Hansen et al paper: 3+ meters SLR by 2100

[AbruptSLR]

With a hat tip to Richard Rathbone in the Antarctic folder:

"At an EGU press conference DeConto said this work implied tipping points for major sea level rise occur between 2 and 2.7C above pre-industrial.

http://client.cntv.at/egu2016/press-conference-8 (DeConto starts about 22:10) "

Also, SkS has updated their 2C Tracker through April 2016, and they indicate that the 12-month running average (baseline to pre-industrial or 1880 - 1909) has increased up to +1.246C (note that at the end of March 2016 this value was +1.210C.

[AbruptSLR]

I note that discussion in the linked thread on "Southern Ocean Cold Spots" (in the Antarctic folder) is particularly relevant to this thread:

http://forum.arctic-sea-ice.net/index.php/topic,1549.0.html

[AbruptSLR]

The linked (open access) reference focuses on the impacts of marine instability primarily of the Wilkes Basin (but also other basins as indicated by the attached images showing impacts on AABW formation due to different assumed marine glacier instability scenarios in different basins) on Southern Ocean dynamics.  This research supports the Hansen et al (2016) findings:

Phipps, S. J., Fogwill, C. J., and Turney, C. S. M.: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics, The Cryosphere Discuss., doi:10.5194/tc-2016-111, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-111/

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 ºC at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.


Caption for attached image: "Figure 3. Rate of AABW formation (Sv) in the control simulation (black), and in experiments WILKES (red), WEST (green) and EAST (blue). Thin lines indicate individual ensemble members; thick lines indicate the ensemble means. The values shown are 100-year running means. Vertical dashed lines indicate the years in which the freshwater hosing begins and ends."

[AbruptSLR]

The linked refer indicates that to ensure that cliff failures and hydrofracturing (calving) of marine glaciers do not occur that the GMST departure above pre-industrial could be as low as 1C, but is not higher than 3C (and at the EGU conference DeConto said that the most likely range was between 2 and 2.7C, assuming the current consensus climate sensitivity).

Robert DeConto and David Pollard (2016), "Commitments to future retreat of Antarctic and Greenland ice sheets",  EGU General Assembly, Geophysical Research Abstracts, Vol. 18, EGU2016-10930


http://meetingorganizer.copernicus.org/EGU2016/EGU2016-10930.pdf

Abstract: "The agreement reached at the COP21 United Nations Conference on Climate Change is aimed at limiting future increases in global mean temperature below 2ºC. Here, we use a continental ice sheet/shelf model with new treatments of meltwater-enhanced calving (hydrofracturing) and marine terminating ice-cliffs, to explore future commitments to sea-level rise given limits of global mean warming between 1 and 3ºC. In this case, ice-sheet model physics are calibrated against past ice-sheet response to temperatures warmer than today. The ice-sheet model is coupled to highly resolved atmosphere and ocean-model components, with imposed limits on future warming designed to mimic the idealized limits discussed at COP21. Both the short and long-term potential rise in global mean sea level are discussed in light of the range of allowances agreed in Paris. We also explore the sensitivity of Greenland and Antarctic ice sheets to plausible ranges of atmospheric versus ocean warming consistent with global mean temperatures between 1 and 3ºC; and the resulting long-term commitments to sea-level rise over the coming centuries and millennia."

Edit: See also Reply #550

[AbruptSLR]

The linked reference uses both field and modeled parameters to demonstrate that passive advection caused delayed surface warming south of the Antarctic Circumpolar Current, ACC, and enhanced warming to the north.  This combined circumpolar upwelling and equatorward transport has and will continue delaying AGW warming of the Southern Ocean (see attached image of the SAT departure distribution for the past 50-years).  Even though this mechanism is not associated with the freshening of Southern Ocean surface waters due to ice meltwater; nevertheless, the associate surface cooling of the Southern Ocean contributes to Hansen's ice-climate feedback mechanism:

Emily R. Newsom et al. (May 2016), "Southern Ocean warming delayed by circumpolar upwelling and equatorward transport", Nature Geoscience, DOI: 10.1038/ngeo2731

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2731.html

Abstract: "The Southern Ocean has shown little warming over recent decades, in stark contrast to the rapid warming observed in the Arctic. Along the northern flank of the Antarctic Circumpolar Current, however, the upper ocean has warmed substantially. Here we present analyses of oceanographic observations and general circulation model simulations showing that these patterns—of delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north—are fundamentally shaped by the Southern Ocean’s meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas-induced surface heat uptake is largely balanced by anomalous northward heat transport associated with the equatorward flow of surface waters; and heat is preferentially stored where surface waters are subducted to the north. Further, these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in ocean circulation are secondary. These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves. It is against this background of gradual warming that multidecadal Southern Ocean temperature trends must be understood."




Also see:
http://phys.org/news/2016-05-deep-antarctic-ocean-hasnt.html

Extract: "Observations and climate models show that the unique currents around Antarctica continually pull deep, centuries-old water up to the surface - seawater that last touched Earth's atmosphere before the machine age, and has never experienced fossil fuel-related climate change.

…
Gale-force westerly winds that constantly whip around Antarctica act to push surface water north, continually drawing up water from below. The Southern Ocean's water comes from such great depths, and from sources that are so distant, that it will take centuries before the water reaching the surface has experienced modern global warming.
Other places in the oceans, like the west coast of the Americas and the equator, draw seawater up from a few hundred meters depth, but that doesn't have the same effect.
"The Southern Ocean is unique because it's bringing water up from several thousand meters [as much as 2 miles]," Armour said. "It's really deep, old water that's coming up to the surface, all around the continent. You have a lot of water coming to the surface, and that water hasn't seen the atmosphere for hundreds of years."

[sidd]

" ... deep old water coming to the surface ..."

deep old warm water, or at least warmer than the pressure melting point at the keel of the icesheets.

The Kraken breathes.

[AbruptSLR]

The following series of linked references & an associated video address both field and modeling efforts to study the mid-Miocene dynamics of the Antarctic ice sheet (focused on the Ross Ice Shelf).  Considering that if we use a GWP100 for methane of 35 that we are already at a CO₂-e of 517ppm, these findings should be cause for alarm, considering the findings of Hansen et al 2016:

The first linked reference is:

Edward Gasson, Robert M. DeConto, David Pollard and Richard H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1516130113

http://www.pnas.org/content/113/13/3459

Significance: "Atmospheric concentrations of carbon dioxide are projected to exceed 500 ppm in the coming decades. It is likely that the last time such levels of atmospheric CO2 were reached was during the Miocene, for which there is geologic data for large-scale advance and retreat of the Antarctic ice sheet. Simulating Antarctic ice sheet retreat is something that ice sheet models have struggled to achieve because of a strong hysteresis effect. Here, a number of developments in our modeling approach mean that we are able to simulate large-scale variability of the Antarctic ice sheet for the first time. Our results are also consistent with a recently recovered sedimentological record from the Ross Sea presented in a companion article."

Abstract: "Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability."

