Support the Arctic Sea Ice Forum and Blog

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - DavidR

Pages: [1]
1
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.

2
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."

3
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)

4
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.

5
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

6
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.

7
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.   

8
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!"

9
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.

10
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.

11
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.

12
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.

13
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.
 

14
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%. 


15
Arctic sea ice / Re: Global sea ice area and extent data
« on: September 17, 2018, 06:53:15 AM »
Ger - any chance you could differentiate 2018 a bit better - dotted / thicker line / contrasting colour ?  Many thanks
Here's a more focussed look at this month. I  have taken out the years before 2001 but included them in Max Min and Average from 1988 - 2017.  2018 in black 2016 in red.

16
Arctic sea ice / Re: When will the Arctic Go Ice Free?
« on: July 30, 2018, 10:15:06 AM »
I think it would be very surprising if the Arctic wasn't ice free year round after another 2-4 decades.
I disagree. Even with storms, clouds, humidity, fog and whatever not - when the sun doesn't shine for 6 months, with the vagaries of weather there will come a calm clear day when temps fall below -10oC, and the surface will freeze somewhere in the central arctic basin. IMHO what could prevent such freezing is a major change of arctic ocean circulation, which could well happen at some point but not in a few decades.
I  come down on the side of a few decades before the Arctic will be ice free year round.  If we extrapolate from the volume decline the prediction is 2023 +- 2 for the first ice free summer days and 2053 for the first ice free year.  Currently the average year to year volume decline is still increasing.   If the trends are correct by 2035 we should see the Arctic Ice free from about July  1st.  That  means three months of insolation doing nothing but warming the ocean.  The combination of the extra heat in the ocean combined with more dynamic activities would seem to  suggest a shorter time to ice free all year rather than a longer period. 

If we look at how  fast SST's are increasing in the area above 80N+ , within 50 years they should be warm enough (> -10 degC in winter) to  prevent  much  ice forming.

17
Arctic sea ice / Re: 2018 sea ice area and extent data
« on: July 26, 2018, 12:38:49 AM »
Apologies if this is the wrong place to ask this, but how common have 200k daily extent losses been in previous years?
There have been two drops of over 200 K both on 24th July. 2012 had a 228 K drop.  So 24 July 2018 this year wasn't the biggest on this day, but  it was bigger than every other day in the Jaxa record since 2003.

There have been 23 days where the decline was greater that 150K. Six in 2012, three  in 2015 and three so far this year. The earliest was Mar 23, 2014 and the latest was Aug 9th, 2012.

18
In 2012 ...  The GAC was of course followed by massive loss of ice, although there is an argument that the ice had already been set up to melt by previous conditions and the GAC played a relatively minor role.
If we look at that from a volume perspective 2012 didn't lose that much ice after the cyclone.
           Aug 1 Vol          Aug Loss           Aug  Loss after Aug 9
2010   7.283K km^ 3   2.483K km^3    1.764K km^3
2012   6.538K km^3    2.619K km^3    1.774K km^3
2015   8.483K km^3    2.521K km^3    1.944K km^3
2016   7.449K km^3    2.808K km^3    2.006K km^3
2017   6.616K km^3    1.945K km^3    1.264K km^3

As you can see the ice loss in August was greater in 2016 than 2012 and in both 2015 and 2016 the ice loss after August 9 when the GAC was finished was also greater than 2012. Even 2010 went very close to the 2012 loss after August 9. However the 2012 ice was much thinner at the start of August leading to much greater extent  loss in August than in 2010, 2015 or 2016. I think there is a lot of substance to the view that  it was the thinness at the start of August  that  was responsible for the greater extent  loss in 2012. 

19
You can't change your vote before polling closes?

And the top bin isn't open ended.

Neven will fix the poll so votes can be altered.  The creation system is a bit touchy about  that.

The top bin is now open ended.

20
Arctic sea ice / Re: The 2018 melting season
« on: June 12, 2018, 11:49:19 AM »
I'm imagining that the amount of energy to reverse the Beaufort Gyre (even locally) and the amount of heat generated as a result of it, must be quite enormous?

