Pan-Arctic Sea Ice Decline and Permafrost Coastal Vulnerability: An Exploratory 168-Year Assessment

The Arctic is warming nearly four times faster than the global mean, driving unprecedented sea ice loss and threatening permafrost coasts and human settlements. Existing pan-Arctic vulnerability indices typically rest on satellite-era baselines and on expert-driven weighting schemes whose robustness is rarely tested. Here, we present an integrated, multi-centennial framework that jointly ingests SIBT1850 sea ice concentration (1850–2017), extended to 2024 with the NOAA/NSIDC Climate Data Record of Passive Microwave Sea Ice Concentration v6 (G02202 v6), together with ESA CCI Permafrost products (1997–2019), the Arctic Coastal Dynamics database, and pan-Arctic settlement inventories. Using non-parametric Mann–Kendall trend tests, Sen’s slope, and the Pettitt change point test across nine Seas (S1–S9), five permafrost-adjacent core seas exhibit summer Sen’s slopes of −0.105 to −0.185% yr −1 with Pettitt change points clustered in 1929–1953 (mean 1936), whereas three of four support seas cluster around 1978, suggesting an approximately bimodal regime shift timing that we interpret cautiously given the limited sample. A Composite Vulnerability Index integrating six normalised indicators identifies the Chukchi (CVI = 0.630) and East Siberian (0.624) seas as the highest-priority hotspots at the SIBT1850 baseline. A satellite-era robustness check using NSIDC G02202 v6 confirms that the Chukchi–East Siberian–Laptev corridor remains in the top three highest-vulnerability basins under the 1850–2024 extension, with the Beaufort Sea retaining rank 5, validating the basin mean conclusions of the SIBT1850-based analysis. Robustness checks—PCA re-weighting, one-at-a-time and global (Sobol, PAWN) sensitivity analyses, and Monte Carlo Dirichlet perturbation—confirm that the top-two ranking is stable across weighting schemes (baseline–PCA Spearman ρ = 0.80). We explicitly avoid claiming forecasting validation, operational testing, or benchmarking against existing pan-Arctic vulnerability indices, all of which we identify as priority directions for future work. The framework provides a transparent, reproducible basis for prioritising adaptation across the Chukchi–East Siberian–Laptev corridor.