A Cross-Calibrated Multi-Mission Assessment of Mediterranean Sea-Level Budget Closure (2005–2025)

Sea-level rise is a key indicator of climate change, increasing the vulnerability of the Mediterranean’s densely populated, socio-economically important coastlines. This study investigates Mediterranean sea-level variability and its physical components over 2005–2025. Multi-mission altimetry products, which retain inter-mission differences despite standard geodetic corrections, were cross-calibrated into a homogeneous time series and analyzed with harmonic Ordinary, Weighted, and Generalized Least Squares models, accounting for observational uncertainty and temporal correlation. Adopting the uncapped, maximum-likelihood-consistent correlated-noise variance as the primary convention, the final GLS altimetric trend is +3.277 mm/yr. The signal was decomposed into steric (thermosteric, halosteric) and manometric components, using GLORYS, ARMOR3D and Argo data for the steric terms and GRACE/GRACE-FO for the manometric term. GLS steric trends range from +1.445 to +2.149 mm/yr; the JPL manometric estimate, corrected for atmospheric loading on a common JPL/AVISO/LEGOS mask and estimated by GLS, is +1.318 mm/yr. Combining each steric and manometric estimate gives six budget-closure residuals from −0.623 to +0.514 mm/yr; correctly propagating their non-independence gives a grand-mean residual of −0.049 ± 1.616 mm/yr, statistically indistinguishable from zero (p = 0.98)—the budget closes within uncertainty. The altimetric trend and bias solution are independently validated against 47 GNSS-corrected Mediterranean tide gauges, giving a mean geocentric trend of +2.365 ± 0.263 mm/yr, consistent with the altimetric estimate (p = 0.49).