Support the Arctic Sea Ice Forum and Blog

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - AbruptSLR

Pages: [1] 2 3 ... 37
1
With a hat-tip to vox mundi, the linked reference validates the use of RCP 8.5 (or SSP5) for climate simulations:

Christopher R. Schwalm el al., "RCP8.5 tracks cumulative CO2 emissions," PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.2007117117

https://www.pnas.org/content/early/2020/07/30/2007117117

Abstract: "Climate simulation-based scenarios are routinely used to characterize a range of plausible climate futures. Despite some recent progress on bending the emissions curve, RCP8.5, the most aggressive scenario in assumed fossil fuel use for global climate models, will continue to serve as a useful tool for quantifying physical climate risk, especially over near- to midterm policy-relevant time horizons. Not only are the emissions consistent with RCP8.5 in close agreement with historical total cumulative CO2 emissions (within 1%), but RCP8.5 is also the best match out to midcentury under current and stated policies with still highly plausible levels of CO2 emissions in 2100."

2
For those who think that a Super El Nino is the only perturbation that might trigger an MICI-type of collapse of the Thwaites/BSB ice, I note that in September 2012 the Thwaites Ice Tongue flow rate surged and continued flowing at a high rate through the end of 2012 (and this high flow rate can be associated with the surface elevation depression shown in the first image)

In this regards, the linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014 (see the last three attached images), and that these subglacial lakes can refill within 20-years which indicates that another associated surge of ice in the Thwaites Ice Tongue may occur in the 2032 to 2033 timeframe:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."

There is more information on the June 2013 to Jan 2014 drainage of four subglacial lakes beneath the Thwaites Glacier.  The article is entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-thwaites-glacier/

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."

3
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 03, 2020, 10:18:20 PM »
The attached image is just a reminder that thru 2019 our CO2 emissions were still closely tracking the RCP 8.5 emissions scenario.

4
For those who still do not believe that once unpinned that the icebergs within the Thwaites Ice Tongue can float away to the northwest I attach an image of the ice tongue from May 31, 2020 annotated by baking where the feature that he names the 'Shear Zone' are going just that and the feature that he names 'Calving Zone' indicates the iceberg that I believe could expose ice cliffs once they float away due to a perturbation (such as a Super El Nino event).

5
As a follow-on to my last post:

The first image shows the relationship between the ENSO cycle and the surface elevation of the ice shelves in the Amundsen Sea Sector; clearly increasing that these ice shelves float up on El Nino events and down on La Nina events; which causes flexure and cracking of the ice shelves (which weakens them and makes them more susceptible to the influence of warm CDW).

The second image shows how during the combination of an El Nino event and a positive SAM event tropical heat energy is advected from the Tropical Pacific directly to the coastal West Antarctica; where it can episodically accelerate local ice mass loss (along the coastal areas).

The third image shows how the Amundsen Bellingshausen Sea Low, ABSL (or ASL), can direct winds directly into the ASE, which also drags along ocean currents that advect more warm CDW into the ASE which accelerates local ice mass loss.

The fourth image shows the average potential temperature of the warm CDW (above freezing) typically being advected into the ASE, and the associate marine glacier ice flow velocities (because of the reduced buttressing from the degrading ice shelves and the retreating grounding lines).  Also, I note that relatively rapid ice flow velocities cause internal friction within the ice of the marine glaciers, which induces more basal meltwater beneath the marine glaciers (which further destabilize the marine glaciers).

The first linked reference concludes with regard to the Amundsen Sea Region, ASR, that:

"In contrast, the El Niño–ASR teleconnection in austral summer, which more closely resembles the Southern Annular Mode, is found to increase linearly for El Niño amplitudes up to 3 K."

As austral summer is also when surface ice melting occurs in the Amundsen Sea Region, and as El Nino events push warm CDW into the Amundsen Sea Embayment, ASE, we should be very concerned about the impacts of coming Super El Nino events on marine glaciers in the ASE.

Yu Yeung Scott Yiu and Amanda C. Maycock (2020 Apr), "The linearity of the El Niño teleconnection to the Amundsen Sea region", Q J R Meteorol Soc.; 146, (728), 1169–1183, doi: 10.1002/qj.3731

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.3731

Abstract: El Niño Southern Oscillation (ENSO) drives interannual variability in West Antarctic climate through altering atmospheric circulation in the Amundsen Sea region (ASR). The El Niño–ASR teleconnection is known to be strongest in austral winter and spring, but its variation with El Niño amplitude is underexplored. This study uses experiments from the HadGEM3‐A climate model to investigate the El Niño–ASR teleconnection for a range of imposed SST perturbations spanning weak (0.75 K) to strong (3 K) amplitudes. In austral winter, the El Niño–ASR teleconnection behaves linearly for El Niño amplitudes up to 2.25 K, but is found to weaken for stronger forcing (3 K). The anomalous Rossby wave source in the subtropical South Pacific increases monotonically with El Niño amplitude. However, a Rossby wave reflection surface originally located in the western South Pacific sector extends progressively eastward with increasing El Niño amplitude, reducing wave propagation into the ASR. The wave reflection surface is associated with curvature in the upper tropospheric zonal winds which intensifies as the subtropical jet strengthens under El Niño forcing. In contrast, the El Niño–ASR teleconnection in austral summer, which more closely resembles the Southern Annular Mode, is found to increase linearly for El Niño amplitudes up to 3 K. The results explicitly demonstrate that a linear approximation of the El Niño teleconnection to the ASR is reasonable based on the range of El Niño amplitudes observed in recent history.

See also:

Dätwyler, C., Grosjean, M., Steiger, N. J., and Neukom, R.: Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium, Clim. Past, 16, 743–756, https://doi.org/10.5194/cp-16-743-2020, 2020.

https://cp.copernicus.org/articles/16/743/2020/

Abstract
The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Because of the limited length of instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability over time. Using proxy-based reconstructions and last-millennium climate model simulations, we find that ENSO and SAM indices are mostly negatively correlated over the past millennium. Pseudo-proxy experiments indicate that currently available proxy records are able to reliably capture ENSO–SAM relationships back to at least 1600 CE. Palaeoclimate reconstructions show mostly negative correlations back to about 1400 CE. An ensemble of last-millennium climate model simulations confirms this negative correlation, showing a stable correlation of approximately −0.3. Despite this generally negative relationship we do find intermittent periods of positive ENSO–SAM correlations in individual model simulations and in the palaeoclimate reconstructions. We do not find evidence that these relationship fluctuations are caused by exogenous forcing nor by a consistent climate pattern. However, we do find evidence that strong negative correlations are associated with strong positive (negative) anomalies in the Interdecadal Pacific Oscillation and the Amundsen Sea Low during periods when SAM and ENSO indices are of opposite (equal) sign.

6
I am less pessimistic than someone like AbruptSLR, I think the timeline is more like 100 years before we really see massive ice sheet instabilities.

But again I trying to see which glacier will go first.
One vote for Jakobshavn it is.

While Jakobshavn is already undergoing ice cliff failures and may very well undergo and temporary acceleration of ice cliff failures once the grounding line / calving front reaches the retrograde bed slope, but once that bed slope changes to a prograde slope then the temporary acceleration will stop and the ice cliff failures will slowdown to something like their current rate of calving.  Thus, if you are asking which glacier will be the first to lead to a collapse of a ice sheet, then the only marine glacier that is reasonable to cite is the Thwaites Glacier.

To me, it is more productive to discuss the validity of the reasons that I have previously cited (& for which I have previously provided references) as to why Thwaites Glacier has a good probability of triggering a MICI-type of collapse of the WAIS before 2045.  While it is not possible to cite one specific scenario I am slowly preparing a summary, but here I cite a few key points.

A freshwater hosing event (like the temporary collapse of Jakobshavn's calving front and/or as short-term reversal of the Beaufort Gyre) say between 2025 and 2035, could slow the MOC sufficiently to trigger a Super El Nino  say by 2035 to 2040 that would cause both a sufficient perturbation of both CDW pulse into the ASE and surface ice melting to trigger an ice cliff front at the base of the current Thwaites Ice Tongue in the bed trough leading to the BSB.

See also:

Title: "NASA Space Laser Missions Map 16 Years of Ice Sheet Loss"

https://www.nasa.gov/feature/goddard/2020/nasa-space-laser-missions-map-16-years-of-ice-sheet-loss

7
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 01, 2020, 07:53:31 PM »
The linked reference cites that increased rainfall is already accelerating permafrost degradation in Alaska; which, means it is likely already happening in Siberia; which leads to more Arctic Amplification.

Thomas A. Douglas, Merritt R. Turetsky, Charles D. Koven. Increased rainfall stimulates permafrost thaw across a variety of Interior Alaskan boreal ecosystems. npj Climate and Atmospheric Science, 2020; 3 (1) DOI: 10.1038/s41612-020-0130-4

https://www.nature.com/articles/s41612-020-0130-4

Abstract: "Earth’s high latitudes are projected to experience warmer and wetter summers in the future but ramifications for soil thermal processes and permafrost thaw are poorly understood. Here we present 2750 end of summer thaw depths representing a range of vegetation characteristics in Interior Alaska measured over a 5 year period. This included the top and third wettest summers in the 91-year record and three summers with precipitation close to mean historical values. Increased rainfall led to deeper thaw across all sites with an increase of 0.7 ± 0.1 cm of thaw per cm of additional rain. Disturbed and wetland sites were the most vulnerable to rain-induced thaw with ~1 cm of surface thaw per additional 1 cm of rain. Permafrost in tussock tundra, mixed forest, and conifer forest was less sensitive to rain-induced thaw. A simple energy budget model yields seasonal thaw values smaller than the linear regression of our measurements but provides a first-order estimate of the role of rain-driven sensible heat fluxes in high-latitude terrestrial permafrost. This study demonstrates substantial permafrost thaw from the projected increasing summer precipitation across most of the Arctic region."

8
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 01, 2020, 03:08:28 PM »
With a hat tip to Tom Mazanec, the linked reference concludes that:

"We argue that the Arctic is currently experiencing an abrupt climate change event, and that climate models underestimate this ongoing warming."

This indicates that Arctic Amplification is likely higher than assumed by consensus climate models.

Jansen, E., Christensen, J.H., Dokken, T. et al. Past perspectives on the present era of abrupt Arctic climate change. Nat. Clim. Chang. 10, 714–721 (2020). https://doi.org/10.1038/s41558-020-0860-7

https://www.nature.com/articles/s41558-020-0860-7

Abstract: "Abrupt climate change is a striking feature of many climate records, particularly the warming events in Greenland ice cores. These abrupt and high-amplitude events were tightly coupled to rapid sea-ice retreat in the North Atlantic and Nordic Seas, and observational evidence shows they had global repercussions. In the present-day Arctic, sea-ice loss is also key to ongoing warming. This Perspective uses observations and climate models to place contemporary Arctic change into the context of past abrupt Greenland warmings. We find that warming rates similar to or higher than modern trends have only occurred during past abrupt glacial episodes. We argue that the Arctic is currently experiencing an abrupt climate change event, and that climate models underestimate this ongoing warming."

9
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 05:45:55 PM »
It certainly is not good news (w.r.t. Arctic Amplification) that two Arctic ice caps have already disappeared:

Title: "Going, Going, GONE: Two Arctic Ice Caps Have Disappeared"

https://www.discovermagazine.com/environment/going-going-gone-two-arctic-ice-caps-have-disappeared

Extract: "Two little Arctic ice caps that Mark Serreze studied as a graduate student in the early 1980s might not have been as grand and dramatic as other features of our planet's cryosphere, but to him they nonetheless were quite special.

Were quite special — past tense — because Serreze, who now directs the National Snow and Ice Data Center, has confirmed that the two ice caps on the Hazen Plateau of Canada's Ellsmere Island have disappeared. They're the victims of human-caused warming that has occurred three times more rapidly in the Arctic than anywhere else.

The disappearance was confirmed using recent images from the ASTER instrument aboard NASA’s Terra satellite."

10
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 04:06:02 PM »
...findings certainly support the concept that episodic bipolar MICI events between the marine glaciers in the NH and the SH may well have dominated SLR in this period.
This may be much different today, given different novel atmospheric chemistry (ie. ozone loss at both poles), and because of the CO2 buildup rate. Thus, where is the bipolarity now, the geological record will show both poles recording responses.


...

