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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3750 on: September 11, 2020, 09:45:18 AM »

What the fuck have any of these to do with ocean heat content ?


Thanks KG, excellent reference! I knew I had seen smth similar somewhere, but couldn't find it.

As regards your question, the second graph of SH midlatitudes is almost entirely ocean, except for small part of South America, southernmost parts of South Africa, and Australia, and of course NZ. Supposedly 2m temperature trends should be similar to SST trends.

RoxTheGeologist

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3751 on: September 11, 2020, 03:44:17 PM »

As we see in the Arctic, stratification prevents heat loss. Ice is an added insulator. More stratification from freshwater, colder surface waters, more ice, less heat loss and therefore warmer deep waters to melt glaciers.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3752 on: September 11, 2020, 03:47:31 PM »
I try not to post about the likely climate impacts of wildfires too frequently; however, with 2020 showing record high burning in both the Arctic and the Amazon (see the two linked articles), it needs to be reiterated that consensus climate model projection underestimate the highly likely risk that wildfires will accelerate climate change in the coming years and decades:

Title: "The Arctic is burning like never before — and that’s bad news for climate change"

https://www.nature.com/articles/d41586-020-02568-y

Extract: "Wildfires blazed along the Arctic Circle this summer, incinerating tundra, blanketing Siberian cities in smoke and capping the second extraordinary fire season in a row. By the time the fire season waned at the end of last month, the blazes had emitted a record 244 megatonnes of carbon dioxide — that’s 35% more than last year, which also set records. One culprit, scientists say, could be peatlands that are burning as the top of the world melts."

&

Title: "Tens of thousands of fires are pushing the Amazon to a tipping point"

https://www.cnn.com/2020/09/10/americas/brazil-amazon-fires-carlos-nobre-intl/index.html

Extract: "The more fires there are, the faster the rainforest is transformed into grasslands for illicit cattle and soy-growing operations. According to research from NGO MapBiomas, which tracks land use in Brazil, 95% of the deforested area in Brazil in 2019 wasn't authorized. "Most of (the fires) are illegal," said Tasso Azevedo, a former head of Brazil's forest service and coordinator of MapBiomas.

Deforestation in the Brazilian Amazon biome reached 1,830 square miles, an area bigger than Rhode Island state, in the period from January to July 2020,. August figures for deforestation are yet to be released.

As the trend goes on, the Amazon is speeding toward a tipping point, when large areas of the rainforest will no longer be able to produce enough rain to sustain itself, according to Carlos Nobre, one of Brazil's leading climate scientists and researcher at the University of Sao Paulo.

Once that happens, the rainforest will begin to die, eventually turning into savannah, said Nobre.

The Amazon serves as an "air conditioner" for the planet, scientists say, influencing global temperature and rainfall patterns. And a healthy Amazon also absorbs carbon dioxide, while fires do the opposite, releasing massive quantities of heat-trapping carbon dioxide into the atmosphere."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3753 on: September 11, 2020, 04:10:36 PM »

As we see in the Arctic, stratification prevents heat loss. Ice is an added insulator. More stratification from freshwater, colder surface waters, more ice, less heat loss and therefore warmer deep waters to melt glaciers.

In addition to KiwiGriff's reference/comments on Ocean Heat Content, OHC, in the Southern Ocean, I provide the following open access reference that provides additional explanations of why the Southern Ocean (primarily in the West Antarctic region) OHC is increasing while the SST for the Southern Ocean has cooling in recent decades.  Furthermore, I believe that people who focus on the cooling SST trend in the Southern Ocean are missing the climate risks that:

a) The mechanisms described in the linked reference work to slow the MOC, which increases TCR and increase the risk of a MICI-type of collapse of the WAIS; and
b) Very few people live around the Southern Ocean, to benefit from the low SSTs; while many people live in the NH where regional surface temperatures are increasing faster than the GMSTA.

F. Alexander Haumann, Nicolas Gruber and Matthias Münnich (06 May 2020), "Sea‐Ice Induced Southern Ocean Subsurface Warming and Surface Cooling in a Warming Climate", AGU Advances, https://doi.org/10.1029/2019AV000132

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019AV000132

Abstract
Much of the Southern Ocean surface south of 55° S cooled and freshened between at least the early 1980s and the early 2010s. Many processes have been proposed to explain the unexpected cooling, including increased winds or freshwater fluxes. However, these mechanisms so far failed to fully explain the surface trends and the concurrent subsurface warming (100 to 500 m). Here, we argue that these trends are predominantly caused by an increased wind‐driven northward sea‐ice transport, enhancing the extraction of freshwater near Antarctica and releasing it in the open ocean. This conclusion is based on factorial experiments with a regional ocean model. In all experiments with an enhanced northward sea‐ice transport, a strengthened salinity‐dominated stratification cools the open‐ocean surface waters between the Subantarctic Front and the sea‐ice edge. The strengthened stratification reduces the downward mixing of cold surface water and the upward heat loss of the warmer waters below, thus warming the subsurface. This sea‐ice induced subsurface warming mostly occurs around West Antarctica, where it likely enhances ice‐shelf melting. Moreover, the subsurface warming could account for about 8 ± 2% of the global ocean heat content increase between 1982 and 2011. Antarctic sea‐ice changes thereby may have contributed to the slowdown of global surface warming over this period. Our conclusions are robust across all considered sensitivity cases, although the trend magnitude is sensitive to forcing uncertainties and the model's mean state. It remains unclear whether these sea‐ice induced changes are associated with natural variability or reflect a response to anthropogenic forcing.

Plain Language Summary
While most of the global ocean surface has been warming in response to increasing atmospheric greenhouse‐gas concentrations, parts of the polar Southern Ocean surface have been cooling over recent decades. This cooling seems surprising, since most climate models suggest that also this region should have been warming. Using a regional ocean model, we find that the cooling can be reproduced when forcing the model with observed sea‐ice changes. Sea ice forms during the cold winter mostly along the Antarctic coast, leaving the salt that is contained in the seawater behind, and is then being pushed to the open ocean by strong winds. In the open ocean, the sea ice melts and makes the surface waters fresher there. This lateral sea‐ice transport has strengthened over recent decades, most likely due to stronger winds. In our model, the resulting freshening leads to a surface cooling, because the mixing of these waters with the warmer waters below is hindered. Thereby, the heat stays below the ocean's surface and cannot be released to the atmosphere. This retention of large amounts of heat at the subsurface possibly enhanced the melting of the Antarctic glaciers and possibly contributed to the slowdown of global warming over this period.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3754 on: September 12, 2020, 08:18:54 PM »
The linked reference reconfirms that particularly cloud feedback represents a major climate risk in the coming century; however, I note that CMIP6 models largely discount ice-climate feedback mechanisms this century:

Richard G Williams, Paulo Ceppi and Anna Katavouta (11 September 2020), "Controls of the transient climate response to emissions by physical feedbacks, heat uptake and carbon cycling", Environmental Research Letters, Volume 15, Number 9, https://doi.org/10.1088/1748-9326/ab97c9

https://iopscience.iop.org/article/10.1088/1748-9326/ab97c9

Abstract
The surface warming response to carbon emissions is diagnosed using a suite of Earth system models, 9 CMIP6 and 7 CMIP5, following an annual 1% rise in atmospheric CO2 over 140 years. This surface warming response defines a climate metric, the Transient Climate Response to cumulative carbon Emissions (TCRE), which is important in estimating how much carbon may be emitted to avoid dangerous climate. The processes controlling these intermodel differences in the TCRE are revealed by defining the TCRE in terms of a product of three dependences: the surface warming dependence on radiative forcing (including the effects of physical climate feedbacks and planetary heat uptake), the radiative forcing dependence on changes in atmospheric carbon and the airborne fraction. Intermodel differences in the TCRE are mainly controlled by the thermal response involving the surface warming dependence on radiative forcing, which arise through large differences in physical climate feedbacks that are only partly compensated by smaller differences in ocean heat uptake. The other contributions to the TCRE from the radiative forcing and carbon responses are of comparable importance to the contribution from the thermal response on timescales of 50 years and longer for our subset of CMIP5 models and 100 years and longer for our subset of CMIP6 models. Hence, providing tighter constraints on how much carbon may be emitted based on the TCRE requires providing tighter bounds for estimates of the physical climate feedbacks, particularly from clouds, as well as to a lesser extent for the other contributions from the rate of ocean heat uptake, and the terrestrial and ocean cycling of carbon.

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3755 on: September 13, 2020, 07:21:37 PM »
The topic of tipping points and abrupt climate change is so complicated that it can be hard to see the forest for the trees, so I repost the linked CarbonBrief article that focuses on nine tipping points.  Nevertheless, here I emphasize that at a tipping point, and/or an irreversible tipping point, just one more straw may be sufficient to 'break the camel's back' and that all current ESMs leave many straws out of their assessments including:

1.   Correctly modeling initial parameters and boundary conditions such as: a) the current fragility of many key Antarctic ice shelves; b) the fragility of the Beaufort Gyre w.r.t. the risk of significant freshwater hosing event; and c) the fragility positive feedbacks associated with the Southern Ocean's response to its ozone hole.
2.   Correctly modeling cloud feedback mechanisms.
3.   Correctly modeling the impacts on TCR of current and future slowing of the MOC, particularly w.r.t. freshening of surface waters in both the North Atlantic and the Southern Ocean.
4.   Cascading of numerous smaller feedback mechanisms near tipping points.

Title: "Explainer: Nine ‘tipping points’ that could be triggered by climate change"

https://www.carbonbrief.org/explainer-nine-tipping-points-that-could-be-triggered-by-climate-change

Extract: "And while climate records are being routinely broken, the cumulative impact of these changes could also cause fundamental parts of the Earth system to change dramatically and irreversibly.

These “tipping points” are thresholds where a tiny change could push a system into a completely new state.

That extra bit of warming would be, as the saying goes, the straw that breaks the camel’s back.

It is worth noting that a tipping point can be caused by natural fluctuations in the climate as well as by an external forcing, such as global warming. These are called “noise-induced” tipping points and include, for example, periods of abrupt change during the last ice age called “Dansgaard-Oeschger (D-O) events”.

Passing an irreversible tipping point would mean a system would not revert to its original state even if the forcing lessens or reverses, explains Dr Richard Wood, who leads the Climate, Cryosphere and Oceans group in the Met Office Hadley Centre.

This shutdown could happen because the AMOC is a self-reinforcing system, explains Rahmstorf:

The circulation itself brings salty water into the high-latitude Atlantic and the salty water increases the density. And so we can say the water is able to sink because it is salty and it is salty because there is this circulation. So it’s like a self-reinforcing system.

Such a system can only be pushed “up to a limit”, says Rahmstorf, after which the self-reinforcing system actually works to further weaken the circulation. Too much freshwater in the North Atlantic slows the circulation, preventing it from pulling salty water up from the south. Thus, the North Atlantic freshens even more and the circulation weakens further – and so on. It “really is an on-off system”, he adds.

Finally, research suggests that the collapse of the AMOC could itself trigger other tipping points. As the SROCC explains:

For example, a collapse of the AMOC may induce causal interactions like changes in ENSO [El Niño–Southern Oscillation] characteristics, dieback of the Amazon rainforest and shrinking of the West Antarctic Ice Sheet due to seesaw effect, ITCZ [Intertropical Convergence Zone] southern migration and large warming of the Southern Ocean.

However, the SROCC notes that “such a worst-case scenario remains very poorly constrained” as a result of the large uncertainties around how systems such as AMOC will respond to warming."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3756 on: September 14, 2020, 06:46:08 PM »
Per Gavin Schmidt and his attached image: "With August data in, 2020 is still more likely than not to be a record warm year in GISTEMP (63%)."

Edit: I note that currently 2020 is in a neutral ENSO condition.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3757 on: September 15, 2020, 12:14:03 AM »
The linked article makes some good points about whether, and how, to use 20-year or 100-year GWP for methane, w.r.t. climate risk:

Title: "Climate Explained: Methane Is Short-Lived in the Atmosphere but Leaves Long-Term Damage"

https://www.ecowatch.com/methane-long-term-climate-effects-2647534679.html?rebelltitem=3#rebelltitem3

Extract: "Methane is a shorter-lived greenhouse gas - why do we average it out over 100 years? By doing so, do we risk emitting so much in the upcoming decades that we reach climate tipping points?

Fully considered using the 100-year GWP and including natural feedbacks, the IPCC's report says fossil sources of methane - most of the gas burned for electricity or heat for industry and houses - can be up to 36 times worse than carbon dioxide. Methane from other sources - such as livestock and waste - can be up to 34 times worse.

While some uncertainty remains, a well-regarded recent assessment suggested an upwards revision of fossil and other methane sources, that would increase their GWP values to around 40 and 38 times worse than carbon dioxide respectively.

The scientific understanding of climate change goes well beyond simple metrics like GWP. Shuffling between metrics - such as 20-year or 100-year GWP - cannot avoid the fact our very best chance of avoiding ever-worsening climate harm is to massively reduce our reliance on coal, oil and gas, along with reducing our emissions from all other sources of greenhouse gas."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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ShortBrutishNasty

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3758 on: September 15, 2020, 03:54:13 AM »
Miami vs. The Sea - Part 5:  The King Tide Cometh

In less than 48 hours, the first King Tide of 2020!

Fort Lauderdale is well prepared with “No Wake” signs on roadways to encourage drivers to proceed slowly through neighborhoods to prevent additional damage.....

https://www.fortlauderdale.gov/departments/city-manager-s-office/strategic-communications/king-tides

Read the offender's post history.  That's not difficult.  --Goethe c. 1609

KiwiGriff

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3759 on: September 15, 2020, 07:27:53 AM »
I know what you are saying abslr
Just not well enough to explain it
This is the third time I have pulled H up on useing sst as a proxy for ocean heat content. Having spent thousand of hours in on and under the water the temp in the surface layer has little correlation to the temp at depths.
H is getting misleading information from unrealible sources and spreading fud on here.



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Notebooks of Lazarus Long.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3760 on: September 15, 2020, 09:05:59 PM »
With a hat-tip to Juan C. Garcia:

Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment
Stef Lhermitte, Sainan Sun, Christopher Shuman, Bert Wouters, Frank Pattyn, Jan Wuite, Etienne Berthier, and Thomas Nagler

https://doi.org/10.1073/pnas.1912890117

Abstract
Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.

https://www.pnas.org/content/early/2020/09/08/1912890117h

Edit: See the associated image
« Last Edit: September 16, 2020, 06:53:55 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3761 on: September 15, 2020, 09:47:39 PM »
I know what you are saying abslr
Just not well enough to explain it
This is the third time I have pulled H up on useing sst as a proxy for ocean heat content. Having spent thousand of hours in on and under the water the temp in the surface layer has little correlation to the temp at depths.
H is getting misleading information from unrealible sources and spreading fud on here.

As a moderately extreme example of your point is illustrated by the attached image from Hansen et. al (2016); which shows that an abrupt freshwater hosing (in either the North Atlantic, the Southern Ocean, or both) event between 2050 and 2100 would result in a marked temporary decrease in GMSTA associated with a marked temporary surge in the Earth's Energy Imbalance, and I note that the such a large temporary surge of the Earth's Energy Imbalance might be sufficient to to warm the tropical ocean SSTA by over 5C (above pre-industrial); which if it were to occur would be sufficient to irreversibly increase the Earth's climate state sufficiently to increase ECS into the 5.5C to 6C range, due to associated changes in key positive cloud feedback mechanisms.
« Last Edit: September 15, 2020, 10:27:54 PM by AbruptSLR »
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3762 on: September 16, 2020, 08:15:57 AM »
...
3.   Correctly modeling the impacts on TCR of current and future slowing of the MOC, particularly w.r.t. freshening of surface waters in both the North Atlantic and the Southern Ocean.
...
For example, a collapse of the AMOC may induce causal interactions like changes in ENSO [El Niño–Southern Oscillation] characteristics, dieback of the Amazon rainforest and shrinking of the West Antarctic Ice Sheet due to seesaw effect, ITCZ [Intertropical Convergence Zone] southern migration and large warming of the Southern Ocean.
...

ASLR quotes research that claims that the (A)MOC is weakening, and that this might trigger climate tipping points.
I have repeatedly been quoting research that claims that the (A)MOC is currently strengthening, see my posts upthread.
With a hat tip to binntho, here are two more recent papers that support this claim:

1. "On freshwater fluxes and the Atlantic meridional overturning circulation", by Cael and Jansen, january 2020
From the Abstract: "Our results robustly suggest that for the equilibrium state of the modern ocean, freshwater fluxes strengthen the AMOC..."
https://aslopubs.onlinelibrary.wiley.com/doi/full/10.1002/lol2.10125

2. "Indian Ocean warming can strengthen the Atlantic meridional overturning circulation. Nature Climate Change, in press (September 2019)., Hu, S., and Fedorov, A.V.
From Abstract: "Here, we describe how a salient feature of anthropogenic climate change – enhanced warming of the tropical Indian ocean (TIO) – can strengthen the Atlantic meridional overturning circulation (AMOC) by modulating salinity distribution in the Atlantic (Hu and Fedorov 2019). "
https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/649185

The big issue is, where are those freshwater pulses going to come from that might trigger those tipping points? I don't see enough of Greenland glacier melt-off for that during the coming decades. And the volume of freshwater in the lens on top of the Arctic won't be enough, supposedly.
Furthermore, the theory isn't even settled, as this quote from paper 1. shows: "Our results robustly suggest that for the equilibrium state of the modern ocean, freshwater fluxes strengthen the AMOC, in the sense that an amplification of the existing freshwater flux‐forcing pattern leads to a strengthening of the AMOC and vice versa. A simple physical argument explains these results: the North Atlantic is anomalously salty at depth and increased freshwater fluxes act to amplify that salinity pattern, resulting in enhanced AMOC transport."

