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The Retreating Glaciers of Kilimanjaro
Volume 9, Number 38: 20 September 2006

On the floor of the U.S. Senate during debate on Senate Bill 139 back in 2004, Arizona Senator John McCain described his affection for the writings of Ernest Hemingway, especially his famous short story "The Snows of Kilimanjaro." Then, showing photos of the magnificent landmark taken in 1993 and 2000, he attributed the decline of glacial ice atop the mount during the intervening years to CO2-induced global warming, calling this attribution not only a fact, but a fact "that cannot be refuted by any scientist."

In subsequent debate on the same bill, New York Senator Hillary Clinton echoed Senator McCain's sentiments. Displaying a second set of photos taken from the same vantage point in 1970 and 1999 - the first depicting "a 20-foot-high glacier" and the second "only a trace of ice" - she said that in those pictures "we have evidence in the most dramatic way possible of the effects of 29 years of global warming."

Sadly, and despite the absolute certitude with which the two senators expressed their views on the subject - which allowed for no "wiggle room" whatsoever - both were as wrong as they could possibly be, according to the conclusions of six of the best scientists ever to study the legendary mountain and its once majestic ice-capped peaks.

What we presume is the correct view of the matter is elucidated by Cullen et al. (2006). These six scientists - three from the Tropical Glaciology Group of the Department of Earth and Atmospheric Sciences at Austria's University of Innsbruck, two from the Cooperative Institute for Research in Environmental Sciences at the University of Colorado, and one from the Climate System Research Center of the Department of Geosciences at the University of Massachusetts - take up the subject because, as they recount it, "the retreat of glaciers on Kilimanjaro has in recent years attracted broad attention, with their disappearance sometimes linked to tropical warming."

So what's the real story?

In terms of what has actually happened to Kilimanjaro's glaciers, Cullen et al. report that "all ice bodies on Kilimanjaro have retreated drastically between 1912-2003," but they add that the highest glacial recession rates on Kilimanjaro "occurred in the first part of the 20th century, with the most recent retreat rates (1989-2003) smaller than in any other interval [our italics]." In addition, they say that no temperature trends over the period 1948-2005 have been observed at the approximate height of the Kilimanjaro glaciers, but that there has been a small decrease in the region's specific humidity over this period.

In terms of why glacier retreat on Kilimanjaro was so dramatic over the 20th century, the six researchers note that for the mountain's plateau glaciers, there is no alternative for them "other than to continuously retreat once their vertical margins are exposed to solar radiation," which appears to have happened sometime in the latter part of the 19th century. They also say, in this regard, that the "vertical wall retreat that governs the retreat of plateau glaciers is irreversible, and changes in 20th century climate have not altered their continuous demise." Consequently, the 20th-century behavior of Kilimanjaro's plateau glaciers is a long-term response to what we could call "relict climate change" that likely occurred in the late 19th century.

In the case of the mountain's slope glaciers, Cullen et al. say that their rapid recession in the first part of the 20th century clearly shows they "were drastically out of equilibrium," which they take as evidence that the glaciers "were responding to a large prior [our italics] shift in climate." In addition, they report that "no footprint of multidecadal changes in areal extent of slope glaciers to fluctuations in 20th century climate is observed, but their ongoing demise does suggest they are still out of equilibrium," and in this regard they add that their continuing but decelerating demise could be helped along by the continuous slow decline in the air's specific humidity.

Consequently, and in light of all the facts they present and the analyses they and others have conducted over many years, Cullen et al. confidently conclude that the glaciers of Kilimanjaro "are merely remnants of a past climate rather than sensitive indicators of 20th century climate change," the adamant prior statements of U.S. Senators McCain and Clinton notwithstanding. What we wonder now, therefore, is whether one or both of the senators will be willing to admit to having previously been mistaken on this important subject.

Sherwood, Keith and Craig Idso

Cullen, N.J., Molg, T., Kaser, G., Hussein, K., Steffen, K. and Hardy, D.R. 2006. Kilimanjaro glaciers: Recent areal extent from satellite data and new interpretation of observed 20th century retreat rates. Geophysical Research Letters 33: 10.1029/2006GL027084.