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The Ice Fields of Kilimanjaro: Why Did They Recede So Steadily for So Many Years?
Volume 7, Number 6: 11 February 2004

Modern glacier recession on Kilimanjaro began around 1880, the same time the planet began to recover from the several-hundred-year cold spell of the Little Ice Age.  As a result, a number of people who apparently have yet to learn that correlation does not prove causation have vociferously declared that the ice fields retreated because of the rising temperatures, encouraged in this contention by a few reports in the scientific literature that promote the same scenario (Alverson et al., 2001; Irion, 2001; Thompson et al., 2002).  This view, however, is "highly simplified," in the words of Molg et al. (2003a), who demonstrate in a recent study that it is also just plain wrong.

The trio of glaciologists begin their analysis of the subject by reviewing some pertinent facts about the historic, climatic and geographic context of the long-term retreat of the Kilimanjaro ice fields.  They note, first of all, that "glacierization in East Africa is limited to three massifs close to the equator: Kilimanjaro (Tanzania, Kenya), Mount Kenya (Kenya), and Rwenzori (Zaire, Uganda)," all three of which sites experienced strong ice field recession over the past century or more.  In that part of the world, however, they report "there is no evidence of a sudden change in temperature at the end of the 19th century (Hastenrath, 2001)," and that "East African long-term temperature records of the 20th century show diverse trends and do not exhibit a uniform warming signal (King'uyu et al., 2000; Hay et al., 2002)."  Moreover, with respect to Kilimanjaro, they say that "since February 2000 an automatic weather station has operated on a horizontal glacier surface at the summit's Northern Icefield," and that "monthly mean air temperatures only vary slightly around the annual mean of -7.1°C, and air temperatures [measured by ventilated sensors, e.g., Georges and Kaser (2002)] never rise above the freezing point," which makes it pretty difficult to understand how ice could melt under such conditions.

So what caused the Ice Fields of Kilimanjaro to recede so steadily for so many years?  Citing "historical accounts of lake levels (Hastenrath, 1984; Nicholson and Yin, 2001), wind and current observations in the Indian Ocean and their relationship to East African rainfall (Hastenrath, 2001), water balance models of lakes (Nicholson and Yin, 2001), and paleolimnological data (Verschuren et al., 2000)," Molg et al. note that "all data indicate that modern East African climate experienced an abrupt and marked drop in air humidity around 1880," and they say that the resultant "strong reduction in precipitation at the end of the 19th century is the main reason for modern glacier recession in East Africa," as it considerably reduces glacier mass balance accumulation, as has been demonstrated for the region by Kruss (1983) and Hastenrath (1984).  In addition, they note that "increased incoming shortwave radiation due to decreases in cloudiness - both effects of the drier climatic conditions - plays a decisive role for glacier retreat by increasing ablation, as demonstrated for Mount Kenya and Rwenzori (Kruss and Hastenrath, 1987; Molg et al., 2003b)."

In further investigating this phenomenon, Molg et al. (2003a) apply a radiation model to an idealized representation of the 1880 ice cap of Kilimanjaro, calculating the spatial extent and geometry of the ice cap for a number of subsequent points in time and finding that "the basic evolution in spatial distribution of ice bodies on the summit is modeled well."  The model they used, which specifically addresses the unique configuration of the summit's vertical ice walls, additionally provided, in their words, "a clear indication that solar radiation is the main climatic parameter governing and maintaining ice retreat on the mountain's summit plateau in the drier climate since ca. 1880."  Consequently, Molg et al. conclude that "modern glacier retreat on Kilimanjaro is much more complex than simply attributable to 'global warming only'."  Indeed, they say it is "a process driven by a complex combination of changes in several different climatic parameters [e.g., Kruss, 1983; Kruss and Hastenrath, 1987; Hastenrath and Kruss, 1992; Kaser and Georges, 1997; Wagnon et al., 2001; Kaser and Osmaston, 2002; Francou et al., 2003; Molg et al., 2003b], with humidity-related variables dominating this combination."

In light of these several observations, many of which stretch back in time a number of years and are well-described in the scientific literature, it is disingenuous at best - and deceptive at worst - for climate alarmists to claim that 20th-century global warming was either the sole or primary cause of the historical recession of the Kilimanjaro Ice Fields.  The two phenomena were essentially independent occurrences.