No paleo case matches today's situation and yet all scientists (consensus and otherwise) understand that there are lessons to be learned from the past behavior of various Earth Systems that can then be applied to ESMs in order to improve projections of future behavior.  Furthermore, when attempting to learn from paleo cases it is helpful to ask questions about the Earth Systems that are relevant rather than focusing on irrelevant cases (such as suggesting that because there are no paleo cases where the aerosol and/or ozone cases match our current anthropogenically driven situation that this invalidates the possibility of learning about the bipolar seesaw from paelo-evidence).

For example, the first image shows how the SST in the North Atlantic is associated with heat advected through the atmosphere from the North Atlantic to the Tropical Pacific where it can then be advected to either the WAIS or the Bering Sea area (depending on ENSO & SAM) as shown in the second image.  The SST of the North Atlantic can be impacted by freshwater hosing events whether due to paleo ice cliff calving from a marine glacier in the Barents Sea (see the third image) or due to a reversal of the Beaufort Gyre (see the fourth image) in a few years flushing freshwater into the North Atlantic; which could trigger a bipolar seesaw mechanism by advecting energy to the Tropical Pacific and then on to the WAIS.

11
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 12:05:31 AM »
While the linked reference does not prove that MICI dominated SLR during Meltwater Pulse 1A; its findings certainly support the concept that episodic bipolar MICI events between the marine glaciers in the NH and the SH may well have dominated SLR in this period.  Also, ice note that during this period there is a lot of direct evidence of ice-rafted debris accumulations in both the NH and the SH and that ice-rafted debris must come from MICI events as MISI ice mass loss occurs in marine glaciers with ice shelves which cannot generate ice-rafted debris (see the first image from the second linked reference).  So while consensus climate scientists can (and do) refuse to incorporate MICI mechanism into their climate models; there is a lot of ice-rafted debris (see the second image) around the would that suggests that they would be wise if they should do so:

Brendryen, J., Haflidason, H., Yokoyama, Y. et al. Eurasian Ice Sheet collapse was a major source of Meltwater Pulse 1A 14,600 years ago. Nat. Geosci. 13, 363–368 (2020). https://doi.org/10.1038/s41561-020-0567-4

https://www.nature.com/articles/s41561-020-0567-4?proof=true%3Ca+href%3D

Abstract: "Rapid sea-level rise caused by the collapse of large ice sheets is a threat to human societies. In the last deglacial period, the rate of global sea-level rise peaked at more than 4 cm yr−1 during Meltwater Pulse 1A, which coincided with the Bølling warming event some 14,650 years ago. However, the sources of the meltwater have proven elusive, and the contribution from Eurasian ice sheets has been considered negligible. Here, we present a regional carbon-14 calibration curve for the Norwegian Sea and recalibrate marine 14C dates linked to the Eurasian Ice Sheet retreat. We find that marine-based sectors of the Eurasian Ice Sheet collapsed at the Bølling transition and lost an ice volume of 4.5–7.9 m sea-level equivalents (SLE) over 500 years. During peak melting, 3.3–6.7 m SLE of ice was lost, potentially explaining up to half of Meltwater Pulse 1A. A mean meltwater flux of 0.2 Sv over 300 years was injected into the Norwegian Sea and the Arctic Ocean at a time when proxy evidence suggests vigorous Atlantic meridional overturning circulation. Our reconstruction shows that massive marine-based ice sheets can collapse in as little as 300–500 years."

See also:
Smith, J.A., Graham, A.G.C., Post, A.L. et al. The marine geological imprint of Antarctic ice shelves. Nat Commun 10, 5635 (2019). https://doi.org/10.1038/s41467-019-13496-5

https://www.nature.com/articles/s41467-019-13496-5

Abstract: "Reductions in the thickness and extent of Antarctic ice shelves are triggering increased discharge of marine-terminating glaciers. While the impacts of recent changes are well documented, their role in modulating past ice-sheet dynamics remains poorly constrained. This reflects two persistent issues; first, the effective discrimination of sediments and landforms solely attributable to sub-ice-shelf deposition, and second, challenges in dating these records. Recent progress in deciphering the geological imprint of Antarctic ice shelves is summarised, including advances in dating methods and proxies to reconstruct drivers of change. Finally, we identify several challenges to overcome to fully exploit the paleo record."

12
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 30, 2020, 08:34:39 AM »
The linked reference confirms that the ocean is warming globally and that the AMOC has been observed to be currently slowing and is expected to continue slowing with continuing global warming:

Johnson, G.C., Lyman, J.M. Warming trends increasingly dominate global ocean. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0822-0

https://www.nature.com/articles/s41558-020-0822-0
&
https://www.nature.com/articles/s41558-020-0822-0.epdf?sharing_token=XAe_EpnEyT3mMAOw2OZDodRgN0jAjWel9jnR3ZoTv0Mu-QJ5YGgHpvNJjdXiiG_qsknU8mrV_B-C6CX0vjXjFxpmNGcEQwLX8XSvp4LTRyEDVYltt34LeVCrAc_rDGn1A8vK8pSfCRMMpEF6hZ3-YibM4CvAT9JASjTXDvQz998%3D

Abstract: "The ocean takes up about 93% of the global warming heat entering Earth’s climate system. In addition, the associated thermal expansion contributes substantially to sea-level rise. Hence, quantifying the oceanic heat uptake rate and its statistical significance has been a research focus. Here we use gridded ocean heat content maps to examine regional trends in ocean warming for 0–700 m depth from 1993–2019 and 1968–2019, periods based on sampling distributions. The maps are from four research groups, three based on ocean temperature alone and one combining ocean temperature with satellite altimeter sea-level anomalies. We show that use of longer periods results in larger percentages of ocean area with statistically significant warming trends and less ocean area covered by statistically significant cooling trends. We discuss relations of these patterns to climate phenomena, including the Pacific Decadal Oscillation, the Atlantic Meridional Overturning Circulation and global warming."

Extract: "The 1993–2019 trend towards a warmer upper ocean (and higher sea levels) along the east coast of North America and cooling (with lower sea levels) in the subpolar North Atlantic (Fig. 1) is highly reminiscent of a pattern that has been linked to a reduction in the strength of the AMOC in models. Similar trends are visible for the 1968–2019 period, with the subpolar cooling muted over the longer period. A reduction in AMOC strength starting in 2009 relative to 2004–2008 has also been documented observationally and discussed, with 2004 being the first year of AMOC observations with a trans-Atlantic moored array. Our analysis indicates that the changes are large and long-term enough to support a statistically significant pattern in the 1993–2019 trends of upper-ocean heat content and even the 1968–2019 trends. However, the link of the cooling in the subpolar North Atlantic to reductions in the AMOC is difficult to disentangle, with a strong interannual cool event centred around 2015 being caused mostly by strong heat loss from the ocean to the atmosphere, rather than reduced advection of warm water northward associated with an AMOC reduction, which is expected to occur on longer timescales."


13
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 30, 2020, 08:16:43 AM »
The linked reference offers hope that regional climate forecasts may improve in the future by better representing the atmospheric eddy spectrum; however, it also indicates that a lot of physics is still missing from the current generation of climate models:

Smith, D.M., Scaife, A.A., Eade, R. et al. North Atlantic climate far more predictable than models imply. Nature 583, 796–800 (2020). https://doi.org/10.1038/s41586-020-2525-0

https://www.nature.com/articles/s41586-020-2525-0

Abstract: "Quantifying signals and uncertainties in climate models is essential for the detection, attribution, prediction and projection of climate change. Although inter-model agreement is high for large-scale temperature signals, dynamical changes in atmospheric circulation are very uncertain. This leads to low confidence in regional projections, especially for precipitation, over the coming decades. The chaotic nature of the climate system may also mean that signal uncertainties are largely irreducible. However, climate projections are difficult to verify until further observations become available. Here we assess retrospective climate model predictions of the past six decades and show that decadal variations in North Atlantic winter climate are highly predictable, despite a lack of agreement between individual model simulations and the poor predictive ability of raw model outputs. Crucially, current models underestimate the predictable signal (the predictable fraction of the total variability) of the North Atlantic Oscillation (the leading mode of variability in North Atlantic atmospheric circulation) by an order of magnitude. Consequently, compared to perfect models, 100 times as many ensemble members are needed in current models to extract this signal, and its effects on the climate are underestimated relative to other factors. To address these limitations, we implement a two-stage post-processing technique. We first adjust the variance of the ensemble-mean North Atlantic Oscillation forecast to match the observed variance of the predictable signal. We then select and use only the ensemble members with a North Atlantic Oscillation sufficiently close to the variance-adjusted ensemble-mean forecast North Atlantic Oscillation. This approach greatly improves decadal predictions of winter climate for Europe and eastern North America. Predictions of Atlantic multidecadal variability are also improved, suggesting that the North Atlantic Oscillation is not driven solely by Atlantic multidecadal variability. Our results highlight the need to understand why the signal-to-noise ratio is too small in current climate models, and the extent to which correcting this model error would reduce uncertainties in regional climate change projections on timescales beyond a decade."

See also:

Title: "Missed wind patterns are throwing off climate forecasts of rain and storms"

https://www.sciencemag.org/news/2020/07/missed-wind-patterns-are-throwing-climate-forecasts-rain-and-storms

Extract: "Kirtman thinks something fundamental is wrong with the models’ code. For the time being, he says, “You’re probably making pretty profound mistakes in your climate change assessment” by relying on regional forecasts. For example, models predicted that the Horn of Africa, which is heavily influenced by Indian Ocean winds, would get wetter with climate change. But since the early 1990s, rains have plummeted and the region has dried.

The missing predictability also undermines so-called event attribution, which attempts to link extreme weather to climate change by using models to predict how sea surface warming is altering wind patterns. The changes in winds, in turn, affect the odds of extreme weather events, like hurricanes or floods. But the new work suggests “the probabilities they derive will probably not be correct,” Smith says.

What’s not clear yet is why climate models get circulation changes so wrong. One leading hypothesis is that the models fail to capture feedbacks into overall wind patterns from individual weather systems, called eddies. “Part of that eddy spectrum may simply be missing,” Smith says. Models do try to approximate the effects of eddies, but at just kilometers across, they are too small to simulate directly. The problem could also reflect poor rendering of the stratosphere, or of interactions between the ocean and atmosphere. “It’s fascinating,” says Jennifer Kay, a climate scientist at the University of Colorado, Boulder. “But there’s also a lot left unanswered.”"

14
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:29:40 PM »
The linked articles (& associated linked references) indicate that anthropogenic GHG emissions is causing the mesosphere above Antarctica to cool at rates up to 10 times faster than the rate of increase of GMSTA.  Furthermore, this research identifies a new natural cycle not previously identified in the Antarctic upper atmosphere; which is a four-year cycle that the authored called the Quasi-Quadrennial Oscillation (QQO), which caused observed mesosphere temperatures to vary by 3-4 degrees C.  As it is not likely that the CMIP projections to date account for this QQO cycle in their models future generations (CMIP7) of ESM projects should be adjusted to simulate this signal which plausibly arises from an ocean–atmosphere response, and appears to have a signature in Antarctic sea ice extent.  Lastly, I note that the current ozone hole over Antarctica also serves to cool the upper atmosphere over Antarctica; so as the ozone hole heals itself this GHG driven cooling of the mesosphere over Antarctica will likely maintain current conditions that have causes the westerly winds over the Southern Ocean to accelerate since the 1970s; which will likely at least maintain the current upwelling volumes of warm CDW that has been accelerating ocean related ice melting around the Antarctic coastline since the 1970s.


Title: "Carbon Emissions Are Chilling The Atmosphere 90 Km Above Antarctica"

https://www.sciencealert.com/carbon-emissions-are-chilling-the-atmosphere-90km-above-antarctica-at-the-edge-of-space

Extract: "While greenhouse gases are warming Earth's surface, they're also causing rapid cooling far above us, at the edge of space.

In fact, the upper atmosphere about 90 kilometres (56 miles) above Antarctica is cooling at a rate 10 times faster than the average warming at the planet's surface.

Rising greenhouse gas emissions are contributing to the temperature changes we recorded, but a number of other influences are also at play. These include the seasonal cycle (warmer in winter, colder in summer) and the Sun's 11-year activity cycle (which involves quieter and more intense solar periods) in the mesosphere.

One challenge of the research was untangling all these merged "signals" to work out the extent to which each was driving the changes we observed.

Surprisingly in this process, we discovered a new natural cycle not previously identified in the polar upper atmosphere. This four-year cycle which we called the Quasi-Quadrennial Oscillation (QQO), saw temperatures vary by 3-4 degrees C in the upper atmosphere.