The second linked reference is:

Richard Levy, David Harwood, Fabio Florindo, Francesca Sangiorgi, Robert Tripati, Hilmar von Eynatten, Edward Gasson, Gerhard Kuhn, Aradhna Tripati, Robert DeConto, Christopher Fielding, Brad Field, Nicholas Golledge, Robert McKay, Timothy Naish, Matthew Olney, David Pollard, Stefan Schouten, Franco Talarico, Sophie Warny, Veronica Willmott, Gary Acton, Kurt Panter, Timothy Paulsen, Marco Taviani & SMS Science Team (2016), "Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene", PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1516030113

http://www.pnas.org/content/113/13/3453

Significance: "New information from the ANDRILL-2A drill core and a complementary ice sheet modeling study show that polar climate and Antarctic ice sheet (AIS) margins were highly dynamic during the early to mid-Miocene. Changes in extent of the AIS inferred by these studies suggest that high southern latitudes were sensitive to relatively small changes in atmospheric CO2 (between 280 and 500 ppm). Importantly, reconstructions through intervals of peak warmth indicate that the AIS retreated beyond its terrestrial margin under atmospheric CO2 conditions that were similar to those projected for the coming centuries."

Abstract: "Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene."

http://phys.org/news/2016-02-antarctic-ice-sheet-vulnerable-co2.html


See also, the third link which leads to a 2015 video focused on the findings of the Andrill project to drill through the Ross Ice Shelf into the seafloor.  I suspect that these findings likely gave DeConto & Pollard incentive to produce their ground-breaking 2016 paper modeling the impact of cliff failures and hydrofracturing on marine glaciers (primarily in Antarctica):

NOVA's: Antarctica Meltdown - Secrets Beneath the Ice Antarctic Drilling Project


Also see:
http://phys.org/news/2016-02-antarctic-ice-sheet-vulnerable-co2.html

Caption for the first attached image: "The authors state that taken together, findings from companion papers in PNAS highlight that large changes in the Antarctic ice sheets may be possible at lower levels of atmospheric carbon dioxide than previous studies have shown. Credit: University of Massachusetts Amherst"

The second attached image comes from:

http://sites01.lsu.edu/faculty/swarny/wp-content/uploads/sites/30/2016/03/Levy-et-al.-2016-Antarctic-ice-sheet-sensitivity-to-atmospheric-CO2-variations-in-the-early-to-mid-Miocene.pdf

[TerryM]

ASLR
Much as I hate to bring it up. Does anyone really believe that we have one hundred years before we worry about the accumulative effects of methane?
As long as CH4 levels are increasing, it seems to me that we have to apply highest multiplier available. What we are measuring is not those 12.5 yr. old molecules that have been converted to CH2 and water, but viable CH4 molecules which have their full greenhouse potential when measured.
We could, at that time, say that over 20 years these will have a GWP of 86, or that over 100 years these molecules will only have a GWP of 35, but today, the day we do the measuring, isn't each measured bit of CH4 at it's full potency?
The 20 yr. and 100 yr. figures only should only be applied, I believe, when no further emissions are being added to the mix, and when forcasting their effect at some future point in time.
Terry

[AbruptSLR]

ASLR
Much as I hate to bring it up. Does anyone really believe that we have one hundred years before we worry about the accumulative effects of methane?
As long as CH4 levels are increasing, it seems to me that we have to apply highest multiplier available. What we are measuring is not those 12.5 yr. old molecules that have been converted to CH2 and water, but viable CH4 molecules which have their full greenhouse potential when measured.
We could, at that time, say that over 20 years these will have a GWP of 86, or that over 100 years these molecules will only have a GWP of 35, but today, the day we do the measuring, isn't each measured bit of CH4 at it's full potency?
The 20 yr. and 100 yr. figures only should only be applied, I believe, when no further emissions are being added to the mix, and when forcasting their effect at some future point in time.
Terry

Terry,

I agree with you and in the following NOAA data the value of CO2-e of 485ppm for 2015 was calculated using GWP100 of 25; so when I use a GWP100 of 35, I get a CO2-e of 518ppm:


http://esrl.noaa.gov/gmd/aggi/aggi.html


         Global Radiative Forcing, CO2-equivalent mixing ratio, and the AGGI 1979-2013
                         Global Radiative Forcing (W m-2)           CO2-eq
                                                                                     (ppm)        AGGI
Year     CO2     CH4    N2O   CFC12 CFC11 15-minor  Total Total   1990 = 1   %change

2013   1.882  0.496   0.184   0.167   0.059   0.114  2.901   478      1.340        2.0
2014   1.908  0.499   0.187   0.166   0.058   0.116  2.935   481      1.356        1.6
2015   1.939  0.504   0.190   0.165   0.058   0.118  2.974   485      1.374        1.8

CH4   ΔF = β(M½ - Mo½) - [f(M,No) - f(Mo,No)]   β = 0.036



As I am not sure whether CO2-e may be defined over a 100-year period, I hesitate to calculate a comparable value over a 20-year period; however, prorating the global radiative forcing values given above one could certainly do so very easily.

Best,
ASLR

Edit: I also note that the references on the mid-Miocene peak were more or less in equilibrium, while we are not in equilibrium (if for nothing else due to the ocean's thermal inertia) now, and what our pathway going forward will be depends not only on how successful you believe the Paris Pact will be, but also whether our models (say DeConto & Pollard 2016) include the correct parameters for: climate sensitivity, phases of multi-decadal cycles like the PDO, activation/acceleration of non-linear positive feedbacks, whether to paleo-parameter used to calibrate DeConto & Pollards cliff failures and hydrofracturing err on the side of least drama with regard to such considerations as erosion on bed topology, extreme weather events (e.g. atmospheric river events with rain) due to radiative forcing well over 10 times that during the PETM, etc. 

Finally, I provide the following linked reference on GTP and GWP for short-term forcers:

W. J. Collins, M. M. Fry, H. Yu, J. S. Fuglestvedt, D. T. Shindell, and J. J. West (2013), "Global and regional temperature-change potentials for near-term climate forcers", Atmos. Chem. Phys., 13, 2471–2485, doi:10.5194/acp-13-2471-2013


http://www.atmos-chem-phys.net/13/2471/2013/acp-13-2471-2013.pdf

[AbruptSLR]

