Equilibrium-line altitudes of the Last Glacial Maximum for the Himalaya and Tibet: an assessment and evaluation of results

Contemporary equilibrium-line altitudes (ELAs) for glaciers in the high mountains of the Himalaya and Tibet have considerable variation because the region is influenced by two major climatic systems (the mid-latitude westerlies and the south Asian summer monsoon) and glaciers are subject to strong topographic controls. Reconstructions of past ELAs based on the former extent of glaciers are numerous, but were estimated using a variety of methods some of which are not appropriate for high-altitude glaciers which are strongly influenced by topography and have extensive supraglacial debris cover. Furthermore, few of the reconstructions have adequate chronological control because of the difficulty of dating glacial landforms in high-altitude regions where organic matter for radiocarbon dating is sparse or absent. Cosmogenic radionuclide surface exposure and optically-stimulated luminescence dating are providing data to define the timing of glaciation and these, together with objective analysis of glacier dynamics, may allow better estimates of ELA changes in the future. However, there are currently only two regions (the Hunza Valley and the Khumbu Himal) which are sufficiently well dated to allow reconstructions of Last Glacial Maximum glacier extent and hence ELAs. These two regions cannot provide an adequate assessment of ELA changes for the Himalayan-Tibetan region.