Jump to content
  • Member Statistics

    15,348
    Total Members
    7,904
    Most Online
    diamondtae
    Newest Member
    diamondtae
    Joined
ORH_wxman

Arctic Sea Ice Extent, Area, and Volume

Recommended Posts

18 hours ago, bdgwx said:

Hmm...I think there may still be some confusion here. When we say "forcing" we are talking about a perturbation or anomaly above or below a reference point. 

For example, a solar grand maximum might have +1.0 W/m2 of "forcing" relative to a long term average. A solar grand minimum might have -1.0 W/m2 of "forcing" relative to the same long term average.

Likewise, CO2 "forcing" is relative to a reference point. Typically we use the 280 ppm preindustrial concentration as the reference point.

There's actually a coincidental and rather convenient temporal alignment of these two reference points as a result of the Sun being midway between the Maunder Minimum and Modern Maximum just before the CO2 concentrations spiked up from 280 ppm.

A "forcing" in this context is a change. We aren't saying that the total effect of CO2 is more powerful than the total effect of the Sun. What we are saying is that the change in the CO2 effect is bigger than the change in the Sun effect today. So if the Sun goes -1.0 W/m2 and CO2 goes +2.0 W/m2 and all other things remain equal then the net effect is +1.0 W/m2. This is because the change in the CO2 effect was bigger than the change in the Sun effect.

Professor Valentina Zharkova recently gave a presentation and suggested at the worst of the GSM, the forcing loss could be as low as - 8.0 W/m2. 

Share this post


Link to post
Share on other sites
38 minutes ago, Fantom X said:

Professor Valentina Zharkova recently gave a presentation and suggested at the worst of the GSM, the forcing loss could be as low as - 8.0 W/m2. 

I believe this figure is in reference to TSI which is incident radiation normal to the beam angle. To get the integrated radiation over the entire Earth you have to multiple by Earth's cross sectional area. Conveniently the cross sectional area of a sphere is 1/4 the surface area. That means the power going into the geosphere is actually 1360 / 4  = 340 W/m2. So you need to take that -8.0 W/m2 and divide it by 4 as well. This gives us a normalized value of -2.0 W/m2 of force that's being applied. Note that Zharkova's super grand solar minimum claim is 4x the magnitude of the Maunder Minimum (a fact she acknowledges). So will this hypothetical Modern Minimum really be 4x as deep as the Maunder Minimum? Maybe. But, I'm not going to hold my breath. Furthermore, I believe this is the maximal effect. It's not the mean forcing you'd derive if you integrated the radiation reduction over the several decades in which the minimum is taking place. Remember, it will slope down on the entry and slope up on the exit. And of course, this in no way turns off the CO2 effect. It's persistent positive radiative forcing effect is still very much in play. And it will remain in play (unless we go to a negative CO2 emissions regime) for 100s or even 1000s of years easily outlasting this hypothetical grand minimum.

  • Thanks 1

Share this post


Link to post
Share on other sites

November mean extent came in at 9.81e6. This is lower than my estimation of 9.9e6 from my earlier post. Extents are hugging the lower interdecile range of the 1981-2010 average. Even assuming we hit the climatological average for December of 12.8e6 (I don't see how that's possible at this point) then 2018 will easily land in the top 5 lowest for annual mean extent. If December comes in at a more modest (but still high by recent standards) 12.4e6 then 2018 could make a run for the second lowest behind only 2016.

Share this post


Link to post
Share on other sites

I looked at the data this morning. Assuming I didn't miscalculate at the current pace 2018 is on track to have the 2nd lowest annual mean sea ice extent. The top 3 lowest would be 2016, 2018, and 2017.

Share this post


Link to post
Share on other sites

And combined SH and NH sea ice extents are now 2nd lowest. And aside from a couple of brief blips global sea ice has remained below 2σ from the mean for about 2.5 years now. And much of that time it was actually 3σ below the mean. 

YGAn701.png

  • Like 1

Share this post


Link to post
Share on other sites

The Antarctic season has been remarkably bad and is now dead last in both extent and by a large margin in area. It's also in considerably worse shape (concentration wise) than even 2016.

  • Like 1

Share this post


Link to post
Share on other sites
On 1/1/2019 at 12:15 PM, csnavywx said:

The Antarctic season has been remarkably bad and is now dead last in both extent and by a large margin in area. It's also in considerably worse shape (concentration wise) than even 2016.

I don't follow SH weather patterns. What do you think is the cause?

Share this post


Link to post
Share on other sites
14 hours ago, WidreMann said:

I don't follow SH weather patterns. What do you think is the cause?

Warmer temps, less clouds and unfavorable winds. The last 3 years have been pretty bad, but this one takes the cake with all of the early ponding and breakup.

Share this post


Link to post
Share on other sites

Preliminary numbers show that the annual mean extents for the NH finished second lowest behind 2016. SH was similar...it finished second lowest behind 2017. 

The SH is whole different beast, but the fact that we had 2018 end badly lends a bit of credence to the idea that 2017 may not have a fluke. I wonder if we're beginning to observe the paradigm shift down there too. Any thoughts csnavy?

