Please support this Forum and Neven's Blog

Author Topic: Hansen et al paper: 3+ meters SLR by 2100  (Read 152727 times)

sidd

  • ASIF Upper Class
  • Posts: 1392
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #650 on: April 26, 2017, 06:46:00 PM »
Hansen not so farfetched: 3m SLR by 2100 doi: 10.1088/1748-9326/aa6512

I see Drijfhout is an author. They put in DeConto-Polard model for Antarctica and a couple other tweaks. Open access. Read all about it

sidd

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #651 on: May 05, 2017, 09:53:51 AM »
The linked reference indicates that freshwater hosing events in the North Atlantic can result in warming of the Nordic Seas (see the attached image); which can accelerate Arctic Amplification:

Mélanie Wary et. al. 92017), "Regional seesaw between North Atlantic and Nordic Seas
during the last glacial abrupt climate events", Clim. Past Discuss., doi:10.5194/cp-2017-14

http://www.clim-past-discuss.net/cp-2017-14/cp-2017-14.pdf

Abstract. Dansgaard-Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle.  Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48-30 ka BP interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional paleorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit.
« Last Edit: May 05, 2017, 05:17:00 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #652 on: May 05, 2017, 06:42:10 PM »
The linked video entitled: "Climate Change: Hansen Paper: Multimeter Sea Level Rise by 2075?", provides an easily accessible overview of the key points of Hansen et al (2016):

https://www.youtube.com/watch?v=tHV2j8Hypes
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #653 on: July 10, 2017, 04:31:17 AM »
The linked reference indicates that much of the weaker polar amplification of Antarctica as compared to the Arctic is due to its (high) surface elevation.  This makes me wonder how much the Antarctic polar amplification will increase if/when the WAIS collapses:

Salzmann, M. (2017) The polar amplification asymmetry: Role of antarctic surface height, Earth Systems Dynamics,doi:10.5194/esd-8-323-2017

http://www.earth-syst-dynam.net/8/323/2017/esd-8-323-2017.pdf

Abstract: “Previous studies have attributed an overall weaker (or slower) polar amplification in Antarctica compared to the Arctic to a weaker Antarctic surface albedo feedback and also to more efficient ocean heat uptake in the Southern Ocean in combination with Antarctic ozone depletion. Here, the role of the Antarctic surface height for meridional heat transport and local radiative feedbacks, including the surface albedo feedback, was investigated based on CO2-doubling experiments in a low-resolution coupled climate model. When Antarctica was assumed to be flat, the north–south asymmetry of the zonal mean top of the atmosphere radiation budget was notably reduced… between 24 and 80%… of the polar amplification asymmetry was explained by the difference in surface height, but… might to some extent also depend on model uncertainties.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #654 on: July 18, 2017, 07:49:00 PM »
The linked reference finds that: "The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events.":

Julien P. Nicolas et. al. (2017, "January 2016 extensive summer melt in West Antarctica favoured by strong El Niño", Nature Communications 8, Article number: 15799, doi:10.1038/ncomms15799

http://www.nature.com/articles/ncomms15799

Abstract: "Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #655 on: July 31, 2017, 02:02:57 AM »
The linked reference discusses how decreasing cloud cover over the Greenland Ice Sheet is contributing to accelerated ice mass loss; which could progressively feed into Hansen's ice-climate feedback:

Stefan Hofer, Andrew J. Tedstone, Xavier Fettweis & Jonathan L. Bamber (28 June 2017), “Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet”, Science Advances, Vol. 3, no. 6, e1700584, DOI: 10.1126/sciadv.1700584

http://advances.sciencemag.org/content/3/6/e1700584

Abstract: “The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #656 on: July 31, 2017, 03:14:31 AM »
The linked reference indicates that new decadal-scale model projections for the Southern Ocean indicate that some component of the recent high levels of sea ice extents has been associated with weakening of the AABW cell in the Weddell Sea.  To me this weakening of this AABW cell supports Hansen's ice-climate feedback mechanism:

Zhang, Liping, Thomas L Delworth, Xiaosong Yang, Richard G Gudgel, Liwei Jia, Gabriel A Vecchi, and Fanrong Zeng, July 2017: Estimating decadal predictability for the Southern Ocean using the GFDL CM2.1 model. Journal of Climate, 30(14), DOI:10.1175/JCLI-D-16-0840.1

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0840.1

Abstract: “This study explores the potential predictability of the Southern Ocean (SO) climate on decadal time scales as represented in the GFDL CM2.1 model using prognostic methods. Perfect model predictability experiments are conducted starting from 10 different initial states, showing potentially predictable variations of Antarctic bottom water (AABW) formation rates on time scales as long as 20 years. The associated Weddell Sea (WS) subsurface temperatures and Antarctic sea ice have potential predictability comparable to that of the AABW cell. The predictability of sea surface temperature (SST) variations over the WS and the SO is somewhat smaller, with predictable scales out to a decade. This reduced predictability is likely associated with stronger damping from air–sea interaction. As a complement to this perfect predictability study, the authors also make hindcasts of SO decadal variability using the GFDL CM2.1 decadal prediction system. Significant predictive skill for SO SST on multiyear time scales is found in the hindcast system. The success of the hindcasts, especially in reproducing observed surface cooling trends, is largely due to initializing the state of the AABW cell. A weak state of the AABW cell leads to cooler surface conditions and more extensive sea ice. Although there are considerable uncertainties regarding the observational data used to initialize the hindcasts, the consistency between the perfect model experiments and the decadal hindcasts at least gives some indication as to where and to what extent skillful decadal SO forecasts might be possible.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 12759
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #657 on: August 01, 2017, 11:48:24 PM »
The linked reference discusses state of the art surface temperature at the West Antarctic Divide for the past ~ 40,000 years (see image bottom panel).  Findings indicate that current climate models are challenged to hind cast the observed findings and that models with low climate sensitivities can be eliminated from consideration.  Furthermore, they find that an Antarctic Amplification of 2 to 3 time GMSTA.  These findings do not bode well for the stability of the WAIS with continued global warming:

Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, and Jeffrey P. Severinghaus (2016), "Deglacial temperature history of West Antarctica", PNAS, vol. 113 no. 50, 14249–14254, doi: 10.1073/pnas.1609132113

http://www.pnas.org/content/113/50/14249

Abstract: "The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8 ∘  11.3±1.8∘ C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted."

Extract: "Of greatest immediate interest, however, is our demonstration that the global deglacial temperature change was amplified by a factor of 2–3 in the Antarctic, that Antarctic warming was largely achieved by 15 ka in coherence with records from Southern Hemisphere mountain ranges, and that climate models of the deglaciation perform well on average, but that the ones with lowest sensitivity can be discounted. The early warming of the Southern Hemisphere, which our study helps to quantify, arose from combined effects of reduced northward oceanic heat transport, increased insolation, and increasing atmospheric CO2. Quantitative simulation of this phenomenon could provide an illuminating challenge for model studies."
« Last Edit: August 02, 2017, 12:04:35 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson