Sea-level variability to increase with ocean warming

LIHU‘E — A recent study out of the University of Hawai‘i at Manoa School of Ocean and Earth Science and Technology suggests future sea levels will be more variable this century as ocean warming increases.

The study was published in Communications Earth &Environment and led by Matthew Widlansky, associate director of the UH Sea Level Center. It assessed future sea-level projections from global climate models.

The research team found that while future sea-level variability changes are uncertain in many locations, nearly all of the 29 models they analyzed agreed on an overall tendency for the variability to increase on seasonal-to-interannual timescales.

“Whereas it is well understood that the rate of global mean sea-level rise will accelerate with future warming, in part due to the oceans expanding faster at higher temperatures, it was previously unexplored how this nonlinear thermal expansion property of seawater will affect future sea-level variability,” said Widlansky.

Sea-level variability alters tidal cycles and enhances the risks of coastal flooding and erosion beyond changes associated with sea-level rise.

Sea-level rise, according to researchers, is occurring as Earth warms due to two main factors: melting of land-based ice such as glaciers and ice sheets, and the expansion of seawater as it warms — termed thermal expansion. Previously unknown was whether the rate of thermal expansion, which accelerates with warming, will also affect the variability of sea level.

“Following thermodynamic laws, sea-level variability increases in a warmer climate because the same temperature variations, for example related to the seasonal cycle, cause larger buoyancy and sea-level fluctuations,” added Fabian Schloesser, a researcher at the UH Sea Level Center who collaborated on the study.

In places where changes due to ocean thermodynamics and other climate variability processes align, the team found the largest increases in future sea-level variability.

Coastal flooding occurs increasingly often due to a combination of slowly rising sea levels and ocean variability. The new findings, therefore, further emphasize the importance of sea-level monitoring and forecasting.

“Forecasting can potentially provide alerts months in advance if sea levels are likely to cause tides to be more extreme than otherwise expected,” said Widlansky.

While the science team explores how to develop better forecast outlooks, the UH Sea Level Center is actively monitoring extremes through a global network of tide gauge observations, including in Honolulu.

On Kaua‘i, several efforts are ongoing to monitor sea-level rise, the impact of King Tides, and to assess the potential future impacts of rising waters.

One of those efforts is the West Kaua‘i Community Vulnerability Assessment, which combined local knowledge of the landscape of West Kaua‘i with researchers’ data to document areas of West Kaua‘i that are vulnerable to sea-level rise.

The final report for the West Kaua‘i Community Vulnerability Assessment was released in June 2020, and lists an inventory of exposed assets, including potable water supply infrastructure and agricultural areas that could be prone to flooding; details the levels of high-tide flooding; and lists cultural and historic resources that could be threatened by sea-level rise.


Jessica Else, editor-in-chief, can be reached at 245-0457 or

  1. Uncleaina August 22, 2020 8:34 am Reply

    Here’s the facts: sea levels have risen about 22 cm since 1920. The rate of increase has risen some lately and the accepted rate of rise currently is about 3mm per year or 30cm per century. That means in 2120 the ocean will be about 10” higher than it is now. Not 3 feet! It would take about 400 years to be 3 feet higher.

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