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sidd

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AMOC slowdown
« on: October 06, 2016, 05:44:51 AM »
Kelly et al. trace AMOC slowdown to Agulhas leakage.

doi:10.1002/2016GL069789

No role for salinity,  AMOC slowdown not due to freshening in the north, rather they see increased salinity from precipitation decrease. This is a new development, Ruth Curry saw the opposite earlier.

johnm33

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Re: AMOC slowdown
« Reply #1 on: October 06, 2016, 10:23:35 AM »
I read that as coincident rather than causative/consequential.  I'm still looking for some work which convinces me that it's not the inertia of melt/arctic waters hugging the coast through Labrador/Newfoundland impeding the flow of the gulf stream across to the east. My thinking is that these two streams cause each other to back up, and when mixed to flow east slower. Most of the meltwaters from the Arctic and Greenland make their way south by this route.

AbruptSLR

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Re: AMOC slowdown
« Reply #2 on: October 06, 2016, 11:55:43 AM »
Per the linked reference: "In this period, increased ocean heat uptake has largely arisen from reduced heat loss associated with reduced winds over the Agulhas Return Current and southward displacement of Southern Ocean westerlies.":

S. S. Drijfhout, A. T. Blaker, S. A. Josey, A. J. G. Nurser, B. Sinha and M. A. Balmaseda, (2014), "Surface warming hiatus caused by increased heat uptake across multiple ocean basins" Geophysical Research Letters, DOI: 10.1002/2014GL061456

http://onlinelibrary.wiley.com/doi/10.1002/2014GL061456/abstract

Abstract: "The first decade of the twenty-first century was characterised by a hiatus in global surface warming. Using ocean model hindcasts and reanalyses we show that heat uptake between the 1990s and 2000s increased by 0.7 ± 0.3Wm−2. Approximately 30% of the increase is associated with colder sea surface temperatures in the eastern Pacific. Other basins contribute via reduced heat loss to the atmosphere, in particular the Southern and subtropical Indian Oceans (30%), and the subpolar North Atlantic (40%). A different mechanism is important at longer timescales (1960s-present) over which the Southern Annular Mode trended upwards. In this period, increased ocean heat uptake has largely arisen from reduced heat loss associated with reduced winds over the Agulhas Return Current and southward displacement of Southern Ocean westerlies."

See also:

http://www.reportingclimatescience.com/news-stories/article/heat-uptake-by-several-oceans-drives-pause-says-study.html


Also, for the important influence of the Agulhas Current on amplifying global temperatures see: Turney, C. S.M. and Jones, R. T. (2010), Does the Agulhas Current amplify global temperatures during super-interglacials?. J. Quaternary Sci., 25: 839–843. doi: 10.1002/jqs.1423.
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jai mitchell

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Re: AMOC slowdown
« Reply #3 on: October 11, 2016, 11:03:03 PM »
Stefan Rahmstorf October 9th Iceland presentation of recent science confirming AMOC slowdown.

https://www.youtube.com/watch?v=EmiVhT5cHpw

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prokaryotes

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Re: AMOC slowdown
« Reply #4 on: October 12, 2016, 04:47:06 AM »
Stefan Rahmstorf October 9th Iceland presentation of recent science confirming AMOC slowdown.

https://www.youtube.com/watch?v=EmiVhT5cHpw
Btw. made the same mistake, but per video info from University of Iceland on May 27th 2016 at the conference "The Past, the Future. How Fast, How Far? Threats Facing the Climate System"

Gray-Wolf

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Re: AMOC slowdown
« Reply #5 on: November 24, 2016, 09:30:19 PM »
http://www.tellusa.net/index.php/tellusa/article/view/31051

Maybe another way of looking at things? The paper explores a strengthening of The N.A.D. due to melt?

