Startling Discovery: Worst Impacts of Sea Level Rise Will Hit Earlier Than Expected

Flooded City Sea Level Global Warming

Updated land-elevation models reveal many coastal regions are lower than we thought, according to a new study in Earth’s Future. The first 1 to 2 meters of sea level rise will therefore inundate about twice as much land as earlier elevation models suggested.

Newly updated elevation models of coastal regions indicate that the area of land that would be inundated with a 1 to 2 meter rise in sea level could be twice as much as previously estimated.

According to current models, the most significant effects of sea level rise are expected to take place once it reaches several meters. However, a recent study has uncovered that the largest increases in flooding will occur after the first 2 meters (6.6 feet) of sea level rise, affecting an area of land that is more than double what was previously predicted by older elevation models.

The study utilized high-precision land elevation measurements from NASA’s ICESat-2 lidar satellite, launched in 2018, to enhance models of sea level rise and flooding. Prior evaluations were typically based on less accurate radar-based data.

“Radar is unable to fully penetrate vegetation and therefore overestimates surface elevation,” said Ronald Vernimmen, a researcher at the Dutch research firm Data for Sustainability. Many coastal areas are lower than scientists thought they were.

The study was published in the American Geophysical Union’s Earth’s Future, which publishes interdisciplinary research on the past, present, and future of our planet and its inhabitants.

The underestimates of land elevation mean coastal communities have less time to prepare for sea level rise than expected, with the biggest impacts of rising seas occurring earlier than previously thought. After those first few meters of sea level rise, the rate at which land area falls below mean sea level decreases.

Vernimmen, who works on flood protection and spatial planning advisory projects, started using these more accurate measurements of land elevation when he realized that existing land elevation estimates were not suitable for quantifying coastal flooding risk.

Using the new measurements of land elevation, Vernimmen and co-author Aljosja Hooijer found coastal areas lie much lower than older radar data had suggested. Analyses of the new lidar-based elevation model revealed 2 meters of sea-level rise would cover up to 2.4 times the land area as observed by radar-based elevation models.

For example, the lidar data suggest a 2-meter (6.6 feet) increase in sea level could put most of Bangkok and its 10 million residents below sea level, while older data suggested that Bangkok would still be largely above the mean sea level under that same amount of sea level rise. In total, after 2 meters (6.6 feet) of sea level rise, Vernimmen and Hooijer estimate that 240 million more people will live below the mean sea level. After 3 and 4 meters (9.8 and 13 feet) of sea level rise, that number increases by 140 million and by another 116 million, respectively.

Cities below future sea levels may not necessarily be submerged because levees, dikes, and pumping stations can protect some areas from rising seas; Amsterdam and New Orleans are modern examples of this. However, such protection measures can be expensive and take decades to implement. If vulnerable communities want to mitigate the most damage, they need to act before the sea rises those first few meters, according to Vernimmen.

Reference: “New LiDAR-Based Elevation Model Shows Greatest Increase in Global Coastal Exposure to Flooding to Be Caused by Early-Stage Sea-Level Rise” by Ronald Vernimmen and Aljosja Hooijer, 2 January 2023, Earth’s Future.
DOI: 10.1029/2022EF002880

9 Comments on "Startling Discovery: Worst Impacts of Sea Level Rise Will Hit Earlier Than Expected"

  1. “Worst is ewrlier” is not quite what this article is saying. It’s saying a larger area would be inundated at the forecast rise in sea level.

    Is that “worst”?

    It’s simply “more”.

  2. All coastal cities should be starting to migrate themselves inland or completely relocating to a new location – if they start doing that NOW it will happen, if they just sit around talking about it they will eventually get drowned. NOW is the time to start ! I live up a hill but I have 2 kids living at currently about 2 ft above sea level on the coast – I will be long gone before the worst happens, but my grandchildren will have to face the problem – but nobody is listening !!!

    • Even your great-grandchildren will not be alive in 500 years, which is about how long it will take for 1 meter (~3′) rise in sea level. The home your children are living in will not last even 100 years.

  3. If sea level rise was an issue people would already be moving out of coastal cities.

  4. In the 80’s I was walking along the Humber estuary sea wall and the water level was above the embankment I was walking on and only the metre high concrete wall stopped inundation. With this in mind when I purchased a house may years later one of the criterior was to be more than 80m above sea level.

  5. My take on this is that the maps are wrong. However, the people living along the coast know where the mean high tide line is, and they know where 2 meters above that is.

    Sea level is currently rising about 2 mm, or 0.002 m, per year. At that rate, it will take about 1,000 years to rise 2 meters. That is more than enough time to either build dikes like the Dutch have, or simply move away from the coast after the structures currently there wear out. Why did the authors not mention this? A lot of hand waving without numbers. I’m sure that people working with LIDAR are not innumerate.

    • Typical stupid comment from the same stupid person who continues to try to deflect the ongoing reality. Spencer – you’re a goddamned idiot. You’re assumption is full of holes. You’re stupidly projecting that sea level rise will be a constant – and you know sure as s#!t it won’t. Why did YOU not even mention this? Because your entire purpose here is to deflect reality, deny science, pretend that you’re idiotic conjectures are instead the only ones worth listening to. F*** off a**hole, I’m through trying to get you to pull your head out of your a**.

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