Support the Arctic Sea Ice Forum and Blog

Author Topic: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)  (Read 251293 times)

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2100 on: December 03, 2019, 09:42:57 PM »
...
The consensus ECS is from 2.0 to 4.5 degrees K with most paleo evidence indicating a most likely ECS around 3 degrees K.  So with the adjustment, the one example given went from being outside of the consensus (at 1.9 K), to almost at the median value (3.2 K).

While the linked (open access) reference has many appropriate qualifying statements and disclaimers, it notes that the AR5 paleo estimates of ECS were linear approximations that change when non-linear issues are considered.  In particular they find for the specific ECS, S[CO2,LI], during the Pleistocence (ie the most recent 2 million years) that:

"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions."

Therefore, researchers such as James Hansen who relied on paleo findings that during recent full glacial periods ECS was about 3.0C, did not know that during interglacial periods this value would be 45% larger, or 4.35C.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.

http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2101 on: December 03, 2019, 09:47:09 PM »
The first two linked articles appear in the May 28 2014 online version of Nature, about new paleo-evidence about how quickly the AIS can contribute to rapid SLR (including during Meltwater Pulse 1A):

Trevor Williams, (2014), "Climate science: How Antarctic ice retreats", Nature, doi:10.1038/nature13345

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13345.html

Summary: "New records of iceberg-rafted debris from the Scotia Sea reveal episodic retreat of the Antarctic Ice Sheet since the peak of the last glacial period, in step with changes in climate and global sea level."

&

M. E. Weber, P. U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M. O. Chikamoto, T. Friedrich & C. Ohlwein, (2014), "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation", Nature, (2014), doi:10.1038/nature13397

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature13397.html

See also:

http://news.discovery.com/earth/global-warming/antarctic-iceberg-flotilla-caused-huge-sea-level-rise-140528.htm

Extract: "Antarctica's melting glaciers launched so many icebergs into the ocean 14,600 years ago that sea level rose 6.5 feet (2 meters) in just 100 years, a new study reports. The results are the first direct evidence for dramatic melting in Antarctica's past — the same as predictions for its future.

"The Antarctic Ice Sheet had been considered to be fairly stable and kind of boring in how it retreated," said study co-author Peter Clark, a climate scientist at Oregon State University. "This shows the ice sheet is much more dynamic and episodic, and contributes to rapid sea-level rise.""

Also, the following extract from the third linked article about the Weber et al (2014) paper, not only reinforces the importance of AIS SLR contribution to Meltwater Pulse 1A, but more importantly that the fresh melt water causes a stratification of ocean water with a cool surface and warmer deep waters that creates a positive feedback mechanism that accelerates the rate of grounding-line retreat of Antarctic marine glaciers, particularly like those in the ASE; which supports Hansen et al (2016)'s ice-climate feedback mechanism
 
http://www.abc.net.au/science/articles/2014/05/29/4014978.htm

Extract: "Feedback system

Recent studies have shown that a significant amount of warming occurs directly from the ocean transferring heat to the ice shelves from underneath and causing melt.
"Our models indicate that when you add the fresh water, you initiate a positive feedback through subsurface ocean warming," says Menviel.

Fresh water from the Antarctic ice sheet melts into the Southern Ocean causing stratification of ocean water into separate layers, resulting in cool water on the surface, and warmer water deeper down which further erodes the ice sheet.

"So what starts as a small melting can be amplified leading to more rapid melting than just through changes in atmospheric temperature," says Menviel."

Thus there is plenty of paleo-evidence of past armadas of icebergs being released by the AIS.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2102 on: December 03, 2019, 11:10:55 PM »
The first linked reference studies ice-climate feedback calibrated to 'freshwater hosing' events in the North Atlantic over the past 720,000 years, in order to study state dependence of climatic instabilities within a CMIP class of climate model.  Such research can help to calibrate models (say CMIP7) for such 'freshwater hosing' events such as the possible collapse of the WAIS this century:

Ayako Abe-Ouchi, et. al. (2017), "State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling", Science Advances, Vol. 3, no. 2, e1600446, DOI: 10.1126/sciadv.1600446

http://advances.sciencemag.org/content/3/2/e1600446
&
http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/218067/1/sciadv.1600446.pdf

Abstract: "Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear.  Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets."

The Last Glacial Termination, LGT, occurred from 18,000 to 11,650 kya, and the following reference, reconstructs the dynamic response of the Antarctic ice sheets to warming in this period in order to better evaluate Hansen's ice-climate feedback mechanisms.  The abstract from the second linked reference concludes: "Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections.  With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise."

Fogwill, et. al. (2017), "Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the last Glacial Termination", Scientific Reports 7, Article number 39979, doi:10.1038/srep39979

https://www.nature.com/articles/srep39979

Finally (for this post), can you imagine how the timing of a rain-dominated Arctic will be affected by Hansen's ice-climate feedback mechanism driven by a WAIS collapse circa 2040-2060 (which almost all ESM projections currently ignore), and or pulses of methane emission from thermokarst lakes?  I also note that the third linked reference assumes that ECS is only around 3C.

Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4402.pdf

Abstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”

See also the fourth linked reference:

R. Bintanja et al. Towards a rain-dominated Arctic, Nature Climate Change (2017). DOI: 10.1038/nclimate3240

http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3240.html

Extract: "Rain causes more (extensive) permafrost melt [Refs. 7,26], which most likely leads to enhanced emissions of terrestrial methane [Ref. 27] (a powerful greenhouse gas), more direct runoff (a smaller seasonal delay) and concurrent freshening of the Arctic Ocean [Ref 18]. Rainfall also diminishes snow cover extent and considerably lowers the surface albedo of seasonal snow, ice sheets and sea ice [Ref. 9] , reinforcing surface warming and amplifying the retreat of ice and snow; in fact, enhanced rainfall will most likely accelerate sea-ice retreat by lowering its albedo (compared with that of fresh snowfall) "
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2103 on: December 03, 2019, 11:29:30 PM »
I note that in the linked research: "Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal-to-noise model, or whether they interact, resulting in steplike warming."  The reference concludes that indeed steplike warming occurs due to "… a store-and-release mechanism from the ocean to the atmosphere…" like the classical Lorenzian attractor case of ENSO decadal cycles.  Such steplike behavior raises the issue of what I call "Ratcheting Quasi-static Equilibrium States" (see the attached image) that can accelerate non-linear Earth Systems response beyond the linear Earth Systems response assumed by AR5/CMIP5 researchers.  As the authors point-out such AR5/CMIP5 researcher likely missed this behavior because: "This may be due in part to science asking the wrong questions."; and they advise that such AR5/CMIP5 researchers should change how they view the output from their models.  For example, the reference shows global warming increasing much faster for a steplike response if ECS is 4.5 than for a the traditional AR5/CMIP5 interpretation; which means that ESLD researchers are exposing society to far more risk of the consequences of high ECS values than AR5/CMIP5 are leading us to believe:

Jones, R. N. and Ricketts, J. H.: Reconciling the signal and noise of atmospheric warming on decadal timescales, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2016-35, in review, 2016.

http://www.earth-syst-dynam-discuss.net/esd-2016-35/
&
http://www.earth-syst-dynam-discuss.net/esd-2016-35/esd-2016-35.pdf

Abstract. Interactions between externally forced and internally generated climate variations on decadal timescales is a major determinant of changing climate risk. Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal-to-noise model, or whether they interact, resulting in step-like warming. The multistep bivariate test is used to detect step changes in temperature data. The resulting data are then subject to six tests designed to distinguish between the two statistical hypotheses, hstep and htrend. Test 1: since the mid-20th century, most observed warming has taken place in four events: in 1979/80 and 1997/98 at the global scale, 1988/89 in the Northern Hemisphere and 1968–70 in the Southern Hemisphere. Temperature is more step-like than trend-like on a regional basis. Satellite temperature is more step-like than surface temperature. Warming from internal trends is less than 40 % of the total for four of five global records tested (1880–2013/14). Test 2: correlations between step-change frequency in observations and models (1880–2005) are 0.32 (CMIP3) and 0.34 (CMIP5). For the period 1950–2005, grouping selected events (1963/64, 1968–70, 1976/77, 1979/80, 1987/88 and 1996–98), the correlation increases to 0.78. Test 3: steps and shifts (steps minus internal trends) from a 107-member climate model ensemble (2006–2095) explain total warming and equilibrium climate sensitivity better than internal trends. Test 4: in three regions tested, the change between stationary and non-stationary temperatures is step-like and attributable to external forcing. Test 5: step-like changes are also present in tide gauge observations, rainfall, ocean heat content and related variables. Test 6: across a selection of tests, a simple stepladder model better represents the internal structures of warming than a simple trend, providing strong evidence that the climate system is exhibiting complex system behaviour on decadal timescales. This model indicates that in situ warming of the atmosphere does not occur; instead, a store-and-release mechanism from the ocean to the atmosphere is proposed. It is physically plausible and theoretically sound. The presence of step-like – rather than gradual – warming is important information for characterising and managing future climate risk.

Extract: "Climate conceptualised as a mechanistic system and described using classical statistical methods is substantially different from climate conceptualised as a complex system.
With record atmospheric and surface ocean temperatures in 2015/16 variously being described as a singular event, a reinvigoration of trend-like warming or a wholesale shift to a new climate regime, this issue is too important to be left unresolved."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2104 on: December 04, 2019, 04:45:37 PM »

Given that we can measure the concentration of methane in the atmosphere and thus calculate the total net emissions (all sources minus all sinks), if two sources were underestimated that implies that another source (or multiple sources) were overestimated or that the sinks were underestimated.


The attached NOAA plot of the atmospheric methane concentrations at the South Pole from 2006 to Dec 2, 2019 indicate that the trend line of this methane concentration is accelerating; thus if some methane sources are not changing then other sources are currently accelerating, and may accelerate even more in the future due to global warming.

The linked article & reference provide further insights about the origins of the current trend of increasing methane emissions and associated atmospheric methane concentrations:

Title: "Atmospheric Methane Levels Are Going Up—And No One Knows Why"

https://www.wired.com/story/atmospheric-methane-levels-are-going-up-and-no-one-knows-why/

Extract: "Levels of heat-trapping methane are rising faster than climate experts anticipated, triggering intense debate about why it's happening

“Is atmospheric methane increasing as a consequence of climate change, not of our direct emissions? Are some thresholds being passed?”

“It is a wicked problem,” Kort adds, “but it’s not unsolvable.”

Any convincing explanation needs to answer three questions. What explains the long-term increase in methane levels over the past 40 years? Why was there a pause? And why was there such an abrupt surge after 2006? Only three elements of the global methane budget are large enough to be plausible culprits: microbial emissions (from livestock, agriculture, and wetlands); fossil fuel emissions; and the chemical process by which methane is scrubbed from the atmosphere."

