Greenland Ice Sensitivity

Discussion in 'Environment' started by Old Rocks, Jun 7, 2012.

  1. Old Rocks
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    Old Rocks Diamond Member

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    http://www.nature.com/nclimate/journal/v2/n6/full/nclimate1449.html


    Multistability and critical thresholds of the Greenland ice sheet
    Alexander Robinson,
    Reinhard Calov
    & Andrey Ganopolski
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    Corresponding author
    Nature Climate Change 2,429–432(2012)doi:10.1038/nclimate1449Received 16 February 2011 Accepted 13 February 2012 Published online 11 March 2012


    Recent studies have focused on the short-term contribution of the Greenland ice sheet to sea-level rise, yet little is known about its long-term stability. The present best estimate of the threshold in global temperature rise leading to complete melting of the ice sheet is 3.1 °C (1.9–5.1 °C, 95% confidence interval) above the preindustrial climate1, determined as the temperature for which the modelled surface mass balance of the present-day ice sheet turns negative. Here, using a fully coupled model, we show that this criterion systematically overestimates the temperature threshold and that the Greenland ice sheet is more sensitive to long-term climate change than previously thought. We estimate that the warming threshold leading to a monostable, essentially ice-free state is in the range of 0.8–3.2 °C, with a best estimate of 1.6 °C. By testing the ice sheet’s ability to regrow after partial mass loss, we find that at least one intermediate equilibrium state is possible, though for sufficiently high initial temperature anomalies, total loss of the ice sheet becomes irreversible. Crossing the threshold alone does not imply rapid melting (for temperatures near the threshold, complete melting takes tens of millennia). However, the timescale of melt depends strongly on the magnitude and duration of the temperature overshoot above this critical threshold
     
  2. IanC
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    IanC Gold Member

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    paywalled.

    the GIC isnt melting anytime soon. "no sense going off halfcocked". I think we need to observe for at least one 60 year cycle before we freak out
     
  3. Old Rocks
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    Old Rocks Diamond Member

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    LOL. So we do nothing and observe this '60 year cycle', and at the end of that cycle, the sea level is a meter or two higher, the CO2 level is at 700 ppm, CH4 at 6 ppm. Then we say, oops, should not have let that level go over 350 ppm?

    At some point in the not very distant future we will cross a threshold from which there is not going back. Of course, your life will have been lived, and who the hell cares anything about those that come after. Let the bastards do for themselves.
     
  4. Mad Scientist
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    Mad Scientist Deplorable Gold Supporting Member Supporting Member

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    [ame=http://www.youtube.com/watch?v=PA43ETEU1Vg]Lies - Thompson Twins (HQ Audio) - YouTube[/ame]
     
  5. TheGreatGatsby
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    TheGreatGatsby Gold Member

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    Greenland wishes there was global warming. Then they could grow grass and qualify to have a FIFA team.
     
  6. Old Rocks
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    Old Rocks Diamond Member

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    AGW Observer

    GREENLAND ICE SHEET, THE PRESENT: Watching that Greenland ice flow

    Ice flow in Greenland for the International Polar Year 2008–2009 – Rignot & Mouginot (2012)

    Abstract: “A digital representation of ice surface velocity is essential for a variety of glaciological, geologic and geophysical analyses and modeling. Here, we present a new, reference, comprehensive, high-resolution, digital mosaic of ice motion in Greenland assembled from satellite radar interferometry data acquired during the International Polar Year 2008 to 2009 by the Envisat Advanced Synthetic-Aperture Radar (ASAR), the Advanced Land Observation System (ALOS)’s Phase-Array L-band SAR (PALSAR) and the RADARSAT-1 SAR that covers 99% of the ice sheet in area. The best mapping performance is obtained using ALOS PALSAR data due to higher levels of temporal coherence at the L-band frequency; but C-band frequency SAR data are less affected by the ionosphere. The ice motion map reveals various flow regimes, ranging from patterned enhanced flow into a few large glaciers in the cold, low precipitation areas of north Greenland; to diffuse, enhanced flow into numerous, narrow, fast-moving glaciers in the warmer, high precipitation sectors of northwest and southeast Greenland. We find that the 100 fastest glaciers (v > 800 m/yr) drain 66% of the ice sheet in area, marine-terminating glaciers drain 88% of Greenland, and basal-sliding motion dominates internal deformation over more than 50% of the ice sheet. This view of ice sheet motion provides significant new constraints on ice flow modeling.”

