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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4050 on: December 17, 2020, 10:36:31 PM »
The linked reference concludes that:

"… the amount of solar energy absorbed by the streams on the ice sheet likely depends on the health and longevity of this bacteria and further warming in Greenland may lead to more extensive sediment deposits in glacial streams."

Which indicates that with continued local warming Greenland's albedo will continue to decrease.

Sasha Z. Leidman, Åsa K. Rennermalm, Rohi Muthyala, Qizhong Guo & Irina Overeem (06 December 2020), "The Presence and Widespread Distribution of Dark Sediment in Greenland Ice Sheet Supraglacial Streams Implies Substantial Impact of Microbial Communities on Sediment Deposition and Albedo", Geophysical Research Letters, https://doi.org/10.1029/2020GL088444

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088444?af=R

Abstract
Melting on the Greenland Ice Sheet leads to extensive supraglacial stream networks. These streams accumulate low‐albedo sediments disproportionately contribute to melting. Studies analyzing supraglacial sediment distribution and hydrodynamic properties are rare. Here, we examine a 130 m supraglacial stream reach in southwest Greenland using drone imagery, bathymetry, and hydrology measurements from 2017. Sediment covered 24% of the channel and had a mass‐median diameter of 0.027 mm. We applied calculations of critical Shields stress to determine the minimum water depth needed to initiate sediment movement. In order for theoretical critical water depths to match observed depths, sediment grains would need to be 2.48 mm (near the grain size for cryoconite granules) indicating that microbial growth within sediment caused extensive flocculation. Without flocculation, sediment would flush out of floodplains and supraglacial streams would have significantly higher albedos. Supraglacial stream albedo might therefore be sensitive to changing stream chemistry, temperature, and meltwater supply.

Plain Language Summary
Meltwater formed on the surface of the Greenland Ice Sheet drains through abundant networks of rivers and streams on the ice surface. These streams consolidate dark‐colored sediment that can increase the amount of solar energy absorbed by the ice. To investigate the extent and causes of these deposits, we collected samples of sediment from southwest Greenland along with drone imagery, high‐resolution GPS measurements of the stream geometry, and measurements of the water flow over the course of a week in 2017. We analyzed the sediment to determine its size and applied our findings to fluid dynamics equations. These calculations showed that sediment in glacial streams can only be present if the sediment is being consolidated into millimeter‐scale granules by bacteria growing in the sediment. Thus, the amount of solar energy absorbed by the streams on the ice sheet likely depends on the health and longevity of this bacteria and further warming in Greenland may lead to more extensive sediment deposits in glacial streams.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4051 on: December 17, 2020, 10:58:27 PM »
The linked reference concludes that:

"The fact that the actual historical development is consistent with rapid-growth narratives in the non-OECD regions might have important implications for future greenhouse gas emissions and associated climatic change."

Which indicates to me that anthropogenic GHG emissions may continue to grow in the future even if OECD countries reach zero emission levels in coming decades.

Jiesper Strandsbjerg et al. (January 2021), "An assessment of the performance of scenarios against historical global emissions for IPCC reports", Global Environmental Change
Volume 66, 102199, https://doi.org/10.1016/j.gloenvcha.2020.102199

https://www.sciencedirect.com/science/article/pii/S0959378020307822?dgcid=rss_sd_all

Abstract
Long-term emissions scenarios have served as the primary basis for assessing future climate change and response strategies. Therefore, it is important to regularly reassess the relevance of emissions scenarios in light of changing global circumstances and compare them with long-term developments to determine if they are still plausible, considering the newest insights. Four scenario series, SA90, IS92, SRES, and RCP/SSP, were central in the scenario-based literature informing the five Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC) and the sixth assessment cycle. Here we analyze the historical trends of carbon dioxide (CO2) emissions from fossil fuel combustion and industry and emissions drivers between 1960 and 2017. We then compare the emission scenario series with historical trends for the period 1990–2017/2018. The results show that historical trends are quite consistent with medium scenarios in each series. As a result, they can be regarded as valid inputs for past and future analyses of climate change and impacts. Global CO2 emissions 1960–2018 (and 1990–2018) comprised six (and three) overall subperiods of emissions growth significantly higher and lower than average. Historically, CO2 emissions (in absolute numbers and growth rate) are tightly coupled with primary energy and indirectly with GDP. Global emissions generally followed a medium-high pathway, captured by “middle-of-the-road” scenario narratives in the earlier series, and by combinations of “global-sustainability” and “middle-of-the-road” narratives in the most recent series (SRES and SSP-baselines). Historical non-OECD trends were best captured by “rapid-growth” and “regional-competition” scenarios, while OECD trends were close to regional-sustainability and global-sustainability scenarios. Areas where the emissions scenarios captured the historical trends less well, are renewable and nuclear primary energy supply. The fact that the actual historical development is consistent with rapid-growth narratives in the non-OECD regions might have important implications for future greenhouse gas emissions and associated climatic change.
“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 #4052 on: December 19, 2020, 03:33:05 PM »
As some people may need a refresher on Hansen et al. (2016), I provide the handy NASA link and associated citation and abstract.  As I essentially concur with Hansen et al. (2016)'s big picture (that you can read for yourself); here I will only focus on the underlined part of the abstract where he notes that abrupt ice mass loss into the Southern Ocean and/or into the North Atlantic '… increases precipitation on the Southern Ocean'.  So as not to miss the significance of this statement I note that accelerated warming of the Tropical Pacific (due to a slowdown of the MOC) will advect significant quantities of rainfall to lower altitude regions of the West Antarctic coastal areas; which will not only accelerate local hydrofracturing but will all result in rapid (seasonal) reductions of sea ice area that will decrease albedo and will indirectly advect more warm CDW beneath for the FRIS and the RIS.  Furthermore, as the BSB rapidly loses ice mass due to MICI-type ice cliff calving, that the local ocean area and coastal extent will increase proportionally abruptly; which will further promote reduced local albedo and promote more ice hydrofracturing; and eventually will lead to new ocean current pathways from the South Atlantic to the South Pacific thru new seaways (see the black pathways on the first attached image and cross-sections shown in the second attached image) where the WAIS currently sits.

https://pubs.giss.nasa.gov/abs/ha04710s.html

Hansen, J., M. Sato, P. Hearty, R. Ruedy, M. Kelley, V. Masson-Delmotte, G. Russell, G. Tselioudis, J. Cao, E. Rignot, I. Velicogna, B. Tormey, B. Donovan, E. Kandiano, K. von Schuckmann, P. Kharecha, A.N. LeGrande, M. Bauer, and K.-W. Lo, 2016: Ice melt, sea level rise and superstorms: Evidence from paleoclimate data, climate modeling, and modern observations that 2°C global warming could be dangerous. Atmos. Chem. Phys., 16, 3761-3812, doi:10.5194/acp-16-3761-2016.

https://acp.copernicus.org/articles/16/3761/2016/

Abstract
We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10-40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500-2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6-9 m with evidence of extreme storms while Earth was less than 1°C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2°C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50-150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.
“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 #4053 on: December 19, 2020, 03:37:40 PM »
My quote references SSP 8.5, and the attached plot shows Energy and Industry CO2 emissions thru December 2019 vs the SSP scenarios, and which indicates that we are relatively close to SSP 8.5.

It's interesting that energy and industry CO2 emissions were on the RCP 8.5 pathway yet the CO2 concentrations are closer to the RCP 2.6 pathway.  That suggests that either natural emissions are lower or the carbon sinks absorb more CO2 than consensus science estimates.

The attached image shows that the total anthropogenic carbon dioxide emissions thru 2019 were closer to the RCP 8.5 pathway than that for only the energy and industry carbon dioxide emissions.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4054 on: December 19, 2020, 04:51:29 PM »
As a follow-on to my Reply # 4032, where I state that:

'In this regard, the first linked reference indicates that in recent decades the calving face of Jakobshavn has retreated or advanced in a correlation with the Atlantic Multidecadal Oscillation (AMO) index that influences the ocean water temperature in Disko Bay.'

In this regard, the first attached image shows that in August 2013 to August 2015 timeframe the retreat of the Jakobshavn calving face came very close to the sill of a retrograde bed slope shown on this first image, that once crossed would likely accelerate image mass loss from Jakobshavn due to ice cliff failures.  However, the second image from Joughin et al. (2020) shows that since 2013 the Jakobshavn calving face has advanced downstream until 2019 apparently due a correlation with the AMO [see the third (from the second linked website) and fourth (from NOAA) images, and I note that 2020 has been a very active calving season for Jakobshavn, driven by the presence of relatively warm water in Disko Bay].

Given that the current warm phase of the AMO that started in about 2002 may, on average, last about 25 to 40 years (see the third linked website) this means that it is likely that the Jakobshavn calving face will cross the retrograde bed sill (see the first image) sometime between 2027 and 2042; and if so such an event would work to increase the probability of the an MICI-type of collapse of the ice in the BSB (via the bipolar seesaw mechanism) in the 2030 to 2040 timeframe.

Ian Joughin et al (2020): "A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity", The Cryosphere, 14, 211–227, https://doi.org/10.5194/tc-14-211-2020

https://www.the-cryosphere.net/14/211/2020/

Title: "Atlantic multidecadal oscillation"

https://en.wikipedia.org/wiki/Atlantic_multidecadal_oscillation

Extract: "The Atlantic Multidecadal Oscillation (AMO), also known as Atlantic Multidecadal Variability (AMV), is a climate cycle that affects the sea surface temperature (SST) of the North Atlantic Ocean based on different modes on multidecadal timescales. While there is some support for this mode in models and in historical observations, controversy exists with regard to its amplitude, and in particular, the attribution of sea surface temperature change to natural or anthropogenic causes, especially in tropical Atlantic areas important for hurricane development. The Atlantic multidecadal oscillation is also connected with shifts in hurricane activity, rainfall patterns and intensity, and changes in fish populations."

Caption for the third image: "Atlantic Multidecadal Oscillation Index according to the methodology proposed by van Oldenborgh et al. 1880-2018."

&

Title: "State of the Ocean Climate – AMO"

https://stateoftheocean.osmc.noaa.gov/atm/amo.php

Extract: "The Atlantic Multidecadal Oscillation (AMO) index reflects an argued 50-80 year pattern of North Atlantic coupled ocean-atmosphere variability. It is associated with changes in rainfall over North America and Europe, the frequency of North American droughts, and the intensity of North Atlantic hurricanes. It may mask or exaggerate signals of global change, though the argument that it is a separate signal from the forced global change signal is disputed."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4055 on: December 21, 2020, 10:45:03 PM »
Don't worry, ASLR, we can wait.

While we all wait a year (or so) for me to create an annual summary of long-tailed climate risk issues in a tightly grouped series of cross-correlated posts ...

It has been a while since I said that I would create an updatable overview of my opinion of how an 'Ice Apocalypse' could unfold in something like the next hundred years, so I decided to make this post to:

a) Motivate myself to assemble such an overview and

b) To note that I currently propose to subdivide this updatable overview into three threads:

   i) A Maximum Credible Domino Scenario (MCDS) thread underpinned by Hansen et al. (2016) and their 5-year doubling freshwater hosing scenario (see the first two images); and by the early MICI work by DeConto, Pollard and Alley (2015-2018) and by output from the CMIP6 'Wolf Pack' model projections (see the third image).  These MCDS scenarios would be based on roughly 10-year intervals (from 2020 to 2150) of Bayesian Networks (see the fourth image for the period from 2030 to 2040) using Domino Effect Analysis (see the first linked reference).

   ii) A Domino Fault Tree analysis (see the second linked reference and open source Fault Three analysis software from the GitHub link) thread to try to substantiate the 'credible' probability of such Domino Bayesian Networks of freshwater hosing events and their associated rough-order probabilities.

   iii) A list of references used to support a 5-year doubling MCDS scenario, and/or other members of a family of such scenarios (in the tradition of the IPCC's radiative forcing scenario families such as: RCP or SSP).

c) To invite any comments on items 'a' and 'b' before I proceed to develop the several hundred posts required to reasonable summarize such an updatable overview of an 'Ice Apocalypse' through 2150.

Caption for the first image: "Figure 5. (a) Total freshwater flux added in the North Atlantic and Southern oceans and (b) resulting sea level rise. Solid lines for 1m sea level rise, dotted for 5m.  One Sverdrup (Sv) is 106 m3 s-1, which is ~ 3 x 104 Gt year-1."

Caption for the second image: "Figure 7. (a) Surface air temperature (oC) relative to 1880-1920-for several scenarios. (b) Global energy imbalance (Wm-2) for the same scenarios."

Nima Khakzad et al. (09 June 2012), "Domino Effect Analysis Using Bayesian Networks", Risk Analysis, https://doi.org/10.1111/j.1539-6924.2012.01854.x

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1539-6924.2012.01854.x

Abstract
A new methodology is introduced based on Bayesian network both to model domino effect propagation patterns and to estimate the domino effect probability at different levels. The flexible structure and the unique modeling techniques offered by Bayesian network make it possible to analyze domino effects through a probabilistic framework, considering synergistic effects, noisy probabilities, and common cause failures. Further, the uncertainties and the complex interactions among the domino effect components are captured using Bayesian network. The probabilities of events are updated in the light of new information, and the most probable path of the domino effect is determined on the basis of the new data gathered. This study shows how probability updating helps to update the domino effect model either qualitatively or quantitatively. The methodology is applied to a hypothetical example and also to an earlier‐studied case study. These examples accentuate the effectiveness of Bayesian network in modeling domino effects in processing facility.

&

Antioco López-Molina et al. (), "A Methodology Based on Fault Tree Analysis to Assess the Domino Effect Frequency", IChemE, Hazards 24, Symposium Series No. 159

https://www.icheme.org/media/8929/xxiv-paper-34.pdf

Abstract: "Several tragic industrial accidents have produced domino effects in their occurrences and, hence, several approaches have been presented to estimate the probability of their effects. Some of these approaches are focused on estimating the damage probability due to fire or explosion whereas others apply Monte Carlo simulations to predict the domino frequency. In this work an easy to perform methodology has been developed to predict the occurrence frequency of the domino effect. The methodology considers the failure frequency for each unit process, the damage probability due to escalation vectors, and the use of active and passive safeguards. This methodology is based on the fault tree analysis framework. The approach can be used into the QRA analysis without any extra effort, since all aspects are previously assessed by the procedure. A case study is presented to show the application of this approach."


To download an open source fault tree analysis package, one can go to:

Title: "cmu-sei/emfta"

https://github.com/cmu-sei/emfta
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Sciguy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4056 on: December 23, 2020, 06:53:47 PM »

It has been a while since I said that I would create an updatable overview of my opinion of how an 'Ice Apocalypse' could unfold in something like the next hundred years, so I decided to make this post to:

a) Motivate myself to assemble such an overview and

b) To note that I currently propose to subdivide this updatable overview into three threads:

   i) A Maximum Credible Domino Scenario (MCDS) thread underpinned by Hansen et al. (2016) and their 5-year doubling freshwater hosing scenario (see the first two images); and by the early MICI work by DeConto, Pollard and Alley (2015-2018) and by output from the CMIP6 'Wolf Pack' model projections (see the third image).  These MCDS scenarios would be based on roughly 10-year intervals (from 2020 to 2150) of Bayesian Networks (see the fourth image for the period from 2030 to 2040) using Domino Effect Analysis (see the first linked reference).

   ii) A Domino Fault Tree analysis (see the second linked reference and open source Fault Three analysis software from the GitHub link) thread to try to substantiate the 'credible' probability of such Domino Bayesian Networks of freshwater hosing events and their associated rough-order probabilities.

   iii) A list of references used to support a 5-year doubling MCDS scenario, and/or other members of a family of such scenarios (in the tradition of the IPCC's radiative forcing scenario families such as: RCP or SSP).

