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Sunday, May 19, 2013

MUST READ: Jason Box: Greenland ice sheet mass budget theory with surface runoff, meltwater inflow, ice deformational flow and underwater glacial front melting [Phillips and Motyka Effects]

3 part study reconstructs Greenland ice sheet mass budget since 1840 and presents a theory connecting surface meltwater with ice deformational flow

by Jason Box, Melt Factor blog, May 16, 2013

It took 7 years to pull together a full ice sheet mass budget closure based on a fusion of observationally based records from coastal and inland weather station temperature readings; ice cores; and regional climate modeling.

Below are links to pre-prints. The papers’ abstracts capture key results but are constrained by 250-word limits. I emphasize Part III below. Parts I and II were foundational works with interesting aspects. Part III brings in necessary data from parts I and II.

Greenland ice sheet mass balance reconstruction. Part I: net snow accumulation (1600-2009)
Jason E. Box, Noel Cressie, David H. Bromwich, Ji-Hoon Jung, Michiel van den Broeke, J. H. van Angelen, Richard R. Forster, Clement Miège, Ellen Mosley-Thompson, Bo Vinther, Joseph R. McConnell. AbstractPDF (3210 KB)

Greenland ice sheet mass balance reconstruction. Part II: surface mass balance (1840-2010)
Jason E. Box. AbstractPDF (3322 KB)

Greenland ice sheet mass balance reconstruction. Part III: marine ice loss and total mass balance (1840-2010). Jason E. Box, William Colgan. AbstractPDF (2452 KB)

Paper III puts forth a theory* linking surface melting with ice flow dynamics. The two are by now too often examined in isolation. Our not so old science of glaciology, beginning in earnest in the late 1950s, can now begin unifying surface and ice dynamics processes at the ice sheet scale. In stark contrast to the messaging that the recent Nick et al. modeling study produced, we may expect plenty more sea level contribution from Greenland than current models predict. The misreporting of otherwise good science refers to ice flow to the sea as “melt.” Ice deformational flow is a distinct process from melt. Yet, melt and ice deformational flow are in fact intertwined processes. Self-reinforcing amplifying feedbacks outnumbering damping feedbacks by a large margin (Cuffey and Patterson, 2010, chapter 14) ensure that given a climate warming perturbation, a.k.a. the Hockey Stick, we’ll see a stronger response of ice to climate than is currently encoded by models. More on that later.

Because the peak statistical sensitivity between meltwater runoff and ice flow discharge emerges at the decadal scale (11-13 years), it seems that the ice softening due to more meltwater in-flow to the ice sheet -- the Phillips Effect, if you will -- is a central physical process behind a link between runoff and ice flow dynamics (Phillips et al. 2010, 2013).

Yet, on shorter time scales and resulting from a rising trend of surface melting, also to be considered is the effect of meltwater ejection at the underwater front of marine-terminating glaciers. The effect is to force a heat exchange between the glacier front and relatively warm sea water with the ice (Motyka et al. 2003), melting it. This is, if you will, the Motyka Effect. Underwater melting undercuts the glacier front, promoting ice berg calving and thus providing a direct and immediate link between surface runoff and ice flow. Calving reduces flow resistance, causing ice flow acceleration.  [Readers, these are two key elements to mass balance theory, with a combined effect I suspect is larger than most previously thought.]

January-February 2013: As I responded to 3 critical anonymous external reviewers and the sands of time were running low to make the 15 March, 2013 deadline for the IPCC AR5, in a bid to increase the likelihood of paper III’s acceptance, I brought on Liam Colgan. His fresh and sharp eyes would comb out any potential text and methodological snags from my major revision. While you may know Liam to be a frequent user of Monte Carlo methods, I already had that in this paper before thinking of his involvement. To his credit, Liam contributed the crevasse-widening aspect to the theory that builds coincidentally via Colgan et al. (2011)’s building on Pfeffer and Bretherton (1987). The Colgan Effect is thus the 3rd aspect of the unified theory this part III study puts forth.

As to the result of the mass budget reconstruction, it’s not surprising that Greenland ice sheet contribution to sea level has accelerated. After all, climate has emerged from the dim-sun Little Ice Age into the greenhouse gas-forced new post-industrial climate epoch, the Anthropocene. Greenland’s going. It’s a question of how fast. I’m happy to report that more to this story is in the works. So, stay tuned.

* A theory is a broad collection of knowledge based on hypotheses (emphasis plural) that have withstood skeptical inquiry and are accepted, unless otherwise proven, as Fact.
J. Climate Editor Anthony J Broccoli deserves thanks for, presumably, working extra in recognition of critical timeline.

Works Cited
  • Colgan, W., K. Steffen, W. McLamb, W. Abdalati, H. Rajaram, R. Motyka, T. Phillips, and R. Anderson, 2011a: An increase in crevasse extent, West Greenland: Hydrologic implications, Geophy. Res. Lett. 38, doi:10.1029/2011GL048491
  • Cuffey, K.M. and W.S.B. Paterson (2010). The Physics of Glaciers, Fourth Edition. Elsevier, 693 pp.
  • Motyka, R. J., L. Hunter, K. A. Echelmeyer, and C. Conner, 2003: Submarine melting at the terminus of a temperate tidewater glacier, LeConte Glacier, Alaska, U.S.A., Ann. Glaciol. 36, 57-65.
  • Nick, F.M., A. Vieli, M.L. Andersen, I. Joughin, A. Payne, T.L. Edwards, F. Pattyn and R.S.W. van de Wal, 2013, Future sea-level rise from Greenland’s main outlet glaciers in a warming climateNature 497, 235–238 (09 May 2013) doi:10.1038/nature12068
  • Pfeffer, W. and C. Bretherton, 1987: The effect of crevasses on the solar heating of a glacier surface, IAHS Publication 170, 191-205. 
  • Phillips, T., H. Rajaram, and K. Steffen, 2010: Cryohydrologic warming: A potential mechanism for rapid thermal response of ice sheetsGeophys. Res. Lett. 37, L20503, doi:10.1029/2010GL044397.
  • Phillips, T., W. Colgan, H. Rajaram and K. Steffen. Evaluation of cryo-hydrologic warming as an explanation for increased ice velocities near the equilibrium line, Southwest Greenland, J. Geophys. Res., 2012JF002584; submitted 7 July 2012, revised 31 December 2012.

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