But the finding has big implications for climate modelling. The physics that drive this cycle are unlikely to be included in global models currently used to predict climate change. But a variation of 3-4 degrees C every four years is a large signal to ignore.

We don't yet know what's driving the oscillation. But whatever the answer, it also seems to affect the winds, sea surface temperatures, atmospheric pressure and sea ice concentrations around Antarctica.

See also:

Title: "Antarctic research unlocks mysteries of the upper atmosphere"

https://www.antarctica.gov.au/news/2020/antarctic-research-unlocks-mysteries-of-the-upper-atmosphere/

&

French, W. J. R., Mulligan, F. J., and Klekociuk, A. R.: Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 1: long-term trends, Atmos. Chem. Phys., 20, 6379–6394, https://doi.org/10.5194/acp-20-6379-2020, 2020.

https://www.atmos-chem-phys.net/20/6379/2020/acp-20-6379-2020.html

Abstract
The long-term trend, solar cycle response, and residual variability in 24 years of hydroxyl nightglow rotational temperatures above Davis research station, Antarctica (68∘ S, 78∘ E) are reported. Hydroxyl rotational temperatures are a layer-weighted proxy for kinetic temperatures near 87 km altitude and have been used for many decades to monitor trends in the mesopause region in response to increasing greenhouse gas emissions. Routine observations of the OH(6-2) band P-branch emission lines using a scanning spectrometer at Davis station have been made continuously over each winter season since 1995. Significant outcomes of this most recent analysis update are the following: (a) a record-low winter-average temperature of 198.3 K is obtained for 2018 (1.7 K below previous low in 2009); (b) a long-term cooling trend of −1.2±0.51 K per decade persists, coupled with a solar cycle response of 4.3±1.02 K per 100 solar flux units; and (c) we find evidence in the residual winter mean temperatures of an oscillation on a quasi-quadrennial (QQO) timescale which is investigated in detail in Part 2 of this work.
Our observations and trend analyses are compared with satellite measurements from Aura/MLS version v4.2 level-2 data over the last 14 years, and we find close agreement (a best fit to temperature anomalies) with the 0.00464 hPa pressure level values. The solar cycle response (3.4±2.3 K per 100 sfu), long-term trend (−1.3±1.2 K per decade), and underlying QQO residuals in Aura/MLS are consistent with the Davis observations. Consequently, we extend the Aura/MLS trend analysis to provide a global view of solar response and long-term trend for Southern and Northern Hemisphere winter seasons at the 0.00464 hPa pressure level to compare with other observers and models.

&

French, W. J. R., Klekociuk, A. R., and Mulligan, F. J.: Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 2: Evidence of a quasi-quadrennial oscillation (QQO) in the polar mesosphere, Atmos. Chem. Phys., 20, 8691–8708, https://doi.org/10.5194/acp-20-8691-2020, 2020.

https://www.atmos-chem-phys.net/20/8691/2020/

Abstract
Observational evidence of a quasi-quadrennial oscillation (QQO) in the polar mesosphere is presented based on the analysis of 24 years of hydroxyl (OH) nightglow rotational temperatures derived from scanning spectrometer observations above Davis research station, Antarctica (68∘ S, 78∘ E). After removal of the long-term trend and solar cycle response, the residual winter mean temperature variability contains an oscillation over an approximately 3.5–4.5-year cycle with a peak-to-peak amplitude of 3–4 K. Here we investigate this QQO feature in the context of the global temperature, pressure, wind, and surface fields using satellite, meteorological reanalysis, sea surface temperature, and sea ice concentration data sets in order to understand possible drivers of the signal. Specifically, correlation and composite analyses are made with data sets from the Microwave Limb Sounder on the Aura satellite (Aura/MLS v4.2) and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite (TIMED/SABER v2.0), ERA5 reanalysis, the Extended Reconstructed Sea Surface Temperature (ERSST v5), and Optimum-Interpolation (OI v2) sea ice concentration. We find a significant anti-correlation between the QQO temperature and the meridional wind at 86 km altitude measured by a medium-frequency spaced antenna radar at Davis (R2∼0.516; poleward flow associated with warmer temperatures at ∼0.83±0.21 K (ms−1)−1). The QQO signal is also marginally correlated with vertical transport as determined from an evaluation of carbon monoxide (CO) concentrations in the mesosphere (sensitivity 0.73±0.45 K ppmv−1 CO, R2∼0.18). Together this relationship suggests that the QQO is plausibly linked to adiabatic heating and cooling driven by the meridional flow. The presence of quasi-stationary or persistent patterns in the ERA5 data geopotential anomaly and the meridional wind anomaly data during warm and cold phases of the QQO is consistent with tidal or planetary waves influencing its formation, which may act on the filtering of gravity waves to drive an adiabatic response in the mesosphere. The QQO signal plausibly arises from an ocean–atmosphere response, and appears to have a signature in Antarctic sea ice extent.

Edit:  The first image shows that the Stratosphere and Troposphere are at much lower altitudes than the mesosphere (at 90km up), the second image shows that the ozone hole produces an atmospheric geopotential well over all of Antarctic and the third image shows that the low pressure typically over Antarctica (which is associated with the atmospheric geopotential well) not only contributes to accelerated westerly winds over the Southern Ocean but also contributes to accelerated katabatic winds that can contribute to accelerated surface ice melting along the Antarctic coastal areas as occurred over the Ross Ice Shelf a few years ago.

15
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:13:07 PM »
The linked reference indicates that in addition to the freshwater accumulated in the Beaufort Gyre the entire Arctic Ocean surface layer has been accumulating atypically high volumes of freshwater that are only recently beginning to leak atypically high volumes of freshwater into the North Atlantic.  This implies that for many years now the fully impacts of unusually high (anthropogenically driven) discharges of freshwater into the Arctic Ocean (and then on to the North Atlantic) have been masked.  As thick layers of freshwater in the Arctic Ocean reduce the rate of heat flux from the deeper/warming layers of ocean water into the Arctic atmosphere, this atypically high accumulation of freshwater in the Arctic Ocean surface layers implies that in recent years the Arctic has been cooler than it otherwise would have been (without this atypically high accumulation).  Thus if/when the Beaufort Gyre finally reverses it will likely not only release excessively high freshwater volumes accumulated in the Gyre into the North Atlantic, but it would likely also flush excess freshwater from the atypically high accumulations from the ocean surface layers in much of the Arctic Ocean and would likely melt large portions of the existing sea ice; which, would flush even more freshwater into the North Atlantic where as of this additional freshwater flux would serve to rapidly slow the AMOC:

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

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088854?af=R

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

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

Key points
•   The observed increase in Arctic liquid freshwater (FW) storage is likely already driven by climate change
•   A forced change in liquid FW flux through Nares Strait is likely to emerge within the next decade
•   The already changing nature of many FW budget terms can delay detection of shift and emergence from observations

16
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:00:00 PM »
The linked reference confirms that, within the study area, a multidecadal trend of decreasing anthropogenic aerosol emissions has been observed.  While this is good, as aerosol radiative forcing/feedback is negative, it means that if the tend continues (as expected) that anthropogenic GHG emissions need to be cut-back to a net zero scenario as soon as possible:

Collaud Coen, M., Andrews, E., Alastuey, A., Arsov, T. P., Backman, J., Brem, B. T., Bukowiecki, N., Couret, C., Eleftheriadis, K., Flentje, H., Fiebig, M., Gysel-Beer, M., Hand, J. L., Hoffer, A., Hooda, R., Hueglin, C., Joubert, W., Keywood, M., Kim, J. E., Kim, S.-W., Labuschagne, C., Lin, N.-H., Lin, Y., Lund Myhre, C., Luoma, K., Lyamani, H., Marinoni, A., Mayol-Bracero, O. L., Mihalopoulos, N., Pandolfi, M., Prats, N., Prenni, A. J., Putaud, J.-P., Ries, L., Reisen, F., Sellegri, K., Sharma, S., Sheridan, P., Sherman, J. P., Sun, J., Titos, G., Torres, E., Tuch, T., Weller, R., Wiedensohler, A., Zieger, P., and Laj, P.: Multidecadal trend analysis of in situ aerosol radiative properties around the world, Atmos. Chem. Phys., 20, 8867–8908, https://doi.org/10.5194/acp-20-8867-2020, 2020.

https://www.atmos-chem-phys.net/20/8867/2020/

Abstract
In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

17
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 03:54:33 PM »
The linked reference (which includes Gavin Schmidt as a co-author) finds that:

"ECS estimates from ≥300‐year coupled simulations from current US models range from 3.1°C to 7.0°C ..."

However, the reference also cautions that different modeling assumptions and different methodologies result in different values for ECS and that:

"Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models."

John P. Dunne et al. (23 July 2020), "Comparison of equilibrium climate sensitivity estimates from slab ocean, 150‐year, and longer simulations", Geophysical Research Letters, https://doi.org/10.1029/2020GL088852

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088852?af=R

Abstract

We compare equilibrium climate sensitivity (ECS) estimates from pairs of long (≥ 800‐year) control and abruptly quadrupled CO2 simulations with shorter (150, 300 year) coupled atmosphere‐ocean simulations and Slab Ocean Models (SOM). Consistent with previous work, ECS estimates from shorter coupled simulations based on annual averages for years 1‐150 underestimate those from SOM (‐8% ± 13%) and long (‐14% ± 8%) simulations. Analysis of only years 21‐150 improved agreement with SOM (‐2% ± 14%) and long (‐8% ± 10%) estimates. Use of pentadal averages for years 51‐150 results in improved agreement with long simulations (‐4% ± 11%). While ECS estimates from current generation US models based on SOM and coupled annual averages of years 1‐150 range from 2.6°C to 5.3°C, estimates based longer simulations of the same models range from 3.2°C to 7.0°C. Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models.

Plain Language Summary
Precise definition and estimation of Equilibrium Climate Sensitivity (ECS) continues to challenge model inter‐comparison. While annual analyses of years 1‐150 of coupled atmosphere‐ocean models agree with slab ocean model simulations, they underestimate coupled ECS estimates from multi‐centennial to millennial scale simulations. However, long‐term ECS estimates can be largely recovered through a combination of 1) ignoring the first 50 years of abrupt 4x preindustrial CO2 simulation dominated by early timescales of ocean response and 2) using pentadal (5‐year) averages instead of annual ones for years 51‐150. This variation between methods argues for reconsideration of ECS estimation and application acknowledging that slab‐ocean estimates systematically ignore potential sources of enhanced sensitivity and simulations longer than 150 years are necessary for precise estimation of the long‐term trend.

Key Points
•   Equilibrium Climate Sensitivity (ECS) estimates for a single coupled model can vary by more than 1°C (20%) depending on analysis method
•   ECS estimates from ≥300‐year coupled simulations from current US models range from 3.1°C to 7.0°C, another method giving 2.7°C to 5.3°C
•   Analysis of years 21‐150 agrees with slab ocean ECS, but pentadal analysis of years 51‐150 reduces bias against long, coupled simulations


18
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 03:44:14 PM »
The linked reference indicates that current ESM projections (such as the high-end CMIP6 models like E3SMv1) that include Antarctic ice shelf melting do not yet account for tidal impacts; which according to the reference significantly increases ice shelf melting and should be accounted for in future (CMIP7) generations of projections.  When this tidal impacts are included, future projections will likely project most significant future slowing of the MOC.

Richter, O., Gwyther, D. E., King, M. A., and Galton-Fenzi, B. K.: Tidal Modulation of Antarctic Ice Shelf Melting, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-169, in review, 2020.

https://tc.copernicus.org/preprints/tc-2020-169/

Abstract. Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 °C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 °C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (150 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.

19
Antarctica / Re: The State of Wilkes Basin Glaciers
« on: July 27, 2020, 07:13:42 PM »
Regarding what is the real 'doomsday glacier', the IPCC’s SROCC says that “Thwaites Glacier is particularly important because it extends into the interior of the WAIS, where the bed is >2000m below sea level in places”. 

Although, the SROCC also notes that while MISI requires a retrograde bed slope to occur, MICI could even happen on a flat or seaward-inclined bed where combined with hydrofracturing (see the first attached image from the SROCC).  So a key question regarding the Wilkes MICI stability is when will the local coastal surface temperatures (say at EL +100m) be high enough to induce frequent ice surface melting in the January to February timeframe; which is a function of both TCR and ECS (see the second image from E3SMv1 which includes the influence of a slowdown of the MOC due to projected freshening of the North Atlantic and Southern Ocean surface waters).

