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jai mitchell

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AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« on: October 19, 2015, 02:15:14 PM »
Something I have been thinking about lately, It seems that the increased freshwater supply from Greenland and (I presume) early snowmelt of the northern hemisphere is currently impacting the AMOC, causing a measured 33% slowdown (or so) over the last 5 years.

This trend is obviously going to continue in strength as the arctic moves to a september ice free condition.

However, once it does, and the arctic becomes Ice free.  What will be the impacts on the AMOC during the next re-freeze period?  Significant volumes of latent heat will be extracted, much warmer sea surface temperatures, increased melt rates in Greenland during that previous melt season.  .  .

many changes that will both inhibit the Overturning circulation and will also act to strengthen it.

I am currently of the opinion that the year we have full Arctic Sea Ice loss will be the year that the AMOC goes to about 20% of the 1980 median.  And that the refreeze period will still have so much freshening that it will not be able to create enough increase in overturning to restart the AMOC, this will lead to semi-permanent (multi-decadal) shifts in the atlantic basin currents (strengthening of the Atlantic Gyre) which will then produce a complete shutdown of the AMOC (probably by 2019 but no later than 2025) with a resultant Sea Level Rise of 80cm on the U.S. Eastern Seaboard.

But I am still thinking about it. . .
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Timothy Astin

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #1 on: October 19, 2015, 10:07:33 PM »
Hansen has some interesting things to say about the slowing of AMOC. See within

http://www.columbia.edu/~jeh1/mailings/2015/20151012_IceMeltPredictions.pdf

While he expects slowing to be faster than predictied by models, and he predicts "almost surely" shutdown under the current forcing trajectory, he doesn't support your timeframe, referring to "slowdown ... becoming clearer in coming decades"


jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #2 on: October 20, 2015, 02:00:50 PM »
Thanks Timothy, The reason I believe the above is because it is already happening with a measurement of 30% reduction in AMOC in the last 5 years.

From 6 days ago
http://onlinelibrary.wiley.com/doi/10.1002/2015GL065730/full

Concerns about North Atlantic Meridional Overturning Circulation (NAMOC) changes imply the need for a continuous, large-scale observation capability to detect changes on interannual to decadal time scales. Here we present the first measurements of Lower North Atlantic Deep Water (LNADW) transport changes using only time-variable gravity observations from Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 until now. Improved monthly gravity field retrievals allow the detection of North Atlantic interannual bottom pressure anomalies and LNADW transport estimates that are in good agreement with those from the Rapid Climate Change-Meridional Overturning Circulation and Heatflux Array (RAPID/MOCHA). Concurrent with the observed AMOC transport anomalies from late 2009 through early 2010, GRACE measured ocean bottom pressures changes in the 3000–5000 m deep western North Atlantic on the order of 20 mm-H2O (200 Pa), implying a southward volume transport anomaly in that layer of approximately −5.5 sverdrup. Our results highlight the efficacy of space gravimetry for observing AMOC variations to evaluate latitudinal coherency and long-term variability.

---------
-5.5Sv = ~30% of 1980 estimated flowrate
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AbruptSLR

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #3 on: October 20, 2015, 05:13:07 PM »
The linked article confirms that the change in AMOC exceeds the natural variability; however, there is a disagreement in the scientific community about how much weight to give to natural vs anthropogenic factors:

http://www.washingtonpost.com/news/energy-environment/wp/2015/09/30/everything-you-need-to-know-about-the-cold-blob-in-the-north-atlantic-ocean/


Extract: "The disagreement turns on how much weight to give to the different factors in explaining what we’re currently seeing. “My assessment is the component due to natural variability is much larger than what we’re seeing from global warming,”  says Tom Delworth, a researcher at NOAA’s Geophysical Fluid Dynamics Laboratory in Princeton, NJ, at least on the time scale of one or more decades. But Delworth agrees that in the long term, global warming should slow the circulation.

