CLIMATE CHANGE AND GLACIER RESPONSE IN THE HIMALAYAS - PAST AND PRESENT

Glaciers in the eastern Himalayas sit in the bulls-eye of high snow accumulation glaciers. Sensitivity tests using a surface energy- and mass-balance model show that high accumulation glaciers are extremely temperature-sensitive, and far less sensitive to changes in precipitation. Therefore, eastern Himalayan glaciers form a highly suitable natural laboratory to investigate glacier sensitivity to temperature change. In this study, we map Himalayan glacier area and volume changes over the past forty years, and show significant changes and rapid retreat of these glaciers over the past several decades. In addition, we map former glacier extents for key glacierized regions in the eastern Himalayas, and produce a ¹⁰Be chronology for glacier fluctuations for two of these regions. Finally, we model the glacier changes over multiple centuries using new tree-ring temperature reconstructions as climate input. In combination, the results show that both glacier-length variability over the past 800 years and recent glacier retreat rates can be explained by temperature changes alone. This result strongly supports the theoretical studies suggesting monsoonal glaciers are dominantly temperature sensitive, and suggest high accumulation glaciers may be particularly useful for paleo-temperature reconstructions. In addition, we show that much of the apparent spatial variability in glacier length and timing of advance are driven by differences in glacier hypsometry, and not by spatial variability in climate change. Importantly, our results highlight the recent glacier retreat in the Himalayas as anomalous in the last at least 800 years, and show that even large increases in precipitation are highly unlikely to compensate for impacts of future warming on Himalayan glacier systems.