Are you going to estimate the probabilities for your scenarios?  For risk analysis models using Bayesian approaches, that's a critical first step.

In you MCDS scenario, you start with a very, very, low probability event, MICI.  According to DeConto and Pollard, for MICI to start, hydrofracturing, which requires water ponding on the ice shelves, must occur.  And hydrofracturing to the extent required doesn't start until the ocean temperatures around Antarctica increase by 2 degrees C.  They needed to artificially increase the ocean temperatures in their models instantaneously by 2 C just to get MICI starting in the 2070s.  So MICI would appear to be very less likely than 1% to start before the end of the century.

What about events that appear to be mutually exclusive?  For "the wolfpack" climate scenarios to be correct, the clouds over the southern ocean need to warm, change from ice to water and eventually disappate to get the extreme climate sensitivities they predict.  However, for Hansen's fresh water feedback to occur, precipitation needs to increase over the southern ocean, freshening it.  This would seem to imply more clouds to cause more precipitation.  Which is more likely and how do those two seemingly contradictory scenarios interact?


kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4057 on: December 23, 2020, 09:35:27 PM »
It is important to note that what they do in a model is not the same as a requirement in the real world.

Earth is the best model because it actually accounts for all variables while the models are crude. A lot better then they were but still crude.

A more detailed look has been posted before but basically there are some areas prone to this. There is an underlying physical principle which is rather sound so the question is when. The research on the local ice condition sort of hints we don´t need the forcings like in the model.

The other points are valid. It is what happens when you try to look at all those processes.

A lot of those are not in our current models we use to check if we are short of ´dangerous climate change´.

What is the probability estimate that the IPCC is ´right´?
What is the probability that they do not actually have a definition of dangerous climate change?

We can set a target but what does preventing a 1,5C overall rise do if it still kills ASI which then kicks the global temperatures up a notch?
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4058 on: December 24, 2020, 01:56:30 AM »
...
Are you going to estimate the probabilities for your scenarios?  For risk analysis models using Bayesian approaches, that's a critical first step.

In you MCDS scenario, you start with a very, very, low probability event, MICI.  According to DeConto and Pollard, for MICI to start, hydrofracturing, which requires water ponding on the ice shelves, must occur.  And hydrofracturing to the extent required doesn't start until the ocean temperatures around Antarctica increase by 2 degrees C.  They needed to artificially increase the ocean temperatures in their models instantaneously by 2 C just to get MICI starting in the 2070s.  So MICI would appear to be very less likely than 1% to start before the end of the century.

What about events that appear to be mutually exclusive?  For "the wolfpack" climate scenarios to be correct, the clouds over the southern ocean need to warm, change from ice to water and eventually disappate to get the extreme climate sensitivities they predict.  However, for Hansen's fresh water feedback to occur, precipitation needs to increase over the southern ocean, freshening it.  This would seem to imply more clouds to cause more precipitation.  Which is more likely and how do those two seemingly contradictory scenarios interact?

The purpose of these three MCDS threads is to summarize how I see the associated climate risk not fully addressed by Consensus Climate Science (CCS), including my understanding of probabilities, and it is not to provide a peer reviewable document nor to answer contrarian red herrings.  That said, I also plan to cite short-comings in climate model projections by Hansen, DeConto, Pollard, Alley, etc.  For instance, I believe that a MICI mechanism can form in the Thwaites Gateway between 2030 & 2040 without any hydrofracturing and I plan to discuss my reasoning.  Also, net precipitation (P-E) from clouds into the Southern Ocean is well understood until at least 2030 and after that the freshwater input from calved ice shelves and from calved key marine glaciers will dominate the freshwater signature of the Southern Ocean no later than 2040 (if my opinions have merit).

Feel free to ignore my summaries, when I post them in new threads sometime next year, as I am not necessarily trying to convince anyone of my beliefs; and I am mainly providing the summaries to help readers to at least understand what I have been posting about for many years now about climate risks not adequately covered by CCS projections.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4059 on: December 24, 2020, 01:59:49 AM »
It is important to note that what they do in a model is not the same as a requirement in the real world.

Earth is the best model because it actually accounts for all variables while the models are crude. A lot better then they were but still crude.

A more detailed look has been posted before but basically there are some areas prone to this. There is an underlying physical principle which is rather sound so the question is when. The research on the local ice condition sort of hints we don´t need the forcings like in the model.

The other points are valid. It is what happens when you try to look at all those processes.

A lot of those are not in our current models we use to check if we are short of ´dangerous climate change´.

What is the probability estimate that the IPCC is ´right´?
What is the probability that they do not actually have a definition of dangerous climate change?

We can set a target but what does preventing a 1,5C overall rise do if it still kills ASI which then kicks the global temperatures up a notch?

+1
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4060 on: December 24, 2020, 04:44:56 PM »
The linked reference helps to quantify the amount and condition of the Arctic's subsea permafrost carbon stocks on continental ocean shelves flooded between 18,000 to 14,000 years ago (see attached images).  While many readers may take comfort that consensus climate science (CCS) projections indicated that this carbon will be releases over a period of multiple hundreds of years (even with projected anthropogenic global warming); I note that these CCS projections do not consider the risks associated with freshwater hosing events (like a short-term reversal of the Beaufort Gyre, or a collapse of the WAIS, in coming decades) that could direct warm Atlantic ocean water over this currently thawing subsea permafrost that could result in an abrupt pulse of methane currently capped by the degrading subsea permafrost (possibly as soon as 2060).

Sayedeh Sara Sayedi et al. (2020), "Subsea permafrost carbon stocks and climate change sensitivity estimated by expert assessment", Environ. Res. Lett. 15 124075; https://doi.org/10.1088/1748-9326/abcc29

https://iopscience.iop.org/article/10.1088/1748-9326/abcc29

Abstract
The continental shelves of the Arctic Ocean and surrounding seas contain large stocks of organic matter (OM) and methane (CH4), representing a potential ecosystem feedback to climate change not included in international climate agreements. We performed a structured expert assessment with 25 permafrost researchers to combine quantitative estimates of the stocks and sensitivity of organic carbon in the subsea permafrost domain (i.e. unglaciated portions of the continental shelves exposed during the last glacial period). Experts estimated that the subsea permafrost domain contains ~560 gigatons carbon (GtC; 170–740, 90% confidence interval) in OM and 45 GtC (10–110) in CH4. Current fluxes of CH4 and carbon dioxide (CO2) to the water column were estimated at 18 (2–34) and 38 (13–110) megatons C yr−1, respectively. Under Representative Concentration Pathway (RCP) RCP8.5, the subsea permafrost domain could release 43 Gt CO2-equivalent (CO2e) by 2100 (14–110) and 190 Gt CO2e by 2300 (45–590), with ~30% fewer emissions under RCP2.6. The range of uncertainty demonstrates a serious knowledge gap but provides initial estimates of the magnitude and timing of the subsea permafrost climate feedback.


Caption for the attached 2 images of panels extracted from Figure 1: "Figure 1. Extent and carbon dynamics of the subsea permafrost domain. We define the subsea permafrost domain as the unglaciated continental shelf areas exposed during the Last Glacial Maximum (LGM) that are currently inundated. (a) Extent of continental shelf permafrost at the LGM (data from Lindgren et al (2016)) and current subsea permafrost extent (data from Overduin et al (2019)). (b)–(d) Conceptual drawings of the thermal, physical, and biogeochemical changes initiated in the subsea permafrost domain by deglaciation and sea level rise. Major stocks are shown in white text and major fluxes are shown in black text. Soil organic matter (SOM) refers to the SOM that accumulated on the exposed continental shelf in tundra and steppe ecosystems prior to sea level rise (Lindgren et al 2018). Deposited Sediment refers to the sediment and associated organic matter eroded from coastal and terrestrial environments that was deposited on top of subsea permafrost during and after sea level rise (Vonk et al 2012, Tesi et al 2016). CH4 Stocks and CH4 Hydrates refer to methane trapped in the subsurface in free, dissolved, or clathrate states (Ruppel and Kessler 2017). Thermogenic CH4 refers to methane formed abiotically in deeper geological processes (Thornton et al 2016a, Ruppel and Kessler 2017). The quantitative estimates of carbon pools (white) and fluxes (black) are the median values from this study (see text for uncertainty ranges)."
« Last Edit: December 24, 2020, 07:46:14 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4061 on: December 25, 2020, 12:04:37 AM »
The linked article indicates that the April 2020 book: "Our Final Warming: Six Degrees of Climate Emergency" by Mark Lynas; provides ample evidence that climate change is happening faster than consensus climate scientists had been expecting.

Title: "Mark Lynas's 'Final warning' on climate: 'It's all on us, here, now,' says reviewer"

https://yaleclimateconnections.org/2020/08/mark-lynas-final-warning-on-climate-its-all-on-us-here-now/

Extract: "The motto for 21st-century climate science might be, “That happened faster than I expected.” Antarctic researcher Christina Hulbe suggested this to some colleagues a few years ago, and indeed the dwindling of the Arctic Ocean ice pack and the forces promoting disintegration of the Greenland Ice Sheet and Antarctic ice shelves have come decades earlier than expected. But other features of climate change are also showing up sooner than many climate scientists expected.

Suffice it to say that at three degrees above our grandparents’ climate, it’s hard to see how the world could sustain a broadly prosperous and tolerant civilization such as many now enjoy. At four degrees, maintaining any kind of civilization at all becomes problematic. And it’s more likely than not that today’s young people will experience such global temperatures (or worse) in their lifetimes, unless we make radical policy changes."

Edit: It has been pointed-out to me that Lynas supports the idea that we still have a carbon budget of 10-years; which in my opinion errs on the side of least drama (so I am only pointing-out that many of the experts that Lynas talked to when writing his book indicated that they were observing climate change sooner (faster) than they had been expecting (which generally implies that climate sensitivity is greater than they previously believed).
« Last Edit: December 26, 2020, 10:56:17 AM by AbruptSLR »
“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 #4062 on: December 25, 2020, 10:23:16 AM »
Just for interest is the GRACE-FO data for AIS+GIS ice mass loss since 2002.

Total mass loss = over 17 mms of sea level rise (very close to 1 mm per year)
I thought annual rise was ~3 mm. What is the other two...thermal expansion? Glacier melt?

The linked references answer your question as other contributions (both negative and positive) to eustatic SLR include:

1. Terrestrial water storage (TWS) both natural and manmade;
2. Thermostatic;
3. Ice caps and mountain glaciers;
4. Groundwater depletion
5. Dam Impoundments
6. Barystatic.

Also, I note that there is a glacial isostatic adjustment (GIA) factor.

Frederikse, T., Landerer, F., Caron, L. et al. The causes of sea-level rise since 1900. Nature 584, 393–397 (2020). https://doi.org/10.1038/s41586-020-2591-3

https://www.nature.com/articles/s41586-020-2591-3

Abstract: "The rate of global-mean sea-level rise since 1900 has varied over time, but the contributing factors are still poorly understood. /snip/... Our results reconcile the magnitude of observed global-mean sea-level rise since 1900 with estimates based on the underlying processes, implying that no additional processes are required to explain the observed changes in sea level since 1900."

The claim that there are "no additional processes" is disputed by Iz and Shum in "The certitude of a global sea level acceleration during the satellite altimeter era", 2020, in J. Geod. Sci., open access.
DOI: https://doi.org/10.1515/jogs-2020-0101

"Abstract: Recent studies reported a uniform global sea
level acceleration during the satellite altimetry era (1993–
2017) by analyzing globally averaged satellite altimetry
measurements. Here, we discuss potential omission errors
that were not thoroughly addressed in detecting and estimating
the reported global sea level acceleration in these
studies. Our analyses results demonstrate that the declared
acceleration in recent studies can also be explained
equallywell by alternative kinematic models based on previously
well-established multi-decadal global mean sea
level variations of various origins, which suggests prudence
before declaring the presence of an accelerating
global mean sea level with confidence during the satellite
altimetry /SA/ era."

They perform a thorough statistical analysis of previous research on the satellite data for SLR, and compares to tidal gauge data (TG). The time series display severe autocorrelation in the residuals, and they try to track down how this can be understood and explained. They write:
"There may be other error sources, omission errors,
which occur due to various contributors/confounders of
physical origin on sea level variations that are ignored in
the kinematic models..." Specifically, they critically analyze the two recent studies by Nerem, et, al. (2019), and Ablain, et, al. (2018), where both find an acceleration in SLR.

"Sea level variations are multi-causal. Some of the effects
are global isostatic adjustment, periodic changes in sea
levels induced by wind, pressure, external forcing such as
of lunar solar origin, and thermosteric effects of warming
oceans, or they are eustatic in nature. The effects may be
secular, episodic, transient, periodic at semi-annual, annual,
interannual, decadal, or decadal and multidecadal
time scales, all contributing to sea level anomalies. These
effects are also local, regional, and could be global. Yet,
the two recent studies that reported global sea level accelerations,
by Nerem et al, (2018) and Ablain et al. (2019),
ignored the contribution of these multidecadal effects in
their analyses in detecting the GMSL acceleration. /..,./
The omission of the effect of potential confounders including
a potential jerk or multidecadal sea level variations
(Ablain at al., 2019), or using a conjecture that they will
average out because of the superior global coverage of SA
by Nerem at al. (2018) is a leap of faith without evidence in
quantifying a GMSL acceleration
and its uncertainty using
globally averaged SA time series. Moreover, conducting
projections as in Nerem at al. (2018) without ascribing
proper uncertainties to the model estimates have no
meaning."

Basically, they find that the claimed acceleration in SLR can be equally well be explained by different natural cycles of various frequency, see attached figure. They say that "it would be misleading to declare a global sea level acceleration during the SA
era with an acceptable uncertainty and make predictions
if the origin of the perceived acceleration is likely to be an
unmodeled periodicity or periodicities."

Caption to figure: "Fig. 8. The amplitudes and the standard errors (error bars) are the
weighted averages of the estimated amplitudes across 27 TG stations.
All weighted averages are statistically significant. Weights
are the inverse variances of the amplitude estimates at each TG station,
which are regionally correlated with a spatial correlation of
0.80 among the stations (estimated from their residuals) but not
correlated among the regions (Iz et al., 2018)."


kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4063 on: December 25, 2020, 07:26:45 PM »
So they argue that there is no evidence for acceleration of SLR from the satellite data (1993-2017) because the observed changes can still fit in the known cycles.

This could be 100% true.

It is only 24 years of data. This is only 1 full 20 year cycle and not even half of the 60 year one.
In time this record will tell us more about those.

Of course the real world includes all influences and if you peek at figure 1 you see SLR goes up and up which is response to some well known forcing.

This article can not be generalized otherwise then Nerem and Ablains claim cannot be backed up by the current sat record vs known variance which says exactly zilch about the real world.

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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4064 on: December 26, 2020, 05:40:11 AM »
So they argue that there is no evidence for acceleration of SLR from the satellite data (1993-2017) because the observed changes can still fit in the known cycles.

This could be 100% true.

It is only 24 years of data. This is only 1 full 20 year cycle and not even half of the 60 year one.
In time this record will tell us more about those.

Of course the real world includes all influences and if you peek at figure 1 you see SLR goes up and up which is response to some well known forcing.

This article can not be generalized otherwise then Nerem and Ablains claim cannot be backed up by the current sat record vs known variance which says exactly zilch about the real world.

There is an undisputed positive trend in SLR and on top of that a presumed 'acceleration' in the SLR that occurs since we started to get satellite data.

"The real world" is the way we interpret data that are sampled. Leading SLR researches such as  Nerem and Ablains interpret the data as an acceleration.

What Iz and Shum demonstrate is that the acceleration interpretation is an "a leap of faith without evidence", as the very same data can be equally well interpreted as a combination of various natural cycles in the ocean.
I think this tells us a lot:
1. we should be very careful with our interpretations of SLR data
2. we should not make forecasts based on such data
3. we should always look to make sound statistical analyses of data before rushing to conclusions, or projections.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4065 on: December 26, 2020, 11:38:23 AM »
The linked reference provides paleo-evidence that changes in ocean currents (say due to changes in the MOC from freshwater hosing events) can lead to abrupt sea level rise of many meters in just a few decades, due to the abrupt collapse of a marine glacier:

Skye Yunshu Tian, Moriaki Yasuhara, Yuanyuan Hong, Huai-Hsuan M. Huang, Hokuto Iwatani, Wing-Tung Ruby Chiu, Briony Mamo, Hisayo Okahashi, Tine L. Rasmussen. Deglacial–Holocene Svalbard paleoceanography and evidence of meltwater pulse 1B. Quaternary Science Reviews, 2020; 233: 106237 DOI: 10.1016/j.quascirev.2020.106237

https://www.sciencedirect.com/science/article/abs/pii/S0277379119309485?via%3Dihub

Abstract: "Better understanding of deglacial meltwater pulses (MWPs) is imperative for future predictions of human-induced warming and abrupt sea-level change because of their potential for catastrophic damage. However, our knowledge of the second largest meltwater pulse MWP-1B that occurred shortly after the start of the Holocene interglacial remains very limited. Here, we studied fossil ostracods as paleoenvironmental indicators of water depth, salinity, and temperature in two marine sediment cores from Storfjorden, Svalbard margin (the Arctic Ocean), to investigate near-field (i.e. areas located beneath continental ice sheets at the Last Glacial Maximum) evidence of MWP-1B. The depositional environment changed from a cold bathyal environment to a warmer bathyal environment at ∼11,300 yr BP indicating incursion of warm Atlantic water into the Nordic seas, and eventually to a cold neritic environment by ∼11,000 yr BP because of melting of the Svalbard-Barents Sea ice sheet and resultant isostatic rebound. This process corresponds to rapid relative sea-level fall of 40–80 m of MWP-1B from ∼11,300 to 11,000 yr BP."

See also:

Title "Paleontologists discover solid evidence of formerly elusive abrupt sea-level jump"

https://www.sciencedaily.com/releases/2020/03/200310094223.htm

Summary:
Meltwater pulses (MWPs) known as abrupt sea-level rise will inevitably affect cities especially those on coastal plains of low elevation. A recent study presented evidence of abrupt sea level change between 11,300-11,000 years ago in the Arctic Ocean, solving the puzzle of second largest meltwater pulse (labelled as ''MWP-1B'' next to the largest and already well understood MWP-1A).
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pietkuip

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4066 on: December 26, 2020, 01:06:55 PM »
https://www.cell.com/action/showPdf?pii=S2590-3322%2820%2930592-3

Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures

Martin Siegert, Richard B. Alley, Eric Rignot, John Englander, and Robert Corell

Quote
Will sea-level rise in the coming century be restricted to less than about 1 m, as indicated by the ‘‘likely’’ (IPCC terminology for >66% probability) range in the SROCC, or could it be larger? Judging from records of the last deglaciation, ice sheets can respond to global warming through rapid mass loss, at rates and by amounts much higher than observed to date, leading to sea-level rise of several meters per century.

It is true that the ice sheets then differed from today’s in many ways, but process understanding and other indicators show that rapid rise is possible under the higher levels of warming that might occur this century. In this perspective, we discuss the potential for large (>1 m) sea-level rise this century from the ice-sheet response to strong warming, assess limitations to sea-level projection, and offer ways in which the scientific problem may be better understood and translated.

[...]
We suggest that the IPCC could greatly aid stakeholders by more strongly and prominently bringing forward
  • appreciation that ice-sheet and ocean dynamics can act to deliver higher, but not lower, sea level outcomes;
  • acknowledgment that such processes are omitted within many ice-sheet models relied on by the IPCC, as there is still uncertainty on how they operate and interact on sub-century time scales; and
  • awareness that observations of rapid mass loss in both Greenland and Antarctica over the last ≈40 years provide a wealth of evidence that these physical processes are already active today in some places and could drive much larger, more rapid sea-level rise under further warming.
[...]

Some treat the high end of the likely range as a worst-case scenario or else the upper end for practical designs. Such a situation is far from ideal because the upper limit of the IPCC likely range was never intended as a worst-case scenario.

There is also a page-sized box about instabilities with a large figure illustrating MISI and MICI on the next page.

Excellent article. I am going to recommend it to my students as an example of good science writing. Their writing assignment is about different subjects, but this shows how to do it. And it is important for them to read.
« Last Edit: December 26, 2020, 02:33:33 PM by pietkuip »

kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4067 on: December 26, 2020, 05:29:47 PM »
There is an undisputed positive trend in SLR and on top of that a presumed 'acceleration' in the SLR that occurs since we started to get satellite data.

"The real world" is the way we interpret data that are sampled. Leading SLR researches such as  Nerem and Ablains interpret the data as an acceleration.

What Iz and Shum demonstrate is that the acceleration interpretation is an "a leap of faith without evidence", as the very same data can be equally well interpreted as a combination of various natural cycles in the ocean.
I think this tells us a lot:
1. we should be very careful with our interpretations of SLR data
2. we should not make forecasts based on such data
3. we should always look to make sound statistical analyses of data before rushing to conclusions, or projections.

They are still just arguing about a data set. One solution is to wait a couple of decades because then we have a better set which will show acceleration. More data will teach us more about the alleged 20 and 60 year cycles. Since those are celestial in origin they should just drag water around so of themselves they should not really contribute to SLR?

Of course we can guesstimate the likely hood of sea accelerated level rise.

1 As more land ice gets lost it will most likely end up it the oceans.
2 Sea ice that gets lost also gets added to the oceans.
3 And the CO2 warming push will continue for a while so more thermal expansion.

Then there are thing that are bound to happen like the collapse of the arctic sea ice some time this decade (or the next two for more conservative views but those always underestimate the speed which things happen) which in itself should give global temps a nice kick upwards.

None of that appears in the Sat record until it happens. 

Also not sure if any of the papers actually include a reference to the paper that explained part of the lack of sea level rise was due to our hydro projects which kept a lot of water on continents and lot of that overlapped with the beginning of the Sat records.

It still just is a technical discussion of a dataset where absence of proof does not mean it is not there. The problem will go away with time and more data, and also re-evalutions of prior cycles (the long time patterns from tide gauge data) with better data.

What you cannot do is focus on an article discussing a specific thing and then expect it to act as a shield against everything that is happening. All research has it´s limits and fits into all kinds of other research.

I like looking at paleo stuff. If the HCO can provoke really quick local change in the Arctic our current qualitatively different type of warming can do that too plus it effects Antarctica more.
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Tor Bejnar

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4068 on: December 26, 2020, 07:30:44 PM »
Quote
2 Sea ice that gets lost also gets added to the oceans.
Um... It's already there, lost or not, and doesn't affect sea level differently, lost, found or melted.
Arctic ice is healthy for children and other living things.

kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4069 on: December 27, 2020, 12:08:03 AM »
Quote
2 Sea ice that gets lost also gets added to the oceans.
Um... It's already there, lost or not, and doesn't affect sea level differently, lost, found or melted.

Really?

When water is ice it is cold.

When the ice fields shatter and the ice melts the temperature goes up. Ice turns to water. All increases from 4C result in thermal expansion. This happened to most ice missing from the long year Piomas missing volume because it turns into water that floats somewhere and then warms up.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4070 on: December 27, 2020, 04:01:20 PM »
Quote
2 Sea ice that gets lost also gets added to the oceans.
Um... It's already there, lost or not, and doesn't affect sea level differently, lost, found or melted.

Really?

When water is ice it is cold.

When the ice fields shatter and the ice melts the temperature goes up. Ice turns to water. All increases from 4C result in thermal expansion. This happened to most ice missing from the long year Piomas missing volume because it turns into water that floats somewhere and then warms up.

As kassy points out, when sea ice disappears there is an associated flip in albedo levels that directly contributes to global warming, that then contributes to increasing ocean temperatures that then leads to SLR (by thermal expansion of seawater).  However, the first linked article indicates that per the Archimedes' Principle, sea ice floats because it is less dense than seawater, so as stated by the article:

"Thus, when freshwater ice melts in the ocean, it contributes a greater volume of melt water than it originally displaced."

Furthermore, per the second and third linked references, indicate than an increase in Arctic Sea Ice loss results in an increase in freshwater flux into the North Atlantic, where it is likely contributing to a slowdown of the MOC; which is projected to accelerate global warming and likely an acceleration of ice mass loss from marine terminating, and marine, glaciers; which are currently accelerating observed SLR.

Title: "Melting of Floating Ice Will Raise Sea Level"

https://nsidc.org/news/newsroom/20050801_floatingice.html

Extract: "In a paper titled "The Melting of Floating Ice will Raise the Ocean Level" submitted to Geophysical Journal International, Noerdlinger demonstrates that melt water from sea ice and floating ice shelves could add 2.6% more water to the ocean than the water displaced by the ice, or the equivalent of approximately 4 centimeters (1.57 inches) of sea-level rise.

The common misconception that floating ice won’t increase sea level when it melts occurs because the difference in density between fresh water and salt water is not taken into consideration. Archimedes’ Principle states that an object immersed in a fluid is buoyed up by a force equal to the weight of the fluid it displaces. However, Noerdlinger notes that because freshwater is not as dense as saltwater, freshwater actually has greater volume than an equivalent weight of saltwater. Thus, when freshwater ice melts in the ocean, it contributes a greater volume of melt water than it originally displaced."

&

Haine, T. W. N. (09 November 2020), "Arctic Ocean Freshening Linked to Anthropogenic Climate Change: All Hands on Deck", Geophysical Research Letters, https://doi.org/10.1029/2020GL090678

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL090678

Abstract
Arctic Ocean freshwater storage increased since the mid‐1990s, but the cause was unknown. Jahn and Laiho (2020, https://doi.org/10.1029/2020GL088854) use ensemble runs of a coupled climate model to suggest that the observed increase is anthropogenic. The paper quantifies when the anthropogenic signals should emerge from the noise of natural variability. This result contextualizes research on the Arctic Ocean freshwater system and sketches an unprecedented opportunity. Future work should elucidate mechanisms, seek to observe the anthropogenic freshwater changes, and investigate the impacts on biogeochemistry and the North Atlantic Ocean circulation.

Plain Language Summary
The Arctic is a region of clear man‐made climate change. Changes in the Arctic Ocean salinity and currents have been seen, but the cause was unknown. A new paper shows that the changes are probably due to man‐made climate change. The reason is they only occur in a climate model with man‐made climate forcing. This is an important result because it helps scientists focus their research into how the changes work. It also points to a valuable opportunity to watch the Arctic Ocean respond to man‐made climate change. There might be important future impacts on North Atlantic oceanography and North Atlantic climate that scientists can now look for.

Caption for the attached image: "Figure 1 Climate model projections and observations of the Arctic Ocean freshwater cycle. The left and right subplots show the principal time series of freshwater (FW) inflows and outflows (km3 yr−1 relative to a salinity of 34.80; positive poleward). The middle subplots show the freshwater storage in the Arctic Ocean as sea ice (solid, top) and liquid (bottom) freshwater (km3 relative to 34.80). Results from the Community Earth System Model (CESM) control (gray), large ensemble (LE, purple), and low warming (LW, green) experiments are shown in each case, adapted from Jahn and Laiho's (2020) Figure 2. The subplots show the times when the models show emergence of a forced, anthropogenic signal (meaning the time of first permanent departure from the ±3.5 σ envelope of control variability, where σ is the standard deviation; horizontal and vertical lines). The observations synthesized by Haine et al. (2015) are plotted in red (with updates from de Steur et al., 2018, Woodgate, 2018, and Spreen et al., 2020; the liquid storage data are adjusted to match the Jahn & Laiho, 2020 Arctic Ocean control volume by excluding Baffin Bay). For estimates and discussion of the uncertainty in the observations, see Haine et al. (2015). The basemap shows the liquid freshwater content, which is the vertically integrated salinity anomaly relative to 34.80, based on Haine et al.'s (2015) Figure 6."

&

Jahn, A. and Rory Laiho (27 July 2020), "Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century", Geophysical Research Letters, https://doi.org/10.1029/2020GL088854

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088854

Abstract
Arctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multidecadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state‐of‐the‐art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first flux to show emergence outside the range of background variability, with this change potentially already occurring. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability.

Plain Language Summary
The surface waters of the Arctic Ocean are fresher than the rest of the world oceans, due to the input of large amounts of river runoff. The very fresh surface ocean affects the ocean circulation and climate not just in the Arctic Ocean but also at lower latitudes, especially in the North Atlantic. The last two decades have seen a freshening of the surface Arctic Ocean, for reasons that are currently unknown. Here we demonstrate that this freshening is likely already driven by climate change. Furthermore, we find that due to manmade climate change, Arctic freshwater fluxes to the North Atlantic are also likely to soon start showing signs of change beyond the range of the variability we have observed in the past. The information provided here about the expected timing of the emergence of climate change signals will allow us to monitor upcoming changes in real time, to better understand how changes in the Arctic Ocean can impact climate worldwide.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4071 on: December 27, 2020, 04:12:43 PM »
As a follow-on to my last post, the linked reference (& associated image) indicates that per CESM2(WACCM6) (which was part of CMIP6), the Arctic Ocean is projected to most likely be seasonally ice free by, or before, 2040; which, will accelerate SLR as described in my Reply #4070.

DeRepentigny, P., Alexandra Jahn, Marika M. Holland and Abigail Smith (17 July 2020), "Arctic Sea Ice in Two Configurations of the CESM2 During the 20th and 21st Centuries", JGR Oceans, https://doi.org/10.1029/2020JC016133

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JC016133

Abstract
We provide an assessment of the current and future states of Arctic sea ice simulated by the Community Earth System Model version 2 (CESM2). The CESM2 is the version of the CESM contributed to the sixth phase of the Coupled Model Intercomparison Project (CMIP6). We analyze changes in Arctic sea ice cover in two CESM2 configurations with differing atmospheric components: the CESM2(CAM6) and the CESM2(WACCM6). Over the historical period, the CESM2(CAM6) winter ice thickness distribution is biased thin, which leads to lower summer ice area compared to CESM2(WACCM6) and observations. In both CESM2 configurations, the timing of first ice‐free conditions is insensitive to the choice of CMIP6 future emissions scenario. In fact, the probability of an ice‐free Arctic summer remains low only if global warming stays below 1.5°C, which none of the CMIP6 scenarios achieve. By the end of the 21st century, the CESM2 simulates less ocean heat loss during the fall months compared to its previous version, delaying sea ice formation and leading to ice‐free conditions for up to 8 months under the high emissions scenario. As a result, both CESM2 configurations exhibit an accelerated decline in winter and spring ice area, a behavior that had not been previously seen in CESM simulations. Differences in climate sensitivity and higher levels of atmospheric CO2 by 2100 in the CMIP6 high emissions scenario compared to its CMIP5 analog could explain why this winter ice loss was not previously simulated by the CESM.

Plain Language Summary
We provide a first look at the current and future states of Arctic sea ice as simulated by the Community Earth System Model version 2 (CESM2), which is part of the newest generation of large‐scale climate models. The CESM2 model has two configurations that differ in their representation of atmospheric processes: the CESM2(CAM6) and the CESM2(WACCM6). We find several differences in the simulated Arctic sea ice cover between the two CESM2 configurations, as well as compared to the previous generation of the CESM model. Over the historical period, the CESM2(CAM6) model simulates a winter ice cover that is too thin, which leads to lower summer ice coverage compared to the CESM2(WACCM6) model and observations. In both CESM2 configurations, the probability of the Arctic becoming nearly ice free at the end of the summer remains low only if global warming stays below 1.5°C. In addition, the specific year a first ice‐free Arctic is reached is not sensitive to the future greenhouse gas emissions trajectories considered here. In contrast to the previous generation of the CESM, both CESM2 configurations project an accelerated decline in winter and spring ice area by the end of the 21st century if greenhouse gases emissions remain high.