Also, as noted in the "Human Stupidity" thread, the link leads to a April 2016 EGU General Assembly press conference 8 video clip roughly focused on the implications of the Paris Pact:


http://client.cntv.at/egu2016/press-conference-8

While the entire video is worth watching I provide the four attached screenshots from the video.  The first two images are from the second (MIT EGU) speaker with:
(a) The first image showing the impact of the faux hiatus on both effective ECS (top panel) and effective oceanic diffusion (bottom panel), and the blue lines showing PDF values using observations until 2000 and the black lines showing PDF values using observations until 2010 (including part of the faux hiatus).  Further the lower panel clearly indicates that the faux hiatus (in GMST departures) was due to more heat content temporarily being sequestered into the oceans during the faux hiatus (some of which heat is now being released from the oceans).  Thus I believe that the blue line climate parameter distributions (with observations to 2000) is more "Realistic" (and indicates a mean ECS value of about 4C) and the black line climate parameter distributions is more "Pollyannaish" (and is best ignored).
(b) The second image shows the implications of both MIT's more "Realistic" climate parameters (left panel, which is good to consider) and "Pollyannaish" climate parameters (right panel, which is best ignored) for different carbon emission scenarios described in the video but with the current Paris pledges indicated by the red lines for which the more "Realistic" climate parameters indicate that we will reach 2C by about 2050 and 2.7C by about 2060.
The last two images are from the DeConto & Pollard EGU presentation with:
(c) The third image showing different carbon concentration pathways with the upper left panel showing the RCP scenarios used by DeConto & Pollard (2016) for their SLR projections; and the bottom left panel showing three new pathways postulated by DeConto where we follow the RCP 8.5 50%CL scenario until we reach 2C (by about 2040), 2.7C (by about 2065) and 3.6C (by about 2090), respectively for the blue, green and red lines.
(d) The fourth image shows DeConto & Pollard's (2016 EGU) projections of Antarctic contributions to changes in global mean sea level, GMSL, by the 2C (blue line), 2.7C (green line) and 3.6C (red line) forcing scenarios.  I believe that DeConto & Pollard's 2C scenario is not achievable in the real world (as confirmed by the second attached MIT analysis), and that by 2100 the 2.7C and the 3.6C forcing scenario produce essentially the same amount of increase in GMSL.  Taken together with the more "Realistic" MIT analysis the DeConto & Pollard (2016 EGU) findings indicate it likely that the WAIS collapse will begin about 2050 following the current Paris Pact pledges (and also ignoring the increase in carbon emissions associated with increasing agricultural growth).

Also I note that the indicated DeConto & Pollard (2016 EGU) findings do not include Hansen et al (2016)'s ice-climate feedback, nor the current positive PDO phase, nor higher ECS values, nor the activation/acceleration of non-linear positive feedback mechanisms and thus errs on the side of least drama.

[Laurent]

How is it possible they are still speaking of staying under 2°c ? Planning for 2°C ! Am I stupid or they criminally underplay the problem, seeing the last Eemian only at 2°c we are on track for 10 to 20 meters. But 2°c is in sight for around 2030... and there is absolutely no way that the energy stored right now in the oceans (12 nuclear bomb/s) will go out out within the next 100 years only, that mean we are set for centuries at best.

[AbruptSLR]

How is it possible they are still speaking of staying under 2°c ? Planning for 2°C ! Am I stupid or they criminally underplay the problem, seeing the last Eemian only at 2°c we are on track for 10 to 20 meters. But 2°c is in sight for around 2030... and there is absolutely no way that the energy stored right now in the oceans (12 nuclear bomb/s) will go out out within the next 100 years only, that mean we are set for centuries at best.

From a state elite point of view, they are the law so their behavior cannot be criminal by their definition.  Furthermore, even though the Paris Pact says that they will try to stay well below 2C (note RCP2.5 would might have resulted in a 50% CL of 1.6C if it had been followed); they know full well that the public in developed countries are use to a factor of safety, so there will not be any political impact on elite who make a big effort and allow say a 2.7C increase; as the no one in the media or general public realizes that the WAIS will certainly begin to collapse in the 2040 to 2060 timeframe if we stay on (or above) RCP 8.5 50% CL for the next decade or two (when considering the energy already in the ocean, Arctic Amplification, the rate of aerosol emission reductions and the rate of increase in agriculturally related CH4 emissions).

Edit: I note that this past May was the warmest may on record so the chance that the GMST departure for 2016 will be close to 1.5C is steadily increasing.

[AbruptSLR]

The linked reference discusses both model and paleo findings to evaluate "Southern Ocean deep convection as a driver of Antarctic warming events".  As most of the pre-conditions for the first stage (see the attached image) of such an Antarctic warming event are currently happening today, it is possible that we may see more rapid warming of Antarctica with continued global warming than was previously (AR5) expected:

J. B. Pedro, T. Martin, E. J. Steig, M. Jochum, W. Park & S. O. Rasmussen (12 March 2016), "Southern Ocean deep convection as a driver of Antarctic warming events", Geophysical Research Letters, DOI: 10.1002/2016GL067861


http://onlinelibrary.wiley.com/doi/10.1002/2016GL067861/abstract;jsessionid=FA93F2EAE8AAFF6CE6C82E0AADC2FF5C.f02t03

Abstract: "Simulations with a free-running coupled climate model show that heat release associated with Southern Ocean deep convection variability can drive centennial-scale Antarctic temperature variations of up to 2.0°C. The mechanism involves three steps: Preconditioning: heat accumulates at depth in the Southern Ocean; Convection onset: wind and/or sea ice changes tip the buoyantly unstable system into the convective state; and Antarctic warming: fast sea ice-albedo feedbacks (on annual-decadal time scales) and slow Southern Ocean frontal and sea surface temperature adjustments to convective heat release (on multidecadal-century time scales) drive an increase in atmospheric heat and moisture transport toward Antarctica. We discuss the potential of this mechanism to help drive and amplify climate variability as observed in Antarctic ice core records."

See also:
https://ice2ice.b.uib.no/2016/03/29/pin-the-tail-on-the-donkey-southern-ocean-deep-convection-and-the-global-dansgaard-oeschger-variation/

Extract: "In our paper we show that heat loss from the convective zone in the Weddell Sea ultimately causes warming of up to 2°C on the Antarctic continent. Four factors are important (in almost equal measure) in driving the Antarctic warming: ocean to atmosphere heat flux from the convective zone; sea-ice loss and albedo feedback; southward migration of the ACC; and increased heat and moisture transport to Antarctica. The southward migration of the ACC, which takes around 50 years, was a surprise. We put this migration down to heat (i.e. buoyancy) loss from the convective zone dragging the outcropping isopycnals southward. A southward-shifted ACC can also be viewed as a southward shift in the sub-tropical front, which in turn means warmer sea surface temperatures in the mid-latitudes. In response to the mid-latitude warming the atmosphere fluxes more heat toward Antarctica."

[AbruptSLR]

The linked reference provides evidence that indeed the rate of GMSL rise has been accelerating recently.  Not only does this mean that sea level will be higher in the future, but also that Hansen et al (2016)'s ice-climate feedback is beginning:

P. J. Watson (16 June 2016), "A new perspective on global mean sea-level (GMSL) acceleration", Geophysical Research Letters, DOI: 10.1002/2016GL069653


http://onlinelibrary.wiley.com/doi/10.1002/2016GL069653/abstract

Abstract: "The vast body of contemporary climate change science is largely underpinned by the premise of a measured acceleration from anthropogenic forcings evident in key climate change proxies – greenhouse gas emissions, temperature and mean sea-level. By virtue, over recent years, the issue of whether or not there is a measurable acceleration in global mean sea-level has resulted in fierce, widespread professional, social and political debate. Attempts to measure acceleration in global mean sea-level (GMSL) have often used comparatively crude analysis techniques providing little temporal instruction on these key questions. This work proposes improved techniques to measure real-time velocity and acceleration based on five GMSL reconstructions spanning the time frame from 1807-2014 with substantially improved temporal resolution. Whilst this analysis highlights key differences between the respective reconstructions, there is now more robust, convincing evidence of recent acceleration in the trend of GMSL."

