What Do We Really Know About 20th Century Global Mean Sea Level?
Event: 2015 Ocean Surface Topography Science Team Meeting
Session: OSTST Opening Plenary Session
Presentation type: Type Keynote/invited
Recent studies have resulted in a range of published estimates for the 20th century trend in global mean sea level (GMSL). Discrepancies can be attributed to two factors: 1) differences in analysis and/or reconstruction techniques; and 2) differences in tide gauge selection and quality control of the data. While it is difficult to conclusively determine the best method for estimating GMSL over the past century, it is possible to critically assess the impact of tide gauge selection and editing. Questions remain regarding to what extent the tide gauge network can inform us about GMSL over the past century. Here, we provide an in-depth examination of the tide gauge record and its utility in estimating GMSL both during the altimeter era and further into the past. As a starting point, we show how tide gauge selection choices can affect estimates of the long-term trend in GMSL. Extending beyond this simple test, we also provide a new approach to tide gauge selection and editing, relying on quantitative selection criteria wherever possible and accounting for the potential impact of spatial and temporal sparseness of the tide gauge record on the computation of GMSL and associated error estimates. We further attempt to address challenges posed by vertical land motion in our quality control process, either correcting or removing gauges significantly impacted by the movement of land. In doing so, we arrive at a quality-controlled set of tide gauges that yields an improved estimate of GMSL during the 20th century, and that can be broadly used in studies of regional and global sea level. Finally, using a simple data experiment, we constrain the 20th century rate of GMSL change, providing a lower bound on the trend estimate. Through this work, we will obtain an improved understanding of GMSL during the 20th century and provide context for the increased trend observed during the satellite altimeter era.