Henry H. Brecher

Glacier loss on Kilimanjaro continues unabated

The dramatic loss of Kilimanjaros ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased ≈1% per year from 1912 to 1953 and ≈2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was ≈1.9 and ≈5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of ≈3.6% and ≈24%, respectively. Furtwängler Glacier thinned ≈50% at the drill site between 2000 and 2009. Ice volume changes (2000–2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaros ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought ≈4,200 years ago that lasted ≈300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaros ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.

Tropical glaciers, recorders and indicators of climate change, are disappearing globally

Abstract In this paper we review the interaction of El Niño Southern Oscillation (ENSO) variability and warming trends recorded in ice-core records from high-altitude tropical glaciers, discuss the implications of the warming trends for the glaciers and consider the societal implications of glacier retreat. ENSO has strong impacts on meteorological phenomena that directly or indirectly affect most regions on the planet and their populations. Many tropical ice fields have provided continuous annually resolved proxy records of climatic and environmental variability preserved in measurable parameters, especially oxygen and hydrogen isotopic ratios (δ18O, δD) and the net mass balance (accumulation). These records present an opportunity to examine the nature of tropical climate variability in greater detail and to extract new information on linkages between rising temperatures on tropical glaciers and equatorial Pacific sea surface temperatures in critical ENSO indicator regions. The long-term climate records from a collection of high-altitude tropical ice cores provide the longer-term context essential for assessing the significance of the magnitude and rate of current climate changes that are in large measure driving glacier retreat. The well-documented ice loss on Quelccaya in the Peruvian Andes, Naimona’nyi in the Himalaya, Kilimanjaro in eastern Africa and the ice fields near Puncak Jaya in Papua, Indonesia, presents a grim future for low-latitude glaciers. The ongoing melting of these ice fields (response) is consistent with model predictions for a vertical amplification of temperature in the tropics (driver) and has serious implications for the people who live in these areas.

Elevation change and ice flow at Horseshoe Valley, Patriot Hills, West Antarctica

Abstract Patriot Hills is located at 80˚18’ S, 81˚22’W, at the southernmost end of the Heritage Range, Ellsworth Mountains, West Antarctica. A comparison of glacier elevation data and ice velocities obtained by the differential global positioning system in the period 1996–97 is presented. Ablation/accumulation rates measured at a network of stakes in Horseshoe Valley show average accumulation of 70 kg m–2 a–1 in the central part of the valley, and a maximum ablation of ∼170 kg m–2 a–1 at the edge of the blue-ice area, close to Patriot Hills. Changes in the surface elevation of the glacier measured at 81 stakes in the period 1995–97 show a mean thickening of +0.43±0.42ma–1, which, considering the uncertainties, indicates that the ice sheet around Patriot Hills is in near steady state. Surface velocities, in combination with ice thicknesses obtained by ground-based radio-echo sounding, are used to compute the ice flux across the Horseshoe Valley transect. A total outflow of 0.44 ±0.08km3 a–1 is obtained. Considering a catchment area for Horseshoe Valley of 1087 km2 upstream from the flow transect, and a net accumulation rate of 100 kg m–2 a–1, a total input of 0.11 ±0.04km3 a–1 by snow accumulation is obtained. Accepting a near-equilibrium condition for the ice sheet, the flux difference, i.e. 0.33 km3 a–1, must be supplied by flow from the inland ice sheet through ice cliffs located in mountain gaps in the Heritage Range. If Horseshoe Valley is not in steady state but is thickening, the positive mass balance could be due to increased snow accumulation or enhanced ice flow from the interior of the ice sheet. New data are needed to elucidate this.

Response to Mölg et al.: Glacier loss on Kilimanjaro is consistent with widespread ice loss in low latitudes

Our paper (1) does not seek to review all potential controls on glacier mass balance (MB) but to (i) present ice volume-change calculations, revealing that glacier thinning now accounts for ∼50% of the ice-volume loss for the summit ice fields, (ii) update changes in the areal extent of the ice fields based on newer (2007) aerial photographs, and (iii) highlight that ice loss on Kilimanjaro is not exceptional. We disagree with Molg et al. (2) that we inappropriately propose that Kilimanjaro’s “shrinking ice fields are not unique” (1). The reduction in areal extent and ice volume (shrinking) of Kilimanjaro’ si cefields is not unique; it isconsistentwiththewell-documentedwidespread glacier retreat in lower latitudes. Molg et al. (2) obfuscate the issue of Kilimanjaro’s glacier recession by not differentiating between processes responsible for decreasing ice area (i.e., vertical wall retreat) and more typical MB processes acting on horizontal surfaces, where the balance is currently negative. In fact, since 2000, we have documented area-weighted plateau thinning of ∼4 m, a tremendous increase over the rate of 1 m per

Ice Cores from Tropical Mountain Glaciers as Archives of Climate Change

The 20th century has seen the acceleration of unprecedented global and regional-scale climatic and environmental changes to which humans are vulnerable, and by which we will become increasingly more affected in the coming centuries. One-half of the Earth’s surface area lies in the tropics between 30°N and 30°S, and this area supports almost 70% of the global population. Thus, temporal and spatial variations in the occurrence and intensity of coupled ocean-atmosphere phenomena such as El Nino and the Monsoons, which are most strongly expressed in the tropics and subtropics, are of worldwide significance. Unfortunately, meteorological observations in these regions are scarce and of short duration. However, ice core records are available from low-latitude, high-altitude glaciers, and when they are combined with high-resolution proxy histories such as those from tree rings, lacustrine and marine cores, corals, etc., they provide an unprecedented view of the Earth’s climatic history over several millennia. This paper provides an overview of these unique glacier archives of past climate and environmental changes on millennial to decadal time scales. Also included is a review of the recent, global-scale retreat of these alpine glaciers under present climate conditions, and a discussion of the significance of this retreat with respect to the longer-term perspective, which can only be provided by the paleoclimate records.