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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1650 on: October 02, 2019, 05:24:18 PM »
The linked article provides an update on the progress being made with the CMIP6 program.  In the extracts below, I focus on the fact that all preliminary assessments of ECS from CMIP6 are substantially higher than that reported in either AR5 or CMIP5:

Title: "The CMIP6 landscape", (September 2019)
Nature Climate Change,  9, 727, DOI: https://doi.org/10.1038/s41558-019-0599-1

https://www.nature.com/articles/s41558-019-0599-1

Extract: "But the CMIP6 archive does appear to be reaching critical mass, and results are trickling into scientific discourse. One major discussion point centres on the models’ equilibrium climate sensitivity (ECS) — the global temperature change estimated from a doubling of CO2. As of March 2019, more than half of CMIP6 models exhibited an ECS of 5 °C or higher (https://go.nature.com/2kJv8YV; ref. 3), notably larger than the upper value of the CMIP5 range of 4.5 °C. By late August, with additional models available, a similar proportion still registered at 4.7 °C or higher (https://go.nature.com/2lOJHdZ).

If the higher CMIP6 ECS estimates hold true as the archive fills out, this will represent a departure from over four decades of research. Higher-sensitivity climates experience a greater probability of long-term temperature pauses and short-term trends, which can translate to more warming hiatuses or periods of fast temperature increase."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1651 on: October 02, 2019, 05:42:36 PM »
There are large areas of peatlands in both the Northern and Tropical areas of the Earth; which in the observed record have been a net carbon sink but increasingly appear to be headed to become significant carbon sources.  Therefore, without further comment, I provide the four linked recent references the discuss different aspects of the various ways that peatland are currently trending towards eventually becoming carbon sources, with continued climate change for the next few decades:

Susan Waldron et al. C mobilisation in disturbed tropical peat swamps: old DOC can fuel the fluvial efflux of old carbon dioxide, but site recovery can occur, Scientific Reports (2019). DOI: 10.1038/s41598-019-46534-9

https://www.nature.com/articles/s41598-019-46534-9

Abstract: "Southeast-Asian peat swamp forests have been significantly logged and converted to plantation. Recently, to mitigate land degradation and C losses, some areas have been left to regenerate. Understanding how such complex land use change affects greenhouse gas emissions is essential for modelling climate feedbacks and supporting land management decisions. We carried out field research in a Malaysian swamp forest and an oil palm plantation to understand how clear-felling, drainage, and illegal and authorized conversion to oil palm impacted the C cycle, and how the C cycle may change if such logging and conversion stopped. We found that both the swamp forest and the plantation emit centuries-old CO2 from their drainage systems in the managed areas, releasing sequestered C to the atmosphere. Oil palm plantations are an iconic symbol of tropical peatland degradation, but CO2 efflux from the recently-burnt, cleared swamp forest was as old as from the oil palm plantation. However, in the swamp forest site, where logging had ceased approximately 30 years ago, the age of the CO2 efflux was modern, indicating recovery of the system can occur. 14C dating of the C pool acted as a tracer of recovery as well as degradation and offers a new tool to assess efficacy of restoration management. Methane was present in many sites, and in higher concentrations in slow-flowing anoxic systems as degassing mechanisms are not strong. Methane loading in freshwaters is rarely considered, but this may be an important C pool in restored drainage channels and should be considered in C budgets and losses."

&

Anna Ferretto et al. (2019), "Potential carbon loss from Scottish peatlands under climate change", Regional Environmental Change, pp 1–11, DOI: https://doi.org/10.1007/s10113-019-01550-3

https://link.springer.com/article/10.1007/s10113-019-01550-3

Abstract: "The Scottish Government is committed to reduce carbon emissions by 80% by 2050 (compared to a 1990–1995 baseline). Peatlands have been recognised as a key environment for the carbon balance as they sequester and store great quantities of carbon, but they also have the potential to release it. In Scotland, peatlands cover more than 20% of the surface (more than 90% of which is blanket bog) and store more than 2500 Mt of carbon. Blanket bogs are very climate reliant, and as a consequence of climate change, many areas in Scotland may not be able to support peatlands in the near future. In this study, two bioclimatic envelope models (Linsday Modified model and Blanket Bog Tree model) have been used to obtain a first estimate of how the distribution of blanket bogs in Scotland could vary according to climate change in the 2050s and in the 2080s. The potential losses of carbon arising from climate change have then been calculated. Results showed that in 2050, more than half of the carbon currently stored in Scottish blanket bogs will be at risk of loss. This is 4.4–6.6 times the amount of carbon emitted in 2016 from all the sectors in Scotland and, if emissions from peatland occur and are taken into account, it will greatly hamper efforts to meet emission reduction targets set out in the Climate Change (Scotland) Act of 2009."

&

Anna M. Laine et al. Warming impacts on boreal fen CO 2 exchange under wet and dry conditions, Global Change Biology (2019). DOI: 10.1111/gcb.14617

https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14617

Abstract: "Northern peatlands form a major soil carbon (C) stock. With climate change, peatland C mineralization is expected to increase, which in turn would accelerate climate change. A particularity of peatlands is the importance of soil aeration, which regulates peatland functioning and likely modulates the responses to warming climate. Our aim is to assess the impacts of warming on a southern boreal and a sub‐arctic sedge fen carbon dioxide (CO2) exchange under two plausible water table regimes: wet and moderately dry. We focused this study on minerotrophic treeless sedge fens, as they are common peatland types at boreal and (sub)arctic areas, which are expected to face the highest rates of climate warming. In addition, fens are expected to respond to environmental changes faster than the nutrient poor bogs. Our study confirmed that CO2 exchange is more strongly affected by drying than warming. Experimental water level draw‐down (WLD) significantly increased gross photosynthesis and ecosystem respiration. Warming alone had insignificant impacts on the CO2 exchange components, but when combined with WLD it further increased ecosystem respiration. In the southern fen, CO2 uptake decreased due to WLD, which was amplified by warming, while at northern fen it remained stable. As a conclusion, our results suggest that a very small difference in the WLD may be decisive, whether the C sink of a fen decreases, or whether the system is able to adapt within its regime and maintain its functions. Moreover, the water table has a role in determining how much the increased temperature impacts the CO2 exchange."

&

Korkiakoski, M., Tuovinen, J.-P., Penttilä, T., Sarkkola, S., Ojanen, P., Minkkinen, K., Rainne, J., Laurila, T., and Lohila, A.: Greenhouse gas and energy fluxes in a boreal peatland forest after clear-cutting, Biogeosciences, 16, 3703–3723, https://doi.org/10.5194/bg-16-3703-2019, 2019.

https://www.biogeosciences.net/16/3703/2019/

Abstract
The most common forest management method in Fennoscandia is rotation forestry, including clear-cutting and forest regeneration. In clear-cutting, stem wood is removed and the logging residues are either removed or left on site. Clear-cutting changes the microclimate and vegetation structure at the site, both of which affect the site's carbon balance. Peat soils with poor aeration and high carbon densities are especially prone to such changes, and significant changes in greenhouse gas exchange can be expected. We measured carbon dioxide (CO2) and energy fluxes with the eddy covariance method for 2 years (April 2016–March 2018) after clear-cutting a drained peatland forest. We observed a significant rise (23 cm) in the water table level and a large CO2 source (first year: 3086±148 g CO2 m−2 yr−1; second year: 2072±124 g CO2 m−2 yr−1). These large CO2 emissions resulted from the very low gross primary production (GPP) following the removal of photosynthesizing trees and the decline of ground vegetation, unable to compensate for the decomposition of logging residues and peat. During the second summer (June–August) after the clear-cutting, GPP had already increased by 96 % and total ecosystem respiration decreased by 14 % from the previous summer. The mean daytime ratio of sensible to latent heat flux decreased after harvesting from 2.6 in May 2016 to 1.0 in August 2016, and in 2017 it varied mostly within 0.6–1.0. In April–September, the mean daytime sensible heat flux was 33 % lower and latent heat flux 40 % higher in 2017, probably due to the recovery of ground vegetation that increased evapotranspiration and albedo of the site. In addition to CO2 and energy fluxes, we measured methane (CH4) and nitrous oxide (N2O) fluxes with manual chambers. After the clear-cutting, the site turned from a small CH4 sink into a small source and from N2O neutral to a significant N2O source. Compared to the large CO2 emissions, the 100-year global warming potential (GWP100) of the CH4 emissions was negligible. Also, the GWP100 due to increased N2O emissions was less than 10 % of that of the CO2 emission change.
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Tor Bejnar

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1652 on: October 02, 2019, 10:06:14 PM »
earlier today
Quote
"... If the higher CMIP6 ECS estimates hold true as the archive fills out, this will represent a departure from over four decades of research. Higher-sensitivity climates experience a greater probability of long-term temperature pauses and short-term trends, which can translate to more warming hiatuses or periods of fast temperature increase."
very interesting, indeed.  More data for deniers ("pauses") and then ghost-white faces.  :'(
Arctic ice is healthy for children and other living things.

Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1653 on: October 02, 2019, 10:18:19 PM »
One significant reason (others include: more than expected heat has gone into the oceans and into melting ice and that the negative impact of aerosols were greater than previously assumed) that estimates of ECS based on observed changes in mean global temperature are lower than what society is likely going to face for the rest of this century...

Recent studies indicate that the aerosol effect has been overestimated, not underestimated.

https://www.nature.com/articles/s41467-018-05592-9

Quote
Abstract
Uncertainty in pre-industrial natural aerosol emissions is a major component of the overall uncertainty in the radiative forcing of climate. Improved characterisation of natural emissions and their radiative effects can therefore increase the accuracy of global climate model projections. Here we show that revised assumptions about pre-industrial fire activity result in significantly increased aerosol concentrations in the pre-industrial atmosphere. Revised global model simulations predict a 35% reduction in the calculated global mean cloud albedo forcing over the Industrial Era (1750–2000 CE) compared to estimates using emissions data from the Sixth Coupled Model Intercomparison Project. An estimated upper limit to pre-industrial fire emissions results in a much greater (91%) reduction in forcing. When compared to 26 other uncertain parameters or inputs in our model, pre-industrial fire emissions are by far the single largest source of uncertainty in pre-industrial aerosol concentrations, and hence in our understanding of the magnitude of the historical radiative forcing due to anthropogenic aerosol emissions.

Quote
Depending on the emitted species, modelled total global fire emissions in the PI are estimated to be between approximately two-and-a-half and five times higher than those in the CMIP6 dataset (Supplementary Table 2), reflecting the large contribution to the uncertainty in fire emissions from fire modelling processes and assumptions about land use change (see Methods). These differences also lie well outside the perturbations assumed in multi-model sensitivity studies36, and have a different spatial distribution due to differences in fire emissions corresponding with changes in the location of PI fire occurrence rather than a uniform global increase. Seasonal patterns in fire emissions are similar between fire models, except in spring where LMfire simulates significantly more emissions than SIMFIRE-BLAZE in both hemispheres (Supplementary Figure 4). Overall, the fire model simulations suggest that a large source of PI aerosol emissions is currently missing from climate models and the CMIP6 experiments.

https://www.nature.com/articles/s41467-019-08407-7

Quote
Abstract
Organic nucleation is an important source of atmospheric aerosol number concentration, especially in pristine continental regions and during the preindustrial period. Here, we improve on previous simulations that overestimate boundary layer nucleation in the tropics and add changes to climate and land use to evaluate climate forcing. Our model includes both pure organic nucleation and heteromolecular nucleation of sulfuric acid and organics and reproduces the profile of aerosol number concentration measured in the Amazon. Organic nucleation decreases the sum of the total aerosol direct and indirect radiative forcing by 12.5%. The addition of climate and land use change decreases the direct radiative forcing (−0.38 W m−2) by 6.3% and the indirect radiative forcing (−1.68 W m−2) by 3.5% due to the size distribution and number concentration change of secondary organic aerosol and sulfate. Overall, the total radiative forcing associated with anthropogenic aerosols is decreased by 16%.

Unfortunately, it appears that the CMIP6 models are being run with aerosol effects that are higher than they should be, so that may explain why they're coming in with higher ECS than the CMIP5 models (which tend to run hotter than observations).

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1654 on: October 03, 2019, 12:11:30 AM »
...

Recent studies indicate that the aerosol effect has been overestimated, not underestimated.

...

