years was 4.41 million km2).

There is a contrast developing with NSIDC data, which has recently showed strong area losses. jdallen has pointed out that this fall from 2nd to 7th place only represents about a week of middling melt. Nevertheless, rather than seeing the June Cliff, in June we have seen a gradual slowing of extent loss to below the average.

[Wipneus]

JAXA Extent 10,126,025 km2（June 17, 2018)

NSIDC Total Area  as at 17th June (5 day trailing average) =  8,723,055 km2

Pardon my ignorance, but why is there such a big difference between the JAXA and NSIDC extents?  Do they define the edge of the ice, or minimum concentration to be counted, differently?

A. You are mixing JAXA extent and NSIDC area.
B. The algorithms have different resolutions, so will produce diffetent results for the 15% rule.
C. The data comes from different satellites with different microwave wavelengths and all that stuff.
D. Different coastal masks and other minor issues.
Wipneus can explain in full, but even when you compare extents they will be very different.

That sums it up nicely.

Gridsize is probably the main cause: 25x25km for NSIDC and 10x10km for Jaxa. The instantaneous field of view (IFOV) sizes differ even more: up to 45x73km for NSIDC.
(http://nsidc.org/sites/nsidc.org/files/technical-references/SeaIce_CDR_CATBD_final.pdf).

That means NSIDC will see more extent along the ice edge (the mentioned 15% rule) and that more microwave emissions from land (land spill-over) is contaminating the measurements over water (land is seen as >>100% sea ice concentration).

[Wipneus]

Most of the extent losses are still away from the high arctic. For instance Hudson should be nosediving now, but seems a bit late.

The inner Arctic Basin extent is second lowest right behind 2017 for Uni Hamburg, Jaxa and NSIDC. Area is a bit behind for the NSIDC data.

The idea is of course that the current Arctic Basin is more relevant for September extent and area than more peripheral regions.

https://sites.google.com/site/arctischepinguin/home/amsr2/grf/basin-extent-multiprod.png
https://sites.google.com/site/arctischepinguin/home/amsr2/grf/basin-area-multiprod.png

[gerontocrat]

NSIDC Total Area  as at 18th June (5 day trailing average) = 8,611,220 km2
This is 142k above the 2010-2017 average on this date.

Total Area loss 111k, Central Seas 67 k Periphery 16k, Other Seas 28k.   

Another big loss.

Analysis of individual seas.

Pacific Side
- The Okhotsk Sea area is 17 k (It just will not die).
- The Bering Sea area is 3k.    (It just will not die)
- Chukchi Sea loss 2 k,
- Beaufort Sea gain 2 k
i.e. Pacific side slow...

Atlantic Side
- Total area loss of the Baffin, Greenland, and Barents Seas just 16 k,
of which the Baffin loss was 10k
- The Laptev Sea area loss just 5 k  .
- The Kara Sea area loss 13 k.

CAB
- The Central Arctic Sea lost13k. after significant gains in the last five days?
- The Canadian Archipelago loss 27 k (120k in the last five days - wow?).
- East Siberian Sea loss 8 k

Other seas
- St Lawrence area is still 2 k,
- Hudson Bay area loss 30 k, area now at 1990's average - i.e.a bit of catch-up.

Area loss this year to date has followed the 2010-17 average very closely indeed. Individual seas leaders matched by the laggards.

[Pagophilus]

Thank you oren, gerontocrat, Wipneus -- my extent of understanding is expanding.  Learning can be embarrassing because one makes mistakes, but it is a whole lot easier when one has understanding, patient mentors.

 

A. You are mixing JAXA extent and NSIDC area.
B. The algorithms have different resolutions, so will produce diffetent results for the 15% rule.
C. The data comes from different satellites with different microwave wavelengths and all that stuff.
D. Different coastal masks and other minor issues.
Wipneus can explain in full, but even when you compare extents they will be very different.

That sums it up nicely.

Gridsize is probably the main cause: 25x25km for NSIDC and 10x10km for Jaxa. The instantaneous field of view (IFOV) sizes differ even more: up to 45x73km for NSIDC.
(http://nsidc.org/sites/nsidc.org/files/technical-references/SeaIce_CDR_CATBD_final.pdf).

That means NSIDC will see more extent along the ice edge (the mentioned 15% rule) and that more microwave emissions from land (land spill-over) is contaminating the measurements over water (land is seen as >>100% sea ice concentration).

[Stephan]

Both deviation (from the mean values of each month between Jan 79 and May 18) of extent as well as of volume are above the linear trend line from Jan 1979 to May 2018 (last update May 2018 averages). See attached figures.