Extract: "This suggests that the CESM2(WACCM6), with its present‐day Arctic sea ice mean state closer to observations, is the more appropriate CESM2 configuration contributed to CMIP6 to use for in‐depth studies of future sea ice changes in the Arctic.

Caption for the attached image: "Figure 5 Timing of first ice‐free Arctic: (a) Year of first September ice‐free conditions in the CESM2(CAM6) (circles) and the CESM2(WACCM6) (diamonds) over the historical period (black) and the different future emissions scenarios (colors). The symbols with a dot in the middle indicate that two ensemble members reach first ice‐free conditions in the same year. (b) Percentage of the total number of ensemble members reaching first September ice‐free conditions in a given year in the CESM2(CAM6) (orange; total of 13 ensemble members), the CESM2(WACCM6) (blue; total of 10 ensemble members), and the CESM‐LE (gray; total of 40 ensemble members). For the CESM2(CAM6) and the CESM2(WACCM6), this is done by combining the historical and all future simulations into one single distribution."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4072 on: December 29, 2020, 01:11:29 AM »
In the linked reference, the authors used the Regional Circulation Model (RCM) MAR to dynamically downscale projections from six CMIP5 models and from five CMIP6 models related to the Greenland Ice Sheet (GrIS), and they found that the projected loss surface mass balance (SMB) for the GrIS projected (for the twenty-first century) by the CMIP6 models under SSP585 forcing was markedly greater than that projected by the CMIP5 models under RCP8.5 forcing (see the first attached image), and in particular for the UKESM1-0-LL projection (see the lowest light orange curves in the first attached image) as this CMIP6 model has a mean projected ECS of 5.36C (see the second attached image).  Also, I note that dynamically calved ice mass loss from the GrIS in this timeframe would need to be added to the corresponding SMB values in order to estimate the total ice mass loss from the GrIS in the twenty-first century.  Finally, I note that such ice mass loss this century will serve to slow the AMOC/MOC, which is a positive feedback mechanism.

Hofer, S., Lang, C., Amory, C. et al. Greater Greenland Ice Sheet contribution to global sea level rise in CMIP6. Nat Commun 11, 6289 (2020). https://doi.org/10.1038/s41467-020-20011-8

https://www.nature.com/articles/s41467-020-20011-8

Abstract: "Future climate projections show a marked increase in Greenland Ice Sheet (GrIS) runoff during the 21st century, a direct consequence of the Polar Amplification signal. Regional climate models (RCMs) are a widely used tool to downscale ensembles of projections from global climate models (GCMs) to assess the impact of global warming on GrIS melt and sea level rise contribution. Initial results of the CMIP6 GCM model intercomparison project have revealed a greater 21st century temperature rise than in CMIP5 models. However, so far very little is known about the subsequent impacts on the future GrIS surface melt and therefore sea level rise contribution. Here, we show that the total GrIS sea level rise contribution from surface mass loss in our high-resolution (15 km) regional climate projections is 17.8 ± 7.8 cm in SSP585, 7.9 cm more than in our RCP8.5 simulations using CMIP5 input. We identify a +1.3 °C greater Arctic Amplification and associated cloud and sea ice feedbacks in the CMIP6 SSP585 scenario as the main drivers. Additionally, an assessment of the GrIS sea level contribution across all emission scenarios highlights, that the GrIS mass loss in CMIP6 is equivalent to a CMIP5 scenario with twice the global radiative forcing."

Extract: "Higher Greenland mass loss in SSP585 than RCP8.5.  There is a stark contrast in future GrIS surface melt and meltwater runoff between the two model suites (Fig. 3). At the end of the twenty-first century, MAR SSP585 projects a doubling in the reduction of GrIS SMB compared to the CMIP5 (RCP8.5) forced MAR simulation."

Caption for the first image: "Fig. 3 Greenland surface mass balance comparison between downscaled CMIP5 and CMIP6 MAR simulation. a Annual Greenland Ice Sheet wide integrated annual SMB from six CMIP5 forced MAR simulations (blue) and five CMIP6 MAR simulations (orange) in Gigatonnes per year (Gt/yr). The dark blue line represents the mean of all CMIP5 MAR simulation (6, RCP8.5) and dark orange is the mean of all CMIP6 MAR simulations (5, SSP585).  The individual runs are shown in lighter colors. b Same as a but for the cumulative GrIS SMB anomalies (Gt), based on the 1961-1990 average of the simulations."

Edit: I do not believe that the CMIP6 projects of SMB for the GrIS fully considered the risks of either surface darkening decreasing albedo nor of atmospheric river events causing rain related surface ice melting in South Greenland.
« Last Edit: December 29, 2020, 04:26:23 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4073 on: December 29, 2020, 10:17:27 PM »
The linked reference cites results from a simple energy balance model (EBM), with an ECS of 4.34K, and indicates a clear risk of the Earth climate state similar to that existed during the Pliocene epoch just before 2100 for RCP 8.5 forcing and just after 2100 for RCP 6.0 forcing as indicated by panel b of the attached image.  Further, I note that if the CMIP6 model UK ESM1-0-LL (with an ECS of 5.36K) is correct then such an abrupt tipping into a higher (Pliocene-like) climate state could occur well before 2100, and still earlier than that if positive ice-climate feedbacks were to be considered.

Kypke, K. L., Langford, W. F., and Willms, A. R.: Anthropocene climate bifurcation, Nonlin. Processes Geophys., 27, 391–409, https://doi.org/10.5194/npg-27-391-2020, 2020.

https://npg.copernicus.org/articles/27/391/2020/

Abstract

This article presents the results of a bifurcation analysis of a simple energy balance model (EBM) for the future climate of the Earth. The main focus is on the following question: can the nonlinear processes intrinsic to atmospheric physics, including natural positive feedback mechanisms, cause a mathematical bifurcation of the climate state, as a consequence of continued anthropogenic forcing by rising greenhouse gas emissions? Our analysis shows that such a bifurcation could cause an abrupt change to a drastically different climate state in the EBM, which is warmer and more equable than any climate existing on Earth since the Pliocene epoch. In previous papers, with this EBM adapted to paleoclimate conditions, it was shown to exhibit saddle-node and cusp bifurcations, as well as hysteresis. The EBM was validated by the agreement of its predicted bifurcations with the abrupt climate changes that are known to have occurred in the paleoclimate record, in the Antarctic at the Eocene–Oligocene transition (EOT) and in the Arctic at the Pliocene–Paleocene transition (PPT). In this paper, the EBM is adapted to fit Anthropocene climate conditions, with emphasis on the Arctic and Antarctic climates. The four Representative Concentration Pathways (RCP) considered by the IPCC (Intergovernmental Panel on Climate Change) are used to model future CO2 concentrations, corresponding to different scenarios of anthropogenic activity. In addition, the EBM investigates four naturally occurring nonlinear feedback processes which magnify the warming that would be caused by anthropogenic CO2 emissions alone. These four feedback mechanisms are ice–albedo feedback, water vapour feedback, ocean heat transport feedback, and atmospheric heat transport feedback. The EBM predicts that a bifurcation resulting in a catastrophic climate change, to a pre-Pliocene-like climate state, will occur in coming centuries for an RCP with unabated anthropogenic forcing, amplified by these positive feedbacks. However, the EBM also predicts that appropriate reductions in carbon emissions may limit climate change to a more tolerable continuation of what is observed today. The globally averaged version of this EBM has an equilibrium climate sensitivity (ECS) of 4.34 K, near the high end of the likely range reported by the IPCC.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4074 on: December 31, 2020, 07:18:29 PM »
The linked, open access, commentary reference indicates that traditional consensus climate science (CCS) communication to decision-makers '… has taken a probabilistic approach producing large model ensembles and exploring likely ranges, thereby neglecting low likelihood but potentially high impact events that pose significant risks to society', see the attached image.  Thus, the authors recommend augmenting this tradition CCS approach with what they call 'event-based storylines', in that:

'Event‐based storylines are emerging as an alternative way to explore future high‐impact events while taking into account aspects of vulnerability and exposure of the considered system with an emphasis on plausibility rather than probability. This concept links directly to common practices in disaster risk management using "stress‐testing" for emergency preparedness based on events that are conditional on specific, but plausible assumptions.'

I note that this event-based storyline approach is very similar to the maximum credible domino scenario Bayesian network approach related that I expect to present (in three separate threads) sometime next year.

Sillmann J. et al. (14 December 2020), "Event‐based storylines to address climate risk", Earth's Future, https://doi.org/10.1029/2020EF001783

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020EF001783

Abstract
The climate science community is challenged to adopt an actionable risk perspective, which is difficult to align with the traditional focus on model‐based probabilistic climate change projections. Event‐based storylines can provide a way out of this conundrum by putting emphasis on plausibility rather than probability. This links directly to common practices in disaster risk management using "stress‐testing" for emergency preparedness based on events that are conditional on specific and plausible assumptions. Event‐based storylines allow for conditional explanations, without full attribution of every causal factor, which is crucial when some aspects of the latter are complex and highly uncertain.

Plain Language Summary
One of today's major challenges is how to use insights and information from climate sciences to inform decision making regarding managing risks from climate change, where weather and climate extremes represent a major component of climate‐related risk. So far climate science has taken a probabilistic approach producing large model ensembles and exploring likely ranges, thereby neglecting low likelihood but potentially high impact events that pose significant risks to society. Event‐based storylines are emerging as an alternative way to explore future high‐impact events while taking into account aspects of vulnerability and exposure of the considered system with an emphasis on plausibility rather than probability. This concept links directly to common practices in disaster risk management using "stress‐testing" for emergency preparedness based on events that are conditional on specific, but plausible assumptions. When co‐developed by climate scientists and stakeholders, event‐based storylines can be informed by physical climate and impact modeling and can provide a useful way of communicating and assessing climate‐related risk in a specific decision making context.
« Last Edit: December 31, 2020, 07:52:46 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4075 on: December 31, 2020, 09:50:55 PM »
The linked reference indicates that the Amazon Rainforest will pass a dieback tipping point by 2064 (see the attached image):

Walker, R.T. (23 Dec 2020), "Collision Course: Development Pushes Amazonia Toward Its Tipping Point", Environment: Science and Policy for Sustainable Development Volume 63, Issue 1, https://doi.org/10.1080/00139157.2021.1842711

https://www.tandfonline.com/doi/full/10.1080/00139157.2021.1842711

Caption for attached image: "Figure 2. Amazonian tipping-point timing and cascade.
Note: Southern Amazonia is defined as the rectangle given by 70–50 degrees W and 5–15 degrees S. Here, the dry season has been lengthening at ∼6.5 days per decade. The 2005 drought, identified as a 100-year event, was ∼30 days longer than the long-term mean, interpretable as a 1-year event. Thus, at the observed rate of dry season lengthening, the 2005 drought will become the new normal in 2066, after 4.6 decades. Given that it took >4 (= 5) years for the canopy to recover from the 2005 drought, such conditions cannot occur more frequently than once every 5 years if the forest is to survive. Assume conservatively that the 2005 drought has retained its 100-year return cycle until the present time, from which it now declines as a linear function of time. Also assume that dry season length and associated fires fully determine tree mortality. In such a situation, the tipping point is reached in 2064, when the return cycle of the 2005 drought drops below 6 years. The transgression in 2064—likely to be hastened by the Initiative for the Integration of the Regional Infrastructure of South America—will inhibit moisture transport south to the La Plata River Basin and therefore recharge of the Guarani Aquifer. The figure depicts a cascade of forest degradation from southern Amazonia to the west-northwest. The ∼30 day extension of the 2005 drought was calculated from figure 3 of reference 28 by averaging drought conditions for Porto de Moz, Porto Velho, and Rio Branco."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4076 on: December 31, 2020, 10:54:59 PM »
I’m surprised the Amazon has that long.
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4077 on: January 01, 2021, 09:42:46 AM »
The linked, open access, reference concludes that:

"Our study suggests increased North African dust emissions, whether driven by AMOC changes or atmospheric circulation changes, could amplify the risk of an AMOC collapse. Therefore, it is important to include dust as an interactive component of the climate system."

This indicates that consensus climate models are once again erring on the side of least drama with regard to coming climate risk by ignoring the identified dust-climate feedback.

Murphy, L. N., M. Goes and A. C. Clement (09 November 2017), "The Role of African Dust in Atlantic Climate During Heinrich Events", Paleoceanography and Paleoclimatology, https://doi.org/10.1002/2017PA003150

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003150

Abstract
Increased ice discharge in the North Atlantic is thought to cause a weakening, or collapse, of the Atlantic meridional overturning circulation (AMOC) during Heinrich events. Paleoclimate records indicate that these periods were marked by severe tropical aridity and dustiness. Although the driver of these events is still under debate, large freshwater input is necessary for climate models to simulate the magnitude, geographical extent, and abruptness of these events, indicating that they may be missing feedbacks. We hypothesize that the dust‐climate feedback is one such feedback that has not been previously considered. Here we analyze the role of dust‐climate feedbacks on the AMOC by parameterizing the dust radiative effects in an intermediate complexity model and consider uncertainties due to wind stress forcing and the magnitude of both atmospheric dust loading and freshwater hosing. We simulate both stable and unstable AMOC regimes by changing the prescribed wind stress forcing. In the unstable regime, additional dust loading during Heinrich events cools and freshens the North Atlantic and abruptly reduces the AMOC by 20% relative to a control simulation. In the stable regime, however, additional dust forcing alone does not alter the AMOC strength. Including both freshwater and dust forcing results in a cooling of the subtropical North Atlantic more comparable to proxy records than with freshwater forcing alone. We conclude that dust‐climate feedbacks may provide amplification to Heinrich cooling by further weakening AMOC and increasing North Atlantic sea ice coverage.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4078 on: January 01, 2021, 08:26:56 PM »
Barrett et al. (2020) studied recent observed extreme Greenland atmospheric blocking events (see the first image & associated caption) and found that such events are both increasing in frequency and more frequently directing atmospheric moisture to Greenland, both from atmospheric Rossby wave events (see the second image) and from Atmospheric River events (frequently from precursors to and to hurricane events, see the third image; which increase in intensity with global warming as shown in the fourth image).  This all implies that we will see increasingly frequent and increasingly severe, rainfall events (and associated accelerated ice mass loss) for the GrIS in coming decades.

Barrett, B.S. et al. (16 June 2020), "Extreme Greenland blocking and high‐latitude moisture transport", Atmospheric Science Letters, https://doi.org/10.1002/asl.1002

https://rmets.onlinelibrary.wiley.com/doi/10.1002/asl.1002

Abstract
Blocked atmospheric flows over Greenland and the North Atlantic Arctic (NAA) can be defined by the appearance of an anomalous ridge, many times off the western margin of continents, that deflects traveling cyclones from their usual storm tracks. Atmospheric blocking often produces a strong equatorward deflection of polar air on the eastern flank of the anticyclone, including severe cold episodes in winter, and severe droughts and heat waves in summer. Recent changes in low‐frequency atmospheric circulation in the NAA have increased sensible heat and moisture advection from the mid‐latitudes into this region. In this study, we explore the frequency and seasonality of extreme Greenland blocking, and we explore the relationship between extreme blocking and moisture transport into and over the region.
We quantify atmospheric flow blocking over Greenland using the Greenland Blocking Index, and extreme blocking is defined from 1980 to 2019 at the 90th, 95th, 97th, and 99th percentiles for both summer (June to August) and winter (December to February) seasons. Moisture transport over Greenland was defined by calculating daily integrated vapor transport from the ERA‐Interim reanalysis over the region from 15° to 85°W and 55° to 80°N. The frequency of extreme blocking over Greenland was found to have increased in the most recent two decades (2000–2019) compared to the period 1980–1999. In addition, the probability of above‐average moisture transport occurring on a day with extreme blocking is high in both summer and winter, with the highest probability of high moisture transport during an extreme Greenland Blocking Index day in winter. These findings are unique to this work and suggest future work on the role of moisture transport in developing or sustaining blocks over Greenland.

