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Messages - AbruptSLR

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1
It looks like JP Morgan agrees with the primary theme of this thread:

Title: "World's Biggest Fossil Fuel Funder Notes Climate Change Could End 'Human Life as We Know it'"

https://earther.gizmodo.com/worlds-biggest-fossil-fuel-funder-notes-climate-change-1841835204

Extract: "The finance industry is issuing some of the direst warnings about climate change while funding the industry most responsible for it. Today’s example: JP Morgan.

The bank is the single biggest funder of fossil fuels in the world. But its economists wrote an internal report leaked to Extinction Rebellion on Friday stating that they “cannot rule out catastrophic outcomes where human life as we know it is threatened.”

The analysis is most worried about the tail risks of climate change. In plain language, that’s the less likely but utterly catastrophic outcomes of the climate crisis that keeps economists and scientists up at night.

We’re talking things like the sudden collapse of the West Antarctic Ice Sheet, sending sea levels more than 10 feet higher and displacing millions of people. Or a feedback loop where melting permafrost releases more carbon dioxide that causes more warming that causing more thawing and carbon emissions. These things are already happening but at a rate, we can somewhat handle. What’s worrisome is that we could cross a tipping point where they happen suddenly and humanity is left having to deal with a new, unsteady state.

“Although precise predictions are not possible, it is clear that the earth is on an unsustainable trajectory,” the JP Morgan analysts wrote. “Something will have to change at some point if the human race is going to survive.”

In a logical world, this would be enough to convince world leaders to act. The report calls for a global price on carbon as the single, most effective climate policy the world could pursue. Instead, governments are basically engaged in a game of chicken with the climate as they approve more fossil fuel development that will almost surely screw future generations."

2
The linked Nature magazine editorial re-emphasizes a major theme of this thread that:

“If carbon emissions are not drastically reduced by 2030, we will be entering uncharted territory, including the possibility (…) of passing irreversible tipping points such as the widespread loss of Antarctic ice.”

Title: "Nature Magazine Editorial: Research decade must focus on climate"

https://www.pik-potsdam.de/news/in-short/nature-magazine-editorial-research-decade-must-focus-on-climate

“The pace of warming means that the window for avoiding temperature rises of 1.5 or 2°C is now frighteningly small. The 2020s will be a make-or-break,” Nature maintains in unequivocal terms. “If carbon emissions are not drastically reduced by 2030, we will be entering uncharted territory, including the possibility (…) of passing irreversible tipping points such as the widespread loss of Antarctic ice.”

See also:

Title: "The scientific events that shaped the decade"

https://www.nature.com/articles/d41586-019-03857-x

Extract: "The 2010s have seen breakthroughs in frontiers from gene editing to gravitational waves. The coming one must focus on climate change."

3
If anyone will be attending the EGU General Assembly 2020 in Vienna, Austria May 3-8, 2020; it would be nice to hear back about presentations made at any of the CR5 – Ice Sheets, ice shelves and glaciers sessions, such as:

CR5 – lce sheets, ice shelves and glaciers

CR5.2
Modelling ice sheets and glaciers

This session is intended to attract a broad range of ice-sheet and glacier modelling contributions, welcoming applied and theoretical contributions. Theoretical topics that are encouraged are higher-order mechanical models, data inversion and assimilation, representation of other earth sub-systems in ice-sheet models, and the incorporation of basal processes and novel constitutive relationships in these models.

Applications of newer modelling themes to ice-sheets and glaciers past and present are particularly encouraged, in particular those considering ice streams, rapid change, grounding line motion and ice-sheet model intercomparisons.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34957

Convener: Fabien Gillet-Chaulet Co-conveners: Stephen Cornford, Gael Durand, Sainan Sun

CR5.4
Ice-sheet and climate interactions

Ice sheets play an active role in the climate system by amplifying, pacing, and potentially driving global climate change over a wide range of time scales. The impact of interactions between ice sheets and climate include changes in atmospheric and ocean temperatures and circulation, global biogeochemical cycles, the global hydrological cycle, vegetation, sea level, and land-surface albedo, which in turn cause additional feedbacks in the climate system. This session will present data and modelling results that examine ice sheet interactions with other components of the climate system over several time scales. Among other topics, issues to be addressed in this session include ice sheet-climate interactions from glacial-interglacial to millennial and centennial time scales, the role of ice sheets in Cenozoic global cooling and the mid-Pleistocene transition, reconstructions of past ice sheets and sea level, the current and future evolution of the ice sheets, and the role of ice sheets in abrupt climate change.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34963

Co-organized by CL4
Convener: Heiko Goelzer Co-conveners: Alexander Robinson, Ricarda Winkelmann, Philippe Huybrechts, Stefanie Mack

CR5.7
Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling

Ice shelves and tidewater glaciers are sensitive elements of the climate system. Sandwiched between atmosphere and ocean, they are vulnerable to changes in either. The recent disintegration of ice shelves such as Larsen B and Wilkins on the Antarctic Peninsula, current thinning of the ice shelves in the Amundsen Sea sector of West Antarctica, and the recent accelerations of many of Greenland's tidewater glaciers provide evidence of the rapidity with which those systems can respond. Changes in marine-terminating outlets appear to be intimately linked with acceleration and thinning of the ice sheets inland of the grounding line, with immediate consequences for global sea level. Studies of the dynamics and structure of the ice sheets' marine termini and their interactions with atmosphere and ocean are the key to improving our understanding of their response to climate forcing and of their buttressing role for ice streams. The main themes of this session are the dynamics of ice shelves and tidewater glaciers and their interaction with the ocean, atmosphere and the inland ice, including grounding line dynamics. The session includes studies on related processes such as calving, ice fracture, rifting and mass balance, as well as theoretical descriptions of mechanical and thermodynamic processes. We seek contributions both from numerical modelling of ice shelves and tidewater glaciers, including their oceanic and atmospheric environments, and from observational studies of those systems, including glaciological and oceanographic field measurements, as well as remote sensing and laboratory studies.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/36133

Co-organized by OS1
Convener: Adrian Jenkins Co-conveners: Rachel Carr, Angelika Humbert, Nicolas Jourdain, Inga Monika Koszalka

CR5.8
Hydrology of ice shelves, ice sheets and glaciers - from the surface to the base

Dynamic subglacial and supraglacial water networks play a key role in the flow and stability of ice sheets. The accumulation of meltwater on the surface of ice shelves has been hypothesized as a potential mechanism controlling ice-shelf stability, with ice-shelf collapse triggering substantial increases in discharge of grounded ice. Observations and modelling also suggest that complex hydrological networks occur at the base of glaciers and these systems play a prominent role in controlling the flow of grounded ice. This session tackles the urgent need to better understand the fundamental processes involved in glacial hydrology that need to be addressed in order to accurately predict future ice-sheet evolution and mass loss, and ultimately the contribution to sea-level rise .
We seek contributions from both the modelling and observational communities relating to any area of ice-sheet hydrology. This includes but is not limited to: surface hydrology, melt lake and river formation; meltwater processes within the ice and firn; basal hydrology; subglacial lakes; impacts of meltwater on ice-sheet stability and flow; incorporation of any of these processes into large-scale climate and ice-sheet models.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34964

Co-organized by HS2.1
Convener: Sammie Buzzard Co-conveners: Ian Hewitt, Amber Leeson, Martin Wearing

CR5.9
Subglacial Environments of Ice Sheets and Glaciers

Subglacial environments are among the least accessible regions on Earth and represent one of the last physical frontiers of glaciological research, while emerging as a unique ecological habitat. The subglacial environment is a key component in the dynamic behaviour of ice sheets and glaciers, involving complex and precise mass and energy transfers between the ice and its substrate of water, air, bedrock, or sediment, and the oceans at ice sheet boundaries. In particular, determining the distribution and nature of water flows at the ice-mass bed is highlighted as a priority for understanding and predicting ice dynamics. For example, both remote sensing and ground-based observations across Antarctica and Greenland highlight the existence of subglacial water in a variety of forms, ranging from vast subglacial lakes (providing distinctive habitats for potentially unique life forms) to mm-thick water flows at the ice-substrate interface. Feedbacks between increased surface melting, glacier bed conditions and ice flow also affect alpine glaciers, potentially contributing to increased glacial retreat in low and mid-latitude mountain regions.

It is clear that subglacial processes impact ice dynamics, transcending ice-mass scales from valley glaciers to large ice sheets and, through feedback loops, contribute to changes in sea level, ocean circulation, and climate evolution. Quantitative characterisation of the basal environment therefore remains an outstanding glaciological problem, as does scaling of this knowledge for use in modelling ice sheet and glacier behaviour.

We invite scientific contributions that include, but are not limited to, measurements and/or modelling of: (i) flow of subglacial water at the bed and through subglacial sediments; (ii) linkages between subglacial hydrology and ice dynamics; (iii) theoretical-, field-, or laboratory-based parameterisation of subglacial processes in numerical ice-flow models; (v) formation, geometry and potential hydrological linkages between subglacial lakes; (v) subglacial and supraglacial lake drainage and subglacial floods from ice margins; and (vi) geomorphological evidence of subglacial water flows from contemporary ice-sheet margins and across formerly glaciated continental-scale regions.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34965

Convener: Adam Booth Co-conveners: Robert Bingham, Christine Dow, Bryn Hubbard, Harold Lovell


See also:

CR – Cryospheric Sciences

https://meetingorganizer.copernicus.org/EGU2020/sessionprogramme/CR?cosession=5e4ffc4ae69d84-89874115-m#s34964

   CR1 – The State of the Cryosphere: Past, Present, Future
   CR2 – Instrumental and paleo-archive observations and analysis of the cryosphere
   CR3 – Snow and ice: properties, processes, hazards
   CR4 – Frozen ground, debris-covered glaciers and geomorphology
   CR5 – lce sheets, ice shelves and glaciers
   CR6 – Sea Ice
   CR7 – The cryosphere in the Earth system: interdisciplinary topics
   CR8 – Short courses

4
While many people like to count on technological advances to fight climate change, the linked article cites just one example of how advances in fracking technology for both oil and gas is only getting started; which will likely make it difficult for policy makers from supporting a natural gas energy bridge to the future, even though natural gas has the same (or worse) carbon footprint as coal:

Title: "Water reuse could be key for future of hydraulic fracturing"

https://phys.org/news/2020-02-reuse-key-future-hydraulic-fracturing.html

Extract: "Enough water will come from the ground as a byproduct of oil production from unconventional reservoirs during the coming decades to theoretically counter the need to use fresh water for hydraulic fracturing operations in many of the nation's large oil-producing areas. But while other industries, such as agriculture, might want to recycle some of that water for their own needs, water quality issues and the potential costs involved mean it could be best to keep the water in the oil patch."

5
The linked report indicates that by 2035 we may cross a '... tipping point, after which no practicable amount of effort can reduce the risk of a slide to a plus-2 degree C world ..'.

Title: "Global risks 2035 update: Decline or new renaissance?" Oct. 30, 2019, by Mathew Burrow

https://www.atlanticcouncil.org/in-depth-research-reports/report/global-risks-2035-update/

Extract: "Experts have been warning about the impacts of climate change for years—if not decades. The temptation—especially when the impacts are less widespread—is to take small steps toward managing the risks. Research is now showing that the world is on the verge of a tipping point, after which no practicable amount of effort can reduce the risk of a slide to a plus-2-degree C world in which life would become unbearable for a great many."

6
The image from the linked reference confirms that if one is worried about crossing potential tipping points in the next few decades (as I am) that it would be a good idea to immediately start reducing methane (and other GHG) emissions:

Title: "Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contracting impacts of short- and long-lived climate pollutants" by Lynch et al. (2020).

https://iopscience.iop.org/article/10.1088/1748-9326/ab6d7e/pdf


7
With a hat-tip to baking the first attached image shows the ice mélange near the seaward outlet of the PIIS southern shear margin with the Southern Ice Shelf (circa February 20, 2020).  If/when the icebergs are released to the open ocean, the Southern Ice Shelf will be subject to calving; which might likely serve to reduce the stability of the ice shelf of the Southwest Tributary Glacier:

Caption for the first image: "Chaos where the southern shear margin of Pine Island Glacier meets the sea, seen in pre-dawn light this morning. Immense forces are at work here, shattering, rotating, tilting and thrusting large blocks of ice."