[jai mitchell]

How is it possible they are still speaking of staying under 2°c ? Planning for 2°C ! Am I stupid or they criminally underplay the problem, seeing the last Eemian only at 2°c we are on track for 10 to 20 meters. But 2°c is in sight for around 2030... and there is absolutely no way that the energy stored right now in the oceans (12 nuclear bomb/s) will go out out within the next 100 years only, that mean we are set for centuries at best.

It should be noted here that the Eemian maximum was associated with increased solar incident radiation in the northern hemisphere due to the Milankovitch cycles resulting in much higher northern hemisphere warming and lower southern hemisphere warming relative to the current GHG induced warming cycle.  Therefore, it should be expected that the current Anthropogenic-induced collapse of the WAIS would happen MORE quickly due to larger temperature increases in the southern latitudes proportional to the global average and compared to MIS-5.

Though this is not certain as the current WAIS melt is being induced by increased temperatures of the Cirumpolar Deep Water current, undercutting the grounding line.  My view is that the impact to CPD water in the current period is much greater than that experienced during the Eemian, primarily due to rapid shifts in wind circulations that are faster than the polar see-saw effect by orders of magnitude.

[AbruptSLR]

The linked Scribbler article indicates that global warming is flattening the atmospheric slope to the extent that Tropical Pacific atmospheric energy (from both the NH & the SH) is being directed to Western Antarctica via atmospheric gravity waves (see attached NOAA image of June 2016 SAT departures).  Clearly, this could accelerate the timeline for the collapse of the WAIS with continued anthropogenic global warming, which in-turn would accelerate the Hansen et al (2016) ice-climate positive feedback mechanism:

https://robertscribbler.com/2016/06/28/gigantic-gravity-waves-to-mix-winter-with-summer-wrecked-jet-stream-now-runs-from-pole-to-pole/#comments

Extract: "The upper level air flow that originated near the North Pole joins with a building Southern Hemisphere Jet Stream ridge pattern over the Southeast Pacific. Feeding into very strong upper level winds, it turns southward into a high amplitude wave that crosses the Horn of South America and slams itself, carrying with it a big pulse of extreme warmth, into the upper level airs over Western Antarctica.

…

All these observations combined point to a very serious concern that Polar warming is flattening the atmospheric slope from Equator to Pole to such an extent that an increasing violation of the Hemisphere to Hemisphere seasonal dividing line may be a new climate change related trend. And that’s a kind of weather weirding that we are not at all really prepared to deal with."

[AbruptSLR]

The linked reference discusses how Southern Ocean sea ice formation dominates shallow overturning in the Southern Ocean; which is part of Hansen et al (2016)'s ice-climate interaction mechanism:

Nathaniel L. Bindoff & William R. Hobbs (2016), "Southern ocean: Sea-ice-driven shallow overturning", Nature Geoscience, doi:10.1038/ngeo2766

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2766.html

Abstract: "Circumpolar upwelling circulation near the Antarctic has mainly been attributed to winds. An analysis of water-mass transformation shows that the dominant driver is instead the formation of sea ice near Antarctica and its melt offshore."

[AbruptSLR]

As a follow-on to my Reply #565, and in the interest of full disclosure Scribbler has updated his recent post on the influence of atmospheric gravity waves and cross-equator Jetstream activity (see extract below).  As with all climate change issue this topic is nuanced, but it will be interesting to see whether ACME projects such behavior when they publish the runs that they are beginning this month:

https://robertscribbler.com/2016/06/28/gigantic-gravity-waves-to-mix-winter-with-summer-wrecked-jet-stream-now-runs-from-pole-to-pole/

Extract: "UPDATE — A Necessary Statement on the Accuracy of the Above Article and Related Edits
The original article prompted a reaction from a few atmospheric scientists (including noted climate skeptic Roy Spencer) as shown here in this Washington Post opinion piece by Jason Samenow, weather editor for the Post. In consideration of the information shared in this piece, I have made a couple of corrections to the information concerning upper-level equatorial wind patterns.
However, the inference taken from my article was somewhat misconstrued. Stating that a global climate emergency due to loss of seasonality is currently upon us and is far-reaching. The message in my article is that the situation appears to be worsening and that this particular global climate crisis may be something that we’ll face over the coming years and decades. The article was intended to highlight the risk posed by weakening dividing lines between climate zones, an apparent observed increase in meridional upper air patterns, and in this case, an observation of the upper-level wind pattern that crossed from pole to pole.
As I mentioned in my article, large meridional upper-level wind flows and related extreme weather, along with what appears to be a growing trend toward a loss of seasonality is a very big deal. Apparently not everyone agrees with me on this point. Regardless, the concern over loss of seasonal variation due to human-caused climate change remains an issue. While there is no guarantee that risk and climate meta-analysis will result in 100 percent accuracy, it is a worthwhile process nonetheless to both identify potential risks under the rapidly changing climate states of our world and to ask the hard questions.
In closing, I must gently disagree with the assertions Mr. Samenow put forth in his opinion piece. On the contrary, it is the height of responsibility to highlight issues that so many others have tended to ignore or discount at great risk to our global civilization.
Paul Beckwith has made his own statements in response to the above article. His statements and conclusions are his own.
If you do not listen to me, then please listen to what the Earth System is telling us. It is very, very concerning. Warmest regards to all and best wishes."


See also:
https://www.washingtonpost.com/news/capital-weather-gang/wp/2016/06/30/claim-that-jet-stream-crossing-equator-is-climate-emergency-is-utter-nonsense/

[Darvince]

As a follow-on to my Reply #565, and in the interest of full disclosure Scribbler has updated his recent post on the influence of atmospheric gravity waves and cross-equator Jetstream activity (see extract below).  As with all climate change issue this topic is nuanced, but it will be interesting to see whether ACME projects such behavior when they publish the runs that they are beginning this month

I have been following his blog for around a month now, reading all of his new articles the day they are posted, and if they're concerning enough, sharing them with my friends. Simply put, I found this very concerning, but one of my friends, who is highly meteorologically inclined, pointed me in the direction that these occurrences were normal. And in fact, they seem to be. I went through large portions of the past three years on Nullschool, and found five such similar events since the beginning of April. Additionally, there was a great deal of hemispheric mixing from January to March of 2014, when a westerly wind pattern set up over the Niño 3 and Niño 1+2 region, and at its beginning and end, mixing massive amounts of upper-level air between the two hemispheres.

Although, of course, Nullschool only goes back to 2012, and I only searched back to 2014, so any conclusions that I make about their increased intensity or their increased frequency are likely to be null in the grander picture, as climate change does not usually take place on the scale of single years but rather over many years. So an increase in frequency may very well have happened, which does seem rather likely. Although something interesting about these events is that they only happen in the Western Hemisphere, between the IDL and Africa, with a tendency to happen most frequently over the Pacific Niño and Atlantic Niño areas.