Extract1: "Extreme moisture transport, particularly through features called atmospheric rivers, can result in ice melt and mass loss as melt energy is provided by turbulent heat fluxes, driven by enhanced barrier winds that are in turn generated by a strong synoptic pressure gradient combined with an enhanced local temperature contrast between cool near‐ice air and anomalously warm surrounding air (Mattingly et al., 2018; 2020). Furthermore, Greenland blocking, and in particular extreme Greenland blocking, has increased in frequency and magnitude between 1980–1999 and 2000–2019 (Table 1 and Figure 2). It is thus important to examine the GBI–IVT relationship in greater depth.  One way to do that is to repeat the above analysis, but for extreme IVT days, and examine the frequency of above‐normal GBI during extreme IVT days. In winter, 63.4% of the days with IVT above the 90th percentile was associated with above‐normal GBI (Table 2). That frequency of above‐average GBI increased to 82.9% for the most extreme winter IVT (e.g., IVT at the 99th percentile). In summer, however, the relationship was mixed: between 45% and 50% of days characterized by extreme IVT (above the 90th percentile) featured above‐normal GBI. Thus, while high GBI is strongly associated with high IVT in both winter and summer, the reverse is mixed: wintertime extreme IVT days do tend to occur when the GBI is above normal, but summertime extreme IVT days do not necessarily occur when the GBI is above normal."

Note:    1. IVT = integrated vapor transport.
   2. GBI = Greenland Blocking Index.

Extract2: " It is important to note that there may be a relationship between geopotential height over Greenland and other leading modes of atmospheric variability, both on shorter time scales (the NAO; Hanna et al., 2015) and longer ones (the PDO; Collow et al., 2017). In this study, we did not consider co‐variability between the GBI and those leading modes and suggest future work on that topic.
In addition, the probability of above‐average IVT occurring on a day with extreme blocking is high in both summer and winter, with the highest probability of above‐average IVT during an extreme GBI day in winter. The reverse relationship was more complex, with above‐average blocking likely to occur during extreme winter IVT but not extreme summer IVT. This agrees with two related studies by Rimbu et al. (2007; 2008), who showed that during high blocking frequency over Greenland the axis of maximum moisture transport extends northward to Greenland relative to the times of low blocking frequency, leading to a more active storm track and greater moisture transport to the ice sheet. Finally, the highest values of IVT were found to occur in advance of extreme GBI, tending to lead extreme GBI by between up to 2.5 days (in summer) and 3.6 days (in winter). These findings are unique to this work and lead to questions about the role of moisture transport in developing or sustaining blocks over Greenland, related to questions posed by McLeod and Mote (2015) on the role of precursor cyclones."

Caption for the first attached image: "FIGURE 1 Height field (in m) at 500‐hPa on days in (a) DJF and (b) JJA when the NOAA Greenland Blocking Index (GBI) was above the 95th percentile. Both shading and contours indicate mean heights, and contours are drawn between 5,200 and 5,800 m at 60‐m increments. Red boxed region indicates the spatial domain averaged to calculate the NOAA GBI index, and the magenta boxed region indicates the domain used to calculate integrated vapor transport (IVT) from the ERA‐interim reanalysis. Note the color scale is different in panel (a) and (b)"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4079 on: January 02, 2021, 09:42:02 PM »
The linked reference indicates that the Amazon Rainforest will pass a dieback tipping point by 2064 (see the attached image):

Walker, R.T. (23 Dec 2020), "Collision Course: Development Pushes Amazonia Toward Its Tipping Point", Environment: Science and Policy for Sustainable Development Volume 63, Issue 1, https://doi.org/10.1080/00139157.2021.1842711

https://www.tandfonline.com/doi/full/10.1080/00139157.2021.1842711

...

While the quoted reference indicates that the majority of the Amazon Rainforest is on track to begin collapsing circa 2064; Hubau et al. (2020) indicates that while transitioning more slowing than the Amazon, the Congo Rainforest is already in the process of turning from a carbon sink into a carbon source.

Hubau, W.et al. (2020), "Asynchronous carbon sink saturation in African and Amazonian tropical forests", Nature, volume 579, pages80–87, doi: 10.1038/s41586-020-2035-0

https://www.nature.com/articles/s41586-020-2035-0

Abstract: "Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions. Climate-driven vegetation models typically predict that this tropical forest ‘carbon sink’ will continue for decades. Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53–0.79), in contrast to the long-term decline in Amazonian forests. Therefore, the carbon sink responses of Earth’s two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature. Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth’s intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth’s climate."

Furthermore, Creese et al. (2019) indicates that depending on future changes in atmospheric convection over the Maritime Continent; the Congo Basin may possibly experience more frequent droughts during the December thru February months; which (if so) could further accelerate carbon emissions from the Congo Rainforest.

Creese, A., Washington, R. & Jones, R. Climate change in the Congo Basin: processes related to wetting in the December–February dry season. Clim Dyn 53, 3583–3602 (2019). https://doi.org/10.1007/s00382-019-04728-x

https://link.springer.com/article/10.1007/s00382-019-04728-x

Abstract: "The Congo Basin is one of three key areas of tropical convection and contains the planet’s second largest rainforest. Understanding how global warming might change its climate is crucial, particularly during the dry seasons, when rainfall amounts currently bring the rainforest boundaries close to the threshold of viability. There is considerable uncertainty in projections of future rainfall change from the Coupled Model Intercomparison Project (CMIP5) under the high-emissions experiment (RCP8.5). Whilst there is a general trend towards wetting in most months, its magnitude varies considerably. In the December to February dry season, the projected change in seasonal rainfall varies from 2 to 160 mm across models. This study uses a regionally-focused process-based assessment to understand inter-model differences in rainfall projections, as a first step to assessing their plausibility. Models which produce the most wetting by the end of the century feature enhanced convection over the Congo Basin region, enhanced subsidence in the African subtropics, and decreased uplift over the Maritime Continent. In contrast, models with a small wetting response feature reduced convection over the Congo Basin. This indicates that wetting over the Congo Basin is related to a weakening of the Indian Ocean Walker circulation, reminiscent of a positive Indian Ocean Dipole state. Models with the highest magnitude wetting also feature greater low-to-mid-level moisture flux from the north and the east compared to models with less wetting. These results indicate that the future degree of wetting over the Congo Basin will be linked to changes in convection over the Maritime Continent."

Lastly, Abbott & Cronin (2020), and the associated linked article, indicate that future high aerosol concentrations in the tropics (say from more frequent dust storms [say from the Sahara] and/or increasing tropical wildfires [say from dying tropical rainforests]) would both dissipate low-altitude cloud cover (with a negative feedback) and increase high-altitude cloud cover (with positive feedback); which, implies that climate sensitivity will likely not only increase, in coming decades, not only from the transformation of tropical rainforests from carbon sinks into carbon sources, but also from changing net cloud feedback from negative to positive.

Abbott, T.H. and Timothy W. Cronin (01 Jan 2021), "Aerosol invigoration of atmospheric convection through increases in humidity", Science, Vol. 371, Issue 6524, pp. 83-85, DOI: 10.1126/science.abc5181

https://science.sciencemag.org/content/371/6524/83.abstract

Abstract
Cloud-aerosol interactions remain a major obstacle to understanding climate and severe weather. Observations suggest that aerosols enhance tropical thunderstorm activity; past research, motivated by the importance of understanding aerosol impacts on clouds, has proposed several mechanisms that could explain that observed link. We find that high-resolution atmospheric simulations can reproduce the observed link between aerosols and convection. However, we also show that previously proposed mechanisms are unable to explain the invigoration. Examining underlying processes reveals that, in our simulations, high aerosol concentrations increase environmental humidity by producing clouds that mix more condensed water into the surrounding air. In turn, higher humidity favors large-scale ascent and stronger convection. Our results provide a physical reason to expect invigorated thunderstorms in high-aerosol regions of the tropics.

See also:

Title: "Aerosols from pollution, desert storms, and forest fires may intensify thunderstorms"

https://news.mit.edu/2020/aerosols-pollution-storms-fires-intensify-1231

Extract: "Now MIT scientists have discovered a new mechanism by which aerosols may intensify thunderstorms in tropical regions. Using idealized simulations of cloud dynamics, the researchers found that high concentrations of aerosols can enhance thunderstorm activity by increasing the humidity in the air surrounding clouds.

An aerosol is any collection of fine particles that is suspended in air. Aerosols are generated by anthropogenic processes, such as the burning of biomass, and combustion in ships, factories, and car tailpipes, as well as from natural phenomena such as volcanic eruptions, sea spray, and dust storms. In the atmosphere, aerosols can act as seeds for cloud formation.

If a cloud contains many aerosol particles that suppress rain, it might be able to evaporate more water to the its surroundings. In turn, this could increase the humidity of the surrounding air, providing a more favorable environment for the formation of thunderstorms. This chain of events, therefore, could explain aerosols’ link to thunderstorm activity.

They put their idea to the test using the same simulation of cloud dynamics, this time noting the temperature and relative humidity of each grid cell in and around clouds as they increased the aerosol concentration in the simulation. The concentrations they set ranged from low-aerosol conditions similar to remote regions over the ocean, to high-aerosol environments similar to relatively polluted air near urban areas.

They found that low-lying clouds with high aerosol concentrations were less likely to rain out. Instead, these clouds evaporated water to their surroundings, creating a humid layer of air that made it easier for air to rise quickly through the atmosphere as strong, storm-brewing updrafts.
“After you’ve established this humid layer relatively low in the atmosphere, you have a bubble of warm and moist air that can act as a seed for a thunderstorm,” Abbott says. “That bubble will have an easier time ascending to altitudes of 10 to15 kilometers, which is the depth clouds need to grow to to act as thunderstorms.”"

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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4080 on: January 02, 2021, 11:12:53 PM »
Re: January 01, 2021, 02:26:56 PM
Interesting that increased precipitation in Greenland means ice loss and not gain.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4081 on: January 03, 2021, 10:36:17 PM »
The linked reference quantifies the influence of the observed Antarctic Melt Anomaly (AAMA) that was missing from all CMIP5 projections and most CMIP6 projections, see the associated images; but which was largely accounted for Hansen et al. (2016):


Rye, C.D., J.Marshall, M. Kelley, G. Russell, L.S. Nazarenko, Y. Kostov, G.A. Schmidt, and J. Hansen, 2020: Antarctic Glacial Melt as a Driver of Recent Southern Ocean Climate Trends, Geophysical Research Letters 47, 11, doi:10.1029/2019GL086892.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL086892

Abstract
Recent trends in Southern Ocean (SO) climate—of surface cooling, freshening, and sea ice expansion—are not captured in historical climate simulations. Here we demonstrate that the addition of a plausible increase in Antarctic meltwater to a coupled climate model can produce a closer match to a wide range of climate trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model to compute “climate response functions” (CRFs) for the addition of meltwater. These imply a cooling and freshening of the SO, an expansion of sea ice, and an increase in steric height, all consistent with observations since 1992. The CRF framework allows one to compare the efficacy of Antarctic meltwater as a driver of SO climate trends, relative to greenhouse gas and surface wind forcing. The meltwater CRFs presented here strongly suggest that interactive Antarctic ice melt should be included in climate models.
Plain Language Summary
Climate models do not capture recent Southern Ocean (SO) climate trends of surface cooling, freshening, and sea ice expansion. Here we demonstrate that including a realistic increase in Antarctic meltwater can improve a model's representation of SO trends. We use an ensemble of simulations of the Goddard Institute for Space Studies Earth system model. Model results suggest that Antarctic meltwater drives a cooling and freshening of the SO and an expansion of winter sea ice, all consistent with observations. Results suggest that a better representation of Antarctic ice melt should be included in climate models.

Extract: "CMIP5 earth system models (ESM) do not explicitly represent the increase in Antarctic glacial melt (AAMA) over recent decades. The Antarctic grounded ice sheet mass loss has increased to perhaps 250 Gt/yr in 2017 (IMBIE 2018). The thinning and retreat of floating ice shelves is thought to have also contributed as much as 280 Gt/yr in recent years (2003-2015; Paolo 2015). Furthermore, a series of large ice-shelf retreats not included in the above estimates has contributed an additional flux of perhaps 210 Gt/yr over the period 1988 to 2008 (Shepherd et al., 2010).

Finally, Rye et al., (2014) highlights an anomalous trend in Antarctic Subpolar Sea Surface Height (SSH) and finds that an AAMA of around 430 Gt/yr is sufficient to drive a steric height increase consistent with observations."

Caption for the first image: "Figure 3| Modeled response to a 200 Gt yr-1 step change in AMMA. Decadal trends calculated over 30 year model runs from a 20-member ensemble in (a) SST, (b) SSS (c) zonal-average potential temperature (d) zonalaverage salinity (e) Interior temperature, averaged between 500 and 3000 m depth. (f) SSH. Red and Green contours denote the winter Sea Ice extent in the control run and after 30 years of perturbation experiment respectively."

Caption for the second image: "Figure 4| Linear convolution projections of Southern Ocean SST. ModelE Southern Ocean SST CRFs for: (a) 200 Gt/yr step change in AAMA, (b) a 1-standard deviation step-change in the Southern Annular mode (Doddridge 2019). Grey area: CMIP-5 multi-model spread. (c) Double CO2 forcing. In all plots: Grey lines: Individual ensemble members. Black lines: Ensemble means. Blue. Green and Red lines: Exponential fits. (d) Observed forcing histories. Red line: Green House Gases (GHG; Butler et al., 1999). Blue line: Combined AAMA (IMBIE 2018; Paolo et al., 2015). Green line: Southern Annular Mode (SAM; Marshall 2003). (e) The convolution of CRFs (a-c) with forcing histories (d). Red line: GHGs. Green line: SAM (wind). Blue line: AAMA. Black line: combined response. The purple dashed line and markers: observed Southern Ocean SST cooling (HadSST; Kennedy et al., 2019). (f) Summary of SST trends. Red bars: GHG. Green bars: SAM (Wind). Blue bar: AAMA. Grey bars: Combined forcing. For GHG, Wind and Total, the left-side bar shows convolution results for ModelE and the right-side bar shows results for the CMIP-5 multi-model mean derived from Kostov et al., (2018) and Doddridge et al., (2019). For AAMA and Total, the full bars denote convolutions for the time histories of grounded Antarctic mass loss anomaly; the shaded bars denote convolutions for the combined time history of grounded ice and floating ice shelves mass loss anomaly. The purple line: observed Southern Ocean cooling. Black whiskers: standard deviation."

