Editing Global mean sea level

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{| class="wikitable" style="float:right; clear:right; margin:0 0 1em 1em; width:320px;"
|+ SIGNAL Earth Structured Data
|-
! Object type
| Damage Signal
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! SIGNAL Earth ID
| DS-00003
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! Observable type
| Global mean sea level
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! Unit
| mm (millimeters)
|-
! Temporal structure
| Continuous
|-
! Monitoring backbone
| NASA / PO.DAAC
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{{SignalTerm|type=DS|id=DS-00003|label=Global mean sea level}} (GMSL) is a key indicator of changes in the Earth's oceanic and climatic systems. It represents the average height of the ocean's surface measured across the globe, integrating variations caused by thermal expansion, melting ice sheets, glaciers, and other factors. Monitoring GMSL is essential for understanding long-term trends in ocean volume and the impacts of climate change on coastal environments.

Changes in global mean sea level affect a range of environmental and societal systems, including coastal erosion, flooding, and habitat shifts. As a state variable within the ocean-physical domain, GMSL reflects the cumulative effects of multiple processes influencing ocean water volume and distribution. Its continuous measurement provides critical data for climate science, oceanography, and hazard assessment.

The study of GMSL involves integrating satellite altimetry, tide gauge records, and oceanographic observations to capture spatial and temporal variability. This comprehensive monitoring supports efforts to quantify sea-level rise rates and understand their drivers in a changing climate context.

== Geographic / System Context ==
Global mean sea level pertains to the Earth's oceans as a whole, encompassing all ocean basins and marginal seas. It is a spatially aggregated measure that averages sea surface height variations worldwide, smoothing regional differences caused by factors such as ocean currents, atmospheric pressure, and gravitational anomalies. The geographic scope includes the interconnected global ocean system, which covers approximately 71% of the Earth's surface and interacts dynamically with the atmosphere, cryosphere, and terrestrial hydrosphere.

== Monitoring and Measurement ==
The primary methods for monitoring global mean sea level include satellite altimetry and tide gauge networks. Satellite altimeters, such as those operated by NASA and coordinated through the Physical Oceanography Distributed Active Archive Center (PO.DAAC), provide precise, continuous measurements of sea surface height relative to a reference ellipsoid. Tide gauges contribute long-term records from coastal locations, offering valuable historical context. Combining these datasets enables scientists to assess both short-term variability and long-term trends in sea level. Additional oceanographic data, including temperature and salinity profiles, support understanding of the physical processes driving sea-level changes.

Within the SIGNAL system, this phenomenon is treated as a defined environmental signal whose boundaries and measurement conventions are described below.

== Signal Definition ==
Global mean sea level is defined as the spatially averaged height of the ocean surface relative to a standardized geodetic reference, expressed in millimeters. It is derived from the observable type 'Global mean sea level' and represents a state condition within the ocean-physical domain. This signal captures variations in ocean volume resulting from thermal expansion, mass changes in ice sheets and glaciers, and other chemical and physical processes influencing sea water volume.

== Boundary Conditions ==
Boundary inclusions for global mean sea level encompass all oceanic waters globally, integrating contributions from open ocean basins and coastal seas. The signal excludes inland water bodies such as lakes and reservoirs, as well as transient phenomena that do not affect the long-term average sea surface height, including short-term tidal fluctuations and storm surge events. The measurement focuses on persistent state changes rather than episodic or localized anomalies.

== Aggregation Semantics ==
Geographically, global mean sea level is aggregated across the entire ocean surface, providing a single representative value that smooths regional variations. Temporally, the signal is continuous, with measurements aggregated over daily to decadal timescales to capture both short-term variability and long-term trends. Cross-signal aggregation involves integrating global mean sea level data with related environmental signals such as ice sheet mass and ocean heat content to understand causal relationships and compound effects. This aggregation approach supports comprehensive assessments of oceanic and climatic state changes.

== Observational Status ==
Monitoring of global mean sea level is ongoing and supported by established satellite altimetry missions coordinated by NASA and other agencies, with data archived and distributed through PO.DAAC. Tide gauge networks provide complementary historical records. Current observational capabilities allow for near-real-time tracking of sea-level changes and improved understanding of underlying processes. Future SIGNAL releases may incorporate enhanced spatial resolution, integration with additional oceanographic parameters, and refined boundary definitions as scientific understanding advances.

== Related Signals ==
* Coastal erosion extent
* Coastal flood inundation extent
* Coastal salinity intrusion extent
* Coastal storm surge height
* Flooded area extent
* Ice sheet mass
* Ice volume (glaciers)
* Ocean heat content (0–2000m) (global)

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== Key Associated People ==
* '''Anny Cazenave''' — Steward-candidate (LEGOS CNES) [Domain expert]
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== Sources ==
* {{cite journal | title=The rate of sea-level rise | journal=Science | year=2010 | doi=10.1126/science.1185782 | url=https://doi.org/10.1126/science.1185782}}
* {{cite journal | title=Sea-level rise and variability from satellite altimetry | journal=Nature | year=2001 | doi=10.1038/35066500 | url=https://doi.org/10.1038/35066500}}
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