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

- Large contribution of the reference frame realization on the SLC rate uncertainty.
- Non-negligible contribution of uncertainty in the geodetic VLM estimates.
- Differences in GIA VLM have the largest impact on regional SLC.
- VLM errors can induce significant spurious SLC acceleration.
- The impact of the relative VLM between GPS and TG is quantified globally.

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 ±4.8×10−3 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−1 and 2.8×10−3 mmyr−2, increasing up to 0.5 mm yr−1 and 9×10−3 mmyr−2 for the regional SLC. Errors in VLM corrections need to be budgeted when considering past and future SLC scenarios.