New Paper On The Climate of Mount Kilimanjaro

There is a new August 31, 2006 paper on the climate of Mount Kilimanjaro (Thanks to Timo Hämeranta and Koni Steffen for bringing this peer-reviewed contribution to my attention). The Geophysical Research Letters article is entitled “Kilimanjaro Glaciers: Recent areal extent from satellite data and new interpretation of observed 20th century retreat rates” (subscription required) and is authored by Nicolas J.Cullen, Thomas Mölg, Georg Kaser, Khalid Hussein, Konrad Steffen, and Douglas R. Hardy. The abstract of the paper reads,

“Recent and long term variations in ice extent on Kilimanjaro are investigated in the context of 20th century climate change in East Africa. Quickbird satellite data show that the areal extent of glaciers on Kilimanjaro is 2.51 km2 in February 2003. To assess glacier retreat on Kilimanjaro two glacier systems are identified: (1) plateau (≥5700 m) and (2) slope (<5700 m). Vertical wall retreat that governs the retreat of plateau glaciers is irreversible, and changes in 20th century climate have not altered their continuous demise. Rapid retreat of slope glaciers at the beginning of the 20th century implies a strong departure from steady state conditions during this time. This strong imbalance can only be explained by a sudden shift in climate, which is not observed in the early 20th century. Results suggest glaciers on Kilimanjaro are merely remnants of a past climate rather than sensitive indicators of 20th century climate change. ”

Text in the conclusion of the paper reads,

“All ice bodies on Kilimanjaro have retreated drastically between 1912–2003. Despite air temperatures always being below freezing, areal retreat of plateau glaciers is governed mostly by solar radiation induced melt on vertical walls that characterize their north and south margins [Mölg et al., 2003]. Though the processes responsible for the formation of the vertical walls is still not well understood, once established, the vertical wall retreat is irreversible, and no change in 20th century climate appears to have significantly altered their ongoing demise. However, the apparent and near disintegration of the Northern Ice Field and Furtwangler glaciers into two ice entities, respectively, can only accelerate present retreat rates of these two ice bodies.

“Though constant shrinkage of the plateau glaciers could have started as a result of a slow change in climate, through a process that allowed the glaciers to reach some threshold to produce vertical walls, evidence for a sudden change in climate prior to the 20th century appears to come from the slope glaciers. The rapid recession of slope glaciers in the first part of the 20th century clearly shows that they were drastically out of equilibrium. The strong imbalance at the beginning of the 20th century can only be explained by a sudden shift in climate shortly before the strong retreat rates began. If such a change in climate had occurred much earlier, the slope glacier imbalance would not have been as large. Slope glaciers are still out of equilibrium, and though 20th century changes in air temperature at the height of the glaciers do not appear responsible (Figure 4), we cannot rule out that changes in moisture (reduction in specific humidity) may be linked to their ongoing imbalance.”

“Rather than changes in 20th century climate being responsible for their demise, glaciers on Kilimanjaro appear to be remnants of a past climate that was once able to sustain them. Hastenrath [2001, 2006] suggests an increase in net shortwave radiation, accompanied by a decrease in cloudiness and precipitation, initiated the retreat of the glaciers during the last two decades of the 19th century. This is supported by a recent finding that a higher frequency of climatically significant Indian Ocean Zonal Mode events in the 19th century (1820–1880) may have provided a mechanism to contribute to a wetter climate in East Africa, and thus stable glaciers [Mölg et al., 2006]. To fully understand what climatic conditions enabled glaciers to accumulate and grow prior to the onset of modern glacier recession on Kilimanjaro, more effort to reconstruct 19th century climate is necessary.”

This observational study provides further research support as to why a regional focus on climate variability and change are required, rather than using a global average surface temperature trend as the climate metric to communicate to policymakers. The conclusion that

“a higher frequency of climatically significant Indian Ocean Zonal Mode events in the 19th century (1820–1880) may have provided a mechanism to contribute to a wetter climate in East Africa, and thus stable glaciers [Mölg et al., 2006]”

indicates that the multi-decadal climate models must have the skill to predict these weather conditions in response to human- and natural-climate forcings if we are to provide useful information.

There is, however, no evidence that the models can provide accurate forecasts of this regional climate feature (the Indian Ocean Zonal Mode). In addition, although not investigated in this study, the prevalance of biomass burning and landscape degradation and resulting blowing dust in the tropics, with the potential for the deposition of this material on the surface of tropical glaciers, should be explored. Such deposition would lower the albedo and result in accelerated sublimation and/or melting. With respect to the Mount Kilimanjaro region, as I can attest by first hand experience, dust is lofted well into the atmosphere by numerous dust devils that occur during the day in adjacent land such as in Amboseli National Park in Kenya which is just north of the Mountain. The land in Amboseli National Park was clearly overgrazed.

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