In the Global Sea Level Observing System (GLOSS) Implementation Plans of 1997 and 2012 (IOC Technical Series No. 50), a set of water level stations around the world have been identified for the detection and monitoring of long term sea level trends and accelerations. NOAA/CO-OPS operates and maintains 27 of these stations and presents routinely-updated analyses of the long-term trends and variability.

In addition the sea level trend analysis has been extended to 240 non-CO-OPS global stations, including over 130 stations in the GLOSS Core Network (GCN). The product suite includes coverage of 65 countries worldwide to capture the variability in local relative sea level change and contribute to global sea level rise estimates. The data for these stations were obtained from the Permanent Service for Mean Sea Level (PSMSL), a data bank for sea level information from the global network of tide gauges. The data sets analyzed are relative to the Revised Local Reference (RLR) datums as established by PSMSL (approximately 7 meters below mean sea level). These products support the Global Sea Level Observing System (GLOSS), an international program under both the World Meteorological Organization (WMO) and Intergovernmental Oceanographic Commission (IOC). They also support the NOAA Climate Program Office's mission to produce essential climate variability and change products and parameters.

Water level records are a combination of the fluctuations of the ocean and the vertical land motion at the location of the station. The sea level variations determined are the linear trend, the average seasonal cycle, and the interannual variability at each station. All the calculated trends are also available as a table in millimeters/year and in feet/century