Quantifying Climate Change in the Tropical Midtroposphere over East Africa from Glacier Shrinkage on Kilimanjaro

Abstract

Slope glaciers on Kilimanjaro (ca. 5000-6000 m MSL) reached their most recent maximum extent in the late nineteenth century (L19) and have receded since then. This study quantifies the climate signal behind the recession of Kersten Glacier, which generates information on climate change in the tropical midtroposphere between L19 and present. Multiyear meteorological measurements at 5873 m MSL serve to force and verify a spatially distributed model of the glacier's mass balance (the most direct link between glacier behavior and atmospheric forcing). At present the glacier is losing mass (522 6 105 kg m 22 yr 21 ), terminates at 5100 m, and the interannual variability of mass and energy budgets largely reflects variability in atmospheric moisture. Backward modeling of the L19 steady-state glacier extent (down to 4500 m) reveals higher precipitation (1160 to 1240 mm yr 21 ), higher air humidity, and increased fractional cloud cover in L19 but no significant changes in local air temperature, air pressure, and wind speed. The atmosphere in the simulated L19 climate transfers more energy to the glacier surface through atmospheric longwave radiation and turbulent heat-but this is almost entirely balanced by the decrease in absorbed solar radiation (due to both increased cloudiness and higher surface albedo). Thus, the energy-driven mass loss per unit area (sublimation plus meltwater runoff) was not appreciably different from today. Higher L19 precipitation rates therefore dominated the mass budget and produced a larger glacier extent in the past.

Altered Ecologies: Fire, climate and human influence on terrestrial landscapes: Terra Australis 32

“…Hastenrath and Kruss (1992) proposed that continued glacier recession from 1963 until 1987 was mainly caused by an increase in atmospheric humidity that forced more efficient use of available energy to increase melting. More recently, Mölg et al (2003), Kaser et al (2004), Cullen et al (2006), and Mölg et al (2009) proposed that the 20th century recession of Kilimanjaro's glaciers was driven entirely by decreasing precipitation and atmospheric drying. As part of the proof, Mölg and Hardy (2004), Cullen et al (2007) and Mölg et al (2008Mölg et al ( , 2009 showed, using energy and mass-balance modelling, that the retreat of Kilimanjaro glaciers since 2000 reflects atmospheric aridity and the associated increased receipt of solar radiation.…”

Glacier loss on Kilimanjaro is an exceptional case

“…Considering mass fluxes, the undeniable fact that melting occurred in former centuries is based on the observation of "strong and widespread melting" in the 1880s by early scientists (6), and this is consistent with the physically based mass-flux reconstruction for that time (2). Therefore, concluding "the absence of surface melting" on Kilimanjaro before recent decades (1) is invalid.…”

“…We think it is essential to acknowledge these details, because they provide an exceptional opportunity to unravel changes of multiscale linkages in the climate system (sections 6 and 7 in ref. 2).…”

“…Physically, absolute rates of area or volume loss are, however, the most meaningful manifestation of climate forcing (2). Even if outlined conversely by Thompson et al (1), there is now agreement that slope glaciers are losing mass (522 ± 105 kg m −2 yr −1 ) (2).…”

“…In summary, there is consensus that glacier loss on Kilimanjaro continues (1)(2)(3) and that global warming has probably impacted this loss in recent decades (1, 2), most likely through regional shifts in precipitation zones that result from large-scale warming of air and oceans (ref. …”