20
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 26, 2020, 03:09:26 PM »
Don't worry, ASLR, we can wait.

While we all wait a year (or so) for me to create an annual summary of long-tailed climate risk issues in a tightly grouped series of cross-correlated posts, I present the attached images (from the two linked references) showing the bathymetries of key ASE marine glaciers and how the Thwaites gateway at base of the Thwaites Ice Tongue is deep enough to sustain ice-cliff failure mechanisms that could propagate upstream into the BSB once initiated:

Hogan, K. A., Larter, R. D., Graham, A. G. C., Arthern, R., Kirkham, J. D., Totten Minzoni, R., Jordan, T. A., Clark, R., Fitzgerald, V., Anderson, J. B., Hillenbrand, C.-D., Nitsche, F. O., Simkins, L., Smith, J. A., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Revealing the former bed of Thwaites Glacier using sea-floor bathymetry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-25, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-25/

Caption of image 1: "Figure 2: (a) New MBES grid for the inner Amundsen Sea Embayment. Ice-velocity data from the MEaSUREs V2 dataset (Mouginot et al., 2019); grounding lines for 1992 and 2011 are from Rignot et al. (2011), and that for 2017 from Milillo et al. (2019); red arrows delineate CDW pathways after Dutrieux et al. (2014) and Milillo et al. (2019). The black dashed line marks the boundaries of the drainage basin of Thwaites Glacier (Vaughan et al., 2001). (b) NBP19-02 data coverage versus other MBES datasets (Table 1). The dark blue coastline illustrates the ice-shelf and ice-mélange extent during survey on NBP19-02 and was digitised from Landsat 8 imagery."

&

Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-294, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2019-294/

Extract: "Airborne gravity provides a good first order estimate of sub-ice-shelf bathymetry. Despite the relatively high uncertainty (~100 m standard deviation) comparisons with different gravity inversion techniques, and new observational bathymetric data, indicate that the pattern of sub-ice-shelf bathymetry is well resolved.

Thwaites Glacier is connected to the deep ocean by a major trough >800 m deep and 20 km wide. In contrast the grounding lines of the of Dotson and Crosson ice shelves are accessible through relatively narrow channels and thin sub shelf cavities. In the Thwaites, Dotson and Crosson region, areas of ice shelf which developed before and after 1993 form distinct populations. The most recently un-grounded areas are underlain by thin cavities (average 112 m) where the ice shelf base closely tracks the underlying bed topography."

Caption of image 2: "Figure 2: New bathymetry and cavity maps. a) Final topography from terrain shift method. White lines A-D mark profiles in Fig. 3. Yellow outline encloses region constrained by gravity data. Pink line shows -800m depth contour. Light grey lines mark grounding lines and ice shelf edge."

Caption of image 3: "Figure 3: Profiles across ice shelves. Upper panel shows ice surface from REMA DEM (Howat et al., 2019) and base of ice shelf calculated assuming hydrostatic equilibrium, together with gravity-derived bathymetric estimates. Second panel shows input freeair gravity anomaly. Third panel shows magnetic anomalies derived from ITGC survey data (REF data doi) and ADMAP2 (Golynsky et al., 2018). a) Thwaites Eastern Ice Shelf. b) Thwites Glacier Tongue. c) Crosson Ice Shelf. d) Dotson Ice Shelf. Note 520 thin cavity in regions of ice sheet grounding line retreat since 1993 (grey boxes)."

The forth image shows conceptual models for the formation of the subglacial cavities for the key ASE marine glaciers

21
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 25, 2020, 04:45:36 PM »
In this talk from October 2019, Eric Rignot suggests the possibility of 4 meters of sea level rise per century.
...

Rignot is a very honorable climate scientist who acknowledges that there is a lot of deep uncertainties associated ice sheet instability in the coming century, which raises the risk of 4 meter eustatic SLR this century (whether 2000 or 2020).  Unfortunately, this long-tail ice mass climate risk is too complicated for him to effectively express to either the public and/or to decision makers; and I get the feeling that this thread is at best a small flashlight peering into a large black cave; where most readers forget what they just saw as the flashlight moves around the cave.  As I have other work to do today, I will just mention a very few fat-tail ice-climate risk factors that Rignot's talk did not have the time to express:

1. Abrupt ice sheet mass loss can quickly slow the MOC; which can abruptly increase climate sensitivity.
2. Anthropogenic warming has been occurring for 250-years since pre-industrial times so many slow-response positive feedback mechanisms are already being activated today.
3. The frequency of Super El Nino events are projected to increase with continued global warming; which will accelerate the telecommunication of Tropical Pacific heat energy directly to West Antarctica.
4. If/when the ASE marine glaciers collapse, this will advect a pulse of freshened surface ocean water counter-clockwise around the coast of Antarctica (all the way to the Weddell Sea) that will accelerate the upwelling of warm CDW to the grounding line of key marine glaciers in both East and West Antarctica.
5. Marine ice cliff instability can progress back/up along a mild prograde bed slope.
6. The grounding line at the base of the Thwaites Ice Tongue has progressed further upstream than Rignot's 2019 talk indicates.
7. Rignot did not mention the probability of a cascade of freshwater hosing tipping events between the NH and the SH that characterized the Meltwater Pulse 1A event that Rignot cited as evidence that 4m of eustatic SLR might occur this century.

I need to go now, but readers should not forget to use the search function of this thread to look up past posts that discuss issues like: a) seismic/volcanic activity, b) geothermal heat flux, c) aerosol masking, d) methane feedback mechanisms etc. etc. etc.

22
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 10:26:43 PM »
Very good.

23
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 09:14:21 PM »
...
Thanks for trying to help me understand this topic. So does this mean that CS is a dynamic value, could be today 3C, and in 30 years increase to 5C?

...

Currently working on a video which ends with this, 'Both the Aurora, and Wilkes Basin ice is prone to the so called marine ice sheet instability, the potential for ice sheets grounded below sea level to destabilize in a runaway fashion.'

Regarding your first question on changes of climate sensitivity (CS) with time; this is a complex topic to appreciate the numerous subtle issues; nevertheless, CS does change with GMST as clearly indicated by the paleorecord (with warmer periods having higher CS values), but also with the rate of radiative forcing, initial climate parameters (such as the ozone hole over Antarctica, etc).  Some feedbacks impact both TCR (& consequently ECS) such as the ice content of the clouds over the Southern Ocean (as shown by several high end CMIP6 projections) and possible slowing of the MOC due for freshwater hosing (as partially demonstrated by E3SMv1).  Furthermore, ECS can progressively increase due to tipping points of Earth Systems such as: permafrost, rainforest carbon sinks and changes in albedo (such as from changes in snow cover and/or sea ice coverage).  Also, ECS might currently be masked (say by highly negative aerosol forcing) to say effectively be 3C (see the first image) as measured by observations, but its true value of say 5C (see the second image) could be unmasked in say 30 years if there were to be a marked decrease in anthropogenic aerosol emissions in that time.  Finally, an abrupt freshwater hosing event would temporarily increase the planetary imbalance of radiative forcing (see the third image) and which might increase the tropical ocean SSTA by say 5C, which would increase high-energy evaporation from the tropical ocean which would produce more high altitude clouds (an fewer low altitude clouds) for a marked increase in net radiative forcing (see the fourth image) that might abruptly increase both TCR and ECS over several decades time.

Also, when you make your video on marine ice sheet instability (MISI) try to explain the difference between MISI and MICI and note that different marine glaciers could experience tipping points in a cascade, where say the initial collapse of Thwaites Glacier could trigger the collapse of other marine glaciers in Antarctic and/or via the bipolar seesaw of marine terminating glaciers in Greenland.

24
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 04:54:41 PM »
Transient Climate Response, TCR, only addresses fast feedback mechanisms (and not the slow feedback mechanisms) and thus TCR is smaller than ECS.  Furthermore, IPCC's AR5 explicitly calculates a Carbon Budget using TCR values, and they ignore uncertainties in estimating TCR such as cloud feedback uncertainties, aerosol feedback uncertainties (see the first image) and freshwater hosing uncertainties (see the second image from E3SMv1 where the high 2.93C value for TCR has been attributed to hosing images on the MOC).

Also, both TCR and ECS (see the third image) have numerous different definitions depending on timeframe and method of approximation.  Lastly, all AR and CMIP projections of both TCR and ECS assume that we will not cross a tipping point (see the fourth image) possibly leading to an abrupt increasing in climate sensitivity within the next hundred years.

25
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 08:21:26 PM »
Gavin Schmidt makes a few good points about Sherwood et al (2020) in the linked article:

Title: "Climate Sensitivity: A new assessment"

http://www.realclimate.org/index.php/archives/2020/07/climate-sensitivity-a-new-assessment/#more-23158

Extract: "The paper is exhaustive (and exhausting – coming in at 166 preprint pages!) and concludes that equilibrium climate sensitivity is likely between 2.3 and 4.5 K, and very likely to be between 2.0 and 5.7 K.

I should be clear that although (I think) this is the best and most thorough assessment of climate sensitivity to date, I don’t think it is the last word on the subject. During the research on this paper, and the attempts to nail down each element of the uncertainty, there were many points where it was clear that more effort (with models or with data analysis) could be applied (see the paper for details). In particular, we could still do a better job of tying paleo-climate constraints to the other two classes. Additionally, new data will continue to impact the estimates – whether it’s improvements in proxy temperature databases, cloud property measurements, or each new year of historical change. New, more skillful, models will also help, perhaps reducing the structural uncertainty in some of the parameters (though there is no guarantee they will do so)."


26
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 12:51:30 AM »
...
Thanks ASLR for linking to this new, major study.

Their approach to not using GCM's is refreshing: "...we avoid relying on GCMs to tell us what values to expect for key feedbacks except where the feedback mechanisms can be calibrated against other evidence." (p 8 of a total of 184 pages)

I believe this is good advice for everyone.

To me human bias (including bias by consensus climate science) is what got us all in to the current climate emergency that we are all facing; and thinking that humans will find a path forward through this crisis without using the best ESMs available now and incrementally in the future (such as E3SMv4 calibrated using machine learning ) is shortsighted.

27
Antarctica / Re: Antarctic Methane Concentrations
« on: July 22, 2020, 05:20:56 PM »
The linked reference discusses how gas hydrates in the bed sediment beneath marine glaciers can cause 'sticky spots' that can regulate ice stream flow rates:

Winsborrow, M., K. Andreassen, A. Hubbard, A. Plaza-Faverola, E. Gudlaugsson and H. Patton (2016). "Regulation of ice stream flow through subglacial formation of gas hydrates." Nature Geosci 9(5): 370-374, DOI: 10.1038/NGEO2696

https://www.nature.com/articles/ngeo2696
&
http://www.nature.com/articles/ngeo2696.epdf?referrer_access_token=IHHHsNRUI3lD2eFpTMWvl9RgN0jAjWel9jnR3ZoTv0N6H6twa9eus1zouX_OVF0HHps81v4XTc0_11DCSpeGLDxz98tw1yul2mr16lbVJL4uOjHYggNVEvnorXQDpPb-4F8Dx03N10vp8xTpF1OSQUCQuGQbrx_agiKHwJMiE0Vb3p9RlZE1kgUDa_7CPZDbIHfa0-zC2RtwAc1-HEOzfwPw5ovCnEJWlCwr6K4nmQjxYGctlb4MLBBjUrGaOUBg&tracking_referrer=austhrutime.com

 Abstract: "Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice–bed interface remains elusive. Basal resistance is critical, especially sticky spots—localized zones of high basal traction—for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea–Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction—a sticky spot— that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon."

Also see:

Title: "Regulation of Ice Stream Flow Through Subglacial Formation of Gas Hydrates"

http://austhrutime.com/ice_stram_flow_regulation_subglacial_gas_hydrates.htm

Extract: "Based on the presence of extensive sedimentary basins and modelling studies (Wadham et al., 2012; Wallmann et al., 2012) it is proposed that abundant gas hydrate accumulations are present beneath the ice sheets of Greenland and Antarctica. Also, gas hydrates have been identified in ice core samples obtained from above the subglacial Lake Vostok in East Antarctica (Uchida et al., 1994). The role of potentially widespread gas hydrate reservoirs in the modification of the thermomechanical regime at the base of contemporary ice sheets, which makes them critically sensitive, as well as their impact on ice steam force balance and dynamics has, so far, not been recognised. This control that was previously unforeseen, given the current lack of knowledge with regard to the distribution of gas hydrate, represents a significant unknown in attempts to model the current and future discharge and evolution of contemporary ice sheets, as well as their contribution to rising global sea levels."

