Many Pacific island nations are grappling with how to cope with sea level rise as the oceans heat up and polar ice caps melt.

Now there’s something else to worry about: More frequent sea level extremes associated with the El Nino and La Nina weather phenomena and an even greater chance of periodic erosion, flooding and coastal inundation.

That’s the conclusion of a new study by a pair of scientists at the University of Hawaii at Manoa and a colleague from Australia’s national science agency, who found that such sea level extremes will double in frequency by the end of the century.

Fortunately, Hawaii doesn’t have to worry about this particular phenomenon because the islands sit at the middle of the Pacific at the midpoint of a seesaw of ocean water that is pushed back and forth by winds associated with El Nino and La Nina.

It is the islands at the far ends of the sea-level seesaws — in the West, East, North and South Pacific — that must adapt to the new extremes, the scientists said.

El Nino is that irregularly cyclical phenomenon in which a band of warm water forms in the eastern tropical Pacific and affects weather patterns around the globe.

For Hawaii, El Nino interrupts the flow of tradewinds and brings warm, humid and wet summers followed by winter drought. La Nina is essentially the opposite, featuring strong summer tradewinds and winter rain. La Nina often follows El Nino.

Scientists have already documented that warm water and high sea levels shift eastward during El Nino, leaving behind low sea levels in the western Pacific.

This east-west seesaw is often followed six months to a year later by a similar north-south sea level seesaw with water levels dropping by up to 1 foot in the Southern Hemisphere.

Such sea level drops, scientists say, expose shallow marine ecosystems in the South Pacific, prompting massive coral die-offs. In Samoa it offers a foul-smelling tide called “taimasa” (pronounced kaimasa) and hampers fishing.

Meanwhile the opposite is true during the La Nina weather event, resulting in higher sea levels in the western Pacific.

Matthew Widlansky and Axel Timmermann of UH’s International Pacific Research Center collaborated with Wenju Cai of Australia’s Commonwealth Scientific and Industrial Research Organisation, using computer modeling to account for increasing greenhouse gases and tide-gauge analysis to verify the model results.

The experiments showed that the intensified wind and weather impacts of strong El Nino and La Nina events are likely to double the frequency of extreme sea level occurrences, especially in the tropical southwestern Pacific, according to the study, published in the journal Science Advances.

That means instead of seeing these extreme events every 15 to 20 years, they will start happening every 10 years or so, Widlansky said.

From their previous work, the researchers learned that toward the end of a strong El Nino event — like the one we’re experiencing right now — the tide-gauge measurements around Guam quickly return to normal, reflecting the east-west seesaw, but those near Samoa continue to drop as a result of the lagging north-south seesaw, Widlansky said.

Timmermann said the researchers set out to understand how future changes in wind, projected by most climate models, would affect the El Nino and La Nina swings in sea level.

“We noted a trend in greater variability and were surprised at first to find not only more frequent and prolonged drops in sea level, but also more frequent high sea level events,” Timmermann said in a news release. “This will further increase the risk of coastal inundations.”

The results are consistent with previous scientific findings that indicate that the atmospheric effects of both El Nino and La Nina are likely to become stronger and more common in a future world with a warmer climate, the researchers said.

Widlansky said he’s hoping advances in the science of prediction — not only of rising sea levels, but El Nino and La Nina sea level fluctuations — will help Pacific island communities adapt to the impacts of climate change as well as shorter-term climate events such as the current El Nino.