Visualizing Sea Level Rise in the Marshall Islands

A best-case scenario for sea level rise over the next ~100 years.
An optimistic scenario for sea level rise over the next ~100 years (pen & ink, colored in GIMP because Photoshop ain’t cheap).

In the past few weeks, I’ve been reading this book on climate change and tradition in the Marshall Islands, and it’s yielded some interesting quotes on how the Marshallese perceive sea level rise.

For example, when asked what would happen if the Marshall Islands are submerged, one resident had a simple solution:

“Float!”

It’s a funny answer, but it masks the nervous uncertainty that many Marshallese people share about their future.  In the coming decades, the rate of sea level rise will depend on how aggressively we mitigate our carbon emissions, so estimates of future sea level rise can vary.  Some Marshallese imagine a future in which the ocean engulfs the tops of their palm trees.  That’s a bit extreme: most estimates put sea level rise between 0.6 and 1 meter by 2100.

At the other extreme, there’s a widespread misconception (debunked here and in my animation here) that sea level rise isn’t accelerating, or, wronger still, that it isn’t rising at all.

These misconceptions led me to dig through the tide gauge records on Kwajalein Atoll, available here:

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Monthly mean sea level for Kwajalein Atoll in the Marshall Islands.  Between 1946 and 2015, sea level rose by 2.2 mm/yr (±0.82 mm/yr), but that rate is accelerating.

Some observations: 1) Sea level is rising.  2) There are sudden but temporary dips in sea level, in 1983 and 1997 for example.  These drops in sea level match El Niño events.  For the same reason, sea level dropped in 2015, but has since risen back up to pre-El Niño levels.

Sea level rise will continue to accelerate in the next century, reaching ~0.4 meters by 2100 (compared to 1986-2005) in the very best case, but more likely between 0.6 and 1 m.

Is that enough to put the Marshall Islands under water?

It helps to put these numbers into context.  The average elevation of the Marshalls is ~1.8 m (6 feet).  So, we can hope that 0.4-1 m of sea level rise might not flood the entire nation, but it would certainly do some damage.

What might that damage be?  Well, sea level rise will likely erode the shores, and leak saltwater into reservoirs of drinking water.  At the same time ocean acidification and warming will likely lead to more common bleaching events (discussed here), which might make reef fish less common.

I wanted to speculate what that future might look like.  Pulling out the pen and paper, I sketched a the smoothed sea level data from Kwajalein, and added the 1 m of sea level rise in a dotted line on the end.  This sea level figure became the waves in my hypothetical (and a bit fanciful) drawing of the Marshall Islands, 1950-2100:

What happens if sea level rises one meter over the next ~100 years.
What happens if sea level rises one meter over the next ~100 years (pen & ink, colored in GIMP).  In warming, acidifying waters, corals bleach and die, and the shoreline erodes as the ocean creeps upward.

As the ocean rises, warms, and acidifies, the corals lose their color, and some of the less resilient species (the branched corals, for example) disappear as we move toward the right (into the future).  On the shoreline, trees are few and far between, and ones near the beach tilt toward the water as they are undercut by erosion.

If this future looks a bit bleak to you, have hope: in a low-emissions world, sea level rises by ~0.4 meters, yielding something like this:

A best-case scenario for sea level rise over the next ~100 years.
A more optimistic scenario for sea level rise over the next ~100 years.  Coastal erosion is less severe; beneath the waves, corals suffer less bleaching and mortality, and reef fish thrive.

Sure, these drawings are a whimsical take on climate projections, so there will be some discrepancies: the colors aren’t true to life, and I’m pretty sure these fish species don’t actually exist.

That being said, I hope these drawings illustrate a few key points:

  1. Sea level is rising, and will continue to rise over the next century.
  2. Without climate mitigation, sea level could rise by one meter, and as the ocean warms, reef ecosystems degrade and die.
  3. If we take climate action, we can minimize sea level rise, and help to ensure the survival of the Marshall Islands and its reefs.

 

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