Thus, the question remains completely unsettled, both empirically and theoretically.

I know what you are saying abslr
Just not well enough to explain it
This is the third time I have pulled H up on useing sst as a proxy for ocean heat content. Having spent thousand of hours in on and under the water the temp in the surface layer has little correlation to the temp at depths.
H is getting misleading information from unrealible sources and spreading fud on here.

I haven't provided any "misleading information from unrealible sources" regarding this issue, as I have only given reference and quoted from peer reviewed scientific articles.
Yes, I did bring up SST graphs, for two reasons:
1. Subsurface temperature data isn't available on the re-analysis pages. Such data is available from specific research articles, but isn't updated like the SST's are.
2. Surface temperatures are also an important part of the picture of what's going on in the Ocean.

It's not FUD, it's just an attempt to provide an alternative view to the alarmist construct.
« Last Edit: September 16, 2020, 01:28:49 PM by Hefaistos »

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3763 on: September 16, 2020, 04:17:08 PM »
...
3.   Correctly modeling the impacts on TCR of current and future slowing of the MOC, particularly w.r.t. freshening of surface waters in both the North Atlantic and the Southern Ocean.
...
For example, a collapse of the AMOC may induce causal interactions like changes in ENSO [El Niño–Southern Oscillation] characteristics, dieback of the Amazon rainforest and shrinking of the West Antarctic Ice Sheet due to seesaw effect, ITCZ [Intertropical Convergence Zone] southern migration and large warming of the Southern Ocean.
...

ASLR quotes research that claims that the (A)MOC is weakening, and that this might trigger climate tipping points.
I have repeatedly been quoting research that claims that the (A)MOC is currently strengthening, see my posts upthread.
...

The linked reference presents evidence in the form of a 'salinity pile-up' in the South Atlantic that indicates that indeed the AMOC is slowing over its entire range of circulation (which is not good news):

Zhu, C., Liu, Z. Weakening Atlantic overturning circulation causes South Atlantic salinity pile-up. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0897-7

https://www.nature.com/articles/s41558-020-0897-7

Abstract
The Atlantic Meridional Overturning Circulation (AMOC) is an active component of the Earth’s climate system and its response to global warming is of critical importance to society. Climate models have shown an AMOC slowdown under anthropogenic warming since the industrial revolution, but this slowdown has been difficult to detect in the short observational record because of substantial interdecadal climate variability. This has led to the indirect detection of the slowdown from longer-term fingerprints such as the subpolar North Atlantic ‘warming hole’. However, these fingerprints, which exhibit some uncertainties, are all local indicators of AMOC slowdown around the subpolar North Atlantic. Here we show observational and modelling evidence of a remote indicator of AMOC slowdown outside the North Atlantic. Under global warming, the weakening AMOC reduces the salinity divergence and then leads to a ‘salinity pile-up’ remotely in the South Atlantic. This evidence is consistent with the AMOC slowdown under anthropogenic warming and, furthermore, suggests that this weakening has likely occurred all the way into the South Atlantic.
« Last Edit: September 16, 2020, 04:53:43 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3764 on: September 16, 2020, 04:53:09 PM »
The linked reference confirms that current climate models provide reasonably good projections/hindcasts of AMOC behavior (which they project to be currently slowing); however, that recent interpretations of both field and model data merit refinement w.r.t. AMOC variability:

Matthew B. Menary, Laura C. Jackson and M. Susan Lozier (09 September 2020), "Reconciling the Relationship Between the AMOC and Labrador Sea in OSNAP Observations and Climate Models", Geophysical Research Letters, https://doi.org/10.1029/2020GL089793

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL089793?af=R

Abstract
The AMOC (Atlantic Meridional Overturning Circulation) is a key driver of climate variability. Our understanding, based largely on climate models, is that the Labrador Sea has an important role in shaping the evolution of the AMOC. However, a recent high‐profile observational campaign (Overturning in the Subpolar North Atlantic, OSNAP) has called into question the importance of the Labrador Sea, and hence the credibility of the AMOC representation in climate models. Here, we attempt to reconcile these viewpoints by making the first direct comparison between OSNAP and a coupled climate model. The model compares well to the observations, demonstrating a more prominent role for overturning in the eastern than western subpolar gyre. Density anomalies generated by surface forcing in the Irminger Sea propagate into the Labrador Sea, where they dominate the density variability. Thus, the Labrador Sea may not be the origin of AMOC variability despite correlations with densities there.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3765 on: September 17, 2020, 05:09:08 AM »
If it is not clear to some readers, large Antarctic sea ice extents, and/or relatively fresh surface seawaters, help to inhibit the radiation of heat into the atmosphere (& then long-wave radiation into space) from relatively warm water delivered to the Southern Ocean by the MOC.  Thus, the fact that in 2020 Antarctica will have record high sea ice extents (see the attached image created by Gerontocrat) implies that the Southern Ocean is continuing to build-up record high ocean heat content; which is currently helping to destabilize key Antarctic marine glaciers like Thwaites Glacier.