Share this post


Link to post
Share on other sites
1 hour ago, bdgwx said:

Preliminary numbers show that the annual mean extents for the NH finished second lowest behind 2016. SH was similar...it finished second lowest behind 2017. 

The SH is whole different beast, but the fact that we had 2018 end badly lends a bit of credence to the idea that 2017 may not have a fluke. I wonder if we're beginning to observe the paradigm shift down there too. Any thoughts csnavy?

It could be the trapped heat finally reaching the surface.

https://www.carbonbrief.org/natural-ocean-fluctuations-help-explain-antarctic-sea-ice-changes/amp?__twitter_impression=true

 

There’s clearly an ocean component to this story, which this study seems to clarify. Assuming this theory is correct, we might expect to see a decrease in sea ice cover in coming years, as, eventually, enough heat builds up that it has to come to the surface and melt ice – combined with the impacts of human emissions.”

It is possible that this could explain why, during 2016, sea ice levels reached record lows, he adds:

“It’s intriguing to wonder whether this is what happened in 2016 when Antarctic sea ice suddenly dropped to record lows, but more work would be needed to state whether that was actually the case, or just due to an atmospheric anomaly.”

Although the overall magnitude of changes to ocean convection is not yet known, it is possible that the trapped heat could escape to the surface, Zhang says:

“The trapped heat can reach the sea surface and melt sea ice once the subsurface heat has accumulated to a strong enough degree.”

Share this post


Link to post
Share on other sites
3 hours ago, bdgwx said:

Preliminary numbers show that the annual mean extents for the NH finished second lowest behind 2016. SH was similar...it finished second lowest behind 2017. 

The SH is whole different beast, but the fact that we had 2018 end badly lends a bit of credence to the idea that 2017 may not have a fluke. I wonder if we're beginning to observe the paradigm shift down there too. Any thoughts csnavy?

It's possible we've turned the corner down in the SH, but it's hard to say with only 3 years. Some of the bad conditions this year are undoubtedly just weather. However, the reappearance of stronger deep convection (for example, -- Weddell Sea polynya -- after decades of absence) could mean that we're returning to a circulation regime less conducive to retaining sea ice in the melt season. A great deal of heat burial has taken place in the Southern Ocean over the past 20-30 years, so any relaxation of that pattern will of course allow some of that to resurface and augment the background GHG forcing.

Interestingly, this heat burial mechanism is occurring under the Arctic as well via transport from the Pacific through the Bering and under the Chukchi Sea into the CAB. It is also coming from the Atlantic via the Barents (where the intermediate warm layer has intensified rapidly and shoaled over time). Once that reaches critical mass (10-15 years), it too will surface and bite into the CAB.

Share this post


Link to post
Share on other sites

What is 'heat burial'?

I'd been under the impression that while polar waters were slightly below 0*C, deep ocean water was around 4*C, with the temperature falling as the depth increases in temperate/tropical waters. 

Am I off base?  Is there some paper that would help lay out the process in more detail?

Share this post


Link to post
Share on other sites

Diffusion of heat down the water column via mixing or and/or subduction under a vertical salinity gradient. Stronger winds will increase the depth of the mixed layer, bringing up colder intermediate and (in some cases) deep water to mix with near-surface waters, for instance. When combined with increased heat uptake due to GHG (and other) forcing, that causes said heat to be "buried" at depth, even though surface waters may cool. This can give the illusion that the extra heat is gone, but in reality, it has simply been mixed or subducted down. The situation can change if the circulation state (via natural variability or otherwise) changes, allowing some of that heat to effectively resurface.

 

Share this post


Link to post
Share on other sites
31 minutes ago, csnavywx said:

Diffusion of heat down the water column via mixing or and/or subduction under a vertical salinity gradient. Stronger winds will increase the depth of the mixed layer, bringing up colder intermediate and (in some cases) deep water to mix with near-surface waters, for instance. When combined with increased heat uptake due to GHG (and other) forcing, that causes said heat to be "buried" at depth, even though surface waters may cool. This can give the illusion that the extra heat is gone, but in reality, it has simply been mixed or subducted down. The situation can change if the circulation state (via natural variability or otherwise) changes, allowing some of that heat to effectively resurface.

 

The subduction you explain makes perfect sense. It is the heat surfacing that is puzzling.

Will not the water coming up from below still be somewhat colder than the surface water it displaces? So even if it is warmer than it was without the GHG effect, it would still continue to take up heat, only at a lesser rate.  

Is this a reasonable description of the expected effect?

