Arctic sea ice is declining rapidly, yet how climate warming alters the memory and recovery characteristics of the sea-ice system remains poorly understood. Here, we combine observational products and climate-model simulations to quantify changes in the effective memory timescale of Arctic sea-ice thickness. Observations reveal pronounced spatial and seasonal heterogeneity in sea-ice thickness memory, but also a coherent long-term decline across most Arctic regions and calendar months. Over the past four decades, the effective memory timescale has decreased by nearly 50% in many months, indicating that thickness anomalies persist for substantially shorter periods than in the past. Climate-model simulations under continued warming also show a progressive reduction in sea-ice thickness memory, indicating that the observed decline is consistent with the expected response of the Arctic sea-ice system to a warmer climate. This widespread loss of persistence may signal a weakening of the stabilizing processes underpinning Arctic sea-ice resilience, potentially increasing the system’s susceptibility to rapid state changes under continued warming. These findings highlight the importance of resolving the seasonal and regional structure of sea-ice memory when assessing Arctic sea-ice stability, resilience, and proximity to critical transitions.