Global warming and sea level rise will lead to a widespread increase in the frequency and severity of storms, which will cause coastal erosion, salt water intrusion into river estuaries,
have a negative impact on tourism and reduce the availability of fresh water. Member States' concern over these effects stimulated UNESCO's Intergovernmental Oceanographic
Commission (IOC) to propose an international network for systematic measurement of sea level in many parts of the world, using standard techniques and pooling the data for use in
sophisticated computer models - and then making the analyses widely available. Member States reacted enthusiastically, establishing the Global Sea Level Observing System
(GLOSS) in 1986. Now 85 countries, both large and small, are taking part.

Measures of sea level have been made for many years for local practical purposes. The French port of Brest has kept records of tides for navigation since 1804. But a much wider
network is required to identify global changes. Now, the Global Sea Level Observing System links 287 tide gauges world-wide, some of them in hostile environments like the Arctic
and Antarctic. GLOSS also provides training and technology transfer to enable scientists and technicians in developing nations to play an active part.

Ten years later, 70-75 percent of the proposed tide gauge stations are operational. Meanwhile, the launch of the Franco-American TOPEX/Poseidon satellite - now near the end of its
mission - has been an enormous boost. The satellite uses radar altimetry to measure sea surface height to within five centimetres and has been instrumental in monitoring the current
El Niño phenomenon as it develops in the equatorial Pacific. Using the combined data from tide gauges and satellite, scientists now estimate a sea level rise of about 50 centimetres
by the end of the next century - much less than the two to three metre increase forecasts before GLOSS was set up.

Information courtesy of UNESCO: