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