To me warm will always search out cold so I was never keen of us ( here in the UK) seeing cooling whilst the rest of the planet bakes!!! ;)
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Cate

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Re: AMOC slowdown
« Reply #6 on: January 06, 2017, 01:46:31 PM »
This piece mentions neither the AMOC or climate change, but I'm gonna stick it here anyway: there's curious warming of the ocean bottom on Canada's east coast. The person interviewed says they see no significant trends, however.

http://www.cbc.ca/news/canada/nova-scotia/water-waters-climate-change-dfo-oceans-fisheries-science-1.3922876

Department of Fisheries and Oceans Canada has published its sea conditions report for 2015---yes, 2015. 2016 report is yet to come. "Every year the department measures temperatures throughout the water column off Newfoundland and Labrador, the Gulf of St. Lawrence, the Scotian Shelf, the Gulf of Maine and the Bay of Fundy."

"Scientists have struggled to explain what is causing the most intriguing aspect of the recent trend: the warming of ocean bottom water, which is not influenced by surface weather events.
Hebert said the latest theory is based on model results that see the Gulf Stream moving northward and intersecting with the tail of the Grand Banks.

"That is stopping the cold Labrador Sea water from coming around the tail of the Grand Banks," he said. "That's where we normally get the cold water that refreshes the [Scotian] Shelf. That hasn't been rhappening.

"And what we are seeing is the warm slope water getting onto the shelf, sort of pumping more warm salty water, year after year, and the shelf will slowly change its conditions."

« Last Edit: January 06, 2017, 01:54:24 PM by Cate »

budmantis

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Re: AMOC slowdown
« Reply #7 on: January 07, 2017, 04:53:50 PM »
The linked article asserts that a significant enough warming in the arctic could potentially cause the AMOC to stagnate and shut down.

http://www.huffingtonpost.com/entry/atlantic-ocean-current-collapse-warning_us_587031f3e4b02b5f8588fa35?f02haoyl8e6xq1tt9

Extract: The Atlantic Meridional Overturning Circulation (AMOC) transports warm water from the tropics to the North Atlantic and helps regulate climate and weather patterns all over the world. As it releases the warmth into the air, the cooling water sinks and flows back to the tropics to repeat the process. But researchers fear that as the air in the north warms significantly due to climate change, the AMOC won’t be able to transfer its warmth to the atmosphere and the great circulatory engine of the ocean could stagnate and shut down. 

AbruptSLR

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Re: AMOC slowdown
« Reply #8 on: January 09, 2017, 11:09:49 PM »
The linked reference concludes that:

"We propose that such centennial-millennial productivity/climate variability in the NW Pacific and sequence of sub-stadial/interstadials in the EAM from the LGM to EH are a persistent regional features, synchronous with the Greenland/North Atlantic short-term changes. We speculate that such climate synchronicity was forced also by changes in Atlantic meridional overturning circulation coupled with Intertropical Convergence Zone shifting and the northern westerly jets reorganization." 

Where: EAM = East Asian Monsoon, LGM = Last Glacial Maximum and EH = Early Holocene.

This paleo-evidence of the synchronicity of the ITCZ, the AMOC and the northern westerly jets implies to me that the Earth's climate sensitivity is higher than consensus science currently acknowledges:

Gorbarenko et. al. (2016), "Centennial to millennial climate variability in the far northwestern Pacific (off Kamchatka) and its linkage to East Asian monsoon and North Atlantic from the Last Glacial Maximum to the Early Holocene", Clim. Past Discuss., doi:10.5194/cp-2016-102

http://www.clim-past-discuss.net/cp-2016-102/cp-2016-102.pdf

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GeoffBeacon

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Re: AMOC slowdown
« Reply #9 on: January 10, 2017, 09:39:09 PM »
How do short term climate forcing agents (like methane and black carbon) contribute to the danger of triggering a tipping point in the Gulf Stream System? I’ve just found Centuries of thermal sea-level rise due to anthropogenic emissions of short-lived greenhouse gases by Ramanathan et. al.

Seems relevant but I haven’t yet paid to access it. The “significance” includes:

Our study shows that short-lived GHGs contribute to thermal expansion of the ocean over much longer time scales than their atmospheric lifetimes. Actions taken to reduce emissions of short-lived gases could mitigate centuries of additional future sea-level rise.

A bit from the abstract:

For example, at least half of the TSLR due to increases in methane is expected to remain present for more than 200 y, even if anthropogenic emissions cease altogether, despite the 10-y atmospheric lifetime of this gas. Chlorofluorocarbons and hydrochlorofluorocarbons have already been phased out under the Montreal Protocol due to concerns about ozone depletion and provide an illustration of how emission reductions avoid multiple centuries of future TSLR. We examine the “world avoided” by the Montreal Protocol by showing that if these gases had instead been eliminated in 2050, additional TSLR of up to about 14 cm would be expected in the 21st century, with continuing contributions lasting more than 500 y.


Any thoughts?
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GeoffBeacon

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Re: AMOC slowdown
« Reply #10 on: January 10, 2017, 09:46:58 PM »
Correction: That paper was by   Kirsten Zickfeld, Susan Solomon, and Daniel M. Gilford
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jai mitchell

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Re: AMOC slowdown
« Reply #11 on: January 11, 2017, 05:29:07 PM »
The linked reference concludes that:

"We propose that such centennial-millennial productivity/climate variability in the NW Pacific and sequence of sub-stadial/interstadials in the EAM from the LGM to EH are a persistent regional features, synchronous with the Greenland/North Atlantic short-term changes. We speculate that such climate synchronicity was forced also by changes in Atlantic meridional overturning circulation coupled with Intertropical Convergence Zone shifting and the northern westerly jets reorganization." 

Where: EAM = East Asian Monsoon, LGM = Last Glacial Maximum and EH = Early Holocene.

This paleo-evidence of the synchronicity of the ITCZ, the AMOC and the northern westerly jets implies to me that the Earth's climate sensitivity is higher than consensus science currently acknowledges:

Gorbarenko et. al. (2016), "Centennial to millennial climate variability in the far northwestern Pacific (off Kamchatka) and its linkage to East Asian monsoon and North Atlantic from the Last Glacial Maximum to the Early Holocene", Clim. Past Discuss., doi:10.5194/cp-2016-102

http://www.clim-past-discuss.net/cp-2016-102/cp-2016-102.pdf


This is a very (VERY) complex paper!  could you give your ideas on how it implies higher sensitivity?  Is it a function of the meltwater lensing you have been discussing as implicated by the Hansen paper?  Or is it a combination of other effects?

I am finding some really difficult translations between paleoclimate studies and current impacts simply due to the incredibly rapid warming and scale changes we are experiencing.  It is so very difficult to compare previous conditions to today!

Thank you for posting it, this is incredibly valuable (which is why I am asking!)
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AbruptSLR

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Re: AMOC slowdown
« Reply #12 on: January 11, 2017, 10:06:41 PM »
This is a very (VERY) complex paper!  could you give your ideas on how it implies higher sensitivity?  Is it a function of the meltwater lensing you have been discussing as implicated by the Hansen paper?  Or is it a combination of other effects?

I am finding some really difficult translations between paleoclimate studies and current impacts simply due to the incredibly rapid warming and scale changes we are experiencing.  It is so very difficult to compare previous conditions to today!

Thank you for posting it, this is incredibly valuable (which is why I am asking!)

Such matters are complex (think interacting Lorenz attractors).  So to be as simple as possible (& to focus on the primary interaction mechanism): as the thermohaline (say due accelerated WAIS loss as cited by Hansen) slows down, heat accumulates along the equator, particularly in the Equatorial Pacific Ocean; which causes both the ITCZ to move poleward and also advects heat through the atmosphere towards the poles (thus impacting the polar atmospheric jet-streams).

Edit: See the influence on high climate sensitivity of the warming of the Equatorial Pacific in the middle panel of the first attached image (with ECS near 5C).

Edit2: Also see the last three related images: (a) the first shows multiple mechanisms associated with the ENSO/ITCZ; (b) Deep convection near the Equatorial Pacific expanding ITCZ zone and moving the associated clouds poleward; and (c) A strong El Nino advecting (atmospheric bridge) atmospheric energy from the equator directly to the poles.
« Last Edit: January 12, 2017, 02:22:29 AM by AbruptSLR »
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jai mitchell

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Re: AMOC slowdown
« Reply #13 on: January 12, 2017, 06:08:30 PM »
Thanks ASLR,

I am finding that the rates of changes is moving so much more rapidly now that the models are unable to keep up, the paleoclimate analogies are useless and local climate impact predictions understate the rates of changes by decades or more.   For example, if the current West Coast El Nino winter (in a NON El Nino year!) is a function of last year's water vapor pulse and as a result of perceptible reductions in high-temp coal combustion operations (iron, older less efficient power production closures) then we are seeing indications of what the climate SHOULD be at 490 ppm CO2e forcing rates.

remember, the Chinese smokestacks that don't have wet scrubbers exhaust superheated CO2 that rises rapidly to the upper troposphere.  not like our scrubbed smokestacks.  the use of scrubber technology rapidly reduces the upper tropospheric loading of this SO2 to near zero since the emissions of remaining SO2 are much cooler.

These emissions also have an effect on AMOC circulation rates.

see: http://journals.ametsoc.org/doi/full/10.1175/JAS-D-12-0331.1
http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20178/full
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bbr2314

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Re: AMOC slowdown
« Reply #14 on: January 12, 2017, 10:08:56 PM »
Thanks ASLR,

I am finding that the rates of changes is moving so much more rapidly now that the models are unable to keep up, the paleoclimate analogies are useless and local climate impact predictions understate the rates of changes by decades or more.   For example, if the current West Coast El Nino winter (in a NON El Nino year!) is a function of last year's water vapor pulse and as a result of perceptible reductions in high-temp coal combustion operations (iron, older less efficient power production closures) then we are seeing indications of what the climate SHOULD be at 490 ppm CO2e forcing rates.

remember, the Chinese smokestacks that don't have wet scrubbers exhaust superheated CO2 that rises rapidly to the upper troposphere.  not like our scrubbed smokestacks.  the use of scrubber technology rapidly reduces the upper tropospheric loading of this SO2 to near zero since the emissions of remaining SO2 are much cooler.

These emissions also have an effect on AMOC circulation rates.

see: http://journals.ametsoc.org/doi/full/10.1175/JAS-D-12-0331.1
http://onlinelibrary.wiley.com/doi/10.1002/jgrc.20178/full


I wonder if the pulses of their emissions can be timed to be worse with the coldest outbreaks over China? In that, as temperatures plummet, heating requirements increase and so does automobile use, provoking a pollution-related response that is significantly worse than normal? This would evidently amplify the cold outbreaks (or weaken who knows, one or the other I suppose) as the winter drags on, abating as solar input increases again in the spring.

AbruptSLR

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Re: AMOC slowdown
« Reply #15 on: January 13, 2017, 05:10:43 PM »
Thanks ASLR,

I am finding that the rates of changes is moving so much more rapidly now that the models are unable to keep up, the paleoclimate analogies are useless and local climate impact predictions understate the rates of changes by decades or more. 


jai,
I believe that the paleo-record has value for helping to calibrate ESMs if Lorenz attractors and masking factors (like paleo dust) are considered in the calibration.  Once the models are appropriately calibrated to the best paleo data that we have, then looking to the future, we need to extrapolate probable Earth System responses that likely will exceed those within the paleo-record, but which conform to physics of a chaotic system with Lorenz attractors and ratcheting of quasi-static equilibrium system states (see the attached image for ENSO driven ratcheting).

As we both understand how complex state-of-the-art ESMs (like ACME), I will not pretend that I can appropriately account by hand for all of the feedbacks and interactions; which a good portion of my over 10,000 posts focus on (including carbon cycle feedbacks, natural and anthropogenic aerosol forcing & feedbacks, albedo flips, ice-climate feedbacks, ENSO/PDO interactions, etc. etc.); nevertheless, to add a very small amount of complexity to my Replies #12 & #2, with continued global warming one can expect more Agulhas Current leakage; which per the linked reference means that one can expect the AMOC to continue slowing; which should work synergistically with Hansen's ice-climate feedback to accelerate global warming beyond levels currently assumed.


Kathryn A. Kelly, Kyla Drushka, LuAnne Thompson, Dewi Le Bars & Elaine L. McDonagh (25 July 2016), "Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports", Geophysical Research Letters, DOI: 10.1002/2016GL069789

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069789/abstract

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ASLR
« Last Edit: January 13, 2017, 05:43:32 PM by AbruptSLR »
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AbruptSLR

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Re: AMOC slowdown
« Reply #16 on: January 13, 2017, 10:22:54 PM »
jai,

With regards to the use of paleoclimate data and strange attractors to constraint ECS, see the linked article that indicates that using this approach clearly indicates that ECS is likely higher than commonly assumed:

A.S. Von der Heydt and Peter Ashwin (2016), "State-dependence of climate sensitivity: attractor constraints and palaeoclimate regimes", arXiv:1604.03311v1

http://arxiv.org/pdf/1604.03311v1.pdf
or
https://arxiv.org/pdf/1604.03311v2.pdf

Abstract: "Equilibrium climate sensitivity is a frequently used measure to predict long-term climate change. However, both climate models and observational data suggest a rather large uncertainty on climate sensitivity (CS). The reasons for this include: the climate has a strong internal variability on many time scales, it is subject to a non-stationary forcing and it is, on many timescales, out of equilibrium with the changes in the radiative forcing. Palaeo records of past climate variations give insight into how the climate system responds to various forcings although care must be taken of the slow feedback processes before comparing palaeo CS estimates with model estimates. In addition, the fast feedback processes can change their relative strength and time scales over time. Consequently, another reason for the large uncertainty on palaeo climate sensitivity may be the fact that it is strongly state-dependent. Using a conceptual climate model, we explore how CS can be estimated from unperturbed and perturbed model time series. Even in this rather simple model we find a wide range of estimates of the distribution of CS, depending on climate state and variability within the unperturbed attractor. For climate states perturbed by instantaneous doubling of CO2, the sensitivity estimates agree with those for the unperturbed model after transient decay back the attractor. In this sense, climate sensitivity can be seen as a distribution that is a local property of the climate attractor. We also follow the classical climate model approach to sensitivity, where CO2 is prescribed and non-dynamic, leading to CS values consistently smaller than those derived from the experiments with dynamic CO2. This suggests that climate sensitivity estimates from climate models may depend significantly on future dynamics, and not just the level of CO2."


Extract: “... the presence of variability on the attractor on a number of timescales means there are clear and non-trivial distributions of sensitivities, even for unperturbed climates. The distribution of sensitivities depends strongly on the background state as well as on the timescale considered. This suggests that it could be useful to think of the unperturbed climate sensitivity as a local property of the “climate attractor”. For a perturbed system (we have considered instantaneously doubled CO2) this is still useful once an initial transient has decayed. This transient will depend in particular on ocean heat uptake, though also on carbon cycle and biosphere processes that act on time scales roughly equivalent with the forcing time scale. If the climate system has more than one attractor, the perturbed system may clearly evolve to a completely different set of states than the original attractor – a situation that did not occur in the climate model used here. In less extreme cases, there may still be very long transients for some perturbations associated parts of the climate system that are associated with slow feedbacks.

Such perturbations (illustrated in Fig. 1b,d) are not normally applied in climate models used for climate predictions [IPCC, 2013], where climate sensitivity is derived from model simulations considering prescribed, non-dynamic atmospheric CO2. In our conceptual model, we have derived climate sensitivities from both types of perturbations and find that the classical climate model approach (section 2.2, Fig. 4f) leads to significantly lower values of the climate sensitivity than the perturbations away from the attractor with dynamic CO2 (section 2.3, Fig. 11a). This emphasises the importance of including dynamic carbon cycle processes into climate prediction models. Moreover, it supports the idea that the real observed climate response may indeed be larger than the model predicted one, because those models never will include all feedback processes in the climate system.“

Edit, see also:

A. S. von der Heydt, H. A. Dijkstra, R. S. W. van de Wal, R. Caballero, M. Crucifix, G. L. Foster,  M. Huber, P. Köhler, E. Rohling, P. J. Valdes, P. Ashwin, S. Bathiany, T. Berends, L. G. J. van Bree, P. Ditlevsen, M. Ghil, A. Haywood, J. Katzav, G. Lohmann, J. Lohmann, V. Lucarini, A. Marzocchi, H. Pälike, I. Ruvalcaba Baroni, D. Simon, A. Sluijs, L. B. Stap, A. Tantet, J. Viebahn and M. Ziegler Lessons on climate sensitivity from past climate changes, Curr. Clim. Change Rep. (2016), doi:10.1007/s40641-016-0049-3.


