Greenland meltdown

After a record-breaking 2010 in terms of surface melt area in Greenland Tedesco et al, 2011, numbers from 2011 have been eagerly awaited. Marco Tedseco and his group have now just reported their results. This is unrelated to other Greenland meltdown this week that occurred at the launch of the new Times Atlas.

The melt index anomaly is the number of days with detectable surface melt compared to the baseline period of 1979-2010. The higher the number, the more melt days there were. While this did not match the record 2010 levels, depending on the analysis 2011 was either the 3rd or 6th year in the rankings.

Analysis of the surface mass balance via regional modelling demonstrates that there has been an increasing imbalance between snowfall and runoff over recent years, leading to a lowering of ice elevation, even in the absence of dynamical ice effects (which are also occurring, mostly near the ice sheet edge).

Figure 2. Regional model-based estimates of snowfall (orange), surface melt and runoff (yellow) and the net accumulation (Gt/yr) (blue) since 1958.

The estimated 2010 or 2011 surface mass imbalance (~300 Gt/yr) is comparable to the GRACE estimates of the total mass loss (which includes ice loss via dynamic effects such as the speeding up of outlet glaciers) of 248 ± 43 Gt/yr for the years 2005-2009 Chen et al, 2011. Data for 2010 and 2011 will thus be interesting to see.

While the accelerating mass loss from Greenland is of course a concern, the large exaggeration of that loss rate by Harper Collins in the press release for the 2011 edition of the Times Atlas was of course completely wrong. The publishers have issued a ‘clarification’, which doesn’t really clarify much (Update (Sep 22, 2011): The clarification has been clarified from the original statement). As discussed on the CRYOLIST listserv, the confusion came most likely from a confusion in definitions of what is the permanent ice sheet, and what are glaciers, with the ‘glaciers’ being either dropped from the Atlas entirely or colored brown (instead of white) (No-one that I have seen has posted the legend from the Atlas that gives the definition of the various shadings, though in the 1994 edition I have, glaciers are (unsurprisingly) white, not brown).

The Times is still claiming that it stands by its maps (Update: The new clarification no longer makes this claim). This is quite silly, and presumably reflects the fact that it would be very expensive to reprint all the atlases that may have already been printed. In case this isn’t already clear, there is simply no measure — neither thickness nor areal extent — by which Greenland can be said to have lost 15 % of its ice. As a letter written by a group of scientists from the Scott Polar Research Institute says, “Recent satellite images of Greenland make it clear that there are in fact still numerous glaciers and permanent ice cover where the new Times Atlas shows ice-free conditions and the emergence of new lands”.

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References

  1. M. Tedesco, X. Fettweis, M.R. van den Broeke, R.S.W. van de Wal, C.J.P.P. Smeets, W.J. van de Berg, M.C. Serreze, and J.E. Box, "The role of albedo and accumulation in the 2010 melting record in Greenland", Environ. Res. Lett., vol. 6, pp. 014005, 2011. http://dx.doi.org/10.1088/1748-9326/6/1/014005
  2. J.L. Chen, C.R. Wilson, and B.D. Tapley, "Interannual variability of Greenland ice losses from satellite gravimetry", Journal of Geophysical Research, vol. 116, 2011. http://dx.doi.org/10.1029/2010JB007789