Tracing glacier changes since the 1960s on the south slope of Mt. Everest (central Southern Himalaya) using optical satellite imagery

摘要

This contribution examines glacier changes on the south side of Mt. Everestfrom 1962 to 2011 considering five intermediate periods using opticalsatellite imagery. The investigated glaciers cover ~ 400 km2and present among the largest debris coverage (32%)and the highest elevations (5720 m) of the world. We found an overallsurface area loss of 13.0 ± 3.1% (median 0.42 ± 0.06 % a?1),an upward shift of 182 ± 22 m (3.7 ± 0.5 m a?1)in snow-line altitude (SLA), a terminus retreat of 403 ± 9 m (median6.1 ± 0.2 m a?1), and an increase of 17.6 ± 3.1%(median 0.20 ± 0.06% a?1) in debris coverage between 1962 and2011. The recession process of glaciers has been relentlessly continuousover the past 50 years. Moreover, we observed that (i) glaciers that haveincreased the debris coverage have experienced a reduced termini retreat (r = 0.87,p < 0.001). Furthermore, more negative mass balances (i.e.,upward shift of SLA) induce increases of debris coverage (r = 0.79,p < 0.001); (ii) since early 1990s, we observed a slight but statisticallyinsignificant acceleration of the surface area loss (0.35 ± 0.13% a?1in 1962–1992 vs 0.43 ± 0.25% a?1 in 1992–2011),but an significant upward shift of SLA which increased almost three times(2.2 ± 0.8 m a?1 in 1962–1992 vs 6.1 ± 1.4 m a?1 in1992–2011). However, the accelerated shrinkage in recent decades (both interms of surface area loss and SLA shift) has only significantly affectedglaciers with the largest sizes (> 10 km2), presentingaccumulation zones at higher elevations (r = 0.61, p < 0.001) andalong the preferable south–north direction of the monsoons. Moreover, thelargest glaciers present median upward shifts of the SLA (220 m) that arenearly double than that of the smallest (119 m); this finding leads to a hypothesisthat Mt. Everest glaciers are shrinking, not only due to warmingtemperatures, but also as a result of weakening Asian monsoons registeredover the last few decades. We conclude that the shrinkage of the glaciers insouth of Mt. Everest is less than that of others in the western and easternHimalaya and southern and eastern Tibetan Plateau. Their position in higherelevations have likely reduced the impact of warming on these glaciers, buthave not been excluded from a relentlessly continuous and slow recessionprocess over the past 50 years.