Recent observations and glacier modeling point towards near complete glacier loss in western Austria (Ötztal and Stubai mountain range) if 1.5 °C is not met

Abstract. Most glaciers in Austria are expected to disappear in the coming decades. The general trend to deglaciation is apparent from observations of past glacier change as well as projections of future glacier evolution in the region. However, the projected timing of ice loss varies considerably between models and data sources. We enhance observations of regional glacier area and volume change with a new inventory for the Ötztal and Stubai range in western Austria and use this data to initialize and calibrate the Open Global Glacier Model (OGGM), generating projections for all glaciers in the study region until 2100 under different climate scenarios. Observations show that approximately 19 % of glacier area and 23 % of glacier volume were lost between 2006 and 2017 (values are relative to 2006 area and volume and equivalent to annual loss rates of 1.7 % and 2.1 %, respectively). Five glaciers disappeared between 2006 and 2017 and are no longer included in the 2017 inventory. Estimating future change by extrapolating the change rates observed between 2006 and 2017 produces a considerably slower glacier decline than the model projections for all scenarios, highlighting the need for dynamic, climate-aware glacier models to quantify the range of possible futures and trajectories to deglaciation. By adapting OGGM to incorporate the multitemporal, high-resolution observational data available for the study region, the model performance improved compared to using global, lower resolution data and, for the first time, enabled the model to simultaneously match observed area and volume changes at a regional scale. This increases confidence in the regional projections, which show 2.7 % of the 2017 glacier volume in the region remaining by 2100 in a global warming scenario of +1.5 °C above pre-industrial temperatures. Applying a +2 °C scenario, this volume is reached around 30 years earlier and deglaciation is near complete by 2100 (0.4 % of 2017 volume remaining). Gepatschferner, the largest glacier in the region, is expected to retain 5.4 % of its 2017 volume in a +1.5 °C scenario and 0.4 % in a +2 °C scenario. Over 100 glaciers, i.e. roughly one third of the glaciers in the study region, are likely to disappear by 2030 even in the +1.5 °C scenario. Glacier loss in the study region under current warming trajectories (+2.7 °C) is expected to be near total before 2075 (less than 1 % of 2017 volume remaining).