Caption for the third image: "Figure 5| Southern Ocean Climate Response Functions. ModelE CRFs for a 200 Gt/yr step change in Antarctic glacial melt. Grey lines: individual ensemble members. Black line: Ensemble mean. Red lines: Exponential or linear fit to ensemble mean. (a) Sea Surface Salinity averaged over 55 to 70 S. (b) Winter Sea Ice Extent. (c) Antarctic Subpolar Sea Sea Surface Height averaged between the continent and 70 S. (d-f) convolutions of CRF’s a-c with AAMA forcing shown in Figure 4d. d. Response of Southern Ocean SSS. e. Response of Southern Ocean SIE f. Response of Antarctic Subpolar Sea SSH."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4082 on: January 03, 2021, 10:45:14 PM »
The linked reference quantifies the Earth energy imbalance (EEI), between 1960 and 2018, and indicates that EEI is the most critical number for representing prospects for continued global warming and climate change, even more so than GMSTA (see also the associated images).  This work helps to bring the implications of Hansen et al. (2016) into perspective.

von Schuckmann, K., Cheng, L., Palmer, M. D., Hansen, J., Tassone, C., Aich, V., Adusumilli, S., Beltrami, H., Boyer, T., Cuesta-Valero, F. J., Desbruyères, D., Domingues, C., García-García, A., Gentine, P., Gilson, J., Gorfer, M., Haimberger, L., Ishii, M., Johnson, G. C., Killick, R., King, B. A., Kirchengast, G., Kolodziejczyk, N., Lyman, J., Marzeion, B., Mayer, M., Monier, M., Monselesan, D. P., Purkey, S., Roemmich, D., Schweiger, A., Seneviratne, S. I., Shepherd, A., Slater, D. A., Steiner, A. K., Straneo, F., Timmermans, M.-L., and Wijffels, S. E.: Heat stored in the Earth system: where does the energy go?, Earth Syst. Sci. Data, 12, 2013–2041, https://doi.org/10.5194/essd-12-2013-2020, 2020.

https://essd.copernicus.org/articles/12/2013/2020/

Abstract
Human-induced atmospheric composition changes cause a radiative imbalance at the top of the atmosphere which is driving global warming. This Earth energy imbalance (EEI) is the most critical number defining the prospects for continued global warming and climate change. Understanding the heat gain of the Earth system – and particularly how much and where the heat is distributed – is fundamental to understanding how this affects warming ocean, atmosphere and land; rising surface temperature; sea level; and loss of grounded and floating ice, which are fundamental concerns for society. This study is a Global Climate Observing System (GCOS) concerted international effort to update the Earth heat inventory and presents an updated assessment of ocean warming estimates as well as new and updated estimates of heat gain in the atmosphere, cryosphere and land over the period 1960–2018. The study obtains a consistent long-term Earth system heat gain over the period 1971–2018, with a total heat gain of 358±37 ZJ, which is equivalent to a global heating rate of 0.47±0.1 W m−2. Over the period 1971–2018 (2010–2018), the majority of heat gain is reported for the global ocean with 89 % (90 %), with 52 % for both periods in the upper 700 m depth, 28 % (30 %) for the 700–2000 m depth layer and 9 % (8 %) below 2000 m depth. Heat gain over land amounts to 6 % (5 %) over these periods, 4 % (3 %) is available for the melting of grounded and floating ice, and 1 % (2 %) is available for atmospheric warming. Our results also show that EEI is not only continuing, but also increasing: the EEI amounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization of climate, the goal of the universally agreed United Nations Framework Convention on Climate Change (UNFCCC) in 1992 and the Paris Agreement in 2015, requires that EEI be reduced to approximately zero to achieve Earth's system quasi-equilibrium. The amount of CO2 in the atmosphere would need to be reduced from 410 to 353 ppm to increase heat radiation to space by 0.87 W m−2, bringing Earth back towards energy balance. This simple number, EEI, is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control, and we call for an implementation of the EEI into the global stocktake based on best available science. Continued quantification and reduced uncertainties in the Earth heat inventory can be best achieved through the maintenance of the current global climate observing system, its extension into areas of gaps in the sampling, and the establishment of an international framework for concerted multidisciplinary research of the Earth heat inventory as presented in this study. This Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/, last access: 7 August 2020) under the DOI https://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2 (von Schuckmann et al., 2020).

Caption for the first image: "Figure 6. Earth heat inventory (energy accumulation) in ZJ (1 ZJ = 1021 J) for the components of the Earth’s climate system relative to 1960 and from 1960 to 2018 (assuming constant cryosphere increase for the year 2018). See Sects. 1–4 for data sources. The upper ocean (0–300 m, light blue line, and 0–700 m, light blue shading) accounts for the largest amount of heat gain, together with the intermediate ocean (700–2000 m, blue shading) and the deep ocean below 2000 m depth (dark blue shading). Although much lower, the second largest contributor is the storage of heat on land (orange shading), followed by the gain of heat to melt grounded and floating ice in the cryosphere (gray shading). Due to its low heat capacity, the atmosphere (magenta shading) makes a smaller contribution. Uncertainty in the ocean estimate also dominates the total uncertainty (dot-dashed lines derived from the standard deviations (2σ) for the ocean, cryosphere and land; atmospheric uncertainty is comparably small). Deep ocean (> 2000 m) is assumed to be zero before 1990 (see Sect. 1 for more details). The dataset for the Earth heat inventory is published at the German Climate Computing Centre (DKRZ, https://www.dkrz.de/) under the DOI https://doi.org/10.26050/WDCC/GCOS_EHI_EXP_v2. The net flux at TOA from the NASA CERES program is shown in red (https://ceres.larc.nasa.gov/data/, last access: 7 August 2020; see also for example Loeb et al., 2012) for the period 2005–2018 to account for the golden period of best available estimates. We obtain a total heat gain of 358 ± 37 ZJ over the period 1971–2018, which is equivalent to a heating rate (i.e., the EEI) of 0.47±0.1 W m−2 applied continuously over the surface area of the Earth (5.10×1014 m2 ). The corresponding EEI over the period 2010–2018 amounts to 0.87±0.12 W m−2 . A weighted least square fit has been used taking into account the uncertainty range (see also von Schuckmann and Le Traon, 2011)."

Caption for the second image: "Figure 7. Overview on EEI estimates as obtained from previous publications; references are listed in the figure legend. For IPCC AR5, Rhein et al. (2013) is used. The color bars take into account the uncertainty ranges provided in each publication, respectively. For comparison, the estimates of our Earth heat inventory based on the results of Fig. 6 have been added (yellow lines) for the periods 1971–2018, 1993–2018 and 2010–2018, and the trends have been evaluated using a weighted least square fit (see von Schuckmann and Le Traon, 2011, for details on the method)."

Caption for the third image: "Figure 8. Schematic presentation on the Earth heat inventory for the current anthropogenically driven positive Earth energy imbalance at the top of the atmosphere (TOA). The relative partition (in %) of the Earth heat inventory presented in Fig. 6 for the different components is given for the ocean (upper: 0–700 m, intermediate: 700–2000 m, deep: > 2000 m), land, cryosphere (grounded and floating ice) and atmosphere, for the periods 1971–2018 and 2010–2018 (for the latter period values are provided in parentheses), as well as for the EEI. The total heat gain (in red) over the period 1971–2018 is obtained from the Earth heat inventory as presented in Fig. 6. To reduce the 2010–2018 EEI of 0.87 ± 0.12 W m−2 towards zero, current atmospheric CO2 would need to be reduced by −57 ± 8 ppm (see text for more details)."

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4083 on: January 03, 2021, 10:51:42 PM »
The linked reference quantifies the influence that Sudden Stratospheric Warming (SSW) events can have on the Beaufort Gyre sea ice.  This information help to better understand the risk that a major SSW event in the boreal summertime could temporarily reverse the direction of rotation of the Beaufort Gyre circulation long enough to trigger a major freshwater hosing discharge from the Arctic Ocean into the North Atlantic, where the freshwater could trigger a major slowdown of the AMOC.

Lukovich, J. V. et al. (17 January 2009), "Atmospheric forcing of the Beaufort Sea ice gyre: Surface‐stratosphere coupling", JGR: Oceans, https://doi.org/10.1029/2008JC004849

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2008JC004849%4010.1002/%28ISSN%292169-9291.BEAUFORTG1

Abstract: "In a companion article we examined the nature of correspondence between synoptic weather patterns and reversals in the Beaufort Sea ice gyre. In this paper we extend this analysis to examine the role of stratospheric forcing on surface phenomena. Investigated in particular is the correspondence between reversals in stratospheric winds at 10 mbar during winter as defined by stratospheric sudden warmings (SSW) and mean sea level pressure synoptic types in the Beaufort Sea region. Connections between stratospheric and surface events are characterized using relative vorticity and the square of strain computed at different pressure levels from the stratosphere to the surface in the Beaufort Sea region. We quantify the correspondence between stratospheric flow and surface phenomena through investigation of the frequency in synoptic types derived in a companion article during stratospheric sudden warming events. Investigation of stratospheric wind gradients averaged over the Beaufort Sea region demonstrates a prevalence in anticyclonic activity during SSWs that persists for approximately 20 days. Examination of the evolution in synoptic types in the Beaufort Sea region also shows an increase in the number of synoptic types associated with anticyclonic activity during SSWs.

Extract: "Examination of the evolution in wind gradient fields and their anomalies from the stratosphere to the surface during SSWs demonstrates a band of anticyclonic activity that extends from the stratosphere to the surface during SSWs. Investigation of the evolution in synoptic types during SSWs demonstrates an increase in the number of anticyclones and concomitant strengthening of the Beaufort High during SSWs, thereby providing a signature of the correspondence between stratospheric flow and surface cyclone types in the BSR. An interesting avenue for future research includes an extension of this analysis to explore the predictive skill of zonal wind anomalies, horizontal wind gradients, and anticyclone development in the BSR.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4085 on: January 04, 2021, 07:44:16 AM »
... This simple number, EEI, is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control, and we call for an implementation of the EEI into the global stocktake based on best available science. ...

That research community paper by von Schuckmann et al. more or less confirms what has already been established.
The important thing is what they say in the bolded statement.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4086 on: January 05, 2021, 11:24:24 AM »
... This simple number, EEI, is the most fundamental metric that the scientific community and public must be aware of as the measure of how well the world is doing in the task of bringing climate change under control, and we call for an implementation of the EEI into the global stocktake based on best available science. ...

That research community paper by von Schuckmann et al. more or less confirms what has already been established.
The important thing is what they say in the bolded statement.

I assume that the majority of people in the world are not doing more to fight climate change because they do not know any better.  So I note that it is also important for people to realize that EEI is accelerating earlier and faster than GMSTA as indicated by the following statements from von Schuckmann et al. (2020):

"The study obtains a consistent long-term Earth system heat gain over the period 1971–2018, with a total heat gain of 358±37 ZJ, which is equivalent to a global heating rate of 0.47±0.1 W m−2.
...
Our results also show that EEI is not only continuing, but also increasing: the EEI amounts to 0.87±0.12 W m−2 during 2010–2018. Stabilization of climate, the goal of the universally agreed United Nations Framework Convention on Climate Change (UNFCCC) in 1992 and the Paris Agreement in 2015, requires that EEI be reduced to approximately zero to achieve Earth's system quasi-equilibrium.  The amount of CO2 in the atmosphere would need to be reduced from 410 to 353 ppm to increase heat radiation to space by 0.87 W m−2, bringing Earth back towards energy balance.
"
« Last Edit: January 05, 2021, 05:37:42 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4087 on: January 05, 2021, 05:39:11 PM »
The Silvers & Robinson (2020) indicate that, with regard to the Walker Circulation in the tropics, their higher resolution model (sufficient to simulate cloud-system effects) projected the formation of more upper level (high altitude) clouds while their lower resolution model projected the formation of more low level (low altitude) clouds, with continued anthropogenic radiative forcing.  As the future replacement of low altitude cloud cover with more high altitude cloud cover is an indication of relatively high climate sensitivity, it seems likely that as more computation capacity become more available to run high resolution climate models that more positive cloud feedback will be projected for the topical areas (including the Tropical Pacific).

Silvers, L.G. and Thomas Robinson (23 December 2020), "Clouds and Radiation in a mock‐Walker Circulation", JAMES, https://doi.org/10.1029/2020MS002196

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020MS002196

Abstract
The Walker circulation connects the regions with deep atmospheric convection in the western tropical Pacific to the shallow‐convection, tropospheric subsidence, and stratocumulus cloud decks of the eastern Pacific. The purpose of this study is to better understand the multi‐scale interactions between the Walker circulation, cloud systems, and interactive radiation. To do this we simulate a mock‐Walker Circulation with a full‐physics general circulation model using idealized boundary conditions. Our experiments use a doubly‐periodic domain with grid‐spacing of 1, 2, 25, and 100km. We thus span the range from General Circulation Models (GCMs) to Cloud‐system Resolving Models (CRMs). Our model is derived from the Geophysical Fluid Dynamics Laboratory atmospheric GCM (AM4.0). We find substantial differences in the mock‐Walker circulation simulated by our GCM‐like and CRM‐like experiments. The CRM‐like experiments have more upper level clouds, stronger overturning circulations, and less precipitation. The GCM‐like experiments have a low‐level cloud fraction that is up to 20% larger. These differences lead to opposite atmospheric responses to changes in the longwave cloud radiative effect (LWCRE). Active LWCRE lead to increased precipitation for our GCMs, but decreased precipitation for our CRMs. The LWCRE leads to a narrower rising branch of the circulation and substantially increases the fraction of precipitation from the large‐scale cloud parameterization. This work demonstrates that a mock‐Walker circulation is a useful generalization of radiative convective equilibrium that includes a large‐scale circulation.

Plain Language Summary
Interactions between clouds, radiation, and dynamics all contribute to the large‐scale tropical motions and are fundamental to the Walker circulation. The Walker circulation is a loop consisting of surface winds towards the western tropical Pacific, strong upward motion and deep convection in that region, and the return eastward winds aloft that eventually sink towards the surface in the eastern Pacific basin. We focus on an idealization of the Walker circulation (a mock‐Walker circulation) in which the strong rising motion and deep convection is driven by a patch of warm sea surface temperature. Our results show that the response of the atmosphere to the radiative flux of energy depends strongly on the relative amount of clouds at different heights. It is further shown that our GCM‐like models are dominated by low‐clouds while our CRM‐like models are dominated by high‐clouds. This work also argues that an idealized Walker circulation is an excellent configuration with which to better understand the interactions between clouds, radiation and circulation and to push the development of models forward. Models of mock‐Walker circulations represent an intermediate tier in a hierarchy of models between Earth‐like models and models of radiative convective equilibrium.

&

Saint-Martin et al. (2020) indicate that much of the increase in their ESM's projections of climate sensitivity between their CMIP5 and CMIP6 versions occurred due to a significant positive increase in the tropical longwave cloud feedback projected by their CMIP6 version (see the attached image).

Saint‐Martin, D. et al. (22 December 2020), "Tracking changes in climate sensitivity in CNRM climate models", JAMES, https://doi.org/10.1029/2020MS002190

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020MS002190

Abstract
The equilibrium climate sensitivity in the latest version of CNRM climate model, CNRM‐CM6‐1, and in its high resolution counterpart, CNRM‐CM6‐1‐HR, is significantly larger than in the previous version (CNRM‐CM5.1). The traceability of this climate sensitivity change is investigated using coupled ocean‐atmosphere model climate change simulations. These simulations show that the increase in equilibrium climate sensitivity is the result of changes in the atmospheric component. A particular attention is paid to the method used to decompose the equilibrium temperature response difference, by using a linearized decomposition of the individual radiative agents diagnosed by a radiative kernel technique. The climate sensitivity increase is primarily due to the cloud radiative responses, with a predominant contribution of the tropical longwave response (including both feedback and forcing adjustment) and a significant contribution of the extratropical and tropical shortwave feedback changes. A series of stand‐alone atmosphere experiments is carried out to quantify the contributions of each atmospheric development to this difference between CNRM‐CM5.1 and CNRM‐CM6‐1. The change of the convection scheme appears to play an important role in driving the cloud changes, with a large effect on the tropical longwave cloud feedback change.

Plain Language Summary
The global equilibrium temperature change in response to a doubling of the atmospheric carbon dioxide concentration is an important characteristic of the climate system known as the equilibrium climate sensitivity. Many climate models contributing to CMIP6 (Coupled Model Intercomparison Project phase 6) have a larger equilibrium climate sensitivity than their CMIP5 predecessors. Here we investigate the origins of this increase for the CNRM model and its high‐resolution version. We find that it primarily results from changes in the atmospheric component, in particular in the convection scheme, through its impact on the cloud radiative responses.

