Sea Level Reconstruction: Validation and Value

The ability to see how sea level has changed from past states or to accurately project how it will change in the future is limited by historical sea level data. Tide gauge measurements have a long temporal record but limited spatial coverage and satellite altimetry provides global measurements but has only been available for 20 years. Reconstructions extend spatially dense datasets, such as those from satellite altimetry, by decomposing the dataset into basis functions and fitting those functions to in-situ tide gauge measurements with a longer temporal record. A longer temporal record allows one to separate signals that cannot be found in the relatively short altimeter record. However, the fidelity and utility of sea level reconstructions is still a topic of discussion. I compare and evaluate two methods for reconstructing sea level and show how reconstructions can be beneficial where other sea level datasets are limited. The compared sea level reconstruction methods differ in the technique for calculating basis functions, i.e. empirical orthogonal functions (EOFs) versus cyclostationary EOFs (CSEOFs). Additionally, I use published sea level reconstruction datasets to analyze changes in the North Equatorial Current bifurcation point, in regional trends in the Southeast Asian Seas, and in the contribution of the Pacific Decadal Oscillation (PDO) to global sea level over the last 60 years. These results give direction for making high quality sea level reconstructions and identify significant scientific findings made possible through reconstructing sea level. Sea level reconstructions provide the ability to separate natural recurring signals from those that are historically unprecedented, such as the rise in global mean sea level, which is an unparalleled virtue given the current state of the climate