Pyrenean glaciers are disappearing fast: state of the glaciers after the extreme mass losses in 2022 and 2023

Abstract

Given rapid glacier thinning and retreat observed in the Pyrenees in recent decades, an updated glacier inventory and continuous mass balance assessments are important to understand the ongoing variability and changes of these very small glaciers (< 0.5 km2). The mass balance years 2021/22 and 2022/23 were characterised by prolonged extreme heat waves and reduced snow duration that severely affected the Pyrenees, which also impacted their glaciers. This paper reviews the criteria for classifying ice bodies as glaciers or ice patches, presents the latest high-resolution glacier inventory for the Pyrenees, and quantifies the mass losses caused by the extreme climate conditions in 2022 and 2023. The glacierised area was determined by manual mapping of high-resolution (0.2 m spatial resolution) aerial orthomosaics acquired by unmanned aerial vehicles (UAVs) and aerial orthophotos (0.25 m spatial resolution) for the few glaciers not surveyed by UAVs. 3D point clouds, also obtained from UAV flights, were used to update the results for the change in surface elevation (glacier thickness) and mass balance between 2020 and 2023. For the Pyrenees, the total glacierised area in 2023 is 143.2 ± 1.8 ha in 15 different glaciers and 8 ice masses were degraded to ice patches according to our criteria. The resulting area change between 2020 and 2023 is -94.8 ha, representing a -39.8% decrease of the glaciarised area from 2020 to 2023, increasing the annual ratio of area change from 2020 to 2023 by -8.7% yr−1 compared to the period 2011–2020 (-2.4% yr−1). The change in glacier thickness measured on 12 glaciers shows a decrease of -2.52 m yr−1 for the period 2020–2023, which represents a significant acceleration in glacier thickness loss compared to -0.80 m yr−1 for the period 2011–2020. The three glaciers (Infiernos, Monte Perdido and Aneto) on which annual geodetic measurements were carried out showed slightly higher glacier thickness losses (-0.91 m yr−1) in the first mass balance year (2020/21) than in the previous decade (2011–2020), while the losses in the last two mass balance years (2021/22 and 2022/23) were three to four times higher (-3.42 m yr−1 and -3.07 m yr−1 respectively) and exceeded the record values.