The paper quoted by KiwiGriff in post #3749, Sallée, J.-B. 2018. "Southern Ocean warming", shows warming during a very short timespan, from 2005 - 2015. According to Figure 4, the warming trend for deep waters is around 0.05 degrees per decade during the 2000's, whereas previous decades from the 1930's show cooling trends of similar size. (Fig 4, panel a., which is quoted from Gille, 2008, and panel c., which is quoted from Rhein et al 2013)

Which made me wonder, what is the time frame for the bolded quote from ASLR, that a "record high ocean heat content" (OHC) is built up in the Southern Ocean?

For a long term perspective of OHC trends, see attached chart, from Rosenthal et al, "Pacific Ocean Heat Content During the Past 10,000 Years", Science  2013, Vol. 342, Issue 6158, pp. 617-621
DOI: 10.1126/science.1240837

This is not for the SO, but for a part of the Pacific Ocean. Still, it indicates the magnitudes of OHC over a period of the last 10.000 years. Researches extracted bottom sediment cores and calculated the intermediate water temperatures (IWT).
The chart is from the paper, Figure 3B, showing IWT trends for the last 2000 years. These IWT trends correspond to changes in the OHC on the depths from around 500 - 900 meters. From about 7,000 years ago until the start of the Medieval Warm Period in northern Europe, at about 1100, the water cooled gradually, by almost 1 degree C. The rate of cooling then picked up during the Little Ice Age that followed, dropping another 1 degree C, until about 1600. The cooling from 7,000 years ago until the Medieval Warm Period is attributed in the paper to sun-earth natural variablilty. In 1600 or so, temperatures started gradually going back up.

I have added in the recent rise in subsurface temperatures, in red. This is based on the rise in OHC for the 0 - 700 meters depth. The red line is very approximate, but is there just to demonstrate how small this increase is in a context of a longer time-frame, and in a context of purely natural variations.
According to ASLR it represents a build-up of "record high ocean heat content". This seems to be an exaggeration in the longer time-frame.

Another issue is if the recent increase in OHC that is analyzed in the quoted papers can at all be attributed to AGW? The intermediate water masses, and bottom water masses, are all in transit for 100's of years. What is seen as warming of these watermasses today is unlikely to be caused by the more recent AGW, and most of it is more likely due to natural variations.
« Last Edit: September 17, 2020, 05:26:40 AM by Hefaistos »

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3766 on: September 17, 2020, 06:48:31 AM »
Re: OHC

Ocean heat content (OHC) should probably be discussed in the thread "Ocean Warming"

Searching this forum for OHC, or "ocean heat content" or "Levitus" or "Purkey" (beautiful paper on southern ocen heat content) or "Balmaseda" is probably useful, leads to various threads.

Or look at

https://forum.arctic-sea-ice.net/index.php/topic,2270.msg285491.html#msg285491

for the recent von Schuckmann paper linking earth energy imbalance to OHC

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3767 on: September 17, 2020, 09:51:41 AM »
The linked May 2020 reference makes it clear that air-sea heat flux is a major consideration in the rate of high-latitude ocean heat uptake; which is a relatively quick process and which is affected by the presence of both sea ice and relatively fresh surface waters; both of which can trap OHC within the Southern Ocean by limiting heat flux into the air.

Kewei Lyu; Xuebin Zhang; John A. Church and Quran Wu (2020), "Processes Responsible for the Southern Hemisphere Ocean Heat Uptake and Redistribution under Anthropogenic Warming", J. Climate, 33 (9): 3787–3807, https://doi.org/10.1175/JCLI-D-19-0478.1

https://journals.ametsoc.org/jcli/article/33/9/3787/344998/Processes-Responsible-for-the-Southern-Hemisphere

Abstract
The Southern Hemisphere oceans absorb most of the excess heat stored in the climate system due to anthropogenic warming. By analyzing future climate projections from a large ensemble of the CMIP5 models under a high emission scenario (RCP8.5), we investigate how the atmospheric forcing and ocean circulation determine heat uptake and redistribution in the Southern Hemisphere oceans. About two-thirds of the net surface heat gain in the high-latitude Southern Ocean is redistributed northward, leading to enhanced and deep-reaching warming at middle latitudes near the boundary between the subtropical gyres and the Antarctic Circumpolar Current. The projected magnitudes of the ocean warming are closely related to the magnitudes of the wind and gyre boundary poleward shifts across the models. For those models with the simulated gyre boundary biased equatorward, the latitude where the projected ocean warming peaks is also located farther equatorward and a larger poleward shift of the gyre boundary is projected. In a theoretical framework, the subsurface ocean changes are explored using three distinctive processes on the temperature–salinity diagram: pure heave, pure warming, and pure freshening. The enhanced middle-latitude warming and the deepening of isopycnals are attributed to the pure heave and pure warming processes, likely related to the wind-driven heat convergence and the accumulation of extra surface heat uptake by the background ocean circulation, respectively. The equatorward and downward subductions of the surface heat and freshwater input at high latitudes (i.e., pure warming and pure freshening processes) result in cooling and freshening spiciness changes on density surfaces within the Subantarctic Mode Water and Antarctic Intermediate Water.
« Last Edit: September 17, 2020, 10:07:15 AM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3768 on: September 17, 2020, 10:06:42 AM »
The linked reference discusses the importance and uncertainties associated with air-sea-ice fluxes in the Southern Ocean.

Sebastiaan Swart et al. (31 July 2019), "Constraining Southern Ocean Air-Sea-Ice Fluxes Through Enhanced Observations", Front. Mar. Sci., | https://doi.org/10.3389/fmars.2019.00421

https://www.frontiersin.org/articles/10.3389/fmars.2019.00421/full

Abstract
Air-sea and air-sea-ice fluxes in the Southern Ocean play a critical role in global climate through their impact on the overturning circulation and oceanic heat and carbon uptake. The challenging conditions in the Southern Ocean have led to sparse spatial and temporal coverage of observations. This has led to a “knowledge gap” that increases uncertainty in atmosphere and ocean dynamics and boundary-layer thermodynamic processes, impeding improvements in weather and climate models. Improvements will require both process-based research to understand the mechanisms governing air-sea exchange and a significant expansion of the observing system. This will improve flux parameterizations and reduce uncertainty associated with bulk formulae and satellite observations. Improved estimates spanning the full Southern Ocean will need to take advantage of ships, surface moorings, and the growing capabilities of autonomous platforms with robust and miniaturized sensors. A key challenge is to identify observing system sampling requirements. This requires models, Observing System Simulation Experiments (OSSEs), and assessments of the specific spatial-temporal accuracy and resolution required for priority science and assessment of observational uncertainties of the mean state and direct flux measurements. Year-round, high-quality, quasi-continuous in situ flux measurements and observations of extreme events are needed to validate, improve and characterize uncertainties in blended reanalysis products and satellite data as well as to improve parameterizations. Building a robust observing system will require community consensus on observational methodologies, observational priorities, and effective strategies for data management and discovery.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3769 on: September 17, 2020, 05:16:38 PM »
If it is not clear to some readers, large Antarctic sea ice extents, and/or relatively fresh surface seawaters, help to inhibit the radiation of heat into the atmosphere (& then long-wave radiation into space) from relatively warm water delivered to the Southern Ocean by the MOC.  Thus, the fact that in 2020 Antarctica will have record high sea ice extents (see the attached image created by Gerontocrat) implies that the Southern Ocean is continuing to build-up record high ocean heat content; which is currently helping to destabilize key Antarctic marine glaciers like Thwaites Glacier.

...

This is not for the SO, but for a part of the Pacific Ocean. Still, it indicates the magnitudes of OHC over a period of the last 10.000 years. Researches extracted bottom sediment cores and calculated the intermediate water temperatures (IWT).
...

The air-sea-ice flux of the Pacific Ocean is not relevant to that of the Southern Ocean.  So if you want to post about the OHC of the Pacific Ocean, I support sidd's suggestion that you take that topic to another thread.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3770 on: September 17, 2020, 05:31:51 PM »
While it has been reported that the Covid pandemic has so far reduce fossil fuel consumption as compared to 2019; nevertheless, atmospheric CO2 concentrations continue to follow the same trend line that they have been following in recent decades.  Perhaps organic sources of GHG emissions, including from food waste (see the linked article), have increased this year:

Title: "Guest post: Coronavirus food waste comes with huge carbon footprint"

https://www.carbonbrief.org/guest-post-coronavirus-food-waste-comes-with-huge-carbon-footprint

Extract: "As the coronavirus pandemic disrupts supply chains around the world, it is likely that more food is being wasted than ever before at a time when more people are also going hungry.
With such waste already accounting for around 8% of global greenhouse gas emissions, this could also have serious implications for the food system’s climate impact.

Based on reports as the pandemic began to take hold, I estimate that early food losses from the US meat sector alone have resulted in a carbon footprint roughly equivalent to a small country.

There is another epidemic hiding in the shadow of coronavirus that is also causing large amounts of waste. African swine fever caused China to lose up to 40% of its 360m pigs last year.
How such losses will affect climate mitigation in the long term is uncertain. The US and China are both already looking to Brazil to fulfill their meat demand, signing long-term contracts that will dramatically increase the nation’s meat production.

This cannot be good for deforestation in the Amazon, but maybe high meat prices will also translate into long-term reduction in meat consumption habits."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3771 on: September 18, 2020, 12:55:44 AM »
In the linked article Stefan Rahmstorf cites new peer reviewed evidence that the AMOC is currently slowing and that some CMIP6 projections indicate further weakening (~34 to 45% by 2100); however, the CMIP6 projections do not consider a significant freshwater hosing event (such as from the Beaufort Gyre and/or the WAIS) in coming decades.  In my opinion an abrupt slowing of the (A)MOC in the coming decades could raise the Tropical Pacific SSTA by about 5C; which could irreversibly push the Earth into a higher climate state (before 2100) due to a decadal-scale freshwater hosing event.

Title: "New studies confirm weakening of the Gulf Stream circulation (AMOC)"

http://www.realclimate.org/index.php/archives/2020/09/new-studies-confirm-weakening-of-the-gulf-stream-circulation-amoc/

Extract: "Two new studies now provide further independent evidence of this weakening. In August a paper by Christopher Piecuch of the Woods Hole Oceanographic Institution on the Florida Current – the part of the Gulf Stream system along the Florida coast – was published. Although continuous measurements of the current have only been available since 1982, Piecuch was able to reconstruct the strength of the Florida Current over the last 110 years from measurements of the sea level difference between the two sides of the current. To do so, he used 46 tide gauge stations in Florida and the Caribbean as well as a simple physical principle: the Coriolis force deflects currents in the northern hemisphere to the right, so that the water on the right side of a current stands higher than on the left. The stronger the current, the greater the difference in sea level. Comparison with measurements since 1982 shows that the method works reliably.

The result: the Florida current has weakened significantly since 1909 and in the last twenty years has probably been as weak as never before. Piecuch’s calculations also show that the resulting reduction of heat transport is sufficient to explain the ‘cold blob’ in the northern Atlantic.

This Monday, in Nature Climate Change a further study appeared, of researchers of Peking University and Ohio State University (Chenyu Zhu and Zhengyu Liu). For the first time, their paper provides evidence for an AMOC slowdown based on data from outside the North Atlantic. Model simulations show that a weakening of the AMOC leads to an accumulation of salt in the subtropical South Atlantic. This is due to the fact that strong evaporation in this region constantly increases the salinity, while the upper branch of the ocean circulation drains the salty water northwards, continually bringing in less salty water from the south. When this current weakens, the water in this region becomes saltier. This is exactly what the measured data show, in accordance with computer simulations. The authors speak of a “salinity fingerprint” of the weakening Atlantic circulation.

However, the latest generation (CMIP6) of climate models shows one thing: if we continue to heat up our planet, the AMOC will weaken further – by 34 to 45% by 2100. This could bring us dangerously close to the tipping point at which the flow becomes unstable."
« Last Edit: September 18, 2020, 01:01:30 AM by AbruptSLR »
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3772 on: Today at 02:19:37 PM »
...In my opinion an abrupt slowing of the (A)MOC in the coming decades could raise the Tropical Pacific SSTA by about 5C; which could irreversibly push the Earth into a higher climate state (before 2100) due to a decadal-scale freshwater hosing event.


To raise the Tropical pacific SSTA by 5C you must first do away with convection, with clouds, with tropical thunderstorms. The tropics of today is a self-regulating system, in many ways acting as a thermostate.

What is it that will dispel all the clouds from the tropics in such a short time frame?

Meanwhile, cloud cover in the Tropical Pacific is UP in a long term trend.
And SST are more or less constant.