Projecting the evolution of the Northern Patagonian Icefield until the year 2200

Abstract. The Northern Patagonian Icefield (NPI), Chile, is the second-largest ice mass in the Southern Hemisphere outside Antarctica and a major remnant of the Patagonian ice sheet from the Last Glacial Period. It is located in the Southern Andes, which is among the world's glacierized regions with the most negative specific mass balances. The NPI is a highly dynamic system, with high amounts of accumulation and ablation, and includes Glaciar San Rafael, the tidewater calving glacier closest to the equator. Using the ice-sheet model SICOPOLIS, we reproduce the dynamical state and observed changes of the NPI in the early 21st century and project its evolution until 2200. Calving is represented by prescribing an additional mass loss for ocean-terminating grid cells (Glaciar San Rafael). A spin-up experiment generates an icefield comparable to conditions around the year 2000, which we then force with present-day and projected surface mass balance under climate scenarios SSP1-2.6 and SSP5-8.5. In the committed mass loss run, the NPI stabilizes by 2100 at around 75 % of its current volume. Under climate change scenarios, mass loss accelerates from the mid-21st century and continues until 2200, despite assuming constant climate during the final century. The NPI exhibits a response time of approximately 100 years, highlighting the need for caution when interpreting current trends. By 2200, the remaining volume strongly depends on the emission pathway: 64 ± 10 % under SSP1-2.6 versus 32 ± 14 % under SSP5-8.5. These results confirm that for Patagonia, as found elsewhere, every fraction of a degree of warming matters.