Glacier Retreat

This document accompanies the paper by Thompson et al. published November 3, 2009 in PNAS.  The supplemental text on the PNAS web site indicated that additional information would be provided here. This addendum includes (1) a detailed discussion of each domain and its ice entities present in the different aerial photographs and (2) additional examples of the interpretative discrepancies between the areal coverage determinations by Cullen et al. (2003) and Thompson et al. (2002). Addendum

The discussion below reflects the new information published in our 2009 PNAS paper (10.1073/pnas.0909029106).

An aerial photograph taken on October 15, 2007 (below) was used to produce a current, detailed map of ice cover extent on the summit plateau. The compilation of six maps (lower right) of ice extent since 1912, the first four of which were assembled by Hastenrath and Greischar (J. Glaciology, 43, 1997), demonstrates a sustained loss of ice on Kilimanjaro over the last century. The three remaining ice fields on the plateau and on the slopes are both shrinking laterally and rapidly thinning.  Summit ice cover (areal extent) decreased ~1% per year from 1912 to 1953 and ~2.5% per year from 1989 to 2007.  Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone.  From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was ~1.9 and 5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of ~3.6% and 24%, respectively.  Furtwängler Glacier thinned ~50% at the drill site between 2000 and 2009.  Ice volume changes (2000 - 2007) calculated for two ice fields reveal that nearly-equivalent ice volumes are now being lost to thinning and lateral shrinking.

Two aerial photos, 2000 and 2007, from above Mt. Kilimanjaro

PNAS paper 2009



The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration.  Kilimanjaro’s ice loss is contemporaneous with widespread glacier retreat in mid- to low-latitudes.  The NIF has persisted at least 11,700 years and survived a widespread drought ~4,200 years ago that lasted ~300 years.  We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro’s ice fields is unique within an 11,700 year perspective.  If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.