I think the problem that people have with the article is its implication that this is the first event ever to occur in this area, which a simple search through Nullschool (which is exactly what I did) will prove that false, and show even stronger events only two months ago. In fact, that was my initial interpretation of the article, which is why my meteorologist friend was so skeptical about it and drove me to search for other events like it.

[AbruptSLR]

As a follow-on to my Reply #565, and in the interest of full disclosure Scribbler has updated his recent post on the influence of atmospheric gravity waves and cross-equator Jetstream activity (see extract below).  As with all climate change issue this topic is nuanced, but it will be interesting to see whether ACME projects such behavior when they publish the runs that they are beginning this month

I have been following his blog for around a month now, reading all of his new articles the day they are posted, and if they're concerning enough, sharing them with my friends. Simply put, I found this very concerning, but one of my friends, who is highly meteorologically inclined, pointed me in the direction that these occurrences were normal. And in fact, they seem to be. I went through large portions of the past three years on Nullschool, and found five such similar events since the beginning of April. Additionally, there was a great deal of hemispheric mixing from January to March of 2014, when a westerly wind pattern set up over the Niño 3 and Niño 1+2 region, and at its beginning and end, mixing massive amounts of upper-level air between the two hemispheres.

Although, of course, Nullschool only goes back to 2012, and I only searched back to 2014, so any conclusions that I make about their increased intensity or their increased frequency are likely to be null in the grander picture, as climate change does not usually take place on the scale of single years but rather over many years. So an increase in frequency may very well have happened, which does seem rather likely. Although something interesting about these events is that they only happen in the Western Hemisphere, between the IDL and Africa, with a tendency to happen most frequently over the Pacific Niño and Atlantic Niño areas.

I think the problem that people have with the article is its implication that this is the first event ever to occur in this area, which a simple search through Nullschool (which is exactly what I did) will prove that false, and show even stronger events only two months ago. In fact, that was my initial interpretation of the article, which is why my meteorologist friend was so skeptical about it and drove me to search for other events like it.

I think that Scribbler makes many good points; however, with regards to climate change induced changes to Jetstream patterns it is best to accumulate several years of data and to statistically show a change in the signal vs noise.  In this regards the patterns that you found in Nullschool for the past three years serve to support Scribbler's point rather than refute it (as climate change has been going on for more than three years).

[Laurent]

The point of mister Scribbler (I think) is that crossing of jet stream is one thing but also the wide stretch of air at that height ( ~10.000 m above sea level) nearly from the pole to the equator from north to south.
Among the 3 scientific mentioned in the Washington post it seems there is 2 deniers and one climate over optimist. That doesn’t change the fact that there isn't statistical evidences on both sides. Even thought the idea in mister Scribbler isn't statistically proved the point is to warn that there is something fishy going on, and if we haven't reacted to the threat yet, it should be time to act NOW !

[Shared Humanity]

I think it will take at least 7 decades of data before we can be certain. Lets see how things look in 2100. 

[Laurent]

https://en.wikipedia.org/wiki/Roy_Spencer_(scientist)
https://wattsupwiththat.com/author/ryanmaue/
http://cliffmass.blogspot.fr/2012/04/extreme-silliness.html

[Darvince]

Yes, let's wait several more decades to do anything in case we aren't all going to suffer horrifically as the food industry fails, coastal cities worldwide are flooded, and dangerous heat kills millions every year.

[jai mitchell]

this is a good graphic found in this article from February '15.  Regional sea level rise will vary depending on many different factors including regional subsidence (sinking land), wind pattern shifts, gulf stream changes, proximity to Antarctica and Greenland as well as other factors.

Here is Miami
http://www.wired.com/2015/02/rising-sea-levels-already-making-miamis-floods-worse/#slide-1

[bligh8]

Jia

That’s some graph, wow! I’ve read other articles where tide gauges have been observed in this area of the world showing close to these numbers.   It seems this area of the planet is quite unique, where you have both the Northern hemisphere and the Southern hemisphere trade winds blowing water into this area along with the North and South equatorial currents driving water into the same area.  Combined with the Gulf Stream it’s not difficult to understand why this is happening.

At the Western end of the equatorial Pacific, Ocean waters that are driven by the same mechanisms are allowed to flow West, North of Australia into the Arafura and Timor sea’s into the Southern Indian Ocean. The resulting tidal flow through this area is significant, North of Thursday Island and the Gulf of Carpentaria tidal flow exceeds 4 knots.

In the below graph one can see how the coastal stations in the Gulf of Mexico exceed the GMSL rise trend.
https://tidesandcurrents.noaa.gov/sltrends/tropicaltrends.htm

[AbruptSLR]

In the first linked article entitled: "Coastal Cities, Critical Infrastructure Unprepared to Face the Rising Tides of Climate Change", Scribbler discusses risks to coastal cities from SLR. In this article Scribbler cites the AVISO April 21 2016 SLR trend slope of 3.39 mm/yr as evidence that the rate of SLR is accelerating; however, this linear slope of the SLR trend line is averaged from 1993 to today; while if one considers only the Jason-2 satellite data the slope of the SLR trend line since 2008 is 4.49 mm/yr (see attached plot thru April 21 2016,see the second link), which is a clear indication of accelerating SLR contribution from marine glaciers as assumed by Hansen et al 2016:

https://robertscribbler.com/2016/07/08/coastal-cities-critical-infrastructure-unprepared-to-face-the-rising-tides-of-climate-change/

http://www.aviso.altimetry.fr/en/data/products/ocean-indicators-products/mean-sea-level/products-images.html
(click on Time-Series and Jason-2)

[AbruptSLR]

In just a week and a half the slope of the Jason 2 SLR trend line has increased from 4.49 mm/yr to 4.50 mm/yr for the period ending May 1 2016 (see attached plot):

[AbruptSLR]

The linked University of Colorado plot of detrended GMSL vs MEI thru June 30, 2016, indicates that the MEI is dropping much faster than GMSL.  This raises the prospect that the WAIS (and/or the GIS) contribution to sea level rise may be accelerating:

http://sealevel.colorado.edu/

[AbruptSLR]

The first linked article (see also the attached image) is entitled: "NASA: First Map Of Thawed Areas Under Greenland Ice Sheet", and this study is discussed by Scribbler in the second linked article.  The indicated higher levels of ice mass loss from the GIS should help to drive Hansen's ice-climate feedback mechanism:

http://www.nasa.gov/feature/goddard/2016/nasa-first-map-of-thawed-areas-under-greenland-ice-sheet

&

https://robertscribbler.com/2016/08/09/nasa-map-shows-large-portions-of-greenland-are-melting-from-below/

Extract: "During recent years, as human fossil-fuel emissions have forced the Earth to warm, observations of Greenland’s surface has indicated a rising rate of melt. What has been less well-observed is melt rates beneath the ice and near the ice base. This is important because the pooling of water beneath the great ice sheet can help speed its movement toward ocean outlets, along with accumulating heat at the base of the ice — which can also quicken the pace of overall melt.
A new scientific study headed by NASA researchers has developed one of the first comprehensive maps of melt along Greenland’s basal zone, where the ice contacts the ground surface. What they have found is that large portions of Greenland are melting from below:"

[AbruptSLR]

The linked reference discusses the Ice Sheet Model Intercomparison Project (ISMIP6) that will be used to support the CMIP6 calibration efforts.  Unfortunately, while ISMIP6 refers to DeConto & Pollard (2016), their models focus on the ice2sea effort, which does not include cliff failure nor hydrofracturing mechanisms. 

