Acronyms & Definitions
Expand the selections below for brief definitions of terms used in our sea-level report cards.
GIA (Glacial Isostatic Adjustment)Ongoing movement of land once burdened by ice-age glaciers. Vertical land movement of other origins are also recognized. |
GMSL (Global Mean Sea Level)World-wide average sea level measured relative to the center of the Earth or a reference ellipsoid. |
IPCC (Intergovernmental Panel on Climate Change)A scientific and intergovernmental body under the auspices of the United Nations. |
MMSL (Monthly Mean Sea Level)Average water level observed over a calendar month. |
MSL (Mean Sea Level)Tidal datum defined by NOAA for a specific tidal datum epoch. |
NOAA (National Oceanographic and Atmospheric Administration)The U.S. federal agency responsible for operating the nation's official tide-gauge network; and of gathering, analyzing, and archiving tide-gauge data. |
NTDE (National Tidal Datum Epoch)Nineteen-year period—currently 1983-2001—used for averaging water levels to determine tidal datum elevations at U.S. tide stations. |
PSMSL (Permanent Service for Mean Sea Level)Established in 1933, PSMSL is responsible for collecting, analyzing, and interpretating tide gauge data on a global basis. It is based in Liverpool at the National Oceanography Centre (NOC), which is a component of the UK Natural Environment Research Council (NERC). |
RSL (Relative Sea Level)Sea level measured relative to a fixed-point datum on land. |
VLM (Vertical Land Movement)Due to various causes including subsurface extraction of water and hydrocarbons, regional tectonics and faulting in addition to GIA |