A critical role of ocean–sea ice interactions in the pronounced warmth during the Miocene Climatic Optimum

The Miocene Climatic Optimum was characterized by global mean temperatures 8-10 °C above the preindustrial level, yet such extreme warmth remains difficult to reproduce in climate models. Using two climate models (IPSL-CM5A2 and NorESM1-F) with updated boundary conditions, we show that the simulated climate of this interval strongly depends on ocean-ice dynamics. The NorESM1-F model produces surface temperatures more consistent with proxy reconstructions, driven by a stronger overturning circulation, enhanced poleward heat and salt transport, and near-permanent sea-ice loss. In contrast, IPSL-CM5A2 simulates a weaker overturning circulation and limited polar amplification, which is generally consistent with previous modeling results. Our results suggest that the Miocene Climatic Optimum may represent a distinct high-latitude climate regime, emphasizing the critical role of ocean–ice feedbacks in driving the strong polar amplification and the necessity of multi-model comparisons together with proxy constraints to understand the climate of this interval. Ocean-ice interactions play a pivotal role in amplification of polar climate change, as demonstrated by contrasting results for the magnitude of northern high-latitude warming during the Miocene Climatic Optimum from NorESM1-F and IPSL-CM5A2 climate models