In particular, Delworth mentioned two related sources of natural variability — the so-called “North Atlantic Oscillation,” which refers to variability in winds and pressures over the Atlantic, and the “Atlantic Multidecadal Oscillation,” or AMO, which refers to changes in sea-surface temperatures.

But Mann disagrees that the AMO can account for what we’re seeing right now. Noting that he originally coined the term, he adds by email:


The AMO displays a completely different pattern of sea surface temperatures in the Atlantic as my collaborators and I have shown in past work, and the AMO doesn’t exhibit a long-term decline over the past century, which this particular pattern does.

And another team of researchers also would appear to agree with Mann and Rahmstorf."
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Bruce Steele

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #4 on: October 20, 2015, 05:22:17 PM »
In this Brix Gerges 2003 paper they describe a semiannual hemispheric seesaw between flow rates of AABW and LNADW. If on the other hand there has been a 5.5Sv drop in the LNADW and also a 8.2 +\- 2.6Sv drop in AABW ( Purkey and Johnson 2012 ) then something other than a seesaw is occurring.
 I am just pointing out an inconsistency between the described theory of a hemispheric seesaw effect and measured flow rates. Maybe someone could resolve this problem for me. 
    
http://web.atmos.ucla.edu/~gruber/publication/pdf_files/brix_gerdes_jgr_03.pdf


jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #5 on: October 21, 2015, 01:48:52 AM »
Bruce,
your 2002 model of wind pattern shifts on NADW has very little to do with this:

first image:August 2010

second image: August 2015
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bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #6 on: October 21, 2015, 11:34:46 PM »
could this be directly related to AMOC slowdown? Through the mid-90s would assume it was our old relatively stable climate, marked decline showed as warming continued while AMOC slowdown was just getting started through ~2010, then since....


bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #7 on: October 23, 2015, 04:42:52 AM »
This October is likely to have the highest NHEM snowcover on record (or come in 2nd behind 1976).


jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #8 on: October 23, 2015, 12:57:46 PM »
bb

Yes, that is a good point, as the earth warms, increases in snowcover during the winter months and earlier spring snowcover losses leads to much more freshwater in the critical north atlantic basin, not sure how this compares to greenland melt though. 

compare
northern hemisphere snow cover anomalies for February

http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=2

Vs.

Northern hemisphere snow cover anomalies for may

http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=5
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bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #9 on: October 26, 2015, 06:57:06 AM »
jai, i agree. but i think that people may be misunderstanding the Hansen study (or perhaps it's because he does not explicitly come out and say what the data really means).

i think that if the anomalies he depicts turn out to verify, we may currently be in the beginning phase of a new glaciation that will rapidly kick into high gear over the next few years. the initial area this seems to be occurring in appears to be Quebec, but soon it will also be the UK, and other areas most dependent on AMOC heat transport.

see, while wintertime temps may still warm somewhat, it's spring/summer that are most affected by AMOC slowdown. and with all the extra moisture in the air, that means that a much larger chunk of the year becomes conducive to snowpack growth.

so while at the moment we still see everything melt year in and out, i anticipate this may soon change.

i think another thing that has not been explored properly is what happens to the polar cell as AGW accelerates. and this also ties in directly to arctic ice loss. if you look at the maps even this year, it's clear that cold airmasses are now generated from land-based snowcover, and their passage over the Arctic Ocean is how it cools/ices over.

so what happens as AMOC slowdown accelerates while summer arctic sea ice continues to decline?

i am beginning to wonder if the earth's natural reset mechanism kicks in at the point when the CAB becomes ice-free, which would potentially act to split the polar cell in two as the NHEM enters the fall season. what does this entail...?

well, since the generation of cold airmasses is not actually dependent on the Arctic Ocean, and due to the fact that peripheral seas are faster to refreeze, it would seem to me that once this happens, it "confines" the cold to the landmasses vs. the oceans (in general -- or at least encourages their "residency" over both Eurasia and North America). and because the cell splits, Greenland actually becomes a cold air source for North America.