Sherwood, Keith and Craig Idso

Alverson, K., Bradley, R., Briffa, K., Cole, J., Hughes, M., Larocque, I., Pedersen, T., Thompson, L.G. and Tudhope, S.  2001.  A global paleoclimate observing system.  Science 293: 47-49.

Francou, B., Vuille, M., Wagnon, P., Mendoza, J. and Sicart, J.E.  2003.  Tropical climate change recorded by a glacier in the central Andes during the last decades of the 20th century: Chacaltaya, Bolivia, 16°S.  Journal of Geophysical Research 108: 10.1029/2002JD002473.

Georges, C. and Kaser, G.  2002.  Ventilated and unventilated air temperature measurements for glacier-climate studies on a tropical high mountain site.  Journal of Geophysical Research 107: 10.1029/2002JD002503.

Hastenrath, S.  1984.  The Glaciers of Equatorial East Africa.  D. Reidel, Norwell, MA, USA.

Hastenrath, S.  2001.  Variations of East African climate during the past two centuries.  Climatic Change 50: 209-217.

Hastenrath, S. and Kruss, P.D.  1992.  The dramatic retreat of Mount Kenya's glaciers between 1963 and 1987: Greenhouse forcing.  Annals of Glaciology 16: 127-133.

Hay, S.I., Cox, J., Rogers, D.J., Randolph, S.E., Stern, D.I., Shanks, G.D., Myers, M.F. and Snow, R.W.  2002.  Climate change and the resurgence of malaria in the East African highlands.  Nature 415: 905-909.

Irion, R.  2001.  The melting snows of Kilimanjaro.  Science 291: 1690-1691.

Kaser, G. and Georges, C.  1997.  Changes in the equilibrium line altitude in the tropical Cordillera Blanca (Peru) between 1930 and 1950 and their spatial variations.  Annals of Glaciology 24: 344-349.

Kaser, G. and Osmaston, H.  2002.  Tropical Glaciers.  Cambridge University Press, Cambridge, UK.

King'uyu, S.M., Ogallo, L.A. and Anyamba, E.K.  2000.  Recent trends of minimum and maximum surface temperatures over Eastern Africa.  Journal of Climate 13: 2876-2886.

Kruss, P.D.  1983.  Climate change in East Africa: A numerical simulation from the 100 years of terminus record at Lewis Glacier, Mount Kenya.  Z. Gletscherk, Glazialgeol. 19: 43-60.

Kruss, P.D. and Hastenrath, S.  1987.  The role of radiation geometry in the climate response of Mount Kenya's glaciers, part 1: Horizontal reference surfaces.  International Journal of Climatology 7: 493-505.

Molg, T., Georges, C. and Kaser, G.  2003b.  The contribution of increased incoming shortwave radiation to the retreat of the Rwenzori Glaciers, East Africa, during the 20th century.  International Journal of Climatology 23: 291-303.

Molg, T., Hardy, D.R. and Kaser, G.  2003a.  Solar-radiation-maintained glacier recession on Kilimanjaro drawn from combined ice-radiation geometry modeling.  Journal of Geophysical Research 108: 10.1029/2003JD003546.

Nicholson, S.E. and Yin, X.  2001.  Rainfall conditions in Equatorial East Africa during the nineteenth century as inferred from the record of Lake Victoria.  Climatic Change 48: 387-398.

Thompson, L.G., Mosley-Thompson, E., Davis, M.E., Henderson, K.A., Brecher, H.H., Zagorodnov, V.S., Mashiotta, T.A., Lin, P.-N., Mikhalenko, V.N., Hardy, D.R. and Beer, J.  2002.  Kilimanjaro ice core records: Evidence of Holocene climate change in tropical Africa.  Science 298: 589-593.

Verschuren, D., Laird, K.R. and Cumming, B.F.  2000.  Rainfall and drought in equatorial east Africa during the past 1,100 years.  Nature 403: 410-414.

Wagnon, P., Ribstein, P., Francou, B. and Sicart, J.E.  2001.  Anomalous heat and mass budget of Glaciar Zongo, Bolivia, during the 1997/98 El Niņo year.  Journal of Glaciology 47: 21-28.