Edit: The second image shows a Sentinel 1 view of the PIIS Southern Shear Margin filled with icebergs that calved off of the PIIS South Ice Shelf and which could float-out into the ocean within the next year; which would leave an exposed calving face for the PIIS South Ice Shelf.

8
While the authors of the linked reference are all well regarded ice modeling scientists; to me this reference illustrates how painfully slow the consensus building process is for risk assessment associated with ice sheet modeling driven by projected future climate change scenarios.  While I concur with the reference that ice shelf response to climate change is one of the key mechanisms determining future ice mass loss from Antarctica, I believe that the cited model projections all significantly underestimated the ice shelf responses that we have seen this year in the Amundsen Sea Embayment, ASE; and the MISI models used explicitly do not consider MICI-type mechanisms.

Therefore, in my opinion, the most significant finding of the cited study is that:

"We thus have to conclude that uncertainty with respect to the ice dynamic contribution of Antarctica due to future warming is still increasing and thus that coastal planning has to take into account that multi-decadal sea level projections are likely to change with an increasing understanding of the ice dynamics and their representation in ice sheet models."

Thus the big issue is will consensus climate science officially recognize the significant risk of abrupt ice mass loss from Antarctica this century before, or after, key Antarctic marine glaciers have already crossed they thresholds for 'irreversible' continuing ice mass loss this century:

Levermann, A., Winkelmann, R., Albrecht, T., Goelzer, H., Golledge, N. R., Greve, R., Huybrechts, P., Jordan, J., Leguy, G., Martin, D., Morlighem, M., Pattyn, F., Pollard, D., Quiquet, A., Rodehacke, C., Seroussi, H., Sutter, J., Zhang, T., Van Breedam, J., Calov, R., DeConto, R., Dumas, C., Garbe, J., Gudmundsson, G. H., Hoffman, M. J., Humbert, A., Kleiner, T., Lipscomb, W. H., Meinshausen, M., Ng, E., Nowicki, S. M. J., Perego, M., Price, S. F., Saito, F., Schlegel, N.-J., Sun, S., and van de Wal, R. S. W.: Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2), Earth Syst. Dynam., 11, 35–76, https://doi.org/10.5194/esd-11-35-2020, 2020.

https://www.earth-syst-dynam.net/11/35/2020/

Abstract
The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.

Extract: "In summary, for each emission scenario the procedure works as follows (each of the items is described in more detail below and in Levermann et al., 2014).
1.   Randomly select a global mean temperature realization of the respective RCP scenario from the 600 MAGICC 6.0 realizations constrained by the observed temperature record. The time series start in 1850 and end in 2100.
2.   Randomly select one of 19 CMIP5 models in order to obtain a scaling factor and a time delay for the relation between global mean surface air temperature and subsurface ocean warming in the respective regional sector in the Southern Ocean.
3.   Randomly select a melting sensitivity in order to scale the regional subsurface warming outside the cavity of the Antarctic ice shelves onto basal ice shelf melting.
4.   Select an ice sheet model that is forced via its linear response function with the time series of the forcing obtained from steps 1–3.
5.   Compute the sea level contribution of this specific Antarctic ice sheet sector according to linear response theory.
6.   Repeat steps 1–5 20 000 times with different random selections in each of the steps in order to obtain a probability distribution of the sea level contribution of each Antarctic sector and each carbon emission scenario.

Thus, the 20 000 selections are obtained by randomly choosing one temperature time series, one CMIP5 ocean model, one melt sensitivity, and one ice sheet model. The procedure is also used for each of the ice sheet models separately. In this case the random selection in step 4 is replaced by a fixed selection of the model. The procedure is illustrated in Fig. 1. For the computation of the total sea level contribution from all Antarctic sectors together, the forcing is selected consistently for all sectors. That means that for each of the 20 000 computations of the sea level contribution one global mean temperature realization is selected, as is one ocean model for the subsurface temperature scaling and one basal melt sensitivity. Although there are other possibilities, this approach was chosen because it preserves the forcing structure as provided by the ocean models. Details of steps 1–5 are given in the upcoming subsections.

However, due to the very large potential sea level contribution of Antarctica and its high sea level commitment compared to the other contributions (Levermann et al., 2013), the rate of change increases strongly over the century. Under the RCP8.5 scenario the median rate of sea level contribution by the end of the 21st century from basal-melt-induced ice loss from Antarctica alone is with 4.1 mm yr−1 larger than the mean rate of sea level rise observed at the beginning of this century (Dangendorf et al., 2019; Hay et al., 2015; Oppenheimer et al., 2019).
Although the method described here has a large number of caveats it provides an estimate of the role of the uncertainty in the oceanic forcing for the uncertainty in Antarctica's future contribution to sea level rise. By comparison with the earlier study using the same method but only three ice sheet models of an earlier model generation, we find a shift of the sea level contribution to higher values and an increase in the ranges of uncertainty. We thus have to conclude that uncertainty with respect to the ice dynamic contribution of Antarctica due to future warming is still increasing and thus that coastal planning has to take into account that multi-decadal sea level projections are likely to change with an increasing understanding of the ice dynamics and their representation in ice sheet models. This study provides an estimate of the uncertainty in the future contribution of Antarctica to global sea level rise only based on known ice dynamics but including the full range of forcing uncertainty. It substantiates the result of the previous study that Antarctica can become the largest contributor to global sea level rise in the future, in particular if carbon emissions are not abated."

Caption: "Figure 11 Projections from all models of the future sea level contribution of the different Antarctic sectors following the procedure depicted in Fig. 1 and detailed in Sect. 2. The white line represents the median value, the dark shading the likely range (66th percentile around the median), and the light shading the very likely range (90th percentile around the median)."

9
...
Citing forecasts, Shell said that LNG demand was expected to double by 2040 to 700 million tons, with natural gas set to play “a growing role in shaping a lower-carbon energy system.”"

Several of my recent posts have indicated that anthropogenic methane emissions have been, and are likely to remain, higher than previously assumed.  When such relatively high anthropogenic methane emissions are combined together with possible/probable increases in natural methane emissions (say from: permafrost degradation, thermokarst lakes and/or methane hydrates) the future atmospheric concentration of methane may become high enough to increase the GWP of such atmospheric methane.  In this regard, the two images come from Isaksen et al. (2011) who used computer models to estimate methane's atmospheric burden.  Isaksen et al (2011) found (see the first image) that as the assumed emission rate increased the chemistry of the atmosphere would change, resulting in increased lifetime for methane, thus increasing the associated radiative forcing (see the second image).

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/abstract

10
The linked article/video provides some nice color commentary about this season's ITGC field mission:

Title: "A risky expedition to study the ‘doomsday glacier’"

https://www.pbs.org/newshour/show/visiting-the-most-vulnerable-place-on-earth-the-doomsday-glacier


11
With LNG suitable for replacing diesel fuel for both long-haul trucks and ships, and with CNC cars being increasingly used around the world, and with shale gas cheap and available; there is little wonder that Shell forecasts a doubling of global LNG demand by 2040.  However, due to gas leaks LNG has a heavier carbon footprint than coal so we can all expect the global atmospheric methane concentration to continue rising for some time to come:

Title: "Demand for liquefied natural gas set to double by 2040, according to Shell"

https://www.cnbc.com/2020/02/20/demand-for-liquefied-natural-gas-set-to-double-by-2040-shell.html

Extract: "Worldwide demand for liquefied natural gas, or LNG, rose by 12.5% to hit 359 million tons last year, according to Royal Dutch Shell’s annual LNG Outlook report.

Citing forecasts, Shell said that LNG demand was expected to double by 2040 to 700 million tons, with natural gas set to play “a growing role in shaping a lower-carbon energy system.”"

12
The linked article points out that the surface greening of the Arctic is only the tip of the associate positive albedo feedback 'iceberg', as the associated root development in permafrost regions could significantly accelerate permafrost degradation and associated GHG emissions:

Title: "The Arctic Is Getting Greener. That's Bad News for All of Us"

https://www.wired.com/story/arctic-greening/

Extract: "Right now the Arctic is warming twice as fast as the rest of the planet, and transforming in massively consequential ways. Rapidly melting permafrost is gouging holes in the landscape. Thousands of years’ worth of wet accumulated plant matter known as peat is drying out and burning in unprecedented wildfires. Lightning—a phenomenon more suited to places like Florida—is now striking within 100 miles of the North Pole.

All the while, researchers are racing to quantify how the plant species of the Arctic are coping with a much, much warmer world. In a word, well. And probably: too well. Using satellite data, drones, and on-the-ground fieldwork, a team of dozens of scientists—ecologists, biologists, geographers, climate scientists, and more—is finding that vegetation like shrubs, grasses, and sedges are growing more abundant. The phenomenon is known as “Arctic greening,” and with it comes a galaxy of strange and surprising knock-on effects with implications both for the Arctic landscape and the world’s climate at large.

A permafrost melt also releases more water into the soil, leading to yet more knock-on effects for the vegetation. “When the ground is frozen, plants don't have any access to water,” says Kerby. “So it's almost like being in a desert for part of the year.”

Frozen ground limits when the plants can grow. But an earlier thaw could mean that plants kickstart their growth earlier in the year. As those soils thaw deeper and deeper, they will also release gobs of nutrients that have been trapped underground for perhaps thousands of years, supercharging the growth of these increasingly abundant Arctic plant species. This means the landscape could get even greener and even more hospitable to plants that can take advantage of warmer temperatures.

And really, underground is where so much of the Arctic mystery still lies: In these tundra ecosystems, up to 80 percent of the biomass is below ground. (Remember that in the deep chill of winter, roots survive underground.) “So when you see the green surface, that's just the tip of the iceberg, in terms of the biomass in these systems,” says Myers-Smith. “So it could be that a lot of the climate change responses of these plants are actually all in the below-ground world that we have a very difficult time tracking and monitoring.”"

13
Consequences / Re: Chinese coronavirus
« on: February 19, 2020, 07:07:07 PM »
While the linked article indicates that the coronavirus has temporarily reduced China's CO2 emission by a quarter, the article does not point out that the associated anthropogenic aerosol emission are down by even a larger percentage of Chinese emissions; which might be related to the fact that global mean surface temperature anomalies, GMSTA, have been running unusually high in January and February of 2020, during a non-El Nino season.  If so, and if a coronavirus pandemic were to occur then we could see GMSTA temporarily spike in 2020 due to an associated abrupt reduction in global anthropogenic aerosol emissions:

Title: "Analysis: Coronavirus has temporarily reduced China’s CO2 emissions by a quarter"

https://www.carbonbrief.org/analysis-coronavirus-has-temporarily-reduced-chinas-co2-emissions-by-a-quarter

Extract: "All told, the measures to contain coronavirus have resulted in reductions of 15% to 40% in output across key industrial sectors. This is likely to have wiped out a quarter or more of the country’s CO2 emissions over the past two weeks, the period when activity would normally have resumed after the Chinese new-year holiday."


14
The linked reference indicates that anthropogenic fossil fuel related methane emissions are underestimated by "25 to 40 per cent of recent estimates".  To me this highlights the risk that fuel methane emissions from fracking operation may also be severely underestimated:

Hmiel, B., Petrenko, V.V., Dyonisius, M.N. et al. Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions. Nature 578, 409–412 (2020). https://doi.org/10.1038/s41586-020-1991-8

https://www.nature.com/articles/s41586-020-1991-8

Abstract
Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year) between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)—an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions.

See also:

Title: "Methane emissions from fossil fuels ‘severely underestimated’"

https://www.carbonbrief.org/methane-emissions-from-fossil-fuels-severely-underestimated

Extract: "Human-caused emissions of methane from the extraction and use of fossil fuels may have been “severely underestimated”, a new study suggests.

The research indicates that “natural” emissions of fossil methane, that seeps out of deeply-held reserves, make up a much smaller fraction of total methane emissions than previously thought.
This means that the levels of fossil methane in the atmosphere are likely being driven by the methane escaping as coal, oil and natural gas are mined, drilled and transported.

The implication is that methane emissions from fossil fuels are 25-40% higher than earlier estimates suggest, the lead researcher tells Carbon Brief."

15
The linked commentary discusses the findings that the business leads rank the urgency of climate change risks significantly lower than do consensus scientists and this goes on to discuss ways of addressing this gap in climate change risk assessment.  Unfortunately, the commentary makes statements like:

"It is essential, however, that multiplicity does not simply lead to a cacophony of diverging risk perceptions which could impede action.  Rather, a range of perspectives must be collected to better understand challenges and to drive strategies to converge around solutions."

When I read statements like this from consensus climate scientists, I hear a call to limit the range of risks considered by cutting off the right-tail risks, particularly those related to abrupt sea level rise and to ice-climate feedback mechanisms.  In this regard, I provide a second link to a Dutch reference on how they address adapting to uncertain rates of SLR due to the risk of Antarctic ice mass loss.

Matthias Garschagen et al. (12 February 2020), "Too big to ignore: Global risk perception gaps between scientists and business‐leaders", Earth's Future, https://doi.org/10.1029/2020EF001498

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020EF001498?af=R
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020EF001498

Abstract: "Two major reports assessing global systemic risks have been published recently, presenting large‐scale panel data on the risk perceptions of different key communities, most notably business leaders and global change scientists. While both of these global communities agree on ranking environmental risks the highest, followed by societal, geopolitical, technological and economic risks, business leaders perceive the urgency of these risks (i.e. their likelihood and potential impact) as significantly lower than scientists. This gap implies vexing questions in relation to building a shared sense of urgency and facilitating collective action. These questions need to be addressed through new ways of co‐creating risk assessments and strategic futures analysis."

See also:

M Haasnoot et al (2020), "Adaptation to uncertain sea-level rise; how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands", Environmental Research Letters, Volume 15, Number 3, https://doi.org/10.1088/1748-9326/ab666c

https://iopscience.iop.org/article/10.1088/1748-9326/ab666c
https://iopscience.iop.org/article/10.1088/1748-9326/ab666c/pdf

Abstract: "Uncertainties in the rate and magnitude of sea-level rise (SLR) complicate decision making on coastal adaptation. Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase SLR in the second half of this century. The implications of SLR may be existential for a low-lying country like the Netherlands and warrant exploration of high-impact low-likelihood scenarios. To deal with uncertain SLR, the Netherlands has adopted an adaptive pathways plan. This paper analyzes the implications of storylines leading to extreme SLR for the current adaptive plan in the Netherlands, focusing on flood risk, fresh water resources, and coastline management. It further discusses implications for coastal adaptation in low-lying coastal zones considering timescales of adaptation including the decisions lifetime and lead-in time for preparation and implementation. We find that as sea levels rise faster and higher, sand nourishment volumes to maintain the Dutch coast may need to be up to 20 times larger than to date in 2100, storm surge barriers will need to close at increasing frequency until closed permanently, and intensified saltwater intrusion will reduce freshwater availability while the demand is rising. The expected lifetime of investments will reduce drastically. Consequently, step-wise adaptation needs to occur at an increasing frequency or with larger increments while there is still large SLR uncertainty with the risk of under- or overinvesting. Anticipating deeply uncertain, high SLR scenarios helps to enable timely adaptation and to appreciate the value of emission reduction and monitoring of the Antarctica contribution to SLR."

Extract: "The Netherlands has adopted an adaptive plan that allows for adaptation over time depending on how the future unfolds. Recent SLR observations and projections have raised concerns about the plausibility of an uncertain strong acceleration of SLR after 2050 due to rapid mass-loss of the Antarctic ice sheet, which is not accounted for in the current adaptive plan."

16
The linked open access reference evaluates limits (including ice mélange buttressing) on the rate of calving for marine glaciers with bear ice cliffs (sometimes called MICI).  To me the proposed model is more suitable for application for Greenland's marine terminating glaciers rather than to ASE marine glacier; nevertheless, the high end of calving rates are alarmingly fast:

Schlemm, T. and Levermann, A.: A simple model of mélange buttressing for calving glaciers, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-50, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-50/
https://www.the-cryosphere-discuss.net/tc-2020-50/tc-2020-50.pdf

Abstract. Both ice sheets on Greenland and Antarctica are discharging ice into the ocean. In many regions along the coast of the ice sheets, the icebergs calf into a bay. If the addition of icebergs through calving is faster than their transport out of the embayment, the icebergs will be frozen into a mélange with surrounding sea ice in winter. In this case, the buttressing effect of the ice mélange can be considerably stronger than any buttressing by mere sea ice would be. This in turn stabilizes the glacier terminus and leads to a reduction in calving rates. Here we propose a simple but robust buttressing model of ice mélange which can be used in numerical and analytical modeling.

17
Antarctica / Re: Antarctic Ice Sheet
« on: February 19, 2020, 04:25:51 PM »
...
GIA Correction
Glacial Isostatic Adjustment (GIA) denotes the surface deformation of the solid Earth (lithosphere and mantle) caused by ice-mass redistribution over the last 100,000 years, dominated by the termination of the last glacial cycle. Due to the Earth's viscoelastic response to mass redistribution between the ice sheets and the ocean, the Earth's gravity field is affected by long term secular trends mainly in previously glaciated regions such as North America, Fennoscandia and Antarctica. Moreover, also coefficients of low degrees and orders are affected.

The Level-2B/Level-3 products provided here are corrected using a GIA model based on ICE-5G ice load history (Peltier, 2004) as applied to the 3D-Viscoelastic Lithosphere and Mantle Model VILMA (Martinec, 2000; Klemann et al., 2008).[/size]


[/quote]

I believe that the GIA correction for GRACE-FO uses the same isostatic model used by GRACE not because it is an accurate model but rather because of a shortage of field data (see the first linked reference); however, the second linked reference indicates that corrections from this model is likely 40% too low for the ASE area:

Li, F., Ma, C., Zhang, S. et al. Evaluation of the glacial isostatic adjustment (GIA) models for Antarctica based on GPS vertical velocities. Sci. China Earth Sci. (2020). https://doi.org/10.1007/s11430-018-9532-5

https://link.springer.com/article/10.1007/s11430-018-9532-5

Abstract: "Due to the scarcity of data, modeling the glacial isostatic adjustment (GIA) for Antarctica is more difficult than it is for the ancient ice sheet area in North America and Northern Europe. Large uncertainties are observed in existing GIA models for Antarctica. Modern space-based geodetic measurements provide checks and constraints for GIA models. The present-day uplift velocities of global positioning system (GPS) stations at 73 stations in Antarctica and adjacent regions from 1996 to 2014 have been estimated using GAMIT/GLOBK version 10.5 with a colored noise model. To easily analyze the effect of difference sources on the vertical velocities, and for easy comparison with both GIA model predictions and GPS results from Argus et al. (2014) and Thomas et al. (2011), seven sub-regions are divided. They are the northern Antarctic Peninsula, the Filchner-Ronne Ice Shelf, the Amundsen Sea coast, the Ross Ice Shelf, Mount Erebus, inland Southwest Antarctica and the East Antarctic coast, respectively. The results show that the fast uplift in the north Antarctic Peninsula and Pine Island Bay regions may be caused by the elastic response to snow and ice mass loss. The fast subsidence near Mount Erebus may be related to the activity of a magma body. The uplift or subsidence near the East Antarctic coast is very slow while the uplift for the rest regions is mainly caused by GIA. By analyzing the correlation and the associated weighted root mean square (WRMS) between the GIA predictions and the GPS velocities, we found that the ICE-6G_C (VM5a) model and the Geruo13 model show the most consistency with our GPS results, while the W12a and IJ05_R2 series models show poor consistency with our GPS results. Although improved greatly in recent years, the GIA modeling in Antarctica still lags behind the modeling of the North American. Some GPS stations, for example the Bennett Nunatak station (BENN), have observed large discrepancies between GIA predictions and GPS velocities. Because of the large uncertainties in calculating elastic responses due to the significant variations of ice and snow loads, the GPS velocities still cannot be used as a precise constraint on GIA models."

Therefore, I am re-posting the following from Reply #71 of the "Surge" thread, reminding all that the GRACE satellite SLR contributions previously reported by NASA are probably 40% too low for at least the ASE area and probably for all of the WAIS due to treating the GIA correction for the WAIS like any other part of the earth when, as I have indicated in my prior posts in this thread, West Antarctica has a relatively unique tectonic history and current condition:

A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich (2012), "An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica", Global and Planetary Change, Vol 98-99, pp 45-53, http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

https://www.sciencedirect.com/science/article/pii/S0921818112001567?via%3Dihub

"Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%."

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

The second figures shows the GRACE data from 2003 to 2009 which the papers says needs to be corrected to indicate about 40% more ice mass loss than previously reported

18
...
The linked reference provides paleo-evidence that supports many aspects of the ice apocalypse scenario that I have previously discussed in this thread; however, it does indicate that there is still uncertainty about the time-scale at which such a scenario might unfold.  Also, to me, this evidence supports many aspects of the scenario cited in DeConto and Pollard (2016):

Chris S. M. Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran, Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, and Alan Cooper (February 11, 2020), "Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica", PNAS, https://doi.org/10.1073/pnas.1902469117

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1


 Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.

In the linked article, study co-author Zoe Thomas makes it clear that the quoted study indicates that once a certain threshold is past, ice mass loss from Antarctica will become effectively 'irreversible' for hundreds, or thousands, of years:

Title: " Global Warming Creating 'Irreversible' Ice Melt in Antarctica: Scientist"

https://www.insurancejournal.com/news/international/2020/02/19/558780.htm

19

The loss of ice shelves — Mercer proposed — would allow the ice sheet to thin, grounding lines to retreat and the ice sheet to disintegrate via calving. This is a much faster means of losing mass than melting in place. Mercer further commented that the loss of ice shelves on the Antarctic Peninsula, as has since been observed, would be an indicator that this process of ice sheet loss due to global warming was underway.

...

Mercer proposed that the loss of ice shelves on the Antarctic Peninsula would precede the loss of ice shelves in front of critical ice sheets like the WAIS, and the linked article presents a evidence that the George VI ice shelf and others on the Antarctic Peninsula are at risk from melt-pond failure mechanisms.  I would not be surprised to read about at least one ice shelf collapse on the Antarctic Peninsula in the 2020-2021 melt season (but likely not the George VI ice shelf itself; which is sandwiched between the Antarctic Peninsula and Alexander Island):

Title: "Widespread Melt on the George VI Ice Shelf"

https://earthobservatory.nasa.gov/images/146189/widespread-melt-on-the-george-vi-ice-shelf

Extract: "Alison Banwell, a glaciologist at the University of Colorado Boulder who currently has a three-year fieldwork project on the shelf, noticed the melt in images acquired that same day with the European Space Agency’s Sentinel-2 satellite. “This is the biggest melt event we know to have occurred on the George VI ice shelf,” she said.

“What’s worrying is if George VI looks like this, other ice shelves on the peninsula probably have plenty of meltwater too,” Banwell said. “And those ice shelves are less stable.” At the time, clouds prevented satellites from getting a good look at the other ice shelves."

20
Antarctica / Re: Antarctic Ice Sheet
« on: February 18, 2020, 11:01:34 PM »
In addition to processing error, correct interpretation of GRACE, & GRACE-FO, data must also consider issue such as atmospheric river events, local ice discharge events (such as from the Thwaites Ice Tongue), and isostatic round (see the linked references):


Whitehouse, P.L., Gomez, N., King, M.A. et al. Solid Earth change and the evolution of the Antarctic Ice Sheet. Nat Commun 10, 503 (2019). https://doi.org/10.1038/s41467-018-08068-y

https://www.nature.com/articles/s41467-018-08068-y

Abstract: "Recent studies suggest that Antarctica has the potential to contribute up to ~15 m of sea-level rise over the next few centuries. The evolution of the Antarctic Ice Sheet is driven by a combination of climate forcing and non-climatic feedbacks. In this review we focus on feedbacks between the Antarctic Ice Sheet and the solid Earth, and the role of these feedbacks in shaping the response of the ice sheet to past and future climate changes. The growth and decay of the Antarctic Ice Sheet reshapes the solid Earth via isostasy and erosion. In turn, the shape of the bed exerts a fundamental control on ice dynamics as well as the position of the grounding line—the location where ice starts to float. A complicating issue is the fact that Antarctica is situated on a region of the Earth that displays large spatial variations in rheological properties. These properties affect the timescale and strength of feedbacks between ice-sheet change and solid Earth deformation, and hence must be accounted for when considering the future evolution of the ice sheet."

