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Arctic Sea Ice Extent, Area, and Volume


ORH_wxman
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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.

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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.

 

 

 

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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.

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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.

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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.

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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

 


 

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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. 

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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.

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What is interesting is despite the record low areal coverage for sea ice so late in the fall is that cold air masses still originate over the land. In fact, that is always the case. North America is seeing some extraordinary cold and snow cover for so early in the fall season despite the very low sea ice. The Islands of northern Canada and the Arctic waters just north of Canada and Greenland are much deeper than the shallower waters on the Siberian side. Therefore it's going to take a lot more warming to get rid of this ice on a seasonal basis. Plus there is NO albedo effect this time of year up there. The Sun is down. Even in the summer, it depends on storminess and how much cloud cover you have to decrease the albedo for a positive feedback. I don't understand how a climate model that can't explicitly predict cloud cover can forecast with any accuracy the positive feedback from the loss of sea ice. Open water many times leads to low clouds and fog up in the Arctic and no change in albedo. This has happened in many low sea ice years. Once climate or any atmospheric model can simulate clouds with accuracy then the results will be more convincing. Right now it still gets very cold over the land regardless of sea ice concentration.  It is incredible how cold it has been in the Plains. -27F in Montana a few days ago.  Records being broke by more than 10 degrees. Temperatures up to 50 degrees below normal!  Snow in Texas in October! This stuff barely makes the news. Tremendous bias. If it was 50 degrees above normal the media and many of you would be going nuts blaming climate change.  When it is cold, it is just weather. When it is warm it is climate change! 

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While the record cold around the Rockies and Plains has  been impressive, it’s focused over a very small geographic region of the planet. The coverage of the record cold is much smaller than the areas and magnitude of record warmth as the world warms. It’s no coincidence that the record October cold near Montana is occurring in an isolated pocket relative to the overall extent of the global temperature increases. Montana represents a portion of the only 17 out of 2,844 stations with under 6 months of warming over the last 30 years.

 

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On 10/29/2020 at 5:52 PM, LibertyBell said:

Also isn't it true that alpine areas warm more slowly and areas close to the oceans are warming much faster because the oceans act as heat sinks?  Same reason why the arctic warms much faster than antarctica

 

     Speaking of Antarctica ..... "Ice extent is now well above the 1981 to 2020 median extent. This follows a remarkable transition from generally below median extent beginning in August 2016 to well above median extent just in the seven weeks preceding October 1, 2020". Why are we seeing the shift from near record low extent in the north, to near record high extent in the south? If this is a "global" issue, someone please explain the anomaly with Antarctic ice extent. 

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6 hours ago, CAD_Wedge_NC said:

     Speaking of Antarctica ..... "Ice extent is now well above the 1981 to 2020 median extent. This follows a remarkable transition from generally below median extent beginning in August 2016 to well above median extent just in the seven weeks preceding October 1, 2020". Why are we seeing the shift from near record low extent in the north, to near record high extent in the south? If this is a "global" issue, someone please explain the anomaly with Antarctic ice extent. 

It's complicated. First understand that this is not entirely unexpected. In fact, the IPCC AR5 WG1 prediction for SH sea ice, although significantly more uncertain than predictions for the NH, shows a slight preference for increases through about 2030 with the possibility of record highs persisting even through 2060 before things turn south (pun intended) down there too. I must caveat that by saying the uncertainty envelope does include the possibility of the secular decline starting around 2020 as well. The unfortunate state of affairs with SH sea ice is that our understanding of its behavior in a warming world is still quite nebulous compared to our understanding of NH sea ice behavior. Second understand that the see-sawing of temperatures and sea ice between hemisphere has been shown to occur during previous significant climatic change events so it is not unprecedented nor is it inconsistent with climatic shifts.

Anyway here are some things to consider...