Nowicki, S. M. J., Payne, T., Larour, E., Seroussi, H., Goelzer, H., Lipscomb, W., Gregory, J., Abe-Ouchi, A., and Shepherd, A.: Ice Sheet Model Intercomparison Project (ISMIP6) contribution to CMIP6, Geosci. Model Dev. Discuss., doi:10.5194/gmd-2016-105, in review, 2016.

http://www.geosci-model-dev-discuss.net/gmd-2016-105/
http://www.geosci-model-dev-discuss.net/gmd-2016-105/gmd-2016-105.pdf

Abstract. Reducing the uncertainty in the past, present and future contribution of ice sheets to sea level change requires a coordinated effort between the climate and glaciology communities. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) is the primary activity within the Coupled Model Intercomparison Project – phase 6 (CMIP6) focusing on the Greenland and Antarctic Ice Sheets. In this paper, we describe the framework for ISMIP6 and its relationship to other activities within CMIP6. The ISMIP6 experimental design relies on CMIP6 climate models and includes, for the first time within CMIP, coupled ice sheet – climate models as well as standalone ice sheet models. To facilitate analysis of the multi-model ensemble and to generate a set of standard climate inputs for standalone ice sheet models, ISMIP6 defines a protocol for all variables related to ice sheets. ISMIP6 will provide a basis for investigating the feedbacks, impacts, and sea level changes associated with dynamic ice sheets and for quantifying the uncertainty in ice-sheet-sourced global sea level change.


See also:
http://www.climate-cryosphere.org/activities/targeted/ismip6
&
http://www.climate-cryosphere.org/media-gallery/1410-sophienowicki-ismip6-1?album_id=63

Therefore, I am concerned that the increasing international effort on geoengineering (see the following special issue on GeoMIP; which indicates that international governments realize that ECS is close to 4.5C and ESS like will manifest its full potential values faster than previously recognized) will not consider Hansen et al (2016)'s ice-climate feedback (which means that future generations will carry the burden of this risk without adequate warning):

The Geoengineering Model Intercomparison Project (GeoMIP): Simulations of solar radiation reduction methods (ACP/GMD inter-journal SI)
Editor(s): U. Lohmann, N. Vaughan, L. M. Russell, B. Kravitz, and H. Wang

http://www.atmos-chem-phys.net/special_issue376.html


Edit, for background on the CMIP6 calibration efforts, the GMD now has a special issue devoted to CMIP6:

Coupled Model Intercomparison Project Phase 6 (CMIP6) Experimental Design and Organization
Editor(s): GMD topical editors | Coordinator: V. Eyring

http://www.geosci-model-dev.net/special_issue590.html

[jai mitchell]

it seems clear to me that the GeoMIP project is vital to global interests and that we will be using this technology beginning sometime between 2020 and 2030 (if we haven't already).  There were some very stark similarities between the current GeoMIP model runs and "the blob" high pressure north east pacific region of 2013 and 2014. 

However, I must question, is the scale of the hansen sea ice coldwater lense as a mechanism for reduced longwave emissions going to account for a significant increase in warming?  It seems to me that the impact is quite low (as compared to, say, aerosol forcing or even changes in dimethyl sulfide production under a regime of increased ocean acidification)?  do you have a sense of scale over some time period in the way of Watts/M^2?

Love the reading of these posts btw very much valuable! 

[AbruptSLR]

However, I must question, is the scale of the hansen sea ice coldwater lense as a mechanism for reduced longwave emissions going to account for a significant increase in warming?  It seems to me that the impact is quite low (as compared to, say, aerosol forcing or even changes in dimethyl sulfide production under a regime of increased ocean acidification)?  do you have a sense of scale over some time period in the way of Watts/M^2?

As I have previously mentioned, the attached image is Figure 7 from Hansen et al (2016), with the following caption:

"Figure 7. (a) Surface air temperature (oC) relative to 1880–1920 for several scenarios. (b) Global energy imbalance (Wm-2/ for the same scenarios."

This figure shows both Hansen's planetary (Earth) energy imbalance (EEI), and Hansen's temperature change.  However, I believe that Hansen et al (2016) errs on the side of least drama, because his EEI is too low (I estimate by 1 W/sq m) and his climate sensitivity is probably too low because he does not consider that aerosol forcing/feedback is more negative than AR5 assumes, and that ECS may well be 4.6C.

[AbruptSLR]

The linked open access reference studies AABW production in the Cape Darnley Polyna, adjoining Prydz Bay in East Antarctica. The reference concludes that: "Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."  The reference implies that the AABW is the "canary in the coal mine" for Hansen et al (2016)'s slowing of the global thermohaline circulation, which should result in a positive ice-climate feedback that may increase the planetary energy imbalance as indicated by Figure 7 from Hansen et al (2016), shown in the immediate prior post:


G. D. Williams, L. Herraiz-Borreguero, F. Roquet, T. Tamura, K. I. Ohshima, Y. Fukamachi, A. D. Fraser, L. Gao, H. Chen, C. R. McMahon, R. Harcourt & M. Hindell (August 23 2016), "The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay", Nature Communications, Volume: 7, Article number: 12577, doi:10.1038/ncomms12577

http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html

Abstract: "A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate."

Extract: "There has been a lot of attention recently on the decadal-scale impact of icescape changes to AABW, resulting from major ice front calving events in polynyas regions, such as along Adélie Land after the calving of the Mertz Glacier. This study suggests the more ubiquitous process of enhanced ocean/ice shelf interaction could be a far greater long-term threat to AABW production. Given the growing number of reports of accelerating and irreversible mass loss from Antarctica’s major ice sheets linked to increased oceanic heat input, it is likely that Antarctica’s AABW production is already compromised and will decrease further into the future."

See also:
https://www.washingtonpost.com/news/energy-environment/wp/2016/08/23/how-elephant-seals-in-antarctica-are-helping-to-reveal-another-threat-caused-by-melting-ice/?utm_term=.42f9a2381634

Extract: "The new study “significantly improves our understanding of the details of bottom water production around Antarctica,” said Rahmstorf, who was not involved in the new research, by email. “Scientists have long feared that global warming will slow down this vital process of deep and bottom water production, both in the North Atlantic and in Antarctic waters. With too much global warming, a critical threshold could be crossed where this process grinds to a halt, with incalculable and potentially catastrophic consequences for marine life and climate.” 

