Reconciling global mean and regional sea level change in projections and observations

John A Church,Jinping Wang,Xuebin Zhang,Xianyao Chen

doi:10.1038/s41467-021-21265-6

Abstract

The ability of climate models to simulate 20th century global mean sea level (GMSL) and regional sea-level change has been demonstrated. However, the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) and Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) sea-level projections have not been rigorously evaluated with observed GMSL and coastal sea level from a global network of tide gauges as the short overlapping period (2007–2018) and natural variability make the detection of trends and accelerations challenging. Here, we critically evaluate these projections with satellite and tide-gauge observations. The observed trends from GMSL and the regional weighted mean at tide-gauge stations confirm the projections under three Representative Concentration Pathway (RCP) scenarios within 90% confidence level during 2007–2018. The central values of the observed GMSL (1993–2018) and regional weighted mean (1970–2018) accelerations are larger than projections for RCP2.6 and lie between (or even above) those for RCP4.5 and RCP8.5 over 2007–2032, but are not yet statistically different from any scenario. While the confirmation of the projection trends gives us confidence in current understanding of near future sea-level change, it leaves open questions concerning late 21st century non-linear accelerations from ice-sheet contributions.

Highlights

The ability of climate models to simulate 20th century global mean sea level (GMSL) and regional sea-level change has been demonstrated
We show the trends of the Intergovernmental Panel on Climate Change (IPCC) AR5 and SROCC sealevel projections under three Representative Concentration Pathway (RCP) scenarios from both GMSL and regional weighted mean at 177 tide-gauges stations agree well with satellite and tide-gauge observations over the common peiod 2007–2018 within 90% confidence level (90% CL), after considering the impacts of natural climate variability and correcting local residual vertical land motion (VLM)
We find the central values of observed GMSL and regional weighted mean at tide-gauge stations (1970–2018) show larger accelerations than that from projections under RCP2.6 and lie between projected accelerations under RCP4.5 and RCP8.5, while not yet statistically different from any scenario

Summary

Introduction

The ability of climate models to simulate 20th century global mean sea level (GMSL) and regional sea-level change has been demonstrated. We show the trends of the IPCC AR5 and SROCC sealevel projections under three RCP scenarios from both GMSL and regional weighted mean at 177 tide-gauges stations agree well with satellite and tide-gauge observations over the common peiod 2007–2018 within 90% confidence level (90% CL), after considering the impacts of natural climate variability and correcting local residual VLM. We find the central values of observed GMSL (satellite altimeter over 1993–2018; sea-level reconstruction over 1970–2018) and regional weighted mean at tide-gauge stations (1970–2018) show larger accelerations than that from projections under RCP2.6 and lie between projected accelerations under RCP4.5 and RCP8.5, while not yet statistically different from any scenario. The sea-level acceleration need to be reduced to be consistent with the lower and falling RCP2.6 mitigation emission scenario and the Paris targets in the late 21st century

Methods

Results

Conclusion