An Arctic Sea Ice Energy Budget for the Last Interglacial

With ongoing anthropogenic warming, the Arctic is increasingly dominated by thin, first-year ice. Understanding the ice-ocean-atmosphere interactions in warmer climates is therefore essential. We analyse the Arctic sea-ice energy budget in nine CMIP6-PMIP4 lig127k simulations of the Last Interglacial warm Arctic. All models show reduced Last Interglacial summer sea ice, but with substantial inter-model spread. We demonstrate that this arises from differences in surface energy anomalies, which is highly correlated with sea ice anomalies. Ice-albedo feedbacks dominate this response: reduced ice cover exposes more open ocean, enhances shortwave absorption, and warms the upper ocean. This heat is released in autumn, delaying sea-ice regrowth. Although modern anthropogenic warming is driven primarily by longwave forcing, our results highlight that shortwave absorption from reduced albedo is a key driver of summer sea-ice loss, underscoring the need for accurate representation of surface heat-balance processes in future Arctic projections. The Assessment Fast Track contains an idealised palaeoclimate experiment called abrupt127k, which is designed to explore Arctic sea ice response in CMIP7 models. We will, therefore, expand the analysis to include emerging CMIP7 results.