  • The NH is characterized by ocean surrounded by land whereas the SH is land surrounded by ocean. This trivial fact accounts for the bulk of the differences between NH and SH sea ice behavior. The consequences of this can be quite dramatic and contradictory between the NH vs. SH.
  • A positive phase of the Southern Annular Mode (SAM) is associated with increasing SH sea ice. Global warming tips the SAM toward a positive phase.
  • ENSO negative/positive phases reinforce positive/negative SAM phases.
  • The Montreal Protocol through its ban of CFCs, repair of stratospheric ozone, associated cooling tendencies and other effects on weather patterns has been linked to SH sea ice increases.
  • Increasing GHGs actually have a cooling effect on the Antarctica continent itself especially during the SH winter when the upper atmosphere is often warmer than the surface. Remember, GHGs act like a thermal barrier preventing IR radiation from passing through. This causes the warm/cool side of the barrier to warm/cool further. Positive/negative lapse rates get more positive/negative. Antarctica often has a negative lapse rate during the winter so GHGs cause cooling at the surface and warming in the upper atmosphere. This effect (among others) suppresses polar amplification in the SH.

Disclaimer...I'm not well informed regarding SH sea ice so hopefully others who know more about the behavior down there can chime in on points I've missed or mischaracterized.

The main take away here is that sea ice is mainly a NH issue right now. Most scientists do not expect NH-style declines in sea ice down in the SH anytime soon. And the fact that the SH responds differently than the NH is probably more the rule than the exception. 

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It's complicated. First understand that this is not entirely unexpected. In fact, the IPCC AR5 WG1 prediction for SH sea ice, although significantly more uncertain than predictions for the NH, shows a slight preference for increases through about 2030 with the possibility of record highs persisting even through 2060 before things turn south (pun intended) down there too. I must caveat that by saying the uncertainty envelope does include the possibility of the secular decline starting around 2020 as well. The unfortunate state of affairs with SH sea ice is that our understanding of its behavior in a warming world is still quite nebulous compared to our understanding of NH sea ice behavior. Second understand that the see-sawing of temperatures and sea ice between hemisphere has been shown to occur during previous significant climatic change events so it is not unprecedented nor is it inconsistent with climatic shifts.

Anyway here are some things to consider...

  • The NH is characterized by ocean surrounded by land whereas the SH is land surrounded by ocean. This trivial fact accounts for the bulk of the differences between NH and SH sea ice behavior. The consequences of this can be quite dramatic and contradictory between the NH vs. SH.
  • A positive phase of the Southern Annular Mode (SAM) is associated with increasing SH sea ice. Global warming tips the SAM toward a positive phase.
  • ENSO negative/positive phases reinforce positive/negative SAM phases.
  • The Montreal Protocol through its ban of CFCs, repair of stratospheric ozone, associated cooling tendencies and other effects on weather patterns has been linked to SH sea ice increases.
  • Increasing GHGs actually have a cooling effect on the Antarctica continent itself especially during the SH winter when the upper atmosphere is often warmer than the surface. Remember, GHGs act like a thermal barrier preventing IR radiation from passing through. This causes the warm/cool side of the barrier to warm/cool further. Positive/negative lapse rates get more positive/negative. Antarctica often has a negative lapse rate during the winter so GHGs cause cooling at the surface and warming in the upper atmosphere. This effect (among others) suppresses polar amplification in the SH.
Disclaimer...I'm not well informed regarding SH sea ice so hopefully others who know more about the behavior down there can chime in on points I've missed or mischaracterized.

The main take away here is that sea ice is mainly a NH issue right now. Most scientists do not expect NH-style declines in sea ice down in the SH anytime soon. And the fact that the SH responds differently than the NH is probably more the rule than the exception. 

The Greenland ice sheet was the last to form so

It will be first to go. The Antarctic ice sheets where the first to form so will be last to go.

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5 hours ago, TriPol said:

Can someone tell me what the cause was of the Siberian heatwave this year? I've never seen anything like it before.

According to the best estimate from this study anthropogenic manipulation of the climate made the 2020 Siberean Heat Wave 100,000x more likely as compared to a purely natural evolution of the climate.

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On 11/1/2020 at 12:56 PM, bdgwx said:

It's complicated. First understand that this is not entirely unexpected. In fact, the IPCC AR5 WG1 prediction for SH sea ice, although significantly more uncertain than predictions for the NH, shows a slight preference for increases through about 2030 with the possibility of record highs persisting even through 2060 before things turn south (pun intended) down there too. I must caveat that by saying the uncertainty envelope does include the possibility of the secular decline starting around 2020 as well. The unfortunate state of affairs with SH sea ice is that our understanding of its behavior in a warming world is still quite nebulous compared to our understanding of NH sea ice behavior. Second understand that the see-sawing of temperatures and sea ice between hemisphere has been shown to occur during previous significant climatic change events so it is not unprecedented nor is it inconsistent with climatic shifts.