Extract: "The climate sensitivity increase is primarily due to the cloud radiative responses, with positive contributions of the longwave component (including both feedback and forcing adjustment) and of the shortwave feedback change. The contribution of the short-wave cloud forcing adjustment is negative. Tropical and extratropical regions contributes rather equally to the increase in SW cloud feedback whereas the LW cloud feedback mainly increases in the tropics. This LW tropical cloud feedback change seems to be due to a change in the climatology of high- level clouds. The convection scheme change appears to play an important role in driving the change in tropical climatological high clouds.

Caption: "Figure 6. Zonal-mean (a) SW and (b) LW cloud feedback parameter changes for AM6 minus AM5 (’all’, black lines) and for all intermediate atmospheric configuration changes listed in Table3 : AM5-s6 minus AM5 (’sst’ : SST effect), AM5-d 6 minus AM5-s6 (’dyn’ : vertical resolution + dynamics), AM5-m6 minus AM5-d6 (’mic’ : large-scale microphysics), AM5-t6 minus AM5-m6 (’tur’ : turbulence + large-scale cloud), AM5-c6 minus AM5-t6 (’con’ : convection) AM6 - AM5-c6 (’rad’ : cloud optical properties). Zonal-mean values are plotted against the sine of latitude. (c) Fractional contributions of regional mean terms to the total cloud feedback change. Colors indicate magnitude of the contributions which is also given by numbers in each cell. The tropical mean (TROP; 30S-30N average), the extratropical Northern Hemisphere mean (eNH; 30N-90N average) change and the extratropical Southern Hemisphere mean (eSH; 30S-90S average) change are multiplied by the fractional area of each region, so the global mean change is the sum of the tropical mean change, the extratropical Northern Hemisphere mean change and the extratropical Southern Hemisphere mean change."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4088 on: January 07, 2021, 07:56:30 PM »
The linked reference indicates that the current high rate of radiative forcing is contributing to a high effective climate sensitivity, particularly with regard to spatial inhomogeneities in both sea surface temperature (SST) and sea ice change.  Here, I note that the authors do not consider changes in effective radiative forcing associated with abrupt freshwater hosing events.

Zhou, C., Zelinka, M.D., Dessler, A.E. et al. Greater committed warming after accounting for the pattern effect. Nat. Clim. Chang. (2021). https://doi.org/10.1038/s41558-020-00955-x

https://www.nature.com/articles/s41558-020-00955-x

Abstract
Our planet’s energy balance is sensitive to spatial inhomogeneities in sea surface temperature and sea ice changes, but this is typically ignored in climate projections. Here, we show the energy budget during recent decades can be closed by combining changes in effective radiative forcing, linear radiative damping and this pattern effect. The pattern effect is of comparable magnitude but opposite sign to Earth’s net energy imbalance in the 2000s, indicating its importance when predicting the future climate on the basis of observations. After the pattern effect is accounted for, the best-estimate value of committed global warming at present-day forcing rises from 1.31 K (0.99–2.33 K, 5th–95th percentile) to over 2 K, and committed warming in 2100 with constant long-lived forcing increases from 1.32 K (0.94–2.03 K) to over 1.5 K, although the magnitude is sensitive to sea surface temperature dataset. Further constraints on the pattern effect are needed to reduce climate projection uncertainty.

Extract: "Properly accounting for the pattern effect has a major impact on the amount of carbon humans can emit before breaching any particular temperature threshold."

Caption for the first image: "Fig. 1 | Attribution of the net TOA fluxes during 1871–2010. a, Time series of effective radiative forcing from IPCC AR5 (red), the linear radiative damping term (−λltΔT, green) and the pattern effect term (blue). b, Time series of reconstructed TOA fluxes. The black line denotes the TOA fluxes reconstructed with equation (4) and the brown line denotes the TOA net flux estimated by ignoring the pattern effect (F – λltΔT). c, Comparison of reconstructed TOA fluxes with observations. The magenta line denotes observed annual TOA net flux from CERES EBAF v.4.0 (ref. 21) and the cyan line denotes net flux observations from merged radiation budget data v.3 (ref. 22), which is calculated from CERES EBAF v.2.8 (ref. 42) and ERBS wide field of view v.3 data43. Thin lines denote values calculated from individual models, while thick lines are model averages."
Caption for the second image: "Fig. 2 | Cumulative energy flux into the Earth system during 1961–2010. The magenta and cyan lines are two estimates of the observed changes in the global heat content24,25 (Methods), the black thick line is the net influx calculated from the reconstructed net energy imbalance of Fig. 1 and the brown thick line denotes net energy influx if the pattern effect is zero. The red, green and blue dashed lines denote individual contributors to the net energy influx. Thin lines denote values calculated from individual models, while thick lines are model averages."

Caption for the third image: "Fig. 3 | Impact of the pattern effect on equilibrium committed warming with constant forcing. Colours denote the committed warming for a range of Pref and λlt values calculated with equation (9), and the two white contours represent the Paris Agreement thresholds. The black line denotes the relationship of Pref and λlt constrained by equation (8). Values printed beside the two black markers denote the committed warming corresponding to Pref = 0 and Pref = −0.63 W m–2, respectively."

Caption for the fourth image: "Fig. 4 | Comparison of TOA fluxes reconstructed with CAM5.3 experiments driven by different SST datasets. The TOA fluxes are reconstructed with equation (1), where the climate forcing is from IPCC AR5 and Rfb is from simulations. The black line is the ensemble mean value calculated from three CAM5.3 AMIP-piForcing experiments, which use prescribed AMIPII SST boundary conditions. The blue line is reconstructed with the ensemble mean value of three CAM5.3 HadISST-piForcing experiments, which use prescribed HadISST SST boundary conditions. The correlation coefficients between the time series of observations and reconstructed TOA fluxes, of which the corresponding P values are all below 0.05, are listed in the figure."

&

Title: "We've already blown past the warming targets set by the Paris climate agreement, study finds"

https://www.livescience.com/already-too-late-to-meet-paris-agreement-climate-goals.html

Extract: "Dessler told the AP. "It's really the rate of warming that makes climate change so terrible. If we got a few degrees over 100,000 years, that would not be that big a deal. We can deal with that. But a few degrees over 100 years is really bad.""
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4089 on: January 08, 2021, 05:24:51 PM »
Per Copernicus, the 2020 GMSTA was tied for the warmest year on record at 1.25C above pre-industrial (see the attached image).

Title: "Copernicus: 2020 warmest year on record for Europe; globally, 2020 ties with 2016 for warmest year recorded"

https://climate.copernicus.eu/2020-warmest-year-record-europe-globally-2020-ties-2016-warmest-year-recorded

Extract: "The Copernicus Climate Change Service (C3S) today reveals that globally 2020 was tied with the previous warmest year 2016, making it the sixth in a series of exceptionally warm years starting in 2015, and 2011-2020 the warmest decade recorded.

•   2020 was 0.6°C warmer than the standard 1981-2010 reference period and around 1.25°C above the 1850-1900 pre-industrial period"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4090 on: January 09, 2021, 10:53:42 PM »
The linked reference discusses regional dynamic sea level simulations from CMIP5 and CMIP6; neither of which ensemble has interactive ice sheet modules, so I am presenting this as background information rather than as information relevant to a possible 'Ice Apocalypse'.

Lyu, K., Xuebin Zhang, and John A. Church (01 Aug 2020), "Regional Dynamic Sea Level Simulated in the CMIP5 and CMIP6 Models: Mean Biases, Future Projections, and Their Linkages", Journal of Climate, DOI: https://doi.org/10.1175/JCLI-D-19-1029.1

https://journals.ametsoc.org/view/journals/clim/33/15/JCLI-D-19-1029.1.xml

Abstrat: "The ocean dynamic sea level (DSL) is an important component of regional sea level projections. In this study, we analyze mean states and future projections of the DSL from the global coupled climate models participating in phase 5 and phase 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6, respectively). Despite persistent biases relative to observations, both CMIP5 and CMIP6 simulate the mean sea level reasonably well. The equatorward bias of the Southern Hemisphere westerly wind stress is reduced from CMIP5 to CMIP6, which improves the simulated mean sea level in the Southern Ocean. The CMIP5 and CMIP6 DSL projections exhibit very similar features and intermodel uncertainties. With several models having a notably high climate sensitivity, CMIP6 projects larger DSL changes in the North Atlantic and Arctic associated with a larger weakening of the Atlantic meridional overturning circulation (AMOC). We further identify linkages between model mean states and future projections by looking for their intermodel relationships. The common cold-tongue bias leads to an underestimation of DSL rise in the western tropical Pacific. Models with their simulated midlatitude westerly winds located more equatorward tend to project larger DSL changes in the Southern Ocean and North Pacific. In contrast, a more equatorward location of the North Atlantic westerly winds or a weaker AMOC under current climatology is associated with a smaller weakening of the AMOC and weaker DSL changes in the North Atlantic and coastal Arctic. Our study provides useful emergent constraints for DSL projections and highlights the importance of reducing model mean-state biases for future projections."

Extract: "In addition, models analysed here still don’t have an interactive ice sheet  module and thus the DSL responses to the freshwater discharge from glaciers and ice sheets are not included, which is a gap potentially to be filled by making use of the simulations from the Ice Sheet Model Intercomparison Project (ISMIP6; Nowicki et al. 2016)."

Caption for first image: "Figure 1. (a) Observed mean ocean dynamic topography over 1992–2012; differences of the (b) CMIP6 and (c) CMIP5 multi-model averaged mean sea level over 1986–2005 from the observed mean dynamic topography; (d) differences between the mean sea level from CMIP6 and CMIP5. (e-h) similar as (a-d) but for mean sea surface zonal wind stress from QuikSCAT observations (1999–2009) and climate model simulations (1986–2005). Stippling in lower panels indicates where the difference between CMIP6 and CMIP5 is statistically significant at 886 the 95% confidence level based on the two-sample t-test."

Caption for the second image: "Figure 9. Regional DSL projections (m) under high-emission scenarios from four modelling groups. (Left) CMIP5 RCP8.5; (Right) CMIP6 SSP5-8.5. The equilibrium climate sensitivity (ECS, K) for each model is given after the model name in the subtitles."

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4091 on: January 14, 2021, 11:09:29 AM »
The linked reference concludes with regard to the terrestrial biosphere that:

"Under business-as-usual emissions, this divergence elicits a near halving of the land sink strength by as early as 2040."

Such a quick near halving of the lank carbon sink will make very difficult to stay off of the SSP5-8.5 radiative forcing pathway in coming decades.

Duffy K.A. el al. (13 Jan 2021), "How close are we to the temperature tipping point of the terrestrial biosphere?," Science Advances ,Vol. 7, no. 3, eaay1052, DOI: 10.1126/sciadv.aay1052

https://advances.sciencemag.org/content/7/3/eaay1052

Abstract
The temperature dependence of global photosynthesis and respiration determine land carbon sink strength. While the land sink currently mitigates ~30% of anthropogenic carbon emissions, it is unclear whether this ecosystem service will persist and, more specifically, what hard temperature limits, if any, regulate carbon uptake. Here, we use the largest continuous carbon flux monitoring network to construct the first observationally derived temperature response curves for global land carbon uptake. We show that the mean temperature of the warmest quarter (3-month period) passed the thermal maximum for photosynthesis during the past decade. At higher temperatures, respiration rates continue to rise in contrast to sharply declining rates of photosynthesis. Under business-as-usual emissions, this divergence elicits a near halving of the land sink strength by as early as 2040.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4092 on: January 14, 2021, 11:44:40 AM »
Temperature dependence of global photosynthesis

The linked reference concludes with regard to the terrestrial biosphere that:

"Under business-as-usual emissions, this divergence elicits a near halving of the land sink strength by as early as 2040."
And that excludes the effects of land-use changes that are already threatening the land-based carbon sinks.

People just don't seem to get that just reducing carbon emissions from fossil fuels is not enough
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4093 on: January 14, 2021, 04:32:25 PM »
Many marine terminating glaciers will be subject to MISI-type of behavior in the coming decades, and the linked reference discussions how differences in bed-conditions will change the behavior of such glaciers as they retreat:

Greenwood, S.L. et al. (13 Jan 2021), "Exceptions to bed-controlled ice sheet flow and retreat from glaciated continental margins worldwide", Science Advances, Vol. 7, no. 3, eabb6291, DOI: 10.1126/sciadv.abb6291

https://advances.sciencemag.org/content/7/3/eabb6291

Abstract
Projections of ice sheet behavior hinge on how ice flow velocity evolves and the extent to which marine-based grounding lines are stable. Ice flow and grounding line retreat are variably governed by the coupling between the ice and underlying terrain. We ask to what degree catchment-scale bed characteristics determine ice flow and retreat, drawing on paleo-ice sheet landform imprints from 99 sites on continental shelves worldwide. We find that topographic setting has broadly steered ice flow and that the bed slope favors particular styles of retreat. However, we find exceptions to accepted “rules” of behavior: Regional topographic highs are not always an impediment to fast ice flow, retreat may proceed in a controlled, steady manner on reverse slopes and, unexpectedly, the occurrence of ice streaming is not favored on a particular geological substrate. Furthermore, once grounding line retreat is under way, readvance is rarely observed regardless of regional bed characteristics.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4094 on: January 14, 2021, 06:34:00 PM »
While Antarctic icebergs behaved much differently during the Pleistocene glacials than they do today; nonetheless, the linked reference demonstrates that icebergs from MICI events (implied by the rafted ice debris cited in the study) leading to the glacials can have a profound impact on the AMOC and consequently on climate state.  The associated linked article indicates that the authors believe that modern MICI events would have a different, but still significant, impact on both the AMOC and on climate state, and consequently the encourage future ESMs to evaluate the potential future impacts of such Antarctic iceberg armadas on future climate states (as Hansen et al. 2016 did).

Starr, A. et al. (2021), "Antarctic icebergs reorganize ocean circulation during Pleistocene glacials", Nature, 589, 236–241, DOI: 10.1038/s41586-020-03094-7

https://www.nature.com/articles/s41586-020-03094-7

Abstract
The dominant feature of large-scale mass transfer in the modern ocean is the Atlantic meridional overturning circulation (AMOC). The geometry and vigour of this circulation influences global climate on various timescales. Palaeoceanographic evidence suggests that during glacial periods of the past 1.5 million years the AMOC had markedly different features from today; in the Atlantic basin, deep waters of Southern Ocean origin increased in volume while above them the core of the North Atlantic Deep Water (NADW) shoaled. An absence of evidence on the origin of this phenomenon means that the sequence of events leading to global glacial conditions remains unclear. Here we present multi-proxy evidence showing that northward shifts in Antarctic iceberg melt in the Indian–Atlantic Southern Ocean (0–50° E) systematically preceded deep-water mass reorganizations by one to two thousand years during Pleistocene-era glaciations. With the aid of iceberg-trajectory model experiments, we demonstrate that such a shift in iceberg trajectories during glacial periods can result in a considerable redistribution of freshwater in the Southern Ocean. We suggest that this, in concert with increased sea-ice cover, enabled positive buoyancy anomalies to ‘escape’ into the upper limb of the AMOC, providing a teleconnection between surface Southern Ocean conditions and the formation of NADW. The magnitude and pacing of this mechanism evolved substantially across the mid-Pleistocene transition, and the coeval increase in magnitude of the ‘southern escape’ and deep circulation perturbations implicate this mechanism as a key feedback in the transition to the ‘100-kyr world’, in which glacial–interglacial cycles occur at roughly 100,000-year periods.

See also:

Title: "Melting icebergs key to sequence of an ice age, scientists find"

https://phys.org/news/2021-01-icebergs-key-sequence-ice-age.html

Extract: "However, due to the increased global temperatures resulting from anthropogenic CO2 emissions, the researchers suggest the natural rhythm of ice age cycles may be disrupted as the Southern Ocean will likely become too warm for Antarctic icebergs to travel far enough to trigger the changes in ocean circulation required for an ice age to develop.