[Pagophilus]

Both deviation (from the mean values of each month between Jan 79 and May 18) of extent as well as of volume are above the linear trend line from Jan 1979 to May 2018 (last update May 2018 averages). See attached figures.

The latest values on these plots are for May2018, so we can expect both plots to drop further and therefore probably below the mean as further melting occurs in June, July and August, correct?

It is interesting and worrying to note the greater variability in both plots in the past decade or so.  Systems often fluctuate more as they move towards threshold conditions.

[El Cid]

The idea is of course that the current Arctic Basin is more relevant for September extent and area than more peripheral regions.

https://sites.google.com/site/arctischepinguin/home/amsr2/grf/basin-extent-multiprod.png
https://sites.google.com/site/arctischepinguin/home/amsr2/grf/basin-area-multiprod.png

Great charts as always! Thank you. I think we need to concentrate on Arctic Basin Area (Extent? I am not so sure), everything else is just smokescreen, eg. the Hudson will melt out anyway, it does not matter in the greater scheme of things...

[Neven]

With NSIDC extent going up another 67K, and area going down a modest 37K, Compactness drops by another percentage point:

[Stephan]

Couldn't we just take the three different extent sources (JAXA, NSIDC, Uni Hamburg) to quantify the day-to-day differences in extent calculation? This would probably solve some discussion here.
Maybe this difference is season-dependent, randomly distributed or maybe increasing over the years?

[Stephan]

The latest values on these plots are for May2018, so we can expect both plots to drop further and therefore probably below the mean as further melting occurs in June, July and August, correct?

It is interesting and worrying to note the greater variability in both plots in the past decade or so.  Systems often fluctuate more as they move towards threshold conditions.

To achieve this the average extent in April should have been 0,21 mio. km² smaller than it has been - for May the difference between the actual value and the trend line was 0,22 mio. km². So a jump might "help" to reach the trend line. But the development of the last 10 days or so do not make it very likely at the moment. I will update this graph monthly.   

[Darvince]

The latest values on these plots are for May2018, so we can expect both plots to drop further and therefore probably below the mean as further melting occurs in June, July and August, correct?

It is interesting and worrying to note the greater variability in both plots in the past decade or so.  Systems often fluctuate more as they move towards threshold conditions.

There was a change with the 2007 season towards lower summer/early fall extents without also lower winter extents, causing the yearly rise and fall of extent and volume anomalies. It is moreso a new yearly behavior than a growing instability.

[Juan C. García]

[ADS-NIPR-JAXA] ASI Extent.

June 19^th, 2018: 10,106,748 km², a drop of -23,685 km².
2018 is the seventh lowest on record.

[gerontocrat]

JAXA Extent 10,106,748 km2（June 19, 2018）

Again,just to add to Juan's post :
Extent loss for the melting season to date is, at 3.78 million km2, 430 k below the average for the last 10 years. That is a significant amount. See the graph on how consistently slower than or average daily melt has been for some time.

Extent is now 65k (0.6%) above the average for 2010-2017.

On average 42% of the melting is done for this season - still a long way to go, on average 85 days.

Excluding 2012 from the 10 year average remaining extent loss. The outcome for the minimum then comes in at 4.46 million km2 as opposed to 4.35 million km2. The range of outcomes from the last 10 years remaining melt is 3.38 to 4.41 million km2, (The average September minimum of the last 10 years was 4.41 million km2).

There is a contrast developing with NSIDC data, which has recently showed strong area losses. jdallen has pointed out that this fall from 2nd to 7th place only represents about a week of middling melt. Nevertheless, rather than seeing the June Cliff, in June we have seen a gradual slowing of extent loss to more and more below the average.

[Daniel B.]

The June slowing of the melt corresponds quite well to the Arctic temperatures dipping below average.  May was warmer, and the sea ice responded accordingly.

http://ocean.dmi.dk/arctic/meant80n.uk.php

[Neven]

You're comparing Arctic-wide melt with modelled temps from 80N to the North Pole. The relation is tenuous at best, especially now. The Arctic has actually been above average temperature-wise, but a lack of winds is keeping winds static, and only the Siberian side is enduring a solar attack. There was more easy ice to melt during May, especially on the Pacific side.

[gerontocrat]

NSIDC Total Area  as at 18th June (5 day trailing average) = 8,513,017 km2
This is 149k above the 2010-2017 average on this date.

Total Area loss 98k, Central Seas 67 k Periphery 18k, Other Seas 31k.   
     