Anyway here are some things to consider...

  • The NH is characterized by ocean surrounded by land whereas the SH is land surrounded by ocean. This trivial fact accounts for the bulk of the differences between NH and SH sea ice behavior. The consequences of this can be quite dramatic and contradictory between the NH vs. SH.
  • A positive phase of the Southern Annular Mode (SAM) is associated with increasing SH sea ice. Global warming tips the SAM toward a positive phase.
  • ENSO negative/positive phases reinforce positive/negative SAM phases.
  • The Montreal Protocol through its ban of CFCs, repair of stratospheric ozone, associated cooling tendencies and other effects on weather patterns has been linked to SH sea ice increases.
  • Increasing GHGs actually have a cooling effect on the Antarctica continent itself especially during the SH winter when the upper atmosphere is often warmer than the surface. Remember, GHGs act like a thermal barrier preventing IR radiation from passing through. This causes the warm/cool side of the barrier to warm/cool further. Positive/negative lapse rates get more positive/negative. Antarctica often has a negative lapse rate during the winter so GHGs cause cooling at the surface and warming in the upper atmosphere. This effect (among others) suppresses polar amplification in the SH.

Disclaimer...I'm not well informed regarding SH sea ice so hopefully others who know more about the behavior down there can chime in on points I've missed or mischaracterized.

The main take away here is that sea ice is mainly a NH issue right now. Most scientists do not expect NH-style declines in sea ice down in the SH anytime soon. And the fact that the SH responds differently than the NH is probably more the rule than the exception. 

I'm not an expert either, but I did a class project on it last spring and that's basically what I found. The change in lapse rates thing is new to me, but it makes total sense.

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1 hour ago, lookingnorth said:

I'm not an expert either, but I did a class project on it last spring and that's basically what I found. The change in lapse rates thing is new to me, but it makes total sense.

Yeah. It's something that is counter intuitive at first, but once you understand exactly how the GHE works and the fact that Antarctica has a unique vertical temperature profile it's pretty obvious it has to be this way. Unfortunately the negative GHE in this isolated region has its limits and will likely turn positive in the future here as well.

Here is an interesting study that quantifies the effect. According to the authors most of the effect is actually attributed to water vapor which is a potent GHG itself. And it is the non-condensing GHGs (like CO2) that provide the secular nudge upward for water vapor concentration via the well known Clausius-Clapeyron lapse-rate feedback. 

https://www.nature.com/articles/s41612-018-0031-y

Of course I don't mean to imply that the negative GHE is the sole or even dominant reason for the SH's weak polar amplification. Obviously many other factors are involved here with the most obvious being the larger percentage of ocean coverage relative to the NH.

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On 11/2/2020 at 11:05 AM, TriPol said:

Can someone tell me what the cause was of the Siberian heatwave this year? I've never seen anything like it before.

Don recently posted a very informative paper on the topic.

https://www.nature.com/articles/s41598-020-71945-4

Extreme weather events in Asia have been occurring with increasing frequency as the globe warms in response to rising concentrations of greenhouse gases. Many of these events arise from weather regimes that persist over a region for days or even weeks, resulting in disruptive heatwaves, droughts, flooding, snowfalls, and cold spells. We investigate changes in the persistence of large-scale weather systems through a pattern-recognition approach based on daily 500 hPa geopotential height anomalies over the Asian continent. By tracking consecutive days that the atmosphere resides in a particular pattern, we identify long-duration events (LDEs), defined as lasting longer than three days, and measure their frequency of occurrence over time in each pattern. We find that regimes featuring positive height anomalies in high latitudes are occurring more often as the Arctic warms faster than mid-latitudes, both in the recent past and in model projections for the twenty-first century assuming unabated greenhouse gas emissions. The increased dominance of these patterns corresponds to a higher likelihood of LDEs, suggesting that persistent weather conditions will occur more frequently. By mapping observed temperature and precipitation extremes onto each atmospheric regime, we gain insight into the types of disruptive weather events that will become more prevalent as particular patterns become more common

 

Over Siberia they found a significant increase in the frequency and duration of warm spells and wet days, while central Asia saw more cold spells and wet days, and east Asia experienced more long wet spells. These results are consistent with an increased (decreased) prevalence of the pattern in node #1 (#12). They also found that warm, wet, and dry spells predominantly lengthened in most parts of Asia, suggesting a general increase in persistence. Another study14 analyzed output from several atmosphere-only models forced by sea-ice and ocean-temperature conditions consistent with a 2 °C warmer world. Similar to our results, they found significantly increased persistence of warm spells over northern and central Asia, as well as wet spells over northern and eastern Asia.

In addition to supporting previous findings, our study demonstrates an increasing frequency of persistent large-scale circulation regimes and associated extreme weather events, especially since the mid-1990s when AAW emerged as a clear signal. As greenhouse gases continue to accumulate in the atmosphere owing to ongoing human activities, we find that patterns characterized by warming in high latitudes will occur more frequently while cold-Arctic patterns will decline. A higher percentage of days/year in any one pattern will increase the likelihood of multiple consecutive days occurring in that pattern, leading to more frequent persistent conditions. Moreover, we demonstrate that the predominant warm-Arctic pattern also exhibits a higher probability of long LDEs occurring relative to days belonging in a node, thus further augmenting the likelihood of persistent weather events. Three of the climate models participating in CMIP5 agree that warm-Arctic patterns will increase several-fold by the end of the century at the expense of cold-Arctic patterns, suggesting a substantial rise in the frequency of persistent circulation regimes and their associated extreme weather. The connections with changes in jet-stream characteristics, such as blocking and other cut-off circulation features, will be addressed in future work.

 

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On 11/1/2020 at 11:56 AM, bdgwx said:

It's complicated. First understand that this is not entirely unexpected. In fact, the IPCC AR5 WG1 prediction for SH sea ice, although significantly more uncertain than predictions for the NH, shows a slight preference for increases through about 2030 with the possibility of record highs persisting even through 2060 before things turn south (pun intended) down there too. I must caveat that by saying the uncertainty envelope does include the possibility of the secular decline starting around 2020 as well. The unfortunate state of affairs with SH sea ice is that our understanding of its behavior in a warming world is still quite nebulous compared to our understanding of NH sea ice behavior. Second understand that the see-sawing of temperatures and sea ice between hemisphere has been shown to occur during previous significant climatic change events so it is not unprecedented nor is it inconsistent with climatic shifts.

Anyway here are some things to consider...

  • The NH is characterized by ocean surrounded by land whereas the SH is land surrounded by ocean. This trivial fact accounts for the bulk of the differences between NH and SH sea ice behavior. The consequences of this can be quite dramatic and contradictory between the NH vs. SH.
  • A positive phase of the Southern Annular Mode (SAM) is associated with increasing SH sea ice. Global warming tips the SAM toward a positive phase.
  • ENSO negative/positive phases reinforce positive/negative SAM phases.
  • The Montreal Protocol through its ban of CFCs, repair of stratospheric ozone, associated cooling tendencies and other effects on weather patterns has been linked to SH sea ice increases.
  • Increasing GHGs actually have a cooling effect on the Antarctica continent itself especially during the SH winter when the upper atmosphere is often warmer than the surface. Remember, GHGs act like a thermal barrier preventing IR radiation from passing through. This causes the warm/cool side of the barrier to warm/cool further. Positive/negative lapse rates get more positive/negative. Antarctica often has a negative lapse rate during the winter so GHGs cause cooling at the surface and warming in the upper atmosphere. This effect (among others) suppresses polar amplification in the SH.

Disclaimer...I'm not well informed regarding SH sea ice so hopefully others who know more about the behavior down there can chime in on points I've missed or mischaracterized.

The main take away here is that sea ice is mainly a NH issue right now. Most scientists do not expect NH-style declines in sea ice down in the SH anytime soon. And the fact that the SH responds differently than the NH is probably more the rule than the exception. 

One other point, if I am remembering correctly, is that SH sea ice is mostly controlled by winds. Temperature of course plays some role but the most important factor is wind and thus changes in winds can easily mask changes in temperature. The SH has warmed - regardless of whether there is more or less ice. But the warming has been less and is more easily masked by the important role winds play in the SH. In the NH, sea ice is less impacted by winds probably partially related to the surrounded by land vs surrounded by ocean point you made. And the warming is obviously much more extreme.

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