Variable Vertical Land Motion Over the 20th Century Inferred at Tide Gauges

Vertical land motion (VLM) is a key driver of relative sea-level (RSL) changes in coastal areas. Rates of VLM can vary in time due to both anthropogenic (e.g., subsurface fluid extraction) and natural (e.g., sediment compaction, volcano-tectonic activity) processes. However, such nonlinear behavior has not been included in 20th century sea-level budgets or in sea-level projections due to a lack of long-term observations over relevant temporal and spatial scales. Here, we use a probabilistic reconstruction of large-scale climate-related sea level (CSL) from 1900 to 2021 to estimate VLM at a global set of tide gauge stations. We interpret differences between CSL and tide-gauge records (CSL-TG) primarily in terms of VLM and argue that the CSL-TG residuals quantify previously overlooked temporal variations in VLM primarily related to subsurface fluid withdrawal, seismic, and volcanic activity. We demonstrate that decadal variations in the resulting regional RSL trends can be an order of magnitude larger than variations due to CSL, introducing misestimates of up to ~ 75 mm yr ^− 1 in sea level projections based on linear extrapolations. Our variable VLM estimates provide new constraints on geophysical models of anthropogenic and volcano-tectonic crustal motions and pave the way for more robust, site-specific sea-level projections.