i believe it has been shown that Hudson Bay was the origin of the Laurentian ice sheet. and this makes sense for the above reason: if the ocean warms enough to the point where the polar cell splits in two, and Greenland then becomes a cold air source for North America (versus spilling cold air all across the Arctic Ocean/Eurasia), then Hudson Bay/Davis Straits become a natural location for the Polar Vortex, with the additional water vapor in the atmosphere acting as a ++++modifier for snowfall.

so basically, with heat transport to Quebec/Hudson Bay partially broken down due to AMOC slowdown, they become prime areas for vast amounts of snowfall/ice to accumulate, eventually linking with Greenland. and as snowpack keeps getting more and more impressive in these regions even in spite of general warming (since "warmth" is fine as long as temps stay below 32 -- and when you average 0-10deg F in winter, even a +10 monthly anomaly is actually a boon for snow), we see additional AMOC slowdown each yr as the amount of melt increases with snowpack.

eventually this hits a point (and I think we're close) where snowpack is retained through the summer.... and then from there, things get nasty.

(i don't know whether the above is likely at all and i know it sounds crazy but perhaps it is a natural mechanism & explains why the earth suddenly enters ice ages so often? ultimately it comes down to an ice-free arctic ocean...)

i would also add that the ice-free CAB becomes a major source for cyclones that eventually deposit even more prolific amounts of snow over far nrn latitudes than we currently see. and you end up with storms tracking along both the Eurasian Arctic Coast, and the North American Arctic Coast as seasons turn from summer into fall... further accelerating the process.

the below graphic is a crude description of this crazy idea (which could be just insane ramblings). the ferrell cell ends up displaced into the Arctic Ocean/colder northern oceans, the Hadley Cells expand somewhat, and the Polar Cell splits.
« Last Edit: October 26, 2015, 09:05:41 AM by bbr2314 »

johnm33

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #10 on: October 26, 2015, 02:21:01 PM »
bbr2314 I've been having similar thoughts, except in my scenario the 3 cells collapse to 1, and then the prevailing winds blow to the south and west. After a chaotic period the remaining NAD gets pushed against the east coast of Greenland through Fram and then into the CAB. So lots of rain on Greenland, and an ice free north CAA. The warm current bathes eastern Siberia giving it a permanent spring climate. The fresh waters flowing into the Arctic, from Siberia, are pushed west, by prevailing winds, and emerge into the north Atlantic around Britain plunging it into permanent winter, with the North sea frozen over for much of the year. Pacific waters continue to flow in and carry most of the fresher waters, from Alaskan and Canadian rivers, with them through the CAA. Lots more snow to the west of Greenland/Baffin/Hudson and in Europe to the west of the Urals and on the northern slopes of the Pyrenees/Alps/Carpathians. So two cold 'poles' to make the weather interesting.

bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #11 on: October 27, 2015, 02:23:46 PM »
bbr2314 I've been having similar thoughts, except in my scenario the 3 cells collapse to 1, and then the prevailing winds blow to the south and west. After a chaotic period the remaining NAD gets pushed against the east coast of Greenland through Fram and then into the CAB. So lots of rain on Greenland, and an ice free north CAA. The warm current bathes eastern Siberia giving it a permanent spring climate. The fresh waters flowing into the Arctic, from Siberia, are pushed west, by prevailing winds, and emerge into the north Atlantic around Britain plunging it into permanent winter, with the North sea frozen over for much of the year. Pacific waters continue to flow in and carry most of the fresher waters, from Alaskan and Canadian rivers, with them through the CAA. Lots more snow to the west of Greenland/Baffin/Hudson and in Europe to the west of the Urals and on the northern slopes of the Pyrenees/Alps/Carpathians. So two cold 'poles' to make the weather interesting.

that might make more sense than mine, but glad to see we both came to the same conclusion independently... even though it is a bad conclusion if it is legitimate...

would you mind diagramming out what you described? also, i would assume the single-cell configuration would not preclude wintertime/spring cold in areas not under Greenland/AMOC-slowdown influence?

jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #12 on: October 27, 2015, 10:01:17 PM »
I find the idea of a perpetually frozen north sea very implausible with the projected warming of the arctic based on locked in AGW and the reduction in aerosols.  The arctic amplification work will prevent this from occurring.  In addition, the slowdown in the AMOC appears to be based primarily on increased meltrate from Greenland.  If this process is reduced then the AMOC will not be impacted. 

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #13 on: October 27, 2015, 10:36:06 PM »
bbr2314 when I have time I'll try the diagram meanwhile [esp slide 26]
http://slideonline.com/presentation/6848-hadley-cell-expansion-langford-pdf
I think winter would be confined to areas where snow and ice can accumulate.
jai, much of the year not all, somewhat like Hudson bay.

wili

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #14 on: November 05, 2015, 04:53:44 PM »
They seem to now have a better measure of just how much the AMOC has slowed:

5.5 sverdrups!

That is a mind-blowing number! Each Sv is about equal to the flow of all rivers on earth into the sea.

https://www.washingtonpost.com/news/energy-environment/wp/2015/11/04/nasa-can-now-detect-worrying-ocean-circulation-changes-from-space/?sf
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bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #15 on: November 06, 2015, 08:35:18 PM »
I noticed that SSH anomalies spiked dramatically over Hudson Bay in both September and early October (per GODAS on Nasa's site). This was not accompanied by an increase in SSTs, rather it seems it caused a plunge.

I suspect that a secondary manifestation of AMOC slowdown is now playing out up north. The freshwater pulse has resulted in the highest sea ice in the region since the volcanism-tinged years of 1983 and 1992. And this is after sea ice had fallen off nearly completely (until mid-November in HB/surrounding areas) since about 1999 (since then, the only other year that comes close is... wait for it.... 2009).

The cold SSTAs are also independent of corresponding surface temp anomalies that would justify their magnitude.

jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #16 on: November 07, 2015, 07:54:19 PM »
SSH = Sea Surface Height?
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bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #17 on: November 07, 2015, 08:47:29 PM »

johnm33

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #18 on: February 03, 2016, 08:13:30 PM »
Can't spot a better place for this, no slowdown in AMOC
 http://www.sciencedirect.com/science/article/pii/S246801331500008X
Abstract

The Atlantic Meridional Overturning Circulation (AMOC) is part of the great ocean “conveyor belt” that circulates heat around the globe. Since the early 2000s, ocean sensors have started to monitor the AMOC, but the measurements are still far from accurate and the time window does not permit the separation of short term variability from a longer term trend. Other works have claimed that global warming is slowing down the AMOC, based on models and proxies of temperatures. Some other observations demonstrate a stable circulation of the oceans. By using tide gauge data complementing recent satellite and ocean sensor observations, the stability of the AMOC is shown to go back to 1860. It is concluded that no available information has the due accuracy and time coverage to show a clear trend outside the inter-annual and multi-decadal variability in the direction of increasing or decreasing strength over the last decades

Jim Hunt

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #19 on: February 03, 2016, 08:29:20 PM »
However Stefan Rahmstorf still seems to be of the opinion that the AMOC is slowing down:

http://www.realclimate.org/index.php/archives/2016/01/blizzard-jonas-and-the-slowdown-of-the-gulf-stream-system/
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A-Team

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #20 on: February 03, 2016, 09:29:17 PM »
Quote
no slowdown in AMOC
The two Australian authors actually say something quite different, that a slowdown hasn't yet been proven because there is too much background from natural variability. You could say the same thing about their assertion of stability for the AMOC, there's been too much slowdown to prove that it's stable.

Meanwhile, no one has brought up this paper for comment from Stefan Rahmstorf in that Real Climate article (Jim H?). He writes

Quote
Dima and Lohmann concluded that the patterns shown in Fig. 1 and Fig. 2 indicate a change in the AMOC, and they wrote: "The global conveyor has been weakening since the late 1930s."

As a side remark, the IPCC in its last report ignored this result [Dima and Lohmann 2010] and claimed, rather puzzling to me, that there is no evidence for an AMOC slowdown.
M. Dima, and G. Lohmann, "Evidence for Two Distinct Modes of Large-Scale Ocean Circulation Changes over the Last Century", Journal of Climate, vol. 23, pp. 5-16, 2010.
http://journals.ametsoc.org/doi/pdf/10.1175/2009JCLI2867.1 free full text

A-Team

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #21 on: February 04, 2016, 02:32:15 PM »
This article in #18  is not worth our time.

Always a good idea to do a google search on author name: try "albert parker climate denial" (recent name change from Alberto Boretti). He is an automotive engineer formerly with Fiat with a long association with climate rubbish, his motivatlion is unclear.

Here are some other papers he has planted in low impact journals:

https://www.researchgate.net/researcher/2033830937_Albert_Parker

There is sometimes value in devil's advocate writings. However in situations when it is insincere, dishonest, hopelessly ill-informed, ignorant of a large pile of previous papers, sponsored by a coal company or a Murdoch venture, or just a manifestation of mental illness, scientists who work in this field might be forgiven for not paying the slightest attention.

More interesting to me is what this says about these journals and the integrity of their editor and peer review processes. Surely they knew the whole history in this instance without  a 5 second google. Yet there are financial pressures in publishing to get enough articles for an issue, the matter of $3k in author fees and even more paid here for open access, and benefits even to getting the journal name trashed (as it elevates the profile).
« Last Edit: February 04, 2016, 06:23:20 PM by A-Team »

johnm33

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #22 on: February 06, 2016, 01:51:38 AM »
To some extent this http://www.nature.com/ncomms/2016/160122/ncomms10525/full/ncomms10525.html?platform=hootsuite addresses the flow through the CAA, and this http://onlinelibrary.wiley.com/doi/10.1002/grl.50532/full the potential impact of eddies.
   Just from eyeballing Hycom I get the impression that there's an increase in the flow through the CAA. It's not just the increased flow that's relevent but the loss of thick ice at the gateways [especially Banks/Mainland] allows a less saline fraction to pass. Unlike the Greenland sea there's no countercurrent so this water being forced south all shares a similar energetic potential. When it passes into the Labrador sea it's inertia, relative to the rotational speed of the planet, forces it against the coast, which it hugs down as far as Cape Hatteras where it's finally forced to detatch because south of that there's the gulf stream equally inert and coast hugging. Here the two oppositely energised flows are forced out into the ocean creating huge eddies where for want of a better word the various fractions of energetic potential and salinities are refined into layers, eventually, and drift east. The resolution of these opposing energetic differences causes a slowdown of the north atlantic current and backs up the gulf stream and the current from the north. This may or may not have any effect on the saline sinks in Labrador and the Greenland sea/ Denmark strait. What it will do is cover the north atlantic with cool water inhibiting evaporative cooling, and deliver warmer water into the arctic slower and later.

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #23 on: February 11, 2016, 04:16:02 PM »
The linked reference discusses the recent changes in the North Atlantic heat budget & circulation patterns:

R. Somavilla, C. González-Pola, U. Schauer & G. Budéus (2016), "Mid-2000s North Atlantic shift: Heat budget and circulation changes", Geophysical Research Letters, DOI: 10.1002/2015GL067254

http://onlinelibrary.wiley.com/doi/10.1002/2015GL067254/abstract

Abstract: "Prior to the 2000s, the North Atlantic was the basin showing the greatest warming. However, since the mid-2000s during the so-called global warming hiatus, large amounts of heat were transferred in this basin from upper to deeper levels while the dominance in terms of atmospheric heat capture moved into the Indo-Pacific. Here, we show that a large transformation of modal waters in the eastern North Atlantic (ENA) played a crucial role in such contrasting behavior. First, strong winter mixing in 2005 transformed ENA modal waters into a much saltier, warmer, and denser variety, transferring upper ocean heat and salt gained slowly over time to deeper layers. The new denser waters also altered the zonal dynamic height gradient reversing the southward regional flow and enhancing the access of saltier southern waters to higher latitudes. Then, the excess salinity in nothern regions favored additional heat injection through deep convection events in later years."
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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #24 on: February 21, 2016, 02:18:31 AM »
DOI: 10.1038/srep20535

open access

I apologize if this paper has already been discussed. I just reread this paper more carefully, and I wonder if there is an insight here to the cold spot south of Greenland that we see today and of course the relentless decline of nothern sea ice. Fig 4 is good and fig 5 (attached) is yet more convincing.

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #25 on: February 22, 2016, 07:42:04 PM »
I cannot say whether the assumptions made in the linked reference are reasonable, or not; but if they are then in the coming century AMO variability will be a significant factor in the projected global mean temperature variability to 2100:

Petr Chylek, James D. Klett, Manvendra K. Dubey & Nicolas Hengartner (20 February 2016), "The role of Atlantic Multi-decadal Oscillation in the global mean temperature variability", Climate Dynamics, pp 1-9, DOI: 10.1007/s00382-016-3025-7


http://link.springer.com/article/10.1007%2Fs00382-016-3025-7

Abstract: "The global mean 1900–2015 warming simulated by 42 Coupled Models Inter-comparison Project, phase 5 (CMIP5) climate models varies between 0.58 and 1.70 °C. The observed warming according to the NASA GISS temperature analysis is 0.95 °C with a 1200 km smoothing radius, or 0.86 °C with a 250 km smoothing radius. The projection of the future 2015–2100 global warming under a moderate increase of anthropogenic radiative forcing (RCP4.5 scenario) by individual models is between 0.7 and 2.3 °C. The CMIP5 climate models agree that the future climate will be warmer; however, there is little consensus as to how large the warming will be (reflected by an uncertainty of over a factor of three). A parsimonious statistical regression model with just three explanatory variables [anthropogenic radiative forcing due to greenhouse gases and aerosols (GHGA), solar variability, and the Atlantic Multi-decadal Oscillation (AMO) index] accounts for over 95 % of the observed 1900–2015 temperature variance. This statistical regression model reproduces very accurately the past warming (0.96 °C compared to the observed 0.95 °C) and projects the future 2015–2100 warming to be around 0.95 °C (with the IPCC 2013 suggested RCP4.5 radiative forcing and an assumed cyclic AMO behavior). The AMO contribution to the 1970–2005 warming was between 0.13 and 0.20 °C (depending on which AMO index is used) compared to the GHGA contribution of 0.49–0.58 °C. During the twenty-first century AMO cycle the AMO contribution is projected to remain the same (0.13–0.20 °C), while the GHGA contribution is expected to decrease to 0.21–0.25 °C due to the levelling off of the GHGA radiative forcing that is assumed according to the RCP4.5 scenario. Thus the anthropogenic contribution and natural variability are expected to contribute about equally to the anticipated global warming during the second half of the twenty-first century for the RCP4.5 trajectory."
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sidd

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #26 on: February 22, 2016, 10:04:08 PM »
I would be wary of Chylek, a cursory search would reveal my reasons.

The paper by Pedro et al. this year (with both Steig and Rasmussen as co authors) referred to elsewhere has an interesting mode of Southern variablity, which I venture is connected to the phenomena described in the Rasmussen paper. The articles are

Pedro(2016) doi: 10.1002/2016GL067861
Rasmussen(2016) doi: 10.1038/srep20535

johnm33

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #27 on: March 02, 2016, 07:17:35 PM »
RS post on what may be the new normal for the UK http://robertscribbler.com/2016/03/02/gale-after-gale-after-gale-dumped-two-and-a-half-feet-of-rain-upon-scotland-and-wales-this-winter/#comments   
I'm not in the worst affected areas by any means but last sept. I laid some paving and set up a water butt, about 300lts. it's brim full now and I still haven't got around to connecting it to the downpipe.

AbruptSLR

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #28 on: March 08, 2016, 04:51:13 PM »
The linked (open access) reference uses computer models to address the effect of low ancient greenhouse climate temperature gradients (poles to Equator) on the ocean's overturning circulation, and they find that that effect is less than previously expected.  However, I doubt that the computer models used adequately accounted for the hosing effect of abrupt ice sheet mass loss on ocean density gradients that clearly do have a strong influence of ocean over-turning currents (ala Hansen et al (draft 2015, final 2016 in-press)):

Sijp, W. P. and England, M. H.: The effect of low ancient greenhouse climate temperature gradients on the ocean's overturning circulation, Clim. Past, 12, 543-552, doi:10.5194/cp-12-543-2016, 2016.


http://www.clim-past.net/12/543/2016/

Abstract. We examine whether the reduced meridional temperature gradients of past greenhouse climates might have reduced oceanic overturning, leading to a more quiescent subsurface ocean. A substantial reduction of the pole-to-Equator temperature difference is achieved in a coupled climate model via an altered radiative balance in the atmosphere. Contrary to expectations, we find that the meridional overturning circulation and deep ocean kinetic energy remain relatively unaffected. Reducing the wind strength also has remarkably little effect on the overturning. Instead, overturning strength depends on deep ocean density gradients, which remain relatively unaffected by the surface changes, despite an overall decrease in ocean density. Ocean poleward heat transport is significantly reduced only in the Northern Hemisphere, as now the circulation operates across a reduced temperature gradient, suggesting a sensitivity of Northern Hemisphere heat transport in greenhouse climates to the overturning circulation. These results indicate that climate models of the greenhouse climate during the Cretaceous and early Paleogene may yield a reasonable overturning circulation, despite failing to fully reproduce the extremely reduced temperature gradients of those time periods.
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bbr2314

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #29 on: October 21, 2016, 09:54:31 AM »
jai, i agree. but i think that people may be misunderstanding the Hansen study (or perhaps it's because he does not explicitly come out and say what the data really means).

i think that if the anomalies he depicts turn out to verify, we may currently be in the beginning phase of a new glaciation that will rapidly kick into high gear over the next few years. the initial area this seems to be occurring in appears to be Quebec, but soon it will also be the UK, and other areas most dependent on AMOC heat transport.

see, while wintertime temps may still warm somewhat, it's spring/summer that are most affected by AMOC slowdown. and with all the extra moisture in the air, that means that a much larger chunk of the year becomes conducive to snowpack growth.

so while at the moment we still see everything melt year in and out, i anticipate this may soon change.

i think another thing that has not been explored properly is what happens to the polar cell as AGW accelerates. and this also ties in directly to arctic ice loss. if you look at the maps even this year, it's clear that cold airmasses are now generated from land-based snowcover, and their passage over the Arctic Ocean is how it cools/ices over.

so what happens as AMOC slowdown accelerates while summer arctic sea ice continues to decline?

i am beginning to wonder if the earth's natural reset mechanism kicks in at the point when the CAB becomes ice-free, which would potentially act to split the polar cell in two as the NHEM enters the fall season. what does this entail...?

well, since the generation of cold airmasses is not actually dependent on the Arctic Ocean, and due to the fact that peripheral seas are faster to refreeze, it would seem to me that once this happens, it "confines" the cold to the landmasses vs. the oceans (in general -- or at least encourages their "residency" over both Eurasia and North America). and because the cell splits, Greenland actually becomes a cold air source for North America.

