Low Frequency Variations of Relative Sea Level

Tide gauge records of sea level display variability at all frequencies, including centennial. This variability adversely impacts estimates of sea level rise, especially for records shorter than 50-75 years. Variability of sea level at tide gauge locations on the eastern boundaries of the N. Atlantic and N. Pacific oceans is very significant even for periods > 100 years. The longest records in the N. Atlantic (Brest) and N. Pacific (San Francisco), universally used in estimates of global sea level rise, display very different behavior in the latter half of the 19th century compared to the 20th century. We show that this behavior is closely related to, but not explained by, local sea level pressure at these sites. It is possible that the disparate behavior of sea level between the 19th and 20th centuries is related to ocean basin-scale atmospheric forcing. Examination of other long records in the northern and southern hemispheres reveals in many cases a leveling off of sea level after about 1960.