See also:

Giuseppe Etiope and Stefan Schwietzke (2019), "Global geological methane emissions: an update of top-down and bottom-up estimates", Elementa Science of the Anthropocene, 7: 47, doi: https://doi.org/10.1525/elementa.383

https://www.elementascience.org/articles/10.1525/elementa.383/

Abstract

A wide body of literature suggests that geological gas emissions from Earth’s degassing are a major methane (CH4) source to the atmosphere. These emissions are from gas-oil seeps, mud volcanoes, microseepage and submarine seepage in sedimentary (petroleum-bearing) basins, and geothermal and volcanic manifestations. Global bottom-up emission estimates, ranging from 30 to 76 Tg CH4 yr–1, evolved in the last twenty years thanks to the increasing number of flux measurements, and improved knowledge of emission factors and area distribution (activity). Based on recent global grid maps and updated evaluations of mud volcano and microseepage emissions, the global geo-CH4 source is now (bottom-up) estimated to be 45 (27–63) Tg yr–1, i.e., ~8% of total CH4 sources. Top-down verifications, based on independent approaches (including ethane and isotopic observations) from different authors, are consistent with the range of the bottom-up estimate. However, a recent top-down study, based on radiocarbon analyses in polar ice cores, suggests that geological, fossil (14C-free) CH4 emissions about 11,600 years ago were much lower (<15 Tg yr–1, 95% CI) and that this source strength could also be valid today. Here, we show that (i) this geo-CH4 downward revision implies a fossil fuel industry CH4 upward revision of at least 24–35%. (ii) The 95% CI estimates of the recent radiocarbon analysis do not overlap with those of 5 out of 6 other bottom-up and top-down studies (no overlap for the 90% CI estimates). (iii) The contrasting lines of evidence require further discussion, and research opportunities exist to help explain this gap.

Caption for image: "Comparison between current day estimates of geological and other methane sources. Geological emissions are based on the bottom-up and top-down estimates discussed in this work (see Fig. 1 and text). Other natural and anthropogenic emissions refer to the average (and range) of bottom-up and top-down estimates reported by Saunois et al. (2016). Note that a downward revision of the geological source requires an upward revision of the same magnitude for the fossil fuel industry (Section 4). DOI: https://doi.org/10.1525/elementa.383.f2"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2105 on: December 04, 2019, 05:01:53 PM »

 If an MICI-type of failure pushes an armada of icebergs into the Southern Ocean some decade from now, maybe a massive application of this technology could put the icebergs to beneficial use while concurrently cooling potential increases in tropical ocean SST values:


If some readers believe that it is totally unrealistic to assume that there could be sufficient economic benefits to pay for moving an armada of Southern Ocean icebergs to the tropical oceans (not only for freshwater supply but possibly for: OTEC (ocean thermal energy conversion); cooling of waste heat, etc.); then consider that:

1. Per the first image a nudge from oceangoing tugboats could push an iceberg out of the ACC and into one of the three indicated cold currents leading north from the Southern Ocean into the Pacific, Atlantic and Indian Oceans.

2. Per the second image these three cold current feed into warm currents that would carry any such icebergs directly to the tropical ocean regions of all three oceans without towing, and would slowly melt along the way, thus both cooling and freshening the surface waters of the tropical oceans.

3. Per the third image (showing a representative thermocline profile for tropical ocean regions) cooling of the SSTA in these regions would both slow/stop increase surface evaporation associated with global warming and for at least decades would prevent the tropical oceans SST from increase by 5C; which is projected to lead to an equable climate.

Such a form of geoengineering would be much less expensive than other currently conceived forms of geoengineering.

As much of the plankton growth in the oceans is limited by iron availability (particularly in the Southern Ocean), and as Antarctic icebergs contain significant quantities of iron, and thus it is likely that an armada of icebergs in the Southern Ocean due to a potential collapse of the WAIS in coming decades could produce an excess of iceberg iron flux.  Thus, if vessels were used to deflect significant numbers of icebergs from such an armada into surface currents leading to the tropical oceans, not only would such iceberg cool the SSTA of these tropical oceans, but would also contribute to plankton blooms that would help to sequester atmospheric carbon on the seafloors of the tropical oceans as would the icebergs remain in the armada w.r.t. the seafloor of the Southern Ocean:

Hopwood, M.J., Carroll, D., Höfer, J. et al. Highly variable iron content modulates iceberg-ocean fertilisation and potential carbon export. Nat Commun 10, 5261 (2019) doi:10.1038/s41467-019-13231-0

https://www.nature.com/articles/s41467-019-13231-0?draft=marketing

Abstract
Marine phytoplankton growth at high latitudes is extensively limited by iron availability. Icebergs are a vector transporting the bioessential micronutrient iron into polar oceans. Therefore, increasing iceberg fluxes due to global warming have the potential to increase marine productivity and carbon export, creating a negative climate feedback. However, the magnitude of the iceberg iron flux, the subsequent fertilization effect and the resultant carbon export have not been quantified. Using a global analysis of iceberg samples, we reveal that iceberg iron concentrations vary over 6 orders of magnitude. Our results demonstrate that, whilst icebergs are the largest source of iron to the polar oceans, the heterogeneous iron distribution within ice moderates iron delivery to offshore waters and likely also affects the subsequent ocean iron enrichment. Future marine productivity may therefore be not only sensitive to increasing total iceberg fluxes, but also to changing iceberg properties, internal sediment distribution and melt dynamics.

See also:
Title: "We Need to Protect Antarctic ‘Blue Carbon’"

https://www.wired.com/story/opinion-we-need-to-protect-antarctic-blue-carbon/

Extract: "As marine ice is lost in coastal waters, marine algae are blooming in higher densities, taking CO2 from the atmosphere to do so. Some of this sinks to the seafloor and is buried, and some is eaten by animals who are buried upon death. This “blue carbon sink” has doubled in the last two decades. As the climate warms, ice in polar seas decreases, marine life is clawing back via carbon sequestration."

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

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2106 on: December 04, 2019, 05:05:29 PM »
The first attached image from a 2002 National Geographic map of the Antarctic shows both the sea ice movement and the typical wind flow patterns (circa 2000 to 2001).  The sea ice movement indicates how both the Weddell and the Ross Sea areas manufacture and export sea ice; while the wind pattern shows how some snowfall could be blown into the ocean.

The second attached image from a 2002 National Geographic map of the Antarctic shows how the frontal zone of the RIS (Ross Ice Shelf) in the indicated area is subject to accelerated calving due to local upwelling of warm deep water.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2107 on: December 04, 2019, 05:12:46 PM »
I provide the linked open access reference that indicates that no later than 2070 we can expect the Filchner-Ronne Ice Shelf to be subjected to an marked increase of warm under-base water flow from off-shelf sources that will accelerate basal melting and calving.

Hartmut H. Hellmer, Frank Kauker, Ralph Timmermann, and Tore Hattermann (2017), "The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate:, Journal of Climate, doi: 10.1175/JCLI-D-16-0420.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0420.1

Abstract: "Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2108 on: December 04, 2019, 05:14:57 PM »
The linked reference demonstrates that small changes in ice thickness on the edge of Antarctic ice shelves (like RIS) can induce thinning over distances of more than 900km of the rest of the ice shelf (see the attached image), which also reduces the buttressing action on the adjoining marine glacier:

R. Reese et al (2017), "The far reach of ice-shelf thinning in Antarctica", Nature Climate Change, doi:10.1038/s41558-017-0020-x

http://www.nature.com/articles/s41558-017-0020-x

Abstract: "Floating ice shelves, which fringe most of Antarctica’s coastline, regulate ice flow into the Southern Ocean. Their thinning or disintegration can cause upstream acceleration of grounded ice and raise global sea levels. So far the effect has not been quantified in a comprehensive and spatially explicit manner. Here, using a finite-element model, we diagnose the immediate, continent-wide flux response to different spatial patterns of ice-shelf mass loss. We show that highly localized ice-shelf thinning can reach across the entire shelf and accelerate ice flow in regions far from the initial perturbation. As an example, this ‘tele-buttressing’ enhances outflow from Bindschadler Ice Stream in response to thinning near Ross Island more than 900 km away. We further find that the integrated flux response across all grounding lines is highly dependent on the location of imposed changes: the strongest response is caused not only near ice streams and ice rises, but also by thinning, for instance, well-within the Filchner–Ronne and Ross Ice Shelves. The most critical regions in all major ice shelves are often located in regions easily accessible to the intrusion of warm ocean waters, stressing Antarctica’s vulnerability to changes in its surrounding ocean."

See also:
https://www.pik-potsdam.de/news/press-releases/tiny-ice-losses-at-antarctica2019s-fringes-can-accelerate-ice-loss-far-away

Caption: "Ross Ice Shelf: changes in speed resulting from 1m thinning (red: area of thinning, blue shading: resulting change in ice flow speed, ocean in grey). Fig. 2b from Reese et al, 2017"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2109 on: December 04, 2019, 05:28:02 PM »
As SO2 emissions both have a significant negative impact on human heath and as it is easy to reduce such emissions using existing technology than are associated GHG emissions (see the linked article about reducing SO2 emissions from shipping); it is reasonable to assume that the trend of increasing SO2 emissions will be curtailed sooner that will be GHG emissions.  While from a health point of view this is good news; however, from a climate change risk perspective it is bad news as SO2 emissions represent a negative radiative forcing:

Title: "Shipping sector gears itself for new emissions regulations"

https://www.dw.com/en/shipping-sector-gears-itself-for-new-emissions-regulations/a-50836212

Extract: "From January 1, 2020, ships will be required by the IMO to reduce SO2 emissions by more than 80%. The options for doing so vary, from installing sulphur-removing technology known as scrubbers to moving away from oil-based fuel entirely. What doesn't vary all that much is the cost — complying with the new rules will be expensive.

This forthcoming measure only deals with sulphur though. Measures against carbon pollution, altogether harder to conceive and enforce, are yet to come.

Compliance is expected to be high."
For reference I provide the attached plot of global SO2 emissions (that generate a negative feedback) thru 2018 from the linked website.  It will be interesting to see how this timeseries progresses in the future:

https://openclimatedata.github.io/global-emissions/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2110 on: December 04, 2019, 05:45:01 PM »
I note that while the global average CO2 emission per capita has been essentially flat for the past decade, global fossil fuel emissions keep rising due to both population growth and due to economic growth in China:

Title: "Analysis: Global fossil-fuel emissions up 0.6% in 2019 due to China"

https://www.carbonbrief.org/analysis-global-fossil-fuel-emissions-up-zero-point-six-per-cent-in-2019-due-to-china

Extract: "After increasing at the fastest rate for seven years in 2018, global CO2 emissions are set to rise much more slowly this year – but will, nevertheless, reach another record high."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2111 on: December 04, 2019, 06:01:01 PM »

Given that we can measure the concentration of methane in the atmosphere and thus calculate the total net emissions (all sources minus all sinks), if two sources were underestimated that implies that another source (or multiple sources) were overestimated or that the sinks were underestimated.


The attached NOAA plot of the atmospheric methane concentrations at the South Pole from 2006 to Dec 2, 2019 indicate that the trend line of this methane concentration is accelerating; thus if some methane sources are not changing then other sources are currently accelerating, and may accelerate even more in the future due to global warming.

The linked article & reference provide further insights about the origins of the current trend of increasing methane emissions and associated atmospheric methane concentrations:

Title: "Atmospheric Methane Levels Are Going Up—And No One Knows Why"

https://www.wired.com/story/atmospheric-methane-levels-are-going-up-and-no-one-knows-why/

Extract: "Levels of heat-trapping methane are rising faster than climate experts anticipated, triggering intense debate about why it's happening

“Is atmospheric methane increasing as a consequence of climate change, not of our direct emissions? Are some thresholds being passed?”

“It is a wicked problem,” Kort adds, “but it’s not unsolvable.”

Any convincing explanation needs to answer three questions. What explains the long-term increase in methane levels over the past 40 years? Why was there a pause? And why was there such an abrupt surge after 2006? Only three elements of the global methane budget are large enough to be plausible culprits: microbial emissions (from livestock, agriculture, and wetlands); fossil fuel emissions; and the chemical process by which methane is scrubbed from the atmosphere."

See also:

Giuseppe Etiope and Stefan Schwietzke (2019), "Global geological methane emissions: an update of top-down and bottom-up estimates", Elementa Science of the Anthropocene, 7: 47, doi: https://doi.org/10.1525/elementa.383

https://www.elementascience.org/articles/10.1525/elementa.383/

Abstract

A wide body of literature suggests that geological gas emissions from Earth’s degassing are a major methane (CH4) source to the atmosphere. These emissions are from gas-oil seeps, mud volcanoes, microseepage and submarine seepage in sedimentary (petroleum-bearing) basins, and geothermal and volcanic manifestations. Global bottom-up emission estimates, ranging from 30 to 76 Tg CH4 yr–1, evolved in the last twenty years thanks to the increasing number of flux measurements, and improved knowledge of emission factors and area distribution (activity). Based on recent global grid maps and updated evaluations of mud volcano and microseepage emissions, the global geo-CH4 source is now (bottom-up) estimated to be 45 (27–63) Tg yr–1, i.e., ~8% of total CH4 sources. Top-down verifications, based on independent approaches (including ethane and isotopic observations) from different authors, are consistent with the range of the bottom-up estimate. However, a recent top-down study, based on radiocarbon analyses in polar ice cores, suggests that geological, fossil (14C-free) CH4 emissions about 11,600 years ago were much lower (<15 Tg yr–1, 95% CI) and that this source strength could also be valid today. Here, we show that (i) this geo-CH4 downward revision implies a fossil fuel industry CH4 upward revision of at least 24–35%. (ii) The 95% CI estimates of the recent radiocarbon analysis do not overlap with those of 5 out of 6 other bottom-up and top-down studies (no overlap for the 90% CI estimates). (iii) The contrasting lines of evidence require further discussion, and research opportunities exist to help explain this gap.

Caption for image: "Comparison between current day estimates of geological and other methane sources. Geological emissions are based on the bottom-up and top-down estimates discussed in this work (see Fig. 1 and text). Other natural and anthropogenic emissions refer to the average (and range) of bottom-up and top-down estimates reported by Saunois et al. (2016). Note that a downward revision of the geological source requires an upward revision of the same magnitude for the fossil fuel industry (Section 4). DOI: https://doi.org/10.1525/elementa.383.f2"

While studies can't point unequivocally to the explosion of fracking in the US over the past decade as a cause for the rise, the timing of the shift from the stabilization period and the growth of fracking may be more than coincidental.





There have been studies that have shown that methane leakage from US oil and gas production is 60% higher than what the industry and government claims it is.

https://science.sciencemag.org/content/361/6398/186

Quote
Assessment of methane emissions from the U.S. oil and gas supply chain

Ramón A. Alvarez, Daniel Zavala-Araiza, David R. Lyon, David T. Allen, Zachary R. Barkley, Adam R. Brandt, Kenneth J. Davis, Scott C. Herndon, Daniel J. Jacob, Anna Karion, Eric A. Kort, Brian K. Lamb, Thomas Lauvaux, Joannes D. Maasakkers, Anthony J. Marchese, Mark Omara, Stephen W. Pacala, Jeff Peischl, Allen L. Robinson, Paul B. Shepson, Colm Sweeney, Amy Townsend-Small, Steven C. Wofsy, Steven P. Hamburg

Science  13 Jul 2018

A leaky endeavor

Considerable amounts of the greenhouse gas methane leak from the U.S. oil and natural gas supply chain. Alvarez et al. reassessed the magnitude of this leakage and found that in 2015, supply chain emissions were ∼60% higher than the U.S. Environmental Protection Agency inventory estimate. They suggest that this discrepancy exists because current inventory methods miss emissions that occur during abnormal operating conditions. These data, and the methodology used to obtain them, could improve and verify international inventories of greenhouse gases and provide a better understanding of mitigation efforts outlined by the Paris Agreement.

Abstract

Methane emissions from the U.S. oil and natural gas supply chain were estimated by using ground-based, facility-scale measurements and validated with aircraft observations in areas accounting for ~30% of U.S. gas production. When scaled up nationally, our facility-based estimate of 2015 supply chain emissions is 13 ± 2 teragrams per year, equivalent to 2.3% of gross U.S. gas production. This value is ~60% higher than the U.S. Environmental Protection Agency inventory estimate, likely because existing inventory methods miss emissions released during abnormal operating conditions. Methane emissions of this magnitude, per unit of natural gas consumed, produce radiative forcing over a 20-year time horizon comparable to the CO2 from natural gas combustion. Substantial emission reductions are feasible through rapid detection of the root causes of high emissions and deployment of less failure-prone systems.

I would suggest that increased fracking of natural gas and oil is more likely to be the cause of the recent resumption of methane concentration increases and that reducing and eventually eliminating the use of fossil fuels will lead to a big decrease in the concentrations of methane in the atmosphere.  I've read similar statements from James Hansen but can't find links to them at the moment.



AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2112 on: December 04, 2019, 06:20:59 PM »
Per the linked Twitter feed and associated linked analysis, Andrew Dessler stated:

"The first term is the unforced pattern effect, which is due to internal variability over the 20th century. The second is the forced pattern effect, due to the fact that the surface warming pattern during transient warming is not the same as the pattern at equilibrium.  Together, they could bias ECS measured over the 20th century low by about 0.5 K."

"Potential problems measuring climate sensitivity from the historical record", by Andrew Dressler, submitted to the Journal of Climate in 2019.

https://twitter.com/AndrewDessler/status/1202004214773190657

Abstract
This study investigates potential biases between equilibrium climate sensitivity inferred from warming over the historical period (ECShist) and the climate system’s true ECS (ECStrue). This paper focuses on two factors that could contribute to differences between these quantities. First is the impact of internal variability over the historical period: our historical climate record is just one of an infinity of possible trajectories, and these different trajectories can generate ECShist values 0.3 K below to 0.5 K above (5-95% confidence interval) the average ECShist. Because this spread is due to unforced variability, I refer to this as the unforced pattern effect. This unforced pattern effect in the model analyzed here is traced to unforced variability in loss of sea ice, which affects the albedo feedback, and to unforced variability in warming of the troposphere, which affects the short-wave cloud feedback. There is also a forced pattern effect that causes ECShist to depart from ECStrue due to differences between today’s transient pattern of warming and the pattern of warming at 2xCO2 equilibrium. Changes in the pattern of warming lead to a strengthening low-cloud feedback as equilibrium is approached in regions where surface warming is delayed: the Southern Ocean, East Pacific, and North Atlantic near Greenland. This forced pattern effect causes ECShist to be on average 0.2 K lower than ECStrue (~8%). The net effect of these two pattern effects together can produce an estimate of ECShist as much as 0.5 K below ECStrue.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

nanning

  • Nilas ice
  • Posts: 1069
  • 0Kg CO2, 35 KWh/wk,130L H2O/wk, No heating
    • View Profile
  • Liked: 157
  • Likes Given: 6970
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2113 on: December 04, 2019, 06:25:56 PM »
   Climate models have accurately predicted global heating, study finds

Findings confirm reliability of projections of temperature changes over last 50 years


https://www.theguardian.com/environment/2019/dec/04/climate-models-have-accurately-predicted-global-heating-study-finds
  by Dana Nuccitelli

  First four paragraphs:
Climate models have accurately predicted global heating for the past 50 years, a study has found.

The findings confirm that since as early as 1970, climate scientists have had a solid fundamental understanding of the Earth’s climate system and the ability to project how it will respond to continued increases in the greenhouse effect. Since climate models have accurately anticipated global temperature changes so far, we can expect projections of future warming to be reliable as well.

The research examines the accuracy of 17 models published over the past five decades, beginning with a 1970 study and including 1981 and 1988 models led by James Hansen, the former Nasa climatologist who testified to the US Senate in 1988 about the impacts of anthropogenic global heating. The study also includes the first four reports by the UN’s intergovernmental panel on climate change (IPCC).

“We found that climate models – even those published back in the 1970s – did remarkably well, with 14 out of the 17 model projections indistinguishable from what actually occurred,” said Zeke Hausfather, of the University of California, Berkeley, and lead author of the paper.
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell
   Simple: minimize your possessions and be free and kind    It's just a mindset.       Refugees welcome

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2114 on: December 04, 2019, 06:38:55 PM »
James Hansen produced a very easy to read, plain language paper (in support of a legal brief for a lawsuit, not a peer-reviewed science study) in 2018 that summarizes climate change.  It has a very good explanation of equilibrium climate sensitivity and slow feedbacks.

http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf

Quote
Climate Change in a Nutshell: The Gathering Storm
18 December 2018
James Hansen

Quote
Charney’s derived climate sensitivity of 3 ± 1.5°C, or 0.75 ± 0.25°C per W/m2of climate forcing, was the estimate for equilibrium (eventual) warming after the Earth’s surface and ocean had warmed to restore planetary energy balance, with the assumption that ice sheet sizes remained unchanged.  In reality ice sheets begin to shrink as the world warms, but if one’s interest is only in climate change on a time scale of a century or less, then the change of ice sheet size might be neglected

Quote
Charney’s climate sensitivity thus includes effects of fast feedbacks, such as atmospheric water vapor and clouds, which respond quickly to changed climate, but it excludes slow feedbacks such as ice sheet size.  As detailed information on Earth’s paleoclimate history emerged, it became clear that the paleoclimate data provided an independent empirical evaluation of Charney’s fast feedback climate sensitivity as well as information on the climate system’s slow feedback response.

Slow feedbacks and the CO2 control knob. 

Slow feedbacks include both amplifying and diminishing effects, but empirical evidence shows that the two principal slow feedbacks are both amplifying.The first slow feedback is ice sheet size and albedo (literally its whiteness).  Ice sheets shrink as Earth warms.  The surface thus exposed is darker than the ice, so it absorbs more sunlight, increasing the warming.  Also, with warmer conditions an ice sheet is wet more frequently, from surface meltwater or rainfall, and wet ice is darker and more absorbing, again an amplifying feedback.

The second slow feedback is provided by CO2, CH4 and N2O, but mostly by CO2.  It is an empirical fact that the ocean, soil and biosphere release more of these GHGs as the planet gets warmer.  Part of the reason is that CO2 is less soluble in a warmer ocean, just as in a warm Cola, but more complex ocean chemistry and the rate of ocean overturning also affect the amount of gases released to the air.  GHGs are also released by melting tundra and by wetlands on a warmer planet.

Quote
The close correlation of CO2, temperature and ice sheet size in the paleo record allows empirical evaluation of the (fast-feedback) climate sensitivity that Charney inferred, from climate models, to be 1.5-4.5°C for doubled CO2.  Paleo evaluation is obtained by comparing glacial and interglacial states; GHG amounts and ice sheet size, although they are slow feedbacks on millennial time scales, serve as boundary forcings that maintain these quasi-equilibrium climate states.  These paleo data yield a narrower range (2.5-4°C for doubled CO2) for the fast-feedback climate sensitivity [footnote 3 in Ice Melt (2016)].

Quote
This additional warming (in the pipeline) will occur over coming decades and centuries, if atmospheric composition remains at today’s level.  However, in addition to this fast-feedback in-the-pipeline warming, there will be further slow-feedback warming even if atmospheric composition remains at today’s level, as I quantify below.Slow feedbacks will begin to come into play this century.  As we have noted, paleoclimate data indicate that the response time of ice sheets and sea level to global warming is one to four centuries.  The degree of slow feedback response this century, such as ice sheet mass loss and permafrost melt, will depend on the magnitude of global warming and thus on the rate of continued GHG emissions.

The additional global warming, from Earth’s energy imbalance and from slow feedbacks, can be increased or decreased, if atmospheric GHG amounts increase further or decrease.  Warming in the pipeline need not occur, if emissions decrease at a rate that allows atmospheric GHG amounts to decline.  The same is true for slow feedbacks: they will not occur to a significant degree, if emissions decrease rapidly such that atmospheric GHG amounts stabilize and then slowly decline.

Quote
II.  Emission reductions, at a substantial rate, must begin promptly

CO2 released in fossil fuel burning remains in the climate system for millennia (Archer, 2005).  The portion of CO2 remaining in the air declines rapidly at first (Fig. 25).  Half of the emitted CO2 is taken up in the first 25 years by the ocean, soil and biosphere, but uptake then slows such that almost one-fifth is still in the air after 500 years.  Chemical weathering eventually deposits the fossil fuel carbon on the ocean floor as carbonate sediment, but that process requires millennia

Quote
Emission reductions of 3 percent/year, the green line in Fig. 28, or more are needed to stay below 1.5°C global warming and achieve a downward temperature trend.  Decreasing temperature would tend to limit slow feedback amplifications.

Extraction of CO2 from the air is required, in addition to emission phasedown, in order to bring global temperature back close to the Holocene range (Fig. 28b). Without extraction, global temperature remains well above the Holocene level for centuries, as shown in Fig. 28a, leaving a danger of consequences such as large sea level rise, albeit such consequences are not as certain as with constant emissions.

Extraction of as much as approximately 100 PgC is possible via improved agricultural and forestry practices, which store more carbon in the soil and biosphere, based on estimates discussed in the Burden(2017) paper.  Some researchers have suggested that such potential quasi-natural extraction could be as high as 150 PgC (Robertson, 2018).  This greater extraction, in combination with 6 percent per year reduction of fossil fuel emissions, would return global temperature close to the Holocene range by the end of this century (Fig. 28b).



Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2115 on: December 04, 2019, 06:57:35 PM »
Models not running hot, but pretty accurate, according to Hausfather et al 2019:
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085378

"Plain Language Summary
Climate models provide an important way to understand future changes in the Earth's climate. In this paper we undertake a thorough evaluation of the performance of various climate models published between the early 1970s and the late 2000s. Specifically, we look at how well models project global warming in the years after they were published by comparing them to observed temperature changes. Model projections rely on two things to accurately match observations: accurate modeling of climate physics, and accurate assumptions around future emissions of CO2 and other factors affecting the climate. The best physics‐based model will still be inaccurate if it is driven by future changes in emissions that differ from reality. To account for this, we look at how the relationship between temperature and atmospheric CO2 (and other climate drivers) differs between models and observations. We find that climate models published over the past five decades were generally quite accurate in predicting global warming in the years after publication, particularly when accounting for differences between modeled and actual changes in atmospheric CO2 and other climate drivers. This research should help resolve public confusion around the performance of past climate modeling efforts, and increases our confidence that models are accurately projecting global warming."

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2116 on: December 04, 2019, 07:26:58 PM »
James Hansen produced a very easy to read, plain language paper (in support of a legal brief for a lawsuit, not a peer-reviewed science study) in 2018 that summarizes climate change.  It has a very good explanation of equilibrium climate sensitivity and slow feedbacks.

http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf

...

Of course the equilibrium climate sensitivity that Hansen is referring to in that paper is associated only with fast feedbacks (see dotted curve in the attached image, from Hansen and Sato - 2012); while it is open for discussion in this thread how fast the ice-climate feedbacks (such as albedo changes, see the solid curve in the attached image) will occur, particularly if the WAIS were to collapse abruptly in the coming decades.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2117 on: December 04, 2019, 07:38:49 PM »
The linked study indicates that reducing anthropogenic emissions of methane will lead to a reduction in atmospheric concentrations.

https://www.pnas.org/content/116/8/2805

Quote
Interpreting contemporary trends in atmospheric methane
Alexander J. Turner, Christian Frankenberg, and Eric A. Kort
PNAS February 19, 2019

Abstract
Atmospheric methane plays a major role in controlling climate, yet contemporary methane trends (1982–2017) have defied explanation with numerous, often conflicting, hypotheses proposed in the literature. Specifically, atmospheric observations of methane from 1982 to 2017 have exhibited periods of both increasing concentrations (from 1982 to 2000 and from 2007 to 2017) and stabilization (from 2000 to 2007). Explanations for the increases and stabilization have invoked changes in tropical wetlands, livestock, fossil fuels, biomass burning, and the methane sink. Contradictions in these hypotheses arise because our current observational network cannot unambiguously link recent methane variations to specific sources. This raises some fundamental questions: (i) What do we know about sources, sinks, and underlying processes driving observed trends in atmospheric methane? (ii) How will global methane respond to changes in anthropogenic emissions? And (iii), What future observations could help resolve changes in the methane budget? To address these questions, we discuss potential drivers of atmospheric methane abundances over the last four decades in light of various observational constraints as well as process-based knowledge. While uncertainties in the methane budget exist, they should not detract from the potential of methane emissions mitigation strategies. We show that net-zero cost emission reductions can lead to a declining atmospheric burden, but can take three decades to stabilize. Moving forward, we make recommendations for observations to better constrain contemporary trends in atmospheric methane and to provide mitigation support.

Quote
Preindustrial atmospheric methane levels were stable over the last millenium at ∼600–700 ppb, as inferred from ice core measurements in Antarctica (Fig. 1). Methane concentrations have been altered by humans even before industrialization (32) but began increasing more rapidly in the 1900s (4) due to both human agricultural activities and expanded use of fossil fuels. This rapid rise closely mirrors that of other greenhouse gases that are driven by industrialization and agriculture (e.g., CO2) (1). There is no debate about the cause of the bulk of this rise in atmospheric methane from preindustrial times to the present: human activities.

t is likely that natural sources of methane changed during this period as well; for example, Arora et al. (33) found an increase in simulated wetland emissions from 1850 to 2000 due to changes in temperature and Dean et al. (34) discuss how natural methane emissions may change in response to climatic changes. However, these changes in natural sources are small relative to the more than 300 Tg/y increase in anthropogenic sources from preindustrial times to the present (1, 3, 35). This rise in atmospheric methane from preindustrial levels continued unabated until the 1990s, at which point the methane record diverged from CO2 and N2O (which both showed continued growth).

Quote
Despite the uncertainty of the current relative balance of different controls on atmospheric methane, there is no debate that the large increase from preindustrial times is driven by anthropogenic emissions and that reducing anthropogenic emissions can lead to direct, near-term decreases in atmospheric methane. However, changing methane emissions will alter the methane lifetime via chemical feedbacks with OH [Prather (108, 109)] and, as such, atmospheric abundances can exhibit longer timescales than one may assume. We illustrate this in Fig. 3 by using a simple box model [adapted from Turner et al. (27)] to evaluate four scenarios to bound the future methane abundances: continued growth in anthropogenic methane emissions (case A), a stabilization of methane emissions in 2012 (case B), and an emission decrease over 10 y (case C) or instantaneously (case D). The emissions decrease in the latter two scenarios is based on a recent report from the International Energy Agency (110) that estimates current methane emissions from oil and gas could be reduced by 40–50% with zero net cost.

Quote
While uncertainties in the methane budget exist, they should not detract from the key points discussed here. Namely, reducing anthropogenic methane emissions will slow or reverse the rise in atmospheric concentrations; however, depending on the timescale and magnitude of reduction, it may take decades before atmospheric levels decline. When considering recent decades, the stabilization period is emerging as anomalous due in part to fluctuations in natural sources/sinks, whereas the last decade of growth continues the long-term, increasing trend that is due to human activities.



kassy

  • Grease ice
  • Posts: 859
    • View Profile
  • Liked: 362
  • Likes Given: 377
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2118 on: December 04, 2019, 07:48:48 PM »
Didn´t we prove that for CO2 too?
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2119 on: December 04, 2019, 07:51:18 PM »
James Hansen produced a very easy to read, plain language paper (in support of a legal brief for a lawsuit, not a peer-reviewed science study) in 2018 that summarizes climate change.  It has a very good explanation of equilibrium climate sensitivity and slow feedbacks.

http://www.columbia.edu/~jeh1/mailings/2018/20181206_Nutshell.pdf

...

Of course the equilibrium climate sensitivity that Hansen is referring to in that paper is associated only with fast feedbacks (see dotted curve in the attached image, from Hansen and Sato - 2012); while it is open for discussion in this thread how fast the ice-climate feedbacks (such as albedo changes, see the solid curve in the attached image) will occur, particularly if the WAIS were to collapse abruptly in the coming decades.

The Hansen paper I linked to specifically differentiated between the fast feedbacks (Charney sensitivity) and slow feedback ECS due to loss of ice sheets.  It also included a discussion of timeframes for ice sheet response to forcings and the fact that we can still avoid those impacts by reducing ghg emissions and stabilizing, then reducing, ghg atmospheric concentrations.

You appear to continue to ignore the science on the timing of ice sheet feedbacks.  Even in extreme models with instantaneous 2 degree increases in ocean temperature, continued forcing at the unrealistic RCP8.5 scenario and inclusion of the highly speculative MICI model, the Larsen C shelf wouldn't disintegrate until the 2050s and the Admunsen shelves in front of the PIG and Thwaites portions of the WAIS wouldn't go until the 2100s. 

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2120 on: December 04, 2019, 07:51:58 PM »
Didn´t we prove that for CO2 too?

I'm pretty sure.  But a lot of posters on this forum seem to think that we're doomed and it's too late to do anything.

Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2121 on: December 04, 2019, 08:02:08 PM »
a lot of posters on this forum seem to think that we're doomed and it's too late to do anything.

My impression is that a lot of posters are concerned we're not doing as much as we can, and should, because powerful forces do not think it necessary and/or desirable to do more than we're doing (which has not been much so far).

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2122 on: December 04, 2019, 08:16:17 PM »

The Hansen paper I linked to specifically differentiated between the fast feedbacks (Charney sensitivity) and slow feedback ECS due to loss of ice sheets.  It also included a discussion of timeframes for ice sheet response to forcings and the fact that we can still avoid those impacts by reducing ghg emissions and stabilizing, then reducing, ghg atmospheric concentrations.

You appear to continue to ignore the science on the timing of ice sheet feedbacks.  Even in extreme models with instantaneous 2 degree increases in ocean temperature, continued forcing at the unrealistic RCP8.5 scenario and inclusion of the highly speculative MICI model, the Larsen C shelf wouldn't disintegrate until the 2050s and the Admunsen shelves in front of the PIG and Thwaites portions of the WAIS wouldn't go until the 2100s.

As a reminder the first image indicates that when the radiative forcing imbalance is about 4 W2/m above pre-industrial that the combined fast and slow feedbacks will result in ECS of about 7C; while the second image (from Hansen et al. - 2016)shows that the radiative forcing imbalance could reach 4 W2/m by about 2060 if the WAIS were to begin collapsing circa 2040-2045. 

