Recent history and future demise of Jostedalsbreen, the largest ice cap in mainland Europe

Glaciers and ice caps worldwide are in strong decline, and models project this trend to continue with future warming, with strong natural and socioeconomic implications. The Jostedalsbreen ice cap is the largest ice cap on the European continent (500 km² in 1966, 458 km² in 2019) and occupies 20% of the total glacier area of mainland Norway. Here we simulate the evolution of Jostedalsbreen since 1960, and its fate in a changing climate in the 21st-century and beyond (2300). This ice cap contains glacier units with a great diversity in shape, steepness, hypsometry, and flow speed. We employ a coupled model system annually accounting for the mass-balance elevation feedback, with 3-d ice dynamics and simulated surface mass balance constrained by Bayesian inference. We find that Jostedalsbreen may lose 12-74% of its present-day volume, depending on future emissions. Regardless of scenario, the ice cap is likely to split into three parts during the second half of the 21st century. Our results suggest that Jostedalsbreen will likely be more resilient than many smaller glaciers and ice caps in Scandinavia. However, we show in simulations to the year 2300 that by the year 2100, the ice cap may be committed to a complete disappearance during the 22nd century, under high emissions. Under medium 21st-century emissions, the ice cap is bound to shrink by 90% until 2300. Further simulations indicate that substantial mass losses undergone until 2100 are irreversible. Our study illustrates a model approach for complex ice masses with numerous outlet glaciers such as ice caps, and how tightly linked future mass loss is to future greenhouse-gas emissions. Finally, uncertainties in future climate conditions appear to be the largest source of uncertainty in future evolution of ice caps like Jostedalsbreen.