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The Mass Balance of the Karakoram Glaciers
Reference
Gardelle, J., Berthier, E. and Arnaud, Y. 2012. Slight mass gain of Karakoram glaciers in the early twenty-first century. Nature Geoscience 5: 322-325.

Background
In a world where glaciers are believed to be shrinking almost everywhere, the authors note that at the west end of the Himalayan arc, where China, India and Pakistan meet, "an anomalous gain of mass has been suggested for the Karakoram glaciers," citing the findings of Hewitt (2005) - who first wrote about the "Karakoram anomaly" - as well as the subsequent studies of Zemp et al. (2009), Cogley (2011) and Scherler et al. (2011).

What was done
In an attempt to further explore the subject, which Gardelle et al. describe as suffering "from a severe lack of observations," the three researchers calculated the regional mass balance of glaciers in the central Karakoram between 1999 and 2008, based on the differences they found between two sets of digital elevation data, one generated from the February 2000 Shuttle Radar Topographic Mission (SRTM) and the other from the December 2008 optical stereo imagery acquired by the Satellite Pour l'Observation de la Terre (SPOT5) program.

What was learned
In the words of the three French scientists, "we find a highly heterogeneous spatial pattern of changes in glacier elevation, which shows that ice thinning and ablation at high rates can occur on debris-covered glacier tongues," with the result that "the regional mass balance is just positive at +0.11 ± 0.22 m/year water equivalent." And in further support of this finding, they write that "recent glacier expansion (Hewitt, 2005) and speed-up over the region (Quincey et al., 2009; Heid and Kaab, 2011) tally with the gain of mass calculated in this study." In addition, they note that "more than 50% of Karakoram glaciers were advancing or stable between 2000 and 2008 (Scherler et al., 2011)," and that "Fuita and Nuimura (2011) reported a descending trend in the modeled equilibrium-line altitude in the Karakoram during 1976-1995." And to these findings they add that "Fowler and Archer (2006) reported an increase in winter precipitation since 1961, which is a potential source for greater accumulation in the upper parts of glaciers," citing the work of Hewitt (2005) and Quincey et al. (2009, 2011), while noting that "between 1961 and 2000, mean summer temperature declined at all climate stations (Fowler and Archer, 2006), probably resulting in a decreasing glacier melt."

What it means
Gardelle et al. conclude by stating that their measurements "confirm an anomalous mass balance in the Karakoram region and indicate that the contribution of Karakoram glaciers to sea-level rise was -0.01 mm/year for the period from 1999 to 2008," or "0.05 mm/year lower than suggested before." As for how this complete change of direction in the perceived mass balance history of the Karakoram glaciers could have occurred, Cogley (2012) writes - in a contemporaneous commentary on the work of Gardelle et al. - that "by a quirk of the atmospheric general circulation that is not understood, more snow is being delivered to the mountain range at present, and less heat," which leads one to wonder if there might well be a whole lot of things that are "not understood" about earth's climate ... by even the most brilliant of the world's scientists.

References
Cogley, J.G. 2011. Present and future states of Himalaya and Karakoram glaciers. Annals of Glaciology 52: 69-73.

Cogley, G. 2012. No ice lost in the Karakoram. Nature Geoscience 5: 305-306.

Fowler, H.J. and Archer, D.R. 2006. Conflicting signals of climatic change in the Upper Indus Basin. Journal of Climate 19: 4276-4293.

Fujita, K. and Nuimura, T. 2011. Spatially heterogeneous wastage of Himalayan glaciers. Proceedings of the National Academy of Sciences USA 108: 14,011-14,014.

Heid, T. and Kaab, K. 2011. Worldwide widespread decadal-scale decrease of glaciers speed revealed using repeat optical satellite images. Cryosphere Discussions 5: 3025-3051.

Hewitt, K. 2005. The Karakoram anomaly? Glacier expansion and the 'elevation effect,' Karakoram Himalaya. Mountain Research and Development 25: 332-340.

Quincey, D.J., Braun,M., Glasser, N.F., Bishop, M. P., Hewitt, K. and Luckman, A. 2011. Karakoram glacier surge dynamics. Geophysical Research Letters 38: 10.1029/2011GL049004.

Quincey, D.J., Copland, L., Mayer, C., Bishop, M.P., Luckman, A. M. and Belò, M. 2009. Ice velocity and climate variations for Baltoro Glacier, Pakistan. Journal of Glaciology 55: 1061-1071.

Scherler, D., Bookhagen, B. and Strecker, M.R. 2011. Spatially variable response of Himalayan glaciers to climate change affected by debris cover. Nature Geoscience 4: 156-159.

Zemp, M., Hoelzle, M. and Haeberli, W. 2009. Six decades of glacier mass-balance observations: A review of the worldwide monitoring network. Annals of Glaciology 50: 101-111.

Reviewed 26 September 2012