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

<p>Glaciers and ice caps worldwide are in strong decline, and models project this trend to continue with future warming, with strong environmental and socio-economic implications. The Jostedalsbreen ice cap is the largest ice cap on the European mainland (458 km<span class="inline-formula">²</span> 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 consists of glacier units with a great diversity in shape, steepness, hypsometry, and flow speed. We employ a coupled model system with higher-order three-dimensional ice dynamics forced by simulated surface mass balance that fully accounts for the mass-balance elevation feedback. We find that Jostedalsbreen may lose 12 %–74 % of its present-day volume until 2100, depending on future greenhouse gas emissions. With mid-range results obtained using the climate model ECEARTH/CCLM, Jostedalsbreen is projected to lose 49 % (RCP4.5) and 63 % (RCP8.5) of its contemporary ice volume by 2100. Regardless of emission 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 that by the year 2100, the ice cap may be committed to a complete disappearance during the 22nd century, under high emissions (RCP8.5). Under medium 21st-century emissions (RCP4.5), the ice cap is bound to shrink by 90 % until 2300. Further simulations indicate that substantial mass losses undergone until 2100 are irreversible; the ice cap would not recover to its contemporary volume if the future surface mass balance was reversed to that of the present-day. Our study demonstrates 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, particularly precipitation, appear to be the largest source of uncertainty in future projections of maritime ice masses like Jostedalsbreen.</p>