Arctic Sea Ice Extent, Area, and Volume

[bluewave]

The Central Arctic continues to set records for low extent as we get close to the beginning  of October.

 

[LibertyBell]

On 9/29/2020 at 3:12 PM, bluewave said:

The Central Arctic continues to set records for low extent as we get close to the beginning  of October.

 

Interesting discussion here

 

 

 

[bdgwx]

As of October 13th the 5 day NSIDC average extent is at a record low again beating out 2012. 

[bluewave]

1 hour ago, bdgwx said:

As of October 13th the 5 day NSIDC average extent is at a record low again beating out 2012. 

The  record SST warmth form the Siberian heatwave is slowing down the freeze- up in those regions.

https://theconversation.com/arctic-sea-ice-is-being-increasingly-melted-from-below-by-warming-atlantic-water-144106

All this may be feeding into ever more extreme climate change in the Arctic. Throughout summer 2020 the Siberian heatwavecontinually shattered temperature records, including eastern Arctic sea surface temperatures. And while sea ice reflects much of the sun’s rays back into space, open water is dark and absorbs the sun’s heat. So as the sea ice retreated the surface water is warmed, which in turned further warms the atmosphere above, quite apart from the influence of increasing greenhouse gases. 

There is still much more to learn about the link between the eastwards spread of the influence of Atlantic heat, and the reduction in sea ice it brings, and knock on effects on severe weather at lower latitudes. But it is clear that the Arctic – already warming faster than anywhere else on Earth – could be in the process of transitioning to a “new” state.

 

[donsutherland1]

Yesterday, Arctic sea ice extent on JAXA was 4.929 million square kilometers. That is the latest Arctic sea ice extent has been below 5 million square kilometers. The previous record of October 14 was set just last year.

[bluewave]

Very unusual to see a daily area drop in mid October as the record Arctic warmth is slowing the freeze-up

https://cryospherecomputing.tk

 

[LibertyBell]

2 hours ago, bluewave said:

Very unusual to see a daily area drop in mid October as the record Arctic warmth is slowing the freeze-up

https://cryospherecomputing.tk

 

This is worse than 2012 was.

[bluewave]

18 minutes ago, LibertyBell said:

This is worse than 2012 was.

Yeah, we are well below where 2012 was at this point in October. The the heat on the Siberian Arctic side this year was off the charts.

5.422

7.329

6.871

6.596

5.715

6.515

5.681

5.234

5.108

 

 

[LibertyBell]

15 minutes ago, bluewave said:

Yeah, we are well below where 2012 was at this point in October. The the heat on the Siberian Arctic side this year was off the charts.

5.422

7.329

6.871

6.596

5.715

6.515

5.681

5.234

5.108

 

so this isn't just a lag from the early historic Siberian heat, it actually persisted for most of the year!

 

[LibertyBell]

did you see this Chris?

 

 

[LibertyBell]

Lots of stuff here

 

 

[LibertyBell]

 

[donsutherland1]

5 hours ago, LibertyBell said:

Lots of stuff here

 

 

The link to the full response by Geoffrey Supran and Naomi Oreskes can be found here:

https://iopscience.iop.org/article/10.1088/1748-9326/abbe82

It is abundantly clear what the ExxonMobil Vice President is seeking to do. Hopefully, in the future, ExxonMobil, among others, will have to pay full cost for their externalities (greenhouse gas pollution) and face legal exposure for deliberately misleading the public and investors.  There should be no de facto “too big to be held liable” for fraud exemption.

 

[Bhs1975]

The link to the full response by Geoffrey Supran and Naomi Oreskes can be found here:

https://iopscience.iop.org/article/10.1088/1748-9326/abbe82

It is abundantly clear what the ExxonMobil Vice President is seeking to do. Hopefully, in the future, ExxonMobil, among others, will have to pay full cost for their externalities (greenhouse gas pollution) and face legal exposure for deliberately misleading the public and investors.  There should be no de facto “too big to be held liable” for fraud exemption.

 

All oil and gas assets need to go towards fixing this mess.

[LibertyBell]

39 minutes ago, donsutherland1 said:

The link to the full response by Geoffrey Supran and Naomi Oreskes can be found here:

https://iopscience.iop.org/article/10.1088/1748-9326/abbe82

It is abundantly clear what the ExxonMobil Vice President is seeking to do. Hopefully, in the future, ExxonMobil, among others, will have to pay full cost for their externalities (greenhouse gas pollution) and face legal exposure for deliberately misleading the public and investors.  There should be no de facto “too big to be held liable” for fraud exemption.

 

Right now they are too busy harassing good people on Twitter and putting their social media people on some sort of a "justification" spree for all their bad behavior on an ExxonKnew hashtag and claiming they are doing something to stop climate change.  

[LibertyBell]

32 minutes ago, Bhs1975 said:

All oil and gas assets need to go towards fixing this mess.

As soon as that happens, real reform will begin.

 

[LibertyBell]

This whole escapade reminds me of the big banks and the "too big to fail" fiasco- and please just ignore our predatory lending practices.  

Meanwhile, Wells Fargo is back at it and they've now been caught misrepresenting themselves to steal small business covid response payments and had to fire 125 employees.

https://www.cfo.com/fraud/2020/10/wells-fargo-fires-over-100-employees-for-alleged-covid-19-relief-fraud/

Nevermind all the big banks found to be laundering money for criminals who were propping up extremist regimes.

 

[donsutherland1]

1 hour ago, Bhs1975 said:

All oil and gas assets need to go towards fixing this mess.

This is exactly why they should be paying full cost for their externalities. Otherwise, they are spared having to pay full cost for their product with society left to cover those costs.

[donsutherland1]

54 minutes ago, LibertyBell said:

As soon as that happens, real reform will begin.

 

Once they start paying full cost for their products, they will have incentives to move toward more profitable and environmentally sound energy production. They currently possess the resources to invest in just such a transition. But so long as society covers a sizable part of their cost structure, they have no incentive to change from the status quo.

[donsutherland1]

On October 17, Arctic sea ice extent was 4.959 million square kilometers (JAXA). That further extended 2020’s record for the latest date on which Arctic sea ice extent was below 5 million square kilometers.

[bluewave]

All the extra ocean heat on the Siberian side is really slowing the freeze-up this October. So the the extent is currently the lowest on record for this time of year well below 2012. The Siberian heatwave this year was one of the most extreme events we have seen.

 

 

 

[donsutherland1]

On October 19, Arctic sea ice extent reached 5 million square kilometers for the first time this season. That is the latest on record.

[bluewave]

26 minutes ago, donsutherland1 said:

On October 19, Arctic sea ice extent reached 5 million square kilometers for the first time this season. That is the latest on record.

The last few days set the new all-time extent anomaly record.

 

[etudiant]

Which is the better metric, area or extent?

I've been focused on area,  thinking that extent just adds another variable, yet most contributors prefer to use extent. What are the pros and cons driving the choice?

[ORH_wxman]

16 hours ago, etudiant said:

Which is the better metric, area or extent?

I've been focused on area,  thinking that extent just adds another variable, yet most contributors prefer to use extent. What are the pros and cons driving the choice?

Area is more accurate if you want to know the precise value of surface that is covered with ice.

Extent is better for things like shipping...if a region is covered with 40% ice concentration, you probably don't want to try going through it without an ice breaker. That region would be considered "covered in ice extent" even though there is open water mixed in. Area would give us a lower value because it's only 40% ice.

[bdgwx]

As of 10/20 the NSIDC extent YtD mean is 10.26. This is a tad higher than the current record holder set all the way back in 2019 at 10.23.. The gap is closing though. I think there is a good chance that 2020 will at least end in the bottom 3 in terms of annual mean extent. A new record is certainly a possibility as well.

[etudiant]

8 hours ago, ORH_wxman said:

Area is more accurate if you want to know the precise value of surface that is covered with ice.

Extent is better for things like shipping...if a region is covered with 40% ice concentration, you probably don't want to try going through it without an ice breaker. That region would be considered "covered in ice extent" even though there is open water mixed in. Area would give us a lower value because it's only 40% ice.

Thank you, that makes sense. 

From a climate monitoring perspective, that suggests area is the one to focus on.

In that context, I note that area is the lowest ever for the date, https://cryospherecomputing.tk/

Hard for me to understand why this is a disputed fact.

[bluewave]

https://nsidc.org/arcticseaicenews/faq/#area_extent

What is the difference between sea ice area and extent?

Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method.

A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.

Extent defines a region as “ice-covered” or “not ice-covered.” For each satellite data cell, the cell is said to either have ice or to have no ice, based on a threshold. The most common threshold (and the one NSIDC uses) is 15 percent, meaning that if the data cell has greater than 15 percent ice concentration, the cell is considered ice covered; less than that and it is said to be ice free. Example: Let’s say you have three 25 kilometer (km) x 25 km (16 miles x 16 miles) grid cells covered by 16% ice, 2% ice, and 90% ice. Two of the three cells would be considered “ice covered,” or 100% ice. Multiply the grid cell area by 100% sea ice and you would get a total extent of 1,250 square km (482 square miles).

Area takes the percentages of sea ice within data cells and adds them up to report how much of the Arctic is covered by ice; area typically uses a threshold of 15%. So in the same example, with three 25 km x 25 km (16 miles x 16 miles) grid cells of 16% ice, 2% ice, and 90% ice, multiply the grid cell areas that are over the 15% threshold by the percent of sea ice in those grid cells, and add it up. You would have a total area of 662 square km (255.8 square miles).

Scientists at NSIDC report extent because they are cautious about summertime values of ice concentration and area taken from satellite sensors. To the sensor, surface melt appears to be open water rather than water on top of sea ice. So, while reliable for measuring area most of the year, the microwave sensor is prone to underestimating the actual ice concentration and area when the surface is melting. To account for that potential inaccuracy, NSIDC scientists rely primarily on extent when analyzing melt-season conditions and reporting them to the public. That said, analyzing ice area is still quite valuable. Given the right circumstances, background knowledge, and scientific information on current conditions, it can provide an excellent sense of how much ice there really is “on the ground

 

 

[ORH_wxman]

25 minutes ago, etudiant said:

Thank you, that makes sense. 

From a climate monitoring perspective, that suggests area is the one to focus on.

In that context, I note that area is the lowest ever for the date, https://cryospherecomputing.tk/

Hard for me to understand why this is a disputed fact.

They are pretty closely correlated so it doesn’t matter that much which one you follow for climate purposes. 

For “in-season predictions” though, NSIDC area is a much better predictor of both final minimum extent and area when you are a few months out (June/July). That is why I use NSIDC area to make my minimum predictions at the end of June every year. I should mention that NSIDC area is different from other area metrics because NSIDC uses the SSMI/S satellite which gets fooled by melt ponding. So SSMI/S-derived area in June (when melt ponding tends to peak) is really a good proxy for melt ponds which is the true skilled in-season predictor of final minimum extent and area. 

[bdgwx]

Using a simple extrapolation I'm going to guess 10.18e6 km^2 for the 2020 annual mean. This would be 2nd lowest between 10.163 in 2016 and 10.201 in 2019. The current 3rd lowest figure is 10.335 so I still feel pretty confident that 2020 will end at least in the bottom 3. In fact, even if 2020's freeze trajectory catches up to the 1981-2010 mean by year end we'd still see a finish in the bottom 3. And if freeze rates continue to stay muted then a new record low for the annual mean extent is a definite possibility.