Vertical land motion reconstruction unveils non-linear effects on relative sea level

Abstract

Vertical land movements can cause regional relative sea level changes to differ substantially from climate-driven absolute (geocentric) sea level changes, on the order of mm to cm per year. While absolute sea level has been accurately monitored by satellite altimetry since 1992, vertical land motion is observed only point-wise or modelled following simpli- fied assumptions due to limited observational constraints (i.e., Global Navigation Satellite Systems data). Consequently, although there is evidence of non-linear vertical land motion due to tectonic activity, changes in surface loading, or groundwater extraction, vertical land motion is generally modeled as a linear process. Therefore, the temporal evolution of vertical land motion and its contribution to projected sea level rise, as well as the associated uncertainties, remain unresolved. Here, we generate a probabilistic vertical land motion reconstruction from 1995-2020 to determine the impact of regional scale and non-linear vertical land motion on relative sea level projections up to 2150. We show that regional variations in the projected coastal sea level changes are equally influenced by vertical land motion, as by climate-driven processes, such as ocean-dynamics, steric and mass-driven changes (due to ice melt), causing relative sea level changes to be up to 50 cm larger than the absolute sea level change alone. Accounting for the currently under- represented non-linear vertical land motion increases previous estimates of uncertainties in projected relative sea level change up to 1 m on a regional scale. These results highlight the limitations of our ability to assess future coastal impacts and advocate the inclusion of non-linear vertical land motions to accurately and realistically quantify uncertainty.

Coastal populations experience sea level rise at least twice as large as the global average

“…We use a combination of observational data from GNSS, TGs, altimetry and InSAR, and a GIA model to determine the components of relative sea level change. We use the time-and space-resolving VLM reconstruction by Oelsmann et al [2023] as main information for VLM. The 0.25°-resolution VLM reconstruction is based on more than 10,000 point-estimates from GNSS [Blewitt et al, 2016], TGs [Holgate et al, 2013] and gridded altimetry (as described below) data and resolves height changes at an annual time scale over 1995-2020.…”

“…This probabilistic estimate (hereafter referred to as OE23) was derived in a Bayesian framework using several processing steps. First, the underlying data (GNSS, differences between TG and altimetry) were adjusted/corrected for offsets, single point outliers, and the annual cycle in a semi-automated manner [Oelsmann et al, 2022[Oelsmann et al, , 2023. Second, estimates of long-term linear trends and common modes of variability were obtained using a Bayesian principal component analysis [Wudong et al, 2020].…”

“…While observational limitations are a major challenge in approximating future changes, in many cases future projections VLM are challenging due to the non-linear nature of the processes themselves [Shirzaei et al, 2021, Oelsmann et al, 2023. Thus in addition to accurate and dense VLM observations, the most appropriate and meaningful ways (e.g., process models and assumptions of future scenarios, such as of groundwater extraction [Bootsma et al, 2020, Minderhoud et al, 2020, Fang et al, 2022, or sediment supply in deltas [Zoccarato et al, 2018]) to make projections must be considered.…”

“…Coastal impacts and adaptation are, however, driven by local (or relative) sea-level rise, the estimation of which requires combining global absolute estimates of climate-induced sea-level with estimates of local coastal vertical land motion (VLM) [Nicholls et al, 2021a]. Observations show that VLM can exceed contemporary absolute sea level changes by as much as an order of magnitude in susceptible areas [Wöppelmann and Marcos, 2016, Hammond et al, 2021, Oelsmann et al, 2023. However, there is low confidence in state-of-the-art estimates of VLM and their uncertainties at the global scale [Slangen et al, 2023], and the current and future magnitudes of relative sea-level rise have similar uncertainties.…”

“…Although previous studies have synergized some of these data sources such as GNSS, tide gauge, and altimetry data [Husson et al, 2018, Hawkins et al, 2019, Hammond et al, 2021, Oelsmann et al, 2023, to date no study has combined all three observational techniques to assess the influence of VLM on relative sea level change on a global scale. Previous studies focused on sea level change projections and impacts, mainly for glacial isostatic adjustment (GIA) or tide gauge VLM reconstructions, which poorly resolve VLM at the regional to local scale [Church and White, 2011, Slangen et al, 2014, Jackson and Jevrejeva, 2016, Fox-Kemper et al, 2021, Slangen et al, 2023.…”