Recent decoupling of global mean sea level rise from decadal scale climate variability

Global mean sea level (GMSL) derived from satellite altimetry reflects in an integrated way the overall variability in the Earth's climate system. Linear trend analyses suggest that GMSL is currently rising at a rate of 3.3 mm/yr (Guérou et al., 2023). However, understanding GMSL variations beyond the overall trend is critical to correctly interpret long-term changes. At interannual timescales, variability in GMSL is driven by steric changes in ocean heat content and barystatic variations of water mass, with the El Nino-Southern Oscillation (ENSO) contributing about equally to both.

Here, we are interested in quantifying the impact of internal (multi-) decadal climate variability, which is crucial for assessing the anthropogenic contributions and its role in current GMSL acceleration. Specifically, we focus on the statistical interrelationship between GMSL and the Pacific Decadal Variability as expressed by the Pacific Decadal Oscillation (PDO) index. By studying the co-variability between PDO index and GMSL over the full period of existing satellite altimetry records, we demonstrate that the low-frequency variability superposed to (linear) GMSL rise is almost perfectly consistent with PDO over most of the past decades but exhibits a complete decoupling after 2019. Thus, GMSL rise estimated by statistically accounting for low-frequency climate variability is unprecedented since 2019, supporting the recently reported significant acceleration in the rise of global mean sea level.

This work has been financially supported by INESC TEC via the International Visiting Researcher Programme 2024.