&

Eric Rignot, et al. (January 22, 2019), "Four decades of Antarctic Ice Sheet mass balance from 1979–2017", PNAS, 116 (4) 1095-1103; https://doi.org/10.1073/pnas.1812883116

https://www.pnas.org/content/116/4/1095

Significance Statement
We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

Abstract
We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level.

PS: Isostatic rebound introduces bed mass beneath glaciers that are losing ice mass; thus the GRACE, or GRACE-FO, data must be corrected to subtract the new bed to get the total ice mass lost; however, projecting the new bed mass can be difficult.

21
The linked reference discusses the portioning of climate projection uncertainty in three large ensembles including CMIP5 & CMIP6 (see the attached image).  I note that this reference only considers model response uncertainty internal to the ensemble, and not feedback mechanisms not fully accounted for by the ensemble (like ice-climate feedback mechanisms).  In this regard, I note:

a)  Uncertainty due to climate internal variability (like ENSO variability) are still significant thru 2030 (when say a strong El Nino event might contribute to a collapse of the PIIS and/or the Thwaites Ice Tongue by say 2030, considering the increased frequency of strong El Nino events with global warming and that the last strong El Nino was in the 2015-2016 season).
b) A significant portion of the model uncertainty in CMIP6 is due to the fact that many of the included models considered nonlinearity of several feedback mechanisms that earlier ensembles did not.
c) The SSP scenarios are tied to specific emission pathways while the RCP scenarios only considered concentration pathways, which attributes more uncertainty to the RCP scenarios than to the SSP scenaros.

Lehner, F., Deser, C., Maher, N., Marotzke, J., Fischer, E., Brunner, L., Knutti, R., and Hawkins, E.: Partitioning climate projection uncertainty with multiple Large Ensembles and CMIP5/6, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-93, in review, 2020.

https://www.earth-syst-dynam-discuss.net/esd-2019-93/
https://www.earth-syst-dynam-discuss.net/esd-2019-93/esd-2019-93.pdf

Abstract. Partitioning uncertainty in projections of future climate change into contributions from internal variability, model response uncertainty, and emissions scenarios has historically relied on making assumptions about forced changes in the mean and variability. With the advent of multiple Single-Model Initial-Condition Large Ensembles (SMILEs), these assumptions can be scrutinized, as they allow a more robust separation between sources of uncertainty. Here, the iconic framework from Hawkins and Sutton (2009) for uncertainty partitioning is revisited for temperature and precipitation projections using seven SMILEs and the Climate Model Intercomparison Projects CMIP5 and CMIP6 archives. The original approach is shown to work well at global scales (potential method error < 20 %), while at local to regional scales such as British Isles temperature or Sahel precipitation, there is a notable potential method error (up to 50 %) and more accurate partitioning of uncertainty is achieved through the use of SMILEs. Whenever internal variability and forced changes therein are important, the need to evaluate and improve the representation of variability in models is evident. The available SMILEs are shown to be a good representation of the CMIP5 model diversity in many situations, making them a useful tool for interpreting CMIP5. CMIP6 often shows larger absolute and relative model uncertainty than CMIP5, although part of this difference can be reconciled with the higher average transient climate response in CMIP6. This study demonstrates the added value of a collection of SMILEs for quantifying and diagnosing uncertainty in climate projections.

22
...
With NASA GISS vs 1750, 1.24+0.2, we were pretty much at 1.5 degrees last year, and even closer in 2016 (short by only 0.02 degrees). Reporting that may have helped focus policy makers mind's a bit better.

Quote
The spread between the five data sets was 0.15°C with both the lowest (1.05°C) and the highest (1.20°C) being more than 1°C warmer than the pre-industrial baseline.

Quote
Modern temperature records began in 1850. WMO uses datasets (based on monthly climatological data from Global Observing Systems) from the United States National Oceanic and Atmospheric Administration, NASA’s Goddard Institute for Space Studies, and the United Kingdom’s Met Office Hadley Centre and the University of East Anglia’s Climatic Research Unit in the United Kingdom. 

It also uses reanalysis datasets from the European Centre for Medium Range Weather Forecasts and its Copernicus Climate Change Service, and the Japan Meteorological Agency.  This method combines millions of meteorological and marine observations, including from satellites, with models to produce a complete reanalysis of the atmosphere. The combination of observations with models makes it possible to estimate temperatures at any time and in any place across the globe, even in data-sparse areas such as the polar regions.

https://public.wmo.int/en/media/press-release/wmo-confirms-2019-second-hottest-year-record

For ease of reference I re-post my Reply #724, which is relevant to this topic:

I note that Hawkins et al (2017) defines the pre-industrial baseline to be from 1720-1800 for determining GMSTA, and indicates that as both the CMIP5 and the AR5 projections were baselined to the 1896-2005 baseline (see first image that gives various AR5 baselines), one needs to add between 0.55 and 0.80C (which has a mean value of 0.675C) to the published CMIP5 and AR5 projections values to get correct values for GMSTA.

As the second image from the second linked article by Clive Best indicates that the mean value of the CMIP5 runs for RCP 8.5 in 2040 is about 1.7C, this implies that referenced to pre-industrial for RCP 8.5 (which is less aggressive than SSP5-Baseline) GMSTA in 2040 would be about 2.375C (which is above Mid-Pliocene conditions):

Ed Hawkins et al. (2017), "Estimating Changes in Global Temperature since the Preindustrial Period", BAMS, https://doi.org/10.1175/BAMS-D-16-0007.1

https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-16-0007.1

Abstract: "The United Nations Framework Convention on Climate Change (UNFCCC) process agreed in Paris to limit global surface temperature rise to “well below 2°C above pre-industrial levels.” But what period is preindustrial? Somewhat remarkably, this is not defined within the UNFCCC’s many agreements and protocols. Nor is it defined in the IPCC’s Fifth Assessment Report (AR5) in the evaluation of when particular temperature levels might be reached because no robust definition of the period exists. Here we discuss the important factors to consider when defining a preindustrial period, based on estimates of historical radiative forcings and the availability of climate observations. There is no perfect period, but we suggest that 1720–1800 is the most suitable choice when discussing global temperature limits. We then estimate the change in global average temperature since preindustrial using a range of approaches based on observations, radiative forcings, global climate model simulations, and proxy evidence. Our assessment is that this preindustrial period was likely 0.55°–0.80°C cooler than 1986–2005 and that 2015 was likely the first year in which global average temperature was more than 1°C above preindustrial levels. We provide some recommendations for how this assessment might be improved in the future and suggest that reframing temperature limits with a modern baseline would be inherently less uncertain and more policy relevant."
&

Extract: "We have examined estimates of historical radiative forcings to determine which period might be most suitable to be termed preindustrial and used several approaches to estimate a change in global temperature since this preindustrial reference period. The main conclusions are as follows:

1.   The 1720–1800 period is most suitable to be defined as preindustrial in physical terms, although we have incomplete information about the radiative forcings and very few direct observations during this time. However, this definition offers a target period for future analysis and data collection to inform this issue.
2.   The 1850–1900 period is a reasonable pragmatic surrogate for preindustrial global mean temperature. The available evidence suggests it was slightly warmer than 1720–1800 by around 0.05°C, but this is not statistically significant.
3.   We assess a likely range of 0.55°–0.80°C for the change in global average temperature from preindustrial to 1986–2005.
4.   We also consider a likely lower bound on warming from preindustrial to 1986–2005 of 0.60°C, implying that the AR5 estimate of warming was probably too small and that 2015 was the first year to be more than 1°C above preindustrial levels."

&

Title: "A comparison of CMIP5 Climate Models with HadCRUT4.6" January 21, 2019 by Clive Best

http://clivebest.com/blog/?p=8788

Caption for the second image: Model comparisons to HadCRUT4.6. Spaghetti are individual annual model results for each RCP. Solid curves are model ensemble annual averages.

23
The linked RealClimate article by Mauri Pelto, 2009; reminds us that in 1978 John Mercer argued that a major deglaciation of the WAIS might begin circa 2028, and that in 1981 Terry Hughes argued that such a major deglaciation would likely begin in the Pine Island Bay of the Amundsen Sea Embayment, ASE. Furthermore, Pelto indicated that the evidence through 2009 supported these arguments by Mercer and Hughes; however, to date neither the CMIP community nor the IPCC accept the likelihood of such an occurrence in the near future.

That said, the first image (from Rignot, 2008) and the second image (from Vaughan et al 2006) show that the Pine Island Glacier and the Thwaites Glacier catchment basins abut each other; which may lead to a synergistic degradation of the stability of both catchment basins in coming years.  This is particularly true regarding the potential interaction between the Pine Island Ice Shelf's (PIIS) South Ice Shelf (SIS) and the Southwest Tributary Glacier's (SWT) ice shelf as indicated by third image showing the 2012 PIIS ice surface elevation and the fourth image showing the interface between the SWT ice shelf and the SIS for February 18, 2020 which shows a faint rift about 1km upstream from the calving face.

Title: "Is Pine Island Glacier the Weak Underbelly of the West Antarctic Ice Sheet?", RealClimate Guest post by Mauri Pelto, November 9, 2009

http://www.realclimate.org/index.php/archives/2009/11/is-pine-island-glacier-the-weak-underbelly-of-the-west-antarctic-ice-sheet/

Extract: "A different example, from the same time period, was the 1978 publication by the late John Mercer, Ohio State U., who argued that a major deglaciation of the West Antarctic Ice Sheet (WAIS) may be in progress within 50 years. This conclusion was based on the fact that the WAIS margin was ringed with stabilizing ice shelves, and that much of the ice sheet is grounded below sea level. The loss of ice shelves — Mercer proposed — would allow the ice sheet to thin, grounding lines to retreat and the ice sheet to disintegrate via calving. This is a much faster means of losing mass than melting in place. Mercer further commented that the loss of ice shelves on the Antarctic Peninsula, as has since been observed, would be an indicator that this process of ice sheet loss due to global warming was underway.

Mercer’s ideas led Terry Hughes (1981) (my doctoral advisor at U. of Maine) to propose that the WAIS had a “weak underbelly” in Pine Island Bay. This bay in the Amundsen Sea is where the Pine Island Glacier (PIG) and Thwaites Glacier reach the sea. These are the only two significant outlet glaciers draining the north side of the WAIS. Together they drain 20% of the WAIS. Hughes called this area the “weak underbelly” because these glaciers lack the really huge ice shelves Ross Ice Shelf and the Ronne-Filchner Ice Shelf in which most other large WAIS outlet glaciers terminate.

The evidence does indicate that one of the basic underlying principles, proposed by Mercer and Hughes, of what can stabilize or destabilize WAIS was right on the money. The evidence reviewed does not fully confirm the weak underbelly hypothesis, but it provides enough evidence that we had best monitor the situation and expand our attempts to understand it."




24
Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

Do you use 1750 baseline ?

The +0.256 conversion factor is to the late 19th century.

25
Antarctica / Re: PIG has calved
« on: February 16, 2020, 10:56:05 PM »
What this thread has named the zone of destruction, ZOD, and the second destruction zone, SDZ, might better be considered as the southern shear margin for the PIIS between the southern ice shelf, SIS and the main ice shelf, MIS, as shown by the first attached image from Shean et al. (2019).  Furthermore, it seems to me that the majority of the icebergs in the ZOD came from the calving of the green area in the SIS surrounded by blue basal channel carved by the water circulation beneath the SIS shown in the second attached image, and I believe that the calving of the icebergs from this green area of the SIS is well illustrated by the third gif clip (requiring a click to start) assembled by paolo.  Also, I believe that the fourth image (also from paolo) of the SIS-SWT rift can also be seen in the first image, and that as this SIS-SWT rift widens both the SIS and the ice shelf for the SWT will be further destabilized

Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E., and Berthier, E.: Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica, The Cryosphere, 13, 2633–2656, https://doi.org/10.5194/tc-13-2633-2019, 2019.

https://www.the-cryosphere.net/13/2633/2019/

Finally, I note that the following linked AGU December 2019 presentation by Karen Alley et al. confirms that basal channels are frequently found beneath the shear margins of fast-flowing ice shelves like the PIIS.

Karen Alley et al (from a presentation at the December 2019 AGU Fall Meeting) discuss how basal channels in Antarctic ice shelves can work to destabilize such ice shelves leading to the type of accelerated calving as we have recently witness for the Pine Island Ice Shelf, PIIS.  In my opinion this behavior does not bode well for the stability of either the PIIS or the Thwaites Ice Tongue in coming decades.