Rahmstorf isn’t the only researcher concerned about this issue, either. It’s a key component of a recent paper led by former NASA scientist James Hansen, now at Columbia University’s Earth Institute. The paper outlines a dire scenario in which even 2 degrees Celsius of warming above pre-industrial levels could lead to “dangerous” global consequences.
One of the paper’s key points is that rapid melting of both the Antarctic and Greenland ice sheets may not only contribute to dramatic sea-level rise in the next century, but also affect the world’s oceans in profound ways — including freshening the water at the poles and contributing to a slowdown of the oceans’ overturning circulation.
The new paper “tends to confirm one of the principal phenomena that we were drawing attention to: the effect of freshwater from ice shelves reducing [Antarctic bottom water] formation,” Hansen told The Post by email. “We concluded that this process, slowing down on Antarctic bottom water formation, has already begun.”
…
“While this particular area may not be the hotspot for this kind of activity, the fact that we have all the main players makes it a very unique lab experiment to try to understand how it works,” Williams said. “It provides observational evidence which should renew efforts to look for this happening in more key areas of Antarctica where we do know there’s accelerating melt occurring and where bottom water production is important as well.”"

[Iceismylife]

I think it will take at least 7 decades of data before we can be certain. Lets see how things look in 2100. 

NOAA said maybe 2050 ~2060.  Something to think about.

[jai mitchell]

if I read that graph correctly, around 2100 with RCP 8.5 forcing and icemelt in both hemispheres we will have globally averaged temperatures drop to the pre-industrial levels?  with a top of atmospheric forcing between 2 and 3 watts per meter squared?  That doesn't seem credible to me, of course it would mean an aweful lot of ice melt and that would draw energy from the temp rise. . .

[AbruptSLR]

if I read that graph correctly, around 2100 with RCP 8.5 forcing and icemelt in both hemispheres we will have globally averaged temperatures drop to the pre-industrial levels?  with a top of atmospheric forcing between 2 and 3 watts per meter squared?  That doesn't seem credible to me, of course it would mean an aweful lot of ice melt and that would draw energy from the temp rise. . .

I would recommend focusing on the green curves that show the consequence of the WAIS collapsing; and realizing that for such a case the GMST anom is not the best measure of climate impacts as discussed by Hansen in "Storms of My Grandchildren: The Truth About the Coming Climate Catastrophe and Our Last Chance to Save Humanity".

[Shared Humanity]

Does GMST mean Global Mean surface Temperature? If so, surface temperature is simply not the best measure for global warming. It is simply the easiest to capture. That excess heat is going elsewhere, deep ocean etc.

[bbr2314]

if I read that graph correctly, around 2100 with RCP 8.5 forcing and icemelt in both hemispheres we will have globally averaged temperatures drop to the pre-industrial levels?  with a top of atmospheric forcing between 2 and 3 watts per meter squared?  That doesn't seem credible to me, of course it would mean an aweful lot of ice melt and that would draw energy from the temp rise. . .

I am beginning to suspect that a transition to ice-free Arctic creates a runaway increase in NHEM albedo via increased snowfall over northern regions. Of course it does not happen all at once, but as the Arctic opens through the summer and then later and later into the year, the effects occur progressively.

Eventually we will have a year where high snowfalls coincide with deep low anomalies over much of the North Atlantic (Hansen's projections of 20F+ drops would allow sea ice extending much further south from Greenland and East from Quebec, IMO). At that point the North Atlantic will begin freezing before the Arctic and the Appalachians and Alps will begin accumulating snowfall year-round. Despite the amount of pollution humans have put off, I suspect natural conditions and Greenland/Antarctica's built-in cooling capacity will soon push us wayyyyyyyy back into the other direction globally.

Despite what will probably be the worst year ever for sea ice we are over +1SD for snow cover now:

[AbruptSLR]

Does GMST mean Global Mean surface Temperature? If so, surface temperature is simply not the best measure for global warming. It is simply the easiest to capture. That excess heat is going elsewhere, deep ocean etc.

Yes it does, and I concur.

[AbruptSLR]

The linked reference indicates that the recent expansion of Antarctic sea ice extent is contributing to the recently observed salinity driven (surface freshening) stratification of the Southern Ocean; which by theory should be making a bigger contribution to Hansen et al (2016)'s positive ice-climate feedback mechanism, than previously thought:

F. Alexander Haumann, Nicolas Gruber, Matthias Münnich, Ivy Frenger & Stefan Kern (01 September 2016), "Sea-ice transport driving Southern Ocean salinity and its recent trends", Nature, Volume: 537, Pages: 89–92, doi:10.1038/nature19101

http://www.nature.com/nature/journal/v537/n7618/full/nature19101.html

Abstract: "Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes4, 5. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of −0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters."


See also:

https://www.washingtonpost.com/news/energy-environment/wp/2016/08/31/how-sea-ice-is-making-the-southern-ocean-less-salty-and-what-that-might-mean-for-the-rest-of-the-world/?utm_term=.0b003dd35a67

Extract: "Now, a new study, published Wednesday in Nature, suggests that sea ice may be one of the major culprits. Using satellite data and models, the authors have shown that Antarctic sea ice has been moving farther and farther away from the continental coastline by strengthening winds in recent years, pouring fresh water farther out into the ocean as it melts. 
…
A recent paper, led by Columbia professor and former NASA scientist James Hansen, suggested the stratification could help force the trapped warm water right up to the bases of marine-terminating glaciers on the Antarctic continent, melting them from the bottom up and leading to an even faster influx of fresh water into the ocean.
…
“Haumann and colleagues’ findings emphasize that Antarctic sea ice is not merely a passive indicator of climate change and variability, but also a driver of changes in the climate system,” wrote Maksym wrote in his comment. “…ea ice might have a bigger role than previously thought.”"

[Bruce Steele]

ASLR, Michael Huber and I had a couple posts over on another page that seem more relevant here. We are in a bit of disagreement as to the effects of Antarctic ice expansion and if I am reading your post above correctly Michael may be correct. The article says "The enhanced rejection of salt near the coast of Antarctica associated with stronger sea ice transport counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater." My only problem is that I believe the evidence of Antarctic bottom water slowdown counters both the article above and Michaels 
argument. Maybe you could intervene and explain better this articles ( and Michaels )claim or tell  me where the evidence of this counter action exists ?


Michaels comment
Re: The 2016 melting season
« Reply #4426 on: August 29, 2016, 06:28:33 AM »
Quote
: FishOutofWater  August 29, 2016, 01:24:57 AM
The one ocean that is cold is the southern ocean around Antarctica. And that's really bad news because the southern half of the thermohaline circulation is collapsing as basal melting is creating a fresh surface layer that inhibits deep convection. That means more melting from intermediate water there with less heat loss to the atmosphere while the ocean heat moving north increases.


