Uncertainty of the 20th century sea-level rise due to vertical land motion errors

Assessing the vertical land motion (VLM) at tide gauges (TG) is crucial to understanding global and regional mean sea-level changes (SLC) over the last century. However, estimating VLM with accuracy better than a few tenths of a millimeter per year is not a trivial undertaking and many factors, including the reference frame uncertainty, must be considered. Using a novel reconstruction approach and updated geodetic VLM corrections, we found the terrestrial reference frame and the estimated VLM uncertainty may contribute to the global SLC rate error by ±0.2 mmyr^-1. In addition, a spurious global SLC acceleration may be introduced up to ±4.8 x 10^-3 mmyr^-2. Regional SLC rate and acceleration errors may be inflated by a factor 3 compared to the global. The difference of VLM from two independent Glacio-Isostatic Adjustment models introduces global SLC rate and acceleration biases at the level of ±0.1 mmyr^-1and 2.8 x 10^-3 mmyr^-2, increasing up to 0.5 mm yr^-1 and 9 x 10^-3 mmyr^-2 for the regional SLC. Errors in VLM corrections need to be budgeted when considering past and future SLC scenarios.