Icy contenders weigh in
Posted on 5 February 2013 by Jason Box
Guest post by Jason Box from Meltfactor.org.
Dahl-Jensen et al. (2013)[i] suggest that the Greenland ice sheet was more stable than previously thought[ii], enduring ~6k years of temperatures 5-8 C above the most recent 1000 years during the Eemian interglacial 118-126k years before present, its loss at the time contributing an estimated 2 m (6.6 ft) of global sea level compared to a total of 4-8 m (13-26 ft)[iii], implying Antarctica was and will become the dominant source of sea level change. Consequently, environmental journalist Andrew Revkin writes: “The dramatic surface melting [in Greenland], while important to track and understand has little policy significance.”
Given the non-trivial complexity of the issue and that Greenland has been contributing more than 2:1 that of Antarctica to global sea level in the recent 19 years (1992-2010)[iv], let’s not consider Greenland of neglible policy relevance until that ratio is 1:1 if not reversed, say, 0.5:1. Greenland, currently the leading contender with surface melting dominating its mass budget[v], the positive feedback with surface melting and ice reflectivity doubling Greenland’s surface melt since year 2000[vi]. Professor Richard Alley weighs in again: “We have high confidence that warming will shrink Greenland, by enough to matter a lot to coastal planners.”
That’s not to say that Antarctica couldn’t take over from Greenland the position of number 1 global sea level contributor in the foreseeable future. Nor should one be surprised if it did, given that Antarctica contains a factor of 10 more ice than Greenland[vii],[viii]. And it is probable that the planetary energy imbalance[ix] caused by elevated greenhouse gasses, expressed primarily through massive oceanic heat uptake[x], is delivering enough erosive power to destabilize the 3.3 m of sea level[xi] in the marine-based West Antarctic ice sheet. Yet, for today, consider also that climate change if increasing Antarctic precipitation a few percent can tip its mass balance toward the positive, lessening its sea level contribution[xii] even while its glaciers retreat.
Irrespective of sea level forcing, through its ice mass budget Greenland plays an important role to North Atlantic climate through ocean thermohaline circulation, even being suggested as the Achilles heel of the global climate system[xiii]. I wouldn’t tell our European friends Greenland’s hardly policy-relevant when climate change offers higher amplitude extremes in precipitation if not also temperature, as North Atlantic climate shifts in partial response to changes in neighboring Greenland.
Key differences between the modern Anthropocene and the Eemian interglacial suggest anthropogenic climate change may drive a different cryosphere response than during the Eemian…
Today, greenhouse gas concentrations are rising beyond 120% to 250% of peak Eemian values[xiv],[xv], driving today’s global warming and the aformentioned ocean heat content uptake that contrasts from the Eemian when warming was driven by northern latitudes receiving 30-50 Watts per sq. meter more solar energy, a more regionally-forced climate change. Anthropocene climate is forced an estimated 4/5 by by elevated greenhouse gasses and black carbon aerosols[xvi], the latter rising recently in significance after being more completely bounded[xvii]. Anthropogenic warming is clearly overwhelming the modern orbital cooling[xviii] and the decrease in solar output since the late 1970s[xix].
Because the Greenland ice sheet surface undergoes much more seasonal melting than the surface of the Antarctic ice sheet, in Greenland decanting a factor of 2 increase of meltwater runoff annually since 2000[xx], anthropogenic sources of light absorbing impurities provide a mechanism to multiply the cryospheric albedo feedback in ways presumably not occurring during the Eemian. Today, the combination of a.) land clearing by humans using fire, b.) industrial soot from fossil fuel combustion, and perhaps c.) larger fires the a legacy of fire suppression are in contrast to Eemian wildfire, that (as far as we know) did not include human factors. All me to here plug Dark Snow Project[xxi] that is currently soliciting donations to crowdfund a field and laboratory campaign designed to assess the impact of increasing wildfire on darkening the Greenland ice sheet.
