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Measuring sea level rise in the Pacific

Crucial for decisionmakers

Anticipating the effects of climate change on sea level is a pressing task, particularly in the Pacific. Getting hard data on sea level into the hands of decisionmakers and scientists is one of the roles performed by the Secretariat of the Pacific Community (SPC). Together with the Australian Bureau of Meteorology and Geoscience Australia, SPC contributes technical expertise through its Applied Geoscience and Technology Division (SOPAC) to the Australian-government funded Climate and Oceans Support Programme in the Pacific.

This programme maintains and operates the Pacific Sea Level Monitoring (PSLM) network—an array of sea level gauges across 14 Pacific Islands countries. The system, which was established in 1991, currently produces a 24/7 stream of high-quality data including sea level, barometric pressure, wind direction, wind speed, air and sea-surface temperatures and GPS monitoring. The data produced by the PSLM network provides critical information used in early warning systems, development planning, inundation modelling and research. The high degree of accuracy and reliability of the PSLM network is important for scientists studying sea level rise. Arthur Webb, SPC’s Oceans and Islands Programme Manager, explained the process and says it involves trying to discern a slow, incremental signal for sea level rise amid huge daily and seasonal fluctuations. “If we pick a location, let’s say Fiji, you’ve got a tidal range of 1.5 metres to 2 metres.

Sea level is shifting by this amount on a daily basis. Tidal change over months and years is a part of what we call natural variability and it is completely predictable,” he says. “Over an annual cycle, we also have periods where the tides are either exaggerated or suppressed due to natural cyclic processes as the Earth completes its annual orbit of the sun. The predictable high tides are commonly referred to as a ‘king tide’, although this is not a scientific term. These tidal variations are also easily predictable. “There are decadal and multi-decadal cycles that influence sea level as well. These are more subtle and not so easily recognised, but they are also predictable and part of the natural regime of sea level variability all over the world. “Now, superimpose meteorological variability on top of all this predictable variability. We have things like storms, which cause surge, and El Niño and La Niña seasonal effects, which can last for years or sometimes only months, and these can shift sea levels up or down by up to half a metre in some locations.

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