C53C-1361 - Direct and indirect impacts of basal channels on ice-shelf stability

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/509049

Abstract
Basal channels are frequently found beneath the shear margins of fast-flowing ice shelves, where thinning due to channel formation likely contributes to reduced buttressing and decreased ice-shelf stability. Basal channels are also commonly found in the middle of ice shelves, particularly in areas where warm water is present. In either case, indirect effects on ice-shelf stability related to changes in buttressing and controls on basal melt rates are combined with direct effects, as stresses imparted by basal channels cause fractures, which may initiate calving events. We show that fractures form in association with basal channels on ice shelves throughout Antarctica, both at shear margins and at mid-shelf channels. Upstream channel growth is associated with channel deepening and the upstream propagation of channel-associated fractures on the Getz Ice Shelf. Because basal channels are widespread on Antarctic ice shelves, it is important to ascertain the balance of direct and indirect basal channel influences on ice-shelf stability and the capacity for basal channel change under evolving oceanic conditions.

PS: I find the posts offered recently in this thread to be helpful in better understanding just how rapidly the PIIS is currently being destabilized.

26
Per the linked NASA website, the global January 2020 LOTI Anomaly vs 1951-1980 was 1.17oC, and the first attached image give the zonal mean LOTI anomaly vs 1951-1980 for January 2020; which makes me wonder what the people living near 60o north latitude (like Oslo, Norway) will experience during January 2050:

https://data.giss.nasa.gov/gistemp/maps/index_v4.html

Edit:

The second attached image (from the same website) gives the January 2020 LOTI Anomaly vs 1951-1980; which shows that not only are the people living near Oslo, Norway, effected but also almost all of Siberia (with its extensive permafrost regions) and much of Canada near Hudson Bay (with its extensive sea ice area).

Edit2:

For those who forgot, to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius (so 1.17C with a 1951-1980 baseline converts to +1.426C vs pre-industrial)

27
I re-post the following in order to emphasize that abrupt iceberg calving (without ice shelves being present, resulting in ice-rafted debris as shown in the attached image) not only occurred in much of the WAIS but also in portions of the EAIS in paleo-times.  If this pattern is repeated in the future is could lead to over a century of ice sheet-climate positive feedback for more global warming even without additional anthropogenic radiative forcing after we have reached a MICI tipping point (say beginning in the ASE and then moving progressively to other Antarctic regions):

The linked reference discusses the paleo stability (instability) of the Wilkes Land continental margin (EAIS) in response to the early Pliocene ocean warming (which are conditions that the Earth could approximately replicate before 2100):

Melissa A. Hansen, Sandra Passchier, Boo-Keun Khim, Buhan Song & Trevor Williams (2015), "Threshold behavior of a marine-based sector of the East Antarctic Ice Sheet in response to early Pliocene ocean warming", Paleoceanography, DOI: 10.1002/2014PA002704

http://onlinelibrary.wiley.com/doi/10.1002/2014PA002704/abstract

Abstract: "We investigate the stability of the East Antarctic Ice Sheet (EAIS) on the Wilkes Land continental margin, Antarctica, utilizing a high-resolution record of ice-rafted debris (IRD) mass accumulation rates (MAR) from Integrated Ocean Drilling Program Site U1359. The relationship between orbital variations in the IRD record and climate drivers was evaluated to capture changes in the dynamics of a marine-based ice sheet in response to early Pliocene warming. Three IRD MAR excursions were observed and confirmed via scanning electron microscope microtextural analysis of sand grains. Time series analysis of the IRD MAR reveals obliquity-paced expansions of the ice sheet to the outer shelf prior to ~4.6 Ma. A decline in the obliquity and a transition into a dominant precession response of IRD MAR occur at ~4.6 Ma along with a decline in the amplitude of IRD MAR maxima to low background levels between ~4.0 and ~3.5 Ma. We speculate that as sea surface temperatures began to peak above 3°C during the early Pliocene climatic optimum, the ice shelves thinned, leading to a greater susceptibility to precession-forced summer insolation and the onset of persistent retreat of a marine-based portion of the EAIS."

28
In the linked 2018 Carbon Brief article Hausfather both tries to explain 'How scientists estimate 'climate sensitivity' and tries to support the AR5 consensus ranges for ECS and TCR; which in my opinion discounts much of the actual climate change risk that we are currently facing.  Examples of how consensus climate scientists (including Hausfather) are discounting the risk of higher effective climate sensitivity include:

1. They created definitions of 'climate sensitivity' that discount effective climate sensitivity risks such as abrupt ice sheet mass loss, and sea ice albedo flip, this century.

2. They discount the early activation of various 'slow' feedback mechanisms such as the early upwelling of warm circumpolar deep water, CDW, that is currently accelerating ice shelf calving in Antarctic.

3. They general give too much weight to calculations of climate sensitivity based on short-term observations that are biased by the 'faux hiatus'.

4. They discount the fact that both effective ECS and effective TCR increase with continued forcing and thus the longer we wait to take effective action to stop climate change the harder it will be to take effective action.

Title: "Explainer: How scientists estimate 'climate sensitivity'" by Zeke Hausfather, 2018

https://skepticalscience.com/explainer-how-scientists-estimate-climate-sensitivity.html

Extract: "Climate sensitivity refers to the amount of global surface warming that will occur in response to a doubling of atmospheric CO2 concentrations compared to pre-industrial levels."

CO2 has increased from its pre-industrial level of 280 parts per million (ppm) to around 408 ppm today. Without actions to reduce emissions concentrations are likely to reach 560 ppm – double pre-industrial levels – around the year 2060.

There are three main measures of climate sensitivity that scientists use. The first is equilibrium climate sensitivity (ECS). The Earth’s climate takes time to adjust to changes in CO2 concentration. For example, the extra heat trapped by a doubling of CO2 will take decades to disperse down through the deep ocean. ECS is the amount of warming that will occur once all these processes have reached equilibrium.

The second is transient climate response (TCR). This is the amount of warming that might occur at the time when CO2 doubles, having increased gradually by 1% each year. TCR more closely matches the way the CO2 concentration has changed in the past. It differs from ECS because the distribution of heat between the atmosphere and oceans will not yet have reached equilibrium.

A third way of looking at climate sensitivity, Earth system sensitivity (ESS), includes very long-term Earth system feedbacks, such as changes in ice sheets or changes in the distribution of vegetative cover.

A 2017 paper by Dr Cristian Proistosescu and Prof Peter Huybers at Harvard University found that amplifying feedbacks that play a large role in ECS in climate models have not fully kicked in for current climate conditions. A similar paper by Prof Kyle Armourof the University of Washington suggests feedbacks will increase by about 25% from today’s transient warming as the Earth moves towards equilibrium.

This means that sensitivity estimates based on instrumental warming to date would be on the low side, as they would not capture the larger role of feedbacks in future warming. The authors suggest that “accounting for these…brings historical records into agreement with model-derived ECS estimates”.

This is in part because feedbacks depend strongly on the spatial pattern of warming. Prof Armour elaborates in a discussion on the Climate Lab Book website:

“Nearly all GCMs [global climate models] show global radiative feedbacks changing over time under forcing, with effective climate sensitivity increasing as equilibrium is approached. As a result, climate sensitivity estimated from transient warming appears smaller than the true value of ECS…

As far as we can tell, the physical reason for this effect is that the global feedback depends on the spatial pattern of surface warming, which changes over time…One nice example is the sea-ice albedo feedback in the Southern Ocean: because warming has yet to emerge there, that positive (destabilising) feedback has yet to be activated.

This means that even perfect knowledge of global quantities (surface warming, radiative forcing, heat uptake) is insufficient to accurately estimate ECS; you also have to predict how radiative feedbacks will change in the future.”"

See also:

https://www.climate-lab-book.ac.uk/2016/reconciling-estimates-of-climate-sensitivity/#comment-2565

Extract: "Caldeira & Myrhvold (2013) and the standard “Gregory approach” use simulations where CO2 jumps by 300% immediately (“abrupt4xCO2”) and then you see what happens. In those cases dT/dt is big and then slows down. That’s because forcing is big and causes immediate heating. But if you plot T vs F (F being net top-of-atmosphere imbalance here) you see that dT/dF, which is related to feedbacks, changes with time in a way that means feedbacks get more-positive as warming goes on.

In 1pctCO2 simulations the forcing increases linearly from zero, but the temperature change accelerates. Taking the model average T and looking at the trends for each 30 year period within years 0-120 you get trends in C/decade of: +0.21, +0.27, +0.31, +0.34. Warming accelerates under transient CO2 increases in models.

The differences comes down to dT/dt versus dT/dF. Rugenstein & Knutti is a good place to look for more info and work by people like Armour, Held, Gettelman, Kay & Shell helps explain the physics."

29


Chris S. M. Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran, Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, and Alan Cooper (February 11, 2020), "Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica", PNAS, https://doi.org/10.1073/pnas.1902469117

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1



First, the following extract from Turney et al. (2020) makes it clear how important the bipolar seesaw mechanism is w.r.t. potential future ice mass loss from Antarctica (possibly triggered by a release of relatively fresh/warm water from the Beaufort Gyre in coming decades).

Extract from Turney et al. (2020): "Recent work has proposed that the iceberg-rafted Heinrich 11 event between 135 and 130 ky (during Termination II) may have significantly reduced North Atlantic Deep Water (NADW) formation and shut down the Atlantic meridional overturning circulation (AMOC) (42), resulting in net heat accumulation in the Southern Hemisphere (the bipolar seesaw pattern of northern cooling and southern warming) (43, 44) (Fig. 4A). Under this scenario, surface cooling during Heinrich 11 increased the northern latitudinal temperature gradient and caused a southward migration of the Intertropical Convergence Zone and midlatitude Southern Hemisphere westerly airflow (14, 45). Importantly, Heinrich 11 was probably one of the largest of the iceberg-rafting events over the last 140 ky (including H-1 and H-2) and during a time of likely weakened AMOC (42). In the Southern Ocean, the associated northward Ekman transport of cool surface waters (something akin to today; Fig. 1A) was likely compensated by increased delivery of relatively warm and nutrient-rich Circumpolar Deep Water (CDW) toward the Antarctic margin (14, 34, 43, 45, 46), potentially leading to enhanced thermal erosion of ice at exposed grounding lines (43, 47). This interpretation is supported by the enriched benthic foraminifera 13C values into the LIG (46), a proxy for the influence of NADW on CDW in the south, implying northern (warmer) waters were reaching far south for much of this period (and a cause of persistent loss of ice volume) (Fig. 2I). The unambiguous precise correlation between the Patriot Hills ice and West Antarctic marine records (34) afforded by the Termination II tephra demonstrates that the warming recorded in the BIA is coincident with a major, well-documented peak in marine temperatures and productivity around the Antarctic continent and in the Southern Ocean (34, 45, 46) (Fig. 2). The subsequent delivery of large volumes of associated freshwater into the Southern Ocean during the LIG would have reduced Antarctic Bottom Water (AABW) production (46), resulting in increased deepwater formation in the North Atlantic (43, 48, 49) (Fig. 4C). Recent modeling results suggest that increased heat transport beneath the ice shelves can drive extensive grounding-line retreat, triggering substantial drawdown of the Antarctic ice sheet (2, 14, 20) (Fig. 4B). Of concern, warming of the ocean cavity in the WSE is projected to increase during the 21st century (50)."

Second, the linked article makes it clear that the ice-rafted debris (IRD) already found on the seafloor of the Southern Ocean supported the concept that MICI-types of ice mass loss may be in our future and it discusses efforts to obtain more extensive such evidence (see image).

Title: "Antarctica’s iceberg graveyard could reveal the ice sheet’s future"

https://www.sciencenews.org/article/antarctica-iceberg-graveyard-climate-change

Extract: "“By looking at material carried by icebergs that calved off of the continent, we should be able to infer which sectors of the ice sheet were most unstable in the past,” Raymo says. “We can correlate the age and mineralogy of the ice-rafted debris to the bedrock in the section of Antarctica from which the bergs originated.”

Icebergs breaking off from the edges of Antarctica’s ice sheet tend to stay close to the continent, floating counterclockwise around the continent. But when the bergs reach the Weddell Sea, on the eastern side of the peninsula, they are shunted northward through a region known as Iceberg Alley toward warmer waters in the Scotia Sea.