Richard Alley: “While Antarctica is relatively unknown, Greenland is relatively known and therefore useful to guide policy even if the ice sheet becomes second most important to sea level, and to provide guidance to Antarctic colleagues [in surface melt studies]”
In the end, what matters to our concerns about the rate of sea level rise is the sum total volume change of all land ice. As long as glaciers and ice caps (GICs) (excluding the ice sheets) remain significant contenders (GICs lost mass at a rate of 148 ± 30 Gt per year from January 2003 to December 2010)[xxii], Antarctica lost 40% less during this period than GICs, and Greenland lost more than the two combined, we should stay focused on understanding the dynamics of all crysopheric systems in relation to the serious perturbation imposed by human activity. The Eemian has its own limits of utility in informing humanity of the trajectory we’re on.
[i] Eemian interglacial reconstructed from a Greenland folded ice core, D. Dahl-Jensen, M.R. Albert, A. Aldahan, N. Azuma, D. Balslev-Clausen, M. Baumgartner, A. Berggren, M. Bigler, T. Binder, T. Blunier, J.C. Bourgeois, E.J. Brook, S.L. Buchardt, C. Buizert, E. Capron, J. Chappellaz, J. Chung, H.B. Clausen, I. Cvijanovic, S.M. Davies, P. Ditlevsen, O. Eicher, H. Fischer, D.A. Fisher, L.G. Fleet, G. Gfeller, V. Gkinis, S. Gogineni, K. Goto-Azuma, A. Grinsted, H. Gudlaugsdottir, M. Guillevic, S.B. Hansen, M. Hansson, M. Hirabayashi, S. Hong, S.D. Hur, P. Huybrechts, C.S. Hvidberg, Y. Iizuka, T. Jenk, S.J. Johnsen, T.R. Jones, J. Jouzel, N.B. Karlsson, K. Kawamura, K. Keegan, E. Kettner, S. Kipfstuhl, H.A. Kjær, M. Koutnik, T. Kuramoto, P. Köhler, T. Laepple, A. Landais, P.L. Langen, L.B. Larsen, D. Leuenberger, M. Leuenberger, C. Leuschen, J. Li, V. Lipenkov, P. Martinerie, O.J. Maselli, V. Masson-Delmotte, J.R. McConnell, H. Miller, O. Mini, A. Miyamoto, M. Montagnat-Rentier, R. Mulvaney, R. Muscheler, A.J. Orsi, J. Paden, C. Panton, F. Pattyn, J. Petit, K. Pol, T. Popp, G. Possnert, F. Prié, M. Prokopiou, A. Quiquet, S.O. Rasmussen, D. Raynaud, J. Ren, C. Reutenauer, C. Ritz, T. Röckmann, J.L. Rosen, M. Rubino, O. Rybak, D. Samyn, C.J. Sapart, A. Schilt, A.M.Z. Schmidt, J. Schwander, S. Schüpbach, I. Seierstad, J.P. Severinghaus, S. Sheldon, S.B. Simonsen, J. Sjolte, A.M. Solgaard, T. Sowers, P. Sperlich, H.C. Steen-Larsen, K. Steffen, J.P. Steffensen, D. Steinhage, T.F. Stocker, C. Stowasser, A.S. Sturevik, W.T. Sturges, A. Sveinbjörnsdottir, A. Svensson, J. Tison, J. Uetake, P. Vallelonga, R.S.W. van de Wal, G. van der Wel, B.H. Vaughn, B. Vinther, E. Waddington, A. Wegner, I. Weikusat, J.W.C. White, F. Wilhelms, M. Winstrup, E. Witrant, E.W. Wolff, C. Xiao, and J. Zheng, Nature, vol. 493, pp. 489-494, 2013.
[ii] Substantial contribution to sea-level rise during the last interglacial from the Greenland ice sheet, Kurt M. Cuffey* & Shawn J. Marshall, Nature 404, 591-594 (6 April 2000) | doi:10.1038/35007053
[iii] Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C. & Oppenheimer, M. Probabilistic assessment of sea level during the last interglacial stage. Nature 462, 863–867 (2009). & Dutton, A. & Lambeck, K. Ice volume and sea level during the last interglacial. Science 337, 216–219 (2012).
