Improved techniques to estimate mean sea level, velocity and acceleration from long ocean water level time series to augment sea level (and climate change) research

Abstract

The prominence of the climate change issue has placed more emphasis on examination of the extensive global repository of mean sea level records, which along with temperature and carbon dioxide, remain the key proxy data sets used to monitor and quantify changes in the global climate system. Over the past decade, the scientific literature is replete with conflicting conclusions regarding the detection (or otherwise) of a measurable acceleration in mean sea level attributable to climate change. The key aim of the research program is to develop improved techniques (and associated tools) for estimating mean sea level and associated velocity and acceleration from long individual ocean water level time series to augment climate change research. This task involved extensive time series analysis which identified Singular Spectrum Analysis (SSA) as an optimal analytic for resolving estimates of mean sea level from long tide gauge records with improved accuracy and temporal resolution. SSA was further tested and optimised, then integrated into an open source analytical software package ( msltrend ), specifically customised for sea level research, providing enhanced estimates of mean sea level and associated velocity and acceleration on a year to year basis. The application of this package to the data rich margins of USA and Europe have provided more insight into the temporal and regional characteristics of mean sea level than previously available. In general, key findings across both margins suggest that not only are more recent accelerations no different to other periods elsewhere in the historical records, but, they are neither sufficiently strong nor sustained enough (yet) to accord with those associated with climate change projection models. Further, until such time as the velocities and accelerations are sufficiently large not to be obscured by complex influences inducing decadal to multi-decadal variability and other background noise, the search for accelerations in ocean water level records require more intuitive, diagnostic considerations which are explored in the research. The techniques espoused in this research form an integral part of the evolutionary process by which to measure kinematic properties of mean sea level with improving robustness and consistency.