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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

Thomas Hobbes , English philosopher 1588-1679

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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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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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: September 19, 2020, 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.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3773 on: September 19, 2020, 09:39:16 PM »
"Meat consumption in low- and middle-income countries (LMICs) is continuing to rise ….".  This is not good news:

Title: "Guest post: Are low- and middle-income countries bound to eat more meat?"

https://www.carbonbrief.org/guest-post-are-low-and-middle-income-countries-bound-to-eat-more-meat

Extract: "Meat consumption in low- and middle-income countries (LMICs) is continuing to rise as middle classes expand, with consequences for health, the climate and economies, both locally and globally.

The impact of this trend, if it continues in its current form, could dwarf the impact of falling meat consumption in North America and Europe."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3774 on: September 19, 2020, 11:11:56 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.

As I have discussed this topic in many prior posts, here I will only note that:

1.   The 'Wolfpack' CMIP6 projections have ECS around 5C, and the first image from Andrew at Ringberg 2015 shows that for ECS around 5C the Eastern Tropical Pacific will likely warm-up in coming decades and I believe that a significant freshwater hosing event would slow the MOC and thus would warm the Tropical/Equatorial Pacific SST even more.
2.   The second image shows that as the surface waters of the Tropical/Equatorial Pacific warm, the more energetic associated water evaporation would drive more atmospheric deep convention, which would create more high-altitude clouds (a positive feedback on GMSTA) and would reduce the creation of low-altitude clouds (which would also act as a positive feedback on GMSTA); if so, this would create a positive feedback for more warming of the Tropical/Equatorial Pacific SSTA.

See also:

R. T. Pierrehumbert (February 15, 2000), "Climate change and the tropical Pacific: The sleeping dragon wakes", PNAS, 97 (4) 1355-1358; https://doi.org/10.1073/pnas.97.4.1355

https://www.pnas.org/content/97/4/1355

Extract: " Several energy flows that powerfully affect our climate come to a confluence in the tropical Pacific. The stirrings of this region are currently thought of mainly in connection with the coming and going of El Niño, which has a global impact but only on the 3- to 5-year time scale. There is a growing awareness that related processes have the potential to participate in more ponderous climate variations.

Deep convection over the Pacific occurs in the extensive ascending region associated with the Western Pacific warm pool and in the narrow and intense line-like feature known as the intertropical convergence zone (ITCZ). The regions of ascent are connected to, but not precisely identical with, the regions of warmest ocean waters. The warm pool has no intrinsic cloud, evaporative, or thermodynamically based “thermostat,” and in the absence of heat exports to the extratropics would escalate from its present temperature of 29°C to temperatures of 47°C or even more (7, 8).

The formation of convecting air is tippy in precisely the same sense and for precisely the same reason that formation of North Atlantic deep water is tippy. The tropical atmosphere is very nearly neutrally buoyant with regard to moisture-laden air parcels that release the latent heat of their moisture as they ascend. Hence, a small change in the moisture and temperature of the tropical boundary layer (relative to the overlying air) suffices to determine whether a region produces sufficient buoyancy to convect. Tropical convection creates “top air” in much the same way oceanic convection creates “bottom water.”

One of the more exotic possibilities is that a strengthening of the temperature contrast between the warm pool and the cold tongue could lead to a complete breakdown of the system of tropical easterly trade winds known since time immemorial. This breakdown could happen, if a tropical sea surface temperature anomaly forces a Rossby wave that carries easterly pseudomomentum away from the tropics, leading to a local westerly acceleration. If the forcing were strong enough, the westerly acceleration could overwhelm the easterly Coriolis acceleration caused by equatorward drift in the Hadley cell, whereupon the normal tropical winds would be replaced by a westerly superrotation. If the westerlies were to penetrate to the surface, the normal equatorial upwelling in the ocean would be replaced by downwelling, and other far-reaching climate changes would ensue. The superrotating state is well documented in idealized two-layer models (24) and has been found by several investigators employing realistic multilevel general circulation models (I. Held and D. Hartmann, personal communications; see also ref. 25). There is no evidence that a westerly superrotating state has ever occurred in any climate of the Earth's past, but then again, in some regard the particularly high CO2 climate with glaciated poles that we are now approaching is different from any that has ever before held sway on the planet. If one is tugging on the dragon's tail with little notion of how much agitation is required to wake him, one must be prepared for the unexpected."

&

Sherwood, S. C., S. Bony and J-L. Dufresne, Spread in model climate sensitivity traced to atmospheric convective mixing, Nature, Vol. 505, 2014, 37 42. April

http://web.science.unsw.edu.au/~stevensherwood/SherwoodBD2014.pdf

Edit: The third image shows that the MOC approaches the surface near the mid-point of the Equatorial/Tropical Pacific and push relatively warm water westward into the Pacific Warm Pool while the four image shows how the Humboldt (Peruvian) Current (which is a surface current) coveys relatively cold ACC water to the eastern Equatorial/Tropical Pacific.  If future global warming reverses the direction of the trade winds over the Equatorial Pacific (even for a few decades due to a significant freshwater hosing event), then things could get hot very quickly
« Last Edit: September 21, 2020, 01:14:47 AM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3775 on: September 21, 2020, 06:44:55 PM »
The linked references (& associated linked article) present recent findings from CMIP6 (ISMIP6) consensus SLR contributions from ice sheets in the coming decade.  It is noted here that these consensus contributions increase every new CMIP projection and that these projections do not include risks from freshwater hosing events.

Title: "Special issue | The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6)" Editor(s): William Lipscomb, Sophie Nowicki, Helene Seroussi, Carlos Martin, Christina Hulbe, Douglas Brinkerhoff, Ayako Abe-Ouchi, and Robin Smith

https://tc.copernicus.org/articles/special_issue1019.html

&

Jourdain, N. C., Asay-Davis, X., Hattermann, T., Straneo, F., Seroussi, H., Little, C. M., and Nowicki, S.: A protocol for calculating basal melt rates in the ISMIP6 Antarctic ice sheet projections, The Cryosphere, 14, 3111–3134, https://doi.org/10.5194/tc-14-3111-2020, 2020.

https://tc.copernicus.org/articles/14/3111/2020/

Abstract
Climate model projections have previously been used to compute ice shelf basal melt rates in ice sheet models, but the strategies employed – e.g., ocean input, parameterization, calibration technique, and corrections – have varied widely and are often ad hoc. Here, a methodology is proposed for the calculation of circum-Antarctic basal melt rates for floating ice, based on climate models, that is suitable for ISMIP6, the Ice Sheet Model Intercomparison Project for CMIP6 (6th Coupled Model Intercomparison Project). The past and future evolution of ocean temperature and salinity is derived from a climate model by estimating anomalies with respect to the modern day, which are added to a present-day climatology constructed from existing observational datasets. Temperature and salinity are extrapolated to any position potentially occupied by a simulated ice shelf. A simple formulation is proposed for a basal melt parameterization in ISMIP6, constrained by the observed temperature climatology, with a quadratic dependency on either the nonlocal or local thermal forcing. Two calibration methods are proposed: (1) based on the mean Antarctic melt rate (MeanAnt) and (2) based on melt rates near Pine Island's deep grounding line (PIGL). Future Antarctic mean melt rates are an order of magnitude greater in PIGL than in MeanAnt. The PIGL calibration and the local parameterization result in more realistic melt rates near grounding lines. PIGL is also more consistent with observations of interannual melt rate variability underneath Pine Island and Dotson ice shelves. This work stresses the need for more physics and less calibration in the parameterizations and for more observations of hydrographic properties and melt rates at interannual and decadal timescales.

&

Goelzer, H., Nowicki, S., Payne, A., Larour, E., Seroussi, H., Lipscomb, W. H., Gregory, J., Abe-Ouchi, A., Shepherd, A., Simon, E., Agosta, C., Alexander, P., Aschwanden, A., Barthel, A., Calov, R., Chambers, C., Choi, Y., Cuzzone, J., Dumas, C., Edwards, T., Felikson, D., Fettweis, X., Golledge, N. R., Greve, R., Humbert, A., Huybrechts, P., Le clec'h, S., Lee, V., Leguy, G., Little, C., Lowry, D. P., Morlighem, M., Nias, I., Quiquet, A., Rückamp, M., Schlegel, N.-J., Slater, D. A., Smith, R. S., Straneo, F., Tarasov, L., van de Wal, R., and van den Broeke, M.: The future sea-level contribution of the Greenland ice sheet: a multi-model ensemble study of ISMIP6, The Cryosphere, 14, 3071–3096, https://doi.org/10.5194/tc-14-3071-2020, 2020.

https://tc.copernicus.org/articles/14/3071/2020/

Abstract
The Greenland ice sheet is one of the largest contributors to global mean sea-level rise today and is expected to continue to lose mass as the Arctic continues to warm. The two predominant mass loss mechanisms are increased surface meltwater run-off and mass loss associated with the retreat of marine-terminating outlet glaciers. In this paper we use a large ensemble of Greenland ice sheet models forced by output from a representative subset of the Coupled Model Intercomparison Project (CMIP5) global climate models to project ice sheet changes and sea-level rise contributions over the 21st century. The simulations are part of the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). We estimate the sea-level contribution together with uncertainties due to future climate forcing, ice sheet model formulations and ocean forcing for the two greenhouse gas concentration scenarios RCP8.5 and RCP2.6. The results indicate that the Greenland ice sheet will continue to lose mass in both scenarios until 2100, with contributions of 90±50 and 32±17 mm to sea-level rise for RCP8.5 and RCP2.6, respectively. The largest mass loss is expected from the south-west of Greenland, which is governed by surface mass balance changes, continuing what is already observed today. Because the contributions are calculated against an unforced control experiment, these numbers do not include any committed mass loss, i.e. mass loss that would occur over the coming century if the climate forcing remained constant. Under RCP8.5 forcing, ice sheet model uncertainty explains an ensemble spread of 40 mm, while climate model uncertainty and ocean forcing uncertainty account for a spread of 36 and 19 mm, respectively. Apart from those formally derived uncertainty ranges, the largest gap in our knowledge is about the physical understanding and implementation of the calving process, i.e. the interaction of the ice sheet with the ocean.

&

Seroussi, H., Nowicki, S., Payne, A. J., Goelzer, H., Lipscomb, W. H., Abe-Ouchi, A., Agosta, C., Albrecht, T., Asay-Davis, X., Barthel, A., Calov, R., Cullather, R., Dumas, C., Galton-Fenzi, B. K., Gladstone, R., Golledge, N. R., Gregory, J. M., Greve, R., Hattermann, T., Hoffman, M. J., Humbert, A., Huybrechts, P., Jourdain, N. C., Kleiner, T., Larour, E., Leguy, G. R., Lowry, D. P., Little, C. M., Morlighem, M., Pattyn, F., Pelle, T., Price, S. F., Quiquet, A., Reese, R., Schlegel, N.-J., Shepherd, A., Simon, E., Smith, R. S., Straneo, F., Sun, S., Trusel, L. D., Van Breedam, J., van de Wal, R. S. W., Winkelmann, R., Zhao, C., Zhang, T., and Zwinger, T.: ISMIP6 Antarctica: a multi-model ensemble of the Antarctic ice sheet evolution over the 21st century, The Cryosphere, 14, 3033–3070, https://doi.org/10.5194/tc-14-3033-2020, 2020.

https://tc.copernicus.org/articles/14/3033/2020/

Abstract
Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between −7.8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica mass change varies between −6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28 mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.

See also:

Title: "Melting ice sheets will add over 15 inches to global sea level rise by 2100"

https://www.space.com/melting-ice-sheets-sea-level-rise-2100.html

Extract: "If humans continue emitting greenhouse gases at the current pace, global sea levels could rise more than 15 inches (38 centimeters) by 2100, scientists found in a new study."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3776 on: September 21, 2020, 06:48:07 PM »
The linked reference indicates that the climate forcing from global aviation is higher than previously assumed by consensus climate science:

Lee, D. S. et al. (2020) The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018, Atmospheric Environment, doi:10.1016/j.atmosenv.2020.117834

https://www.sciencedirect.com/science/article/pii/S1352231020305689

Abstract
Global aviation operations contribute to anthropogenic climate change via a complex set of processes that lead to a net surface warming. Of importance are aviation emissions of carbon dioxide (CO2), nitrogen oxides (NOx), water vapor, soot and sulfate aerosols, and increased cloudiness due to contrail formation. Aviation grew strongly over the past decades (1960–2018) in terms of activity, with revenue passenger kilometers increasing from 109 to 8269 billion km yr−1, and in terms of climate change impacts, with CO2 emissions increasing by a factor of 6.8–1034 Tg CO2 yr−1. Over the period 2013–2018, the growth rates in both terms show a marked increase. Here, we present a new comprehensive and quantitative approach for evaluating aviation climate forcing terms. Both radiative forcing (RF) and effective radiative forcing (ERF) terms and their sums are calculated for the years 2000–2018. Contrail cirrus, consisting of linear contrails and the cirrus cloudiness arising from them, yields the largest positive net (warming) ERF term followed by CO2 and NOx emissions. The formation and emission of sulfate aerosol yields a negative (cooling) term. The mean contrail cirrus ERF/RF ratio of 0.42 indicates that contrail cirrus is less effective in surface warming than other terms. For 2018 the net aviation ERF is +100.9 mW (mW) m−2 (5–95% likelihood range of (55, 145)) with major contributions from contrail cirrus (57.4 mW m−2), CO2 (34.3 mW m−2), and NOx (17.5 mW m−2). Non-CO2 terms sum to yield a net positive (warming) ERF that accounts for more than half (66%) of the aviation net ERF in 2018. Using normalization to aviation fuel use, the contribution of global aviation in 2011 was calculated to be 3.5 (4.0, 3.4) % of the net anthropogenic ERF of 2290 (1130, 3330) mW m−2. Uncertainty distributions (5%, 95%) show that non-CO2 forcing terms contribute about 8 times more than CO2 to the uncertainty in the aviation net ERF in 2018. The best estimates of the ERFs from aviation aerosol-cloud interactions for soot and sulfate remain undetermined. CO2-warming-equivalent emissions based on global warming potentials (GWP* method) indicate that aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO2 emissions alone. CO2 and NOx aviation emissions and cloud effects remain a continued focus of anthropogenic climate change research and policy discussions.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3777 on: September 23, 2020, 06:06:43 PM »
Stability Check on Antarctica Reveals High Risk for Long-Term Sea-Level Rise
https://phys.org/news/2020-09-stability-antarctica-reveals-high-long-term.amp

The warmer it gets, the faster Antarctica loses ice - and much of it will then be gone forever. Consequences for the world's coastal cities and cultural heritage sites would be detrimental, from London to Mumbai, and from New York to Shanghai. That's what a team of researchers from the Potsdam Institute for Climate Impact Research, Potsdam University and New York's Columbia University has found out in their new study, published in Nature (cover story), on how much warming the Antarctic Ice Sheet can survive.

... "As the surrounding ocean water and atmosphere warm due to human greenhouse-gas emissions, the white cap on the South Pole loses mass and eventually becomes unstable. Because of its sheer magnitude, Antarctica's potential for sea-level contribution is enormous: We find that already at 2 degrees of warming, melting and the accelerated ice flow into the ocean will, eventually, entail 2.5 meters of global sea level rise just from Antarctica alone. At 4 degrees, it will be 6.5 meters and at 6 degrees almost 12 meters if these temperature levels would be sustained long enough."

Long-term change: it's not rapid, but it's forever

"Antarctica is basically our ultimate heritage from an earlier time in Earth's history. It's been around for roughly 34 million years. Now, our simulations show that once it's melted, it does not regrow to its initial state even if temperatures eventually sink again. Indeed, temperatures would have to go back to pre-industrial levels to allow its full recovery—a highly unlikely scenario. In other words: What we lose of Antarctica now is lost forever."



The animation shows the modelled long-term evolution of the Antarctic Ice Sheet under steadily increasing temperatures.

The upper panel shows the ice sheet's surface elevation change (in meters; grey shading), the ocean-induced melting at the base of the floating ice shelves (in meters per year; purple-orange shading), as well as the topography of the bed underneath the ice sheet and the surrounding ocean (in meters above the present-day sea level; blue-brown shading).

The lower panel shows the total sea-level relevant ice volume change (in meters of sea-level equivalent ; blue curve) and total ice mass flux (in gigatons per year; purple curve).


The hysteresis of the Antarctic Ice Sheet, Nature (2020).
https://www.nature.com/articles/s41586-020-2727-5
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3778 on: September 23, 2020, 11:26:44 PM »
Antarctic Ice Loss Expected to Affect Future Climate Change
https://phys.org/news/2020-09-antarctic-ice-loss-affect-future.html

In a new climate modeling study that looked at the impacts of accelerated ice melt from the Antarctic Ice Sheet (AIS) on future climate, a team of climate scientists reports that future ice-sheet melt is expected to have significant effects on global climate.

... Scientists have long recognized that future meltwater input from the Antarctic will affect the Southern Ocean and global climate, but ice-sheet processes are not now included in most state-of-the-art climate prediction simulations, Sadai says. She and colleagues report that their modeling with the added ice melt information reveals interacting processes.

For this work, Sadai's task was to add accelerated AIS melting and icebergs into simulations of Earth's future climate. One important step was to include the details of where and when the meltwater will go into the ocean.

"We found that future melt water coming off Antarctica leads to huge amounts of thick sea ice around the continent. With higher greenhouse gas emissions, the ice sheet melts faster, which in turn leads to more freshwater flowing into the ocean and more sea ice production."

All this additional meltwater and sea ice production dramatically slows the pace of future warming around Antarctica, the researchers report—seemingly welcome news. And remarkably, the climate impacts are not just restricted to the Antarctic. Condron, previously at UMass Amherst, points out that the cooling effects are felt worldwide.

But ,he adds, "All that said, it's important to note that this is not a global 'cooling' scenario—average global temperatures would still be roughly 3 degrees Celsius warmer than today due to human greenhouse gas emissions, even with the cooling effects of this melt water on climate."

That is not the end of the story. Even though atmospheric warming slows, the deep sea waters around Antarctica actually warm faster in their model. This is because, Condron explains, the new sea ice stops heat from escaping from the deeper waters to the atmosphere. "The subsurface ocean waters warm by as much as one degree Celsius, which can increase melting below parts of the ice sheet. This could make the ice sheet more unstable and accelerate rates of sea level rise beyond current projections."



Shaina Sadai, et.al., "Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming" Science Advances (2020).
https://advances.sciencemag.org/content/6/39/eaaz1169
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3779 on: September 24, 2020, 01:56:41 AM »
...

Shaina Sadai, et.al., "Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming" Science Advances (2020).
https://advances.sciencemag.org/content/6/39/eaaz1169

I provide the follow-on information that the reference concludes (even without considering MICI) that:

"Accounting for Antarctic discharge raises subsurface ocean temperatures by >1°C at the ice margin relative to simulations ignoring discharge.

Our results demonstrate a need to accurately account for meltwater input from ice sheets in order to make confident climate predictions."

Shaina Sadai, Alan Condron, Robert DeConto and David Pollard (23 Sep 2020), "Future climate response to Antarctic Ice Sheet melt caused by anthropogenic warming", Science Advances, Vol. 6, no. 39, eaaz1169, DOI: 10.1126/sciadv.aaz1169

https://advances.sciencemag.org/content/6/39/eaaz1169

Abstract
Meltwater and ice discharge from a retreating Antarctic Ice Sheet could have important impacts on future global climate. Here, we report on multi-century (present–2250) climate simulations performed using a coupled numerical model integrated under future greenhouse-gas emission scenarios IPCC RCP4.5 and RCP8.5, with meltwater and ice discharge provided by a dynamic-thermodynamic ice sheet model. Accounting for Antarctic discharge raises subsurface ocean temperatures by >1°C at the ice margin relative to simulations ignoring discharge. In contrast, expanded sea ice and 2° to 10°C cooler surface air and surface ocean temperatures in the Southern Ocean delay the increase of projected global mean anthropogenic warming through 2250. In addition, the projected loss of Arctic winter sea ice and weakening of the Atlantic Meridional Overturning Circulation are delayed by several decades. Our results demonstrate a need to accurately account for meltwater input from ice sheets in order to make confident climate predictions.

See also:

Title: "Antarctic Ice Loss Expected to Affect Future Climate Change"

https://www.umass.edu/newsoffice/article/antarctic-ice-loss-expected-affect-future

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3780 on: September 25, 2020, 07:47:49 AM »
The linked reference indicates that projected Antarctic sea ice loss by the end of this century will lead to robust Arctic warming:

M R England, L M Polvani and L Sun (17 September 2020), "Robust Arctic warming caused by projected Antarctic sea ice loss", Environmental Research Letters, Volume 15, Number 10

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

Abstract
Over the coming century, both Arctic and Antarctic sea ice cover are projected to substantially decline. While many studies have documented the potential impacts of projected Arctic sea ice loss on the climate of the mid-latitudes and the tropics, little attention has been paid to the impacts of Antarctic sea ice loss. Here, using comprehensive climate model simulations, we show that the effects of end-of-the-century projected Antarctic sea ice loss extend much further than the tropics, and are able to produce considerable impacts on Arctic climate. Specifically, our model indicates that the Arctic surface will warm by 1 °C and Arctic sea ice extent will decline by 0.5 × 106 km2 in response to future Antarctic sea ice loss. Furthermore, with the aid of additional atmosphere-only simulations, we show that this pole-to-pole effect is mediated by the response of the tropical SSTs to Antarctic sea ice loss: these simulations reveal that Rossby waves originating in the tropical Pacific cause the Aleutian Low to deepen in the boreal winter, bringing warm air into the Arctic, and leading to sea ice loss in the Bering Sea. This pole-to-pole signal highlights the importance of understanding the climate impacts of the projected sea ice loss in the Antarctic, which could be as important as those associated with projected sea ice loss in the Arctic.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3781 on: September 27, 2020, 11:16:38 AM »
...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.

As I have discussed this topic in many prior posts, here I will only note that:

1.   The 'Wolfpack' CMIP6 projections have ECS around 5C, and the first image from Andrew at Ringberg 2015 shows that for ECS around 5C the Eastern Tropical Pacific will likely warm-up in coming decades and I believe that a significant freshwater hosing event would slow the MOC and thus would warm the Tropical/Equatorial Pacific SST even more.
2.   The second image shows that as the surface waters of the Tropical/Equatorial Pacific warm, the more energetic associated water evaporation would drive more atmospheric deep convention, which would create more high-altitude clouds (a positive feedback on GMSTA) and would reduce the creation of low-altitude clouds (which would also act as a positive feedback on GMSTA); if so, this would create a positive feedback for more warming of the Tropical/Equatorial Pacific SSTA.

See also:

R. T. Pierrehumbert (February 15, 2000), "Climate change and the tropical Pacific: The sleeping dragon wakes", PNAS, 97 (4) 1355-1358; https://doi.org/10.1073/pnas.97.4.1355

 
&

Sherwood, S. C., S. Bony and J-L. Dufresne, Spread in model climate sensitivity traced to atmospheric convective mixing, Nature, Vol. 505, 2014, 37 42. April

http://web.science.unsw.edu.au/~stevensherwood/SherwoodBD2014.pdf

Edit: The third image shows that the MOC approaches the surface near the mid-point of the Equatorial/Tropical Pacific and push relatively warm water westward into the Pacific Warm Pool while the four image shows how the Humboldt (Peruvian) Current (which is a surface current) coveys relatively cold ACC water to the eastern Equatorial/Tropical Pacific.  If future global warming reverses the direction of the trade winds over the Equatorial Pacific (even for a few decades due to a significant freshwater hosing event), then things could get hot very quickly

ASLR, thanks for your reply!
You bring up a discussion paper by Pierrehumbert from 2000, where he discusses and speculates about various ideas about future changes. This is not a strong reference. Furtermore, when Pierrehumbert refers to potential rise in SST in the Eq.Pacific, he refers only to his own previous research. In the models he constructed, he made some very restrictive assumption. He e.g. says: "Clouds do not alter this conclusion because insofar as Cs + Cl = 0 in the tropics the reduction in solar absorption is compensated by an equal reduction in OLR"
This relates to the fact that in the tropical region the overall cloud effect is close to zero. This is a surprising statement and the subject of much study. These studies are discussed in detail at the SoD site:
https://scienceofdoom.com/2012/12/23/clouds-water-vapor-part-five-back-of-the-envelope-calcs-from-pierrehumbert/

Furthermore, in your post, you say that "things could get hot very quickly", and you quote Pierrehumbert who says: "There is no evidence that a westerly superrotating state has ever occurred in any climate of the Earth's past, ..."

