Accounting for Accelerating Subsidence in the Analysis of Tide Gauge Records

To appreciate the absolute (geocentric) sea level trend in a tide gauge location, it is necessary to subtract from the relative sea level trend measured by the tide gauge instrument, the absolute subsidence of the land where the tide gauge instrument is located. While Global Positioning System (GPS) may permit the computation of the subsidence rate in the last few years, up to 10–15 years, past values of subsidence may only be inferred from Glacial Isostatic Adjustment (GIA) computations. Proper trend analysis for the relative sea levels requires more than 100 years to correctly appreciate the rate of rise and acceleration. The same time window must be also used for the subsidence. The method is presented here, and a few examples of applications are provided. The observed rate of rise and acceleration of the relative sea levels at the world tide gauges has an almost equal contribution from thermosteric absolute sea level rise and subsidence.