I think that's a surface effect where the ice is being blown against the prevailing current. I doubt that the underlying current has changed much. So its easy to see how quickly that  increase in extent could reverse if the window blows with the current.

However pushing the ice through the water should cause some extra melt underwater which may have show up later, although we won't notice it.

21
Arctic sea ice / Re: IJIS Arctic Extent Minimum June Poll
« on: June 05, 2018, 08:09:25 AM »
At this point in time,  with hardly any data relevant to September, the trend is your friend. 3.75-4.25.

Attached is the loss profile for this year for the current date showing losses to date, and from this date, in the last 15 years. Based on this graph a return to the trend would see a further loss of 6.9M+  km^ leading to a final figure around 3.75. On the other hand an average loss would see a final figure of 4.25. Seems like Oren may have picked a good balance.

22
Arctic sea ice / Re: The 2018 melting season
« on: June 03, 2018, 09:13:03 AM »
It is interesting that according to the DMI 80°N temperature, now it is colder than normal there.
That graph makes utterly no sense, when the weather models are all showing *current* positive anomalies.
It looks pretty right to me.  Climate Reanalyzer is currently showing a -0.1 anomaly across the Arctic and most of the negative area is in the plus 80N region.  By Tuesday the anomaly climbs to plus 2 and stays near that for the rest of the week. There's some very hot weather in Northern Russia and the CAB by then.

23
Arctic sea ice / Re: 2018 sea ice area and extent data
« on: June 02, 2018, 06:15:43 AM »
2018 Quickly regains its presumptive second ranking and enters a month where the two leading years 2015 and 2016 have very low melt rates. If 2018 keeps up its dogged decline who knows where it will be by the end of the month. Looking at the IJIS record a decline of at least 2M seems probable putting 2018 well ahead by July 1st.

24
Arctic sea ice / Re: 2018 sea ice area and extent data
« on: June 01, 2018, 06:21:21 AM »
I expect an unspectacular decline in May due to the lack of ice in the Bering with the extent being somewhere near the 2015 (10.8-11.0M) figure by May 31st.   

I think I nailed it! Only a 13K difference according to Jaxa.   May be the only time though.

25
Arctic sea ice / Re: 2018 sea ice area and extent data
« on: April 22, 2018, 04:43:05 AM »
The Chukchi Sea region is still cold enough to resurface itself with ice when big open ocean areas form.  This will stop soon, so I expect to see major drops in ice extent soon.
The Chukchi and Beaufort are going to begin opening wide and clear within the next 10 days. It is going to be a sight to see! More like a zipper instead of a gradual march.

Nothing short of nuclear war between Alaska and Eastern Siberia would put enough energy into the system to acheive this. It  takes more than hot air to melt ice.

Chukchi and the Beaufort take about three months of steady decline to lose their ice. Over that period they will lose about 1 M km^2 in total; A rapid decline would be losing that in 10 weeks. or about 100K per week.  I expect an unspectacular decline in May due to the lack of ice in the Bering with the extent being somewhere near the 2015 (10.8-11.0M) figure by May 31st.   

26
Arctic sea ice / Re: First year PIOMAS volume below 1000km^3 poll 2018
« on: April 18, 2018, 11:22:13 AM »
An alternative view is to look at the gains and losses each year. This graph shows that although some years have greater gains than losses, on average the losses are larger than the gains by about 300 km^2 per year. This gap appears to be accelerating slightly probably as a consequence of Arctic waters warming up.

27
Arctic sea ice / Re: First year PIOMAS volume below 1000km^3 poll 2018
« on: April 18, 2018, 10:59:21 AM »
Wonder if anyone wants to update this graph
<snip>
Is there still a sweet spot somewhere that neither curves up nor down?

Note even if there is, there must be some good chance that melt from [31 May or whenever] will start curving one way or the other and we just haven't seen it yet.

This is not quite up to date but you get  the general impression. All trendlines are simply polynomials extrapolated out to 2025.

I have added the Max and total melt numbers to clarify the picture further. 

Pages: [1]