    Citation: Rignot, E. and J. Mouginot (2012), Ice flow in Greenland for the International Polar Year 2008–2009, Geophys. Res. Lett., 39, L11501, doi:10.1029/2012GL051634.
     
  7. bobgnote
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    bobgnote BANNED

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    I wonder how fast that SLR will actually accelerate, when fresh data rolls in.

    Sat data, modern instrument highs, the whole works point to accelerating warming and SLR.
     
  8. Old Rocks
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    Old Rocks Diamond Member

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    AGW Observer

    Methane under glaciers and ice sheets – what happens when glaciers retreat?

    Methanogenic potential of Arctic and Antarctic subglacial environments with contrasting organic carbon sources – Stibal et al. (2012)

    Abstract: “Subglacial environments are largely anoxic, contain organic carbon (OC) overridden by glacier ice during periods of advance, and harbour active microbial communities. This creates favourable conditions for OC degradation via methanogenesis. It has been hypothesised that OC beneath ice sheets is converted to methane (CH4) and may be released to the atmosphere during retreat. However, there are limited data available to support this contention. Here, we present new data on the abundance, diversity and activity of methanogenic archaea and the amount and character of OC in subglacial sediments from Arctic and Antarctic glacial systems based on different substrate types. We employed long-term laboratory incubations to quantify the CH4 production potential in different subglacial settings. Significant numbers of methanogens (up to 7×104 cells g−1) were detected in the samples and clones of Methanomicrobiales and Methanosarcinales were identified in clone libraries. Long lag periods (up to >200 days) were observed before significant CH4 concentrations were measured. We report order of magnitude differences in rates of CH4 production (101-105 fmol g−1 d−1) in different subglacial sediments, reflecting contrasts in the origin of the sediment and the OC character. Hence, we predict that contrasting rates of CH4 production are likely to occur beneath glaciers and ice sheets that overran different types of substrate. We subsequently estimated the potential for CH4 production beneath the Laurentide/Inuitian/Cordilleran and Fennoscandian Ice Sheets during a typical 85 ka Quaternary glacial/interglacial cycle. CH4 production from lacustrine-derived OC is likely to be an order of magnitude higher (~6.3-27 Pg C) than that from overridden soils (~0.55-0.68 Pg C), possibly due to a difference in lability between lacustrine and soil OC. While representing a fraction of the entire OC pool (~418-610 Pg C), this finding highlights the importance of considering the character of different OC pools when calculating subglacial CH4 production.”
     
  9. IanC
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    IanC Gold Member

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    I love satellite measurements. they have revolutionized many areas of study.

    the difficulty with satellites is to get them properly calibrated and to figure out exactly what they are saying. temp readings have been around for 30 years and are probably pretty reliable. sea level readings have been around for 20 years and may be reliable but do we really know what they are telling us? GRACE gravity readings have been around for 10 years and are incredibly complex to analyze. calibrating GRACE involves making estimates and computer models and then seeing whether the data fit. I wouldnt bet my house on the accuracy of GRACE even if it gives precise results.

    let's step back to the satellite altimetry from the last 20 years-
    [​IMG]

    or this one which is more up-to-date

    [​IMG]

    pretty pictures, even if the second one has a horrifying amount of red in it. what are they saying?

    take a look for yourself. estimate the changes 20 years forward and 20 years in the past. does it make sense to you? will the SE Pacific continue to rise 10mm/yr while the NW Pacific drops?does that mean the SE Pac was lower before and the NW Pac higher? are the oceans sloshing around? is it some sort of standing wave? is it some sort of gravity effect from seismic activity? salinity difference? side effect of ocean temperature? what is it, how long will it last, what does it mean for predicting the future?

    do you think that the GRACE data have any peculiarities that might suggest spurious trends that may not really be there? especially when many people are focussed on finding just those kinds of trend, spurious or not.
     
  10. Old Rocks
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    Old Rocks Diamond Member

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