http://link.springer.com/article/10.1007/s40641-016-0049-3


Abstract: "Over the last decade, our understanding of climate sensitivity has improved considerably. The climate system shows variability on many timescales, is subject to non-stationary forcing and it is most likely out of equilibrium with the changes in the radiative forcing. Slow and fast feedbacks complicate the interpretation of geological records as feedback strengths vary over time. In the geological past, the forcing timescales were different than at present, suggesting that the response may have behaved differently. Do these insights constrain the climate sensitivity relevant for the present day? In this paper, we review the progress made in theoretical understanding of climate sensitivity and on the estimation of climate sensitivity from proxy records. Particular focus lies on the background state dependence of feedback processes and on the impact of tipping points on the climate system. We suggest how to further use palaeo data to advance our understanding of the currently ongoing climate change."

Best,
ASLR
« Last Edit: January 13, 2017, 11:13:26 PM by AbruptSLR »
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nowayout

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Re: AMOC slowdown
« Reply #17 on: January 13, 2017, 11:12:14 PM »
Slightly hidden in the pdf, but I think this catches it:

In this sense, climate sensitivity can be seen as a distribution that is a local
property of the climate attractor. 

Translation: In the end it's all about tipping points. Even climate sensivity.

On AMOC slowdown or collapse: If it is the freshwater intrusion from Greenland to cause it, we should carefully observe what is going on beneath the central Greeenland glaciers. There is enough space to collect sufficient amounts of freshwater. This would be a smaller tipping point, into the "wrong" direction. See Younger Dryas. The (Our) CO2 dynamics will only be stopped for a short time.

Generally: this (our!) relentless and still accellerating pollution of the earth with CO2 could be (and imho is) so strong that some attractors of the climate past that went effective could simply be overrun.

BAU implies this. Sorry.


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Re: AMOC slowdown
« Reply #18 on: January 16, 2017, 09:01:01 PM »
Further to my Replies #15 & #16 about multiple interacting climate attractors,the linked reference provides additional details about the oceanic and atmospheric interconnections between the Equatorial Pacific Ocean and the subpolar North Atlantic Ocean.

L. Chafik, S. Häkkinen, M. H. England, J. A. Carton, S. Nigam, A. Ruiz-Barradas, A. Hannachi & L. Miller (21 October 2016), "Global linkages originating from decadal oceanic variability in the subpolar North Atlantic", Geophysical Research Letters, DOI: 10.1002/2016GL071134

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071134/abstract

Abstract: "The anomalous decadal warming of the subpolar North Atlantic Ocean (SPNA), and the northward spreading of this warm water, has been linked to rapid Arctic sea ice loss and more frequent cold European winters. Recently, variations in this heat transport have also been reported to covary with global warming slowdown/acceleration periods via a Pacific climate response. We here examine the role of SPNA temperature variability in this Atlantic-Pacific climate connectivity. We find that the evolution of ocean heat content anomalies from the subtropics to the subpolar region, likely due to ocean circulation changes, coincides with a basin-wide Atlantic warming/cooling. This induces an Atlantic-Pacific sea surface temperature seesaw, which in turn, strengthens/weakens the Walker circulation and amplifies the Pacific decadal variability that triggers pronounced global-scale atmospheric circulation anomalies. We conclude that the decadal oceanic variability in the SPNA is an essential component of the tropical interactions between the Atlantic and Pacific Oceans."
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jai mitchell

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Re: AMOC slowdown
« Reply #19 on: January 21, 2017, 12:21:15 AM »
http://advances.sciencemag.org/content/3/1/e1601666?utm_campaign=toc_advances_2017-01-20&et_rid=17776844&et_cid=1116593

Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate

Wei Liu et al.
Science Advances  04 Jan 2017:
Vol. 3, no. 1, e1601666
DOI: 10.1126/sciadv.1601666

Abstract:  Changes in the Atlantic Meridional Overturning Circulation (AMOC) are moderate in most climate model projections under increasing greenhouse gas forcing. This intermodel consensus may be an artifact of common model biases that favor a stable AMOC. Observationally based freshwater budget analyses suggest that the AMOC is in an unstable regime susceptible for large changes in response to perturbations. By correcting the model biases, we show that the AMOC collapses 300 years after the atmospheric CO2 concentration is abruptly doubled from the 1990 level. Compared to an uncorrected model, the AMOC collapse brings about large, markedly different climate responses: a prominent cooling over the northern North Atlantic and neighboring areas, sea ice increases over the Greenland-Iceland-Norwegian seas and to the south of Greenland, and a significant southward rain-belt migration over the tropical Atlantic. Our results highlight the need to develop dynamical metrics to constrain models and the importance of reducing model biases in long-term climate projection.
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Re: AMOC slowdown
« Reply #20 on: January 22, 2017, 02:47:32 AM »
To me the linked article by Neven entitled: "A new Arctic feedback (?)", clearly identifies a feedback mechanism that can contribute to the early collapse of the AMOC:

http://neven1.typepad.com/blog/2017/01/a-new-arctic-feedback-.html

Extract: "Yesterday this video was posted on Peter Sinclair's ClimateCrocks blog, showing an interview with Dr Jennifer Francis (Rutgers University) at the AGU 2016 Fall Meeting this past December:"
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logicmanPatrick

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Re: AMOC slowdown
« Reply #21 on: January 22, 2017, 07:12:00 AM »
Double whammy!  AMOC slowdown means more heat transfer south, adding to global warming according to paleoclimate data.


The researchers believe the melting of the Greenland ice sheet weakened the Atlantic Meridional Overturning Circulation, or AMOC, a system of currents that usually brings warmer water from the tropics to the south. As it weakened, sea surface temperatures rose in the southern hemisphere, also contributing to warmer global temperatures.

“It was a double whammy,” Clark said. “Solar insolation warmed the northern hemisphere, a weakened AMOC warmed the south.”

Scientists zero in on global ocean temperatures during last interglaciation period
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AbruptSLR

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Re: AMOC slowdown
« Reply #22 on: January 23, 2017, 07:22:17 PM »
The linked reference indicate that current models likely do not accurately represent CO₂ ventilation from the equatorial Pacific (& Atlantic) Ocean(s) during periods of deglaciation.  The reference states: "In addition, both gradual and rapid deglacial radiocarbon changes in these Pacific records are coeval with changes in the Atlantic records.  This in-phase behavior suggest that the Southern Ocean overturning was the dominant driver of changes in the Atlantic and Pacific ventilation during deglacitions."  This does not bode well for our future.

Natalie E. Umling & Robert C. Thunell (2017), "Synchronous deglacial thermocline and deep-water ventilation in the eastern equatorial Pacific", Nature Communications, doi:10.1038/ncomms14203

http://www.nature.com/articles/ncomms14203
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bbr2314

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Re: AMOC slowdown
« Reply #23 on: February 04, 2017, 01:47:04 AM »

bbr2314

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Re: AMOC slowdown
« Reply #24 on: February 04, 2017, 01:50:15 AM »
I think the 1/17 anomaly map above clearly shows the area primarily effected so far. This anomaly has accumulated year over year since at least 2012 (looking at HYCOM maps) and has steadily worsened (immediately SE of Greenland and SW of Iceland).

It seems that when combined with the ice-free Atlantic side of the Arctic this winter, the result of the AMOC mess + vast areas of newly open water = significantly more snowfall over high elevations in Europe and Northern Africa, explaining the cold anomalies in those regions. Perhaps this is the mechanism that results in Saharan re-greening, because it certainly seems we could be heading that way based on these maps...!

FishOutofWater

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Re: AMOC slowdown
« Reply #25 on: February 06, 2017, 04:43:32 AM »
The isothermal deeply mixed area that is the source of Labrador sea mode water is larger than normal. Note that it is ringed by water that is warmer and saltier than normal. That probably indicates that deep water formation is chugging along this winter. There was a major slowdown in the MOC and the Gulf Stream in 2010. Warm water built up in the tropics in 2010 while the temperate and subpolar north Atlantic cooled. The SST pattern is very different now than 2010. It shows warm water moving across the temperate Atlantic at a good clip and up the coast of Norway towards the Arctic.

Note that the cool region has a negative Sea Surface Height anomaly. That means that it is dense. It is not a light cold fresh surface layer floating over warm salty water. The high density is an indication of mixing, that deep water formation is going on.

johnm33

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Re: AMOC slowdown
« Reply #26 on: February 06, 2017, 01:44:56 PM »
This illustrates your point about ssh rather better

It's easy to see that the dense water exiting the arctic is passing both down the Denmark strait and over the Faroe ridge, the second of those then appears to flow around the ridge which indicates it's close to the bottom http://topex.ucsd.edu/marine_topo/jpg_images/topo4.jpg .
I'm thinking the major slowdown was the result of an increase in the flow of fresh[er] water out of the north, it's inertia keeping it against the coast, and when mixing with the oppositely inclined southern waters both slowed down and backed up, that now seems to be resolving leading to an accelerated flow of mixed southern and northern waters crossing the atlantic further south than the old gulf stream. Following this more circuitous route it arrives warmer and later and having increased in mass persists longer. An interesting feature of this new route, if this is what's happening, is that it more closely follows an arc around the north antlantic amphidromic point [@40w50n] and thus will be accelerated by tidal forces where before it passed through that area which would have mildly disrupted the flow.
The mixing


FishOutofWater

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Re: AMOC slowdown
« Reply #27 on: February 06, 2017, 03:33:30 PM »
Melting of Greenland's ice cap and intense melting of Arctic sea ice may have added a large amount of fresh water to the subarctic seas in 2005 to 2010. There was also a slowdown of transport of water from the Indian ocean to the south Atlantic via Agulhas rings that may have had an effect if I remember correctly. The tricky thing about the south Atlantic is the substantial lag time with deep convection in the subpolar Arctic seas.

A large pulse of freshwater released from the Beaufort gyre helped with the brief sea ice recovery in 2013 and 2014.


The Beaufort fresh water pulse may have slowed down the overturning circulation in 2013 and 2014. The cold dense anomaly may have formed as the water finally chilled and densified enough to begin mixing strongly again.

There are lag times in many of the processes involved with ocean dynamics so it's very tricky interpreting reports on the slowing of the THC because different investigators use different measures of THC activity.

AbruptSLR

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Re: AMOC slowdown
« Reply #28 on: May 23, 2017, 09:35:33 PM »
The linked reference indicates that the Younger Dryas may be due to a comet strike instead of a change in the AMOC:

 Martin B. Sweatman and Dimitrios Tsikritsis (2017), "DECODING GÖBEKLI TEPE WITH ARCHAEOASTRONOMY: WHAT DOES THE FOX SAY?", Mediterranean Archaeology and Archaeometry, Vol. 17, No 1, pp. 233-250,  DOI: 10.5281/zenodo.400780

http://maajournal.com/Issues/2017/Vol17-1/Sweatman%20and%20Tsikritsis%2017%281%29.pdf

Abstract: "We have interpreted much of the symbolism of Göbekli Tepe in terms of astronomical events. By matching low-relief carvings on some of the pillars at Göbekli Tepe to star asterisms we find compelling evidence that the famous ‘Vulture Stone’ is a date stamp for 10950 BC ± 250 yrs, which corresponds closely to the proposed Younger Dryas event, estimated at 10890 BC. We also find evidence that a key function of Göbekli Tepe was to observe meteor showers and record cometary encounters. Indeed, the people of Göbekli Tepe appear to have had a special interest in the Taurid meteor stream, the same meteor stream that is proposed as responsible for the Younger-Dryas event. Is Göbekli Tepe the ‘smoking gun’ for the Younger-Dryas cometary encounter, and hence for coherent catastrophism?"

See also:

https://www.forbes.com/sites/trevornace/2017/04/30/ancient-stone-tablet-found-reveals-comet-impact-sparking-the-rise-of-civilization/#4a16ac9c7342
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TerryM

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Re: AMOC slowdown
« Reply #29 on: May 24, 2017, 11:25:26 AM »
ASLR
The above is a reference to the Black Mat event in the '2017 open thread' found in "The Rest". I had found the connection a little tenuous, but different strokes.
One of many reasons for moving to Ontario was my hope that I could find some evidence of the comet here, close to where the largest piece may have hit ground ice.
Terry