I remind readers that if the Byrd Subglacial Basin, BSB, were to sustain an MICI-type of collapse in the coming decades that it is probably that a meaningful about of methane would be released from the methane hydrates in the bed of the Thwaites, and adjoining, glaciers.

28
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 02:27:40 AM »
The linked article indicates that NSF has now approved $3 million for ice coring on the WAIS/EAIS divide to help determine whether the WAIS collapsed during the Eemian as some climate scientists believe:

Title: "NSF campaign will drill for ice capturing West Antarctica’s last collapse", Jul. 10, 2020

https://www.sciencemag.org/news/2020/07/nsf-campaign-will-drill-ice-capturing-west-antarctica-s-last-collapse

Extract: "Next week, the National Science Foundation will fund a 5-year project, costing more than $3 million, that will seek evidence of this collapse from gases trapped in tiny bubbles encased in a 2.5 kilometer-long tube of ice. The core drilling, likely to start in 2023, will target Hercules Dome, an expanse of ice 400 kilometers from the South Pole. Hercules sits at the saddle between the continent’s western and eastern ice sheets; if the western one collapsed, “Hercules Dome would be sitting on the waterfront, so to speak,” says Eric Steig, the project’s principal investigator and a glaciologist at the University of Washington, Seattle.

The Eemian, the last warm period between the ice ages, lasting from 129,000 to 116,00 years ago, is one of the best analogs for modern Earth. Temperatures were about 1° warmer than now, yet sea levels were 6 meters to 9 meters higher. And recent work, some still unpublished, has suggested much of this melt must have come from Antarctica."

29
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 12:19:02 AM »
The first reference indicates that in West Antarctica subglacial lake formation/filling is related to ice velocities.  The second reference and associated image show the catchment area and ice velocities for the PIG and Thwaite Glacier.  Furthermore, I highlight the following passage from the second reference (as the active subglacial lakes, in a cascade system-type, beneath the trunk of Thwaites Glacier, are currently refilling and could readily cause a surge in ice flow at the base of the Thwaites Ice Tongue circa 2030 to 2035):

"… the subglacial water drainage area of TG is bigger than previously thought and recent investigations (e.g., Smith et al., 2017) have demonstrated the presence of active subglacial lakes, in a cascade system-type, beneath the trunk of TG. Any water accumulation/drainage (e.g., chain of active subglacial lakes) in this area may affect the basal friction of the ice and therefore the ice flow velocity."

E. J. MacKie, D. M. Schroeder, J. Caers, M. R. Siegfried and C. Scheidt (08 March 2020), "Antarctic Topographic Realizations and Geostatistical Modeling Used to Map Subglacial Lakes", JGR Earth Surface, https://doi.org/10.1029/2019JF005420

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JF005420

Abstract
Antarctic subglacial lakes can play an important role in ice sheet dynamics, biology, geology, and oceanography, but it is difficult to definitively constrain their character and locations. Subglacial lake locations are related to factors including heat flux, ice surface slope, ice thickness, and bed topography, though these relationships are not fully quantified. Bed topography is particularly important for determining where water flows and accumulates, but digital elevation models of the ice sheet bed rely on interpolation and are unrealistically smooth, biasing estimates of subglacial lake location and surface area. To address this issue, we use geostatistical methods to simulate realistically rough bed topography. We use our simulated topography to predict subglacial lake distribution across the continent using a binomial logistic regression, which uses physical parameters and known lake locations to calculate the probabilities of lake occurrences. Our results suggest that topography models interpolated without appropriate geostatistics overestimate subglacial lake surface area and that total lake surface area is lower than previously predicted. We find that radar‐detected lakes are more likely to occur in the interior of East Antarctica, while altimetry‐detected (active) lakes are expected to be found in West Antarctica and near the grounding line. We observe that radar‐detected lakes have a high correlation with heat flux and ice thickness, while active lakes are associated with higher ice velocity.

&

Felipe Napoleoni et al. (20 March 2020), "Subglacial lakes and hydrology across the Ellsworth Subglacial Highlands, West Antarctica", The Cryosphere Discussions, http://doi.org/10.5194/tc-2020-68

https://tc.copernicus.org/preprints/tc-2020-68/tc-2020-68.pdf

Extract: "The subglacial hydrological catchments of Pine Island and Thwaites Glaciers We observe that most of the subglacial water draining towards ASE is routed through the Bentley Subglacial Trench in the upper part of the hydrological catchment and driven through the Byrd Subglacial Basin towards the trunk of Thwaites Glacier. The high topography in the mid PIG catchment (Vaughan et al., 2006) means that the hydrological drainage system does not link to the faster flowing trunk of PIG. Instead, the basal hydrological system is captured by Thwaites. This drainage pattern has two main implications. Firstly, the subglacial hydrological catchments of PIG and Thwaites do not correspond to the ice catchments; they do not coincide either in position or size. Secondly, the hydrological system of TG trunk (Schroeder et al., 2013) may be fed by water sourced in the upper glaciological catchment of PIG, within the ESH.

Any change in the water catchment of the TG, at the head of PIG, could therefore have important glaciological consequences for the ice dynamics of Thwaites Glacier and the wider ASE. This is particularly critical since the subglacial water drainage area of TG is bigger than previously thought and recent investigations (e.g., Smith et al., 2017) have demonstrated the presence of active subglacial lakes, in a cascade system-type, beneath the trunk of TG. Any water accumulation/drainage (e.g., chain of active subglacial lakes) in this area may affect the basal friction of the ice and therefore the ice flow velocity. Conversely, this pattern may have a reduced importance for PIG in terms of magnitude or timing due to the topographic barrier disconnecting the drainage upstream with the lower/marginal section of PIG. If we are to clearly understand the potential role of subglacial water on the ice dynamics of the PIG and Thwaites systems, then more investigations of the detailed subglacial and hydrological conditions are required."

Caption: "Figure 9. Mean annual ice surface velocity (Mouginot et al., 2019) of Pine Island Glacier, Rutford Ice Stream, Institute Ice Stream, Bindschedler Ice Stream and Thwaites Glacier. Black line shows ice surface velocities higher than 250 myr−1 . The red line indicates the boundary of the water catchment. The blue lines show the subglacial water drainage and the arrows indicates the general flow direction. The Cryosat-2 Elevation model (1 km), virtual hillshade (Helm et al., 2014) is showed in the background. ASE: Amundsen Sea Embayment; BSB: Byrd Subglacial Basin; BST: Bentley Subglacial Trench. Projection: Antarctic Polar Stereographic (EPSG 3031). B) shows the histogram of surface ice velocity over the central part of each subglacial lakes."

30
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 21, 2020, 08:39:25 PM »
For those who are interested, I provide the following open access linked reference (& associated article) about the thermal and compositional structure of the Antarctic lithosphere (which is thin beneath the WAIS):

F. Pappa, J. Ebbing, F. Ferraccioli and W. van der Wal (25 October 2019), "Modeling Satellite Gravity Gradient Data to Derive Density, Temperature, and Viscosity Structure of the Antarctic Lithosphere", Journal of Geophysical Research: Solid Earth, Volume 124, Issue 11, https://doi.org/10.1029/2019JB017997

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JB017997

Abstract
In this study we combine seismological and petrological models with satellite gravity gradient data to obtain the thermal and compositional structure of the Antarctic lithosphere. Our results indicate that Antarctica is largely in isostatic equilibrium, although notable anomalies exist. A new Antarctic Moho depth map is derived that fits the satellite gravity gradient anomaly field and is in good agreement with independent seismic estimates. It exhibits detailed crustal thickness variations also in areas of East Antarctica that are poorly explored due to sparse seismic station coverage. The thickness of the lithosphere in our model is in general agreement with seismological estimates, confirming the marked contrast between West Antarctica (<100 km) and East Antarctica (up to 260 km). Finally, we assess the implications of the temperature distribution in our model for mantle viscosities and glacial isostatic adjustment. The upper mantle temperatures we model are lower than obtained from previous seismic velocity studies. This results in higher estimated viscosities underneath West Antarctica. When combined with present‐day uplift rates from GPS, a bulk dry upper mantle rheology appears permissible.

Plain Language Summary
The solid Earth structure of the Antarctic continent is still poorly explored due to the coverage of up to 4‐km‐thick ice sheets and its remote location. Robust knowledge of its characteristics is, however, essential to understand the Earth's response to ice mass changes (glacial isostatic adjustment). Of particular interest are the depth and geometry of the main subsurface boundaries, which are the interface between crustal and mantle rocks (Moho discontinuity) and the base of the rigid tectonic plate (lithosphere). Since both of them are accompanied by changes in rock density, we used gravimetric data from the Gravity Field and Steady‐State Ocean Circulation Explorer satellite to build a 3‐D model of Antarctica's deep structure. Rock composition according to temperature and pressure is taken into account. Rock composition according to temperature and pressure is taken into account and the model as a whole is internally consistent. As a result, we present a continental‐scale Moho depth map that shows novel details. From the temperature distribution in our model, we derive present‐day uplift rates of the solid Earth's surface, which are a key parameter in estimating the future ice sheet evolution.

&

Title: "GOCE reveals what’s going on deep below Antarctica"

https://yubanet.com/scitech/goce-reveals-whats-going-on-deep-below-antarctica/

Extract: "“Under West Antarctica, Earth’s crust is comparatively thin at about 25 kilometres, and the mantle is viscous at less than 100 kilometres. East Antarctica, on the other hand, is an old cratonic shield. Here, the mantle rock still has solid properties at a depth of more than 200 kilometres.”"

31
...

But how can rising sea levels cause volcanoes to erupt? The answer lies in the enormous mass of the water pouring into the ocean basins from the retreating ice sheets. The addition of over a hundred metres depth of water to the continental margins and marine island chains, where over 60% of the world's active volcanoes reside, seems to be sufficient to load and bend the underlying crust.

I note that while the eustatic SLR this century may be limited to the 3 to 4m range; nevertheless, the change in the weight of grounded ice bearing on the bed of the WAIS could well be equal to many hundreds of meter of equivalent water height.  Thus, volcanic and seismic activity could become very active in the WAIS region after about 2045 (assuming an MICI-type of collapse of the ice in the Byrd Subglacial Basin, BSB); which would likely accelerate ice mass loss from the Bellingshausen, Weddell, and Ross Sea sectors after this time.  Furthermore, I note that McConnell et al. (2017) provides evidence that about 17.7 ka Mt Takahe (on the edge of the BSB, see the attached image) erupted and sent halogen-rich emissions high into the atmosphere that caused ozone depletion of the stratosphere over Antarctica, and I note that such an ozone depletion could well keep the westerly winds over the Southern Ocean in a range that promotes upwelling of warm CDW that would promote grounding line retreat for key Antarctic marine glaciers (including Totten and Byrd Glaciers in the EAIS).

Joseph R. McConnell el al., "Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1705595114

https://www.pnas.org/content/114/38/10035

Significance
Cold and dry glacial-state climate conditions persisted in the Southern Hemisphere until approximately 17.7 ka, when paleoclimate records show a largely unexplained sharp, nearly synchronous acceleration in deglaciation. Detailed measurements in Antarctic ice cores document exactly at that time a unique, ∼192-y series of massive halogen-rich volcanic eruptions geochemically attributed to Mount Takahe in West Antarctica. Rather than a coincidence, we postulate that halogen-catalyzed stratospheric ozone depletion over Antarctica triggered large-scale atmospheric circulation and hydroclimate changes similar to the modern Antarctic ozone hole, explaining the synchronicity and abruptness of accelerated Southern Hemisphere deglaciation.

32
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 21, 2020, 03:39:30 PM »
The linked reference notes that rhizosphere priming effect is currently not included in any climate model projects but that this effect '… amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area by 2100.'

