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Stephan

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4200 on: March 19, 2021, 09:14:01 PM »
Yes, the CH4 concentration increase rate has accelerated lately. I have no clue whether this can be linked to CoViD19 in any way.
More details in the "Trends in atmospheric CH4" thread in the science section of this forum.
It is too late just to be concerned about Climate Change

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4201 on: March 20, 2021, 02:46:37 AM »
CH4 is the primary constituent of natural gas leaks and venting increase this.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4202 on: March 22, 2021, 04:54:43 PM »
Yes, the CH4 concentration increase rate has accelerated lately. I have no clue whether this can be linked to CoViD19 in any way.
More details in the "Trends in atmospheric CH4" thread in the science section of this forum.

The linked open access reference provides more attribution insights into methane emissions from 2010 to 2018 than I am prepared to cover in this post, so I will only note that the first image indicates that prior atmosphere methane concentration calculations assumed that methane was being oxidized at a higher rate than was actually occurring due the observed trend of decreasing OH concentration in the atmosphere (which indicating the prospect of higher climate sensitivity in the future). While the second image shows that global methane emissions from livestock, rice and wastewater have all been previously underestimated; likely due to a growing trend toward richer diets in developing countries (a trend that is likely to continue for some decades to come).

Zhang, Y., Jacob, D. J., Lu, X., Maasakkers, J. D., Scarpelli, T. R., Sheng, J.-X., Shen, L., Qu, Z., Sulprizio, M. P., Chang, J., Bloom, A. A., Ma, S., Worden, J., Parker, R. J., and Boesch, H.: Attribution of the accelerating increase in atmospheric methane during 2010–2018 by inverse analysis of GOSAT observations, Atmos. Chem. Phys., 21, 3643–3666, https://doi.org/10.5194/acp-21-3643-2021, 2021.

https://acp.copernicus.org/articles/21/3643/2021/acp-21-3643-2021.html

Abstract: "We conduct a global inverse analysis of 2010–2018 GOSAT observations to better understand the factors controlling atmospheric methane and its accelerating increase over the 2010–2018 period. The inversion optimizes anthropogenic methane emissions and their 2010–2018 trends on a 4∘×5∘ grid, monthly regional wetland emissions, and annual hemispheric concentrations of tropospheric OH (the main sink of methane). We use an analytical solution to the Bayesian optimization problem that provides closed-form estimates of error covariances and information content for the solution. We verify our inversion results with independent methane observations from the TCCON and NOAA networks. Our inversion successfully reproduces the interannual variability of the methane growth rate inferred from NOAA background sites. We find that prior estimates of fuel-related emissions reported by individual countries to the United Nations are too high for China (coal) and Russia (oil and gas) and too low for Venezuela (oil and gas) and the US (oil and gas). We show large 2010–2018 increases in anthropogenic methane emissions over South Asia, tropical Africa, and Brazil, coincident with rapidly growing livestock populations in these regions. We do not find a significant trend in anthropogenic emissions over regions with high rates of production or use of fossil methane, including the US, Russia, and Europe. Our results indicate that the peak methane growth rates in 2014–2015 are driven by low OH concentrations (2014) and high fire emissions (2015), while strong emissions from tropical (Amazon and tropical Africa) and boreal (Eurasia) wetlands combined with increasing anthropogenic emissions drive high growth rates in 2016–2018. Our best estimate is that OH did not contribute significantly to the 2010–2018 methane trend other than the 2014 spike, though error correlation with global anthropogenic emissions limits confidence in this result."

Caption for first image: "Figure 13 Methane loss frequency and lifetime against oxidation by tropospheric OH for 2010–2018. Values are annual means with error standard deviations. The loss frequency (k) is as calculated by Eq. (1) and the lifetime (τ) is the inverse. The prior estimate from Wecht et al. (2014) assumes no 2010–2018 trend in OH concentrations; the slight variability seen in the figure is due to temperature."

Caption for second image: "Figure 15 The 2010–2018 global methane anthropogenic emissions and emission trends partitioned by individual sectors. Posterior estimates are from our inversion of GOSAT data. Prior estimates for anthropogenic emission trends are zero. Error bars in (b) show posterior error standard deviations for emission trends. Posterior error standard deviations for mean emissions are small and are thus not shown in (a)."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4203 on: March 23, 2021, 08:24:59 AM »
The linked reference states:

"Our favored model is recurrent leakage of shallow gas reservoirs below the gas hydrate stability zone along the margin of western Svalbard that can be reactivated upon initial instability of the grounded, marine-based ice sheets. Analogous to this model, with the current acceleration of the Greenland ice melt, instabilities of existing methane reservoirs below and nearby the ice sheet are likely."

Thus, per Applegate et al. (2015) methane emissions from/near Greenland could become a problem before the end of this century (see images).

P.-A. Dessandier et al. Ice-sheet melt drove methane emissions in the Arctic during the last two interglacials, Geology (2021). DOI: 10.1130/G48580.1

https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G48580.1/595627/Ice-sheet-melt-drove-methane-emissions-in-the?

Abstract: "Circum-Arctic glacial ice is melting in an unprecedented mode, and release of currently trapped geological methane may act as a positive feedback on ice-sheet retreat during global warming. Evidence for methane release during the penultimate (Eemian, ca. 125 ka) interglacial, a period with less glacial sea ice and higher temperatures than today, is currently absent. Here, we argue that based on foraminiferal isotope studies on drill holes from offshore Svalbard, Norway, methane leakage occurred upon the abrupt Eurasian ice-sheet wastage during terminations of the last (Weichselian) and penultimate (Saalian) glaciations. Progressive increase of methane emissions seems to be first recorded by depleted benthic foraminiferal δ13C. This is quickly followed by the precipitation of methane-derived authigenic carbonate as overgrowth inside and outside foraminiferal shells, characterized by heavy δ18O and depleted δ13C of both benthic and planktonic foraminifera. The similarities between the events observed over both terminations advocate for a common driver for the episodic release of geological methane stocks. Our favored model is recurrent leakage of shallow gas reservoirs below the gas hydrate stability zone along the margin of western Svalbard that can be reactivated upon initial instability of the grounded, marine-based ice sheets. Analogous to this model, with the current acceleration of the Greenland ice melt, instabilities of existing methane reservoirs below and nearby the ice sheet are likely."

I remind readers that Applegate et al. (2015) uses Greenland surface temperature increase (see the first image) rather than GMSTA. Thus, a 12C temperature increase over Greenland would correspond to something like a 6C GMSTA (see the second image).  The second image is for RCP 8.5 which indicates that 12C is reached over Greenland circa 2200:

Applegate, P.J., Parizek, B.R., Nicholas, R.E. et al. (2015), "Increasing temperature forcing reduces the Greenland Ice Sheet’s response time scale", Clim Dyn 45: 2001. https://doi.org/10.1007/s00382-014-2451-7

https://link.springer.com/article/10.1007/s00382-014-2451-7#citeas
&
https://static-content.springer.com/esm/art%3A10.1007%2Fs00382-014-2451-7/MediaObjects/382_2014_2451_MOESM1_ESM.pdf

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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4204 on: March 23, 2021, 06:53:18 PM »
Sea-Level Rise In 20th Century Was Fastest In 2,000 Years Along Much of US East Coast
https://phys.org/news/2021-03-sea-level-20th-century-fastest-years.html



The rate of sea-level rise in the 20th century along much of the U.S. Atlantic coast was the fastest in 2,000 years, and southern New Jersey had the fastest rates, according to a Rutgers-led study.

The global rise in sea-level from melting ice and warming oceans from 1900 to 2000 led to a rate that's more than twice the average for the years 0 to 1800—the most significant change, according to the study in the journal Nature Communications.

The study for the first time looked at the phenomena that contributed to sea-level change over 2,000 years at six sites along the coast (in Connecticut, New York City, New Jersey and North Carolina), using a sea-level budget. A budget enhances understanding of the processes driving sea-level change. The processes are global, regional (including geological, such as land subsidence) and local, such as groundwater withdrawal.



Most sea-level budget studies are global and limited to the 20th and 21st centuries. Rutgers-led researchers estimated sea-level budgets for longer timeframes over 2,000 years. The goal was to better understand how the processes driving sea-level have changed and could shape future change, and this sea-level budget method could be applied to other sites around the world.

Using a statistical model, scientists developed sea-level budgets for six sites, dividing sea-level records into global, regional and local components. They found that regional land subsidence—sinking of the land since the Laurentide ice sheet retreated thousands of years ago—dominates each site's budget over the last 2,000 years. Other regional factors, such as ocean dynamics, and site-specific local processes, such as groundwater withdrawal that helps cause land to sink, contribute much less to each budget and vary over time and by location.

The total rate of sea-level rise for each of the six sites in the 20th century (ranging from 2.6 to 3.6 millimeters per year, or about 1 to 1.4 inches per decade) was the fastest in 2,000 years. Southern New Jersey had the fastest rates over the 2,000-year period: 1.6 millimeters a year (about 0.63 inches per decade) at Edwin Forsythe National Wildlife Refuge, Leeds Point, in Atlantic County and 1.5 millimeters a year (about 0.6 inches per decade) at Cape May Court House, Cape May County. Other sites included East River Marsh in Guilford, Connecticut; Pelham Bay, The Bronx, New York City; Cheesequake State Park in Old Bridge, New Jersey; and Roanoke Island in North Carolina.



Jennifer S. Walker et al, Common Era sea-level budgets along the U.S. Atlantic coast, Nature Communications (2021).
https://www.nature.com/articles/s41467-021-22079-2
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4205 on: March 24, 2021, 03:41:33 PM »
Rignot et al. (2021) indicates that two thirds of the ice mass loss from the Humboldt Gletscher glacier in North Greenland is due to undercutting of grounded ice by warm ocean currents, '… which is a physical process not included in most ice sheet models.' 

This implies that most consensus science projections of ice mass loss from the GrIS with continued global warming err on the side of least drama.

Eric Rignot, E. et al. (10 March 2021), "Retreat of Humboldt Gletscher, North Greenland, driven by undercutting from a warmer ocean", Geophysical Research Letters, https://doi.org/10.1029/2020GL091342

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091342?af=R

Abstract
Humboldt Gletscher is a 100‐km wide, slow‐moving glacier in north Greenland which holds a 19‐cm global sea level equivalent. Humboldt has been the fourth largest contributor to sea level rise since 1972 but the cause of its mass loss has not been elucidated. Multi‐beam echo sounding data collected in 2019 indicate a seabed 200 m deeper than previously known. Conductivity temperature depth (CTD) data reveal the presence of warm water of Atlantic origin at 0°C at the glacier front and a warming of the ocean waters by 0.9 ± 0.1°C since 1962. Using an ocean model, we reconstruct grounded ice undercutting by the ocean, combine it with calculated retreat caused by ice thinning to floatation, and are able to fully explain the observed retreat. Two thirds of the retreat is caused by undercutting of grounded ice, which is a physical process not included in most ice sheet models.

Plain Language Summary
Humboldt Gletscher is the widest glacier in Greenland, slow moving, and terminating in shallow waters in its southern half, but grounded 200 m deeper than previously known in its northern half, with a submarine trough extending more than 100 km inland. The glacier has been retreating at 0.6 km/yr and contributing significantly to sea level rise. We attribute the retreat to undercutting of grounded ice by warmer ocean waters combined with a retreat caused by ice thinning to floatation sooner due to glacier speed up. The glacier, which hosts an ice volume equivalent to a 19‐cm global sea level, will remain a major contributor to sea level rise this Century.
“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 #4206 on: March 24, 2021, 03:46:46 PM »
With regard to a coming tipping point in carbon storage in tundra regions invaded by shrubs, Clemmensen et al (2021) conclude that:

"Advancement of the forest boundary would promote an ectomycorrhizal fungal community with the capacity to release the large organic N reserves and favour tree growth, potentially leading to a strong, positive plant–soil feedback that accelerates tree expansion into former tundra and underpins a positive feedback of tundra to climate warming."

This implies that consensus climate science projections of carbon emissions from tundra regions err on the side of least drama:

Clemmensen, K.E. et al. (22 March 2021), "A tipping point in carbon storage when forest expands into tundra is related to mycorrhizal recycling of nitrogen", Ecology Letters, https://doi.org/10.1111/ele.13735

https://onlinelibrary.wiley.com/doi/10.1111/ele.13735?af=R

Abstract
Tundra ecosystems are global belowground sinks for atmospheric CO2. Ongoing warming‐induced encroachment by shrubs and trees risks turning this sink into a CO2 source, resulting in a positive feedback on climate warming. To advance mechanistic understanding of how shifts in mycorrhizal types affect long‐term carbon (C) and nitrogen (N) stocks, we studied small‐scale soil depth profiles of fungal communities and C–N dynamics across a subarctic‐alpine forest‐heath vegetation gradient. Belowground organic stocks decreased abruptly at the transition from heath to forest, linked to the presence of certain tree‐associated ectomycorrhizal fungi that contribute to decomposition when mining N from organic matter. In contrast, ericoid mycorrhizal plants and fungi were associated with organic matter accumulation and slow decomposition. If climatic controls on arctic‐alpine forest lines are relaxed, increased decomposition will likely outbalance increased plant productivity, decreasing the overall C sink capacity of displaced tundra.
“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 #4207 on: March 24, 2021, 03:51:39 PM »
I think that it is worth noting that Rydsaa et al. (2021) indicate that:

"We find that wintertime extreme transport events on planetary scales are associated with warm temperature anomalies across the entire Arctic, while the extreme events on synoptic scale have less impact on the Arctic temperatures. We show that over the past four decades, there has been a significant increase in the wintertime latent energy transport by planetary‐scale systems, and a decrease by synoptic scale transport. This shift may have contributed to the amplified warming observed in the Arctic winter over the past decades."

This implies that extreme atmospheric transport events from lower to higher latitudes will likely contribute significantly to future Arctic Amplification in coming decades.

Rydsaa, J.H. et al. (22 March 2021), "Changes in atmospheric latent energy transport into the Arctic; planetary versus synoptic scales", RMetS, https://doi.org/10.1002/qj.4022

https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.4022?af=R

Abstract
Atmospheric meridional energy transport into the Arctic plays an important role in the Arctic weather and climate. The transport of latent energy in form of water vapour strongly influences the Arctic atmosphere. The transport is achieved by circulation mechanisms on various scales and is largely comprised by extreme transport events. Here, we use a Fourier‐based method of dividing the latent energy transport into spatial scales and investigate the extent to which extreme events in latent energy transport on planetary and synoptic scales have changed over the past four decades, and how they influence the Arctic winter temperatures. We find that wintertime extreme transport events on planetary scales are associated with warm temperature anomalies across the entire Arctic, while the extreme events on synoptic scale have less impact on the Arctic temperatures. We show that over the past four decades, there has been a significant increase in the wintertime latent energy transport by planetary‐scale systems, and a decrease by synoptic scale transport. This shift may have contributed to the amplified warming observed in the Arctic winter over the past decades.
“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 #4208 on: March 24, 2021, 11:12:44 PM »
In balance, Terrer et al. (2021) indicate that consensus climate science (CCS) has overestimated the potential for terrestrial ecosystems to act as a net carbon sink with continued anthropogenic forcing.  This means that effective climate sensitivity will be higher in coming decades than previously assumed by CCS.

Terrer, C., Phillips, R.P., Hungate, B.A. et al. A trade-off between plant and soil carbon storage under elevated CO2. Nature 591, 599–603 (2021). https://doi.org/10.1038/s41586-021-03306-8

https://www.nature.com/articles/s41586-021-03306-8

Abstract: "Terrestrial ecosystems remove about 30 per cent of the carbon dioxide (CO2) emitted by human activities each year, yet the persistence of this carbon sink depends partly on how plant biomass and soil organic carbon (SOC) stocks respond to future increases in atmospheric CO2. Although plant biomass often increases in elevated CO2 (eCO2) experiments, SOC has been observed to increase, remain unchanged or even decline. The mechanisms that drive this variation across experiments remain poorly understood, creating uncertainty in climate projections. Here we synthesized data from 108 eCO2 experiments and found that the effect of eCO2 on SOC stocks is best explained by a negative relationship with plant biomass: when plant biomass is strongly stimulated by eCO2, SOC storage declines; conversely, when biomass is weakly stimulated, SOC storage increases. This trade-off appears to be related to plant nutrient acquisition, in which plants increase their biomass by mining the soil for nutrients, which decreases SOC storage. We found that, overall, SOC stocks increase with eCO2 in grasslands (8 ± 2 per cent) but not in forests (0 ± 2 per cent), even though plant biomass in grasslands increase less (9 ± 3 per cent) than in forests (23 ± 2 per cent). Ecosystem models do not reproduce this trade-off, which implies that projections of SOC may need to be revised."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4209 on: March 26, 2021, 12:15:50 AM »
The linked reference indicates that the upper ocean is becoming stratified six times faster than consensus climate science previously assumed.  If nothing else the high speed of this stratification will increase climate sensitivity via the SST pattern effect:

Sallée, JB., Pellichero, V., Akhoudas, C. et al. Summertime increases in upper-ocean stratification and mixed-layer depth. Nature 591, 592–598 (2021). https://doi.org/10.1038/s41586-021-03303-x

https://www.nature.com/articles/s41586-021-03303-x

Abstract
The surface mixed layer of the world ocean regulates global climate by controlling heat and carbon exchange between the atmosphere and the oceanic interior. The mixed layer also shapes marine ecosystems by hosting most of the ocean’s primary production and providing the conduit for oxygenation of deep oceanic layers. Despite these important climatic and life-supporting roles, possible changes in the mixed layer during an era of global climate change remain uncertain. Here we use oceanographic observations to show that from 1970 to 2018 the density contrast across the base of the mixed layer increased and that the mixed layer itself became deeper. Using a physically based definition of upper-ocean stability that follows different dynamical regimes across the global ocean, we find that the summertime density contrast increased by 8.9 ± 2.7 per cent per decade (10−6–10−5 per second squared per decade, depending on region), more than six times greater than previous estimates. Whereas prior work has suggested that a thinner mixed layer should accompany a more stratified upper ocean, we find instead that the summertime mixed layer deepened by 2.9 ± 0.5 per cent per decade, or several metres per decade (typically 5–10 metres per decade, depending on region). A detailed mechanistic interpretation is challenging, but the concurrent stratification and deepening of the mixed layer are related to an increase in stability associated with surface warming and high-latitude surface freshening, accompanied by a wind-driven intensification of upper-ocean turbulence. Our findings are based on a complex dataset with incomplete coverage of a vast area. Although our results are robust within a wide range of sensitivity analyses, important uncertainties remain, such as those related to sparse coverage in the early years of the 1970–2018 period. Nonetheless, our work calls for reconsideration of the drivers of ongoing shifts in marine primary production, and reveals stark changes in the world’s upper ocean over the past five decades.

See also:

Title: "Global Warming Is 'Fundamentally' Changing The Structure of Our World's Oceans"

https://www.sciencealert.com/fundamental-changes-to-our-oceans-are-occurring-much-faster-than-we-thought

Climate change has disrupted ocean mixing, a process that helps store away most of the world's excess heat and a significant proportion of CO2.

Water on the surface is warmer – and therefore less dense – than the water below, a contrast that is intensified by climate change.

Global warming is also causing massive amounts of fresh water to flush into the seas from melting ice sheets and glaciers, lowering the salinity of the upper layer and further reducing its density.

This increasing contrast between the density of the ocean layers makes mixing harder, so oxygen, heat and carbon are all less able to penetrate to the deep seas.

"Similar to a layer of water on top of oil, the surface waters in contact with the atmosphere mix less efficiently with the underlying ocean," said lead author Jean-Baptiste Sallee of Sorbonne University and France's CNRS national scientific research center.

He said while scientists were aware that this process was under way, "we here show that this change has occurred at a rate much quicker than previously thought: more than six times quicker."

They said increased rainfall and melting of the Greenland ice sheet have increased the freshwater in the upper ocean, disrupting the normal cycle that carries warm, salty surface water northwards from the equator and sends low-salinity deep water back southwards."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4210 on: March 28, 2021, 06:57:01 PM »
The linked reference indicates that anthropogenic methane emissions from North America are about twice that previously reported by the U.S. EPA.

Maasakkers, J. D., Jacob, D. J., Sulprizio, M. P., Scarpelli, T. R., Nesser, H., Sheng, J., Zhang, Y., Lu, X., Bloom, A. A., Bowman, K. W., Worden, J. R., and Parker, R. J.: 2010–2015 North American methane emissions, sectoral contributions, and trends: a high-resolution inversion of GOSAT observations of atmospheric methane, Atmos. Chem. Phys., 21, 4339–4356, https://doi.org/10.5194/acp-21-4339-2021, 2021.

https://acp.copernicus.org/articles/21/4339/2021/

Abstract: "We use 2010–2015 Greenhouse Gases Observing Satellite (GOSAT) observations of atmospheric methane columns over North America in a high-resolution inversion of methane emissions, including contributions from different sectors and their trends over the period. The inversion involves an analytical solution to the Bayesian optimization problem for a Gaussian mixture model (GMM) of the emission field with up to 0.5∘×0.625∘ resolution in concentrated source regions. The analytical solution provides a closed-form characterization of the information content from the inversion and facilitates the construction of a large ensemble of solutions exploring the effect of different uncertainties and assumptions in the inverse analysis. Prior estimates for the inversion include a gridded version of the Environmental Protection Agency (EPA) Inventory of US Greenhouse Gas Emissions and Sinks (GHGI) and the WetCHARTs model ensemble for wetlands. Our best estimate for mean 2010–2015 US anthropogenic emissions is 30.6 (range: 29.4–31.3) Tg a−1, slightly higher than the gridded EPA inventory (28.7 (26.4–36.2) Tg a−1). The main discrepancy is for the oil and gas production sectors, where we find higher emissions than the GHGI by 35 % and 22 %, respectively. The most recent version of the EPA GHGI revises downward its estimate of emissions from oil production, and we find that these are lower than our estimate by a factor of 2. Our best estimate of US wetland emissions is 10.2 (5.6–11.1) Tg a−1, on the low end of the prior WetCHARTs inventory uncertainty range (14.2 (3.3–32.4) Tg a−1), which calls for better understanding of these emissions. We find an increasing trend in US anthropogenic emissions over 2010–2015 of 0.4 % a−1, lower than previous GOSAT-based estimates but opposite to the decrease reported by the EPA GHGI. Most of this increase appears driven by unconventional oil and gas production in the eastern US. We also find that oil and gas production emissions in Mexico are higher than in the nationally reported inventory, though there is evidence for a 2010–2015 decrease in emissions from offshore oil production."
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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4211 on: April 01, 2021, 02:25:27 PM »
Melting Ice Sheets Caused Sea Levels to Rise Up to 18 Meters
https://phys.org/news/2021-04-ice-sheets-sea-metres.html

New research has found that previous ice loss events could have caused sea-level rise at rates of around 3.6 meters per century, offering vital clues as to what lies ahead should climate change continue unabated.

... Geological records tell us that, at the end of the last ice age around 14,600 years ago, sea levels rose at ten times the current rate due to Meltwater Pulse 1A (MWP-1A); a 500 year, ~18 meter sea-level rise event.

Until now, the scientific community has not been able to agree about which ice sheet was responsible for this rapid rise, with the massive Antarctic Ice Sheet being a likely suspect, but some evidence pointing towards ice sheets in the Northern Hemisphere..

The new study uses detailed geological sea-level data and state-of-the-art modelling techniques to reveal the sources of MWP-1A. Interestingly, most of the meltwater appears to have originated from the former North American and Eurasian ice sheets, with minimal contribution from Antarctica, reconciling formerly disparate views.

In addition to flooding vast areas of low-lying land, this unparalleled discharge of freshwater into the ocean—comparable to melting an ice sheet twice the size of Greenland in only 500 years—will have disrupted ocean circulation, with knock-on effects for global climate. Knowing the source of the meltwater will improve the accuracy of climate models that are used to replicate the past and predict changes in the future.

A reconciled solution of Meltwater Pulse 1A sources using sea-level fingerprinting, Nature Communications, (2021)
https://www.nature.com/articles/s41467-021-21990-y
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4212 on: April 02, 2021, 12:49:56 PM »
Evidence of Antarctic Pine Island Glacier's Tipping Point Confirmed
https://phys.org/news/2021-04-evidence-antarctic-glacier.html

Researchers have confirmed for the first time that Pine Island Glacier in West Antarctica could cross tipping points, leading to a rapid and irreversible retreat which would have significant consequences for global sea level.

While the general possibility of such a tipping point within ice sheets has been raised before, showing that Pine Island Glacier has the potential to enter unstable retreat is a very different question.

Now, researchers from Northumbria University have shown, for the first time, that this is indeed the case.

Their findings are published in leading journal, The Cryosphere.

... For Pine Island Glacier, their study shows that the glacier has at least three distinct tipping points. The third and final event, triggered by ocean temperatures increasing by 1.2C, leads to an irreversible retreat of the entire glacier.

The researchers say that long-term warming and shoaling trends in Circumpolar Deep Water, in combination with changing wind patterns in the Amundsen Sea, could expose Pine Island Glacier's ice shelf to warmer waters for longer periods of time, making temperature changes of this magnitude increasingly likely.

... Should the glacier enter unstable irreversible retreat, the impact on sea level could be measured in metres, and as this study shows, once the retreat starts it might be impossible to halt it."


Figure 3Marine ice sheet instability events for Pine Island Glacier. Shown are (a) grounding-line positions before and after the three MISI-driven glacier collapses with (b) a zoom-in on the initial events (coloured lines). The colour map indicates initially modelled ice velocity, and the model domain boundary is indicated by a dashed black contour in panel (a). Panels (c) and (d) show a transect through the main trunk of PIG, calculated as an average of properties between the two dashed magenta lines in (b). The vertical section along the transect is shown (c) at the initial steady state where fluxes (Qin and Qout) are in balance and (d) during a MISI event where retreat causes an increase in Qout, pushing the glacier to be out of balance and leading to further retreat.



The quasi-equilibrium simulation shows three potential tipping points with respect to the applied melt (Fig. 4). Upon crossing each threshold, indicated by the numbered blue dots in Fig. 4, PIG undergoes periods of not only rapid but also (as we show below) self-sustained and irreversible mass loss.

... Grounding-line positions before each of these retreat events and after the final collapse are shown in Fig. 3. Events 1 and 2 each contribute approximately 20 mm of sea-level rise, while event 3, which arises after slightly more than doubling current melt rates, contributes approximately 100 mm. The actual sea-level rise that would result from this third and largest event is likely to be larger since in our simulation the effects stop at the domain boundary and in reality neighbouring drainage basins would be affected.

... The third event marks the onset of an almost complete collapse of PIG (Fig. 4a). Unlike the previous two, this collapse cannot be reversed to regrow the glacier for any value of the control parameter. This is an example of a permanently irreversible tipping point, as shown in Fig. 1d.

... The third and final tipping point is crossed with an increase in sub-shelf melt rates equivalent to a +1.2 ∘C increase in ocean temperatures from initial conditions and leads to a complete collapse of PIG. Long-term warming and shoaling trends in Circumpolar Deep Water (Holland et al., 2019), in combination with changing wind patterns in the Amundsen Sea (Turner et al., 2017), can expose the PIG ice shelf to warmer waters for longer periods of time and make temperature changes of this magnitude increasingly likely.


Sebastian H. R. Rosier et al, The tipping points and early warning indicators for Pine Island Glacier, West Antarctica, The Cryosphere (2021)
https://tc.copernicus.org/articles/15/1501/2021/
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4213 on: April 07, 2021, 05:35:02 PM »
The linked reference concludes that:

"Combining our findings with relative humidity trends in reanalysis data shows a tendency toward Earth becoming more sensitive to forcing over time."

Thus, projected changes in atmospheric relative humidity is yet one more feedback mechanism by which climate sensitivity is likely to increase by in coming decades.

Bourdin, S., L. Kluft and B. Stevens (06 April 2021), "Dependence of Climate Sensitivity on the Given Distribution of Relative Humidity", Geophysical Research Letters,
https://doi.org/10.1029/2021GL092462

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092462?af=R

Abstract
We study how the vertical distribution of relative humidity (RH) affects climate sensitivity, even if it remains unchanged with warming. Using a radiative‐convective equilibrium model, we show that the climate sensitivity depends on the shape of a fixed vertical distribution of humidity, tending to be higher for atmospheres with higher humidity. We interpret these effects in terms of the effective emission height of water vapor. Differences in the vertical distribution of RH are shown to explain a large part of the 10% to 30% differences in clear‐sky sensitivity seen in climate and storm‐resolving models. The results imply that convective aggregation reduces climate sensitivity, even when the degree of aggregation does not change with warming. Combining our findings with relative humidity trends in reanalysis data shows a tendency toward Earth becoming more sensitive to forcing over time. These trends and their height variation merit further study.

Plain Language Summary
Equilibrium Climate Sensitivity is the change in surface temperature in response to a doubling of atmospheric CO2. We study how the assumed vertical distribution of relative humidity affects this sensitivity. Theoretical considerations show that the more moist an atmosphere is, the more it warms as a response to an increase in CO2. Adding water vapor to the lower troposphere has the counter effect, lowering the sensitivity. We emphasize the importance of climate simulations taking humidity into account, as it is largely responsible for the difference in projections among models without clouds. We note surprising trends in humidity – with substantial drying of the lower troposphere over the ocean – in the last four decades as reported by two reanalyses of meteorological observations. Subject to the accuracy of these reconstructions, there appears to be a change with less moistening than expected, but with moistening/drying profiles which will condition Earth to become more sensitive to forcing over time. We stress the need for a study of observations to more critically evaluate these trends, and know better what models should aim for.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4214 on: April 07, 2021, 06:44:19 PM »
The linked reference finds that lightening strikes in the Arctic could double by 2100; which, would result in an increase in associated wildfires that would accelerate the thawing of the Arctic permafrost & and increase in the associated GHG emissions.

Finney, D.L. Lightning threatens permafrost. Nat. Clim. Chang. (2021). https://doi.org/10.1038/s41558-021-01016-7

https://www.nature.com/articles/s41558-021-01016-7

Abstract: "Thawing Arctic permafrost, and release of its stored carbon, is a known amplifier of global warming. Now research suggests an increase in Arctic lightning could speed up the permafrost’s demise."
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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4215 on: April 08, 2021, 03:35:34 PM »
Third of Antarctic Ice Shelf Area at Risk of Collapse as Planet Warms
https://phys.org/news/2021-04-antarctic-ice-shelf-area-collapse.html

More than a third of the Antarctic's ice shelf area could be at risk of collapsing into the sea if global temperatures reach 4°C above pre-industrial levels, new research has shown.

The University of Reading led the most detailed ever study forecasting how vulnerable the vast floating platforms of ice surrounding Antarctica will become to dramatic collapse events caused by melting and runoff, as climate change forces temperatures to rise.

It found that 34% of the area of all Antarctic ice shelves—around half a million square kilometers—including 67% of ice shelf area on the Antarctic Peninsula, would be at risk of destabilization under 4°C of warming. Limiting temperature rise to 2°C rather than 4°C would halve the area at risk and potentially avoid significant sea level rise.

The researchers also identified Larsen C—the largest remaining ice shelf on the peninsula, which split to form the enormous A68 iceberg in 2017—as one of four ice shelves that would be particularly threatened in a warmer climate.

The new study, published in the Geophysical Research Letters journal, used state-of-the-art, high-resolution regional climate modelling to predict in more detail than before the impact of increased melting and water runoff on ice shelf stability.

Ice shelf vulnerability from this fracturing process was forecast under 1.5°C, 2°C and 4°C global warming scenarios, which are all possible this century.

The researchers identified the Larsen C, Shackleton, Pine Island and Wilkins ice shelves as most at-risk under 4°C of warming, due to their geography and the significant runoff predicted in those areas.



Surface melt and runoff on Antarctic ice shelves at 1.5°C, 2°C and 4°C of future warming, Geophysical Research Letters (2021)
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091733
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

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

FredBear

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4216 on: April 09, 2021, 12:23:59 PM »
Note: The above video is talking about air temperature causing melt and ice shelf disintegration.
It is ignoring sea temperature causing melt (which is why they say Pine Island glacier does not feature as a major problem in their study)!

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4217 on: April 11, 2021, 02:10:35 AM »
While, it would be nice if I were wrong about the fragility of the ice constraints at the base of the Thwaites Ice Tongue; however, the linked open access reference provides recent evidence that the stability of the ice in this area is becoming less and less stable with each passing year.

Wåhlin, A.K., et al. (09 Apr 2021), "Pathways and modification of warm water flowing beneath Thwaites Ice Shelf, West Antarctica", Science Advances, Vol. 7, no. 15, eabd7254, DOI: 10.1126/sciadv.abd7254

https://advances.sciencemag.org/content/7/15/eabd7254

Abstract: "Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4218 on: April 15, 2021, 01:02:07 AM »
The linked article & associated linked report indicate that GMSTA could reach 1.5o C as soon as 2030:

Title: "AIM HIGH, GO FAST: WHY EMISSIONS NEED TO PLUMMET THIS DECADE"

https://www.climatecouncil.org.au/resources/net-zero-emissions-plummet-decade
&
https://www.climatecouncil.org.au/wp-content/uploads/2021/04/aim-high-go-fast-why-emissions-must-plummet-climate-council-report.pdf

Extract: "Multiple lines of evidence strongly suggest the global average temperature rise will exceed 1.5°C during the 2030s."
“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 #4219 on: April 23, 2021, 01:11:58 AM »
The linked reference concludes that:

"Our results suggest that the continued decrease in anthropogenic aerosol emissions that accompany efforts to reduce air pollution will reinforce GHG-induced AMOC weakening over the next few decades – with the caveat that internal AMOC variability will also be important."

Thus, in the coming few decades not only could a domino sequence of freshwater hosing events work to significantly slow the AMOC but also so will the projected coming decrease in anthropogenic aerosol emissions.

Hassan, T., Allen, R. J., Liu, W., and Randles, C. A.: Anthropogenic aerosol forcing of the Atlantic meridional overturning circulation and the associated mechanisms in CMIP6 models, Atmos. Chem. Phys., 21, 5821–5846, https://doi.org/10.5194/acp-21-5821-2021, 2021.

https://acp.copernicus.org/articles/21/5821/2021/

Abstract
By regulating the global transport of heat, freshwater, and carbon, the Atlantic meridional overturning circulation (AMOC) serves as an important component of the climate system. During the late 20th and early 21st centuries, indirect observations and models suggest a weakening of the AMOC. Direct AMOC observations also suggest a weakening during the early 21st century but with substantial interannual variability. Long-term weakening of the AMOC has been associated with increasing greenhouse gases (GHGs), but some modeling studies suggest the build up of anthropogenic aerosols (AAs) may have offset part of the GHG-induced weakening. Here, we quantify 1900–2020 AMOC variations and assess the driving mechanisms in state-of-the-art climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6). The CMIP6 forcing (GHGs, anthropogenic and volcanic aerosols, solar variability, and land use and land change) multi-model mean shows negligible AMOC changes up to ∼ 1950, followed by robust AMOC strengthening during the second half of the 20th century (∼ 1950–1990) and weakening afterwards (1990–2020). These multi-decadal AMOC variations are related to changes in North Atlantic atmospheric circulation, including an altered sea level pressure gradient, storm track activity, surface winds, and heat fluxes, which drive changes in the subpolar North Atlantic surface density flux. To further investigate these AMOC relationships, we perform a regression analysis and decompose these North Atlantic climate responses into an anthropogenic aerosol-forced component and a subsequent AMOC-related feedback. Similar to previous studies, CMIP6 GHG simulations yield robust AMOC weakening, particularly during the second half of the 20th century. Changes in natural forcings, including solar variability and volcanic aerosols, yield negligible AMOC changes. In contrast, CMIP6 AA simulations yield robust AMOC strengthening (weakening) in response to increasing (decreasing) anthropogenic aerosols. Moreover, the CMIP6 all-forcing AMOC variations and atmospheric circulation responses also occur in the CMIP6 AA simulations, which suggests these are largely driven by changes in anthropogenic aerosol emissions. More specifically, our results suggest that AMOC multi-decadal variability is initiated by North Atlantic aerosol optical thickness perturbations to net surface shortwave radiation and sea surface temperature (and hence sea surface density), which in turn affect sea level pressure gradient and surface wind and – via latent and sensible heat fluxes – sea surface density flux through its thermal component. AMOC-related feedbacks act to reinforce this aerosol-forced AMOC response, largely due to changes in sea surface salinity (and hence sea surface density), with temperature-related (and cloud-related) feedbacks acting to mute the initial response. Although aspects of the CMIP6 all-forcing multi-model mean response resembles observations, notable differences exist. This includes CMIP6 AMOC strengthening from ∼ 1950 to 1990, when the indirect estimates suggest AMOC weakening. The CMIP6 multi-model mean also underestimates the observed increase in North Atlantic ocean heat content, and although the CMIP6 North Atlantic atmospheric circulation responses – particularly the overall patterns – are similar to observations, the simulated responses are weaker than those observed, implying they are only partially externally forced. The possible causes of these differences include internal climate variability, observational uncertainties, and model shortcomings, including excessive aerosol forcing. A handful of CMIP6 realizations yield AMOC evolution since 1900 similar to the indirect observations, implying the inferred AMOC weakening from 1950 to 1990 (and even from 1930 to 1990) may have a significant contribution from internal (i.e., unforced) climate variability. Nonetheless, CMIP6 models yield robust, externally forced AMOC changes, the bulk of which are due to anthropogenic aerosols.

Extract: "Consistent with the recent decreases in anthropogenic aerosol emissions, nearly all of the future emission scenarios (shared socio-economic pathways, SSPs) (O'Neill et al., 2014) yield large reductions in future anthropogenic aerosol emissions, with global sulfate emissions projected to decrease by up to 80 % by 2050. Thus, anthropogenic aerosol emissions, including those around the North Atlantic, will likely continue to rapidly decline over the next few decades. Our results suggest that the continued decrease in anthropogenic aerosol emissions that accompany efforts to reduce air pollution will reinforce GHG-induced AMOC weakening over the next few decades – with the caveat that internal AMOC variability will also be important."

“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 #4220 on: April 25, 2021, 09:59:43 PM »
Vignon et al. (2021) provides evidence that future rainfall events in Antarctica's coastal regions should not only occur more frequently, but also with more intensity, in coming decades with continued global warming.  This is not good news w.r.t. the potential for increased hydrofracturing of key glacial formations in Antarctica, nor for this risk of MICI types of failure for key marine glaciers like  the PIG or the Thwaites Glacier.

Vignon, E. et al. (27 March 2021), "Present and Future of Rainfall in Antarctica", Geophysical Research Letters, https://doi.org/10.1029/2020GL092281

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL092281

Abstract
While most precipitation in Antarctica falls as snow, little is known about liquid precipitation, although it can have ecological and climatic impacts. This study combines meteorological reports at 10 stations with the ERA5 reanalysis to provide a climatological characterization of rainfall occurrence over Antarctica. Along the East Antarctic coast, liquid precipitation occurs 22 days per year at most and coincides with maritime intrusions and blocking anticyclones. Over the north‐western Antarctic Peninsula, rainfall occurs more than 50 days per year on average and the recent summer cooling was accompanied by a decrease of −35 annual rainy days per decade between 1998 and 2015 at Faraday‐Vernadsky. Projections from seven latest‐generation climate models reveal that Antarctic coasts will experience a warming and more frequent and intense rainfall by the end of the century. Rainfall is expected to impact new regions of the continent, increasing their vulnerability to melting by the preconditioning of surface snow.

Plain Language Summary
Given the cold temperatures prevailing across the continent, most precipitation over Antarctica falls as snow. Nonetheless, infrequent rainfall events have already been observed causing serious damage to penguin colonies and facilitating the melting of the snow on the ground surface. Here, we provide the first climatological characterization of rainfall occurrence over Antarctica by examining reports of visual meteorological observations at 10 Antarctic stations. We can evidence the contrast between the coasts of East and West Antarctica that experience a few days per year with liquid precipitation and the western part of the Antarctic Peninsula where rainfall occurs more than 50 days per year on average. The latter region also experienced a significant decrease in rainfall occurrence during the first 15 years of the 21st century. Simulations with latest generation numerical climate models further reveal that the Antarctic continent is projected to undergo an overall warming accompanied by more frequent and more intense rainfall events at the end of century. Rainfall is also expected to impact regions of the continent that currently do not receive rainfall, making them vulnerable to intense events of surface snow melting preceded by liquid precipitation.
“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 #4221 on: April 26, 2021, 05:04:28 PM »
The linked reference confirms that there has been a close relationship between polar motion and climate change in the past; which, implies that there will also be such a close relationship in the future.

Deng, S., et al. (22 March 2021), "Polar Drift in the 1990s Explained by Terrestrial Water Storage Changes", Geophysical Research Letters, https://doi.org/10.1029/2020GL092114

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL092114

Abstract
Secular polar drift underwent a directional change in the 1990s, but the underlying mechanism remains unclear. In this study, polar motion observations are compared with geophysical excitations from the atmosphere, oceans, solid Earth, and terrestrial water storage (TWS) during the period of 1981–2020 to determine major drivers. When contributions from the atmosphere, oceans, and solid Earth are removed, the residual dominates the change in the 1990s. The contribution of TWS to the residual is quantified by comparing the hydrological excitations from modeled TWS changes in two different scenarios. One scenario assumes that the TWS change is stationary over the entire study period, and another scenario corrects the stationary result with actual glacier mass change. The accelerated ice melting over major glacial areas drives the polar drift toward 26°E for 3.28 mas/yr after the 1990s. The findings offer a clue for studying past climate‐driven polar motion.

Plain Language Summary
The Earth's pole, the point where the Earth's rotational axis intersects its crust in the Northern Hemisphere, drifted in a new eastward direction in the 1990s, as observed by space geodetic observations. Generally, polar motion is caused by changes in the hydrosphere, atmosphere, oceans, or solid Earth. However, short‐term observational records of key information in the hydrosphere (i.e., changes in terrestrial water storage) limit a better understanding of new polar drift in the 1990s. This study introduces a novel approach to quantify the contribution from changes in terrestrial water storage by comparing its drift path under two different scenarios. One scenario assumes that the terrestrial water storage change throughout the entire study period (1981–2020) is similar to that observed recently (2002–2020). The second scenario assumes that it changed from observed glacier ice melting. Only the latter scenario, along with the atmosphere, oceans, and solid Earth, agrees with the polar motion during the period of 1981–2020. The accelerated terrestrial water storage decline resulting from glacial ice melting is thus the main driver of the rapid polar drift toward the east after the 1990s. This new finding indicates that a close relationship existed between polar motion and climate change in the past.
“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 #4222 on: April 28, 2021, 11:42:09 PM »
As dropstones from ice rafted debris are associated with iceberg calving due to ice cliff failures, the linked reference (and associated YouTube video) indicates that icebergs from ice cliff failures were occurring in the WAIS during the Pliocene and that there likely was a seaway connecting the Amundsen Sea to the Weddell Sea.  This suggest that the WAIS is less stable than many consensus climate scientists assume.

Siddoway, C., Thomson, S., Hemming, S., Buchband, H., Quigley, C., Furlong, H., Hilderman, R., Robinson, D., Watkins, C., Cox, S., and Licht, K. and the IODP Expedition 379 Scientists and Expedition 382 Scientists: U-Pb zircon geochronology of dropstones and IRD in the Amundsen Sea, applied to the question of bedrock provenance and Miocene-Pliocene ice sheet extent in West Antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9151, https://doi.org/10.5194/egusphere-egu21-9151, 2021.

https://meetingorganizer.copernicus.org/EGU21/EGU21-9151.html

Summary: "IODP Expedition 379 to the Amundsen Sea continental rise recovered latest Miocene-Holocene sediments from two sites on a drift in water depths >3900m. Sediments are dominated by clay and silty clay with coarser-grained intervals and ice-rafted detritus (IRD) (Gohl et al. 2021, doi:10.14379/iodp.proc.379.2021). Cobble-sized dropstones appear as fall-in, in cores recovered from sediments >5.3 Ma.  We consider that abundant IRD and the sparse dropstones melted out of icebergs formed due to Antarctic ice-sheet calving events. We are using petrological and age characteristics of the clasts from the Exp379 sites to fingerprint their bedrock provenance. The results may aid in reconstruction of past changes in icesheet extent and extend knowledge of subglacial bedrock.
Mapped onshore geology shows pronounced distinctions in bedrock age between tectonic provinces of West or East Antarctica (e.g. Cox et al. 2020, doi:10.21420/7SH7-6K05; Jordan et al. 2020, doi.org/10.1038/s43017-019-0013-6). This allows us to use geochronology and thermochronology of rock clasts and minerals for tracing their provenance, and ascertain whether IRD deposited at IODP379 drillsites originated from proximal or distal Antarctic sources. We here report zircon and apatite U-Pb dates from four sand samples and five dropstones taken from latest Miocene, early Pliocene, and Plio-Pleistocene-boundary sediments. Additional Hf isotope data, and apatite fission track and 40Ar/39Ar Kfeldspar ages for some of the same samples help to strengthen provenance interpretations.
The study revealed three distinct zircon age populations at ca. 100, 175, and 250 Ma. Using Kolmogorov-Smirnov (K-S) statistical tests to compare our new igneous and detrital zircon (DZ) U-Pb results with previously published data, we found strong similarities to West Antarctic bedrock, but low correspondence to prospective sources in East Antarctica, implying a role for icebergs calved from the West Antarctic Ice Sheet (WAIS). The ~100 Ma age resembles plutonic ages from Marie Byrd Land and islands in Pine Island Bay.  The ~250 and 175 Ma populations match published mineral dates from shelf sediments in the eastern Amundsen Sea Embayment as well as granite ages from the Antarctic Peninsula and the Ellsworth-Whitmore Mountains (EWM). The different derivation of coarse sediment sources requires changes in iceberg origin through the latest Miocene, early Pliocene, and Plio/Pleistocene, likely the result of changes in WAIS extent.
One unique dropstone recovered from Exp379 Site U1533B is green quartz arenite, which yielded mostly 500-625 Ma detrital zircons. In visual appearance and dominant U-Pb age population, it resembles a sandstone dropstone recovered from Exp382 Site U1536 in the Scotia Sea (Hemming et al. 2020, https://gsa.confex.com/gsa/2020AM/meetingapp.cgi/Paper/357276). K-S tests yield high values (P ≥ 0.6), suggesting a common provenance for both dropstones recovered from late Miocene to Pliocene sediments, despite the 3270 km distance separating the sites. Comparisons to published data, in progress, narrow the group of potential on-land sources to exposures in the EWM or isolated ranges at far south latitudes in the Antarctic interior.  If both dropstones originated from the same source area, they could signify dramatic shifts in the WAIS grounding line position, and the possibility of the periodic opening of a seaway connecting the Amundsen and Weddell Seas."

See also the first presentation in the linked video:
Title: " #vEGU21 - Press Conference 2: Scientific sleuthing: Geoforensics and fingerprinting"



“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 #4223 on: April 30, 2021, 04:15:49 PM »
Hankel & Tziperman (2021) provide evidence that coming winter Arctic Sea Ice loss will be both abrupt and likely irreversible:

Hankel, C. and Eli Tziperman (2021), "The Role of Atmospheric Feedbacks in Abrupt Winter Arctic Sea Ice Loss in Future Warming Scenarios", Journal of Climate, Page(s): 4435–4447, DOI: https://doi.org/10.1175/JCLI-D-20-0558.1

https://journals.ametsoc.org/view/journals/clim/34/11/JCLI-D-20-0558.1.xml

Abstract
Winter Arctic sea ice loss has been simulated with varying degrees of abruptness across global climate models (GCMs) run in phase 5 of the Coupled Model Intercomparison Project (CMIP5) under the high-emissions extended RCP8.5 scenario. Previous studies have proposed various mechanisms to explain modeled abrupt winter sea ice loss, such as the existence of a wintertime convective cloud feedback or the role of the freezing point as a natural threshold, but none have sought to explain the variability of the abruptness of winter sea ice loss across GCMs. Here we propose a year-to-year local positive feedback cycle in which warm, open oceans at the start of winter allow for the moistening and warming of the lower atmosphere, which in turn increases the downward clear-sky longwave radiation at the surface and suppresses ocean freezing. This situation leads to delayed and diminished winter sea ice growth and allows for increased shortwave absorption from lowered surface albedo during springtime. Last, the ocean stores this additional heat throughout the summer and autumn seasons, setting up even warmer ocean conditions that lead to further sea ice reduction. We show that the strength of this feedback, as measured by the partial temperature contributions of the different surface heat fluxes, correlates strongly with the abruptness of winter sea ice loss across models. Thus, we suggest that this feedback mechanism may explain intermodel spread in the abruptness of winter sea ice loss. In models in which the feedback mechanism is strong, this may indicate the possibility of hysteresis and thus irreversibility of sea ice loss.

“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 #4224 on: April 30, 2021, 04:25:33 PM »
The linked reference indicates that physiological impacts of eCO2 on the Amazon rainforest can reduce this carbon sink as much as large-scale deforestation.

Sampaio, G., Shimizu, M. H., Guimarães-Júnior, C. A., Alexandre, F., Guatura, M., Cardoso, M., Domingues, T. F., Rammig, A., von Randow, C., Rezende, L. F. C., and Lapola, D. M.: CO2 physiological effect can cause rainfall decrease as strong as large-scale deforestation in the Amazon, Biogeosciences, 18, 2511–2525, https://doi.org/10.5194/bg-18-2511-2021, 2021.

https://bg.copernicus.org/articles/18/2511/2021/

Abstract
The climate in the Amazon region is particularly sensitive to surface processes and properties such as heat fluxes and vegetation coverage. Rainfall is a key expression of the land surface–atmosphere interactions in the region due to its strong dependence on forest transpiration. While a large number of past studies have shown the impacts of large-scale deforestation on annual rainfall, studies on the isolated effects of elevated atmospheric CO2 concentrations (eCO2) on canopy transpiration and rainfall are scarcer. Here, for the first time, we systematically compare the plant physiological effects of eCO2 and deforestation on Amazon rainfall. We use the CPTEC Brazilian Atmospheric Model (BAM) with dynamic vegetation under a 1.5×CO2 experiment and a 100 % substitution of the forest by pasture grasslands, with all other conditions held similar between the two scenarios. We find that both scenarios result in equivalent average annual rainfall reductions (Physiology: −257 mm, −12 %; Deforestation: −183 mm, −9 %) that are above the observed Amazon rainfall interannual variability of 5 %. The rainfall decreases predicted in the two scenarios are linked to a reduction of approximately 20 % in canopy transpiration but for different reasons: the eCO2-driven reduction of stomatal conductance drives the change in the Physiology experiment, and the smaller leaf area index of pasturelands (−72 % compared to tropical forest) causes the result in the Deforestation experiment. The Walker circulation is modified in the two scenarios: in Physiology due to a humidity-enriched free troposphere with decreased deep convection due to the heightening of a drier and warmer (+2.1 ∘C) boundary layer, and in Deforestation due to enhanced convection over the Andes and a subsidence branch over the eastern Amazon without considerable changes in temperature (−0.2 ∘C in 2 m air temperature and +0.4 ∘C in surface temperature). But again, these changes occur through different mechanisms: strengthened west winds from the Pacific and reduced easterlies entering the basin affect the Physiology experiment, and strongly increased easterlies influence the result of the Deforestation experiment. Although our results for the Deforestation scenario agree with the results of previous observational and modelling studies, the lack of direct field-based ecosystem-level experimental evidence regarding the effect of eCO2 on moisture fluxes in tropical forests confers a considerable level of uncertainty to any projections of the physiological effect of eCO2 on Amazon rainfall. Furthermore, our results highlight the responsibilities of both Amazonian and non-Amazonian countries to mitigate potential future climatic change and its impacts in the region, driven either by local deforestation or global CO2 emissions.
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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4225 on: April 30, 2021, 10:57:25 PM »
Nice paper on warm water intrusion under Thwaites: Wahlin et al. doi: 10.1126/sciadv.abd7254

"The warm, salty deep water masses are entering the cavity from both sides of the pinning point at the northern tip of the Eastern Ice Shelf. The substantial heat transport in trough T3 alone is sufficient to melt ice at a rate 85 Gt/year ...This pinning point is one of the last buttressing features restraining the flow of ice from upstream "

"the future melt rate of Thwaites and ice dynamic feedbacks may depend more on local conditions in the Pine Island region, as well as the evolving ice pinning points at Thwaites (28, 29), than predicted by existing models"

Open access. Read the whole thing.

sidd

kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4226 on: May 01, 2021, 02:47:39 PM »
Antarctic ice-sheet melting to lift sea level higher than thought, Harvard study says
New calculations show the rise due to warming would be 30% above forecasts

Global sea level rise associated with the possible collapse of the West Antarctic Ice Sheet has been significantly underestimated in previous studies, meaning sea level in a warming world will be greater than anticipated, according to a new study from Harvard researchers.

The report, published in Science Advances, features new calculations for what researchers refer to as a water expulsion mechanism. This occurs when the solid bedrock the West Antarctic Ice Sheet sits on rebounds upward as the ice melts and the total weight of the ice sheet decreases. The bedrock sits below sea level so when it lifts, it pushes water from the surrounding area into the ocean, adding to global sea level rise.

The new predictions show that in the case of a total collapse of the ice sheet, global sea level rise estimates would be amplified by an additional meter within 1,000 years.

"The magnitude of the effect shocked us," said Linda Pan, a Ph.D. in earth and planetary science in GSAS who co-led the study with fellow graduate student Evelyn Powell. "Previous studies that had considered the mechanism dismissed it as inconsequential."

"If the West Antarctic Ice Sheet collapsed, the most widely cited estimate of the resulting global mean sea level rise that would result is 3.2 meters," said Powell. "What we've shown is that the water expulsion mechanism will add an additional meter, or 30 percent, to the total."

But this is not just a story about impact that will be felt in hundreds of years. One of the simulations Pan and Powell performed indicated that by the end of this century global sea level rise caused by melting of the West Antarctic Ice Sheet would increase 20 percent by the water expulsion mechanism.

"Every published projection of sea level rise due to melting of the West Antarctic ice sheet that has been based on climate modeling, whether the projection extends to the end of this century or longer into the future, is going to have to be revised upward because of their work," said Jerry X. Mitrovica, the Frank B. Baird Jr. Professor of Science in the Department of Earth and Planetary Sciences and a senior author on the paper. "Every single one."

more on:
https://www.sciencedaily.com/releases/2021/04/210430165912.htm
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4227 on: May 01, 2021, 07:43:07 PM »
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4228 on: May 02, 2021, 07:36:07 PM »
Antarctic ice-sheet melting to lift sea level higher than thought, Harvard study says
New calculations show the rise due to warming would be 30% above forecasts

...

The new predictions show that in the case of a total collapse of the ice sheet, global sea level rise estimates would be amplified by an additional meter within 1,000 years.

...

"If the West Antarctic Ice Sheet collapsed, the most widely cited estimate of the resulting global mean sea level rise that would result is 3.2 meters," said Powell. "What we've shown is that the water expulsion mechanism will add an additional meter, or 30 percent, to the total."

But this is not just a story about impact that will be felt in hundreds of years. One of the simulations Pan and Powell performed indicated that by the end of this century global sea level rise caused by melting of the West Antarctic Ice Sheet would increase 20 percent by the water expulsion mechanism.
...

kassy,

The quotes that you provided about Pan et al. (2021), focus primarily on their MISI forecasts for eustatic sea level rise due to ice mass loss and postglacial rebound from the WAIS.

Pan, L., et al. (30 Apr 2021), "Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse", Science Advances, Vol. 7, no. 18, eabf7787, DOI: 10.1126/sciadv.abf7787

https://advances.sciencemag.org/content/7/18/eabf7787

However, Pan et al (2021) also provides projections for instantaneous ice mass loss from the WAIS on global mean sea level rise, as shown by the solid curve in the first image and for relative sea level rise in Panel A of the second image.  In my opinion, the lion share of ice mass loss in the WAIS could occur by about 2060 if one assumes a high-forcing (RCP 8.5) MICI type of scenario.  If so then the second image shows that the GrIS could experience over 4.2m of relative sea level rise by 2060 (& the fourth image shows possibly implications on the retreat of grounding lines of Greenland marine terminating glaciers) and portions of the EAIS could experience up to a 1m relative sea level rise (& the third image shows bed topology for the AIS).  Thus, consensus climate science had gambling a lot that the Thwaites Glacier gateway does not initiate a MICI type  of mechanism in the 2030 to 2040 timeframe.

Caption for the second image: "Fig. 4 Global sea level changes after WAIS collapse.
Predicted sea level changes (A) 0 and (B) 2 ka after an instantaneous collapse of marine-based sectors of WAIS based on the PSU3D1 scenario (Fig. 2F) (17) and computed using the 3D viscoelastic Earth model V3DSD summarized in Fig. 2 (A and B)."
« Last Edit: May 04, 2021, 12:40:01 AM by AbruptSLR »
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kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4229 on: May 02, 2021, 09:51:50 PM »
Didn´t have time yet to dive into it. Thanks for the extra pointers.
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

FredBear

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4230 on: May 03, 2021, 09:57:40 PM »
<snip>
The report, published in Science Advances, features new calculations for what researchers refer to as a water expulsion mechanism. This occurs when the solid bedrock the West Antarctic Ice Sheet sits on rebounds upward as the ice melts and the total weight of the ice sheet decreases. The bedrock sits below sea level so when it lifts, it pushes water from the surrounding area into the ocean, adding to global sea level rise.
<Snip>

From https://www.sciencedaily.com/releases/2021/04/210430165912.htm
"The researchers wanted to investigate how the expulsion mechanism affected sea level change when the low viscosity, or the easy flowing material of the Earth's mantle beneath West Antarctica, is considered. When they incorporated this low viscosity into their calculations they realized water expulsion occurred much faster than previous models had predicted."

Surely the solid bedrock rebound would also be provided from somewhere? - the surrounding area is covered by ocean and would therefore have minimal effect, especially as any lithospheric rebound must lag the ice loss?
Previous warnings I heard about ice loss reducing oceanic gravitational attraction towards Antarctica would produce a much quicker source of water as sea levels would fall in the area?
Resulting water migrating northwards would then slow the earth's spin a tiny bit    .    .    .   etc.,???

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4231 on: May 04, 2021, 12:45:06 AM »

...

Surely the solid bedrock rebound would also be provided from somewhere? - the surrounding area is covered by ocean and would therefore have minimal effect, especially as any lithospheric rebound must lag the ice loss?
Previous warnings I heard about ice loss reducing oceanic gravitational attraction towards Antarctica would produce a much quicker source of water as sea levels would fall in the area?
Resulting water migrating northwards would then slow the earth's spin a tiny bit    .    .    .   etc.,???
[/quote]

The work by Pan et al. (2021) is both open access, and the most accurate projections on this topic published to date.  The article addresses all such concerns.

Pan, L., et al. (30 Apr 2021), "Rapid postglacial rebound amplifies global sea level rise following West Antarctic Ice Sheet collapse", Science Advances, Vol. 7, no. 18, eabf7787, DOI: 10.1126/sciadv.abf7787

https://advances.sciencemag.org/content/7/18/eabf7787

Abstract: "Geodetic, seismic, and geological evidence indicates that West Antarctica is underlain by low-viscosity shallow mantle. Thus, as marine-based sectors of the West Antarctic Ice Sheet (WAIS) retreated during past interglacials, or will retreat in the future, exposed bedrock will rebound rapidly and flux meltwater out into the open ocean. Previous studies have suggested that this contribution to global mean sea level (GMSL) rise is small and occurs slowly. We challenge this notion using sea level predictions that incorporate both the outflux mechanism and complex three-dimensional viscoelastic mantle structure. In the case of the last interglacial, where the GMSL contribution from WAIS collapse is often cited as ~3 to 4 meters, the outflux mechanism contributes ~1 meter of additional GMSL change within ~1 thousand years of the collapse. Using a projection of future WAIS collapse, we also demonstrate that the outflux can substantially amplify GMSL rise estimates over the next century."

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Sciguy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4232 on: May 05, 2021, 07:59:56 PM »
The most recent modelling by Deconto, Pollard, et.al., published today in Nature, indicates that if global temperature increases are kept to 2C or less, MICI wont be initiated.

https://www.nature.com/articles/s41586-021-03427-0

Quote
    Published: 05 May 2021

The Paris Climate Agreement and future sea-level rise from Antarctica

Robert M. DeConto, David Pollard, Richard B. Alley, Isabella Velicogna, Edward Gasson, Natalya Gomez, Shaina Sadai, Alan Condron, Daniel M. Gilford, Erica L. Ashe, Robert E. Kopp, Dawei Li & Andrea Dutton

Nature volume 593, pages83–89(2021)

Abstract

The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius1. The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer timescales through a combination of ocean thermal expansion and loss of land ice2. The Antarctic Ice Sheet (AIS) is Earth’s largest land ice reservoir (equivalent to 57.9 metres of GMSL)3, and its ice loss is accelerating4. Extensive regions of the AIS are grounded below sea level and susceptible to dynamical instabilities5,6,7,8 that are capable of producing very rapid retreat8. Yet the potential for the implementation of the Paris Agreement temperature targets to slow or stop the onset of these instabilities has not been directly tested with physics-based models. Here we use an observationally calibrated ice sheet–shelf model to show that with global warming limited to 2 degrees Celsius or less, Antarctic ice loss will continue at a pace similar to today’s throughout the twenty-first century. However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100—an order of magnitude faster than today4. More fossil-fuel-intensive scenarios9 result in even greater acceleration. Ice-sheet retreat initiated by the thinning and loss of buttressing ice shelves continues for centuries, regardless of bedrock and sea-level feedback mechanisms10,11,12 or geoengineered carbon dioxide reduction. These results demonstrate the possibility that rapid and unstoppable sea-level rise from Antarctica will be triggered if Paris Agreement targets are exceeded.

Note that due to the lag between article submittal and publication, the "current policies" referred to in the abstract do not include recent pledges by the USA and EU to achieve net zero in 2050 and China to achieve net zero by 2060.

gerontocrat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4233 on: May 05, 2021, 10:00:08 PM »
From posting above....

Note that due to the lag between article submittal and publication, the "current policies" referred to in the abstract do not include recent pledges by the USA and EU to achieve net zero in 2050 and China to achieve net zero by 2060.

Another recent report says that the targets that include those recent pledges (not policies) should limit AGW to 2.7 instead of 2.9 degrees celsius.

But that study also notes that targets and pledges are not policies, which are not there yet - (and even policies aren't implementation). So that order of magnitude of increased sea level rise remains an increasing possibility every day that CO2 emissions are not reduced.

We will have to see what COP26 produces and the progress from targets to action that follow, i.e. 2022 is the earliest to see real co-ordinated global action. Meanwhile, (assuming that India's economy does not completely collapse into chaos from covid), India's + China's growth in emissions is likely to exceed efforts by the OECD countries to reduce emissions. 

This paper (stupidly pay-walled) is both a call to action and a strong warning. We are in the "Last Chance Saloon", and the bartender is thinking about stopping to serve drinks.
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oren

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4234 on: May 05, 2021, 11:04:05 PM »
Quote
However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100—an order of magnitude faster than today

FrostKing70

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4235 on: May 05, 2021, 11:48:14 PM »
AbruptSLR,

I think the animation from NASA shows what you are referencing on sea levels falling near Greenland due to ice loss and reduced mass of the ice sheet:

https://climate.nasa.gov/news/2626/evidence-of-sea-level-fingerprints/

regards
FK

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4236 on: May 06, 2021, 08:56:31 PM »
The linked reference provides evidence that the AMOC, has been, and is currently slowing in response to increasing atmosphere GHG concentrations.

Dima, M., Nichita, D.R., Lohmann, G. et al. Early-onset of Atlantic Meridional Overturning Circulation weakening in response to atmospheric CO2 concentration. npj Clim Atmos Sci 4, 27 (2021). https://doi.org/10.1038/s41612-021-00182-x

https://www.nature.com/articles/s41612-021-00182-x

Abstract: "The Atlantic Meridional Overturning Circulation (AMOC), a tipping component of the climate system, is projected to slowdown during the 21st century in response to increased atmospheric CO2 concentration. The rate and start of the weakening are associated with relatively large uncertainties. Observed sea surface temperature-based reconstructions indicate that AMOC has been weakening since the mid-20th century, but its forcing factors are not fully understood. Here we provide dynamical observational evidence that the increasing atmospheric CO2 concentration affects the North Atlantic heat fluxes and precipitation rate, and weakens AMOC, consistent with numerical simulations. The inferred weakening, starting in the late 19th century, earlier than previously suggested, is estimated at 3.7 ± 1.0 Sv over the 1854–2016 period, which is larger than it is shown in numerical simulations (1.4 ± 1.4 Sv)."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4237 on: May 06, 2021, 11:24:44 PM »
The linked reference indicates that CMIP6 models project that Antarctic Shelf Bottom Water (ASBW) should increase in the future resulting in more rapid degradation of ice shelf buttressing action against marine glaciers.

Purich, A. and Matthew H. England (18 April 2021), "Historical and future projected warming of Antarctic Shelf Bottom Water in CMIP6 models", Geophysical Research Letters, https://doi.org/10.1029/2021GL092752

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021GL092752?af=R

Abstract
Understanding warming on the Antarctic shelf is critical for projecting changes in Antarctic ice shelves and ice sheets. Here we assess Antarctic Shelf Bottom Water (ASBW) temperature mean‐state and trends in CMIP6 models. While CMIP6 models do not resolve ice shelves, future shelf water warming will impact ice shelf vulnerability. The CMIP6 multi‐model mean zonal temperature structure and mean‐state ASBW spatial pattern resemble observations, although there is considerable spread across the models and a multi‐model mean warm bias. The multi‐model mean projects an average ASBW warming of 0.36°C (interdecile range 0.07–0.60°C) under SSP245 and 0.62°C (interdecile range 0.16–0.95°C) under SSP585 by 2100, emphasising the influence future emissions have on shelf water warming around Antarctica. Changes in the transport of Circumpolar Deep Water onto the shelf associated with changes in the Southern Annular Mode, as well as Circumpolar Deep Water warming, are predicted to conspire to warm ASBW in the future.

Plain Language Summary
Ocean warming around the Antarctic coast plays a critical role in melting Antarctic ice shelves. To understand future changes in both ice shelves and ice sheets, understanding future changes in Antarctic shelf warming is critical. Here we assess ocean temperature mean‐state and trends around the Antarctic margin in a suite of coupled climate models. On average, these models do a reasonable job of capturing the mean‐state ocean characteristics, but the models are slightly too warm compared to observations. The projections suggest that the ocean around Antarctica will warm under future emission scenarios, with the level of warming under the high emission scenario almost double that under the medium‐low emission scenario. The projected warming around Antarctica is due to both wind‐driven circulation changes, and to ocean warming to the north of coastal regions.
“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 #4238 on: May 06, 2021, 11:46:38 PM »
The most recent modelling by Deconto, Pollard, et.al., published today in Nature, indicates that if global temperature increases are kept to 2C or less, MICI wont be initiated.

https://www.nature.com/articles/s41586-021-03427-0

Quote
    Published: 05 May 2021

The Paris Climate Agreement and future sea-level rise from Antarctica

Robert M. DeConto, David Pollard, Richard B. Alley, Isabella Velicogna, Edward Gasson, Natalya Gomez, Shaina Sadai, Alan Condron, Daniel M. Gilford, Erica L. Ashe, Robert E. Kopp, Dawei Li & Andrea Dutton

Nature volume 593, pages83–89(2021)

Abstract

The Paris Agreement aims to limit global mean warming in the twenty-first century to less than 2 degrees Celsius above preindustrial levels, and to promote further efforts to limit warming to 1.5 degrees Celsius1. The amount of greenhouse gas emissions in coming decades will be consequential for global mean sea level (GMSL) on century and longer timescales through a combination of ocean thermal expansion and loss of land ice2. The Antarctic Ice Sheet (AIS) is Earth’s largest land ice reservoir (equivalent to 57.9 metres of GMSL)3, and its ice loss is accelerating4. Extensive regions of the AIS are grounded below sea level and susceptible to dynamical instabilities5,6,7,8 that are capable of producing very rapid retreat8. Yet the potential for the implementation of the Paris Agreement temperature targets to slow or stop the onset of these instabilities has not been directly tested with physics-based models. Here we use an observationally calibrated ice sheet–shelf model to show that with global warming limited to 2 degrees Celsius or less, Antarctic ice loss will continue at a pace similar to today’s throughout the twenty-first century. However, scenarios more consistent with current policies (allowing 3 degrees Celsius of warming) give an abrupt jump in the pace of Antarctic ice loss after around 2060, contributing about 0.5 centimetres GMSL rise per year by 2100—an order of magnitude faster than today4. More fossil-fuel-intensive scenarios9 result in even greater acceleration. Ice-sheet retreat initiated by the thinning and loss of buttressing ice shelves continues for centuries, regardless of bedrock and sea-level feedback mechanisms10,11,12 or geoengineered carbon dioxide reduction. These results demonstrate the possibility that rapid and unstoppable sea-level rise from Antarctica will be triggered if Paris Agreement targets are exceeded.

Note that due to the lag between article submittal and publication, the "current policies" referred to in the abstract do not include recent pledges by the USA and EU to achieve net zero in 2050 and China to achieve net zero by 2060.

Per the attached image, per the CMIP6 model UKESM1-0-LL projection, GMSTA should exceed 2C before 2040 following SSP8.5.
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― Leon C. Megginson

Sciguy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4239 on: Today at 12:28:20 AM »
Meanwhile, Realclimate is showing this graph:

https://www.realclimate.org/index.php/archives/2021/04/two-graphs-show-the-path-to-1-5-degrees/



And the observed annually averaged global concentration of CO2 was 412.45 ppm.  RCP 8.5 was high at 415 while RCP 2.6 was close at 412.

https://www.esrl.noaa.gov/gmd/webdata/ccgg/trends/co2/co2_annmean_gl.txt

And with coal use having peaked globally, there's virtually no chance that emissions will match RCP 8.5.