[iv]A Reconciled Estimate of Ice-Sheet Mass Balance, Andrew Shepherd, Erik R. Ivins, Geruo A, Valentina R. Barletta, Mike J. Bentley,Srinivas Bettadpur, Kate H. Briggs, David H. Bromwich, René Forsberg, Natalia Galin,Martin Horwath, Stan Jacobs, Ian Joughin, Matt A. King, Jan T. M. Lenaerts, Jilu Li,Stefan R. M. Ligtenberg, Adrian Luckman, Scott B. Luthcke, Malcolm McMillan, Rakia Meister,Glenn Milne, Jeremie Mouginot, Alan Muir, Julien P. Nicolas, John Paden, Antony J. Payne,Hamish Pritchard, Eric Rignot, Helmut Rott, Louise Sandberg Sørensen, Ted A. Scambos,Bernd Scheuchl, Ernst J. O. Schrama, Ben Smith, Aud V. Sundal, Jan H. van Angelen,Willem J. van de Berg, Michiel R. van den Broeke, David G. Vaughan, Isabella Velicogna,John Wahr, Pippa L. Whitehouse, Duncan J. Wingham, Donghui Yi, Duncan Young, H. Jay Zwally, , Science, 338 (6111) 1183-1189, DOI: 10.1126/science.1228102,
[v] Partitioning recent Greenland mass loss, van den Broeke, M. R., J. Bamber, J. Ettema, E. Rignot, E. Schrama, W. J. van de Berg, E. van Meijgaard, I. Velicogna and B. Wouters, 2009: Science, 326, 984-986.
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[x] Global ocean heat content 1955–2008 in light of recently revealed instrumentation problems, Levitus, S., J. I. Antonov, T. P. Boyer, R. A. Locarnini, H. E. Garcia, and A. V. Mishonov, 2009:, Geophys. Res. Lett., 36, L07608, doi:10.1029/2008GL037155.
[xi] Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet, Jonathan L. Bamber, Riccardo E. M. Riva, Bert L. A. Vermeersen, Anne M. LeBrocq, Science 15 May 2009: Vol. 324 no. 5929 pp. 901-903 DOI: 10.1126/science.1169335
[xiv] Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change ,Solomon, S., D. Qin, M. Manning, Z. Chen, M,. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.), IPCC (Intergovernmental Panel on Climate Change), 2007. Cambridge University Press, Cambridge United Kingdom and New York, NY, USA, 996 pp.
[xv] Recent Greenhouse Gas Concentrations, Blasing, T.J., DOI: 10.3334/CDIAC/atg.032 http://cdiac.ornl.gov/pns/current_ghg.html
[xvi] Climate Change 2007: The Physical Science Basis, Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change ,Solomon, S., D. Qin, M. Manning, Z. Chen, M,. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.), IPCC (Intergovernmental Panel on Climate Change), 2007. Cambridge University Press, Cambridge United Kingdom and New York, NY, USA, 996 pp.
[xvii] Bounding the role of black carbon in the climate system: A scientific assessment, T. C. Bond, S. J. Doherty, D. W. Fahey, P. M. Forster, T. Berntsen, B. J. DeAngelo, M. G. Flanner, S. Ghan, B. Kärcher, D. Koch, S. Kinne, Y. Kondo, P. K. Quinn, M. C. Sarofim, M. G. Schultz, M. Schulz, C. Venkataraman, H. Zhang, S. Zhang, N. Bellouin, S. K. Guttikunda, P. K. Hopke, M. Z. Jacobson, J. W. Kaiser, Z. Klimont, U. Lohmann, J. P. Schwarz, D. Shindell, T. Storelvmo, S. G. Warren and C. S. Zender, Accepted manuscript online: 15 JAN 2013 07:30AM EST | DOI: 10.1002/jgrd.50171
[xx] after Estimating Greenland ice sheet surface mass balance contribution to future sea level rise using the regional atmospheric climate model MAR Fettweis, Xavier; Franco, Bruno; Tedesco, M.; van Angelen, J.; Lenaerts, J.; van den Broeke, M.; Gallée, H. in Cryosphere Discussions (The) (2012), 6