Why should we even speculate about totally ungrounded theories of what might happen, when all the data show great stability in the tropical thermostat?!

(The other reference you provide, Sherwood, S. C., S. Bony and J-L. Dufresne, "Spread in model climate sensitivity traced to atmospheric convective mixing", has nothing relevant to provide for the discussion, as it evaluates ECS values in various GCMs, related to clouds.)

I will comment further on the thermostat function in the tropics in a later post.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3782 on: September 28, 2020, 03:42:45 PM »
...
Furthermore, in your post, you say that "things could get hot very quickly", and you quote Pierrehumbert who says: "There is no evidence that a westerly superrotating state has ever occurred in any climate of the Earth's past, ..."

...

First, heat is not uniformly distributed across the globe, so in my comment about things getting hot quickly I meant that a major freshwater hosing event in coming decades (say due to a reversal of the Beaufort Gyre) abruptly slowing the AMOC would quickly advect heat from the Gulf Stream to the Equatorial Pacific (see the first image) where it would likely rapidly increase the frequency of intense El Nino events; which would likely rapidly advect heat from the Equatorial Pacific to rapidly warm areas like the West Antarctica and northern parts of North America (see the second image).  Thus, while it is true that the Equatorial Pacific SSTA would not likely increase by 5C before the end of the century (due to the advection of heat to higher latitudes), this poleward advection of heat would help to prepare the world for a possible abrupt flip into an equable atmospheric pattern soon after 2100 as shown in the third image).

As far as your point that the planet is already heading into scenarios never seen before in the historical, or paleo, record (see the fourth image) that is very true, so please do not point to past saturations that do not model our current situation and conclude that we all will not be exposed to significant climate risk in the coming decades, continuing on for centuries.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3783 on: September 28, 2020, 03:58:05 PM »
As a follow-on to my last post, the first image shows that it is not only the Equatorial Pacific that will rapidly advect tropical ocean heat to higher latitudes, via atmospheric Rossby waves, but also other equatorial oceans; while the second attached image shows how as various feedback factors get triggered (including due to the poleward advection of such tropical heat) that climate sensitivity will increase in coming decades.  Furthermore, the third image shows that as heat stress increases in coming decades the associated damage will increase nonlinearly (indicating rapidly increasing climate risk); while the fourth image from the U.S. National Academy of Sciences shows how our collective climate risk PDF may better be represented by abrupt scenarios with fat right-tail risks rather than by the normal distribution commonly assumed by consensus climate scientists.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3784 on: September 29, 2020, 01:30:51 PM »

First, heat is not uniformly distributed across the globe, so in my comment about things getting hot quickly I meant that a major freshwater hosing event in coming decades (say due to a reversal of the Beaufort Gyre) abruptly slowing the AMOC would quickly advect heat from the Gulf Stream to the Equatorial Pacific (see the first image) where it would likely rapidly increase the frequency of intense El Nino events; which would likely rapidly advect heat from the Equatorial Pacific to rapidly warm areas like the West Antarctica and northern parts of North America (see the second image).  Thus, while it is true that the Equatorial Pacific SSTA would not likely increase by 5C before the end of the century (due to the advection of heat to higher latitudes), this poleward advection of heat would help to prepare the world for a possible abrupt flip into an equable atmospheric pattern soon after 2100 as shown in the third image).

...

As always, thanks ASLR for your replies!
Yes, we have now at least established that the Equatorial Pacific SSTA are unlikely to increase by 5C.
Here is a recent reference to what's going on, as the tropical SST's aren't increasing as a response to forcings, but instead the tropics are expanding polewards. More heat needs to be advected, but it happens by increasing the surface area instead of by raising temperatures.
The equatorial tropical ocean thermostat keeps temperatures stable, see figure.

Hu Yang et al, "Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients", Journal of Geophysical Research: Atmospheres (2020)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JD033158

Fig 13 byline: Sensitivity simulation of SST anomaly under forcing of poleward shift of surface wind. ... (b) SST anomaly under forcing of shifting wind.
The right panel gives the zonal mean SST anomaly (red). Results are based on sensitivity experiment carried out by FESOM. Stippling denotes regions
where the anomalies are significant (Student's t test).

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3785 on: September 29, 2020, 06:19:54 PM »
...
Yes, we have now at least established that the Equatorial Pacific SSTA are unlikely to increase by 5C.
...

While I agree that the Equatorial Pacific SSTA is unlikely to increase by 5C by 2100, I am concerned that due to accelerated polar amplification that shortly after 2100 that a changed atmosphere could flip both the atmosphere and the Equatorial Pacific SSTA (near 5C) into an equable pattern possible as early as 2150.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3786 on: September 30, 2020, 03:41:38 AM »
While I disagree with the timeframes cited in the linked reference, I provide the following information for those who are interested:

Garbe, J., Albrecht, T., Levermann, A. et al. The hysteresis of the Antarctic Ice Sheet. Nature 585, 538–544 (2020). https://doi.org/10.1038/s41586-020-2727-5

https://www.nature.com/articles/s41586-020-2727-5

Abstract: "More than half of Earth’s freshwater resources are held by the Antarctic Ice Sheet, which thus represents by far the largest potential source for global sea-level rise under future warming conditions1. Its long-term stability determines the fate of our coastal cities and cultural heritage. Feedbacks between ice, atmosphere, ocean, and the solid Earth give rise to potential nonlinearities in its response to temperature changes. So far, we are lacking a comprehensive stability analysis of the Antarctic Ice Sheet for different amounts of global warming. Here we show that the Antarctic Ice Sheet exhibits a multitude of temperature thresholds beyond which ice loss is irreversible. Consistent with palaeodata2 we find, using the Parallel Ice Sheet Model3,4,5, that at global warming levels around 2 degrees Celsius above pre-industrial levels, West Antarctica is committed to long-term partial collapse owing to the marine ice-sheet instability. Between 6 and 9 degrees of warming above pre-industrial levels, the loss of more than 70 per cent of the present-day ice volume is triggered, mainly caused by the surface elevation feedback. At more than 10 degrees of warming above pre-industrial levels, Antarctica is committed to become virtually ice-free. The ice sheet’s temperature sensitivity is 1.3 metres of sea-level equivalent per degree of warming up to 2 degrees above pre-industrial levels, almost doubling to 2.4 metres per degree of warming between 2 and 6 degrees and increasing to about 10 metres per degree of warming between 6 and 9 degrees. Each of these thresholds gives rise to hysteresis behaviour: that is, the currently observed ice-sheet configuration is not regained even if temperatures are reversed to present-day levels. In particular, the West Antarctic Ice Sheet does not regrow to its modern extent until temperatures are at least one degree Celsius lower than pre-industrial levels. Our results show that if the Paris Agreement is not met, Antarctica’s long-term sea-level contribution will dramatically increase and exceed that of all other sources."
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3787 on: September 30, 2020, 09:22:58 AM »

While I agree that the Equatorial Pacific SSTA is unlikely to increase by 5C by 2100, I am concerned that due to accelerated polar amplification that shortly after 2100 that a changed atmosphere could flip both the atmosphere and the Equatorial Pacific SSTA (near 5C) into an equable pattern possible as early as 2150.

So, You still believe that the tropics can get in a runaway state with very quick warming, 5C higher  SST's. Only 50 years later, than you said before (current guess: 2150). The mechanism for this remains unclear, all you say is that a "changed atmosphere could flip both the atmosphere and the Equatorial Pacific SSTA (near 5C) into an equable pattern".

I dispute that, as all data show that the tropics is a climatically stable region, and regulates itself almost as a 'thermostat', and is rather undisturbed by increased forcings. The tropical ocean seesaws between the states of net energy absorber before, and net energy supplier after, the deep moist convection, which causes the SST to vacillate between 28 - 30 C, see the figure in post #3772, which shows completely stable SST's in the Eq.Pacific over the last 40 years. This threshhold of less than 30C is expected to rise slowly, as SST's rise, but the convective processes are robust as per the research I review at the end of this post.

In post #3771 you said: "In my opinion an abrupt slowing of the (A)MOC in the coming decades could raise the Tropical Pacific SSTA by about 5C". Now you say that the ensuing "flip to an equable climate" will be caused by a "changed atmosphere", due to increased polar amplification. So, what is the exact mechanism here?

What IS proven to be happening, is that the tropical region is widening (i.e.increasing in latitudes), as more heat needs to be processed and advected there. That the tropics are expanding is shown in the paper "Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients" , by Yang et al., 2020, that I mentioned in my previous post.

There are several references to the robustness of the convective processes, i.e. the thermostatic properties, of the tropics. Most of what is reported in these papers is implicitly confirmed in the Yang et al 2020 paper:

1. "Mechanisms Regulating Sea-Surface Temperatures and Deep Convection in the Tropics"
by Sud, Walker, Lau, GEOPHYSICAL RESEARCH LETTERS, 1999

Quotes: "nevertheless the modus operandi of tropical air-sea interactions has been fully revealed. ...besides suppressing solar irradiation into the ocean with cloud cover, the moist convection dumps cooler and drier air on to the sea-surface by downdrafts which leads to a large increase in surface fluxes. In this way, deep convection is able to nudge the tropical ocean from its state of an energy receiver (warming phase) to that of an energy supplier (cooling phase). This is a thermostat-like control, but it is intrinsically different from Ramanathan and Collins (1991) who used a cloud-radiative thermostat to explain the entire SST regulation."

2. "AGGREGATED CONVECTION AND THE REGULATION OF TROPICAL CLIMATE" by Khairoutdinov and Emanuel, 2010, 29th Conf. on Hurricanes and Tropical Meteorology, Tucson, AZ, Amer. Meteor. Soc., P2.69. [Available online at http://ams.confex.com/ams/29Hurricanes/techprogram/paper_168418.htm

"Summary. Idealized simulations of radiative-convective
equilibrium suggest that the tropical atmosphere may
have at least two stable equilibrium states or phases, one
is convection that is random in time and space, and the
second is the spontaneously aggregated convection. In
this study, we have demonstrated using a simplified and
full-physics cloud-system-resolving models that there is
an abrupt phase transition between these two
equilibrium states depending on the surface temperature,
with higher SST being conducive to the aggregation. A
significant drying of the free troposphere and
consequent reduction of the greenhouse effect
accompany self-aggregation; thus, the sea-surface
temperature in the aggregated state tends to fall until
convection is forced to disaggregate. This leads to the
hypothesis that when surface temperature is allowed to
adjust to variations of net surface fluxes, the convection
may be attracted toward a self-organized critical state
between aggregated and disaggregated states. Tests
using a simplified toy model seem to support this
hypothesis. The toy model also demonstrates that the
climate sensitivity of this self-organized critical state is
much lower than the sensitivity of the conventional
radiative-convective equilibrium. Preliminary results
using a full-physics cloud-system-resolving model
reveal strong hysteresis of the modeled system, ..."

3. "Changes in the sea surface temperature threshold for tropical convection" by Johnson and Xie, in Nature Geoscience,  DOI: 10.1038/NGEO1008,

"Deep convection over tropical oceans is observed generally above a threshold for sea surface temperatures, which falls in the vicinity of 26–28 C. High-resolution models suggest that the related sea surface temperature threshold for tropical cyclones rises in a warming climate..... "
"The variability of the tropical SST threshold for convection is robust and clearly detectable in both observations and in global climate models. As a result of the inextricable link between the SST threshold and upper-tropospheric conditions, the examination of the SST threshold may provide important information on tropical tropospheric trends under global warming, particularly given the non-climatic artefacts found in radiosonde and satellite-derived data sets. Both the observational data and model simulations indicate that, as a consequence of approximate MALR adjustment, the SST threshold for convection has risen and will continue to rise in tandem with the tropical mean SST"

4. "Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models"
Thorsten Mauritsen* and Bjorn Stevens, in Nature Geoscience 2015
DOI: 10.1038/NGEO2414

"Abstract: Equilibrium climate sensitivity to a doubling of CO2 falls between 2.0 and 4.6 K in current climate models, and they suggest
a weak increase in global mean precipitation. Inferences from the observational record, however, place climate sensitivity near the lower end of this range and indicate that models underestimate some of the changes in the hydrological cycle. These discrepancies raise the possibility that important feedbacks are missing from the models. A controversial hypothesis suggests that the dry and clear regions of the tropical atmosphere expand in a warming climate and thereby allow more infrared radiation to escape to space. This so-called iris effect could constitute a negative feedback that is not included in climate models. We find that inclusion of such an effect in a climate model moves the simulated responses of both temperature and the hydrological cycle to rising atmospheric greenhouse gas concentrations closer to observations. Alternative suggestions for shortcomings of models — such as aerosol cooling, volcanic
eruptions or insufficient ocean heat uptake — may explain a slow observed transient warming relative to models, but not the observed enhancement of the hydrological cycle. We propose that, if precipitating convective clouds are more likely to cluster into larger clouds as temperatures rise, this process could constitute a plausible physical mechanism for an iris effect."

5. "Effects of doubled CO2 on tropical sea surface temperatures (SSTs) for onset of deep convection and maximum SST: Simulations based inferences" by Sud et al, 2008, GEOPHYSICAL RESEARCH LETTERS

This is a model based study, so is of limited value: "...the model simulated realistic convective coupling between SSTs and atmospheric soundings and that the simulated-data correlations between SSTs and 300 hPa moist-static energies were similar to the observed. Model predicted SST limits for (i) the onset of deep convection and (ii) maximum SST, increased in the doubled CO2 environment. Changes in cloud heights, cloud frequencies, and cloud mass-fractions showed that convective-cloud changes increased the SSTs, while warmer mixed-layer of the doubled CO2 contained 10% more water vapor; clearly that would be conducive to more intense storms and hurricanes."

doi:10.1029/2008GL033872

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3788 on: September 30, 2020, 05:32:27 PM »
The linked reference reminds use that Southern Ocean Clouds have a major impact on climate sensitivity and that many consensus climate-models do not do a good job of modeling these impacts.  However, the reference indicates that CAM6 (used in some CMIP6 simulations) likely is doing a better job of modelling the physics of these impacts than earlier simulations:

A. Gettelman et al. (27 September 2020), "Simulating Observations of Southern Ocean Clouds and Implications for Climate", JGR Atmospheres, https://doi.org/10.1029/2020JD032619

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JD032619?af=R

Abstract
Southern Ocean (S. Ocean) clouds are important for climate prediction. Yet, previous global climate models failed to accurately represent cloud phase distributions in this observation‐sparse region. In this study, data from the Southern Ocean Clouds, Radiation, Aerosol, Transport Experimental Study (SOCRATES) experiment is compared to constrained simulations from a global climate model (the Community Atmosphere Model, CAM). Nudged versions of CAM are found to reproduce many of the features of detailed in‐situ observations, such as cloud location, cloud phase and boundary layer structure. The simulation in CAM6 has improved its representation of S. Ocean clouds with adjustments to the ice nucleation and cloud microphysics schemes that permit more supercooled liquid. Comparisons between modeled and observed hydrometeor size distributions suggest that the modeled hydrometeor size distributions represent the dual peaked shape and form of observed distributions, which is remarkable given the scale difference between model and observations. Comparison to satellite observations of cloud physics is difficult due to model assumptions that do not match retrieval assumptions. Some biases in the model's representation of S. Ocean clouds and aerosols remain, but the detailed cloud physical parameterization provides a basis for process level improvement and direct comparisons to observations. This is crucial because cloud feedbacks and climate sensitivity are sensitive to the representation of Southern Ocean clouds.

