Melting snows on Mt. Kilimanjaro are not evidence of global warming.

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What is the extent of Al Gore’s argument that Mount Kilimanjaro, in Tanzania, is an indicator of the effects of global warming? In his book he simple shows a series of three pictures: one taken in 1970, one taken in 2000, and one taken in 2005. The two pictures from 1970 and 2000 are taken from the same angle and thus allow the reader to see a large change in the glacial cover. The entire text consists of 109 words and can be seen in my reproductions of pages 42 through 45 in figures 1 and 2 below.

Figure 1. Reproductions of pages 42 and 43 of An Inconvenient Truth. I have “photoshopped” the images from these pages to make the snow and glaciers stand out more clearly. The obvious point that the reader is supposed to be impressed with is the dramatic decline in snow and glaciers on Kilimanjaro between 1970 and 2000.

Figure 2. Reproductions of pages 44 and 45 of An Inconvenient Truth. I have “photoshopped” the images from these pages to make the snow and glaciers stand out more clearly. The reader is supposed to note the further decline in the glaciers up to 2005. But note that the picture is taken form a different angle than those on pages 42 and 43.

In the movie version of An Inconvenient Truth these same pictures are shown with Al Gore speaking over them saying essentially the same thing seen in the text of the above images. That’s all there is. There are no references to any scientific studies done concerning these glaciers and the possible causes for their retreats. We are simply shown these compelling photographs and the clear impression is left that this shrinkage is caused by CO2 induced global warming.

What does the best science say concerning the glaciers on Kilimanjaro?

Georg Kaser (Tropical Glaciology Group, Department of Geography, University of Innsbruck). et. al., concluded in the International Journal of Climatology in 2004 that since the end of the ice age Kilimanjaro’s glacial extensions and recessions reached their maximum in the Little Ice Age. That is, the glaciers on Kilimanjaro were smaller one or two or three thousand years ago than they were 150 years ago. Then around 1880, long before the atmospheric CO2 concentration showed a significant increase, a climate shift caused them to start receding from their Little Ice Age maximum. On page 336 of the journal article they said that temperature increases “have not contributed to the recession process on the summit so far.”

Philip Mote (Department of Atmospheric Sciences, University of Washington Climate Impacts Group) et. al. said in a recent article in American Scientist, “The observations … point to a combination of factors other than warming air—chiefly a drying of the surrounding air that reduced accumulation and increased ablation—as responsible for the decline of the ice on Kilimanjaro since the first observations in the 1880s.” They continue, “If human-induced global warming has played any role in the shrinkage of Kilimanjaro’s ice, it could only have joined the game quite late, after the result was already clearly decided, acting at most as an accessory…”

Thomas Molg (Innsbruck University Network of Climate and Cryospheric Research) and Douglas Hardy (Climate System Research Center, Department of Geosciences, University of Massachusetts) pointed out in the Journal of Geophysical Research that “it has been speculated that general global warming is directly driving the retreat of Kilimanjaro’s glaciers [e.g., Irion, 2001]. However, detailed analyses of glacier retreat in the global tropics uniformly reveal that changes in climate variables related to air humidity prevail in controlling the modern retreat…”

Gore refers to his “friend, Dr. Lonnie Thompson” and said “He predicts that within 10 years there will be no more ‘Snows of Kilimanjaro.'” But Thompson’s paper Kilimanjaro Ice Core Records: Evidence of Holocene Climate Change in Tropical Africa in the journal Science in 2002 is clearly not a ringing endorsement for Gore’s claim that the recession of Kilimanjaro’s glaciers is due to anthropogenic CO2. In fact, nowhere in the article is the term “CO2” ever mentioned. Thompson acquired and studied six ice cores from the oldest glaciers near the summit. In the Northern Ice Field (NIF), which supplied the oldest three ice cores (NIF1, NIF2, and NIF3), only one of the cores (NIF3) indicates that its position was covered with ice at the end of the ice age. Thompson’s analysis of the ice core data “suggests that, at ~4 ka [4 thousand years ago], the NIF was smaller than it is today and that the crater-side ice wall likely retreated past the present-day sites of NIF1 and NIF2.” (emphasis added by Moriarty).

Thompsom provides abundant evidence that the climate in tropical Africa has undergone huge and rapid changes multiple times since the end of the ice age (12,000 years ago). For example, 11,000 to 4,000 years ago lakes in the area were up to 100 meters higher than today. Lake Chad in sub-Saharan Africa expanded “from 17,000 km2 to cover an area between 330,000 and 438,000 km2, comparable to that of the Caspian Sea today.” Then it receded back to its present size (17,000 km2) 4,000 years ago when “conditions became cooler and drier.” In fact Thompson states “The Kilimanjaro record documents three abrupt climate changes in this region: at 8.3, 5.2, and 4 ka.” (“ka” means “thousand years ago”).

It is true that Thompson says “if climatological conditions of the past 88 years continue, the ice on Kilimanjaro will likely disappear between 2015 and 2020.” But nowhere in this paper does he even attempt to link the principle drivers of this ice loss to anthropogenic CO2.

Brief look at CO2, temperature and ice extent at Kilimanjaro

Figure 3. Atmospheric CO2 concentration vs. Kilimanjaro ice extent. CO2 data up to 1953 is from the Siple ice core. CO2 data after 1953 is from Mauna Loa, Hawaii. Ice extent for 1880 is from Osmaston, H. 1989. Glaciers, glaciation and equilibrium line altitudes on Kilimanjaro. In Quaternary and Environmental Research on East African Mountains, ed. W. C. Mahaney. Rotterdam: Brookfield, pp. 7-30. Ice extent from 1912 to present is from “Kilimanjaro Glaciers: Recent areal extent from satellite data and new interpretation of observed 20th century retreat rates” Cullen, et. al., GRL 33, 2006

Figure 4. Kilimanjaro summit temperature and ice extent. Ice extent data is the same as figure 3 and the temperature dat is from the National Centers for Environmental Prediction/National Center for Atmospheric Research; compiled by Doug Hardy, University of Massachusetts, Amherst. I have digitized the data from a graph adapted by Tom Dunne.

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