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Abstract

Arctic amplification (AA) is a prominent signature of climate change, and comprises a stronger warming in the Arctic relative to the global average. Several intertwined mechanisms have been identified to give rise to AA, but their relative importance is still under debate. Albeit state-of-the-art climate models agree on global warming being amplified in the Arctic, they project a considerable range in simulated magnitude of AA.It is well established that the substantial sea-ice loss and associated feedbacks during recent decades have played a central role in the modern era of AA. Previous studies show that ice melt mediates an albedo decrease at the surface, leading to stronger uptake of heat by the ocean, which is subsequently transferred to fall/winter.We argue that sea-ice changes that mediate AA are a direct consequence of the initial sea-ice climatology. In particular, we find that across an ensemble of 44 CMIP6 models, the range in simulated present-day sea ice conditions relates to the inter-model spread in AA at the end of the century. Emerging linear relationships are found between AA, and sea-ice concentration (SIC) and seasonality. Firstly, a higher initial SIC across models produces stronger AA by setting the stage for stronger ice loss. Secondly, a stronger seasonality in sea ice produces stronger AA across models.Based on derived inter-model relationships, we constrain the spread in simulated future AA with respect to observable SIC and sea-ice seasonality. Our emergent constraint predicts a future Arctic warming that is amplified by a factor 2.8 with respect to global average.