Graph of the Day: Total Ice Area on Kilimanjaro, 1912-2007

Outlines of the Kibo (Kilimanjaro) ice fields 1912, 1953, 1976, and 1989 (1), 2000 (2) and updated with Ohio State University aerial photographs taken October 15, 2007. (Inset) Areal extent (km2) versus time with a linear fit (R2 = 0.98). An ice cover map was produced by using the 2007 photos and combined with four previous maps by Hastenrath and Greischar (1) and our map for 2000 to provide a 95-year observational record since 1912 (Fig. 2). Maps were produced for all three sets of our photographs but only those for 2000 and 2007 are shown here (see Fig. S1 for 2006). Contours were generated from digital elevation models of the ice and the surrounding terrain, and maps with outlines of the ice bodies were produced (see Materials and Methods). The areas of the individual ice bodies were computed and aggregated into discrete domains (Fig. S2 and Table S1) as defined by Hastenrath and Greischar (1). The 2000 and 2007 results for the four domains (A, D, E, and F) and the total area are given in Table 1, and the areas of all of the individual ice bodies in 2000, 2006, and 2007 are given in Table S1. The areal extent of Kilimanjaro’s ice cover has decreased85% from 12.06 km2 in 1912 to 1.85 km2 in 2007. Linear extrapolation of ice extent to the time axis [1912 to 2007, R2 = 0.98; Fig. 2 Inset] suggests that the glaciers will disappear from the summit of Kibo in 2022. In view of the likely (but unknown) errors in the determinations of the ice area at each epoch, a straight-line fit to all available values seems justified. However, an argument can be made for a ‘‘better’’ fit to the data by fitting two straight lines to account for the apparent change in rate of area decrease beginning in 1976. Slightly better correlation coefficients are obtained (R2 = 0.998 for 1912 to 1976 and 0.994 for 1976 to 2007) and the predicted disappearance of the ice occurs in 2033. In either case there is a strong likelihood that the ice fields will disappear within a decade or two if current conditions persist.

L. G. Thompsona, H. H. Brechera, E. Mosley-Thompsona, D. R. Hardyd, and B. G. Marka, Glacier loss on Kilimanjaro continues unabated [pdf], Proceedings of the National Academy of Sciences, November 2, 2009, doi:10.1073/pnas.0906029106