Variable vertical land motion for sea level rise projections

Accurate projections of future sea level depend on adequately representing contributions from the land and ocean. The Intergovernmental Panel On Climate Change-6th Assessment Report made significant progress with most contributors to relative sea level rise. However, coastal vertical land motion (VLM) remained unchanged from previous assessments, due in part to challenges with its spatial and temporal variability. Here, we outline a framework for estimating varying VLM in fine detail, and projecting it into the future. Along the 1700-km long California coast, we show that localized VLM, often missing in current frameworks, could double current sea-level projections by 2050 in parts of San Francisco and Los Angeles. We introduce a temporary variability metric to distinguish locations with stable from changing VLM trends, typically driven by human activities. This research underscores nonlinear VLM and its uncertainties in projections, and calls out for localized monitoring to address its impacts on relative sea-level changes.