The pulse of the Pamirs: using remote sensing and in situ data to investigate accelerating glacier mass loss in the Pamirs

Abstract

In situ and satellite observations have unambiguously indicated the hastening rate of global glacier decay over the past two decades. In the region affected by the Karakoram Anomaly, however, the near-zero mass change and relatively high uncertainty from satellite observations combine with complex glacier dynamics to make glacier mass balances difficult to interpret, yet very few direct observations are available to confirm glacier mass changes. A pressing question for this region is therefore whether this glacier mass stability has already ended, or how long it will persist. Our observations over the past several years in the Pamir mountains, located on the periphery of this anomalous zone, have highlighted glaciers suffering from small accumulation areas at the end of the balance year, due to a combination of reduced winter snowfall and increased summer melt. In this study, we draw together a variety of field and remote sensing observations to assess the severity of Pamir glacier changes in recent years as compared to the historical baseline. We first examine historic climatic records and reanalyses from the region to examine the degree to which recent years fit within the observed historic seasonal and annual ranges. We compare the recent period to historic in situ and remote sensing glacier mass balance measurements recorded at Abramov Glacier, the single long-term monitoring reference glacier for the region, and to the historic network of Soviet meteorological measurements. We then consider regional changes to glacier surface albedo and surface temperature over the past 23 years based on satellite measurements. Taken together, these data sources enable us to link direct meteorological and glaciological conditions to broad spatial and temporal patterns of change across the Pamir mountains. Our results highlight progressively worsening conditions for glaciers since 2000, as indicated by warming air temperatures, decreasing precipitation, and decreasing albedo. 2021 and 2022 were likely the worst two years for glaciers at the regional scale, experiencing the hottest air temperatures and land surface temperatures in the 21st century, but poor conditions also occurred in 2006-2008. Our results highlight that Pamir surface albedos in these years were the lowest of the 21st century, excepting in the East Pamir, which also shows the least negative mass balances and the most moderated climatic changes.  Satellite albedo and thinning measurements agree with both reanalysis data and in situ measurements at Abramov Glacier that mass losses have accelerated. However, historic glaciological measurements at Abramov and regional meteorological stations both highlight that similar periods in terms of hot air temperatures, low precipitation and rapid glacier mass loss occurred in the 1970s, and likely the 1940s, across much of the Pamirs.  Consequently, although observations and projections suggest trends towards hotter and drier conditions with increased mass loss, it may be too soon to draw the curtains on the 40-year mass stability of the Karakoram Anomaly.