ON SEA LEVEL VARIABILITY AND TRENDS

As presented in an extensive series of publications, the global rates of the presumptive rise of sea level has been reported to have been between 1.0 to 4.0 mm/yr. These rates have generally been estimated by straightforward averaging from an initial point of observation to an end point or by breaking the spans of the various water level time series into a finite number of segments and averaging overconsecutive segments or overlapping segments. However, no two initial points or end points of observations, no matter the segment lengths, are the same. Inrecent years satellite based altimeter data has been added to water level gage data to produce composite global maps of ocean basin scale sea level rise (SLR). Again these estimates are straight lines drawn through considerable spread in the coastal water level gage and altimeter data. This has createdpublic confusion and consternation about the true nature of what the data are saying. Moreover, there are many questions which should be addressed beforepredictions of future SLR can be made. For example, are the quoted rates ofwater level rise constant for very long periods of time, such as decades tomulti-decades to centuries or do they fluctuate about a trend? And if they do fluctuate about the trend, then what are the frequencies and amplitudes of the variations? And, are trends really straight lines or can so-called trends display non-linear structures? Additionally, do these water level fluctuations relate to either the weather or climate of the oceans or the atmosphere? Finally, just what is the definition of a “trend”? In this presentation, a straightforward mathematical definition of what constitutes a “trend” is proposed, and then using this definition, the variability in the sea level time series from US Atlantic and Pacific Ocean coastlines and Gulf of Mexico coastlines, are revealed and possible linkages with environmental factors are presented. Finally, the question surrounding accelerations and/or decelerations in SLR is discussed.