Another big loss, but a 7k below the 2010-2017 average.

Analysis of individual seas.

Pacific Side
- The Okhotsk Sea area is 19 k, +2k on the day(It just will not die).
- The Bering Sea area is 3k.    (It just will not die)
- Chukchi Sea loss 2 k,
- Beaufort Sea gain 7 k
i.e. Pacific side slow loss or even a slow gain...

Atlantic Side
- Total area loss of the Baffin, Greenland, and Barents Seas just 18 k,
of which the Baffin loss was 12k
- The Laptev Sea area loss just 12 k  .
- The Kara Sea area loss 5 k.

CAB
- The Central Arctic Sea loss 17k
- The Canadian Archipelago loss 18 k
- East Siberian Sea loss 4 k

Other seas
- St Lawrence area is still 2 k,
- Hudson Bay area loss 33 k, area now at 1990's average - i.e.a bit of catch-up.

Area loss this year to date has followed the 2010-17 average very closely indeed. Individual seas leaders matched by the laggards.

[Daniel B.]

You're comparing Arctic-wide melt with modelled temps from 80N to the North Pole. The relation is tenuous at best, especially now. The Arctic has actually been above average temperature-wise, but a lack of winds is keeping winds static, and only the Siberian side is enduring a solar attack. There was more easy ice to melt during May, especially on the Pacific side.

True, but most of the ice resides north of the 80th parallel.

[gerontocrat]

You're comparing Arctic-wide melt with modelled temps from 80N to the North Pole. The relation is tenuous at best, especially now. The Arctic has actually been above average temperature-wise, but a lack of winds is keeping winds static, and only the Siberian side is enduring a solar attack. There was more easy ice to melt during May, especially on the Pacific side.

True, but most of the ice resides north of the 80th parallel.

"True, but most of the ice resides north of the 80th parallel."

Nope.

The area of the Arctic Ocean is 14.06 million Km2.
The area of the Arctic above 80 degrees North is 3.875 million km2, just under 28% of the area of the Arctic ocean

Arctic Ocean - Wikipedia
https://en.wikipedia.org/wiki/Arctic_Ocean
The Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2 (5,427,000 sq mi), almost the size of Antarctica. The coastline is 45,390 km (28,200 mi) long. It is surrounded by the land masses of Eurasia, North America, Greenland, and by several islands.

ps: Apart from the Atlantic side, nearly all melt to date is well below 80+ North (and some not in the Arctic Ocean at all)

Data - such a nuisance

[Daniel B.]

You're comparing Arctic-wide melt with modelled temps from 80N to the North Pole. The relation is tenuous at best, especially now. The Arctic has actually been above average temperature-wise, but a lack of winds is keeping winds static, and only the Siberian side is enduring a solar attack. There was more easy ice to melt during May, especially on the Pacific side.

True, but most of the ice resides north of the 80th parallel.

"True, but most of the ice resides north of the 80th parallel."

Nope.

The area of the Arctic Ocean is 14.06 million Km2.
The area of the Arctic above 80 degrees North is 3.875 million km2, just under 28% of the area of the Arctic ocean

Arctic Ocean - Wikipedia
https://en.wikipedia.org/wiki/Arctic_Ocean
The Arctic Ocean occupies a roughly circular basin and covers an area of about 14,056,000 km2 (5,427,000 sq mi), almost the size of Antarctica. The coastline is 45,390 km (28,200 mi) long. It is surrounded by the land masses of Eurasia, North America, Greenland, and by several islands.

ps: Apart from the Atlantic side, nearly all melt to date is well below 80+ North (and some not in the Arctic Ocean at all)

Data - such a nuisance

You are right.  I was looking at the Arctic at summer minimum.  Most of the melt to date, has been south of the 80 parallel.  Still, I think that the temperature north of 80 does show a good correlation.

[oren]

The temperature of the central arctic ocean in summer is pegged to the melting point, as long as ice is still there. Moreover, when the ice is covered with snow, the air is pegged to 0^oC, but when the snow is gone and the ice is in partial melt the air is pegged to -1.8^oC. So your "cooler summer temps" are nothing but a mirage signalling the deterioration of the arctic.

[Dharma Rupa]

The temperature of the central arctic ocean in summer is pegged to the melting point, as long as ice is still there. Moreover, when the ice is covered with snow, the air is pegged to 0^oC, but when the snow is gone and the ice is in partial melt the air is pegged to -1.8^oC. So your "cooler summer temps" are nothing but a mirage signalling the deterioration of the arctic.