Keuper, F., Wild, B., Kummu, M. et al. Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming. Nat. Geosci. (2020). https://doi.org/10.1038/s41561-020-0607-0

https://www.nature.com/articles/s41561-020-0607-0

Abstract
As global temperatures continue to rise, a key uncertainty of climate projections is the microbial decomposition of vast organic carbon stocks in thawing permafrost soils. Decomposition rates can accelerate up to fourfold in the presence of plant roots, and this mechanism—termed the rhizosphere priming effect—may be especially relevant to thawing permafrost soils as rising temperatures also stimulate plant productivity in the Arctic. However, priming is currently not explicitly included in any model projections of future carbon losses from the permafrost area. Here, we combine high-resolution spatial and depth-resolved datasets of key plant and permafrost properties with empirical relationships of priming effects from living plants on microbial respiration. We show that rhizosphere priming amplifies overall soil respiration in permafrost-affected ecosystems by ~12%, which translates to a priming-induced absolute loss of ~40 Pg soil carbon from the northern permafrost area by 2100. Our findings highlight the need to include fine-scale ecological interactions in order to accurately predict large-scale greenhouse gas emissions, and suggest even tighter restrictions on the estimated 200 Pg anthropogenic carbon emission budget to keep global warming below 1.5 °C.

33
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 20, 2020, 04:51:57 PM »
Andrew Dessler understands that it is not alarmist to be alarmed about something that is alarming (like the potential for an 'Ice Apocalypse' this century):

34
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 19, 2020, 06:42:30 PM »
...
IMO the individual studies are interesting and sometimes brilliant but of very limited value because they lack the component that provides the 'intuitive leap' that gives 'usefulness' to the study. In the case of an 'Ice Apocalypse', a more rationalized and realistic time-frame.

...

Regarding consensus climate science repeated reference to ice sheets losing ice over periods of centuries or millennia, I note that what most people think of as 'the science' is limited to Frequentist (as opposed to Bayesian) interpretation of the scientific method.  A Frequentist interpretation requires the establishment of experiments that simulate all key considerations, run a sufficient number of times to generate statistics that the Frequentists use as probabilities for possible future events.  To generate climate change statistics Frequentists primarily look at: a) the paleoclimate-record; b) the observed climate record and c) climate model projections.  Unfortunately, our current Anthropocene Period has no direct parallel in the paleoclimate record; and the observed record is too short to say much about long-tail climate risks and current climate models (including CMIP6 models) are not yet sufficiently sophisticated to simulate nonlinear extreme/abrupt climate behavior.

Therefore, when Frequentist/consensus climate scientists look at the paleoclimate record they average-out possible MICI-types of event citing poor resolution of the paleo-record and then focus on the slower trends of ice sheet ice mass loss; and when they look at the observed record they only see limited ice cliff failures for individual glaciers (like Jakobshavn) but no MICI-type events and when they look at model results like those of DeConto & Pollard (2016) or James Hansen et al (2016) they discount these preliminary findings as these models depend on some human judgement (which is commonly used in Bayesian methodologies).  Thus if abrupt freshwater hosing events do occur in the coming decades they will likely catch the Frequentist/consensus climate scientists by surprise and they will say that such abrupt behavior reflect 'Black Swan' events that could not be projected, even thou numerous warnings have been made public by the likes of James Hansen, DeConto and Pollard.  At the end of the day, many decision makers like to shirk responsibility for using human judgement and until they start choosing to shoulder responsibility the consensus climate scientists who report to these decision makers will continue to discount long-tail risks and will caveat their incomplete Frequentist statistics (that they present as true probabilities) with small print footnotes that ease their collective guilty consciousness over not presenting the actual risks associated with 'Ice Apocalypse' scenarios.

35
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 19, 2020, 05:02:46 PM »
ShortBrutishNasty was thoughtful enough to send a link to me about James Hansen's latest article about paleo, and model, evidence about slowing of the MOC during periods of high GMSTA, see below:

Title: "Every Rock Has a Story & The Rock Whisperer" by James Hansen July 17, 2020

http://www.columbia.edu/~jeh1/mailings/2020/20200717_RockStories.pdf

Extract: "Curiously, at almost exactly the same moment that I received an e-mail from Ethan Baxter, I received one from the Rock Whisperer, my friend Paul Hearty, with a copy of his current paper on rocks in South Africa. He and co-authors show that in the Mid-Pliocene (about 3 million years ago), when atmospheric CO2 was about the same as today, it was a few degrees warmer and sea level was 15-30 meters higher (50-100 feet). One of Paul’s co-authors is Maureen Raymo, the new Director of Columbia’s Lamont-Doherty Earth Observatory, who dubbed Paul the Rock Whisperer for his remarkable ability to read the story in the rocks.

In 2006, when I was concerned that the IPCC projections of sea level rise were unrealistically conservative, I suspected that something was wrong with the ocean models that IPCC relied on. For one thing, the models did not properly include the cooling effect of ice melt on the North Atlantic and Southern Oceans. So, we ran climate simulations with our coarse-resolution global model, and were startled by the result: we found that the world was on the verge of shutting down both the Southern Ocean and North Atlantic overturning circulations, with enormous potential consequences for future sea level, because of amplifying feedbacks for Antarctic ice.

This would be a hard story to sell, given the coarse resolution of our model, and the fact that our result seemed to differ from all the other models. And why did Earth’s history not reveal such rapid feedback-driven change in the past? That’s when I discovered the papers of Paul Hearty for the last interglacial period, the Eemian, about 120,000 years ago, when global temperature reached levels perhaps as much as 1-2°C warmer than the preindustrial (1880-1920) level.

Hearty’s reading of the rocks painted a picture of the Eemian that was consistent with what we were finding in our climate modeling. We needed to develop that story, so we started to work with Paul Hearty, but first we needed an explanation for what was wrong with the ocean models.

The most crucial information about the ocean models was provided by observations of heat uptake by the oceans. Here the expert, the ocean heat whisperer if there is such a thing, was a young post-doc, Karina von Schuckmann, with whom we began to collaborate in about 2010."

Hearty, P. J., Rovere, A., Sandstrom, M. R., O'Leary, M. J., Roberts, D., & Raymo, M. E. (2020). Pliocene‐Pleistocene stratigraphy and sea‐level estimates, Republic of South Africa with implications for a 400 ppmv CO2 world. Paleoceanography and Paleoclimatology, 35, e2019PA003835. https://doi.org/10.1029/2019PA003835

https://www.essoar.org/doi/10.1002/essoar.10503699.1

Abstract: "The Mid-Pliocene Warm Period (MPWP, 2.9 to 3.3 Ma), along with older Pliocene (3.2 to 5.3 Ma) records, offers potential past analogues for our 400-ppmv world. The coastal geology of western and southern coasts of the Republic of South Africa expose an abundance of marine deposits of Pliocene and Pleistocene age. In this study, we report differential GPS elevations, detailed stratigraphic descriptions, standardized interpretations, and dating of relative sea-level indicators measured across ~700 km from the western and southern coasts of the Cape Provinces. Wave abrasion surfaces on bedrock, intertidal sedimentary structures, and in situ marine invertebrates including oysters and barnacles provide precise indicators of past sea levels. Multiple sea-level highstands imprinted at different elevations along South African coastlines were identified. Zone I sites average +32 ± 5 m (6 sites). A lower topographic Zone II of sea stands were measured at several sites around +17 ± 5 m. Middle and late Pleistocene sites are included in Zone III. Shoreline chronologies using 87Sr/86Sr ages on shells from these zones yield ages from Zone I at 4.6 and 3.0 Ma, and Zone II at 1.04 Ma. Our results show that polar ice sheets during the Plio-Pleistocene were dynamic and subject to significant melting under modestly warmer global temperatures. These processes occurred during a period when CO2 concentrations were comparable to our current and rapidly rising values above 400 ppmv."

36
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 19, 2020, 04:46:00 PM »
...
A very fair point and good example of where the science has joined some of the 'dots' for the purpose of informing the decision makers.
...

D-Penguin,

I have made more posts critiquing consensus climate science projections than anyone else on this forum so I certainly share many of your reservations about 'the science' and/or 'consensus science'.  The fact of the matter is that the world is a much more complicated place than any Earth System Model, ESM, can replicate; therefore, projections from 'the science' can only represent a part of reality, and the parts left unmodeled represent uncertainty (or deep uncertainty); which decision makers can either use to try to ignore consensus science projections (such as the Trump Administration) or they can shoulder responsibility for the uncertainties and evaluate risks (probability times impact) associated with a range of possible scenarios (using the Precautionary Principle) ranging from mild to extreme.

As consensus climate science has a proven bias to err on the side of least drama; I try to use published (peer reviewed) scientific reports (consensus or otherwise) as a starting point and then I try to discuss many of the considerations that they have omitted from their models due to uncertainty/ignorance and/or lack of computational power (note that E3SMv4 will use exascale computers to partially address this short-coming).  For example, in an earlier post that you commented on, I cited the risk of cascading freshwater-hosing-related tipping points accelerated by the bipolar seesaw mechanism, so here I elaborate a little bit on what such an extreme scenario could build on the projections of E3SMv1 presented in CMIP6:

1. E3SMv1 projections indicate that glacial (including ice shelf) ice melting from both the GIS and the AIS is currently contributing to a slow-down of the MOC and that MISI-types of calving will accelerate this slow-down in coming decade, resulting in a relatively high value for TCR of about 2.93C for the rest of this century.  However, this projection ignores both MICI-types of mechanisms and a cascade of freshwater hosing events modulated by the bipolar seesaw mechanism via both atmospheric and oceanic telecommunication mechanism.

2. In my opinion there is a reasonable chance that the current slow-down of the AMOC (which is increasing the ocean heat content particularly in both the Southern Ocean and the North Atlantic Ocean, see the first attached image) will serve to increase the frequency and magnitude of periodic warm ocean water fluxes into the fjords of key marine terminating glaciers in Greenland (and also in Antarctica) so (in my opinion) that in the 2025 to 2030 timeframe that there will be a 5-year long surge of (ice cliff related) accelerated calving events from such key marine terminating glaciers as: Jakobshavn, Petermann, Zachariae, etc. that would both accelerate the slow-down of the MOC (thus warming the SST in the Tropical Pacific which would then atmospherically telecommunicate additional heat to the WAIS) and would contribute to a small increase in sea level in coastal West Antarctica.

3.  The result of the freshwater hosing event cited in item 2 would serve to help destabilize the marine glaciers in the Amundsen Sea Embayment, ASE; which together with a likely Super El Nino event and a likely subglacial lake drainage event beneath Thwaites, in the 2030-2035 timeframe; might likely both cause the PIIS to collapse and cause the Thwaites Glacier to undergo an MICI-type of collapse of the entire Byrd Subglacial Basin (BSB) by 2035.  Such a freshwater hosing event would not only further slow the MOC [by slowing AABW formation, around Antarctica, see Nakayama et al (2020)]; but would also slight rise sea level around Greenland and would push relatively warm Pacific water through the Bering Strait into the Beaufort Sea (see the second attached image from NOAA 2017).

3. The warm Pacific water intruding into the Beaufort Sea by 2035 cited in item 3 would likely trigger an abrupt release of freshwater from the Beaufort Gyre into first the Arctic Ocean (where it would destabilize the halocline resulting in abrupt melting of the Arctic Sea Ice) and then into the North Atlantic, where it would likely contribute to an abrupt slow-down of the AMOC, possibly in the 2035 to 2040 timeframe; which by the bipolar seesaw mechanism could trigger the abrupt collapse of both the FRIS and the RIS in the 2040 to 2045 timeframe that could contribute to the collapse of the vast majority of the remaining WAIS within the 2045 to 2090 time frame.


Nakayama, Y., Timmermann, R., and H. Hellmer, H.: Impact of West Antarctic ice shelf melting on Southern Ocean hydrography, The Cryosphere, 14, 2205–2216, https://doi.org/10.5194/tc-14-2205-2020, 2020.

https://tc.copernicus.org/articles/14/2205/2020/

Abstract
Previous studies show accelerations of West Antarctic glaciers, implying that basal melt rates of these glaciers were previously small and increased in the middle of the 20th century. This enhanced melting is a likely source of the observed Ross Sea (RS) freshening, but its long-term impact on the Southern Ocean hydrography has not been well investigated. Here, we conduct coupled sea ice–ice shelf–ocean simulations with different levels of ice shelf melting from West Antarctic glaciers. Freshening of RS shelf and bottom water is simulated with enhanced West Antarctic ice shelf melting, while no significant changes in shelf water properties are simulated when West Antarctic ice shelf melting is small. We further show that the freshening caused by glacial meltwater from ice shelves in the Amundsen and Bellingshausen seas can propagate further downstream along the East Antarctic coast into the Weddell Sea. The freshening signal propagates onto the RS continental shelf within a year of model simulation, while it takes roughly 5–10 and 10–15 years to propagate into the region off Cape Darnley and into the Weddell Sea, respectively. This advection of freshening modulates the shelf water properties and possibly impacts the production of Antarctic Bottom Water if the enhanced melting of West Antarctic ice shelves continues for a longer period.

Edit: Obviously, this cascade of freshwater-hosing-event-related tipping points modulated by bipolar seesaw mechanisms would likely continue beyond 2090 (and would likely trigger other positive feedback mechanisms prior to 2090); such as:

a) an increase in the frequency and intensity of both El Nino events (promoting more surface melting events in West Antarctica) and of Atmospheric River events impacting Greenland (promoting more surface melting events) both of which should increase hydrofracking of ice cliffs and of ice shelves.

b) Activation of MICI-type of behavior in key EAIS marine glaciers like Totten, and Byrd, possibly as early as 2060 to 2070.


37
...
Title: "Global and Regional Sea Level Rise Scenarios for the United States", January 2017.

https://tidesandcurrents.noaa.gov/publications/techrpt83_Global_and_Regional_SLR_Scenarios_for_the_US_final.pdf

...

As ShortBrutishNasty is interested in how SLR could impact Miami, I attach an image extracted from NOAA (2017) Technical Paper 083 together with the following text extract as to how to apply NOAA's guidance.  I note (as a Civil Engineer) that selection of which of the the NOAA (2017) SLR curves to apply depends on the impacts on key infrastructure and that the Miami area has nuclear power plants (like the St. Lucie nuclear power plant) that merit consideration of NOAA's extreme (upper) SLR curve.  Furthermore, that such key infrastructure is typically designed to a 1% probability of exceedance; which indicates that in the attached image the upper dashed curve should be used for evaluation purposes (together with local relative sea level rise considerations:

Extract: "Key to the decision process is determining the extent to which a given amount of RSL rise may cause impacts to either newly built or existing infrastructure.

For many decisions, it is essential to assess worst-case scenarios, not only those assessed as the scientifically ‘likely’ to happen. For example, drawing on the references cited above, the following is suggested as a potential initial scenario selection strategy for decisions and planning processes for which long-term risk management is paramount:

● Define a scientifically plausible upper-bound (which might be thought of as a worst-case or extreme scenario) as the amount of sea level rise that, while low probability, cannot be ruled out over the time horizon being considered. Use this upper-bound scenario as a guide for overall system risk and long-term adaptation strategies.

● Define a central estimate or mid-range scenario (given assumptions about greenhouse gas emissions and other major drivers). Use this scenario as baseline for shorter-term planning, such as setting initial adaptation plans for the next two decades. This scenario and the upperbound scenario can together be thought of as providing a general planning envelope."

38
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 18, 2020, 04:35:29 AM »
..

Fascinating and way outside current projections based on 'the science'. I would not disagree with one jot of your belief and reasoning related to SLR.

...

Here, I imagine that 'the science' can be translated as 'consensus science' like NOAA (2017). ;)

39
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 17, 2020, 02:52:03 PM »
The linked video provides a consensus science explainer of why/how the Thwaites Glacier is currently falling apart (including the recently identified subglacial cavities); however, it omits consideration of MICI-types of potential collapse:

Title: " Why scientists are so worried about this glacier"

https://www.youtube.com/watch?v=XRUxTFWWWdY&feature=youtu.be

In the interview the demise of Thwaites Glacier and the WAIS is referred to in time-frames of 'hundreds' and 'thousands' of years.

Not only does the interview omit reference to MICI-types of potential collapse, it omits reference to many relevant factors. The Greenland Ice Sheet will substantially melt out within a hundred years and no scientific study that I have seen about the Thwaites Glacier takes into account a rising sea level rise of up to  of up to 7 M.

IMO the current research will read as no more than interesting historic anecdotes after the event. Too late will be the cry!

I believe that a cascade of freshwater hosing events working together with the bipolar seesaw mechanism and ice-climate feedbacks will result in at least 3m of mean SLR by 2090.

40
...

Edit: I note that a nuclear winter would short-circuit such a freshwater driven cascade of tipping points, but that a major conventional war would increase the probability of such a scenario.

FYI

Robock, A. and Zambri, B. (2018) Did smoke from city fires in World War II cause global cooling? Journal of Geophysical Research: Atmospheres, doi:10.1029/2018JD028922

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD028922

Abstract
Between 3 February and 9 August 1945, an area of 461 km2 in 69 Japanese cities, including Hiroshima and Nagasaki, was burned during the U.S. B‐29 Superfortress air raids. In the previous 5 years, 205 km2 in German cities were destroyed, so the smoke that was generated was spread out over a much longer period of time than that from Japan in 1945. Observations of solar irradiance show reductions consistent with the hypothesis that smoke was injected into the stratosphere by the city fires. Historical simulations from the Coupled Model Intercomparison Project 5, with no smoke in their forcing, showed no postwar cooling. Global average surface air temperature observations during and following World War II are problematic, because of issues with measuring sea surface temperatures, but there were no large volcanic eruptions, El Niño, or La Niña during this period to confuse the record. Nevertheless, 1945 and 1946 global average land surface air temperatures were not significantly lower than the average for 1940–1944. Estimates of the amount of smoke generated by the fires are somewhat uncertain. Although the climate record is consistent with an expected 0.1–0.2 K cooling, because of multiple uncertainties in smoke injected to the stratosphere, solar radiation observations, and surface temperature observations, it is not possible to formally detect a cooling signal from World War II smoke.

Plain Language Summary
Nuclear winter theory says that smoke from burning cities targeted with nuclear weapons would rise into the upper atmosphere and spread around the world, absorbing sunlight and cooling the surface. Unfortunately, we have two real‐world examples of this, Hiroshima and Nagasaki, which were burned by U.S. atomic bombs on 6 and 9 August 1945. We discovered that this was actually the culmination of a genocidal U.S. bombing campaign. Between 3 February and 9 August 1945, an area of 461 square kilometers in 69 Japanese cities, including Hiroshima and Nagasaki, was burned during the U.S. B‐29 Superfortress air raids, and the Hiroshima and Nagasaki smoke was less than 5% of the total. We calculated how much smoke was emitted and how much climate change would have been expected. Although there was a small cooling, because of multiple uncertainties in smoke injected to the stratosphere, sunlight observations, and surface temperature observations, we found that it is not possible to say for sure that this was a cooling signal from World War II smoke. However, these results do not invalidate nuclear winter theory that much more massive smoke emissions from nuclear war would cause large climate change and impacts on agriculture.

41
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 16, 2020, 11:59:54 PM »
The title of the linked article says it all:

Title: "Siberia’s 2020 heatwave made ‘600 times more likely’ by climate change"

https://www.carbonbrief.org/siberia-s-2020-heatwave-made-600-times-more-likely-by-climate-change

Extract: "Siberia’s prolonged heat from January to June this year – which broke temperature records and drove polluting megafires – would have been “almost impossible” without human-caused climate change, according to new analysis."

42
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 16, 2020, 11:14:45 PM »
The linked reference reminds us that an increase in strong summer atmosphere river events in Greenland with continued global warming would lead to accelerated ice melt into the North Atlantic where it would contribute to a slowing of the AMOC:

Kyle S. Mattingly et al. (2020), "Strong Summer Atmospheric Rivers Trigger Greenland Ice Sheet Melt through Spatially Varying Surface Energy Balance and Cloud Regimes, J. Climate, 33, (16), 6809–6832.
https://doi.org/10.1175/JCLI-D-19-0835.1

https://journals.ametsoc.org/jcli/article/33/16/6809/348249/Strong-Summer-Atmospheric-Rivers-Trigger-Greenland

ABSTRACT
Mass loss from the Greenland Ice Sheet (GrIS) has accelerated over the past two decades, coincident with rapid Arctic warming and increasing moisture transport over Greenland by atmospheric rivers (ARs). Summer ARs affecting western Greenland trigger GrIS melt events, but the physical mechanisms through which ARs induce melt are not well understood. This study elucidates the coupled surface–atmosphere processes by which ARs force GrIS melt through analysis of the surface energy balance (SEB), cloud properties, and local- to synoptic-scale atmospheric conditions during strong summer AR events affecting western Greenland. ARs are identified in MERRA-2 reanalysis (1980–2017) and classified by integrated water vapor transport (IVT) intensity. SEB, cloud, and atmospheric data from regional climate model, observational, reanalysis, and satellite-based datasets are used to analyze melt-inducing physical processes during strong, >90th percentile “AR90+” events. Near AR “landfall,” AR90+ days feature increased cloud cover that reduces net shortwave radiation and increases net longwave radiation. As these oppositely signed radiative anomalies partly cancel during AR90+ events, increased melt energy in the ablation zone is primarily provided by turbulent heat fluxes, particularly sensible heat flux. These turbulent heat fluxes are driven by enhanced barrier winds generated by a stronger synoptic pressure gradient combined with an enhanced local temperature contrast between cool over-ice air and the anomalously warm surrounding atmosphere. During AR90+ events in northwest Greenland, anomalous melt is forced remotely through a clear-sky foehn regime produced by downslope flow in eastern Greenland.

43
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 16, 2020, 11:03:37 PM »
The linked reference indicates that anthropogenic aerosols increase the life of clouds; which it assumes will result in more negative cloud feedback.  However, high altitude clouds produce positive climate change feedback, so if future global warming creates more high altitude clouds (as projected by many CMIP6 models), then in the future longer-lived clouds may produce more positive feedback than previously assumed:

Matthew W. Christensen et al. (July 13, 2020); "Aerosols enhance cloud lifetime and brightness along the stratus-to-cumulus transition", PNAS, https://doi.org/10.1073/pnas.1921231117

https://www.pnas.org/content/early/2020/07/09/1921231117.short?rss=1

Significance
All cloud droplets on Earth form from tiny airborne particles known as aerosols. Additional aerosols from anthropogenic activity have produced more cloud droplets but at smaller sizes. The smaller, more numerous droplets in clouds do not collide as effectively, therefore resulting in less precipitation. Using a combination of time-lapse satellite imagery and air mass trajectory modeling, we show that aerosols can enhance cloud fraction and extend the lifetime of overcast cloud fields primarily under stable atmospheric conditions as typically found off the west coasts of subtropical stratocumulus-dominated regions. Longer-lived clouds have a stronger cooling influence on climate and therefore, need to be correctly parameterized in atmospheric models so that accurate projections of climate change can be achieved.

Abstract
Anthropogenic aerosols are hypothesized to enhance planetary albedo and offset some of the warming due to the buildup of greenhouse gases in Earth’s atmosphere. Aerosols can enhance the coverage, reflectance, and lifetime of warm low-level clouds. However, the relationship between cloud lifetime and aerosol concentration has been challenging to measure from polar orbiting satellites. We estimate two timescales relating to the formation and persistence of low-level clouds over 1○×1○1○×1○ spatial domains using multiple years of geostationary satellite observations provided by the Clouds and Earth’s Radiant Energy System (CERES) Synoptic (SYN) product. Lagrangian trajectories spanning several days along the classic stratus-to-cumulus transition zone are stratified by aerosol optical depth and meteorology. Clouds forming in relatively polluted trajectories tend to have lighter precipitation rates, longer average lifetime, and higher cloud albedo and cloud fraction compared with unpolluted trajectories. While liquid water path differences are found to be negligible, we find direct evidence of increased planetary albedo primarily through increased drop concentration (NdNd) and cloud fraction, with the caveat that the aerosol influence on cloud fraction is positive only for stable atmospheric conditions. While the increase in cloud fraction can be large typically in the beginning of trajectories, the Twomey effect accounts for the bulk (roughly 3/4) of the total aerosol indirect radiative forcing estimate.

44
It is regrettable that the economist Martin Weitzman died last year as without his 'fat-tail' climate change economic analysis it is not likely that the 2015 Paris Agreement would have adopted its formal goal of staying well below 2oC GMSTA and preferably to stay below 1.5oC GMSTA.  While it is good that his work did result in the formal adoption these goals for limiting climate change; since the time that he published his works on this topic the 'fat-tail' has become fatter but decision makers still belittle these increasingly likely right-tail catastrophes by pretending that tipping points are not real and that mankind can always reverse future climate impacts by eventually limiting anthropogenic GHG emissions at some point in the future.  Unfortunately, such pretenses are not real, and considering the higher ECS values projected by CMIP6 and the positive ice-climate feedback mechanisms not fully evaluated by CMIP6, it is my opinion that we should stay well below 1.5oC GMSTA, and a man like Martin Weitzman may have been capable of conveying that matter to current decision makers as his earlier works were able to impact the 2015 Paris Agreement.