The reason why the southern ocean is anomalously cool is due to intensification of the atmospheric circulation above Antarctica.  This wind blows the ice away from the continent and causes it to expand, and also cools the water.  This wind also brings up more water from below, which results in increased melting of the edges of ice sheets/glaciers (as the water while cold is warm compared to ice).  Finally the southern THC is driven by sea ice formation, and wind driven cooling/evaporation of water near the continents exposed as wind blows the ice away from the continent.  Therefore I would expect the impact of these changes to circulation would be to intensify the THC and not cause it to collapse.
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Bruce Steele
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Re: The 2016 melting season
« Reply #4427 on: August 29, 2016, 07:59:32 AM »
QuoteModifyRemove
Michael, If you might forgive me finding links and rather continue a few logical arguments please allow me.  Bottom water formation is very dependent on location , it  tends to form close the the Antarctic continent  where  ,like you say , cold offshore winds create frazil ice and squeeze out very cold saline water that sinks. Where that water sinks is important or bottom water would form in more areas than it currently does.  It needs to sink onto shelf bottom where it can travel down canyons to depth. If fresh water and cold push the ice edge too far offshore the frasil ice still forms but as the extruded saline water sinks it mixes with the fresh water lens near the surface and further down warm Circumpolar Current waters brought up via divergence. Small scale mixing processes and  eddies dilute the cold /very saline water with fresh and relativly warm water  as it has to sink through a greater distance  before it hits the bottom where it can travel down the canyons that currently carry it deeper. So the distance the saline water drops affects its ability to maintain its density. It isn't that it fails completely because polynyas still will on occasion form closer to shore in locations that favor bottom water formation like the one that some years form in the Weddell but too many formation sites won't work often enough and AABW will  continue to slow.

[AbruptSLR]

ASLR, ... Maybe you could intervene and explain better this articles ( and Michaels )claim or tell  me where the evidence of this counter action exists ?

I believe that the key point is that upwelling of deep warm water can occur along the northern edge of the sea ice, and that the increase stratification (due to the increased freshening of the surface water) along this northern edge is suppress some of this upwelling; which then delivers more of the warm deep water to the grounding line of marine glaciers (see the attached image & the extract below); which accelerated retreat of such grounding lines.  Hansen noted that all current ESMs (even his model) do not adequately suppress this upwelling along the northern edge of the sea ice, so all current models underestimate the ice-climate interaction.  Also, note that this effect occurs primarily in the Ross Sea Sector and less so in the Weddell Sea Sector.

Furthermore, the suppressed upwelling also suppresses venting of CO₂ from the Southern Ocean into the atmosphere, thus accelerating acidification of the ocean:

https://www.washingtonpost.com/news/energy-environment/wp/2016/08/31/how-sea-ice-is-making-the-southern-ocean-less-salty-and-what-that-might-mean-for-the-rest-of-the-world/?utm_term=.93da38feb2ec


Extract: "This translated into a steady freshening trend in the Southern Ocean, particularly in the Ross Sea. The researchers’ estimates of where and by how much the ocean had freshened closely aligned with on-site observations of salinity changes in the region. 
The researchers believe that a strengthening of the winds over the Ross Sea are responsible for the increased northward transport of the sea ice.

…
For one thing, the region right at the edge of the sea ice, where most of the melting and freshwater input is happening, also happens to be a part of the ocean where a key aspect of the ocean’s overturning occurs, in which deep water wells up from the bottom of the sea, carrying both carbon dioxide and a variety of nutrients with it. 

“When you add fresh water there, you actually suppress the upwelling of the deeper waters into the surface layer,” Haumann said. This is because the less dense fresh water has a tendency to get stuck on the surface of the ocean, trapping the warmer, deep water beneath it. It’s a process known as “stratification,” and it could cause big problems for Antarctica and possibly the rest of the world, according to some experts. "

[Bruce Steele]

"The enhanced rejection of salt near the coast of Antarctica associated with stronger sea ice transport counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater."

ASLR, It is this quote that bothers me. I am in agreement with your points and I tried to say the same thing ( although never as clearly as I would like ) in my last post.  The quote above implies IMO that somehow enhanced saline extrusion is counteracting the effects of stratification . I just don't think evidence supports the claims quoted above.

[AbruptSLR]

"The enhanced rejection of salt near the coast of Antarctica associated with stronger sea ice transport counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater."

ASLR, It is this quote that bothers me. I am in agreement with your points and I tried to say the same thing ( although never as clearly as I would like ) in my last post.  The quote above implies IMO that somehow enhanced saline extrusion is counteracting the effects of stratification . I just don't think evidence supports the claims quoted above.

Bruce,

I would say that the increase in Antarctic sea ice is predominately occurring near the Ross Sea Sector, and it is true that the AABW production in this sector is not decreasing as fast as in the Weddell Sea Sector.  Therefore, the statement that you refer to can be true and also, Hansen's ice-climate feedback mechanism could becoming increasingly active.  Furthermore, essentially all climate models project that within a few decades the Antarctic sea ice extent will begin to decrease; at which point the freshening from sea ice will become less prominent and likely the freshening from marine glacial melt will become increasingly prominent.

This is a complex (wicked) problems, and it can be difficult to fully explain in simple terms.

Best,
ASLR

[AbruptSLR]

While mentioned elsewhere in the forum, the linked reference indicates that the Greenland Ice Sheet (GrIS) is losing ice mass at a 7% faster rate than has been previously assumed.  Obviously, this increases the risk that Hansen et al (2016) concerns may be valid:

Shfaqat A. Khan, et al (2016), "Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet" Science Advances, Vol. 2, no. 9, e1600931, DOI: 10.1126/sciadv.1600931

http://advances.sciencemag.org/content/2/9/e1600931

Abstract: "Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year."

[Buddy]

While mentioned elsewhere in the forum, the linked reference indicates that the Greenland Ice Sheet (GrIS) is losing ice mass at a 7% faster rate than has been previously assumed.  Obviously, this increases the risk that Hansen et al (2016) concerns may be valid:

Just another....in a growing list of items, where climate scientists may have been "too conservative".

The past 3 years....and the next 5 years.....may blow some of those assumptions out of the water.

Between surface temps.....and ocean levels......we should know a LOT more in 5 years.  And it likely will NOT be good news as feedbacks continue to rise.

[sidd]

1) antarctic bottom water (AABW) comes from freezing ice in wind driven polynas close to the coast (south of the main ice pack) in three(ish) locations. Suppression of AABW formation has so far been observed at  the Weddell location.

2)freshwater lens comes from land grounded glacial melt and sea ice melt at the northern edge of sea ice

both 1) and 2) are consistent with quoted literature. Keep in mind

3) thermohaline circulation is also suppressed by freshwater up north ... greenland cold spot ...

sidd

[Sleepy]

Latest Saral SLR measurements appears unaffected by the the latest El Nino.

[AbruptSLR]

In Replies #576 & #577 I showed that in just under two weeks the slope of the Jason 2 SLR trend line increased from 4.49 mm/yr to 4.50 mm/yr for the period ending May 1 2016; while the attached plot shows that through July 10 2016 the slope of the Jason 2 SLR trend line increased up to +4.54mm/yr.