The third image shows that only a few meters of hf (height above floatation) is holding down the grounded ice at the base of the Thwaites Ice Tongue (see the fourth image).  Thus, if the few meters of hf were to be overcome say due to ice thinning and ice melting (from mCDW), and the Thwaites Ice Tongue were to collapse (note the pending area of spalling shown in the fourth image), then all of the buttressing ice from the base of the ice tongue to the seafloor trough leading straight into the Byrd Subglacial Basin, BSB, could float away; which could well trigger an MICI-type of failure of the glacial ice in the BSB before 2045.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2123 on: December 04, 2019, 08:32:32 PM »
Didn´t we prove that for CO2 too?

I'm pretty sure.  But a lot of posters on this forum seem to think that we're doomed and it's too late to do anything.

In the early 1980's Hansen warned policy makers that the atmospheric CO2 concentration should not exceed about 350 ppm.  However (ignoring that the AGGI uses a GMP100 for methane of 25 instead of AR5's value of 36), the attached Annual Greenhouse Gas Index, AGGI, shows that since 1990 the radiative forcing from GHG has increased by 43% to 2018.  So I believe there is reason to question the resolve of policy makers to take action appropriate for the current level of climate change risk.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2124 on: December 04, 2019, 08:40:23 PM »
In the early 1980's Hansen warned policy makers that the atmospheric CO2 concentration should not exceed about 350 ppm.

Didn't Hansen give this warning in 2008? See:
https://pubs.giss.nasa.gov/docs/2008/2008_Hansen_ha00410c.pdf

Before then I think he warned to not exceed 450 ppm, but maybe I'm mistaken.

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2125 on: December 04, 2019, 08:53:17 PM »
The attached image is from the linked NOAA reference, which indicates a global mean sea level rise of 2.5m for the central 90% probability range augmented by MICI-type of Antarctic SLR contribution for RCP 8.5 to 2100.

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

While this does not constitute proof of abrupt sea level rise; it does constitute an official warning from NOAA of this possibility.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

gerontocrat

  • First-year ice
  • Posts: 6784
    • View Profile
  • Liked: 1685
  • Likes Given: 22
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2126 on: December 04, 2019, 08:58:00 PM »
In the early 1980's Hansen warned policy makers that the atmospheric CO2 concentration should not exceed about 350 ppm.

Didn't Hansen give this warning in 2008? See:
https://pubs.giss.nasa.gov/docs/2008/2008_Hansen_ha00410c.pdf

Before then I think he warned to not exceed 450 ppm, but maybe I'm mistaken.

1967 - Hansen warns Congress - but no number. Instead debate was about  what would happen if CO2 ppm doubled to 550 ppm.

2007 - 350 from which came 350.org

https://www.washingtonpost.com/wp-dyn/content/article/2007/12/27/AR2007122701942.html?

Remember This: 350 Parts Per Million
By Bill McKibben
Friday, December 28, 2007
Quote
This month may have been the most important yet in the two-decade history of the fight against global warming. Al Gore got his Nobel in Stockholm; international negotiators made real progress on a treaty in Bali; and in Washington, Congress actually worked up the nerve to raise gas mileage standards for cars.

But what may turn out to be the most crucial development went largely unnoticed. It happened at an academic conclave in San Francisco. A NASA scientist named James Hansen offered a simple, straightforward and mind-blowing bottom line for the planet: 350, as in parts per million carbon dioxide in the atmosphere. It's a number that may make what happened in Washington and Bali seem quaint and nearly irrelevant. It's the number that may define our future.

Twenty years ago, Hansen kicked off this issue by testifying before Congress th
at the planet was warming and that people were the cause. At the time, we could only guess how much warming it would take to put us in real danger. Since the pre-Industrial Revolution concentration of carbon in the atmosphere was roughly 275 parts per million, scientists and policymakers focused on what would happen if that number doubled -- 550 was a crude and mythical red line, but politicians and economists set about trying to see if we could stop short of that point. The answer was: not easily, but it could be done.

In the past five years, though, scientists began to worry that the planet was reacting more quickly than they had expected to the relatively small temperature increases we've already seen. The rapid melt of most glacial systems, for instance, convinced many that 450 parts per million was a more prudent target. That's what the European Union and many of the big environmental groups have been proposing in recent years, and the economic modeling makes clear that achieving it is still possible, though the chances diminish with every new coal-fired power plant.

But the data just keep getting worse. The news this fall that Arctic sea ice was melting at an off-the-charts pace and data from Greenland suggesting that its giant ice sheet was starting to slide into the ocean make even 450 look too high. Consider: We're already at 383 parts per million, and it's knocking the planet off kilter in substantial ways. So, what does that mean?

It means, Hansen says, that we've gone too far. "The evidence indicates we've aimed too high -- that the safe upper limit for atmospheric CO2is no more than 350 ppm," he said after his presentation. Hansen has reams of paleo-climatic data to support his statements (as do other scientists who presented papers at the American Geophysical Union conference in San Francisco this month). The last time the Earth warmed two or three degrees Celsius -- which is what 450 parts per million implies -- sea levels rose by tens of meters, something that would shake the foundations of the human enterprise should it happen again.
"Para a Causa do Povo a Luta Continua!"
"And that's all I'm going to say about that". Forrest Gump
"Damn, I wanted to see what happened next" (Epitaph)

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2127 on: December 04, 2019, 09:16:56 PM »
...
1967 - Hansen warns Congress - but no number. Instead debate was about  what would happen if CO2 ppm doubled to 550 ppm.


Indeed, I was vaguely thinking of Hansen's 1988 Congressional testimony (not 1967), when Hansen presented the attached image (with 1960 as a baseline; which is close to a pre-industrial baseline) from the first linked article (that incorrectly thought that Hansen had over estimated climate sensitivity, while in fact GMSTA with a pre-industrial baseline will be over 1.1C in 2019; which, as the second link indicates shows that Hansen's model was spot on):

Title: "What do we learn from James Hansen's 1988 prediction?"

https://skepticalscience.com/Hansen-1988-prediction.htm

&

Title: "Judgment on Hansen's '88 climate testimony: 'He was right' "

https://www.yaleclimateconnections.org/2018/06/judgment-on-hansens-88-climate-testimony-he-was-right/

Extract: "Hansen in that 1988 congressional testimony nailed it, adds Texas A&M scientist Andrew Dessler. “You could have reached an alternative conclusion” based on the science at that time, he says, pointing to the 1990 IPCC conclusion that the observed warming at that point was consistent with global warming evidence, but also with natural variability."

Finally, as Lennart points-out the 350 ppm value was actually first cited in the following 2008 reference:

Hansen, J., Mki. Sato, P. Kharecha, D. Beerling, R. Berner, V. Masson-Delmotte, M. Pagani, M. Raymo, D.L. Royer, and J.C. Zachos, 2008: Target atmospheric CO2: Where should humanity aim? Open Atmos. Sci. J., 2, 217-231, doi:10.2174/1874282300802010217.
« Last Edit: December 04, 2019, 09:30:06 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2128 on: December 04, 2019, 09:43:24 PM »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2129 on: December 04, 2019, 10:46:08 PM »
The linked reference indicates that the Ross Ice Shelf, RIS, is currently being stabilized by 'nails' from adjoining EAIS outlet glaciers (like Byrd Glacier) that are pinning the ice shelf to the Transantarctic Mountains.  Thus destabilization of the RIS would accelerated due to the extraction of the 'nails' associated with continued global warming:

Terence Hughes, Zihong Zhao, Raymond Hintz & James Fastook (27 May 2017), "Instability of the Antarctic Ross Sea Embayment as climate warms", Reviews of Geophysics, DOI: 10.1002/2016RG000545

http://onlinelibrary.wiley.com/doi/10.1002/2016RG000545/abstract

Abstract: "Collapse of the Antarctic Ice Sheet since the Last Glacial Maximum 18,000 years ago is most pronounced in the Ross Sea Embayment, which is partly ice-free during Antarctic summers, thereby breaching the O-ring of ice shelves and sea ice surrounding Antarctica that stabilizes the ice sheet. The O-ring may have vanished during Early Holocene (5000 to 3000 B.C.), Roman (1 to 400 A.D.), and Medieval (900 to 1300 A.D.) warm periods and reappeared during the Little Ice Age (1300 to 1900 A.D.). We postulate further collapse in the embayment during the post-1900 warming may be forestalled because East Antarctic outlet glaciers “nail” the Ross Ice Shelf to the Transantarctic Mountains so it can resist the push from West Antarctic ice streams. Our hypothesis is examined for Byrd Glacier and a static ice shelf using three modeling experiments having plastic, viscous, and viscoplastic solutions as more data and improved modeling became available. Observed crevasse patterns were not reproduced. A new research study is needed to model a dynamic Ross Ice Shelf with all its feeder ice streams, outlet glaciers, and ice calving dynamics in three dimensions over time to fully test our hypothesis. The required model must allow accelerated calving if further warming melts sea ice and discerps the ice shelf. Calving must then successively pull the outlet glacier “nails” so collapse of the marine West Antarctic Ice Sheet proceeds to completion."

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

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2130 on: December 04, 2019, 11:09:25 PM »
The linked reference provides numerous warning about the local impacts of global warming in the Arctic (I note that the statements about Antarctica are more general in nature as the authors do not adequately differentiate between surface warming in East and West, Antarctica):

Eric Post et al. (04 Dec 2019), "The polar regions in a 2°C warmer world", Science Advances, Vol. 5, no. 12, eaaw9883, DOI: 10.1126/sciadv.aaw9883

https://advances.sciencemag.org/content/5/12/eaaw9883

Abstract
Over the past decade, the Arctic has warmed by 0.75°C, far outpacing the global average, while Antarctic temperatures have remained comparatively stable. As Earth approaches 2°C warming, the Arctic and Antarctic may reach 4°C and 2°C mean annual warming, and 7°C and 3°C winter warming, respectively. Expected consequences of increased Arctic warming include ongoing loss of land and sea ice, threats to wildlife and traditional human livelihoods, increased methane emissions, and extreme weather at lower latitudes. With low biodiversity, Antarctic ecosystems may be vulnerable to state shifts and species invasions. Land ice loss in both regions will contribute substantially to global sea level rise, with up to 3 m rise possible if certain thresholds are crossed. Mitigation efforts can slow or reduce warming, but without them northern high latitude warming may accelerate in the next two to four decades. International cooperation will be crucial to foreseeing and adapting to expected changes.

Extract: "In contrast to the GIS, major mass loss over the coming decades from surface runoff is not expected for Antarctica under RCP4.5 or greater emissions (62). However, ongoing mass loss was recently triggered when warmer ocean waters thinned ice shelves, reducing their buttressing effect, allowing for faster flow of nonfloating ice into the ocean [reviewed in (71)]. Sufficient warming to trigger GIS-type ice-shelf loss and tidewater-calving retreat could contribute substantially to sea level rise in the next ~100 years especially from WAIS, even if iceberg calving is limited to rates already exceeded locally in GIS, owing to the much wider WAIS calving front that could develop (72, 73). In addition, because WAIS could produce higher cliffs with less drag from fjord sides than in the GIS, and thus greater stress imbalances driving calving, even faster sea level rise is possible (71).

Within the WAIS, Thwaites Glacier has undergone notably rapid ice loss and appears particularly vulnerable to accelerated ice loss with increased ice-shelf basal melt. In a recent comparison of two simplified model scenarios representing “constant climate” and “warming climate,” Thwaites Glacier collapsed in 80% of constant climate experiments and in 100% of warming climate experiments (74). Collapse of Thwaites Glacier and other Antarctic sources could contribute more than 3 m to global sea level rise over a time span that is poorly characterized but could be less than a century following initiation if ice-shelf loss and cliff retreat become important (72, 75). Further warming could extend these processes into marine basins of EAIS, potentially adding an additional 12 m or more of sea level rise further in the future (72). Geoengineering solutions have been proposed (76), but grave difficulties remain.

Recent work (77, 78) suggests that past ice sheet fluctuations can be modeled without invoking ice-shelf loss and subsequent cliff failure, favoring models that give smaller or slower sea level rise than calculated by some studies (72), but essentially all ice that flows into the ocean ends in calving cliffs. Ice-shelf loss has been observed in several cases with subsequent flow acceleration (75), so models lacking cliff physics are omitting known processes that are critical to ice loss. Uncertainties are very large on many aspects of this topic, including poor knowledge of the threshold warming of ocean or atmosphere needed to trigger major ice-shelf loss for vulnerable drainages. Large, rapid sea level rise under strong warming thus remains possible but unproven."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2131 on: December 04, 2019, 11:53:00 PM »
The linked reference is essentially calling for an international effort (comparable to CERN) to exceed the E3SM program to use exascale computing to adequately model physical laws of the numerous Earth Systems:

Tim Palmer el al., "The scientific challenge of understanding and estimating climate change," PNAS (2019). www.pnas.org/cgi/doi/10.1073/pnas.1906691116

https://www.pnas.org/content/116/49/24390

Abstract
Given the slow unfolding of what may become catastrophic changes to Earth’s climate, many are understandably distraught by failures of public policy to rise to the magnitude of the challenge. Few in the science community would think to question the scientific response to the unfolding changes. However, is the science community continuing to do its part to the best of its ability? In the domains where we can have the greatest influence, is the scientific community articulating a vision commensurate with the challenges posed by climate change? We think not.

Extract: "The idea that the science of climate change is largely “settled,” common among policy makers and environmentalists but not among the climate science community, has congealed into the view that the outlines and dimension of anthropogenic climate change are understood and that incremental improvement to and application of the tools used to establish this outline are sufficient to provide society with the scientific basis for dealing with climate change.

As climate scientists, we are rightfully proud of, and eager to talk about, our contribution to settling important and long-standing scientific questions of great societal relevance. What we find more difficult to talk about is our deep dissatisfaction with the ability of our models to inform society about the pace of warming, how this warming plays out regionally, and what it implies for the likelihood of surprises. In our view, the political situation, whereby some influential people and institutions misrepresent doubt about anything to insinuate doubt about everything, certainly contributes to a reluctance to be too openly critical of our models. Unfortunately, circling the wagons leads to false impressions about the source of our confidence and about our ability to meet the scientific challenges posed by a world that we know is warming globally.

The development of this new generation of models should be sustained, multinational, and coordinated as a flagship application of high-performance computing and information technology. Only as a coordinated technology project will it be possible to meet the computational challenges of running the highest possible resolution models and accessing their full information content. How to structure such an initiative can be debated; indisputable is the necessity to endow it with the same sense of purpose that has made past grand scientific challenges—from weather forecasting to moon landings—so successful.

As our nonlinear world moves into uncharted territory, we should expect surprises. Some of these may take the form of natural hazards, the scale and nature of which are beyond our present comprehension. The sooner we depart from the present strategy, which overstates an ability to both extract useful information from and incrementally improve a class of models that are structurally ill suited to the challenge, the sooner we will be on the way to anticipating surprises, quantifying risks, and addressing the very real challenge that climate change poses for science. Unless we step up our game, something that begins with critical self-reflection, climate science risks failing to communicate and hence realize its relevance for societies grappling to respond to global warming."

See also:

Title: "A CERN for climate change"

https://phys.org/news/2019-12-cern-climate.html

Extract: "Asked whether he feared their critique of the present state of Earth system modelling might be exploited by those attempting to cast doubt on present understanding of global warming, Stevens replies: "It is important that scientists speak candidly. It shouldn't come as a surprise that we can understand some things (like the world is warming because of human activities) but not everything (like what this warming means for regional changes in weather, extremes, and the habitability of the planet). By not talking about the limits of our understanding we run the risk of failing to communicate the need for new scientific approaches, just when they are needed most."

When asked whether spending new money on such an international climate modelling initiative can be justified, Professor Palmer said: "By comparison with new particle colliders or space telescopes, the amount needed, maybe around $100 million per year, is very modest indeed. In addition, the benefit/cost ratio to society of having a much clearer picture of the dangers we are facing in the coming decades by our ongoing actions, seems extraordinarily large. To be honest, all is needed is the will to work together, across nations, on such a project. Then it will happen.""

Edit: I note that consensus climate science is not particularly 'settled' science.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2132 on: December 05, 2019, 04:16:08 PM »
Talking about the implications of any given climate model, or any suite of model projections, is very tricky as '... all models are wrong but some models are useful".  Thus when reading the information from the first linked reference (& associated article), please bear in mind the limitations of the cited analyses and also the message from my immediate prior post (Reply #2131) that a CERN-type of global modeling effort (comparable to E3SM on steroids) following physical laws is justified by the many climate uncertainties:

Zeke Hausfather et al. (04 December 2019), "Evaluating the performance of past climate model projections", Geophysical Research Letters, https://doi.org/10.1029/2019GL085378

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019GL085378

Abstract
Retrospectively comparing future model projections to observations provides a robust and independent test of model skill. Here we analyse the performance of climate models published between 1970 and 2007 in projecting future global mean surface temperature (GMST) changes. Models are compared to observations based on both the change in GMST over time and the change in GMST over the change in external forcing. The latter approach accounts for mismatches in model forcings, a potential source of error in model projections independent of the accuracy of model physics. We find that climate models published over the past five decades were skillful in predicting subsequent GMST changes, with most models examined showing warming consistent with observations, particularly when mismatches between model‐projected and observationally‐estimated forcings were taken into account.

Plain Language Summary

Climate models provide an important way to understand future changes in the Earth's climate. In this paper we undertake a thorough evaluation of the performance of various climate models published between the early 1970s and the late 2000s. Specifically, we look at how well models project global warming in the years after they were published by comparing them to observed temperature changes. Model projections rely on two things to accurately match observations: accurate modeling of climate physics, and accurate assumptions around future emissions of CO2 and other factors affecting the climate. The best physics‐based model will still be inaccurate if it is driven by future changes in emissions that differ from reality. To account for this, we look at how the relationship between temperature and atmospheric CO2 (and other climate drivers) differs between models and observations. We find that climate models published over the past five decades were generally quite accurate in predicting global warming in the years after publication, particularly when accounting for differences between modeled and actual changes in atmospheric CO2 and other climate drivers. This research should help resolve public confusion around the performance of past climate modeling efforts, and increases our confidence that models are accurately projecting global warming.

See also:

Title: "Early climate modelers got global warming right, new report finds"

https://news.berkeley.edu/2019/12/04/early-climate-modelers-got-global-warming-right-new-report-finds/

Extract: "Climate skeptics have long raised doubts about the accuracy of computer models that predict global warming, but it turns out that most of the early climate models were spot-on, according to a look-back by climate scientists at the University of California, Berkeley, Massachusetts Institute of Technology and NASA.

Of 17 climate models published between the early 1970s and the late 2000s, 14 were quite accurate in predicting the average global temperature in the years after publication, said Zeke Hausfather, a doctoral student in UC Berkeley’s Energy and Resources Group and lead author of a new paper analyzing the models.

“The real message is that the warming we have experienced is pretty much exactly what climate models predicted it would be as much as 30 years ago,” he said. “This really gives us more confidence that today’s models are getting things largely right as well.”

One of the iconic climate models, and one that first brought the issue of climate change to broad public attention, was published by James Hansen of NASA in 1988. However, his predictions for temperatures after 1988 were 50% higher than the actual global mean temperatures in those years.

That is in part because Hanson did not anticipate the Montreal Protocol, a treaty that went into effect in 1989 and which banned chlorofluorocarbons, which are potent greenhouse gases. His estimates of future methane emissions were also off, Hausfather said.

“If you account for these and look at the relationship in his model between temperature and radiative forcing, which is CO2 and other greenhouse gases, he gets it pretty much dead on,” he said. “So the physics of his model was right. The relationship between how much CO2 there is in the atmosphere and how much warming you get, was right. He just got the future emissions wrong.”"
&

Title: "Even 50-year-old climate models correctly predicted global warming"

https://www.sciencemag.org/news/2019/12/even-50-year-old-climate-models-correctly-predicted-global-warming

Extract: "Climate change doubters have a favorite target: climate models. They claim that computer simulations conducted decades ago didn’t accurately predict current warming, so the public should be wary of the predictive power of newer models. Now, the most sweeping evaluation of these older models—some half a century old—shows most of them were indeed accurate.

“How much warming we are having today is pretty much right on where models have predicted,” says the study’s lead author, Zeke Hausfather, a graduate student at the University of California, Berkeley."

&

J. Hansen et al. (28 Aug 1981), "Climate Impact of Increasing Atmospheric Carbon Dioxide", Science, Vol. 213, Issue 4511, pp. 957-966, DOI: 10.1126/science.213.4511.957

https://science.sciencemag.org/content/213/4511/957

Abstract
The global temperature rose by 0.2°C between the middle 1960's and 1980, yielding a warming of 0.4°C in the past century. This temperature increase is consistent with the calculated greenhouse effect due to measured increases of atmospheric carbon dioxide. Variations of volcanic aerosols and possibly solar luminosity appear to be primary causes of observed fluctuations about the mean trend of increasing temperature. It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980's. Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climatic zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.

