Sea level reconstruction reveals improved separation of regional climate and trend patterns over the last seven decades

Abstract. Rapidly rising sea level is one of the major adverse consequences of anthropogenic climate change. Sea level rise poses an existential threat to coastal populations, particularly for urban settlements with accelerating growth rates. Contemporary empirical sea level reconstructions have been used to conflate short-term (∼ 3 decades) satellite altimetry geocentric sea level data and long-term (50 years or longer) tide gauge records to better estimate reliable sea level rise towards multi-decadal to centennial time scales. However, adequate separations and quantifications of low-frequency climate patterns and sea level trends globally at regional scales remain elusive. Here, we propose a new sea level reconstruction framework that incorporates Empirical Orthogonal Function (EOF) into the contemporary Cyclostationary EOF with Reduced Space Optimal Interpolation (CSEOF-OI) algorithm to better reconstruct sea level fields. Using 225 selected long-term gap-filled tide gauge records with vertical land motion adjusted and satellite altimetry, our global reconstructed monthly sea level time series, January 1950–January 2022, exhibits distinct delineations between modeled climate patterns and sea level trends at 1°×1° regional scales. The separated sea level patterns include trends, modulated annual cycles, the El Niño Southern Oscillation (ENSO), and the Pacific Decadal Oscillation (PDO). The third principal component of the reconstructed sea level exhibits a Pearson correlation coefficient of 0.87 with the Niño 3.4 ENSO index, and the fourth principal component correlates at 0.75 with the PDO index, indicating good agreement. The global mean sea level trend, accounting for the predominant climate periodicities, is 1.9 ± 0.2 mm yr−1 (95 % confidence), and the estimate during the satellite altimetry era (January 1993–December 2021) is 3.2 ± 0.3 mm yr−1 (95 % confidence). Compared with previous studies, we conclude that our 72-year sea-level reconstruction allows us to better separate the ENSO and PDO climate patterns, as well as the sea level they induced. Finally, we show that the short-term (5-year) rates of ENSO and PDO patterns significantly affect sea level both on a global and regional scale, altering global mean sea level trends by up to 1.1 ± 0.5 mm yr−1 (January 2011–January 2016). Over the past seven decades, the climate patterns exerted a minor impact on sea level trends, but substantially modulated apparent regional sea level accelerations, particularly in the western Pacific (e.g., 0.09 ± 0.05 mm yr−2 at the Kuroshio Current), and in the east and central equatorial Pacific Ocean (e.g., −0.04 ± 0.03 mm yr−2 near Costa Rica). The reconstructed sea level and analysis results datasets are available at https://doi.org/10.5281/zenodo.15288816 (Wang, 2025).