The Federated States of Micronesia, Marshall Islands, and the Solomon Islands were hit by flooding last week that caused widespread damage to buildings and food crops.
Spring tides are normal at this time of year in the western Pacific, and are also known as very high tides. Why is the damage so bad?
Climate change, spring tides, and La Nia are the primary reasons why these nations are enduring flooding.
La Nia is a natural climate phenomenon that brings wet weather to eastern Australia. Sea levels in the western tropical Pacific are raised by La Nia.
The current La Nia is raising sea levels in some western Pacific regions by up to 8 inches, the same sea level rise projected to occur globally by the end of the century regardless of how much we cut global emissions between now and then.
We can expect more flooding over the summer because of this phenomena.
South Pacific nations into third day of high spring tides; places like Solomons and Marshalls are suffering extensive food crop damage.
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Michael Field is from New Zealand.
These spring tides are not unusual.
Millions of people could be forced to find new homes in the coming decades if sea level rise is not stopped on low-lying islands in the Pacific.
Last week's floods show what will happen by the year 2050. In the Marshall Islands, waves washed over boulder barriers, causing flooding on roads half a meter deep.
The recent spring tides coincide with this flooding. This year's spring tides aren't as high as they were in previous years because of the variability in the magnitude of these tides.
The annual maximum sea levels at stations in Lombrom and Dekehtik in the Federated States of Micronesia are up to an inch higher than last year. Betio and Uliga are 3-6 cm (1-2 inches) lower.
Climate change and the ongoing La Nia event have been linked to this year's increased flooding.
A double dose.
The Intergovernmental Panel on Climate Change found that global average sea levels rose between 1901 and 2018).
The sea level rise would lead to more coastal flooding in low-lying areas, like those in the western tropical Pacific. Sea level rise increases at a relatively small rate. Over decades and longer, year to year differences are small.
There are relatively small differences between this year and the previous few years, which means global mean sea level rise has likely contributed to last week's floods.
This is where La Nia makes the biggest difference. We know that the climate of nations across the Pacific can be affected by La Nina events, which can bring high rainfall and tropical storms to some locations.
The easterly trade winds are stronger in La Nia years. Warm water builds up in the western Pacific.
Warm water is thicker than cool water due to thermal expansion, and so it is often accompanied by higher sea levels during La Nia events.
The sea surface height anomalies can be seen in the maps here and here.
Pacific islands west of the date line are at risk of high sea levels during La Nia events.
The western Pacific islands and atolls will likely see more flooding over the summer months. This is because the sea level rise is maintained throughout the period, with more periods with high spring tides.
The high sea levels related to La Nia events in the northern hemisphere tend to peak in November-December, while they do not peak in the southern hemisphere until February-March.
Many western Pacific locations on both sides of the equator will experience further coastal flooding in the short term. The Solomon islands, for example, are likely to have more severe impacts in the southern hemisphere than in the northern hemisphere.
A further 15 to 25 cm of global average sea level rise is expected by the year 2050. Sea levels in these regions can rise up to 20 cm due to La Nia events.
The current event provides an important insight into what will become normal during spring tides given the projected sea level rise in 2050.
Climate projections show that the sea level rise by 2050 is locked in due to the greenhouse gas emissions we've already released.
We know that sea levels will rise for several centuries, and this will largely depend on our future emissions.
To give low-lying island nations a fighting chance at surviving the floods, all nations must cut emissions.
Shayne is an associate professor at the centre of excellence for climate extremes.
The Conversation's article is a Creative Commons licensed one. The original article can be found here.