Title: "The Man Who Got Economists to Take Climate Nightmares Seriously"

https://www.bloomberg.com/news/articles/2019-08-29/the-man-who-got-economists-to-take-climate-nightmares-seriously

Extract: "This is the hallmark of traditional cost-benefit analysis: Figure out the benefits of keeping the climate stable, compare that to the costs of preventing change, and then determine which policies make the most sense.

Weitzman used technical math to make the case that climate change is different because what’s most likely to happen doesn’t matter as much when there’s a possibility of total catastrophe. “Even when you have a low probability of a highly consequential event, those consequences—when they’re of a significant enough magnitude—can really overwhelm your thinking,” said Richard Newell, chief executive of the research nonprofit Resources for the Future and a former Weitzman teaching assistant.
...
Weitzman’s analysis was influential in helping convince global diplomats to adopt a goal for limits on warming—1.5 and 2 degree Celsius—in the 2015 Paris Agreement. Robert Stavins, director of the Harvard Environmental Economics Program, said the Paris targets may not have passed “an economic analysis, unless you take account of Weitzman’s fat tails.”
...
“His fat-tail story in many ways was the story,” Wagner said, “of how those uncertainties could potentially drive everything. He called it the Dismal Theorem. The burden of proof is on those who think that those risks don’t matter. It’s not the other way around.”
...
Newell said one of Weitzman’s biggest accomplishments was “challenging historical orthodoxy concerning long-term discounting, and doing so in a way that has had direct influence on government policy.” President Barack Obama’s team cited Weitzman’s work in technical material supporting its cost estimates for each metric ton of emitted C02."

I point out that Weitzman's work on fat-tailed risk is even more compelling when one considered a possible cascade of tipping points (driven largely from freshwater hosing events) possibly leading to a post-PETM situation such as that evaluated by Romps (2020) where ECS might approach 15C as shown in the first image.  The second image (see caption) shows a risk analysis using likelihood and damage functions (by Weitzman) at ECS up to about 8C.  If decision makers understood this long-tailed risk appropriately they would take immediate action to make sure that it never occurs as an ECS of 15C would likely be an extinction level event for mankind.

Caption for the second attached image: "Figure 1. A schematic representation of how climate change risk depends on equilibrium climate sensitivity (ECS). (a) A possible likelihood distribution consistent with the IPCC AR5 assessment that “Equilibrium climate sensitivity is likely in the range 1.5 to 4.5 _C (high confidence), extremely unlikely less than 1C (high confidence) and very unlikely greater than 6C (medium confidence)”. (b) A schematic illustration of the fact that, for a given emissions scenario, the cost of impacts and adaptation rises very rapidly (shown here as an exponential damage function) with ECS. (c) In this example, the resultant risk (quantified here as likelihood x impact) is highest for high ECS values. The precise shape of the risk curve is dependent on assumptions about the shape of the likelihood and damage functions at high sensitivity (Weitzman, 2011) (figure by Ed Hawkins)."

Edit: I note that a nuclear winter would short-circuit such a freshwater driven cascade of tipping points, but that a major conventional war would increase the probability of such a scenario.

45
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 15, 2020, 07:20:36 PM »
While the linked consensus climate science article provides useful information on how climate change might be impacting wildfires around the world; it does not discuss the probably positive feedback between wildfires and climate change:

Title: "Explainer: How climate change is affecting wildfires around the world"

https://www.carbonbrief.org/explainer-how-climate-change-is-affecting-wildfires-around-the-world

Extract: "This year has seen unprecedented wildfires cause havoc across the world. Australia recently battled its largest bushfire on record, while parts of the Arctic, the Amazon and central Asia have also experienced unusually severe blazes.

It follows on from “the year rainforests burned” in 2019."

46
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 15, 2020, 06:17:22 PM »
The linked open access reference indicates that 16 CMIP6 model projections indicate that the projected increase in El Nino-like warming pattern this century will contribute to an abrupt 77% decrease of the upper-level tropical easterly jet over the tropical eastern Pacific.  I note that if the MOC slows abruptly due to one, or more, significant freshwater hosing events in coming decades that this timeline could be appreciably accelerated:

Sihua Huang, Bin Wang and Zhiping Wen (2020)," Dramatic Weakening of the Tropical Easterly Jet Projected by CMIP6 Models", J. Climate, https://doi.org/10.1175/JCLI-D-19-1002.1

https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-19-1002.1/353358/Dramatic-Weakening-of-the-Tropical-Easterly-Jet?searchresult=1

Abstract
The upper-level tropical easterly jet (TEJ) is a crucial component of the summer monsoon system and tropical general circulation. The simulation and projection of the TEJ, however, have not been assessed. Here we evaluate models’ fidelity and assess the future change of the TEJ by utilizing 16 models that participated in phase six of the Coupled Model Intercomparison Project (CMIP6). Most of the models can reproduce the TEJ reasonably well in terms of climatology, seasonal evolution and interannual variability. Nevertheless, underestimation of the TEJ’s intensity and extent is identified, with the maximum bias occurring in the jet centers over the tropical Indian Ocean (IO) and the tropical eastern Pacific (EP). Under the Shared Socioeconomic Pathway 5-8.5, the multimodel ensemble projects a remarkable reduction in the central TEJ intensity by about 18% over the IO and 77% over the EP toward the end of the 21st century. The mean intensity of TEJ will weaken by about 11%, and the extent will reduce by 6%, suggesting a significantly weakened upper-level monsoon circulation in the future climate. The projected El Niño-like warming pattern over the tropical Pacific may play a critical role in the future weakening of the TEJ via inducing suppressed rainfall over the tropical eastern IO and Central America. The model uncertainties in the projected TEJ changes may arise from the uncertainties in models’ projected tropical EP warming. The sensitivity of future projections to model selection is also examined. Results show that the selection of models based on different physical considerations does not yield a significantly different projection.

47
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 15, 2020, 06:02:42 PM »
The linked video provides a consensus science explainer of why/how the Thwaites Glacier is currently falling apart (including the recently identified subglacial cavities); however, it omits consideration of MICI-types of potential collapse:

Title: " Why scientists are so worried about this glacier"

https://www.youtube.com/watch?v=XRUxTFWWWdY&feature=youtu.be


48
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 15, 2020, 05:44:34 PM »
The linked references, and associated article, discuss the sources of the current record anthropogenic methane emissions:

“Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources” by R B Jackson, M Saunois, P Bousquet, J G Canadell, B Poulter, A R Stavert, P Bergamaschi, Y Niwa, A Segers and A Tsuruta, 15 July 2020, Environmental Research Letters.
DOI: 10.1088/1748-9326/ab9ed2

https://iopscience.iop.org/article/10.1088/1748-9326/ab9ed2

...

Here is a follow-on article about this topic, which indicates that once triggered permafrost degradation could reduce the carbon budget by about 5-years in coming decades:

Title: "Scientists concerned by ‘record high’ global methane emissions"

https://www.carbonbrief.org/scientists-concerned-by-record-high-global-methane-emissions

Extract: "Permafrost – perennially frozen rock and soils – is found across vast swaths of the northern hemisphere’s high latitudes. This ground holds billions of tonnes of carbon, which could be released – as CO2 and/or methane – as the region warms and the soil thaws. This is an example of a “positive feedback” where more greenhouse gases are released as global temperatures rise, thus reinforcing the warming.

Research by Jones and colleagues has suggested that greater emissions of CO2 and methane from wetlands and thawing permafrost as the climate warms could cut the carbon budget for the Paris Agreement temperature limits by around five years."

49
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 15, 2020, 01:11:28 AM »
The linked references, and associated article, discuss the sources of the current record anthropogenic methane emissions:

“Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources” by R B Jackson, M Saunois, P Bousquet, J G Canadell, B Poulter, A R Stavert, P Bergamaschi, Y Niwa, A Segers and A Tsuruta, 15 July 2020, Environmental Research Letters.
DOI: 10.1088/1748-9326/ab9ed2

https://iopscience.iop.org/article/10.1088/1748-9326/ab9ed2

Extract: "Climate stabilization remains elusive, with increased greenhouse gas concentrations already increasing global average surface temperatures 1.1 °C above pre-industrial levels (World Meteorological Organization 2019). Carbon dioxide (CO2) emissions from fossil fuel use, deforestation, and other anthropogenic sources reached ~ 43 billion metric tonnes in 2019 (Friedlingstein et al 2019, Jackson et al 2019). Storms, floods, and other extreme weather events displaced a record 7 million people in the first half of 2019 (IDMC 2019). When global mean surface temperature four million years ago was 2 °C–3 °C warmer than today (a likely temperature increase before the end of the century), ice sheets in Greenland and West Antarctica melted and parts of East Antarctica's ice retreated, causing sea levels to rise 10–20 m (World Meteorological Organization 2019).

Methane (CH4) emissions have contributed almost one quarter of the cumulative radiative forcings for CO2, CH4, and N2O (nitrous oxide) combined since 1750 (Etminan et al 2016). Although methane is far less abundant in the atmosphere than CO2, it absorbs thermal infrared radiation much more efficiently and, in consequence, has a global warming potential (GWP) ~86 times stronger per unit mass than CO2 on a 20-year timescale and 28-times more powerful on a 100-year time scale (IPCC 2014).

Global average methane concentrations in the atmosphere reached ~1875 parts per billion (ppb) at the end of 2019, more than two-and-a-half times preindustrial levels (Dlugokencky 2020). The largest methane sources include anthropogenic emissions from agriculture, waste, and the extraction and use of fossil fuels as well as natural emissions from wetlands, freshwater systems, and geological sources (Kirschke et al 2013, Saunois et al 2016a, Ganesan et al 2019). Here, we summarize new estimates of the global methane budget based on the analysis of Saunois et al (2020) for the year 2017, the last year of the new Global Methane Budget and the most recent year data are fully available. We compare these estimates to mean values for the reference 'stabilization' period of 2000–2006 when atmospheric CH4 concentrations were relatively stable. We present data for sources and sinks and provide insights for the geographical regions and economic sectors where emissions have changed the most over recent decades."

&

Earth System Science Data, doi: 10.5194/essd-12-1561-2020

https://essd.copernicus.org/articles/12/1561/2020/

See also:

Title: "Global Methane Emissions Soar to Record High, Even As Pandemic Has Reduced Carbon Emissions"

https://scitechdaily.com/global-methane-emissions-soar-to-record-high-even-as-pandemic-has-reduced-carbon-emissions/

Extract: "Global emissions of methane have reached the highest levels on record. Increases are being driven primarily by growth of emissions from coal mining, oil and natural gas production, cattle and sheep ranching, and landfills.

Between 2000 and 2017, levels of the potent greenhouse gas barreled up toward pathways that climate models suggest will lead to 3-4 degrees Celsius of warming before the end of this century. This is a dangerous temperature threshold at which scientists warn that natural disasters, including wildfires, droughts and floods, and social disruptions such as famines and mass migrations become almost commonplace. The findings are outlined in two papers published today (July 14, 2020) in Earth System Science Data and Environmental Research Letters by researchers with the Global Carbon Project, an initiative led by Stanford University scientist Rob Jackson."

50
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 14, 2020, 10:08:32 PM »
The linked article on the consequences of Arctic amplification in Siberia has too many consequences to summarize here, so I just highlight the impacts (& positive feedbacks) associated with peat fires in the Siberian tundra:

Title: "Record heat wave in Siberia has far-flung consequences"

https://www.dw.com/en/siberia-fires-permafrost/a-54120019

Extract: "Oil spills, intense heat waves, smoldering wildfires and thawing permafrost: Siberia is experiencing the destructive effects of climate change. And scientists say if action isn't taken soon, it's only going to get worse.

"Every single time peat burns, it is a net carbon contribution to climate change. And you cannot undo it," he said. Plus, peatland blazes are extremely difficult to extinguish. 
"I've been at a peat fire and it's rained for an hour very heavily, and it's still burning at the end," said Smith. "They will just smolder away. And some peat fires are known to last for months." They have even been known to survive underground through the winter months as "zombie fires," flaring up again on the surface in the spring.

Rein called it a "positive feedback loop" with a negative impact: The more peat and trees that burn, the greater the greenhouse gases that are released into the atmosphere. That leads in turn to hotter temperatures and drier, less resilient forests and peatlands — and more wildfires.

Much of the burning peat in Siberia sits on permafrost, only adding to scientists' concerns. Climate change, helped along by increased wildfire activity, is melting this frozen ground and creating a host of new problems."

Pages: [1] 2 3 ... 37