BTW -- my preferred definition of an ice free Arctic is when the DMI 80N is no longer pegged near 0 in Summer.  When there is no longer enough ice to keep it cold then it is effectively ice free.

[Juan C. García]

[ADS-NIPR-JAXA] ASI Extent.

June 20^th, 2018: 10,050,224 km², a drop of -56,524 km².
2018 is the sixth lowest on record.

[El Cid]

BTW -- my preferred definition of an ice free Arctic is when the DMI 80N is no longer pegged near 0 in Summer.  When there is no longer enough ice to keep it cold then it is effectively ice free.

That sounds like the best definition to me!

[gerontocrat]

At 10.07 a.m. GMT (UTC) time today it will be the Summer Solstice with the Earth's tilt towards the sun at its maximum of 23.44 degrees. By 11.08 a.m. the sun will have started its apparent southward movement.

JAXA Extent 10,050,224 km2（June 20, 2018）

Again,just to add to Juan's post :
Extent loss for the melting season to date is, at 3.84 million km2, 440 k below the average for the last 10 years. That is a significant amount, about one weeks average melt for the time of year. See the graph on how consistently slower than or average daily melt has been for some time.

Extent is now 78k (0.8%) above the average for 2010-2017.

On average 43% of the melting is done for this season - still a long way to go, on average 84 days.

Excluding 2012 from the 10 year average remaining extent loss. The outcome for the minimum then comes in at 4.47 million km2 as opposed to 4.37 million km2. The range of outcomes from the last 10 years remaining melt is 3.42 to 4.85 million km2, (The average September minimum of the last 10 years was 4.41 million km2).

There is a contrast developing with NSIDC data, which has recently showed strong area losses. Rather than seeing the June Cliff, in June we have seen a gradual slowing of extent loss to more and more below the average.

[Neven]

BTW -- my preferred definition of an ice free Arctic is when the DMI 80N is no longer pegged near 0 in Summer.  When there is no longer enough ice to keep it cold then it is effectively ice free.

I've often thought about this moment because it would be so seminal, but never viewed it from the ice-free perspective. I hope I'll remember this quote when it happens and write about it. If I don't, remind me. 

[Dharma Rupa]

BTW -- my preferred definition of an ice free Arctic is when the DMI 80N is no longer pegged near 0 in Summer.  When there is no longer enough ice to keep it cold then it is effectively ice free.

I've often thought about this moment because it would be so seminal, but never viewed it from the ice-free perspective. I hope I'll remember this quote when it happens and write about it. If I don't, remind me. 

Several of us had a discussion about this awhile ago.  I'm not sure if I was the one who came up with this definition, but I wasn't the only one who liked it.

[Richard Rathbone]

The temperature of the central arctic ocean in summer is pegged to the melting point, as long as ice is still there. Moreover, when the ice is covered with snow, the air is pegged to 0^oC, but when the snow is gone and the ice is in partial melt the air is pegged to -1.8^oC. So your "cooler summer temps" are nothing but a mirage signalling the deterioration of the arctic.

Top melt happens at 0, bottom melt at -1.8. See the buoy thread for profiles if you want to check how the temperature in the ice changes with the season. There's not nearly enough of the bottom of the ice in contact with air other than via the top of the ice to move the peg down yet.

[gerontocrat]

NSIDC Total Area  as at 20th June (5 day trailing average) =  8,439,254 km2
This is 170k above the 2010-2017 average on this date.

Total Area loss 74 k, Central Seas 35 k Periphery 14k, Other Seas 24k.   

The slow down in June melt now showing in these 5 day averages. Current day is 30k below the 2010-2017 average area loss.

Analysis of individual seas.

Pacific Side
- The Okhotsk Sea area is 20 k, +1k on the day (It just will not die).
- The Bering Sea area is 3k.    (It also just will not die)
- Chukchi Sea loss 10 k,
- Beaufort Sea gain 11 k
i.e. Pacific side slow loss or even a slow gain...

Atlantic Side
- Total area loss of the Baffin, Greenland, and Barents Seas just 14 k,
of which the Baffin loss was 11k and the Barents 3k
- The Laptev Sea area loss just 3 k  .
- The Kara Sea area gain 3 k.

CAB
- The Central Arctic Sea loss 19k
- The Canadian Archipelago loss 13 k
- East Siberian Sea loss 5 k

Other seas
- St Lawrence area is still 2 k,
- Hudson Bay area loss 25 k, area now just below 1990's average - i.e.a bit of catch-up.

Area loss this year to date has followed the 2010-17 average very closely indeed, but is slowing. Individual seas leaders matched by the laggards.

[Tor Bejnar]

Looking at Extent graphs on the ASIG Regional Graphs page, and projecting all the graphs that are not the CAB into mid-September reveals (to me) the potential of a total of about 200k sq km of area above experienced minimums in September 2018.  As the difference between the two lowest CAB graphs is about 400k sq km of area, I continue to believe that (virtually) only the CAB matters when it comes to determining if the September SIE is a record or not.  I certainly understand that lingering 'regional' sea ice extent will delay CAB ice loss in the region borders.  But when I see CAB extent setting a current date minimum, I do not discount the possibility of a new minimum. 

That SIA is only near the current date minimum puts a small damper on this 'pessimistic view' of ice survival.  The two graphs suggest that CAB ice compaction is higher now than in other years, and that is sure to put a damper on future internal CAB melt.

[gerontocrat]

I continue to believe that (virtually) only the CAB matters when it comes to determining if the September SIE is a record or not.  I certainly understand that lingering 'regional' sea ice extent will delay CAB ice loss in the region borders.  But when I see CAB extent setting a current date minimum, I do not discount the possibility of a new minimum. 

That SIA is only near the current date minimum puts a small damper on this 'pessimistic view' of ice survival.  The two graphs suggest that CAB ice compaction is higher now than in other years, and that is sure to put a damper on future internal CAB melt.

If one just looks at the Central Arctic Sea and the Canadian Archipelago then NSIDC area loss data to date does suggest a low September minimum - but..........

[LDorey]

Huh. After all the "bickering" over how to define a Blue Ocean event ( Aka sign of the Apocalypse that 4 year term politico's can't ignore), this is by far the one I like the best. I don't know that "Ice free Arctic" is the right term for it, perhaps something fancy like End of Arctic Temperature Forcing ) EATF (unless the acronym taken already). Anyways It feels like a MUCH better (real) indicator of a large paradigm shift than declaring that a small abritary amount of ice left means "ice free".

Liam

The temperature of the central arctic ocean in summer is pegged to the melting point, as long as ice is still there. Moreover, when the ice is covered with snow, the air is pegged to 0^oC, but when the snow is gone and the ice is in partial melt the air is pegged to -1.8^oC. So your "cooler summer temps" are nothing but a mirage signalling the deterioration of the arctic.

BTW -- my preferred definition of an ice free Arctic is when the DMI 80N is no longer pegged near 0 in Summer.  When there is no longer enough ice to keep it cold then it is effectively ice free.

[jdallen]

<snippage>
That SIA is only near the current date minimum puts a small damper on this 'pessimistic view' of ice survival.  The two graphs suggest that CAB ice compaction is higher now than in other years, and that is sure to put a damper on future internal CAB melt.

I agree - the peripheral seas are secondary to what's happening in the basin proper, which will have the greatest immediate impact on seasonal weather.

While the central basin - particularly the western hemisphere side - hasn't suffered the scorching the rest of the basin has, I'm still concerned about the area immediately north of the Beaufort/Chukchi and on the Atlantic side generally.

If the Kara, Barents and Laptev melt continues as it has or accelerates, that could render the higher CAB compaction and more favorable ice retention conditions moot. 

Of further concern is the possible set-up of high pressure over the Beaufort.  While extent and compaction are better than some years, other factors like ice age and thickness are decidedly *not*.  Late June heat and melt ponds could easily make up for (in that area) a lazy June.

All hinges on the weather.

[Juan C. García]

[ADS-NIPR-JAXA] ASI Extent.

June 21^st, 2018: 9,988,672 km², a drop of -61,552 km².
2018 is the sixth lowest on record.

[gerontocrat]

JAXA Extent 9,988,672 km2（June 21, 2018）

Again,just to add to Juan's post :
Extent loss for the melting season to date is, at 3.90 million km2, 460 k below the average for the last 10 years. That is a significant amount, about one weeks average melt for the time of year. See the graph on how consistently slower than or average daily melt has been for some time.

Extent is now 86k (0.9%) above the average for 2010-2017.

On average 44% of the melting is done for this season - still a long way to go, on average 84 days.

Excluding 2012 from the 10 year average remaining extent loss. The outcome for the minimum then comes in at 4.49 million km2 as opposed to 4.38 million km2. The range of outcomes from the last 10 years remaining melt is 3.41 to 4.88 million km2, (The average September minimum of the last 10 years was 4.41 million km2).

Rather than seeing the June Cliff, in June we continue to see a gradual slowing of extent loss to more and more below the average.

ps: Juan got the data just in time - JAXA seems to be offline now.