The linked reference, and associated article, indicate that previous estimates of the cooling effect of aerosols in recent decades have been underestimated.  Thus, by the time consensus climate scientists finally converge on a more certain determination of the impact of aerosols (including cloud feedbacks); we may already have crossed various Earth System tipping points:

Daniel Rosenfeld, Yannian Zhu, Minghuai Wang, Youtong Zheng, Tom Goren, Shaocai Yu. Aerosol-driven droplet concentrations dominate coverage and water of oceanic low level clouds. Science, 2019; eaav0566 DOI: 10.1126/science.aav0566

https://science.sciencemag.org/content/363/6427/eaav0566

Structured Abstract
INTRODUCTION

Human-made emissions of particulate air pollution can offset part of the warming induced by emissions of greenhouse gases, by enhancing low-level clouds that reflect more solar radiation back to space. The aerosol particles have this effect because cloud droplets must condense on preexisting tiny particles in the same way as dew forms on cold objects; more aerosol particles from human-made emissions lead to larger numbers of smaller cloud droplets. One major pathway for low-level cloud enhancement is through the suppression of rain by reducing cloud droplet sizes. This leaves more water in the cloud for a longer time, thus increasing the cloud cover and water content and thereby reflecting more solar heat to space. This effect is strongest over the oceans, where moisture for sustaining low-level clouds over vast areas is abundant. Predicting global warming requires a quantitative understanding of how cloud cover and water content are affected by human-made aerosols.

RATIONALE
Quantifying the aerosol cloud–mediated radiative effects has been a major challenge and has driven the uncertainty in climate predictions. It has been difficult to measure cloud-active aerosols from satellites and to isolate their effects on clouds from meteorological data. The development of novel methodologies to retrieve cloud droplet concentrations and vertical winds from satellites represents a breakthrough that made this quantification possible. The methodologies were applied to the world’s oceans between the equator and 40°S. Aerosol and meteorological variables explained 95% of the variability in the cloud radiative effects.

RESULTS
The measured aerosol cloud–mediated cooling effect was much larger than the present estimates, especially via the effect of aerosols on the suppression of precipitation, which makes the clouds retain more water, persist longer, and have a larger fractional coverage. This goes against most previous observations and simulations, which reported that vertically integrated cloud water may even decrease with additional aerosols, especially in precipitating clouds. The major reason for this apparent discrepancy is because deeper clouds have more water and produce rainfall more easily, thus scavenging the aerosols more efficiently. The outcome is that clouds with fewer aerosols have more water, but it has nothing to do with aerosol effects on clouds. This fallacy is overcome when assessing the effects for clouds with a given fixed geometrical thickness.

The large aerosol sensitivity of the water content and coverage of shallow marine clouds dispels another belief that the effects of added aerosols are mostly buffered by adjustment of the cloud properties, which counteracts the initial aerosol effect. For example, adding aerosols suppresses rain, so the clouds respond by deepening just enough to restore the rain amount that was suppressed. But the time scale required for the completion of this adjustment process is substantially longer than the life cycle of the cloud systems, which is mostly under 12 hours. Therefore, most of the marine shallow clouds are not buffered for the aerosol effects, which are inducing cooling to a much greater extent than previously believed.

CONCLUSION
Aerosols explain three-fourths of the variability in the cooling effects of low-level marine clouds for a given geometrical thickness. Doubling the cloud droplet concentration nearly doubles the cooling. This reveals a much greater sensitivity to aerosols than previously reported, meaning too much cooling if incorporated into present climate models. This argument has been used to dismiss such large sensitivities. To avoid that, the aerosol effects in some of the models were tuned down. Accepting the large sensitivity revealed in this study implies that aerosols have another large positive forcing, possibly through the deep clouds, which is not accounted for in current models. This reveals additional uncertainty that must be accounted for and requires a major revision in calculating Earth’s energy budget and climate predictions. Paradoxically, this advancement in our knowledge increases the uncertainty in aerosol cloud–mediated radiative forcing. But it paves the way to eventual substantial reduction of this uncertainty.

Also see:

Title: "We need to rethink everything we know about global warming"

https://www.sciencedaily.com/releases/2019/01/190122104611.htm
Extract: "New calculations show scientists have grossly underestimated the effects of air pollution

New research shows that the degree to which aerosols cool the earth has been grossly underestimated, necessitating a recalculation of climate change models to more accurately predict the pace of global warming."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1655 on: October 03, 2019, 07:49:15 PM »
While it is not correct to directly compare our current climate situation with paleo cases, the fact that the linked reference (& associate article) finds GMSL was about 20 meters higher during the mid-Pliocene warm period (when GMSTA was about 2C about pre-industrial) than today is not comforting news:

G. R. Grant et al. (2019), "The amplitude and origin of sea-level variability during the Pliocene epoch", Nature, DOI: https://doi.org/10.1038/s41586-019-1619-z

https://www.nature.com/articles/s41586-019-1619-z

Abstract: "Earth is heading towards a climate that last existed more than three million years ago (Ma) during the ‘mid-Pliocene warm period’, when atmospheric carbon dioxide concentrations were about 400 parts per million, global sea level oscillated in response to orbital forcing and peak global-mean sea level (GMSL) may have reached about 20 metres above the present-day value. For sea-level rise of this magnitude, extensive retreat or collapse of the Greenland, West Antarctic and marine-based sectors of the East Antarctic ice sheets is required. Yet the relative amplitude of sea-level variations within glacial–interglacial cycles remains poorly constrained. To address this, we calibrate a theoretical relationship between modern sediment transport by waves and water depth, and then apply the technique to grain size in a continuous 800-metre-thick Pliocene sequence of shallow-marine sediments from Whanganui Basin, New Zealand. Water-depth variations obtained in this way, after corrections for tectonic subsidence, yield cyclic relative sea-level (RSL) variations. Here we show that sea level varied on average by 13 ± 5 metres over glacial–interglacial cycles during the middle-to-late Pliocene (about 3.3–2.5 Ma). The resulting record is independent of the global ice volume proxy (as derived from the deep-ocean oxygen isotope record) and sea-level cycles are in phase with 20-thousand-year (kyr) periodic changes in insolation over Antarctica, paced by eccentricity-modulated orbital precession between 3.3 and 2.7 Ma. Thereafter, sea-level fluctuations are paced by the 41-kyr period of cycles in Earth’s axial tilt as ice sheets stabilize on Antarctica and intensify in the Northern Hemisphere. Strictly, we provide the amplitude of RSL change, rather than absolute GMSL change. However, simulations of RSL change based on glacio-isostatic adjustment show that our record approximates eustatic sea level, defined here as GMSL unregistered to the centre of the Earth. Nonetheless, under conservative assumptions, our estimates limit maximum Pliocene sea-level rise to less than 25 metres and provide new constraints on polar ice-volume variability under the climate conditions predicted for this century."

See also:

Title: "If warming exceeds 2°C, Antarctica’s melting ice sheets could raise seas 20 metres in coming centuries"

https://theconversation.com/if-warming-exceeds-2-c-antarcticas-melting-ice-sheets-could-raise-seas-20-metres-in-coming-centuries-124484

Extract: "The Pliocene was the last time atmospheric carbon dioxide concentrations were above 400 parts per million and Earth’s temperature was 2°C warmer than pre-industrial times. We show that warming of more than 2°C could set off widespread melting in Antarctica once again and our planet could be hurtling back to the future, towards a climate that existed three million years ago.

Our study has important implications for the stability and sensitivity of the Antarctic ice sheet and its potential to contribute to future sea levels. It supports the concept that a tipping point in the Antarctic ice sheet may be crossed if global temperatures are allowed to rise by more than 2℃. This could result in large parts of the ice sheet being committed to melt-down over the coming centuries, reshaping shorelines around the world."
« Last Edit: October 03, 2019, 08:19:40 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1656 on: October 03, 2019, 11:55:10 PM »
The linked reference warns that potential future increases in precipitation directly into the Arctic Ocean has potential to trigger the release of excess freshwater currently being stored in the Arctic Ocean (see prior discussion of how the Beaufort Gyre stores freshwater, e.g. Reply #1547) into the North Atlantic Ocean in sufficient quantities to ' … affect the global ocean circulation'.  This is not good news as such an abrupt release of freshwater would slow the MOC; which would at least temporarily increase climate sensitivity:

Nicola Jane Brown et al. (21 June 2019), "Arctic Ocean Freshwater Dynamics: Transient Response to Increasing River Runoff and Precipitation", JGR Oceans, https://doi.org/10.1029/2018JC014923

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JC014923

Abstract
Simulations from a coupled ice‐ocean general circulation model are used to assess the effects on Arctic Ocean freshwater storage of changes in freshwater input through river runoff and precipitation. We employ the climate response function framework to examine responses of freshwater content to abrupt changes in freshwater input. To the lowest order, the response of ocean freshwater content is linear, with an adjustment time scale of approximately 10 years, indicating that anomalies in Arctic Ocean freshwater export are proportional to anomalies in freshwater content. However, the details of the transient response of the ocean depend on the source of freshwater input. An increase in river runoff results in a fairly smooth response in freshwater storage consistent with an essentially linear relation between total freshwater content and discharge of excess freshwater through the main export straits. However, the response to a change in precipitation is subject to greater complexity, which can be explained by the localized formation and subsequent export of salinity anomalies which introduce additional response time scales. The results presented here suggest that future increases in Arctic Ocean freshwater input in the form of precipitation are more likely to be associated with variability in the storage and release of excess freshwater than are increases in freshwater input from river runoff.

Plain Language Summary
This paper shows that the Arctic Ocean adjusts to changes in freshwater input over time scales of about one decade. How much of the added freshwater is stored in the Arctic depends, however, on how the freshwater enters the ocean. If it arrives as additional river runoff, the response in Arctic freshwater storage is relatively smooth and predictable. If it falls, instead, as increased precipitation, the response is less easy to predict because it is complicated by interactions between the ocean and sea ice. This is important because the part of the freshwater that is not stored in the Arctic Ocean is exported to the North Atlantic, where it can affect the global ocean circulation.

Edit: I note that consensus models project that with continuing global warming, rainfall will increase in the Arctic in coming decades; which will not only impact: Arctic sea ice extent, potential release of excess freshwater from the Arctic Ocean, glacial ice, but also permafrost (which will not only increase CO2 emissions, but also methane emissions from thermal karst lakes).
« Last Edit: October 04, 2019, 02:56:20 AM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1657 on: October 04, 2019, 07:34:52 AM »

Edit: I note that consensus models project that with continuing global warming, rainfall will increase in the Arctic in coming decades; which will not only impact: Arctic sea ice extent, potential release of excess freshwater from the Arctic Ocean, glacial ice, but also permafrost (which will not only increase CO2 emissions, but also methane emissions from thermal karst lakes).

Imagine what Bintanja (2018) would project if it had used a model with ECS greater than 5C:

R. Bintanja (2018), "The impact of Arctic warming on increased rainfall", Scientific Reports,  8, Article number: 16001, DOI: https://doi.org/10.1038/s41598-018-34450-3

https://www.nature.com/articles/s41598-018-34450-3

Abstract: "The Arctic region is warming two to three times faster than the global mean, intensifying the hydrological cycle in the high north. Both enhanced regional evaporation and poleward moisture transport contribute to a 50–60% increase in Arctic precipitation over the 21st century. The additional precipitation is diagnosed to fall primarily as rain, but the physical and dynamical constraints governing the transition to a rain-dominated Arctic are unknown. Here we use actual precipitation, snowfall, rainfall output of 37 global climate models in standardised 21st-century simulations to demonstrate that, on average, the main contributor to additional Arctic (70–90°N) rainfall is local warming (~70%), whereas non-local (thermo)dynamical processes associated with precipitation changes contribute only 30%. Surprisingly, the effect of local warming peaks in the frigid high Arctic, where modest summer temperature changes exert a much larger effect on rainfall changes than strong wintertime warming. This counterintuitive seasonality exhibits steep geographical gradients, however, governed by non-linear changes in the temperature-dependent snowfall fraction, thereby obscuring regional-scale attribution of enhanced Arctic rainfall to climate warming. Detailed knowledge of the underlying causes behind Arctic snow/rainfall changes will contribute to more accurate assessments of the (possibly irreversible) impacts on hydrology/run-off, permafrost thawing, ecosystems, sea ice retreat, and glacier melt."
« Last Edit: October 04, 2019, 07:57:03 AM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1658 on: October 05, 2019, 03:32:54 AM »
The linked article discusses how in large portions of Siberia not only is the permafrost degrading rapidly, but also the local rise of mean surface temperature is already over 3C above pre-industrial conditions.  While this is bad enough, I remind readers that as the Tropical Pacific Ocean SST increases, this heat energy is telecommunicated via an Atmospheric Bridge directly to the Bering Sea, parts of Alaska and parts of Canada; and all of this heat (in Siberia, the Bering Sea, Alaska and Canada) eventually gets transferred by local winds over the Arctic Ocean, where the heat can cause rain to fall instead of snow; and in the coming decades such rainfall over the Arctic Ocean could trigger an abrupt loss of Arctic Sea Ice area and an associated albedo flip:

Title: "Radical warming in Siberia leaves millions on unstable ground"

https://www.washingtonpost.com/graphics/2019/national/climate-environment/climate-change-siberia/

Extract: "… Siberia has warmed up faster than almost anywhere else on Earth. Scientists say the planet's warming must not exceed 1.5 degrees Celsius — but Siberia's temperatures have already spiked far beyond that.

A Washington Post analysis found that the region near the town of Zyryanka, in an enormous wedge of eastern Siberia called Yakutia, has warmed by more than 3 degrees Celsius since preindustrial times — roughly triple the global average.

For the 5.4 million people who live in Russia’s permafrost zone, the new climate has disrupted their homes and their livelihoods. Rivers are rising and running faster, and entire neighborhoods are falling into them. Arable land for farming has plummeted by more than half, to just 120,000 acres in 2017.

In Yakutia, an area one-third the size of the United States, cattle and reindeer herding have plunged 20 percent as the animals increasingly battle to survive the warming climate’s destruction of pastureland."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1659 on: October 05, 2019, 10:19:19 AM »
The first linked reference indicates that currently major atmospheric river (AR) events can markedly increase ice melting in Greenland, and currently some of the precipitation from such AR events fall as snow, so imagine what will happen with continuing global warming when more of such precipitation will fall as rain.

The second linked reference shows that extratropical cyclones (ECs) and atmospheric rivers (ARs) frequently reinforce one another.  Here I note that both ECs and ARs telecommunicate heat energy poleward from the tropical oceans, and that some of this heat energy get advected into the Artic and Antarctic regions where it can help induce local rainfall that can melt for snow & ice, particularly with continuing global warming.

The third linked reference (& associated article) indicate that with continued global warming, the frequency of intense atmospheric river (AR) events will likely double in coming decades.  As large ARs telecommunicate more energy poleward than less intense ARs this trend will certainly contribute to Polar Amplification:

K. S. Mattingly et al. (25 July 2018) "Atmospheric River Impacts on Greenland Ice Sheet Surface Mass Balance", JGR Atmospheres, https://doi.org/10.1029/2018JD028714

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028714

Abstract: "Greenland Ice Sheet (GrIS) mass loss has accelerated since the turn of the twenty‐first century. Several recent episodes of rapid GrIS ablation coincided with intense moisture transport over Greenland by atmospheric rivers (ARs), suggesting that these events influence the evolution of GrIS surface mass balance (SMB). ARs likely provide melt energy through several physical mechanisms, and conversely, may increase SMB through enhanced snow accumulation. In this study, we compile a long‐term (1980–2016) record of moisture transport events using a conventional AR identification algorithm as well as a self‐organizing map classification applied to MERRA‐2 data. We then analyze AR effects on the GrIS using melt data from passive microwave satellite observations and regional climate model output. Results show that anomalously strong moisture transport by ARs clearly contributed to increased GrIS mass loss in recent years. AR activity over Greenland was above normal throughout the 2000s and early 2010s, and recent melting seasons with above‐average GrIS melt feature positive moisture transport anomalies over Greenland. Analysis of individual AR impacts shows a pronounced increase in GrIS surface melt after strong AR events. AR effects on SMB are more complex, as strong summer ARs cause sharp SMB losses in the ablation zone that exceed moderate SMB gains induced by ARs in the accumulation zone during summer and in all areas during other seasons. Our results demonstrate the influence of the strongest ARs in controlling GrIS SMB, and we conclude that projections of future GrIS SMB should accurately capture these rare ephemeral events."

&

Zhenhai Zhang et al. (10 September 2018), "The Relationship Between Extratropical Cyclone Strength and Atmospheric River Intensity and Position", Geophysical Research Letters, https://doi.org/10.1029/2018GL079071

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL079071

Abstract
Extratropical cyclones (ECs) and atmospheric rivers (ARs) impact precipitation over the U.S. West Coast and other analogous regions globally. This study investigates the relationship between ECs and ARs by exploring the connections between EC strength and AR intensity and position using a new AR intensity scale. While 82% of ARs are associated with an EC, only 45% of ECs have a paired AR and the distance between the AR and EC varies greatly. Roughly 20% of ARs (defined by vertically integrated water vapor transport) occur without a nearby EC. These are usually close to a subtropical/tropical moisture source and include an anticyclone. AR intensity is only moderately proportional to EC strength. Neither the location nor intensity of an AR can be simply determined by an EC. Greater EC intensification occurs with stronger ARs, suggesting that ARs enhance EC deepening by providing more water vapor for latent heat release.

Plain Language Summary
Both extratropical cyclones and atmospheric rivers have impact on precipitation over the U.S. West Coast, and they are often mentioned together. However, the relationship between the two is not completely understood. In this study, we have examined the connections between extratropical cyclone strength and atmospheric river intensity and position. While 82% of atmospheric rivers are related to a cyclone, only 45% of cyclones have an accompanied atmospheric river. The distance between the two varies from about 300 km to over 2,000 km. Roughly 20% of atmospheric rivers occur without a nearby cyclone. These cases are close to the subtropical/tropical moisture source and are related to a high pressure. While cyclones can enhance atmospheric rivers with stronger wind, neither the location nor the intensity of an atmospheric river can be simply determined by a cyclone. On the other hand, atmospheric rivers with strong water vapor transport provide favorable conditions for cyclone intensification. Our results provide a comprehensive analysis of the relationship between atmospheric rivers and extratropical cyclones. This work improves the understanding of the dynamical mechanism for heavy precipitation over the U.S. West Coast and thus provides more reliable information on long‐term flood control and water planning.

&


Vicky Espinoza et al. (19 April 2018), "Global Analysis of Climate Change Projection Effects on Atmospheric Rivers", Geophysical Research Letters, https://doi.org/10.1029/2017GL076968

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017GL076968

Abstract
A uniform, global approach is used to quantify how atmospheric rivers (ARs) change between Coupled Model Intercomparison Project Phase 5 historical simulations and future projections under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 warming scenarios. The projections indicate that while there will be ~10% fewer ARs in the future, the ARs will be ~25% longer, ~25% wider, and exhibit stronger integrated water vapor transports (IVTs) under RCP8.5. These changes result in pronounced increases in the frequency (IVT strength) of AR conditions under RCP8.5: ~50% (25%) globally, ~50% (20%) in the northern midlatitudes, and ~60% (20%) in the southern midlatitudes. The models exhibit systematic low biases across the midlatitudes in replicating historical AR frequency (~10%), zonal IVT (~15%), and meridional IVT (~25%), with sizable intermodel differences. A more detailed examination of six regions strongly impacted by ARs suggests that the western United States, northwestern Europe, and southwestern South America exhibit considerable intermodel differences in projected changes in ARs.

Plain Language Summary
Atmospheric rivers (ARs) are elongated strands of horizontal water vapor transport, accounting for over 90% of the poleward water vapor transport across midlatitudes. These “rivers in the sky” have important implications for extreme precipitation when they make landfall, particularly along the west coasts of many midlatitude continents (e.g., North America, South America, and West Europe) due to orographic lifting. ARs are important contributors to extreme weather and precipitation events, and while their presence can contribute to beneficial rainfall and snowfall, which can mitigate droughts, they can also lead to flooding and extreme winds. This study takes a uniform, global approach that is used to quantify how ARs change between Coupled Model Intercomparison Project Phase 5 historical simulations and future projections under the Representative Concentration Pathway (RCP) 4.5 and RCP8.5 warming scenarios globally. The projections indicate that while there will be ~10% fewer ARs in the future, the ARs will be ~25% longer, ~25% wider, and exhibit stronger integrated water vapor transports under RCP8.5. These changes result in pronounced increases in the frequency (integrated water vapor transport strength) of AR conditions under RCP8.5: ~50% (25%) globally, ~50% (20%) in the northern midlatitudes, and ~60% (20%) in the southern midlatitudes.

See also:

Title: "Climate change may lead to bigger atmospheric rivers"

https://climate.nasa.gov/news/2740/climate-change-may-lead-to-bigger-atmospheric-rivers/

Extract: ""The results project that in a scenario where greenhouse gas emissions continue at the current rate, there will be about 10 percent fewer atmospheric rivers globally by the end of the 21st century," said the study's lead author, Duane Waliser, of NASA's Jet Propulsion Laboratory in Pasadena, California. "However, because the findings project that the atmospheric rivers will be, on average, about 25 percent wider and longer, the global frequency of atmospheric river conditions -- like heavy rain and strong winds -- will actually increase by about 50 percent."

The results also show that the frequency of the most intense atmospheric river storms is projected to nearly double."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1660 on: October 05, 2019, 05:54:16 PM »
ENSO conditions are neutral this year and yet we already having several months of record-breaking heat for such months; with the monthly GMSTA for September 2019 being more than 1.2C above pre-industrial.  We are steadily moving towards an annual GMSTA of 1.5C above pre-industrial:

Title: "Earth just experienced its hottest September, as 2019 heads for the record books"

https://www.washingtonpost.com/weather/2019/10/04/earth-just-experienced-its-hottest-september-heads-record-books/

Extract: "September 2019 was the warmest such month on record, tying the old record set in 2016, according to the Copernicus Climate Change Service, an organization funded by the European Union that tracks global temperatures. This makes September the fourth-straight month “to be close to or breaking a temperature record,” according to an agency statement.

Based on Copernicus’s data, which uses computer models fed with billions of observations from air, land and sea, June 2019 set a record high for that month, July 2019 was the warmest month ever recorded, and August 2019 was the second-warmest such month globally.

According to Copernicus, September was about 1.02 degrees above the 1981-2010 average for the month, and about 1.2 degrees above the preindustrial level. It was also slightly warmer, by about 0.04 degrees, than September 2016, which had been the warmest such month on record."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1661 on: October 06, 2019, 02:34:22 AM »
As in recent posts I have been mentioning that an increase in Arctic rainfall (with continued global warming) could cause an albedo flip in coming decades; I thought that I should post the linked reference that helps to quantify the contributions of both sea ice and land snow to climate feedback:

Lei Duan  Long Cao  Ken Caldeira (07 January 2019), "Estimating Contributions of Sea Ice and Land Snow to Climate Feedback", JGR Atmospheres, https://doi.org/10.1029/2018JD029093

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JD029093

Abstract
In this study, we use the National Center for Atmospheric Research Community Earth System Model to investigate the contribution of sea ice and land snow to the climate sensitivity in response to increased atmospheric carbon dioxide content. We focus on the overall effect arising from the presence or absence of sea ice and/or land snow. We analyze our results in terms of the radiative forcing and climate feedback parameter. We find that the presence of sea ice and land snow decreases the climate feedback parameter (and thus increases climate sensitivity). Adjusted radiative forcing from added carbon dioxide is comparatively less sensitive to the presence of sea ice or land snow. The effect of sea ice on the climate feedback parameter decreases as sea ice cover diminishes at higher CO2 concentration. However, the influence of both sea ice and land snow on the climate feedback parameter remains substantial under the CO2 concentration range considered here (to eight times preindustrial CO2 content). Approximately, one quarter of the effect of sea ice and land snow on the climate feedback parameter is a consequence of the effect of these components on longwave feedback that is mainly associated with cloud change. Polar warming in response to added CO2 is approximately doubled by the presence of sea ice and land snow. Relative to the case in which sea ice and land snow are absent in the model, in response to increased CO2 concentrations, the presence of sea ice and land snow results in an increase in global mean warming by over 40%.

