Acceleration of U.S. Southeast and Gulf Coast Sea-Level Rise Amplified by Internal Climate Variability

Abstract

While there is evidence for an acceleration in global mean sea-level (MSL) since the 1960s, its detection at local levels has been hampered by the considerable influence of natural variability on the rate of MSL change. Here we report an MSL acceleration in tide gauge records along the U.S. Southeast and Gulf coasts that has led to rates (>10 mmyr-1 since 2000) that are unprecedented in at least 120 years. We show that this acceleration is primarily induced by an ocean dynamic signal exceeding the externally forced response from historical climate model simulations. However, when the simulated forced response is removed from observations, the residuals are neither historically unprecedented nor inconsistent with unforced variability in simulations. Furthermore, a large fraction of the residuals can be explained by wind-driven Rossby waves in the tropical North Atlantic. This indicates that the acceleration represents the compounding effects of external forcing and internal climate variability.

Compounding of Sea‐Level Processes During High‐Tide Flooding Along the U.S. Coastline

“…We identify an increasing number of HTF compound events along the East and Gulf coasts and find that SC and NTR (exceeding their 90th percentile thresholds at the same time, sometimes with other components such as TA and/or ID) were important drivers of this change. Changes in atmospheric circulation patterns (i.e., sea‐level pressure and winds), which vary from hourly to decadal time scales (Chelton & Enfield, 1986; Piecuch et al., 2016; Woodworth et al., 2019), could be a possible reason for the stronger compounding effects, at least to some extent, since it is considered a factor to the amplified SC in the Gulf coast (Wahl et al., 2014) and its decadal variability drives a significant portion of decadal variability in mean sea level (here the ID component) (Dangendorf et al., 2023; Piecuch & Ponte, 2015; Thompson & Mitchum, 2014).…”

Unprecedented Historical Erosion of US Gulf Coast: A Consequence of Accelerated Sea‐Level Rise?

“…(2004). (b) Historical sea‐level rates based on tide‐gauge records from 1900 to 2021 CE (from Dangendorf et al., 2023) and Gulf of Mexico IPCC SSP2‐4.5 Projections of ∼30 cm (approximate average of 25 stations from Port Isabel, TX to Naples, FL) through ∼2040 CE (from Fox‐Kemper et al., 2021; Garner et al., 2021; Kopp et al., 2023). Rates have increased to >10 mm yr −1 in some locations since 2010 CE (Dangendorf et al., 2023).…”

Causes of accelerated High-Tide Flooding in the U.S. since 1950

“…3b). Along the South Atlantic Bight coast, where RMSL changes are largely affected by local 25 and remote 21,26 atmospheric and oceanic forcing, the SDSL contributes 1.5-2.0 additional HTF days per year (50%-80% of total increase in HTF days) from the control period (Extended Data Fig. 7b).…”

“…4m). This rapid uptake is related to an unprecedented acceleration in RMSL (rates in excess of 15 cm per decade) and predominantly driven by gyre-scale changes in SDSL 21,31 (Fig. 4f).…”

“…Regionally and locally, there are significant deviations from the global mean due to processes such as (i) variations in Gravity, Rotation, and Deformation (GRD) accompanying global barystatic mass changes, (ii) sterodynamic variations due to changes in ocean circulation, atmospheric pressure and wind forcing, and (iii) Vertical Land Motion (VLM). Along U.S. coasts, these processes contributed to RMSL rise ranging from 0.9 to 7.0 mm per year since 1950 4,[19][20][21] , providing a plausible explanation for the rapid increases in HTF 7 . Although previous studies illustrate a close relationship between RMSL rise and the increases in HTF days, the relative contributions of regional and local processes are not yet fully understood.…”