Share this post


Link to post
Share on other sites

Since PIOMAS is unavailable due to the govt shutdown, here is the latest DMI volume.

image.thumb.png.97845bcecb58199f715f77b5f89fffea.png

 

Antarctic ice loss is slowing down after a rapid drop. It appears the remaining ice is mainly high concentration ice so the loss should level out fairly soon.

image.thumb.png.856c60d2865c31bae5363c8a2b691720.png

 

image.thumb.png.6eb85cd178a3dff5feeed0d6f6b7b7f5.png

Share this post


Link to post
Share on other sites

Rapidly receding Arctic Canada glaciers revealing landscapes continuously ice-covered for more than 40,000 years

Here we show that pre-Holocene radiocarbon dates on plants collected at the margins of 30 ice caps in Arctic Canada suggest those locations were continuously ice covered for > 40 kyr, but are now ice-free. We use in situ 14C inventories in rocks from nine locations to explore the possibility of brief exposure during the warm early Holocene. Modeling the evolution of in situ 14C confirms that Holocene exposure is unlikely at all but one of the sites. Viewed in the context of temperature records from Greenland ice cores, our results suggest that summer warmth of the past century exceeds now any century in ~115,000 years. 

https://www.nature.com/articles/s41467-019-08307-w

Share this post


Link to post
Share on other sites
On 1/27/2019 at 7:22 PM, chubbs said:

Rapidly receding Arctic Canada glaciers revealing landscapes continuously ice-covered for more than 40,000 years

Here we show that pre-Holocene radiocarbon dates on plants collected at the margins of 30 ice caps in Arctic Canada suggest those locations were continuously ice covered for > 40 kyr, but are now ice-free. We use in situ 14C inventories in rocks from nine locations to explore the possibility of brief exposure during the warm early Holocene. Modeling the evolution of in situ 14C confirms that Holocene exposure is unlikely at all but one of the sites. Viewed in the context of temperature records from Greenland ice cores, our results suggest that summer warmth of the past century exceeds now any century in ~115,000 years. 

https://www.nature.com/articles/s41467-019-08307-w

Warmth. Around 130,000-110,000 years ago (the Eemian interglacial), the Earth's climates were generally much like those of today, though somewhat warmer and moister in many regions. The climate record derived from long ice cores taken through the Greenland ice cap suggested that the warm climate of the Eemian might have been punctuated by many sudden and fairly short-lived cold phases, but these results are now thought of as inaccurate because the lower layers of the ice sheet have become buckled and jumbled up. However, at least one major cold and dry event during the Eemian seems to be corroborated by the terrestrial pollen record from Europe and China

Share this post


Link to post
Share on other sites

https://mobile.twitter.com/ajatnuvuk/status/1093786714022105088

It’s February, the coldest month of the year. We have open water in front of Utqiagvik. It is 30 F out at 11:20 at night. Strange days indeed.

https://mobile.twitter.com/AlaskaWx/status/1094296276730925056

Incredible warmth on the North Slope Friday, with temperatures in most places 30 to 50F (18-28C) above the daily normal!

https://mobile.twitter.com/AlaskaWx/status/1094017492580655105

MODIS image from Friday afternoon courtesy

showing impacts on #seaice in the northern Bering & southern Chukchi Seas of recent mild, stormy weather. A lot of water showing up, even significant areas north of the Bering Strait.

 

 

  • Sad 1

Share this post


Link to post
Share on other sites

This is a thread focused on the Arctic region, but it's the Antarctic behavior that's most striking. There was a transition from record highs in 2013, 2014, and 2015 to record lows in 2016, 2017, and 2018. It almost seems like a fluke. I'm wondering if we won't see a reversion to the mean in the next few years. In looking at the IPCC predictions from model simulations there was an expectation that Antarctic sea ice extents would hold steady and perhaps even increase ever so slightly through 2025.

Arctic sea ice is behaving about as expected. I realize the IPCC has underestimated the magnitude of the decline, but at least the general trend (downward) has been correct. The trend could even tolerate a sizable jump at this point perhaps even up to 2008/2013 levels. 

OXO2Yvz.jpg&key=faecc15097d1354a8983fe86f15ad5eecb78ec8f43fd4dd091b3d397b817f92a

 

 

 

Share this post


Link to post
Share on other sites
On 2/12/2019 at 11:58 PM, bdgwx said:

This is a thread focused on the Arctic region, but it's the Antarctic behavior that's most striking. There was a transition from record highs in 2013, 2014, and 2015 to record lows in 2016, 2017, and 2018. It almost seems like a fluke. I'm wondering if we won't see a reversion to the mean in the next few years. In looking at the IPCC predictions from model simulations there was an expectation that Antarctic sea ice extents would hold steady and perhaps even increase ever so slightly through 2025.

Arctic sea ice is behaving about as expected. I realize the IPCC has underestimated the magnitude of the decline, but at least the general trend (downward) has been correct. The trend could even tolerate a sizable jump at this point perhaps even up to 2008/2013 levels.

 

 

 

Antarctic sea ice has large natural variability. Here are a couple of speculations: 1) I don't recall the details but one paper flagged the the large nino in 2015/16. For sea ice the timing does line-up, 2) The antarctic ozone hole is slowly recovering this would tend to weaken winds and produce warming, both of which will reduce sea ice extent 3) Antarctica warming lags because of the deep ocean nearby which is slow to warm. as time proceeds though Antarctica will catch-up. 

Per the chart below, the south pole has also warmed in the past decade in a way that doesn't match enso, so it is likely more than just enso.

southpoletemps.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×