Extreme Pacific Sea Level Seesaws May Double in the Future

The Pacific may be experiencing some severe weather in the future. Scientists have found that as sea levels rise, there may be more frequent interannual sea level swings, which could greatly impact island nations during storms.

During El Niño, warm water and high sea levels shift eastward, leaving in their wake low sea levels in the western Pacific. Scientists have already shown that 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 one foot in the Southern Hemisphere. Such sea level drops expose shallow marine ecosystems in the South Pacific Islands, causing massive coral die-offs.

But how will future global warming affect these seesaws? The researchers used climate models, which accounted for increasing greenhouse gas concentrations together with simulations of the observed climate and tide-gauge records to verify the model results. Then, they determined that projected climate change will enhance El Niño-related sea level extremes. By the end of this century, the experiments show that the intensified wind impacts of strong El Niño and La Niña events are likely to double the frequency of extreme sea level occurrences, especially in the tropical southwestern Pacific.

"From our previous work, we know that toward the end of a very strong El Niño event, 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," said Matthew Widlansky, one of the researchers, in a news release. "During these strong events, the summer rainband over Samoa, called the South Pacific Convergence Zone, shifts toward the equator and alters the trade winds and ocean currents which in turn change the sea level."

The findings reveal a bit more about what might occur in the future and reveal how sea levels could potentially impact these Pacific islands.

The findings are published in the journal Science Advances.

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