But Antarctica may have played a larger role than once thought. In a study published in Nature in 2014, Kuhn, Weber and other colleagues reported that ice-rafted debris from that time period, as recorded in relatively short sediment cores from Iceberg Alley, often occurred in large pulses lasting a few centuries to millennia. Those data suggested that the southernmost continent was shedding lots of bergs much more quickly during those times than once thought.

“The existing [ice core] record from Iceberg Alley taught us Antarctica lost ice through a threshold reaction,” Weber says. That means that when the continent reached a certain transition point, there was sudden and massive ice loss rather than just a slow, gradual melt.

“We have rather firm evidence that this threshold is passed once the ice sheet loses contact with the underlying ocean floor,” he says, adding that at that point, the shedding of ice becomes self-sustaining, and can go on for centuries. “With mounting evidence of recent ice-mass loss in many sectors of West Antarctica of a similar fashion, we need to be concerned that a new ice-mass loss event is already underway, and there is no stopping it.”"

&

Title: "Deep-Sea Drillers Investigate Shedding of Antarctic Icebergs"

https://blogs.ei.columbia.edu/2019/03/25/iodp-icebergs-antarctica-climate-change/

Third, the first linked video illustrates how dramatically the Antarctic iceberg flux has increased from 1976 to 2019.

Title: "Icebergs Alive - Iceberg flux 1976-2019"



Fourth, the second linked video illustrates how much the Thwaites Glacier ice flow velocity has increased through 2019.

Title: "Thwaites Glacier Along Flow Ice Speed"




30
Schwans et al. (a presentation at the December 2019 AGU Fall Meeting) indicates that the Eastern Shear Margin plays an important role in the future dynamics of the Thwaites Glacier.  Furthermore, I note that now that the PIIS is no longer buttressing the Southwest Tributary Glacier it is likely that the Thwaites Eastern Shear Margin will become more dynamic in coming years.

Title: "C53A-05 - Role of the Eastern Shear Margin in Thwaites Glacier’s Dynamics"

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/513156

Abstract
Thwaites Glacier’s (TG’s) accelerating mass loss and connection to major drainages in the WAIS make it the most likely means by which the ice sheet could rapidly destabilize and contribute to sea level rise (SLR).

Results using JPL’s Ice Sheet System Model (ISSM) show how the timing and rate of TG’s retreat into the interior of the WAIS is highly dependent on ill-constrained conditions at the bed and at/near the ice/ocean interface. Another uncertainty in projecting Thwaites’ retreat is whether its Eastern shear margin will remain stable or migrate.
A model ensemble containing various melt scenarios, bed types, initial shelf configurations, and shear margin forcings provides new insight into the relative importance of each of these forcings/conditions, and their interplay, in TG’s evolution over the next few centuries. Simulations activating the entire Eastern shear margin show that, regardless of bed character, this alters retreat patterns across TG’s main trunk, pointing to the margin as an important field target for future data collection efforts on Thwaites.

31
Karen Alley et al (from a presentation at the December 2019 AGU Fall Meeting) discuss how basal channels in Antarctic ice shelves can work to destabilize such ice shelves leading to the type of accelerated calving as we have recently witness for the Pine Island Ice Shelf, PIIS.  In my opinion this behavior does not bode well for the stability of either the PIIS or the Thwaites Ice Tongue in coming decades.

C53C-1361 - Direct and indirect impacts of basal channels on ice-shelf stability

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/509049

Abstract
Basal channels are frequently found beneath the shear margins of fast-flowing ice shelves, where thinning due to channel formation likely contributes to reduced buttressing and decreased ice-shelf stability. Basal channels are also commonly found in the middle of ice shelves, particularly in areas where warm water is present. In either case, indirect effects on ice-shelf stability related to changes in buttressing and controls on basal melt rates are combined with direct effects, as stresses imparted by basal channels cause fractures, which may initiate calving events. We show that fractures form in association with basal channels on ice shelves throughout Antarctica, both at shear margins and at mid-shelf channels. Upstream channel growth is associated with channel deepening and the upstream propagation of channel-associated fractures on the Getz Ice Shelf. Because basal channels are widespread on Antarctic ice shelves, it is important to ascertain the balance of direct and indirect basal channel influences on ice-shelf stability and the capacity for basal channel change under evolving oceanic conditions.

32
In the linked abstract of a presentation made at the December 2019 AGU Convention, Richard Alley et al. point out that ice-shelf stability is one of the most important considerations for determining whether future ice-cliff failure mechanisms may occur with continued global warming, and I note that CMIP6 models make very primitive assumptions about ice-shelf stability that do not appear to be what is currently happening seaward of the PIG and Thwaites Glacier.  Furthermore, Richard Alley et al.  support Hansen et al. (2016)'s observation that a cooling of the ocean surface (as is currently happening in the Southern Ocean) can direct more warm deep ocean water towards the bases of key ice shelves such as the PIIS, TEIS and the Thwaites Ice Tongue; which reduces their stability.  Richard Alley et al. also point out that ice-rafted debris (IRD) cannot occur with ice shelves intact, thus the factor than numerous IRD fields in both the Southern Ocean and the North Atlantic mean the ice-cliff failure mechanism likely occurred in paleo times under conditions similar to our current situation.

C51A-08 - “Then new problems came, from above and below…”: Heinrich Events and the future of West Antarctic ice (Invited)

https://agu.confex.com/agu/fm19/meetingapp.cgi/Paper/587813

Abstract
Heinrich Events (HE), in particular H2, record ice-shelf loss and resulting ice-flow acceleration in a cold surface climate, with implications for the future of sea-level change. Essentially all ice shelves buttress ice inflow, and experience basal melting near the grounding line that reduces or eliminates ice-rafted debris (IRD) before calving. This understanding indicates that IRD pulses in cold climates record ice-shelf loss and not just faster flow with intact ice shelves. Ice-shelf loss has been observed recently in response to atmospheric warming (Larsen B), but also in response to oceanic warming (Jakobshavn) with shelf thinning and flow acceleration causing marginal rifting leading to shelf calving (Joughin et al. 2008 JGR), perhaps preconditioned by marginal troughs (K.E. Alley et al. 2019 SciAdv). As shown by Marcott et al. (2011 PNAS), surface cooling preceding HE allowed warm water to access the grounding zone of the Hudson Strait ice stream, and the IRD pulses then record the ice-shelf loss, accompanied by faster flow in response to loss of buttressing. H2 occurred at a minimum in atmospheric temperatures. Future warming could reach Larsen B-type conditions in West Antarctica. But, if ice-sheet mass loss stabilizes the water column and causes surface cooling but subsurface warming, similar or even greater instability may result, as confirmed by H2. Proper understanding of these processes implemented in models is essential for accurate projections.

33
...

So the impacts of the current glut are that the natural gas producers will be out of business and venting/flaring will be reduced. 

...

I certainly hope that your are correct, but only time will tell what the future brings.

34
Fracked natural gas does not only have a carbon footprint as heavy as that for coal; but it is so cheap and abundant that solar and wind power cannot compete with it, and it is driving utilities to build associated infrastructure that will ensure the use of natural gas for decades to come; all of which will slow progress in the fight against climate change.  Furthermore, virgin plastics made from natural gas is now cheaper than recycled plastics, making it difficult to move towards a circular economy.

Title: "Cheap natural gas is making it very hard to go green."

https://www.treehugger.com/fossil-fuels/cheap-natural-gas-making-it-very-hard-go-green.html

Extract: "We recently noted that the US is drowning in cheap natural gas, and that "Gasmaggedon" will make it even harder to electrify everything. Now we learn from Bloomberg Green that solar and wind power can't compete with gas that's this cheap. Naureen Malik and Brian Eckhouse write:

Gas is such a bargain that it’s being viewed less as a bridge fossil fuel, driving the world away from dirtier coal toward a clean-energy future, and more as a hurdle that could slow the trip down. Some forecasters are predicting prices will stay low for years, making it tough for states, cities and utilities to achieve their goals of being zero-carbon in power production by 2050 or earlier.

According to Jared Paben in Plastics Recycling Update, virgin plastics are now cheaper than recycled plastic, and there is too much of the stuff; Tison Keel of IHS Markit complains that "the supply-demand imbalance is expected to get worse with additional production capacity coming on-line. “What we have coming in the next couple of years is a large overbuild.”"


35
The linked reference assesses and evaluates the differences between climate sensitivity projected by CMIP5 models vs CMIP6 models.  The attached associated image indicates that the CMIP6 ECS distribution is bimodal, with one mode have an ECS of about 3C and the other having an ECS of about 5C.  As I doubt that the true pdf for ECS is bimodal; this bimodal distribution for CMIP6 likely is related to human bias.  While decision makers will likely use the associated uncertainty as an excuse for not taking more strident climate action; I view it as a significant risk that the 5C ECS mode may be correct.

Flynn, C. M. and Mauritsen, T.: On the Climate Sensitivity and Historical Warming Evolution in Recent Coupled Model Ensembles, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-1175, in review, 2020.

https://www.atmos-chem-phys-discuss.net/acp-2019-1175/

Abstract. The Earth's equilibrium climate sensitivity (ECS) to a doubling of atmospheric CO2, along with the transient 35 climate response (TCR) and greenhouse gas emissions pathways, determines the amount of future warming. Coupled climate models have in the past been important tools to estimate and understand ECS. ECS estimated from Coupled Model Intercomparison Project Phase 5 (CMIP5) models lies between 2.0 and 4.7 K (mean of 3.2 K), whereas in the latest CMIP6 the spread has increased: 1.8–5.5 K (mean of 3.7 K), with 5 out of 25 models exceeding 5 K. It is thus pertinent to understand the causes underlying this shift. Here we compare the CMIP5 and CMIP6 model ensembles, and find a systematic shift between CMIP eras to be unexplained as a process of random sampling from modeled forcing and feedback distributions. Instead, shortwave feedbacks shift towards more positive values, in particular over the Southern Ocean, driving the shift towards larger ECS values in many of the models. These results suggest that changes in model treatment of mixed-phase cloud processes and changes to Antarctic sea ice representation are likely causes of the shift towards larger ECS. Somewhat surprisingly, CMIP6 models exhibit less historical warming than CMIP5 models; the evolution of the warming suggests, however, that several of the models apply too strong aerosol cooling resulting in too weak mid 20th Century warming compared to the instrumental record.

Caption: "Figure 1. Histograms displaying number of CMIP5 (top) or CMIP6 (bottom) models that fall with 0.5 K ECS bins.  ECS mean value and standard deviation for CMIP5 and CMIP6 displayed in black and red, respectively, above each histogram."

36
In my opinion, if/when the PIIS calving front retreats upstream of the South Ice Shelf, SIS, (the first image shows the calving front on February 9, 2020); the second image (from the first linked reference) of ice shelves surface elevations circa 2012, indicates that there is a significant piece of the SIS that could calve off (i.e. the green area surrounded by blue).  Furthermore, the third image ( showing the 2009 to 2012 circulation pattern, from the second linked site) shows that relatively warm ocean water actively circulates beneath the SIS.  Also, I provide the fourth image that shows the mid-January 2014 grounding line location, for reference:

Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E., and Berthier, E.: Ice shelf basal melt rates from a high-resolution digital elevation model (DEM) record for Pine Island Glacier, Antarctica, The Cryosphere, 13, 2633–2656, https://doi.org/10.5194/tc-13-2633-2019, 2019.

https://www.the-cryosphere.net/13/2633/2019/

Abstract
Ocean-induced basal melting is responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution digital elevation models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 2002–2015 DEM and altimetry data. We implemented a Lagrangian elevation change (Dh∕Dt) framework to estimate ice shelf basal melt rates at 32–256 m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG ice shelf and lower catchment from 2008 to 2015. We document the evolution of Eulerian elevation change (dh∕dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 2008–2015 period were ∼82–93 Gt yr−1, with ∼200–250 m yr−1 basal melt rates within large channels near the grounding line, ∼10–30 m yr−1 over the main shelf, and ∼0–10 m yr−1 over the North shelf and South shelf, with the notable exception of a small area with rates of ∼50–100 m yr−1 near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt-rate observations. We also document the relative melt rates for kilometer-scale basal channels and keels at different locations on the ice shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice–ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica.
Caption for the second image: "Figure 3 October-December 2012 WorldView/GeoEye DEM mosaic of the PIG ice shelf.  Labels show regions discussed in text: North ice shelf. South ice shelf, Main ice shelf, "ice plain", and fast-flowing South ice shelf tributary.  White outline shows ~2011 grounding line. Elevation values are the corrected surface height (Eq. 1) above the EGM2008 geoid."

&

For the circulation pattern see:

http://nora.nerc.ac.uk/502263/1/1244341RevisedManuscript2.pdf

Caption for the third image: "Fig. 3. Observed and simulated hydrography and circulation in 2009 and 2012. A. Section of observed and simulated 2009 potential temperatures (color) and salinity (black contours) along the eastern Amundsen Sea trough and underneath the PIG ice shelf. White lines show the surface-referenced 27.47 and 27.75 isopycnals. The panel shows observations outside the PIG cavity, and simulation results within it. Observations are linearly interpolated from profiles (black triangles) indicated in figure 1B. B. Same as A but for the 2012 observations and simulation. C. Modeled potential temperature (color) and velocity (black vectors, every fifth vector is shown) averaged within 50 m of the seabed for the 2009 simulation. White vectors show the corresponding velocity observed by Autosub (binned on the model grid, see also Fig. S2A). The cyan line indicates the position of the section used in panels A and B. The white line indicates 750 m seabed depth. D. Same as C but for the difference between the 2012 and the 2009 simulations."

37
With a hat-tip to vox_mundi, the linked reference found over 2 million Arctic permafrost methane emission hotspots during a recent airborne survey using state-of-the-art instrumentation.  This study suggests that thermokarst lakes are already becoming a significant source of methane emissions; which does not bode well for the prospect of increasing such methane emissions with continuing Arctic warming/amplification:

Clayton D. Elder et al. (10 February 2020), "Airborne Mapping Reveals Emergent Power Law of Arctic Methane Emissions", Geophysical Research Letters, https://doi.org/10.1029/2019GL085707

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085707

Abstract
Methane (CH4) emissions from thawing permafrost amplify a climate warming feedback. However, upscaling of site‐level CH4 observations across diverse Arctic landscapes remains highly uncertain, compromising accuracy of current pan‐Arctic CH4 budgets and confidence in model forecasts. We report a 30,000‐km2 survey at 25‐m2 resolution (~1 billion observations) of CH4 hotspot patterns across Alaska and northwestern Canada using airborne imaging spectroscopy. Hotspots covered 0.2% of the surveyed area, concentrated in the wetland‐upland ecotone, and followed a two‐component power law as a function of distance from standing water. Hotspots decreased sharply over the first 40 m from standing water (y = 0.21×−0.649, R2 = 0.97), mirroring in situ flux observations. Beyond 40 m, CH4 hotspots diminished gradually over hundreds of meters (y = 0.004×−0.164, R2 = 0.99). This emergent property quantifies the distribution of strong methanogenic zones from site to regional scales, vastly improving metrics for scaling ground‐based CH4 inventories and validation of land models.

Plain Language Summary

Understanding Arctic methane emissions is crucial to forecasting the region's impact on global climate. Ongoing efforts suffer large uncertainties when upscaling emissions since direct observations rarely cover scales relevant to both process‐level (fine‐scale) biogeochemistry and land models that operate on much larger scales. We bridge these scale gaps via high‐resolution airborne detection of methane hotspots (25‐m2 pixels) across a 30,000‐km2 study domain. We quantified a key spatial property of Arctic methane emissions: their power law dependence on distance to nearest standing water. From the ground, we verified that wide‐ranging methane fluxes follow the same spatial power law pattern as domain‐wide hotspots. These conclusions can improve scaling of emissions in Arctic land models and potentially reduce the disparity between ground‐based and atmospheric emission budgeting.

38
The linked article focuses on the somewhat arbitrary consideration that some people have been overestimating the annual amount of methane currently discharged into the atmosphere from the Arctic Ocean associated with methane seeps in the seafloor.  However, associated study indicates that the amount of methane emitted from methane seeps is sensitive to bottom water temperatures, and the article concludes that:

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."



While I have more frequently cited the risk that the Beaufort Gyre poses to a slowing of the MOC; I also remind readers that the relatively freshwater accumulating is the Beaufort Gyre is also relatively warm and its eventual release from the gyre will not only send relatively warm fresh water into the North Atlantic, but also into the Arctic Ocean; which per the linked reference (previously cited in Reply #2672) would disrupt the halocline which in turn would reduce the Arctic Sea Ice extent beyond the summer season; which in turn would warm the Arctic Ocean waters due to the change in albedo; which puts the hydrate lid on the Arctic Ocean seafloor at greater risk of abruptly degrading in the coming decades.

Mary-Louise Timmermans John Toole and Richard Krishfield (29 Aug 2018), "Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins", Science Advances, Vol. 4, no. 8, eaat6773, DOI: 10.1126/sciadv.aat6773

https://advances.sciencemag.org/content/4/8/eaat6773

Abstract
Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season.

39
A new Antarctic temperature record has just between set:

Title: "Antarctica Just Cracked a Disturbing New Temperature Record of 20 Degrees Celsius" Feb 14, 2020

https://www.sciencealert.com/antarctica-just-smashed-a-new-balmy-heat-record

Extract: "Scientists in Antarctica have recorded a new record temperature of 20.75 degrees Celsius (69.35 Fahrenheit), breaking the barrier of 20 degrees for the first time on the continent, a researcher said Thursday."

40
There is relatively little new information cited in the linked article discussing a potential WAIS 'tipping point'; but it does emphasize that such a tipping point is likely to occur with a GMSTA someplace between 1.5C and 2C and that we are already around 1.1C and states that: '… the margins for avoiding this threshold are fine indeed.'

Title: "Guest post: How close is the West Antarctic ice sheet to a ‘tipping point’?" by Christina Hulbe

https://www.carbonbrief.org/guest-post-how-close-is-the-west-antarctic-ice-sheet-to-a-tipping-point

Extract: "The latest research says that the threshold for irreversible loss of the WAIS likely lies between 1.5C and 2C of global average warming above pre-industrial levels. With warming already at around 1.1C and the Paris Agreement aiming to limit warming to 1.5C or “well-below 2C”, the margins for avoiding this threshold are fine indeed.

The IPCC says:

“Beyond 2050, uncertainty in climate change induced SLR [sea level rise] increases substantially due to uncertainties in emission scenarios and the associated climate changes, and the response of the Antarctic ice sheet in a warmer world.”

The concern around the vulnerability of the WAIS principally lies in something called “marine ice sheet instability” (MISI) – “marine” because the base of the ice sheet is below sea level and “instability” for the fact that, once it starts, the retreat is self-sustaining.

There appears to be a second source of instability for marine ice sheets – one that comes into play if the ice shelves are lost entirely.

This process, illustrated below, is called “marine ice cliff instability” (MICI). The theory suggests that where the height of a glacier face exceeds around 100m above the ocean surface, the cliff will be too tall to support its own weight. It will, therefore, inevitably collapse, exposing a similarly tall cliff face behind it, which, too, will collapse. And so on."

41
The linked article focuses on the somewhat arbitrary consideration that some people have been overestimating the annual amount of methane currently discharged into the atmosphere from the Arctic Ocean associated with methane seeps in the seafloor.  However, associated study indicates that the amount of methane emitted from methane seeps is sensitive to bottom water temperatures, and the article concludes that:

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."

Title: "Climate gas budgets highly overestimate methane discharge from Arctic Ocean"

https://www.sciencedaily.com/releases/2020/01/200113111052.htm

Extract: "We have found that seasonal differences in bottom water temperatures in the Arctic Ocean vary from 1,7°C in May to 3,5°C in August. The methane seeps in colder conditions decrease emissions by 43 percent in May compared to August." says oceanographer Benedicte Ferré, researcher at CAGE Centre for Arctic Gas Hydrate, Environment and Climate at UiT The Arctic University of Norway.

"Right now, there is a large overestimation in the methane budget. We cannot just multiply what we find in August by 12 and get a correct annual estimate. Our study clearly shows that the system hibernates during the cold season."
...
How methane will react in future ocean temperature scenarios is still unknown. The Arctic Ocean is expected to become between 3°C and a whopping 13°C warmer in the future, due to climate change. The study in question does not look into the future, but focuses on correcting the existing estimates in the methane emissions budget. However:

"We need to calculate the peculiarities of the system well, because the oceans are warming. The system such as this is bound to be affected by the warming ocean waters in the future." says Benedicte Ferré;.

A consistently warm bottom water temperature over a 12-month period will have an effect on this system.

"At 400 meters water depth we are already at the limit of the gas hydrate stability. If these waters warm merely by 1,3°C this hydrate lid will permanently lift, and the release will be constant." says Ferré."

Edit:

I forgot to mention that as the linked reference finds that prior estimates of current methane emissions from Arctic seafloor seeps were too high, as the current atmospheric methane concentrations are well known, this implies that some other source of methane emissions is higher than previously estimated (which might be coming from the recent acceleration of permafrost degradation).

42
While the orange dots are preliminary and the green crosses indicates readings from poorly mixed air masses; nevertheless, the range of both the orange and green symbols has increased significantly in recent years for atmospheric methane readings at Barrow, Alaska (see the attached image for atmospheric methane readings at Barrow for the years 2007 thru Feb 13, 2020).  To me, this is an indicator of increasing permafrost degradation in recent years:

Title: "Barrow Atmospheric Baseline Observatory, United States"

https://www.esrl.noaa.gov/gmd/dv/iadv/graph.php?code=BRW&program=ccgg&type=ts

Extract: "Data shown may be measurements of air collected approximately weekly in glass containers and returned to GMD for analysis or averages from air sampled semi-continuously at a GMD baseline observatory. Circle Symbols are thought to be regionally representative of a remote, well-mixed troposphere.

+ Symbols are thought to be not indicative of background conditions, and represent poorly mixed air masses influenced by local or regional anthropogenic sources or strong local biospheric sources or sinks.

A smooth curve and long-term trend may be fitted to the representative measurements when sufficient data exist. Data shown in ORANGE are preliminary. All other data have undergone rigorous quality assurance and are freely available from GMD, CDIAC, and WMO WDCGG."


43
I chopped the attached graph  from a tweet by Deke Arndt into two pieces:

Tweet: "Deke Arndt‏ @DekeArndt Largest non El Niño monthly anomaly in the record. That rightmost grey bar just went where no grey bar has gone before."

44
While the austral summer is rapidly coming to a close, the two attached images from the linked website show that from Nov 1, 2019 to Feb 13, 2020 the ASE region sustained an unusual high number of surface melt days; which likely contributed to the degradation of both the PIIS and the Thwaites Ice Shelf/Tongue.  Furthermore, as there was no El Nino event this ENSO season; the advection of warm CDW beneath these ice shelves/tongue have been typical; but when a strong El Nino event eventually occurs, I believe that not only will the degradation of the ice shelves/tongue be accelerated but also that any calved icebergs/bergy-bits will be more likely to float away; which would further accelerate subsequent degradation of the ice shelves/tongue by relieving congestion induced buttressing from these mélanges.

http://climato.be/cms/index.php?climato=the-2020-melt-season-over-antarctica-as-simulated-by-marv3-10

45
The linked article tries to emphasize positive considerations associated with the risk of "… irreversible emissions of a permafrost 'tipping point'"; nevertheless, it concludes that: "… for permafrost, the science shows that thaw is already underway and the carbon it is releasing will already be contributing to our warming climate."  Furthermore, I not that if for any combination of reasons the NH atmosphere changes into an equable pattern this century (say due to the Equatorial Pacific SSTA increasing by 5C, say due to an abrupt slowdown of the MOC, caused say by an abrupt release of relatively fresh water from the Beaufort Gyre into the North Atlantic in coming decades), this carbon emissions from permafrost will definitely have effectively crossed an irreversible emission 'tipping point' that could sustain such equable conditions for a long time even without any more anthropogenic GHG emissions:

Title: "Guest post: The irreversible emissions of a permafrost ‘tipping point’"

https://www.carbonbrief.org/guest-post-the-irreversible-emissions-of-a-permafrost-tipping-point

Extract: "Scientists estimate that there is about twice as much carbon stored in permafrost as circulating in the atmosphere. This is approximately 1460bn-1600bn tonnes of carbon.

Most of it is currently frozen and preserved, but if even a small fraction is released into the atmosphere, the emissions would likely be large – potentially similar in magnitude to carbon release from other environmental fluxes, such as deforestation.

But, as things stand, permafrost thaw has already been observed in many locations in the Arctic. And as the recent special report on the ocean and cryosphere by the Intergovernmental Panel on Climate Change (IPCC) points out, warming this century will cause substantial emissions from permafrost:

By 2100, near-surface permafrost area will decrease by 2-66% for RCP2.6 and 30–99% for RCP8.5. This could release 10s to 100s of gigatonnes of carbon as CO2 and methane to the atmosphere for RCP8.5, with the potential to accelerate climate change.”"

46
The linked article about the risk of future abrupt 'dieback' of the Amazon rainforest concludes that this risk is real but that: "We are unlikely to know the vulnerability of the rainforest to climate change with any confidence until it is too late."

Title: "Guest post: Could climate change and deforestation spark Amazon ‘dieback’?"

https://www.carbonbrief.org/guest-post-could-climate-change-and-deforestation-spark-amazon-dieback

Extract: "Our model suggested that the CO2 effects had dominated over the 20th century – leading to a carbon sink in the intact rainforest. However, the model had the negative climate effects eventually winning out – resulting in an abrupt dieback of the Amazon rainforest from about 2040 onwards, when global warming had reached about 3C in this projection.
You can see this in the chart below, which shows how our model projected vegetation in the Amazon could change as the climate warmed through to 2100. It shows an Amazon dominated by trees (solid line) for decades, but then the fraction of the region that is covered by trees drops off dramatically through the middle of the 21st century. It is then replaced with grasses (dashed lines) and bare soil (dashed and dotted line).

Our findings were stark. However, recent research hints that Amazon forest may be more resilient to climate change. A lot of relevant research has flowed under the bridge since we published that dieback scenario in 2000 – some good news and some bad news for the forest.

First, the good news. It now seems that climate change is unlikely to be as damaging to the Amazon rainforest as we originally feared. In 2013, we discovered that the year-to-year variation in the annual increase in atmospheric CO2 allows us to estimate the sensitivity of tropical carbon sinks to climate change.

But there is also some less optimistic news. It now also seems that the CO2-fertilisation effect is unlikely to be as large as many early models assumed. This is because first and second generation climate-carbon cycle models did not include nutrient limitations on forest growth.

This, in combination with the dry season becoming long enough to permit regular natural fires, could see the forest transition to a permanent savannah. This would be characterised by a mixed tree and grassland system with an open canopy that allows the soil to become much hotter and drier, as well as store much less carbon.

Therefore, the twin pressures of deforestation and climate change on the Amazon rainforest remain a great concern. We are unlikely to know the vulnerability of the rainforest to climate change with any confidence until it is too late. However, we are sure that human-caused deforestation reduces the resilience of the forest to climate change and other stressors.

Many had thought the problem of Amazonian deforestation was on the path to being solved. The rate of deforestation dropped from a peak in 2004 of 28,000 square kilometres (km2) – equivalent to removing an area of forest almost the size of Belgium each year – to less than a fifth of that rate by 2014.

But that is all in the past now. With deforestation on the up and global warming continuing, there are, once again, multiple threats to the longevity of the Amazon rainforest."

47
18 years has made a big difference in the way the Thwaites Ice Tongue looks and behaves:

Title: "Thwaites Glacier Transformed"

https://earthobservatory.nasa.gov/images/146247/thwaites-glacier-transformed

..
Unlike Pine Island Glacier—which tends to shed large icebergs every few years (now almost annually)—the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits.



While I have discussed this matter in several prior posts, it has come to my attention that some reader do not understand why the Thwaites Ice Tongue breaks into numerous small (~ 1km to 5km) icebergs while the Pine Island Ice Shelf has been producing much larger icebergs when it calves, in recent years.  In my opinion, the most significant reason why the Thwaites Ice Tongue breaks into many smallish icebergs is that its glacial ice is pre-fractured in the pattern shown in the first image before the glacial ice crosses the final grounding line (at the base of the ice tongue).  Furthermore, in my opinion, this pre-fractured pattern in the glacial ice occurs when this ice passes over the sub-glacial cavity, upstream of the base of the ice tongue, due to tensile stresses induced in the ice when it looses basal support over the sub-glacial cavity (which I have previously call the 'Big Ear', as indicated by the title of the last attached image); as indicated in the last three attached images.

Furthermore, in my opinion, this behavior markedly increases the chance that an ice cliff face with over 100m of height above the water line may become exposed at the upstream side of the Big Ear subglacial cavity, if/when all of the downstream small icebergs float away (which might occur during the next one or two Super El Nino events).  Additionally, I remind readers that the Big Ear subglacial cavity occurs over the subglacial trough that leads directly into the BSB, and thus any ice cliff failure mechanism formed at the upstream side of this Big Ear subglacial cavity would likely propagate rapidly into the Byrd Subglacial Basin, BSB.

Edit: I note also that the accompanying images of the extent of the Big Ear subglacial cavity are for 2017; while it is now 2020, so the extent of this key subglacial cavity is almost certainly larger than indicates as it is reportedly substantially created by relatively warm modified circumpolar deep water, CDW, being circulated into the subglacial cavity by tidal action (indicated by the arrows in the second and third attached images).

48
Another positive feedback mechanism that neither CMIP5, nor CMIP6, models do not adequately account for is climate change-driven changes in agricultural zones (see the attached image for RCP 8.5 2060-2080).  As cited in the linked open access reference 'Frontier soils contain up to 177 Gt of C, which might be subject to release, which is the equivalent of over a century of current United States CO2 emissions.'

Lee Hannah et al. (February 12, 2020), "The environmental consequences of climate-driven agricultural frontiers", PloS ONE, https://doi.org/10.1371/journal.pone.0228305

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0228305

Abstract
Growing conditions for crops such as coffee and wine grapes are shifting to track climate change. Research on these crop responses has focused principally on impacts to food production impacts, but evidence is emerging that they may have serious environmental consequences as well. Recent research has documented potential environmental impacts of shifting cropping patterns, including impacts on water, wildlife, pollinator interaction, carbon storage and nature conservation, on national to global scales. Multiple crops will be moving in response to shifting climatic suitability, and the cumulative environmental effects of these multi-crop shifts at global scales is not known. Here we model for the first time multiple major global commodity crop suitability changes due to climate change, to estimate the impacts of new crop suitability on water, biodiversity and carbon storage. Areas that become newly suitable for one or more crops are Climate-driven Agricultural Frontiers. These frontiers cover an area equivalent to over 30% of the current agricultural land on the planet and have major potential impacts on biodiversity in tropical mountains, on water resources downstream and on carbon storage in high latitude lands. Frontier soils contain up to 177 Gt of C, which might be subject to release, which is the equivalent of over a century of current United States CO2 emissions. Watersheds serving over 1.8 billion people would be impacted by the cultivation of the climate-driven frontiers. Frontiers intersect 19 global biodiversity hotspots and the habitat of 20% of all global restricted range birds. Sound planning and management of climate-driven agricultural frontiers can therefore help reduce globally significant impacts on people, ecosystems and the climate system.

Caption: Fig 1. Global climate-driven agricultural frontiers for RCP8.5 2060–2080.
Areas that transition from no current suitability for major commodity crops to suitability for one or more crops are depicted in blue, while currently uncultivated areas that transition to suitability for multiple major commodity crops are shown in red. Intensity of color indicates the level of agreement between simulations driven by different GCMs for the RCP 8.5 radiative concentration pathway. Terrestrial areas in white are either currently suitable for at least one modeled crop or, not suitable for any modeled crops in the projected climatic conditions. Suitability under current and projected climates is defined as universal agreement of suitability methods (EcoCrop, Maxent, Frequency of Extreme Temperatures).

49
18 years has made a big difference in the way the Thwaites Ice Tongue looks and behaves:

Title: "Thwaites Glacier Transformed"

https://earthobservatory.nasa.gov/images/146247/thwaites-glacier-transformed

Extract: "Notice the size of the glacier’s main ice tongue in 2001, when the glacier was advancing by about 4 kilometers per year. The large rift across the glacier eventually spawned Iceberg B-22 in 2002.

In the past ten years, the tongue has continued to fracture and separate from the Thwaites Eastern Ice Shelf. By the time the 2019 image was acquired, the main tongue had retreated substantially, and the ocean in front of Thwaites had become filled with mélange, a mixture of icebergs and sea ice.

Unlike Pine Island Glacier—which tends to shed large icebergs every few years (now almost annually)—the icebergs that now break from Thwaites are generally not large enough to be named and tracked by the U.S. National Ice Center. Instead, the glacier is constantly producing many small broken bits.

The melting of floating ice as it makes contact with the ocean is a key reason why the glacier is coming unglued. Seawater that is a few degrees above freezing is melting the ice shelf from below. Warm water has recently been recorded near the Thwaites Glacier grounding line—the location where the glacial ice rests on the seafloor.

“What the satellites are showing us is a glacier coming apart at the seams,” said Ted Scambos, a senior scientist at the University of Colorado. “Every few years a new area seems to be letting go and accelerating. Like taffy being stretched out, this glacier is being drawn into the ocean.”"

50
ASLR

I was posting it yesterday but had a phone call and forgot  8)

The trouble I see is that we have no idea that the CPDW warming that is now fully documented on WAIS is (most likely) not something that a paleo analog can provide insight into.  The simple fact is that we have tweaked the Global atmospheric circ patterns far far far outside of any paleo analog.

jai,

Trying to communicate our true collective level of climate change risk to the general public is such a difficult task that I suspect that collectively we will have crossed numerous irreversible climate tipping points well before there is enough consensus to take effective action to reduce coming climate consequences this century.  Nevertheless, I will make another feeble attempt at trying to convey both the immediacy and magnitude of our current climate change risk, using Turney et al. (2020) as a foil.  As the current rate of increase of radiative forcing is several thousands of times faster than that leading into the Eemian (LIG or MIS5e), it is clear that Turney et al (2020)'s paleo-data cannot be taken to mean that the Eemian can be used as a simulation of future conditions this century.  Nevertheless, these paleo-findings can be used to encourage CMIP7 modelers to better model the ice-climate feedback mechanisms that CMIP6 discounted including:

1.  Turney et al (2020)'s finding makes it clear that Edwards et al. (2019)'s assessment of the likelihood of a MICI-type of WAIS collapse during the Eemian are out of date.  Note that Turney et al (2020) makes it clear that the WAIS contributed to at least 3.8m of sea level rise during the Eemian, while the first attached image indicates that previously consensus climate scientists only assumed that the WAIS contributed 2.5 m to sea level rise during the Eemian.

2.  The findings from the January 2020 Icefin robot (part of the ITGC) prove that the modified CDW in the subglacial cavities along the Thwaites Glacier grounding line (see the second image) is already 2C above the freezing point of water in the cavities.  Thus, one does not need to wait for the Southern Ocean waters to warm by less than an average of 2C (as was the case during the Eemian); as for key glaciers like the PIG and Thwaites Glacier, we are already there.

3. The third attached image illustrates how rapidly the PIIS calving front has retreated in recent decades through February 11, 2020; which is much quicker than assumed by CMIP6.  Thus, we do not need to wait two hundred years (as was the case for the Eemian) for such key ice shelves to collapse.

4.  The fourth image illustrates how rapidly the Beaufort Gyre energy budget has changed in recent years.  Thus, we do not need to wait for GIS ice melt to slow the MOC as a release of relatively freshwater from the Beaufort Gyre into the North Atlantic, will likely serve this function in the coming decades.

See also:

Title: "Ancient Antarctic ice melt increased sea levels by 3+ meters—and it could happen again"

https://phys.org/news/2020-02-ancient-antarctic-ice-sea-metersand.html

Extract: "Using data gained from their fieldwork, the team ran model simulations to investigate how warming might affect the floating ice shelves. These shelves currently buttress the ice sheets and help slow the flow of ice off the continent.

The results suggest a 3.8m sea level rise during the first thousand years of a 2°C warmer ocean. Most of the modelled sea level rise occurred after the loss of the ice shelves, which collapsed within the first two hundred years of higher temperatures.

Notably, the researchers warn that this tipping point may be closer than we think.

"The Paris Climate Agreement commits to restricting global warming to 2°C, ideally 1.5°C, this century," says Professor Turney.

"Our findings show that we don't want to get close to 2°C warming.""

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