Changes in sea level caused by global warming can be disastrous to modern civilization. Therefore, it is important to use accurate and reliable methods to monitor any change. During this century, and, in particular, the last three decades, tide-gauge records have been used to show these changes related to the world's oceans. Aubrey and Emery suggest, however, that tidal gauges should not be used unquestioningly as a benchmark for measuring eustatic sea-level changes. Tectonism, subsidence, ocean current variability, and human activity can, and do, affect the accuracy of these records. Understanding the reasons for changes in land and sea levels is essential for the proper development of coastal regions. The results of this study provide guiding data for scientific, engineering, and policy solutions to coastal flooding. Determining the true causes of relative subsidence, and how to use geological and oceanological controls, will allow us to exist within our natural environment, rather than force nature to conform to our legal and temporary 'remedies.