Plain Language Summary
Clouds over the Southern Ocean are important for climate prediction, and may influence the evolution of global temperatures. Thus these clouds are important to represent properly in models; however, recent studies have revealed models inadequately represent Southern Ocean cloud occurrence and phase, which drive large biases in radiation and subsequent climate sensitivity. Observations from research aircraft over the Southern Ocean south of Australia are compared to simulations with a global climate model which is `nudged' to reproduce the day to day cloud systems which are sampled. Despite being a coarse horizontal and vertical resolution, the model is able to reproduce many details of cloud phase and water content during the flights. However, the model has some biases, and these observations have been used to improve the model to better represent cloud phase. These results point to specific observational constraints for improving model simulations.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3789 on: September 30, 2020, 05:55:48 PM »
...

So, You still believe that the tropics can get in a runaway state with very quick warming, 5C higher  SST's. Only 50 years later, than you said before (current guess: 2150). The mechanism for this remains unclear, all you say is that a "changed atmosphere could flip both the atmosphere and the Equatorial Pacific SSTA (near 5C) into an equable pattern".

...

The linked reference confirms that Arctic Amplification has led to a deceleration of eastward propagating Rossby waves (which convey heat from the tropics poleward see the attached images).  This partially explains why I expect the advection of heat from the tropical oceans to the poles to progressively slowdown by 2100, sufficiently to change cloud feed enough to cause a flip to an equable atmospheric climate pattern by about 2150.

Jacopo Riboldi et al. (28 September 2020), "On the linkage between Rossby wave phase speed, atmospheric blocking and Arctic Amplification", Geophysical Research Letters, https://doi.org/10.1029/2020GL087796

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL087796?af=R

Abstract
It has been hypothesized that enhanced Arctic warming with respect to midlatitudes, known as Arctic Amplification, had led to a deceleration of eastward propagating Rossby waves, more frequent atmospheric blocking and extreme weather in recent decades. We employ a novel, daily climatology of Rossby wave phase speed between March 1979 and November 2018, based on upper‐level wind data, to test this hypothesis and describe phase speed variability. The diagnostic distinguishes between periods of enhanced or reduced eastward wave propagation and is related to the occurrence of blocking and extreme temperatures over midlatitudes. While remaining tied to the upper‐level geopotential gradient, decadal trends in phase speed did not accompany the observed reduction in the low‐level temperature gradient. These results confirm the link between low phase speeds and extreme temperature events, but indicate that Arctic Amplification did not play a decisive role in modulating phase speed variability in recent decades.

Plain Language Summary
The Arctic is warming more rapidly than midlatitudes and the temperature difference between those regions is being reduced. As a result, it has been hypothesized that the jet stream will decrease in intensity and its meanders will move more slowly eastward, leading to more persistent or even extreme weather conditions. As the persistence of weather can substantially vary within and between seasons, assessing long‐term changes is not trivial. To tackle this problem, we develop a weather speedometer and quantify the west‐east displacements of jet meanders over Northern Hemisphere midlatitudes. This metric diagnoses whether jet meanders are on average propagating eastward (positive values), stagnating or even retrogressing westward (negative values) on each day between March 1979 and November 2018. Using this metric, we confirm that low speed periods are related to temperature extremes over northern midlatitudes. We also assess that there has not been an overall decrease in the propagation of jet meanders despite the significant reduction of the meridional temperature difference observed in recent decades. Results suggest the need of an improved understanding of the factors determining the persistence of weather conditions and remind caution is needed when attributing recent extreme weather to an increased stagnation of jet stream meanders.
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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3790 on: September 30, 2020, 06:41:40 PM »
Greenland Is On Track to Lose Ice Faster Than In Any Century Over 12,000 Years: Study
https://phys.org/news/2020-09-greenland-track-ice-faster-century.html



Greenland's rate of ice loss this century is likely to greatly outpace that of any century over the past 12,000 years, a new study concludes.

The research will be published on Sept. 30 in the journal Nature. The study employs ice sheet modeling to understand the past, present and future of the Greenland Ice Sheet. Scientists used new, detailed reconstructions of ancient climate to drive the model, and validated the model against real-world measurements of the ice sheet's contemporary and ancient size.

The findings place the ice sheet's modern decline in historical context, highlighting just how extreme and unusual projected losses for the 21st century could be, researchers say.

... "If the world goes on a massive energy diet, in line with a scenario that the Intergovernmental Panel on Climate Change calls RCP2.6, our model predicts that the Greenland Ice Sheet's rate of mass loss this century will be only slightly higher than anything experienced in the past 12,000 years," Briner adds. "But, more worrisome, is that under a high-emissions RCP8.5 scenario—the one the Greenland Ice Sheet is now following—the rate of mass loss could be about four times the highest values experienced under natural climate variability over the past 12,000 years."

Jason P. Briner, et.al, Rate of mass loss from the Greenland Ice Sheet will exceed Holocene values this century, Nature (2020)
https://www.nature.com/articles/s41586-020-2742-6
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3791 on: October 01, 2020, 08:57:10 PM »
The linked reference indicates that recent global warming is making the oceans more stable; which increases surface temperatures and reduces the carbon absorbed by the ocean.  This increases the risk of abrupt climate change in the coming decades:

Li, G., Cheng, L., Zhu, J. et al. Increasing ocean stratification over the past half-century. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-00918-2

https://www.nature.com/articles/s41558-020-00918-2

Abstract: "Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down to depths of 2,000 m using the squared buoyancy frequency N2 and newly available ocean temperature/salinity observations. We find that stratification globally has increased by a substantial 5.3% [5.0%, 5.8%] in recent decades (1960–2018) (the confidence interval is 5–95%); a rate of 0.90% per decade. Most of the increase (~71%) occurred in the upper 200 m of the ocean and resulted largely (>90%) from temperature changes, although salinity changes play an important role locally."
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3792 on: October 02, 2020, 08:53:55 AM »

1. "Mechanisms Regulating Sea-Surface Temperatures and Deep Convection in the Tropics"
by Sud, Walker, Lau, GEOPHYSICAL RESEARCH LETTERS, 1999

2. "AGGREGATED CONVECTION AND THE REGULATION OF TROPICAL CLIMATE" by Khairoutdinov and Emanuel, 2010, 29th Conf. on Hurricanes and Tropical Meteorology, Tucson, AZ, Amer. Meteor. Soc., P2.69. [Available online at http://ams.confex.com/ams/29Hurricanes/techprogram/paper_168418.htm

3. "Changes in the sea surface temperature threshold for tropical convection" by Johnson and Xie, in Nature Geoscience,  DOI: 10.1038/NGEO1008,

4. "Missing iris effect as a possible cause of muted hydrological change and high climate sensitivity in models"
Thorsten Mauritsen* and Bjorn Stevens, in Nature Geoscience 2015
DOI: 10.1038/NGEO2414

5. "Effects of doubled CO2 on tropical sea surface temperatures (SSTs) for onset of deep convection and maximum SST: Simulations based inferences" by Sud et al, 2008, GEOPHYSICAL RESEARCH LETTERS
doi:10.1029/2008GL033872

I would add the following two papers to the list of papers showing the climatic stability (the 'thermostat' function) of the tropics:

6. "The lightness of water vapor helps to stabilize tropical climate", by Seidel and Yang, Science Advances , 2020:
DOI: 10.1126/sciadv.aba1951
"Abstract: Moist air is lighter than dry air at the same temperature, pressure, and volume because the molecular weight of water is less than that of dry air. We call this the vapor buoyancy effect. Although this effect is well documented, its impact on Earth’s climate has been overlooked. Here, we show that the lightness of water vapor helps to stabilize tropical climate by increasing the outgoing longwave radiation (OLR). In the tropical atmosphere, buoyancy is horizontally uniform. Then, the vapor buoyancy in the moist regions must be balanced by warmer temperatures in the dry regions of the tropical atmosphere. These higher temperatures increase tropical OLR. This radiative effect increases with warming, leading to a negative climate feedback. At a near present-day surface temperature, vapor buoyancy is responsible for a radiative effect of 1 W/m2 and a negative climate feedback of about 0.15 W/m2 per kelvin."

"Other authors have aggregated all greater-than-surface
warming of the troposphere together into a single “lapse rate feedback”
(22, 30). Such a combined approach may not be appropriate.
The origin and amplitude of the vapor buoyancy feedback depend
on the horizontal distributions of temperature and moisture. Understanding
the vapor buoyancy feedback, therefore, requires at least
two columns or even two dimensions. This is fundamentally different
from the conventional explanation of the tropical lapse rate feedback
based on a single-column process—the temperature profile (the moist
adiabat) is steepening from additional latent heating with warming. ... By excluding the vapor buoyancy effect, these modeling
frameworks have considerable biases in estimating atmospheric
buoyancy, cloud fraction, radiative feedbacks, and, thereby, climate
stability. Therefore, it is desirable to properly represent the vapor
buoyancy ... the vapor buoyancy feedback
may play a profound role in stabilizing Earth’s tropical climate

at present. We expect that it plays an even greater role in explaining
Earth’s past climates. A recent review of paleoclimate data and simulations
of the hot Eocene climate has suggested surface temperatures
as high as 310 K in the tropics (34). Although considerably warmer
than our present climate, such a temperature still reflects greater
stability in tropical climate than in extratropical climate
. Referring
to our Fig. 5D, such surface temperatures would imply a much
stronger vapor buoyancy feedback than at present (about 0.5 W/m2
per kelvin). Therefore, the vapor buoyancy feedback may have played
a leading role in stabilizing tropical climates in the past
."
(This paper has been mentioned by ASLR upthread)

7.  "Tropical Expansion Driven by Poleward Advancing Midlatitude Meridional Temperature Gradients" , by Yang et al., 2020, (mentioned in my previous post #3784 and in other posts on the forum.)

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3793 on: October 02, 2020, 04:55:21 PM »
The linked reference reminds us that the Tropical Pacific is capable of reorganizing itself into a permanent El Nino condition as occurred during the mid-Pliocene:

John C.H. Chiang (30 May 2009), "The Tropics in Paleoclimate", Annual Review of Earth and Planetary Sciences, Vol. 37:263-297, https://doi.org/10.1146/annurev.earth.031208.100217

https://www.annualreviews.org/abs/doi/10.1146/annurev.earth.031208.100217?intcmp=trendmd

Abstract: "The past decade saw a surge in interest in the role of the Tropics in paleoclimate changes. This was motivated by the emergence of outstanding questions in paleoclimate that pointed to a role for the Tropics in addition to advances in tropical climate dynamics. This article reviews these developments, starting from a historical perspective. Three properties of tropical dynamics are prominent in paleoclimate: the sensitivity of the tropical climate to change; the ability of the tropical climate to reorganize; and the ability of the tropical climate to project its influence globally. The El Niño-Southern Oscillation (ENSO) system exemplifies these properties, making ENSO particularly prominent in paleoclimate. Summaries of three paleoclimate cases in which the science developed over the past decade—mid-Holocene ENSO, abrupt climate change during the most recent glacial period, and the mid-Pliocene permanent El Niño scenario—illustrate how the tropical hypothesis worked its way into paleoclimate research. This review closes with a discussion of prevailing views of the Tropics in the paleoclimate changes."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3794 on: October 02, 2020, 09:27:51 PM »
The linked reference, and associate article, confirms that the atmosphere (including trade winds and rainfall patterns) over the Tropical Pacific can be reorganized into a permanent El Nino pattern, within a human lifespan, once GHG concentrations reach Pliocene level (which we have recently reached).  This supports my belief, that with one (or more) significant freshwater hosing event(s) in the coming decades that the Tropical Pacific Ocean SSTAs could increase by 5C over pre-industrial in the 2100 to 2150 timeframe.

Jessica E. Tierney et al, Pliocene warmth consistent with greenhouse gas forcing, Geophysical Research Letters (2019). DOI: 10.1029/2019GL083802

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL083802

Abstract
With CO2 concentrations similar to today (410 ppm), the Pliocene Epoch offers insights into climate changes under a moderately warmer world. Previous work suggested a low zonal sea surface temperature (SST) gradient in the tropical Pacific during the Pliocene, the so‐called “permanent El Niño.” Here, we recalculate SSTs using the alkenone proxy and find moderate reductions in both the zonal and meridional SST gradients during the mid‐Piacenzian warm period. These reductions are captured by coupled climate model simulations of the Pliocene, especially those that simulate weaker Walker circulation. We also produce a spatial reconstruction of mid‐Piacenzian warm period Pacific SSTs that closely resembles both Pliocene and future, low‐emissions simulations, a pattern that is, to a first order, diagnostic of weaker Walker circulation. Therefore, Pliocene warmth does not require drastic changes in the climate system—rather, it supports the expectation that the Walker circulation will weaken in the future under higher CO2.

Plain Language Summary
The Pliocene Epoch is the most recent time in Earth history when CO2 levels exceeded 400 ppm. The climate was warmer than preindustrial times, with smaller ice sheets. Previous studies suggested that the Pacific ocean was stuck in a “permanent El Niño” during the Pliocene. However, climate model simulations do not predict that this would happen at CO2 levels near 400 ppm—unusual changes in climate, such as large changes in cloud cover or hurricane frequency, would be needed to explain it. In this work we reanalyze Pliocene sea surface temperature data and do not find evidence of a permanent El Niño. Our results suggest that difference in temperatures across the tropical Pacific was smaller than it is today, but only by about 1 °C. Climate model simulations agree with our new analysis, suggesting that higher CO2, along with small changes in ice, vegetation, and mountains, is enough to explain Pliocene climate. We also show that the sea surface temperature patterns in the Pliocene Pacific Ocean look similar to those that climate models predict under a low‐emissions climate change scenario. The similarity suggests that the Pliocene can help us understand how the tropics respond to an ongoing increase in CO2.

&

Title: "Ancient plankton help researchers predict near-future climate"

https://phys.org/news/2019-08-ancient-plankton-near-future-climate.html

Extract: "The eastern Pacific got warmer than the western, which caused the trade winds to slacken and changed precipitation patterns. Dry places like Peru and Arizona might have been wetter. These results from the Pliocene agree with what future climate models have predicted, as a result of CO2 levels reaching 400 ppm.

"However, the changes in the atmosphere that happen in response to CO2 - like the changes in the trade winds and rainfall patterns—can definitely occur within the span of a human life."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3795 on: October 03, 2020, 12:08:45 AM »
Quote
confirms that the atmosphere (including trade winds and rainfall patterns) over the Tropical Pacific can be reorganized into a permanent El Nino pattern, within a human lifespan, once GHG concentrations reach Pliocene level

Quote
In this work we reanalyze Pliocene sea surface temperature data and do not find evidence of a permanent El Niño.

Which is it?
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3796 on: October 03, 2020, 12:56:53 AM »
Quote
confirms that the atmosphere (including trade winds and rainfall patterns) over the Tropical Pacific can be reorganized into a permanent El Nino pattern, within a human lifespan, once GHG concentrations reach Pliocene level

Quote
In this work we reanalyze Pliocene sea surface temperature data and do not find evidence of a permanent El Niño.

Which is it?

The confusion may likely be associated with reporting average Pliocene SSTA vs reporting different SSTA values for the early, mid and late Pliocene.  There is evidence that during the early Pliocene El Nino response was weakened; however, based on paleo-evidence from the late Pliocene, the linked reference concludes that:

"Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes."