Edit, see also:

http://www.realclimate.org/index.php/archives/2019/12/how-good-have-climate-models-been-at-truly-predicting-the-future/

« Last Edit: December 05, 2019, 07:43:10 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2133 on: December 05, 2019, 04:26:54 PM »
The linked reference on the in situ mechanical properties of shallow gas hydrates in the seafloor states: "… we were able to observe the hydrate undergoing a catastrophic brittle failure".  To me this highlights the risk that free natural gas accumulating beneath an essentially impermeable shallow gas hydrate cap may eventually develop sufficient pressure to cause a 'catastrophic brittle failure' of the hydrate cap; which would likely result in an abrupt release of the free natural gas beneath the failed cap that would cause a gas bubble that would like reach the atmosphere without much absorption of the methane by the seawater, even in relatively deep continental shelves.  This is yet another risk factor than needs to be considered as the MOC slows and delivers more heat to numerous continental shelves around the world (including in the Arctic Ocean):
 
Jun Yoneda et al. (04 December 2019), "In situ mechanical properties of shallow gas hydrate deposits in the deep seabed", Geophysical Research Letters, https://doi.org/10.1029/2019GL084668

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084668

Abstract

Natural gas hydrates (or methane hydrates) could become a major energy source but could also exacerbate global warming, because as the climate warms, hydrate deposits deep under the oceans or in permafrost may release methane into the atmosphere. There are many shallow deposits of gas hydrates in fine‐grained muddy sediments on the seafloor. However, the mechanical properties of these sediments have not yet been investigated because of the engineering challenges in coring and testing at in situ temperatures and pressures. Here we present the first uniaxial and triaxial strength and stiffness measurements of pure massive natural gas hydrates and muddy sediments containing hydrate nodules obtained by pressure coring. As a result, we were able to observe the hydrate undergoing a catastrophic brittle failure. Its strength and deformation moduli were 3 and 300 MPa, respectively. Muddy sediments containing hydrate nodules had the same strength as that of hydrate‐free sediments.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2134 on: December 05, 2019, 04:34:25 PM »
The linked reference makes various approximate estimates of the influence of iceberg calving on the retreat of the Thwaites Glacier.  I would take these as a lower bound estimates as they do not consider the current fragile/fractured nature of the Thwaites Ice Tongue; nor the risk that the currently grounded ice at the base of the ice tongue could simply float away in coming years due to thinning of the ice in this area:

Hongju Yu et al. (04 December 2019), "Impact of iceberg calving on the retreat of Thwaites Glacier, West Antarctica over the next century with different calving laws and ocean thermal forcing", Geophysical Research Letters, https://doi.org/10.1029/2019GL084066

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084066

Abstract
Thwaites Glacier, West Antarctica, has been a major contributor to global sea level rise over the past decades. Prior studies illustrated the critical role of ice shelf melt and iceberg calving based on cliff height in driving the retreat of Thwaites glacier. Here, we simulate its evolution with various calving laws and rates of frontal melt by the ocean in the absence of a buttressing ice shelf. Over the next century, we find that volume losses increase by 15‐160% with a von Mises calving law compared to the case where the initial ice shelf is kept and the ice front is fixed at its current position, 10‐20% with a buoyancy‐driven calving law, and 5‐50% with frontal melt caused by ocean thermal forcing. Bed topography exerts the ultimate control on the evolution of Thwaites. In all simulations, once Thwaites Glacier retreats past the western subglacial ridge, the retreat becomes rapidly unstoppable.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2135 on: December 05, 2019, 05:37:27 PM »
I have not seen much information provided on sea level rise in the Arctic Ocean, thus I provide the following links and attached associated image.  While, the average SLR in the Arctic Ocean is below the global average the attached image makes it clear that this is due to the negative SLR associated with ice mass loss from Greenland and coastal glaciers; while other portions of the Arctic Ocean have rates of SLR that are two to three times greater than the global average.  For example, the image indicates that the coast of northern Norway may be subjected to accelerated SLR and associated erosion:

Stine Kildegaard Rose et al. Arctic Ocean Sea Level Record from the Complete Radar Altimetry Era: 1991–2018, Remote Sensing (2019). DOI: 10.3390/rs11141672

https://www.mdpi.com/2072-4292/11/14/1672

Abstract: "In recent years, there has been a large focus on the Arctic due to the rapid changes of the region. Arctic sea level determination is challenging due to the seasonal to permanent sea-ice cover, lack of regional coverage of satellites, satellite instruments ability to measure ice, insufficient geophysical models, residual orbit errors, challenging retracking of satellite altimeter data. We present the European Space Agency (ESA) Climate Change Initiative (CCI) Technical University of Denmark (DTU)/Technischen Universität München (TUM) sea level anomaly (SLA) record based on radar satellite altimetry data in the Arctic Ocean from the European Remote Sensing satellite number 1 (ERS-1) (1991) to CryoSat-2 (2018). We use updated geophysical corrections and a combination of altimeter data: Reprocessing of Altimeter Product for ERS (REAPER) (ERS-1), ALES+ retracker (ERS-2, Envisat), combination of Radar Altimetry Database System (RADS) and DTUs in-house retracker LARS (CryoSat-2). Furthermore, this study focuses on the transition between conventional and Synthetic Aperture Radar (SAR) altimeter data to make a smooth time series regarding the measurement method. We find a sea level rise of 1.54 mm/year from September 1991 to September 2018 with a 95% confidence interval from 1.16 to 1.81 mm/year. ERS-1 data is troublesome and when ignoring this satellite the SLA trend becomes 2.22 mm/year with a 95% confidence interval within 1.67–2.54 mm/year. Evaluating the SLA trends in 5 year intervals show a clear steepening of the SLA trend around 2004. The sea level anomaly record is validated against tide gauges and show good results. Additionally, the time series is split and evaluated in space and time."

See also:

Title: "New study reports sea level rise in the Arctic"

https://phys.org/news/2019-07-sea-arctic.html

Extract: "Over the past 22 years, sea levels in the Arctic have risen an average of 2.2 millimeters per year. This is the conclusion of a Danish-German research team after evaluating 1.5 billion radar measurements from satellites using specially developed algorithms.

The enormous volumes of fresh water released in the Arctic not only raise the sea level, they also have the potential to change the system of global ocean currents—and thus, our climate."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2136 on: December 05, 2019, 05:40:50 PM »
As a follow-on to my last post about SLR, I provide the following links to visualization aids to help readers better understand some of the impacts of the risks of abrupt multi-meter SLR (e.g. see the attached image)

Title: "Use these tools to help visualize the horror of rising sea levels"

https://www.theverge.com/2019/2/17/18223808/climate-change-sea-level-rising-data-visualization-environment

&

https://ss2.climatecentral.org/#12/40.7298/-74.0070?show=satellite&projections=0-K14_RCP85-SLR&level=5&unit=feet&pois=hide

&

https://ss2.climatecentral.org/#12/40.7298/-74.0070?show=satellite&projections=0-K14_RCP85-SLR&level=5&unit=feet&pois=hide
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2137 on: December 05, 2019, 06:03:25 PM »
I have periodically suggested that the Jakobshavn Glacier calving front could experience a significant retreat by about +/- 2029; which might then trigger additional ice mass loss in West Antarctica due to the bipolar seesaw.  The linked reference supports the timing of such a significant ice mass loss from Jakobshavn circa 2029:

Guo, X., Zhao, L., Gladstone, R. M., Sun, S., and Moore, J. C.: Simulated retreat of Jakobshavn Isbræ during the 21st century, The Cryosphere, 13, 3139–3153, https://doi.org/10.5194/tc-13-3139-2019, 2019.

https://www.the-cryosphere.net/13/3139/2019/

Abstract
The early 21st century retreat of Jakobshavn Isbræ into its overdeepened bedrock trough was accompanied by acceleration to unprecedented ice stream speeds. Such dramatic changes suggested the possibility of substantial mass loss over the rest of this century. Here we use a three-dimensional ice sheet model with parameterizations to represent the effects of ice mélange buttressing, crevasse-depth-based calving and submarine melting to adequately reproduce its recent evolution. We are the first study on Jakobshavn Isbræ that solves for three-dimensional ice flow coupled with representations of hydro-fracturing-induced calving and mélange buttressing. Additionally, the model can accurately replicate interannual variations in grounding line and terminus position, including seasonal fluctuations that emerged after arriving at the overdeepened basin and the disappearance of its floating ice shelf. Our simulated ice viscosity variability due to shear margin evolution is particularly important in reproducing the large observed interannual changes in terminus velocity. We use this model to project Jakobshavn's evolution over this century, forced by ocean temperatures from seven Earth system models and surface runoff derived from RACMO, all under the IPCC RCP4.5 climate scenario. In our simulations, Jakobshavn's grounding line continues to retreat ∼18.5 km by the end of this century, leading to a total mass loss of ∼2068 Gt (5.7 mm sea level rise equivalent). Despite the relative success of the model in simulating the recent behavior of the glacier, the model does not simulate winter calving events that have become relatively more important.

Caption for image: "Figure 8Upper and lower estimates of July front positions within this century with colors indicating the date (color bar) for (a) lower bound with scalings of (1,0.8 ) and the HadGEM-ES forcing (b) upper bound of mass loss projection with (α, γ) parameter scalings of (1.2,1) and the seven-model-ensemble climate forcing."
« Last Edit: December 05, 2019, 07:19:36 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2138 on: December 05, 2019, 07:17:12 PM »
I have periodically suggested that the Jakobshavn Glacier calving front could experience a significant retreat by about +/- 2029; which might then trigger additional ice mass loss in West Antarctica due to the bipolar seesaw.  The linked reference supports the timing of such a significant ice mass loss from Jakobshavn circa 2029:

Guo, X., Zhao, L., Gladstone, R. M., Sun, S., and Moore, J. C.: Simulated retreat of Jakobshavn Isbræ during the 21st century, The Cryosphere, 13, 3139–3153, https://doi.org/10.5194/tc-13-3139-2019, 2019.

https://www.the-cryosphere.net/13/3139/2019/



I probably should have posted the first image with my immediate previous post, but nevertheless, it presents the measured monthly variations of the thickness of the CDW flow on the ASE shelf.  As the maximum thickness of CDW flow occurs in September of each year, and as the regional sea level rise around the ASE due to the northern hemisphere summer melt of the Greenland Ice Sheet, GIS (see the second image); this implies that the most likely month for the Thwaites (and nearby glaciers) to surge is September (as is what is what likely happened during the Northern Summer of 2012 when there was a lot of ice mass loss from the GIS, followed directly by a surge of ice mass loss from the gateway feeding the Thwaites Ice Tongue).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2139 on: December 05, 2019, 07:24:54 PM »
...
The consensus ECS is from 2.0 to 4.5 degrees K with most paleo evidence indicating a most likely ECS around 3 degrees K.  So with the adjustment, the one example given went from being outside of the consensus (at 1.9 K), to almost at the median value (3.2 K).

While the linked (open access) reference has many appropriate qualifying statements and disclaimers, it notes that the AR5 paleo estimates of ECS were linear approximations that change when non-linear issues are considered.  In particular they find for the specific ECS, S[CO2,LI], during the Pleistocence (ie the most recent 2 million years) that:

"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions."

Therefore, researchers such as James Hansen who relied on paleo findings that during recent full glacial periods ECS was about 3.0C, did not know that during interglacial periods this value would be 45% larger, or 4.35C.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.

http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf

Once again, AbruptSLR cherry picks and leaves out a key sentence.  Here is the full abstract of the paper.

Quote
Abstract. It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S, by using CO2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO2 radiative forcing depends on the CO2 data set used. This non-linearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of ice-sheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S[CO2,LI], for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO2 data uncertainties prevent a well-supported calculation for S[CO2,LI], but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S[CO2,LI], was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large.

Note the bolded phrase.  They are comparing a time without the large North American and Eurasian ice sheets (kinda like now) to the time when those ice sheets were melting (like 25,000 to 10,000 years ago).

The ECS (or slow feedbacks as James Hansen refers to them) relate to the changes in albedo from melting ice sheets.  When the large ice sheets that covered North America and Europe during the ice ages, there were much, much larger albedo changes than would occur if Antarctica or Greenland were to lose their ice sheets.

This paper would seem to support ECS in line with the consensus, not one artificially inflated by 45%.

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2140 on: December 05, 2019, 07:25:47 PM »
Some may not be familiar with the fact that in previous ice ages there use to be numerous marine ice sheets (of which the WAIS is the last remaining example) including in the Arctic Sea such as indicated by the accompany image of the Barents Sea Marine Ice Sheet with the associated Byornoy trough and renna.  I believe that the Byonrnoy trough system has several parallels with the Thwaites Glacier situation including: (a) the Byonrnoy trough has a large amount of sediment deposited at the base of the renna (flow stream or channel in Norwegian) in a similar manner to the sediment in and around the Thwaites grounding line; which allows the glacial ice to form a periodic seal with the sediment which periodical opens to allow burst of basal water to currently flow out for apparently periods of months; and (b) the upstream channel system branches quickly after this sediment filled area.  It should be noted that the Byrd Subglacial Basin connects directly to both the Siple Coast Ice Streams and the Weddell Sea Ice Streams, and this make the Thwaites system less stable than the Barents Sea Marine Ice Sheet was.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2141 on: December 05, 2019, 07:57:47 PM »
The linked reference indicates that well oxygenated lake waters are an important, but long overlooked, source of methane emissions into the atmosphere.  Hopefully, CMIP7 will consider these findings:

Marco Günthel et al, Contribution of oxic methane production to surface methane emission in lakes and its global importance, Nature Communications (2019). DOI: 10.1038/s41467-019-13320-0

https://www.nature.com/articles/s41467-019-13320-0

Abstract: "Recent discovery of oxic methane production in sea and lake waters, as well as wetlands, demands re-thinking of the global methane cycle and re-assessment of the contribution of oxic waters to atmospheric methane emission. Here we analysed system-wide sources and sinks of surface-water methane in a temperate lake. Using a mass balance analysis, we show that internal methane production in well-oxygenated surface water is an important source for surface-water methane during the stratified period. Combining our results and literature reports, oxic methane contribution to emission follows a predictive function of littoral sediment area and surface mixed layer volume. The contribution of oxic methane source(s) is predicted to increase with lake size, accounting for the majority (>50%) of surface methane emission for lakes with surface areas >1 km2."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2142 on: December 05, 2019, 08:59:29 PM »
They are comparing a time without the large North American and Eurasian ice sheets (kinda like
now) to the time when those ice sheets were melting (like 25,000 to 10,000 years ago).

Don't they include the Greenland Ice Sheet among the large Northern ice sheets? This ice sheet was largely present during the interglacials of the (late) Pleistocene, and not during the Pliocene.

Kohler et al 2015 say:
"Whether climate in the future is more comparable to the climate states of interglacials of the late Pleistocene or to the warm Pliocene is difficult to say, although this has, according to our results, major implications for the expected equilibrium temperature rise... The data available so far suggest that the appearance of northern hemispheric land ice sheets changed the climate system and accordingly influenced climate sensitivity. In the Pliocene, STCO2,LIU was therefore probably smaller than during the interglacials of the Pleistocene."

So, it seems to me that ASLR is right in pointing to the probability that ECS is larger now than during full glacial conditions or during Pliocene conditions.

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2143 on: December 05, 2019, 09:32:57 PM »
...
The ECS (or slow feedbacks as James Hansen refers to them) relate to the changes in albedo from melting ice sheets.  When the large ice sheets that covered North America and Europe during the ice ages, there were much, much larger albedo changes than would occur if Antarctica or Greenland were to lose their ice sheets.
...

When comparing glacial to interglacial climate sensitivity over the past 360,000 years, one also needs to consider the nonlinear impact of the equatorial Pacific SST for amplifying climate sensitivity:

Lo, L., Chang, S., Wei, K. et al. Nonlinear climatic sensitivity to greenhouse gases over past 4 glacial/interglacial cycles. Sci Rep 7, 4626 (2017) doi:10.1038/s41598-017-04031-x

https://www.nature.com/articles/s41598-017-04031-x

Abstract: "The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2–4 at atmospheric CO2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO2 levels reach threshold levels."

Caption for image: "Nonlinearity of SST sensitivity to climate in the southern WPWP. The Solomon ΔSST and greenhouse gas radiative forcing ΔRFGHG data are plotted at a 1-kyr interval. Two groups (blue and red circles) were divided at a pCO2 level of 220 ppm via cluster analysis (see Methods). Purple triangles are standard deviations of the mean for ΔSST data points at a segment of radiative forcing corresponding to 10 ppm pCO2. Solid and dashed lines for each group represent the regression line and 95% confidence interval, respectively. The determined slopes are given as lines. The gray vertical bar marks the significant difference threshold for the non-linear SST changes at a pCO2 level of 220 ± 10 ppm."
« Last Edit: December 05, 2019, 10:06:30 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Ken Feldman

  • Grease ice
  • Posts: 814
    • View Profile
  • Liked: 92
  • Likes Given: 102
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2144 on: December 05, 2019, 09:42:03 PM »
They are comparing a time without the large North American and Eurasian ice sheets (kinda like
now) to the time when those ice sheets were melting (like 25,000 to 10,000 years ago).

Don't they include the Greenland Ice Sheet among the large Northern ice sheets? This ice sheet was largely present during the interglacials of the (late) Pleistocene, and not during the Pliocene.

Kohler et al 2015 say:
"Whether climate in the future is more comparable to the climate states of interglacials of the late Pleistocene or to the warm Pliocene is difficult to say, although this has, according to our results, major implications for the expected equilibrium temperature rise... The data available so far suggest that the appearance of northern hemispheric land ice sheets changed the climate system and accordingly influenced climate sensitivity. In the Pliocene, STCO2,LIU was therefore probably smaller than during the interglacials of the Pleistocene."

So, it seems to me that ASLR is right in pointing to the probability that ECS is larger now than during full glacial conditions or during Pliocene conditions.

During the glacial periods of the ice ages, ice sheets were far more extensive than they are today.

https://www.livescience.com/40311-pleistocene-epoch.html

Quote
At the time of the Pleistocene, the continents had moved to their current positions. At one point during the Ice Age, sheets of ice covered all of Antarctica, large parts of Europe, North America, and South America, and small areas in Asia. In North America they stretched over Greenland and Canada and parts of the northern United States. The remains of glaciers of the Ice Age can still be seen in parts of the world, including Greenland and Antarctica.

Here's the wikipedia article on the last glacial maximum:

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

Quote
According to the United States Geological Survey (USGS), permanent summer ice covered about 8% of Earth's surface and 25% of the land area during the last glacial maximum.[8] The USGS also states that sea level was about 125 meters (410 feet) lower than in present times (2012).[8]

Quote
Currently (as of 2012), about 3.1% of Earth's surface and 10.7% of the land area is covered in year-round ice.[8]


Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2145 on: December 05, 2019, 10:29:08 PM »
During the glacial periods of the ice ages, ice sheets were far more extensive than they are today.

Yes, certainly, but during the Pliocene there was much less ice than now, and than during other recent interglacials.

Kohler et al 2015 say, as quoted by ASLR and yourself earlier:
"During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~45 % larger than during Pleistocene full glacial conditions."

Several recent interglacials had even a little less ice than the current interglacial (which by human interference has stopped being an interglacial, or turned into a super-interglacial of at least 50,000-100,000 years).

It looks to me you're not reading Kohler et al carefully enough.

kassy

  • Grease ice
  • Posts: 859
    • View Profile
  • Liked: 362
  • Likes Given: 377
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2146 on: December 05, 2019, 10:36:53 PM »
Quote
In our set-up, in which the radiative forcing of CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S[CO2,LI], for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO2 data uncertainties prevent a well-supported calculation for S[CO2,LI], but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S[CO2,LI], was smaller than during interglacials of the Pleistocene.
We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets.

Note the bolded phrase.  They are comparing a time without the large North American and Eurasian ice sheets (kinda like now) to the time when those ice sheets were melting (like 25,000 to 10,000 years ago).


Ken they are still melting.

The Pleistocene is the current ice age, one we are in geologically except we broke the next ice age or two because we are in the Dumbassic now. The Pleistocene had the big ice sheets and then they were gone, but it is all current geological age.
The pliocene ended with a 50m drop in sea level which must have been ice growth but geologically it was not a time like now, it was growing into the ice ages.
 
The argument is simply that the climate reacts more when the ice sheets are melting forced by CO2. It is sort of obvious when you know that ice sheets are a feedback.

Also nothing about this tells us what is going to happen with a warmer, swampier Siberia. Or with plains drying out when there are no more rivers because the snowcaps have gone. And many other changes which come slowly first then suddenly.

Basically know your unknowns and a thread like this helps filling up a part of that.

PS: Some quotes and a link to an open source science paper are not cherry picking. You can use other language like ´leave out this relevant bit´ or whatever paraphrase of that you prefer.
Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2147 on: December 05, 2019, 10:55:12 PM »
Quote from: Lennart van der Linde link=topic=2205.msg239688#msg239688
Several recent interglacials had even a little less ice than the current interglacial (which by human interference has stopped being an interglacial, or turned into a super-interglacial of at least 50,000-100,000 years).

I myself didn't remember Ganopolski et al 2016 carefully enough:
https://www.nature.com/articles/nature18452

They say:
"our analysis suggests that even in the absence of human perturbations no substantial build-up of ice sheets would occur within the next several thousand years and that the current interglacial would probably last for another 50,000 years. However, moderate anthropogenic cumulative CO2 emissions of 1,000 to 1,500 gigatonnes of carbon will postpone the next glacial inception by at least 100,000 years. Our simulations demonstrate that under natural conditions alone the Earth system would be expected to remain in the present delicately balanced interglacial climate state, steering clear of both large-scale glaciation of the Northern Hemisphere and its complete deglaciation, for an unusually long time."

So a natural super-interglacial has been turned by us into a super-super-interglacial, and maybe we're even tipping the planet into a Hothouse Earth state:
https://www.pnas.org/content/115/33/8252

AbruptSLR

  • Multi-year ice
  • Posts: 17693
    • View Profile
  • Liked: 892
  • Likes Given: 242
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2148 on: December 05, 2019, 11:00:02 PM »
The linked reference indicates that the rate of freshening of the AABW is accelerating rapidly, thus supporting Hansen's ice-climate feedback mechanism:

Viviane V. Menezes, Alison M. Macdonald and Courtney Schatzman (25 Jan 2017), "Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean", Science Advances, Vol. 3, no. 1, e1601426, DOI: 10.1126/sciadv.1601426

http://advances.sciencemag.org/content/3/1/e1601426

Extract: "Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean."

See also the associated article entitled: "Antarctic Bottom Waters Freshening at Unexpected Rate".

https://scripps.ucsd.edu/news/antarctic-bottom-waters-freshening-unexpected-rate

Extract: "Shift could disturb ocean circulation and hasten sea level rise, researchers say.

The team found that the previously detected warming trend has continued, though at a somewhat slower pace. The biggest surprise, however, was its lack of saltiness: AABW in the  region off East Antarctica’s Adélie Land has grown fresher four times faster in the past decade than it did between 1994 and 2007."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

  • Grease ice
  • Posts: 764
    • View Profile
  • Liked: 69
  • Likes Given: 5
Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2149 on: December 05, 2019, 11:23:11 PM »
So a natural super-interglacial has been turned by us into a super-super-interglacial, and maybe we're even tipping the planet into a Hothouse Earth state:
https://www.pnas.org/content/115/33/8252

Again, I should have formulated more precisely, as Steffen et al 2018 do in their Hothouse Earth paper, referring to Ganopolski et al 2016:
"the rapid trajectory of the climate system over the past half-century along with technological lock in and socioeconomic inertia in human systems commit the climate system to conditions beyond the envelope of past interglacial conditions. We, therefore, suggest that the Earth System may already have passed one “fork in the road” of potential pathways, a bifurcation (near A in Fig. 1) taking the Earth System out of the next glaciation cycle (11)."

Maybe we've already passed this fork in the road, or maybe not. In risky territory we certainly seem to be.