Plain Language Summary
Sea ice and land snow are two crucial components that affect the climate response to external forcings. Feedbacks between ice/snow and climate change cause amplified surface warming in high latitudes. In this study, we use a climate model to estimate the contribution of sea ice and land snow to climate change in response to increased CO2 concentrations. We compare the climate response to increased CO2 between the simulations with sea ice and/or land snow and the simulations without them. We show that the existence of sea ice and land snow substantially amplifies the global temperature response to increased CO2 with sea ice having a stronger effect than land snow. Under higher CO2 levels, the effect of sea ice diminishes more rapidly than does the effect of land snow. About one quarter of the total climate feedback from sea ice and land snow is associated with the change in longwave radiation. Also we show that the effect of sea ice and land snow on the sensitivity of top‐of‐atmosphere net energy flux to the global mean temperature change is approximately additive.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1662 on: October 06, 2019, 02:54:51 AM »
By using a high resolution global coupled climate model the authors of the linked reference identified an important mechanism for slowing the AMOC; which is associated with the impacts of weaker local winds on the North Atlantic Subpolar Gyre (SPG); which needs to be added to other mechanisms for slowing the MOC (with continued global warming) such as a collapse of the WAIS (sending an armada of icebergs into the Southern Ocean) and a release of excess freshwater from the Beaufort Gyre triggered by rainfall into the Artic Ocean (particularly on to sea ice):

D. A. Putrasahan  K. Lohmann  J.‐S. von Storch  J. H. Jungclaus  O. Gutjahr  H. Haak (16 April 2019), "Surface Flux Drivers for the Slowdown of the Atlantic Meridional Overturning Circulation in a High‐Resolution Global Coupled Climate Model", JAMES, https://doi.org/10.1029/2018MS001447

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018MS001447

Abstract: "This paper investigates the causation for the decline of the Atlantic Meridional Overturning Circulation (AMOC) from approximately 17 Sv to about 9 Sv, when the atmospheric resolution of the Max Planck Institute‐Earth System Model is enhanced from ∼1° to ∼0.5°. The results show that the slowdown of the AMOC is caused by the cessation of deep convection. In most modeling studies, this is thought to be controlled by buoyancy fluxes in the convective regions, for example, by surface freshwater flux that is introduced locally or via enormous input from glacier or iceberg melts. While we find that freshwater is still the key to the reduction of AMOC seen in the higher‐resolution run, the freshening of the North Atlantic does not need to be directly caused by local freshwater fluxes. Instead, it can be caused indirectly through winds via a reduced wind‐driven gyre circulation and salinity transport associated to this circulation, as seen in the higher‐resolution run."

Extract: "While the enhancement of model resolution is typically expected to provide beneficial improvements to a climate model, challenges still abound. We see that in MPI‐ESM, AMOC of 17 Sv starting from an equilibrium state achieved at a lower atmospheric resolution slows down to almost half its original value when atmospheric resolution is enhanced. This decline of the AMOC is strongly related to the freshening and cooling of the Labrador Sea through the salinity‐advection feedback (Figure 8 ). While resolution‐induced differences in local heat and freshwater fluxes can contribute to the decay in AMOC, weaker surface wind stress seen in the higher‐resolution simulation plays a much more prominent role, particularly the winds over the subpolar North Atlantic. These weaker winds dynamically spin down the SPG, resulting in reduced heat and salt transport from the subtropics, thereby freshening and cooling the subpolar region. This promotes sea ice formation in the Labrador Sea, and the increased presence of sea ice inhibits deep convection and deep water formation, thus slowing down the AMOC. This in turn further reduces the northward transport heat and salt and provides the positive feedback that would prevent the recovery of the AMOC. For future work, it would be of interest to evaluate the impact of enhanced ocean resolution on the AMOC."

Edit: If it is not clear to some readers why a slowdown of the AMOC/MOC would contribute to potential abrupt global warming in coming decades; such a slowdown would increase the SST of the Tropical Oceans; which would accelerate the evaporation of tropical seawater; which would have major impacts of the poleward telecommunication of heat energy from the tropics, and also would promote the formation of more high altitude clouds (resulting in an increase in this positive feedback) and would promote a decrease in low altitude cloud formation (resulting in a decrease in this negative feedback).
« Last Edit: October 06, 2019, 03:06:02 AM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1663 on: October 06, 2019, 04:02:56 PM »
The linked commentary reminds us that the wildfires currently burning in the Gran Chaco rainforest of Bolivia are on track to post a record setting year:

Title: "Fires still being set in blazing Bolivia (commentary)"

https://news.mongabay.com/2019/10/fires-still-being-set-in-blazing-bolivia-commentary/

Extract: "Despite over six weeks of firefighting, the infernos destroying Bolivia’s forests continue to spread. 5.3 million hectares (about 13.1 million acres) — an area larger than the whole of Costa Rica — have been destroyed, and about 40 percent of that area was forest. A perfect storm of factors — from an unusually dry year, probably linked to climate change, to a new law allowing burning of forest lands — have combined to make this one of the worst years this century for forest fires in the megadiverse nation.
But are these fires out of the ordinary?

Fires are set every year in Bolivia, usually to clear land for agriculture. But Assistant Professor Carwil Bjork-James of Vanderbilt University says that the fires this year are especially severe: “We are seeing a dramatic year in terms of the numbers of fires blazing in Bolivia, and the acreage consumed by them. If the fires continue at their current pace, it will be the second worst year of the twenty-first 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 (narrated video)
« Reply #1664 on: October 06, 2019, 04:20:02 PM »
The linked article indicates that the increasing number of observed meltwater ponds/lakes in Antarctica indicates that previously/currently consensus climate science has underestimated the vulnerability of Antarctic ice shelves and marine glaciers to hydrofracturing:

Title: "Antarctica now has more than 65,000 ‘meltwater lakes’ as summer ice melts"

https://theconversation.com/antarctica-now-has-more-than-65-000-meltwater-lakes-as-summer-ice-melts-124362

Extract: "During the Antarctic summer, thousands of mesmerising blue lakes form around the edges of the continent’s ice sheet, as warmer temperatures cause snow and ice to melt and collect into depressions on the surface. Colleagues of mine at Durham University have recently used satellites to record more than 65,000 of these lakes.

Though seasonal meltwater lakes have formed on the continent for decades, lakes had not been recorded before in such great numbers across coastal areas of East Antarctica. This means parts of the world’s largest ice sheet may be more vulnerable to a warming climate than previously thought.

Much of Antarctica is surrounded by floating platforms of ice, often as tall as a skyscraper. These are “ice shelves”. And when some of these ice shelves have collapsed in the past, satellites have recorded networks of lakes growing and then abruptly disappearing shortly beforehand. For instance, several hundred lakes disappeared in the weeks before the catastrophic disintegration of the Larsen B Ice Shelf – when 3,250 km² of ice broke up in just two months in 2002."
“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 (narrated video)
« Reply #1665 on: October 06, 2019, 04:36:48 PM »
The linked article indicates that almost none of the countries that have promised to get to "net zero" by 2050 have presented measurable plans as to how to get to this goal; which makes such goals subject to 'greenwashing' such as the proposed use of 'offsets' that have been tried previously and has failed just as often.

Title: "The word nobody wanted to say at the UN Climate Action Summit
“Offsets.”"


https://www.salon.com/2019/10/05/the-word-nobody-wanted-to-say-at-the-un-climate-action-summit_partner/

Extract: "The leaders of more than 70 countries have made a promise that sounds nothing short of revolutionary. By 2050, they say they will reach “net zero,” putting no more carbon dioxide into the atmosphere than can be somehow canceled out.

Until countries start filling in the details of how they plan to get to net zero, Frédéric Hache, a former investment banker who scrutinizes environmental markets, worries the benefit could wind up existing only on paper. “Everybody talks about the level of ambition and nobody questions the how,” he said. “The how is at least as important, because that’s where all the greenwashing takes place.”"
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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1666 on: October 07, 2019, 02:22:48 AM »
That Stokes paper referenced in the conversation article is 

doi:10.1038/s41598-019-50343-5

open access. I have commented implications for Amery at

https://forum.arctic-sea-ice.net/index.php/topic,2578.msg232196/topicseen.html#msg232196

That paper references and earlier paper by Alley et al.  (doi: 10.1016/j.rse.2018.03.025 )  who evalued antarctic ice shelf vulnerability to hydrofracture. The measure of vulnerability is the fraction of ice saturated firn. I attach a figure showing that most ice shelves are vulnerable.

sidd
« Last Edit: October 07, 2019, 05:28:26 AM by sidd »

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1667 on: October 07, 2019, 04:18:59 AM »
The linked article shows that meltwater ponding and drainage of an Antarctic ice shelf can cause not only immediate deformation, but also fracturing, of the ice-shelf.  If/when the meltwater flows into such fracture, this can trigger hydrofracturing of the ice-shelf.  Currently, consensus ice-self models do not consider the immediate deformation of ice-shelves from meltwater ponding and drainage:

Alison F. Banwell et al. (2019), "Direct measurements of ice-shelf flexure caused by surface meltwater ponding and drainage", Nature Communications  10, Article number: 730, DOI: https://doi.org/10.1038/s41467-019-08522-5

https://www.nature.com/articles/s41467-019-08522-5

Abstract: "Global sea-level rise is caused, in part, by more rapid ice discharge from Antarctica, following the removal of the restraining forces of floating ice-shelves after their break-up. A trigger of ice-shelf break-up is thought to be stress variations associated with surface meltwater ponding and drainage, causing flexure and fracture. But until now, there have been no direct measurements of these processes. Here, we present field data from the McMurdo Ice Shelf, Antarctica, showing that the filling, to ~2 m depth, and subsequent draining, by overflow and channel incision, of four surface lakes causes pronounced and immediate ice-shelf flexure over multiple-week timescales. The magnitude of the vertical ice-shelf deflection reaches maxima of ~1 m at the lake centres, declining to zero at distances of <500 m. Our results should be used to guide development of continent-wide ice-sheet models, which currently do not simulate ice-shelf break-up due to meltwater loading and unloading."
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1668 on: October 07, 2019, 05:55:20 AM »

Thus, I reject calling any of these models "the best".
https://isccp.giss.nasa.gov/role.html
I prefer to think of the scientific method as a process that is continually improving climate change models, and as an example of the next generation (of new & improved) climate change models, I provide the following link to special issues of the JGR Atmospheres publication, update September 13, 2019, focused on the Energy Exascale Earth System Model (E3SM), which is one of the CMIP6 preliminarily indicating that the mean value of ECS is currently over 5C (as discussed earlier in this thread):
Title: "The Energy Exascale Earth System Model"
https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169-8996.ENERGY1

ASLR, thanks for providing those references to the open source project E3SMv1. I read some of the articles that disclose various details about the modelling work, and want to provide some further insights here.

Unsurprisingly, the model makers continue to have insurmountable difficulties to handle the hydrological cycle/convection issues, as evidenced in the previous generation of CMIP5 models.

It's not astonishing that this particular GCM displays a high ECS, over 5.
"E3SMv1's high climate sensitivity is solely due to its large positive cloud feedback, which causes its net feedback parameter (which quantifies how strongly the 4xCO2 forcing is radiatively damped) to be less negative than all but two CMIP5 models"

My impression is that the model makers delibaretely set this model on a trajectory that is sure to yield a high ECS, starting in around 1990, but that is rather inconsistent with GSTs from around 1960, see the attached figure.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018MS001603

Digging deeper, we go into the art of tweaking/tuning of the models:
"...two adjustments were made to the deep convection scheme in EAMv1. One is to reduce the number of negative buoyancy levels (capeten) that deep convection is allowed to penetrate from 5 to 1. The other is to lift the air parcel launch level (liftlevel) from the model bottom level to 2 levels above. Results showed that these two adjustments, and particularly the rise of parcel launch level, could have significant impact on high clouds and precipitation as well as their vertical structure. They typically act to suppresses deep convection over tropical oceans and enhance convection over lands.
...
Similar to what we saw over the TWP, these EAMv1 configurations have substantially underestimated clouds below 6 km and only show one peak in the upper troposphere. The lack of middle and low clouds over deep convection regions is an issue that needs to be addressed in the future development of EAM"
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018MS001350

The model manipulators would like to be able to include 'more convection', but instead have to suppress convection. Convection is not allowed to be as deep in the model as it is in nature - model makers delibaretely chose to suppress convection.

 "The physical processes associated with deep convection, shallow convection along with cloud macrophysics and cloud microphysics are treated via separate parameterizations in EAMv1. In each parameterization scheme there are multiple, often dozens of, uncertain parameters that cannot be constrained by using direct measurements and so they can be tuned within a reasonable range to improve model fidelity."

What they say here is that they have a lack of data on convection, so they have to guess and tune the models with a range of free parameters.

ASLR, you prefer to think of this as a "scientific method"? Is the art of tweaking and tuning a GCM really science? The modelling magicians themselves describe their method in terms of educated guesses that necessitates physical intuition:

"...combining experience, physical understanding, and educated guesses has difficulty anticipating nonlinear relationships between parameters and model output as soon as the number of parameters exceeds a few (Hourdin et al., 2017). The procedure relies heavily on experienced climate scientists and their physical intuition, and the outcome is not always as expected.
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JD028927

I don't deny that GCM models can be useful to get a hunch about where climate is going, but at the end of the day they are nothing more than the educated guesses built on intuition that go into the tweaking and tuning efforts.
« Last Edit: October 07, 2019, 06:03:42 AM by Hefaistos »

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1669 on: October 07, 2019, 06:38:03 AM »
Yes but .
The error goes both ways .
You think because the models are not perfect you can discount the result .
Unfortunately there is plenty of evidence  that models underestimate the result of our unfortunate experiment in atmospheric physics.


Still think you should be banned for spreading denial  FUD .
 

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1670 on: October 07, 2019, 10:45:42 AM »
...
I don't deny that GCM models can be useful to get a hunch about where climate is going, but at the end of the day they are nothing more than the educated guesses built on intuition that go into the tweaking and tuning efforts.

Any short-comings of such CMIP6 models only serve to increase mankind's climate change risk, rather than providing an excuse to minimize mankind's effort to combat climate change.  Furthermore, the E3SM program is scheduled to coming improving their projections until at least 2027 (see image), because of the difficulty and large number of the problems that they are trying to solve.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1671 on: October 07, 2019, 04:36:03 PM »
Yes but .
The error goes both ways .
...

I concur.  For example the right-tail risk of the ECS PDF plot that you show for the Last Millennium is large.  Also, I note that various reported values for ECS do not report the same thing as they are determined using different assumptions and different procedures and AR5 do not both to normalize these different definitions of ECS.

Finally, I note that as a high current value for ECS means a high current variability (both high and low) for climate response; thus for example, the risk of an extreme storm impacting people's lives exists today.
« Last Edit: October 07, 2019, 11:50:12 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1672 on: October 08, 2019, 12:00:46 AM »
Gavin makes a valid point in his attached Tweet; however, I note that the impact of ice meltwater from both the GIS and the AIS distort the meaning of the SSTs indicated in many of the cool regions shown on his graphic:
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1673 on: October 08, 2019, 06:05:12 PM »
Prior consensus climate science estimates of ice mass loss from the Amundsen Sea Embayment based on satellite measurements have underestimated the viscosity of the local mantle and consequently have previously underestimate ice mass loss from this area by approximately 10%.  If one relies on MISI-type of behavior the more rapid uplift of the local crust might help to stability the local marine glaciers, but if one considers MICI-types of behavior the increase rate of uplift of the local crust will not serve to stabilize the local marine glaciers:

Valentina R. Barletta et al. (22 Jun 2018), "Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability", Science, Vol. 360, Issue 6395, pp. 1335-1339, DOI: 10.1126/science.aao1447

https://science.sciencemag.org/content/360/6395/1335

Abstract
The marine portion of the West Antarctic Ice Sheet (WAIS) in the Amundsen Sea Embayment (ASE) accounts for one-fourth of the cryospheric contribution to global sea-level rise and is vulnerable to catastrophic collapse. The bedrock response to ice mass loss, glacial isostatic adjustment (GIA), was thought to occur on a time scale of 10,000 years. We used new GPS measurements, which show a rapid (41 millimeters per year) uplift of the ASE, to estimate the viscosity of the mantle underneath. We found a much lower viscosity (4 × 1018 pascal-second) than global average, and this shortens the GIA response time scale to decades up to a century. Our finding requires an upward revision of ice mass loss from gravity data of 10% and increases the potential stability of the WAIS against catastrophic collapse.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1674 on: October 08, 2019, 08:46:10 PM »
The linked E3SM PPTX discusses the current high degree of uncertainty in current consensus climate change land models (see the attached image) and what the E3SMv1.1 program is doing to reduce that uncertainty (which is not our friend, despite what some left-tail PDF advocates seem to think):

Title: "Uncertainty quantification methods and application for the E3SM land model"

https://e3sm.org/wp-content/uploads/2019/10/190924_Ricciuto_Sargsyan_opt.pdf

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1675 on: October 08, 2019, 09:10:40 PM »
The linked article discusses how new 'Ghost Forests' are a visible sign of climate change:

Title: "New “Ghost Forests” Are a Sign of Climate Change"

https://www.nathab.com/blog/new-ghost-forests-are-a-sign-of-climate-change/

Extract: "Along vast stretches of North America’s East Coast, rising sea levels are killing trees by inundating them in saltwater. Researchers are calling these dead trees in what used to be thriving freshwater environments “ghost forests.” Although this is occurring around the world, new ghost forests are particularly apparent in the United States, with hundreds of thousands of acres of salt-killed trees spreading from Canada down to Florida and over to Texas.

One thing that scientists do agree upon, though, is that the startling sight of dead trees in once-healthy areas aren’t specters, but easy-to-grasp signs of the consequences of climate change."

Edit: If it is not clear to some readers, relative sea level rise can increase groundwater saliently for several miles inland; which can also stunt/kill vegetation along the world's coastlines.
« Last Edit: October 08, 2019, 10:17:25 PM by AbruptSLR »
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gerontocrat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1676 on: October 08, 2019, 09:22:42 PM »
Gavin makes a valid point in his attached Tweet; however, I note that the impact of ice meltwater from both the GIS and the AIS distort the meaning of the SSTs indicated in many of the cool regions shown on his graphic:
As is shown on the attached graphic from the GRACE-FO data
( http://gravis.gfz-potsdam.de/antarctica ) - interactive map

and as I extracted from the ASCII file they provide.
____________________________________________
Note: The German Partners in the GRACE-FO project ( Helmholtz Centre Potsdam
GFZ - German Research Centre for Geosciences) are being very helpful in getting data out to non-scientists like me - instant answers to my e-mails.. I must write & say thanks.

JPL/NASA seem all about the scientists - never an answer to queries. But maybe they are getting strife from Trump acolytes.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1677 on: October 08, 2019, 10:21:51 PM »

As is shown on the attached graphic from the GRACE-FO data
( http://gravis.gfz-potsdam.de/antarctica ) - interactive map

and as I extracted from the ASCII file they provide.
____________________________________________
Note: The German Partners in the GRACE-FO project ( Helmholtz Centre Potsdam
GFZ - German Research Centre for Geosciences) are being very helpful in getting data out to non-scientists like me - instant answers to my e-mails.. I must write & say thanks.

JPL/NASA seem all about the scientists - never an answer to queries. But maybe they are getting strife from Trump acolytes.

As noted in Reply #1673, almost certainly the GRACE-FO ice mass values need to be increase by about 10%, due to more rapid than previously assumed ice rebound (i.e. the increasing mass of the mantle associated with the rapid rebound, can fool gravity measurements into believing that less ice mass has been lost than is actually the case).

Edit:  Also, I note that to date most of the freshwater released from Antarctica into the Southern Ocean has come from ice shelves and this ice mass loss is not measured by GRACE-FO and needs to be added separately, in order to evaluate the impact of the surface water freshening/cooling; which not only reduces the local SSTA but also accelerates the accumulation of warm deep water in the Southern Ocean; which in turn accelerates ice mass loss from both ice shelves and from marine glaciers in Antarctia.
« Last Edit: October 08, 2019, 10:36:03 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1678 on: October 08, 2019, 10:53:40 PM »
In regards to ice mass loss from Antarctic ice shelves, I provide the following information:

Sutterley, T. C., Markus, T., Neumann, T. A., van den Broeke, M., van Wessem, J. M., and Ligtenberg, S. R. M.: Antarctic ice shelf thickness change from multimission lidar mapping, The Cryosphere, 13, 1801–1817, https://doi.org/10.5194/tc-13-1801-2019, 2019.

https://www.the-cryosphere.net/13/1801/2019/

Abstract

We calculate rates of ice thickness change and bottom melt for ice shelves in West Antarctica and the Antarctic Peninsula from a combination of elevation measurements from NASA–CECS Antarctic ice mapping campaigns and NASA Operation IceBridge corrected for oceanic processes from measurements and models, surface velocity measurements from synthetic aperture radar, and high-resolution outputs from regional climate models. The ice thickness change rates are calculated in a Lagrangian reference frame to reduce the effects from advection of sharp vertical features, such as cracks and crevasses, that can saturate Eulerian-derived estimates. We use our method over different ice shelves in Antarctica, which vary in terms of size, repeat coverage from airborne altimetry, and dominant processes governing their recent changes. We find that the Larsen-C Ice Shelf is close to steady state over our observation period with spatial variations in ice thickness largely due to the flux divergence of the shelf. Firn and surface processes are responsible for some short-term variability in ice thickness of the Larsen-C Ice Shelf over the time period. The Wilkins Ice Shelf is sensitive to short-timescale coastal and upper-ocean processes, and basal melt is the dominant contributor to the ice thickness change over the period. At the Pine Island Ice Shelf in the critical region near the grounding zone, we find that ice shelf thickness change rates exceed 40 m yr−1, with the change dominated by strong submarine melting. Regions near the grounding zones of the Dotson and Crosson ice shelves are decreasing in thickness at rates greater than 40 m yr−1, also due to intense basal melt. NASA–CECS Antarctic ice mapping and NASA Operation IceBridge campaigns provide validation datasets for floating ice shelves at moderately high resolution when coregistered using Lagrangian methods.

&

E. Rignot et al. (Jul 2013), "Ice-Shelf Melting Around Antarctica", Science, Vol. 341, Issue 6143, pp. 266-270, DOI: 10.1126/science.1235798

https://science.sciencemag.org/content/341/6143/266.abstract

Major Meltdown
The ice shelves and floating ice tongues that surround Antarctica cover more than 1.5 million square kilometers—approximately the size of the entire Greenland Ice Sheet. Conventional wisdom has held that ice shelves around Antarctica lose mass mostly by iceberg calving, but recently it has become increasingly clear that melting by a warming ocean may also be important. Rignot et al. (p. 266, published 13 June) present detailed glaciological estimates of ice-shelf melting around the entire continent of Antarctica, which show that basal melting accounts for as much mass loss as does calving.

Abstract
We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1679 on: October 08, 2019, 11:17:58 PM »
The linked reference indicates that without sufficient nitrogen, the grow potential of marsh plants is limited at elevated CO2 levels:

Meng Lu et al. (2019), "Nitrogen status regulates morphological adaptation of marsh plants to elevated CO2", Nature Climate Change  9, 764–768, DOI: https://doi.org/10.1038/s41558-019-0582-x

https://www.nature.com/articles/s41558-019-0582-x

Abstract: "Coastal wetlands provide valuable ecosystem services that are increasingly threatened by anthropogenic activities. The atmospheric carbon dioxide (CO2) concentration has increased from 280 ppm to 404 ppm since the Industrial Revolution and is projected to exceed 900 ppm by 2100 (ref. 2). In terrestrial ecosystems, elevated CO2 typically stimulates C3 plant photosynthesis and primary productivity leading to an increase in plant size. However, compared with woody plants or crops, the morphological responses of clonal non-woody plants to elevated CO2 have rarely been examined. We show that 30 years of experimental CO2 enrichment in a brackish marsh increased primary productivity and stem density but decreased stem diameter and height of the dominant clonal species Schoenoplectus americanus. Smaller, denser stems were associated with the expansion of roots and rhizomes to alleviate nitrogen (N) limitation as evidenced by high N immobilization in live tissue and litter, high tissue C:N ratio and low available porewater N. Changes in morphology and tissue chemistry induced by elevated CO2 were reversed by N addition. We demonstrate that morphological responses to CO2 and N supply in a clonal plant species influences the capacity of marshes to gain elevation at rates that keep pace with rising sea levels."

See also:

Title: "High carbon dioxide can create 'shrinking stems' in marshes"

https://phys.org/news/2019-09-high-carbon-dioxide-stems-marshes.html

Extract: "For most plants, carbon dioxide acts like a steroid: The more they can take in, the bigger they get. But in a new study published Sept. 25, scientists with the Smithsonian discovered something strange happening in marshes. Under higher levels of carbon dioxide, instead of producing bigger stems, marsh plants produced more stems that were noticeably smaller."
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1680 on: October 09, 2019, 01:04:06 PM »
...
Still think you should be banned for spreading denial  FUD .

KiwiGriff, I have worked with quantitative models for decades. Not GCMs, but in terms of model structure the kind of models I worked with were to some degree similar, in the field of financial markets. My experience is such that I don't want to put any faith at all in any specific projections made by models. I will only describe them in terms of statistical inference, or maybe error propagation. I said:

"...at the end of the day they are nothing more than the educated guesses built on intuition that go into the tweaking and tuning efforts."

This is a true statement. The model makers are tweaking and tuning their imperfect models built on imperfect theories, fed with incomplete data. They heavily manipulate all their 'free' parameters built on their 'educated guesses' and their 'intuition', as said by the model makers themselves in one of those articles linked to by ASLR.

The model output can never be of higher quality than the model input, that's a truism. Educated guesses are often wrong, whereas intuition of course is always right. :)

Yes, you can call it FUD and you can ban the truth.
« Last Edit: October 09, 2019, 01:09:42 PM by Hefaistos »

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1681 on: October 09, 2019, 01:31:05 PM »
...
I don't deny that GCM models can be useful to get a hunch about where climate is going, but at the end of the day they are nothing more than the educated guesses built on intuition that go into the tweaking and tuning efforts.

Any short-comings of such CMIP6 models only serve to increase mankind's climate change risk, rather than providing an excuse to minimize mankind's effort to combat climate change.  Furthermore, the E3SM program is scheduled to coming improving their projections until at least 2027 (see image), because of the difficulty and large number of the problems that they are trying to solve.

ASLR, I agree, and it will certainly take more than 8 years. Model makers face 3 major challenges, as I see it:
1. GCM's lack a 'general theory' on water vapor on various latitudes and altitudes. Specifically, the tropics are challenging with the very powerful, energy intensive phase changes taking place e.g. in thunderstorms.
2. GCM's don't have the input data for the strongest GHG (water vapor/clouds) as they operate on larger grids than clouds.
3. Computing capacity isn't big enough. Witness the E3SM, where they have severe restrictions on the length of runs they can make, and the number of runs they can afford, in terms of computing capacity and work time involved.

All these challenges are clearly solvable, but I'd guess we need a couple of decades to get models that are truly reliable as forecasting tools.
« Last Edit: October 09, 2019, 03:00:29 PM by Hefaistos »

Klondike Kat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1682 on: October 09, 2019, 03:27:49 PM »

As is shown on the attached graphic from the GRACE-FO data
( http://gravis.gfz-potsdam.de/antarctica ) - interactive map

and as I extracted from the ASCII file they provide.
____________________________________________
Note: The German Partners in the GRACE-FO project ( Helmholtz Centre Potsdam
GFZ - German Research Centre for Geosciences) are being very helpful in getting data out to non-scientists like me - instant answers to my e-mails.. I must write & say thanks.

JPL/NASA seem all about the scientists - never an answer to queries. But maybe they are getting strife from Trump acolytes.

As noted in Reply #1673, almost certainly the GRACE-FO ice mass values need to be increase by about 10%, due to more rapid than previously assumed ice rebound (i.e. the increasing mass of the mantle associated with the rapid rebound, can fool gravity measurements into believing that less ice mass has been lost than is actually the case).

Edit:  Also, I note that to date most of the freshwater released from Antarctica into the Southern Ocean has come from ice shelves and this ice mass loss is not measured by GRACE-FO and needs to be added separately, in order to evaluate the impact of the surface water freshening/cooling; which not only reduces the local SSTA but also accelerates the accumulation of warm deep water in the Southern Ocean; which in turn accelerates ice mass loss from both ice shelves and from marine glaciers in Antarctia.

The vast majority of the continent has experienced no net change in ice.  All the melt is concentration on a small section along the western coastline.  The ice rebound is likely to be  less than 10%, as so little area is affected.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1683 on: October 09, 2019, 05:32:43 PM »

The vast majority of the continent has experienced no net change in ice.  All the melt is concentration on a small section along the western coastline.  The ice rebound is likely to be  less than 10%, as so little area is affected.

First, the 10% increase in ice mass loss, calculated based on GRACE satellite data, only applies to the WAIS and not to the EAIS.

Second, the first image (with a hat tip to sidd) shows that the firn for large portions of the Antarctic ice shelves are already saturated with ice and thus could soon be subject to rapid collapse due to hydrofracturing from surface meltwater during the austral summer months; which would leave bare ice-cliffs.

Third, the second image (for the Wilkes marine glacier) shows how relatively thin the 'ice plug' that stops MICI-types of marine glacier collapse once the ice shelves are lost.

Fourth, the third image [from P. Milillo et al. (30 Jan 2019)] shows a Manhattan-sized cavity in a trough in the seafloor/glacial-bed in the gateway for the Thwaites Glacier; where the trough spans the width of the 'ice plug' from the ocean to the negative slope of the Byrd Subglacial Basin (see the fourth image).  Thus if icebergs calved from ice cliffs in this trough area were to float-out to sea once the ice shelf/ice tongue is lost, then the MICI-type of failure for Thwaites could begin in this trough in the coming decades, thus bypassing the assumed 'ice plug'.

All of this indicates that the ice mass loss along the 'small section along the western coastline' of the key Antarctic marine glaciers is what is actually important for abrupt climate change in coming decades.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1684 on: October 09, 2019, 05:45:19 PM »
...
All these challenges are clearly solvable, but I'd guess we need a couple of decades to get models that are truly reliable as forecasting tools.

While your assessments of the key shortcomings of the CMIP5/6 models have some merit; I point-out that what one considers to be '... truly reliable as forecasting tools' depends very much on how one plans to use such tools.  Businesses (whether under capitalist or socialist systems) commonly face complex situations that cannot be deterministically solved using current business models/computers; but this does not stop such business from making successful use of risk-based evaluations from the output of those limited business models/computers.  In other words intelligent decision makers cannot be absolved from their responsibilities to make wise decisions in the face of uncertainties, just because climate change models are not perfect.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1685 on: October 09, 2019, 06:04:04 PM »
Is the powerful methane seep in the Arctic Ocean cited in the linked article a 'canary-in-the-coal-mine' for a possible rapid acceleration of methane emissions from such seeps with continued global warming for the next few decades?

Title: "Russian scientists find 'most powerful' ever methane seep in Arctic Ocean"

https://www.telegraph.co.uk/news/2019/10/08/russian-scientists-find-powerful-ever-methane-seep-arctic-ocean/

Extract: "A research expedition from the Tomsk polytechnic university found the seep, as methane leaks are known, east of Bennett Island in the East Siberian Sea, where its violent bubbles seemed to make the water “boil” over an area of 50 square feet.

The concentration of methane in the air there was up to 16 parts per million, more than nine times higher than the atmospheric average.

A recent Russian study found that the thawing of underwater permafrost has doubled in the past three decades, reaching 18 centimetres a year. One of the consequences has been massive releases of methane from the seafloor, including from hydrates, ice-like formations of solid methane that can explode into gas if they are destabilised."
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RoxTheGeologist

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1686 on: October 09, 2019, 06:12:44 PM »

The vast majority of the continent has experienced no net change in ice.  All the melt is concentration on a small section along the western coastline.  The ice rebound is likely to be  less than 10%, as so little area is affected.

First, the 10% increase in ice mass loss, calculated based on GRACE satellite data, only applies to the WAIS and not to the EAIS.


Note also that there has to be corresponding reduction in height in from surrounding areas. The location and amount depending on the viscosity and topography of the asthenosphere. I don't see where the rock is coming from mentioned in the paper (my guess is along the rift axis). If the grounding line is the point of the most ice loss, then i would think that it would act to increase the angle of slope to the interior as that is proportionally pushed down. The wavelength of any elastic response is short in rift zones as the lithosphere is elastically weak, on the orders of 5-20 kms. Uplift of the grounding line coupled with decreasing bedrock elevation in the interior does not sound like a recipe for stabilizing West Antarctica to me.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1687 on: October 09, 2019, 07:51:13 PM »

The vast majority of the continent has experienced no net change in ice.  All the melt is concentration on a small section along the western coastline.  The ice rebound is likely to be  less than 10%, as so little area is affected.

First, the 10% increase in ice mass loss, calculated based on GRACE satellite data, only applies to the WAIS and not to the EAIS.


Note also that there has to be corresponding reduction in height in from surrounding areas. The location and amount depending on the viscosity and topography of the asthenosphere. I don't see where the rock is coming from mentioned in the paper (my guess is along the rift axis). If the grounding line is the point of the most ice loss, then i would think that it would act to increase the angle of slope to the interior as that is proportionally pushed down. The wavelength of any elastic response is short in rift zones as the lithosphere is elastically weak, on the orders of 5-20 kms. Uplift of the grounding line coupled with decreasing bedrock elevation in the interior does not sound like a recipe for stabilizing West Antarctica to me.

As this topic has been discussed several times in this thread, here I will note that the assessment of rapid uplift in the Amundsen Sea Embayment area is not based on theory but on physical observations as noted in the two linked references and as illustrated by the two accompanying images.

The first accompanying image shows an overview of the Amundsen Sea sector, West Antarctica. The red line defines the generalized drainage basins of Pine Island Glacier, Thwaites Glacier and Smith Glacier (PITS). Locations of three GPS campaign sites are marked by red triangles.

The second image shows how post-glacial rebound for current ice mass loss from a marine glacier consists of both quick elastic rebound and slower rebound due to the flow of magma in the mantle.  I note that the current GIA corrections to GRACE data are based on conservative assumptions about the viscosity of the magma beneath the Byrd Subglacial Basin, BSB

V.R. Barletta el al. (22 Jun 2018), "Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability," Science, Vol. 360, Issue 6395, pp. 1335-1339, DOI: 10.1126/science.aao1447.

http://science.sciencemag.org/content/360/6395/1335

&

An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica
by: A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich
http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

Edit: Also, I reiterate that such relatively slow rebound will not protect the WAIS from a possible MICI-type of collapse in the coming decades.
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gerontocrat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1688 on: October 09, 2019, 08:03:41 PM »
Antarctica on a knife-edge?

This post is derived from
https://www.pnas.org/content/116/4/1095
Four decades of Antarctic Ice Sheet mass balance from 1979–2017by Eric Rignot et al.
January 2019
& the spreadsheet attached

The point is that Net Ice-Mass Loss is a very small figure when looking at SMB gain (i.e. snowfall) & Ice Loss (discharge) for the 39 years covered by the study.

Summary                        GT Total Ice Loss   GT Total SMB Addition   GT Net Ice Loss
Peninsula                                    12,336              11,427                             -909
West Antarctic Ice Sheet (WAIS)    28,091              25,451                          -2,640
East Antarctic Ice Sheet (EAIS)     43,135              41,925                          -1,211
Weddell Ice Shelf Islands               3,003                3,003                                  0

Antarctica Total                     86,565               81,805                           -4,760

In other words loss exceeded gain by just 5.5%, or 13 mm of sea-level rise. (Graph attached)

But discharge and net mass loss is increasing (Data from Grace-FO graph attached again.)

So what happens if discharge increases but SMB gain does not ? In this case a small percentage increase in discharge would causes a very large percentage increase in NET mass loss.

Current annual SMB gain (estimate)     2,100 GT,
Annual discharge (2017 data)              2,300 GT,
2017 Mass Loss (estimate)                     200 GT.         

Add 10% to discharge, zero to SMB , Annual ice-mass loss increases to 430 GT, i.e. more than doubles.
And there is evidence to show that the EAIS has shifted from being in balance (or even net mass gain) to mass loss.

And, of course, we don't know what will happen, but the bulk of evidence says it's all going the wrong way.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1689 on: October 09, 2019, 10:03:29 PM »

The point is that Net Ice-Mass Loss is a very small figure when looking at SMB gain (i.e. snowfall) & Ice Loss (discharge) for the 39 years covered by the study.


Readers who have been following my posts for the past few (six) years know that Eric Rignot has made it clear that:

a) for many decades the SMB for East Antarctic has changed little except for the fact that in the past decade a few extreme precipitation (snowfall) events associated with atmospheric river events have episodically increased the SMB for East Antarctic as illustrated by the Dronning Maud Land events discussed in the two references cited below.

b) While snowfall (and thus SMB) has increased recently in West Antarctica, the added gravitational load from this mass is serving (& will increasing serve to) accelerate glacial ice flow velocities in key marine glaciers in West Antarctica; which in turn is serving to destabilize the WAIS.

The first and second attached images taken from Tsukernik et al:

May 2009 Atmospheric River Event in the Dronning Maud Land
By: Maria Tsukernik, Amanda Lynch, Maya Wei and Irina Gorodetskaya

The first attached image shows the accumulative and per day precipitation in Dronning Maud Land from 1979 to the end of 2011; which indicates exceptional (unusually high) snowfall/accumulation in this area particularly in May of 2009.  The second figure indicates that this (and possibly other subsequent) high precipitation event(s) was/were due to an Atmospheric River event(s) coming from the Indian Ocean tropical region.  While many scientists who have projected low ice mass loss from AIS have grabbed on to this (and possible subsequent) high precipitation event to say that the future accumulation of large amounts of snow in East Antarctica will largely offset the projected future dynamic ice mass loss in West Antarctica, I do not feel good about any such use of this precipitation data as: (a) The atmospheric rivers are not captured in the GCM models used by these reticent researchers; yet they are happy to grab on to field data without a long trend line and which could be a natural fluctuation; and (b) with increasing global warming future atmospheric river events may bring sufficient warm water from the tropics to Antarctica so that the precipitation falls as rain and not snow; which contribute to episodic rapid ice mass loss from any such impacted area.

&

The following reference and abstract provide valuable analysis of weather data from a station in Dronning Maud Land; and provide further insight into the various factors involved in such events. 

Meteorological regimes and accumulation patterns at Utsteinen, Dronning Maud Land, East Antarctica: Analysis of two contrasting years by: I. V. Gorodetskaya, N. P. M. Van Lipzig, M. R. Van den Broeke, A. Mangold,W. Boot, and C. H. Reijmer; JOURNAL OF GEOPHYSICAL RESEARCH: ATMOSPHERES, VOL. 118, 1–16, doi:10.1002/jgrd.50177, 2013

Abstract: "Since February 2009, an automatic weather station (AWS) has been operating near Utsteinen Nunatak, north of the Sør Rondane Mountains, in Dronning Maud Land at the ascent to the East Antarctic Plateau. This paper gives an assessment of the meteorological conditions, radiative fluxes, and snow accumulation for the first 2 years of operation, 2009 to 2010, analyzed in terms of meteorological regimes. Three major meteorological regimes— cold katabatic, warm synoptic, and transitional synoptic—are identified using cluster analysis based on five parameters derived from the AWS measurements (wind speed, specific humidity, near-surface temperature inversion, surface pressure, and incoming longwave flux indicative of cloud forcing). For its location, the relatively mild climate at Utsteinen can be explained by the high frequency of synoptic events (observed 41%–48% of the time), and a lack of drainage of cold air from the plateau due to mountain sheltering. During the cold katabatic regime, a strong surface cooling leads to a strong near-surface temperature inversion buildup. A large difference in accumulation is recorded by the AWS for the first 2 years: 235mm water equivalent in 2009 and 27mm water equivalent in 2010. Several large accumulation events during the warm synoptic regime occurring mainly in winter were responsible for the majority of the accumulation in 2009. Mostly, small accumulation events occurred during 2010, frequently followed by snow removal. This interannual variability in snow accumulation at the site is related to the intensity of the local synoptic events as recorded by meteorological regime characteristics."
« Last Edit: October 10, 2019, 12:45:25 AM by AbruptSLR »
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Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1690 on: October 09, 2019, 10:14:24 PM »
The linked reference provides information about MISI and MICI and the IPCC's (consensus scientists) acceptance of those hypothesis.  The pertinent section is on pages 3-55 through 3-58 of the report.

https://report.ipcc.ch/srocc/pdf/SROCC_FinalDraft_FullReport.pdf

Quote
Cross-Chapter Box 8: Future Sea Level Changes and Marine Ice Sheet Instability
 
Authors: Rob De Conto (USA), Alexey Ekaykin (Russian Federation), Andrew Mackintosh (Australia), Roderik van de Wal (Netherlands), Jeremy Bassis (USA)
 
Over the last century, glaciers were the main contributors to increasing ocean water mass (Section 4.2.1.2). However, most terrestrial frozen water is stored in Antarctic and Greenland ice sheets, and future changes in their dynamics and mass balance will cause sea level rise over the 21st century and beyond (Section 4.2.3).
 
About a third of Antarctic Ice Sheet (AIS) is ‘marine ice sheet’, i.e. rests on bedrock below sea level (Figure 4.5), with most of the ice-sheet margin terminating directly in the ocean. These features make the overlying ice sheet vulnerable to dynamical instabilities with the potential to cause rapid ice loss - so-called Marine Ice Sheet and Marine Ice Cliff instabilities, as discussed below.
 

Quote
The disappearance of ice shelves may allow the formation of ice cliffs, which may be inherently unstable if they are tall enough (subaerial cliff height between 100 and 285 m) to generate stresses that exceed the strength of the ice (Parizek et al., 2019). This ice cliff failure can lead to ice sheet retreat via a process called marine ice cliff instability (MICI; Figure CB8.1b), that has been hypothesized to cause partial collapse of the West Antarctic Ice Sheet within a few centuries (Pollard et al., 2015; DeConto and Pollard, 2016).
 
Limited evidence is available to confirm the importance of MICI. In Antarctica, marine-terminating ice margins with the grounding lines thick enough to produce unstable ice cliffs are currently buttressed by ice shelves, with a possible exception of Crane glacier on the Antarctic Peninsula (Section 4.2.3.1.2).  Overall, there is low agreement on the exact MICI mechanism and limited evidence of its occurrence in the present or the past. Thus the potential of MICI to impact the future sea level remains very uncertain (Edwards et al., 2019).
 
Limited evidence from geological records and ice sheet modelling suggests that parts of AIS experienced rapid (i.e., on centennial time-scale) retreat likely due to ice sheet instability processes between 20,000 and 9,000 years ago (Golledge et al., 2014; Weber et al., 2014; Small et al., 2019). Both the West (including Pine Island glacier) and the East Antarctic Ice Sheet also experienced rapid thinning and grounding line retreat during the early to mid-Holocene (Jones et al., 2015b; Wise et al., 2017). In the Ross Sea, grounding lines may have retreated several hundred kilometers inland and then re-advanced to their present-day positions due to bedrock uplift after ice mass removal (Kingslake et al., 2018), thus supporting the stabilizing role of glacial isostatic adjustment on ice sheets (Barletta et al., 2018). These past rapid changes have likely been driven by the incursion of Circumpolar Deep Water onto the Antarctic continental shelf (Section 3.3.1.5.1) (Golledge et al., 2014; Hillenbrand et al., 2017) and MISI (Jones et al., 2015b). Limited evidence of past MICI in Antarctica is provided by deep iceberg plough marks on the sea-floor (Wise et al., 2017).
 

In summary, Rob DeConto, one of the co-authors of the MICI papers, believes their is limited agreement or evidence for MICI, which may cause a partial collapse of the WAIS in a few centuries.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1691 on: October 09, 2019, 11:59:55 PM »
...
In summary, Rob DeConto, one of the co-authors of the MICI papers, believes their is limited agreement or evidence for MICI, which may cause a partial collapse of the WAIS in a few centuries.

While the SROCC is a valuable document, and Rob DeConto is an honorable scientist; that does not mean that the SROCC (including portions written by committee's that DeConto was on) has not minimized much of the potential right-tailed risks associated with MICI-type mechanisms in Antarctica (particularly in West Antarctica) in the coming decades (as opposed to centuries), including off the top of my head:

a) DeConto & Pollard assumed that ECS is close to 3C rather than over 5C, and they ignored many mechanisms for cascades of tipping mechanisms associated with the ice-climate feedback mechanisms cited by James Hanson (another honorable scientist).
b) The Southern Ocean has more heat content than assumed by DeConto & Pollard and the upwelling of warm CDW (circumpolar deep water) appears to be occurring more regularly than their models assumed (largely being driven by continuing relatively high velocity westerly winds around the Southern Ocean).
c) The DeConto & Pollard models do not include the bed trough through the Thwaites gateway leading to the Byrd Subglacial Basin, where a large subglacial cavity is growing and through which icebergs from local ice cliff calving events can float-out without grounding.
d) The current rate of increase of radiative forcing is more than a hundred time faster than the during the paleo-periods that DeConto & Pollard conservative calibrated the MICI mechanism against.
e) When DeConto determined the current rate of ice cliff failures for the Jakobshavn Glacier, he divided this observed rate in half to use in his/Pollard's MICI models; while in reality the susceptibility of the Thwaites Glacier to future ice cliff failures may be many time higher than that for Jakobshavn.
f) DeConto & Pollard did not consider effective bipolar mechanisms associated with Arctic freshwater hosing events either from the Beaufort Gyre and/or from Greenland.

I could go on but I would only be repeating points that I have previously made in this thread.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1692 on: October 10, 2019, 12:19:44 AM »
The linked reference identifies yet another observed mechanism for destabilizing Antarctic ice shelves that is not including in consensus climate models, including in those cited by the SROCC report and/or by DeConto & Pollard:

Karen E. Alley, Ted A. Scambos, Richard B. Alley and Nicholas Holschuh (09 Oct 2019), "Troughs developed in ice-stream shear margins precondition ice shelves for ocean-driven breakup", Science Advances, Vol. 5, no. 10, eaax2215, DOI: 10.1126/sciadv.aax2215

https://advances.sciencemag.org/content/5/10/eaax2215

Abstract
Floating ice shelves of fast-flowing ice streams are prone to rift initiation and calving originating along zones of rapid shearing at their margins. Predicting future ice-shelf destabilization under a warming ocean scenario, with the resultant reduced buttressing, faster ice flow, and sea-level rise, therefore requires an understanding of the processes that thin and weaken these shear margins. Here, we use satellite data to show that high velocity gradients result in surface troughs along the margins of fast-flowing ice streams. These troughs are advected into ice-shelf margins, where the locally thinned ice floats upward to form basal troughs. Buoyant plumes of warm ocean water beneath ice shelves can be focused into these basal troughs, localizing melting and weakening the ice-shelf margins. This implies that major ice sheet drainages are preconditioned for rapid retreat in response to ocean warming.

See also:

Title: "Warm ocean water attacking edges of Antarctica's ice shelves"

https://phys.org/news/2019-10-ocean-edges-antarctica-ice-shelves.html

Extract: "Upside-down "rivers" of warm ocean water are eroding the fractured edges of thick, floating Antarctic ice shelves from below, helping to create conditions that lead to ice-shelf breakup and sea-level rise, according to a new study.

The findings, published today in Science Advances, describe a new process important to the future of Antarctica's ice and the continent's contribution to rising seas. Models and forecasts do not yet account for the newly understood and troubling scenario, which is already underway."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1693 on: October 10, 2019, 12:38:24 AM »
In about one more month we will say sayonara to Mt. Fuji :'(
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1694 on: October 10, 2019, 03:40:25 AM »
The linked reference discusses yet another positive feedback mechanism (to contribute to a cascade of other positive feedbacks) associated with the projected increase in Arctic rainfall with continued warming:

Rebecca B. Neumann, Colby J. Moorberg,  Jessica D. Lundquist,  Jesse C. Turner,  Mark P. Waldrop,  Jack W. McFarland,  Eugenie S. Euskirchen,  Colin W. Edgar & Merritt R. Turetsky (03 January 2019), "Warming Effects of Spring Rainfall Increase Methane Emissions From Thawing Permafrost" Geophysical Research Letters, https://doi.org/10.1029/2018GL081274

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL081274

Abstract
Methane emissions regulate the near‐term global warming potential of permafrost thaw, particularly where loss of ice‐rich permafrost converts forest and tundra into wetlands. Northern latitudes are expected to get warmer and wetter, and while there is consensus that warming will increase thaw and methane emissions, effects of increased precipitation are uncertain. At a thawing wetland complex in Interior Alaska, we found that interactions between rain and deep soil temperatures controlled methane emissions. In rainy years, recharge from the watershed rapidly altered wetland soil temperatures, warming the top ~80 cm of soil in spring and summer and cooling it in autumn. When soils were warmed by spring rainfall, methane emissions increased by ~30%. The warm, deep soils early in the growing season likely supported both microbial and plant processes that enhanced emissions. Our study identifies an important and unconsidered role of rain in governing the radiative forcing of thawing permafrost landscapes.

Plain Language Summary
Because the world is getting warmer, permanently frozen ground around the arctic, known as permafrost, is thawing. When permafrost thaws, the ground collapses and sinks. Often a wetland forms within the collapsed area. Conversion of permanently frozen landscapes to wetlands changes the exchange of greenhouse gases between the land and atmosphere, which impacts global temperatures. Wetlands release methane into the atmosphere. Methane is a potent greenhouse gas. The ability of methane to warm the Earth is 32 times stronger than that of carbon dioxide over a period of 100 years. In our study, we found that methane release from a thaw wetland in Interior Alaska was greater in rainy years when rain fell in spring. When spring rainwater entered the wetland, it rapidly warmed wetland soils. Rain has roughly the same temperature as the air, and during springtime in northern regions, the air is warmer than the ground. The microbial and plant processes that generate methane increase with temperature. Therefore, wetland soils, warmed by spring rainfall, supported more methane production and release. Northern regions are expected to receive more rainfall in the future. By warming soils and increasing methane release, this rainfall could increase near‐term global warming associated with permafrost thaw.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1695 on: October 10, 2019, 04:10:21 PM »
Most people follow the 'KISS' (Keep It Simple Stupid) rule when making decisions, including those made about climate change.  As climate change is complex, this means that most people prefer to think about their own economic wellbeing, like the Russians are doing according to the linked article.  Of course this increases the likelihood that the world will remain on a BAU pathway for decades to come:

Title: "New icebreakers, ports and satellites for Northern Sea Route"

https://thebarentsobserver.com/en/2019/10/new-icebreakers-ports-and-satellites-northern-sea-route

Extract: "Russia has big plans for its Arctic and is in the process of building capacities that will enable it to ship out major volumes of goods from the region.

Nuclear icebreakers, sea ports, support vessels and satellites are our main priority, says Maksim Kulinko, a top representative of Rosatom.

According to Kulinko, Russia will not only build eight nuclear powered icebreakers by year 2035, but also 16 rescue and support ships.

In addition, several major seaports are under development, and a total of 12 new satellites are to be put in orbit, he said in a recent conference on Russian offshore developments."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1696 on: October 10, 2019, 05:28:11 PM »
Many left-tail climate-commentators point to paleo climate variability as an example of why people should ignore climate change warnings, as climate has always fluctuated.  However, in reality high climate variability is a first-order indicator of high climate sensitivity.  Also, for the past two millennia the ice sheets have been much as they were during the pre-industrial era, and thus this period provides a good proxy for representing baseline Earth System conditions.  Finally, the linked reference studied the variability of the Northern North Atlantic and Artic Oceans for the last two millennia and found periods of strong variability such as the Medieval Warm Period followed by the Little Ice Age (see the attached image), and as the AMOC is strongly connected to climate sensitivity (note that a slowing MOC results in warmer tropical SSTs, which can increase the positive feedback from high altitude clouds), this paleodata supports the idea that ECS is currently relatively high:

P. Moffa‐Sánchez et al. (18 June 2019), "Variability in the Northern North Atlantic and Arctic Oceans Across the Last Two Millennia: A Review", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2018PA003508

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018PA003508

Abstract
The climate of the last two millennia was characterized by decadal to multicentennial variations, which were recorded in terrestrial records and had important societal impacts. The cause of these climatic events is still under debate, but changes in the North Atlantic circulation have often been proposed to play an important role. In this review we compile available high‐resolution paleoceanographic data sets from the northern North Atlantic and Nordic Seas. The records are grouped into regions related to modern ocean conditions, and their variability is discussed. We additionally discuss our current knowledge from modeling studies, with a specific focus on the dynamical changes that are not well inferred from the proxy records. An illustration is provided through the analysis of two climate model ensembles and an individual simulation of the last millennium. This review thereby provides an up‐to‐date paleoperspective on the North Atlantic multidecadal to multicentennial ocean variability across the last two millennia.

Extract: "Surface ocean reconstructions of the relatively warm Atlantic waters show variable patterns in the three regions studied. The most southern region (30–45°N) shows large variability in the surface temperature conditions, with the most common signal being the anomalous conditions (either cooling or warming) starting in ~1850 CE (Figure 2). This diverging pattern perhaps arises from the complex regional interactions between the Gulf Stream and the Labrador Current (including changes in the Gulf Stream detachment) and/or larger basin scale circulation changes. Farther north in the subpolar North Atlantic, reconstructions from the NAC waters reveal diverging millennial trends likely resulting from seasonal or preferred habitat depth proxy biases (Figure 3). The records from the slope waters across the Scottish shelf are shorter and mostly reveal a common warming trend from 1800 CE to present not clearly recorded in the sediment cores of the subpolar North Atlantic (Figure 3). This geographical difference could be explained by differential warming of coastal/shelf environments versus central subpolar gyre. Surface reconstructions of the Atlantic inflow in the Nordic Seas largely reveal a millennial‐scale cooling and increase drift ice with higher‐resolution records showing a shift around 1300–1450 CE to colder conditions with more drift ice (Figure 4)."

Caption for the first image: "Surface ocean records from the southwest and northwest Atlantic. Percentages of the polar foraminiferal species N. pachyderma from (a) Laurentian Fan (Keigwin & Pickart, 1999) (b) Nova Scotia (Emerald Basin; blue; note that superimposed are two records from the same core: Mg/Ca‐based temperatures based on benthic foraminifera C. lobatus, in pink, and sea surface temperature (SST) record from alkenones, in gray (Keigwin et al., 2003); (c, d) % N. pachydermafrom Laurentian Fan (25MC‐A and 10MC, respectively; Thornalley et al., 2018); (e) δ18O from the bivalve Arctica islandica from the Gulf of Maine (Wanamaker et al., 2008); (f) Ostracod Mg/Ca‐based temperature reconstructions based on three spliced sediment cores from Chesapeake Bay (Cronin et al., 2010); (g) temperature reconstructions based on Sr/Ca in brain coral from Bermuda (Goodkin et al., 2008). Bold lines are weighted three‐point smoothing."

See also:

Title: "New Perspectives on 2,000 Years of North Atlantic Climate Change"

https://eos.org/research-spotlights/new-perspectives-on-2000-years-of-north-atlantic-climate-change

Extract: "Historical and natural clues suggest that Earth’s climate underwent small changes over the past 2,000 years, and variations in North Atlantic ocean circulation may have been a key driver. In a new paper, Moffa-Sánchez et al. compile recent advancements in analytical tools used to probe this period of ocean circulation, presenting a comprehensive overview of current knowledge.

The past 2 millennia have seen several centuries-long climate shifts, such as the Medieval Warm Period, followed by the Little Ice Age, which were particularly recorded around the North Atlantic. The North Atlantic is an important climatological region  because of the strong interactions between ocean, atmosphere, and sea ice, as well as the overturning circulation between surface and deep-ocean currents. Scientists have traditionally proposed that changes in this Atlantic Meridional Overturning Circulation played a key role in the observed climate shifts, but this view remains under debate because of the lack of clear evidence."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1697 on: October 11, 2019, 04:16:19 AM »
The linked article discusses the use of state-of-the-art autonomous floating senors since 2014 to document a significant reduction in the net amount of carbon dioxiode that the Southern Ocean has been aborbing in the past few years (which is not included in consensus climate change models).  While a marked increase in CO2 outgassing in the southern sector of the Southern Ocean apparently due to increased upwelling (possibly due to increased westerly wind velocities associated with both increasing atmospheric GHG concentrations and the Antarctic ozone hole); I am personnelly concerned that the decreasing surface water salinity associated with ice meltwater may be reducing the ability of microorganisms to absorb and sequester CO2 (which could become markedly worse if the WAIS were to undergo a MICI-type of collapse in the coming decades):

Title: "Southern Ocean is absorbing less carbon"

https://www.earthmagazine.org/article/southern-ocean-absorbing-less-carbon

Extract: "In the Southern Ocean surrounding Antarctica, complex and dynamic interactions among the atmosphere, cryosphere, and surface and deep ocean waters play an important role in climate. Although it covers only a quarter of Earth’s oceanic surface area, the Southern Ocean — with its cold temperatures and carbon-sucking algal blooms — has been estimated to take up 40 percent of anthropogenic carbon dioxide emissions. However, new data collected by a fleet of autonomous floating sensors show that the Southern Ocean is taking up significantly less carbon than scientists thought.
...
In the Antarctic southern zone, the team found that the ocean was outgassing about 0.36 billion metric tons of carbon — a “pretty significant amount of carbon dioxide,” Gray says. “This was surprising because previous estimates, based on shipboard data, [suggested] that that region was not emitting anything,” she says.

The float observations show that with strong outgassing and upwelling, the entire Southern Ocean has a net annual carbon dioxide uptake of 0.08 billion metric tons a year. Not only are carbon emissions about 10 times higher than previously thought, carbon uptake is only one-tenth of what observations had suggested — which is “quite a big shift,” Gray says."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1698 on: October 11, 2019, 11:53:42 AM »
This post is a reminder (see the second linked reference) that in 2012 Strugnell et al. provided evidence about octopi (octopods) that indicated that during the Eemian (last interglacial) period seaways existed through the WAIS; which supports the idea of at least a partial collapse of the WAIS at that time.  While in the first linked reference, Strugnell et al. (2018) lays-out a detailed plan to use a molecular genetic approach to confirm that such seaways existed through the WAIS during the Eemian.  Also, I note that if such seaways were to occur in the coming decades they would change the local ocean current circulation patterns in a way that would likely accelerate ice mass loss from the WAIS:

Jan M. Strugnell et al. (1 January 2018), "Dating Antarctic ice sheet collapse: Proposing a molecular genetic approach", Quaternary Science Reviews, Volume 179, Pages 153-157, https://doi.org/10.1016/j.quascirev.2017.11.014

https://www.sciencedirect.com/science/article/abs/pii/S0277379117306340?via%3Dihub

Abstract
Sea levels at the end of this century are projected to be 0.26–0.98 m higher than today. The upper end of this range, and even higher estimates, cannot be ruled out because of major uncertainties in the dynamic response of polar ice sheets to a warming climate. Here, we propose an ecological genetics approach that can provide insight into the past stability and configuration of the West Antarctic Ice Sheet (WAIS). We propose independent testing of the hypothesis that a trans-Antarctic seaway occurred at the last interglacial. Examination of the genomic signatures of bottom-dwelling marine species using the latest methods can provide an independent window into the integrity of the WAIS more than 100,000 years ago. Periods of connectivity facilitated by trans-Antarctic seaways could be revealed by dating coalescent events recorded in DNA. These methods allow alternative scenarios to be tested against a fit to genomic data. Ideal candidate taxa for this work would need to possess a circumpolar distribution, a benthic habitat, and some level of genetic structure indicated by phylogeographical investigation. The purpose of this perspective piece is to set out an ecological genetics method to help resolve when the West Antarctic Ice Shelf last collapsed.
&

J. M. Strugnell, P. C. Watts, P. J. Smith, A. L. Allcock. Persistent genetic signatures of historic climatic events in an Antarctic octopus. Molecular Ecology, 2012; DOI: 10.1111/j.1365-294X.2012.05572.x

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-294X.2012.05572.x

Abstract: "Repeated cycles of glaciation have had major impacts on the distribution of genetic diversity of the Antarctic marine fauna. During glacial periods, ice cover limited the amount of benthic habitat on the continental shelf. Conversely, more habitat and possibly altered seaways were available during interglacials when the ice receded and the sea level was higher. We used microsatellites and partial sequences of the mitochondrial cytochrome oxidase 1 gene to examine genetic structure in the direct‐developing, endemic Southern Ocean octopod Pareledone turqueti sampled from a broad range of areas that circumvent Antarctica. We find that, unusually for a species with poor dispersal potential, P. turqueti has a circumpolar distribution and is also found off the islands of South Georgia and Shag Rocks. The overriding pattern of spatial genetic structure can be explained by hydrographic (with ocean currents both facilitating and hindering gene flow) and bathymetric features. The Antarctic Peninsula region displays a complex population structure, consistent with its varied topographic and oceanographic influences. Genetic similarities between the Ross and Weddell Seas, however, are interpreted as a persistent historic genetic signature of connectivity during the hypothesized Pleistocene West Antarctic Ice Sheet collapses. A calibrated molecular clock indicates two major lineages within P. turqueti, a continental lineage and a sub‐Antarctic lineage, that diverged in the mid‐Pliocene with no subsequent gene flow. Both lineages survived subsequent major glacial cycles. Our data are indicative of potential refugia at Shag Rocks and South Georgia and also around the Antarctic continent within the Ross Sea, Weddell Sea and off Adélie Land. The mean age of mtDNA diversity within these main continental lineages coincides with Pleistocene glacial cycles."

« Last Edit: October 11, 2019, 05:46:23 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1699 on: October 11, 2019, 05:52:40 PM »
As a follow-on to my last post about seaways in West Antarctica, the accompanying figures are from Vaughan et al. 2011, the researcher postulate that the indicated seaways opened in the WAIS during the Eemian period some 124,000 years ago.  Vaughan et al. proved that for an upper bound that the longest of these seaways formed within less than a thousand years (which is well within the timeframe of the Eemian peak proving that WAIS could have contributed at least 3.4 to 3.8 m to eustatic SLR in that period).
« Last Edit: October 11, 2019, 06:02:05 PM by AbruptSLR »
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