As increases in SST is critical to climate risk, to me the findings of this reference indicate that current consensus climate model projections are erring on the side of least drama:

McClymont, E. L., Ford, H. L., Ho, S. L., Tindall, J. C., Haywood, A. M., Alonso-Garcia, M., Bailey, I., Berke, M. A., Littler, K., Patterson, M. O., Petrick, B., Peterse, F., Ravelo, A. C., Risebrobakken, B., De Schepper, S., Swann, G. E. A., Thirumalai, K., Tierney, J. E., van der Weijst, C., White, S., Abe-Ouchi, A., Baatsen, M. L. J., Brady, E. C., Chan, W.-L., Chandan, D., Feng, R., Guo, C., von der Heydt, A. S., Hunter, S., Li, X., Lohmann, G., Nisancioglu, K. H., Otto-Bliesner, B. L., Peltier, W. R., Stepanek, C., and Zhang, Z.: Lessons from a high-CO2 world: an ocean view from  ∼ 3 million years ago, Clim. Past, 16, 1599–1615, https://doi.org/10.5194/cp-16-1599-2020, 2020.

https://cp.copernicus.org/articles/16/1599/2020/

Abstract
A range of future climate scenarios are projected for high atmospheric CO2 concentrations, given uncertainties over future human actions as well as potential environmental and climatic feedbacks. The geological record offers an opportunity to understand climate system response to a range of forcings and feedbacks which operate over multiple temporal and spatial scales. Here, we examine a single interglacial during the late Pliocene (KM5c, ca. 3.205±0.01 Ma) when atmospheric CO2 exceeded pre-industrial concentrations, but were similar to today and to the lowest emission scenarios for this century. As orbital forcing and continental configurations were almost identical to today, we are able to focus on equilibrium climate system response to modern and near-future CO2. Using proxy data from 32 sites, we demonstrate that global mean sea-surface temperatures were warmer than pre-industrial values, by ∼2.3 ∘C for the combined proxy data (foraminifera Mg∕Ca and alkenones), or by ∼3.2–3.4 ∘C (alkenones only). Compared to the pre-industrial period, reduced meridional gradients and enhanced warming in the North Atlantic are consistently reconstructed. There is broad agreement between data and models at the global scale, with regional differences reflecting ocean circulation and/or proxy signals. An uneven distribution of proxy data in time and space does, however, add uncertainty to our anomaly calculations. The reconstructed global mean sea-surface temperature anomaly for KM5c is warmer than all but three of the PlioMIP2 model outputs, and the reconstructed North Atlantic data tend to align with the warmest KM5c model values. Our results demonstrate that even under low-CO2 emission scenarios, surface ocean warming may be expected to exceed model projections and will be accentuated in the higher latitudes.
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3797 on: October 03, 2020, 01:44:40 AM »
The Arctic hasn’t been this warm for 3 million years – and that foreshadows big changes for the rest of the planet
https://theconversation.com/the-arctic-hasnt-been-this-warm-for-3-million-years-and-that-foreshadows-big-changes-for-the-rest-of-the-planet-144544
Quote
Because the Arctic was much warmer in the Pliocene, the Greenland Ice Sheet did not exist. Small glaciers along Greenland’s mountainous eastern coast were among the few places with year-round ice in the Arctic. The Pliocene Earth had ice only at one end – in Antarctica – and that ice was less extensive and more susceptible to melting.


Because the oceans were warmer and there were no large ice sheets in the Northern Hemisphere, sea levels were 30 to 50 feet (9 to 15 meters) higher around the globe than they are today. Coastlines were far inland from their current locations. The areas that are now California’s Central Valley, the Florida Peninsula and the Gulf Coast all were underwater. So was the land where major coastal cities like New York, Miami, Los Angeles, Houston and Seattle stand.

Warmer winters across what is now the western U.S. reduced snowpack, which these days supplies much of the region’s water. Today’s Midwest and Great Plains were so much warmer and dryer that it would have been impossible to grow corn or wheat there.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3798 on: October 03, 2020, 06:25:30 AM »
The linked reference confirms that elevated trace GHGs like methane, contributed directly to polar amplification of the Pliocene climate.

Peter O. Hopcroft et al. (September 22, 2020), "Polar amplification of Pliocene climate by elevated trace gas radiative forcing", PNAS, 117 (38) 23401-23407;  https://doi.org/10.1073/pnas.2002320117

https://www.pnas.org/content/117/38/23401

Significance
Warm periods in Earth’s history provide the only empirical evidence of how the climate system responds to raised atmospheric carbon dioxide (CO2) levels. The Middle Pliocene, 3.3 to 3.0 My B.P., was the last time when CO2 levels were as high as today. However, climate model simulations of the Pliocene underestimate the warming that has been reconstructed from geological archives. Using a numerical model of the global methane cycle we show that the inclusion of enhanced concentrations of non-CO2 trace gases could have been responsible for an additional warming of 0.6 to 1.0 °C, with larger increases over northern land masses. These findings demonstrate the importance of trace gas climate forcing for both the Pliocene and potentially warm periods during much of Earth’s recent history.

Abstract
Warm periods in Earth’s history offer opportunities to understand the dynamics of the Earth system under conditions that are similar to those expected in the near future. The Middle Pliocene warm period (MPWP), from 3.3 to 3.0 My B.P, is the most recent time when atmospheric CO2 levels were as high as today. However, climate model simulations of the Pliocene underestimate high-latitude warming that has been reconstructed from fossil pollen samples and other geological archives. One possible reason for this is that enhanced non-CO2 trace gas radiative forcing during the Pliocene, including from methane (CH4), has not been included in modeling. We use a suite of terrestrial biogeochemistry models forced with MPWP climate model simulations from four different climate models to produce a comprehensive reconstruction of the MPWP CH4 cycle, including uncertainty. We simulate an atmospheric CH4 mixing ratio of 1,000 to 1,200 ppbv, which in combination with estimates of radiative forcing from N2O and O3, contributes a non-CO2 radiative forcing of 0.9  W⋅m−2 (range 0.6 to 1.1), which is 43% (range 36 to 56%) of the CO2 radiative forcing used in MPWP climate simulations. This additional forcing would cause a global surface temperature increase of 0.6 to 1.0 °C, with amplified changes at high latitudes, improving agreement with geological evidence of Middle Pliocene climate. We conclude that natural trace gas feedbacks are critical for interpreting climate warmth during the Pliocene and potentially many other warm phases of the Cenezoic. These results also imply that using Pliocene CO2 and temperature reconstructions alone may lead to overestimates of the fast or Charney climate sensitivity.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3799 on: October 03, 2020, 04:04:13 PM »
The linked reference (& associate linked article) provides evidence of the synchronous timing of abrupt climate changes around the globe during Dansgaard-Oeschger (DO) events during the last glacial period.  To me this clearly demonstrates that freshwater hosing events can trigger multiple abrupt changes; which were stabilized during the last glacial period, but which could abruptly trigger a transition into a new/higher climate state given our current unprecedented rate of climate change:

Ellen C. Corrick et al. (21 Aug 2020), "Synchronous timing of abrupt climate changes during the last glacial period", Science, Vol. 369, Issue 6506, pp. 963-969, DOI: 10.1126/science.aay5538

https://science.sciencemag.org/content/369/6506/963.abstract

Abstract: "Abrupt climate changes during the last glacial period have been detected in a global array of palaeoclimate records, but our understanding of their absolute timing and regional synchrony is incomplete. Our compilation of 63 published, independently dated speleothem records shows that abrupt warmings in Greenland were associated with synchronous climate changes across the Asian Monsoon, South American Monsoon, and European-Mediterranean regions that occurred within decades. Together with the demonstration of bipolar synchrony in atmospheric response, this provides independent evidence of synchronous high-latitude–to-tropical coupling of climate changes during these abrupt warmings. Our results provide a globally coherent framework with which to validate model simulations of abrupt climate change and to constrain ice-core chronologies."

See also:
Title: "Abrupt global climate change events occurred synchronously during last glacial period"

https://eurekalert.org/pub_releases/2020-08/aaft-agc081720.php

Extract: "The abrupt climate warming events that occurred in Greenland during the last glacial period occurred very close in time to other rapid climate change events seen in paleoclimate records from lower latitudes, according to a new study, which reveals a near-synchronous teleconnection of climate events spanning Earth's hemispheres. The new high-resolution paleoclimate chronology, which was derived from thin layers of sedimentary cave rocks from around the world, provides a framework to improve climate change models and constrain ice-core chronologies. This is important in the context of considering future abrupt climate change around the globe. Climate records from Greenland ice cores spanning the last glacial cycle (115,000 to 11,700 years ago) reveal a series of abrupt climate fluctuations between warm and cold conditions. These oscillations, also known as Dansgaard-Oeschger (DO) events, are characterized by an abrupt transition to a period of rapid warming, which is followed by a more gradual, and then abrupt, return to a cooler climate state. The oscillations occur quasi-periodically on a centennial- to millennial-scale. Outside of the Arctic, similar abrupt climate change events during the last glacial have also been identified in a host of other paleoclimate records from far-away regions across the globe."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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