"Likewise as we observe an increase in the mass loss from the Antarctic continent and iceberg activity in the Southern Ocean, resulting from warming associated with current human greenhouse-gas emissions, our study emphasises the importance of understanding iceberg trajectories and melt patterns in developing the most robust predictions of their future impact on ocean circulation and climate," he said."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4095 on: January 14, 2021, 09:42:39 PM »
The linked reference discusses some of the factors driving the acceleration of the PIG between 1996 and 2016.

De Rydt, J., Reese, R., Paolo, F. S., and Gudmundsson, G. H.: Drivers of Pine Island Glacier speed-up between 1996 and 2016, The Cryosphere, 15, 113–132, https://doi.org/10.5194/tc-15-113-2021, 2021.

https://tc.copernicus.org/articles/15/113/2021/

Abstract
Pine Island Glacier in West Antarctica is among the fastest changing glaciers worldwide. Over the last 2 decades, the glacier has lost in excess of a trillion tons of ice, or the equivalent of 3 mm of sea level rise. The ongoing changes are thought to have been triggered by ocean-induced thinning of its floating ice shelf, grounding line retreat, and the associated reduction in buttressing forces. However, other drivers of change, such as large-scale calving and changes in ice rheology and basal slipperiness, could play a vital, yet unquantified, role in controlling the ongoing and future evolution of the glacier. In addition, recent studies have shown that mechanical properties of the bed are key to explaining the observed speed-up. Here we used a combination of the latest remote sensing datasets between 1996 and 2016, data assimilation tools, and numerical perturbation experiments to quantify the relative importance of all processes in driving the recent changes in Pine Island Glacier dynamics. We show that (1) calving and ice shelf thinning have caused a comparable reduction in ice shelf buttressing over the past 2 decades; that (2) simulated changes in ice flow over a viscously deforming bed are only compatible with observations if large and widespread changes in ice viscosity and/or basal slipperiness are taken into account; and that (3) a spatially varying, predominantly plastic bed rheology can closely reproduce observed changes in flow without marked variations in ice-internal and basal properties. Our results demonstrate that, in addition to its evolving ice thickness, calving processes and a heterogeneous bed rheology play a key role in the contemporary evolution of Pine Island Glacier.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4096 on: January 16, 2021, 12:30:50 AM »
According to DeConto and Pollard, ocean temperatures around Antarctic must warm by at least 2C to initiate the massive amounts of hydrofracturing that would enable Marine Ice Cliff Instability (MICI) to occur.  And the "wolfpack" of CMIP6 models that run hot need the southern ocean to run so hot that the clouds above it dry up for their extreme climate sensitivities to kick in.

So what is the Southern Ocean doing?  The linked reference seems to state that it's hotspots have cooled and that after undergoing accelerated warming during "the pause" in global temperature increases from 2003 - 2012 that the warming has slowed down since 2013.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090889?af=R

Quote
Recent Shift in the Warming of the Southern Oceans Modulated by Decadal Climate Variability
Lina Wang, Kewei Lyu, Wei Zhuang, Weiwei Zhang, Salvienty Makarim, Xiao‐Hai Yan
28 December 2020
https://doi.org/10.1029/2020GL090889

Abstract

It has been reported that the Southern Hemisphere oceans experienced rapid warming during the decade‐long global surface warming slowdown (2003–2012) and the earlier period of the Argo record (2006–2013). In this study, we analyze updated observations to show that this rapid warming has slowed down, leading to less contribution of the Southern Hemisphere oceans to the global ocean heat storage (∼65% over the available Argo period 2006–2019). Two warming hotspot regions, the southeast Indian Ocean and South Pacific Ocean, have experienced cooling over 2013–2019. This decadal shift is related to variations in the Southern Annular Mode (SAM) and Interdecadal Pacific Oscillation (IPO). The isopycnal deepening (shoaling) forced by changing winds dominated the regional ocean temperature changes over the earlier warming (later cooling) period. Our finding demonstrates how decadal variability modulates long‐term climate change and provides important observational information for the ongoing calibration of decadal prediction systems.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4097 on: January 16, 2021, 03:36:18 PM »
According to DeConto and Pollard, ocean temperatures around Antarctic must warm by at least 2C to initiate the massive amounts of hydrofracturing that would enable Marine Ice Cliff Instability (MICI) to occur.  And the "wolfpack" of CMIP6 models that run hot need the southern ocean to run so hot that the clouds above it dry up for their extreme climate sensitivities to kick in.

So what is the Southern Ocean doing?  The linked reference seems to state that it's hotspots have cooled and that after undergoing accelerated warming during "the pause" in global temperature increases from 2003 - 2012 that the warming has slowed down since 2013.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090889?af=R

Quote
Recent Shift in the Warming of the Southern Oceans Modulated by Decadal Climate Variability
Lina Wang, Kewei Lyu, Wei Zhuang, Weiwei Zhang, Salvienty Makarim, Xiao‐Hai Yan
28 December 2020
https://doi.org/10.1029/2020GL090889

Abstract

It has been reported that the Southern Hemisphere oceans experienced rapid warming during the decade‐long global surface warming slowdown (2003–2012) and the earlier period of the Argo record (2006–2013). In this study, we analyze updated observations to show that this rapid warming has slowed down, leading to less contribution of the Southern Hemisphere oceans to the global ocean heat storage (∼65% over the available Argo period 2006–2019). Two warming hotspot regions, the southeast Indian Ocean and South Pacific Ocean, have experienced cooling over 2013–2019. This decadal shift is related to variations in the Southern Annular Mode (SAM) and Interdecadal Pacific Oscillation (IPO). The isopycnal deepening (shoaling) forced by changing winds dominated the regional ocean temperature changes over the earlier warming (later cooling) period. Our finding demonstrates how decadal variability modulates long‐term climate change and provides important observational information for the ongoing calibration of decadal prediction systems.

First, just because DeConto & Pollard (2016)'s model assumed that the mean ocean temperature around Antarctica increased abruptly by 2C does not mean that:

"According to DeConto and Pollard, ocean temperatures around Antarctic must warm by at least 2C to initiate the massive amounts of hydrofracturing that would enable Marine Ice Cliff Instability (MICI) to occur."

Reasons that this statement by Ken is a red herring include:

1. For DeConto & Pollard (2016)'s model assumption to be reasonable, the only water around Antarctic that needs to increase is the modified CDW that is in contact with the ice shelves buttressing key marine glaciers such as the PIG and Thwaites Glacier.  In this regard, the first image shows that due to the freshening of the Southern Ocean surface waters, beginning around 2030 the depth of the relatively warm modified CDW will sharping shallow to the level of the subsea troughs on the Antarctic continental shelf leading to such key marine glaciers.  Thus, while DeConto & Pollard (2016)'s model did not have high enough resolution to simulate these warm tongues of modified CDW, their assumption that the mean ocean temperature increased by 2C managed to simulate the impact of these tongues of modified CDW reasonably well.

2. In my opinion, the Thwaites Glacier is a special case in that the Thwaites Ice Tongue is already so degraded that it does not need much further degradation by modified CDW to allow a MICI type of mechanism to form at the location indicated in red on the second attached image circa 2035.

Regarding the impact of the climate sensitivity of the 'Wolf Pack' CMIP6 projections, the third image shows that the Wolf Pack member UKESM1-0-LL projects that circa 2035, GMSTA will already exceed 2C.

Regarding the influence of the SAM and the IPO on the cyclic uptake of ocean heat into the Southern Ocean, the fact that this uptake was relatively high from 2003 to 2012 an relatively low from 2013 to 2019; suggests that sometime after about 2022 (or so) this rate of uptake should  become relatively high again thru about 2030-2035; which is when I believe that the Thwaites Glacier may initiate MICI behavior.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4098 on: January 17, 2021, 02:09:14 AM »
...
Reasons that this statement by Ken is a red herring include:

1. For DeConto & Pollard (2016)'s model assumption to be reasonable, the only water around Antarctic that needs to increase is the modified CDW that is in contact with the ice shelves buttressing key marine glaciers such as the PIG and Thwaites Glacier.  In this regard, the first image shows that due to the freshening of the Southern Ocean surface waters, beginning around 2030 the depth of the relatively warm modified CDW will sharping shallow to the level of the subsea troughs on the Antarctic continental shelf leading to such key marine glaciers.  Thus, while DeConto & Pollard (2016)'s model did not have high enough resolution to simulate these warm tongues of modified CDW, their assumption that the mean ocean temperature increased by 2C managed to simulate the impact of these tongues of modified CDW reasonably well.

2. In my opinion, the Thwaites Glacier is a special case in that the Thwaites Ice Tongue is already so degraded that it does not need much further degradation by modified CDW to allow a MICI type of mechanism to form at the location indicated in red on the second attached image circa 2035.

Regarding the impact of the climate sensitivity of the 'Wolf Pack' CMIP6 projections, the third image shows that the Wolf Pack member UKESM1-0-LL projects that circa 2035, GMSTA will already exceed 2C.

Regarding the influence of the SAM and the IPO on the cyclic uptake of ocean heat into the Southern Ocean, the fact that this uptake was relatively high from 2003 to 2012 an relatively low from 2013 to 2019; suggests that sometime after about 2022 (or so) this rate of uptake should  become relatively high again thru about 2030-2035; which is when I believe that the Thwaites Glacier may initiate MICI behavior.

Here's ARGO temperature data for the oceans circumventing Antarctica.
There is a small positive trend for two of the depths at issue, 200 m and 400 m. But for 100 m depth there seems to be no trend.
Trend changes at these depths are small, around 0.05 - 0.1 K in 15 years. Don't see any evidence for dramatic changes starting around 2030.

https://climate4you.com/SeaTemperatures.htm#Circum-antarctic%20ocean%20temperatures%20from%20surface%20to%202000%20m%20depth


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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4099 on: January 17, 2021, 05:09:43 PM »
...
Reasons that this statement by Ken is a red herring include:

1. For DeConto & Pollard (2016)'s model assumption to be reasonable, the only water around Antarctic that needs to increase is the modified CDW that is in contact with the ice shelves buttressing key marine glaciers such as the PIG and Thwaites Glacier.  In this regard, the first image shows that due to the freshening of the Southern Ocean surface waters, beginning around 2030 the depth of the relatively warm modified CDW will sharping shallow to the level of the subsea troughs on the Antarctic continental shelf leading to such key marine glaciers.  Thus, while DeConto & Pollard (2016)'s model did not have high enough resolution to simulate these warm tongues of modified CDW, their assumption that the mean ocean temperature increased by 2C managed to simulate the impact of these tongues of modified CDW reasonably well.

2. In my opinion, the Thwaites Glacier is a special case in that the Thwaites Ice Tongue is already so degraded that it does not need much further degradation by modified CDW to allow a MICI type of mechanism to form at the location indicated in red on the second attached image circa 2035.

Regarding the impact of the climate sensitivity of the 'Wolf Pack' CMIP6 projections, the third image shows that the Wolf Pack member UKESM1-0-LL projects that circa 2035, GMSTA will already exceed 2C.

Regarding the influence of the SAM and the IPO on the cyclic uptake of ocean heat into the Southern Ocean, the fact that this uptake was relatively high from 2003 to 2012 an relatively low from 2013 to 2019; suggests that sometime after about 2022 (or so) this rate of uptake should  become relatively high again thru about 2030-2035; which is when I believe that the Thwaites Glacier may initiate MICI behavior.

Here's ARGO temperature data for the oceans circumventing Antarctica.
There is a small positive trend for two of the depths at issue, 200 m and 400 m. But for 100 m depth there seems to be no trend.
Trend changes at these depths are small, around 0.05 - 0.1 K in 15 years. Don't see any evidence for dramatic changes starting around 2030.

https://climate4you.com/SeaTemperatures.htm#Circum-antarctic%20ocean%20temperatures%20from%20surface%20to%202000%20m%20depth

Like Ken, you are presenting averaged data all around Antarctica rather than focusing on the Amundsen Sea Embayment, ASE, that I was talking about.  The ASE represents a more sensitive case with regard to the possible/probable influx of relatively warm modified CDW, as illustrated by the four attached images:

The first image (by Fogt 2011) shows how the ASE faces the Tropical Pacific, so that during different combinations of the SAM and the ENSO decadal cycles, atmospheric Rossby wave trains convey tropical heat directly to the ASE, which also generally causes winds to advect warm modified CDW into the ASE.

The second image (by Jenkins et al 2018), shows that during such decadal ocean variability (as shown by Fogt 2011) that ocean temperatures beneath the indicated ice shelves in the ASE vary markedly depending on the combination of SAM and ENSO.

Adrian Jenkins  et al. (2018), "West Antarctic Ice Sheet retreat in the Amundsen Sea driven by decadal oceanic variability", Nature Geoscience, volume 11, pages733–738, DOI: https://doi.org/10.1038/s41561-018-0207-4

https://www.nature.com/articles/s41561-018-0207-4

Abstract: "Mass loss from the Amundsen Sea sector of the West Antarctic Ice Sheet has increased in recent decades, suggestive of sustained ocean forcing or an ongoing, possibly unstable, response to a past climate anomaly. Lengthening satellite records appear to be incompatible with either process, however, revealing both periodic hiatuses in acceleration and intermittent episodes of thinning. Here we use ocean temperature, salinity, dissolved-oxygen and current measurements taken from 2000 to 2016 near the Dotson Ice Shelf to determine temporal changes in net basal melting. A decadal cycle dominates the ocean record, with melt changing by a factor of about four between cool and warm extremes via a nonlinear relationship with ocean temperature. A warm phase that peaked around 2009 coincided with ice-shelf thinning and retreat of the grounding line, which re-advanced during a post-2011 cool phase. These observations demonstrate how discontinuous ice retreat is linked with ocean variability, and that the strength and timing of decadal extremes is more influential than changes in the longer-term mean state. The nonlinear response of melting to temperature change heightens the sensitivity of Amundsen Sea ice shelves to such variability, possibly explaining the vulnerability of the ice sheet in that sector, where subsurface ocean temperatures are relatively high."

Caption for the second image: "Fig. 5 Multi-decadal history of ocean forcing and outlet glacier response in the eastern Amundsen Sea. Time series of glacier outflow changes (righthand axis, with one standard deviation error bars) and ocean forcing (red, warm conditions; blue, cool conditions) as documented here (darker shading) and as inferred (lighter shading) from central tropical Pacific sea surface temperatures (left-hand axis, both normalized). Shaded boxes (outlined and colour-coded by glacier) indicate the range of estimated times for the initiation of the most recent phase of rapid thinning at the grounding lines, while boxes without outlines are inferred times of initial and final detachment of Pine Island Glacier from a submarine ridge."

The third image reinforces the lesson learned from the second image by showing that surface elevation of the ice shelves in the ASE closely parallel the ENSO cycle; as the surface elevation of the ASE ice shelves are directly influenced by the advection (or not) of warm modified CDW into (or not) the ASE (see the first image).

The fourth image shows that the THOR program (of the ITGC) has found (in 2020) that the subsea trough, in the ASE seabed, that directs ocean heat beneath the base of the Thwaites Ice Tongue, has about a 40% larger cross-sectional area and is deeper by about 250 m (750m vs the previously assumed 500m depth); which results in the advection of about twice the ocean heat content to the base of the Thwaites Ice Tongue as previously assumed.

Such considerations indeed to support the proposition that circa 2030 decadal ocean variability will likely advect markedly more ocean heat content to the base of the Thwaites Ice Tongue; which I have previously mentioned has only of few meters of ice height above flotation pinning the icebergs over the subglacial cavity that I have call the 'Big Ear', and that if/when these pinned icebergs float away they may likely abruptly expose an ice cliff that is susceptible to a MICI-type of failure, leading directly into the Byrd Subglacial Basin (BSB).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson