Unprecedented mass loss of Aldegondabreen, central Spitsbergen, Svalbard

Abstract We have been conducting mass-balance monitoring on Aldegondabreen since the early 21st century. Over the most recent five year period (2019/20–2023/24), the glacier has experienced its most negative mass balance, averaging −2.0 m w.e. a −1 . This dramatic loss is linked to rising air temperatures, with several of the warmest years on record for the Arctic land occurring during this interval. In 2024, for the first time, the critical threshold of 1.5°C above pre-industrial levels was exceeded globally, and this resulted in the lowest annual balance observed since the beginning of our monitoring program (−2.48 m w.e. a −1 ). Archival evidence indicates that such intense melting is unprecedented since at least 1911, which marked the end of the Little Ice Age in the region. As of 2025, the glacier’s mean ice thickness has been estimated at 39 m (33 m w.e.) meaning that the loss of 10 m w.e. in just the last five years is an enormous change.