40 years of measuring sea level

Established in 1985 as an intergovernmental programme hosted by the Intergovernmental Oceanographic Commission (IOC) of UNESCO, GLOSS is a core component of the Global Ocean Observing System (GOOS). Its mission is to coordinate a high-quality global network of coastal tide gauges that provide reliable sea level data for research and operational use.

What began as a core network of about 300 stations across more than 90 countries has expanded dramatically. Today, over 2,000 stations operated by national institutions worldwide contribute to GLOSS, supporting applications ranging from climate change assessment and coastal adaptation to tsunami and storm surge early warning, port operations, satellite calibration, and numerical modelling. GLOSS also plays a crucial role in monitoring vertical land motion near tide gauges through benchmark surveys and continuous GNSS measurements, ensuring that sea level trends are accurately interpreted.

The Steering Committee supports the GLOSS Grouf of Experts through:

• Strategic oversight and drafting of plans.
• Stakeholder engagement.
• Technical coordination.
• Data‑quality harmonisation.
• Outreach and capacity development.
• Resource mobilisation.