i believe it has been shown that Hudson Bay was the origin of the Laurentian ice sheet. and this makes sense for the above reason: if the ocean warms enough to the point where the polar cell splits in two, and Greenland then becomes a cold air source for North America (versus spilling cold air all across the Arctic Ocean/Eurasia), then Hudson Bay/Davis Straits become a natural location for the Polar Vortex, with the additional water vapor in the atmosphere acting as a ++++modifier for snowfall.

so basically, with heat transport to Quebec/Hudson Bay partially broken down due to AMOC slowdown, they become prime areas for vast amounts of snowfall/ice to accumulate, eventually linking with Greenland. and as snowpack keeps getting more and more impressive in these regions even in spite of general warming (since "warmth" is fine as long as temps stay below 32 -- and when you average 0-10deg F in winter, even a +10 monthly anomaly is actually a boon for snow), we see additional AMOC slowdown each yr as the amount of melt increases with snowpack.

eventually this hits a point (and I think we're close) where snowpack is retained through the summer.... and then from there, things get nasty.

(i don't know whether the above is likely at all and i know it sounds crazy but perhaps it is a natural mechanism & explains why the earth suddenly enters ice ages so often? ultimately it comes down to an ice-free arctic ocean...)

i would also add that the ice-free CAB becomes a major source for cyclones that eventually deposit even more prolific amounts of snow over far nrn latitudes than we currently see. and you end up with storms tracking along both the Eurasian Arctic Coast, and the North American Arctic Coast as seasons turn from summer into fall... further accelerating the process.

the below graphic is a crude description of this crazy idea (which could be just insane ramblings). the ferrell cell ends up displaced into the Arctic Ocean/colder northern oceans, the Hadley Cells expand somewhat, and the Polar Cell splits.

yikes




johnm33

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #30 on: October 27, 2016, 11:55:23 AM »
I think we may be watching the transition, the north atlantic waters, where they fall into St.Anna trough turn right. Some portion is recycled on the atlantic side of Lomonosov but a large fraction pushes through to the pacific side. I'm thinking that the dynamics there prevent most of it pushing further east, it can't displace the denser basal water present, nor can it prevent the ingress of fresher water from Siberia. The line of least resistence is back towards greenland on the pacific side of lomonosov.



When that water reaches greenland we'll see rapid melt of the north east, meanwhile it inhibits ice thickness and is pushing out the freshest fraction of Beaufort waters through CAA. How long into the season will the Atlantic waters continue to flow? because whilst they do we may see little thickness growth on the NSI side of the CAB, and the ice will be at the mercy of the winds. That means more disturbance of basal waters, which wont improve the ices condition.
 The longer the fresh[ish] water flows through the CAB the greater the build-up in Hudson, and apart from the leaky bellows effect of Baffin tides there are no sources of heat to inhibit the freeze there.

budmantis

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #31 on: October 27, 2016, 02:35:05 PM »

yikes


Is this the same theory you recently brought up in the 2016/2017 refreezing thread? Don't know if it will happen, but it sure sounds plausible. Great stuff BBR!

jai mitchell

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Re: AMOC Behaviour Post Arctic Sea-Ice Free Conditions
« Reply #32 on: October 27, 2016, 05:59:07 PM »
Quote
i think that if the anomalies he depicts turn out to verify, we may currently be in the beginning phase of a new glaciation that will rapidly kick into high gear over the next few years.

this isn't really a possibility since anthropogenic GHG forcing levels would have to drop by over 2/3 to get to a point where glacial nucleation could begin to start again.

having increases in early fall snowcover anomalies has absolutely no significance to future climate states when these increases are paired every year with earlier and more extreme negative snow cover anomalies on the spring side.

http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=5
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