Abstract :
[en] Antarctic surface mass balance (SMB) projections are a major source of uncertainty in future sea-level rise estimates, and regional climate models (RCMs), thanks to their finer resolution and polar-tailored physics, are increasingly used to refine and complement Earth System Model (ESM) projections. Here, three recent downscalings of the ESM CESM2 with the RCMs MAR, RACMO, and HIRHAM under SSP5-8.5 produce consistent contemporary Antarctic SMB, but diverge strongly by 2100, especially over ice shelves. Projected SMB anomalies there range from a large decline in HIRHAM to a moderate decrease in MAR, while RACMO maintains near balance. These differences mainly reflect contrasting melt–albedo feedbacks and present-day melt and refreezing levels, particularly in HIRHAM, where melt and refreezing rates are about five and four times higher than both MAR and RACMO, reaching levels the other two models only attain by the end of the century, along with a persistent 1–2 °C temperature offset between MAR and RACMO. CESM2 shows a decline similar in magnitude to MAR, with high melt partly compensated by extensive refreezing. Over grounded ice, all models project increased SMB from higher snowfall, though runoff still drives their SMB spread. Despite identical boundary conditions and similar present-day SMB, the four models diverge substantially by 2100. Yet CESM2, despite its coarser resolution as an ESM, reproduces integrated behavior consistent with MAR. These results show that inter-model agreement on present-day SMB does not guarantee reliable future projections, underscoring the need for continued RCM development to better constrain the Antarctic contribution to sea-level rise.
