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Insights, inspiration and opportunities to create a more vibrant and resilient future.

What Do Sea Level Rise Maps Even Mean?

Lyndon Valicenti

By now, we have all probably seen those scary sea level rise maps indicating future inundation of our coastal cities and landscapes. But what do they really mean?

Now, I’ll be honest, I am still trying to wrap my head around all this. But what I do know is that sea level rise projection maps are often a composite of a couple of things:
- Elevation data of the land.
- Sea level rise (SLR) projections, based on the latest climate science literature.
- Local high tide data; sea level rise is often mapped on top of mean higher high water (MHHW), aka the average high tide.
- Some maps might also include storm surge risk, based on historic water levels and the conservative assumption that coastal storm frequency or intensity will not change in the future.

They usually do not include future changes to coastal geomorphology (i.e., erosion, loss of marshland, etc.) or impacts of overland and riverine flooding on coastal inundation. They also don’t usually incorporate any levee data, because the built environment is likely to change significantly before the water levels shown arrive.

Sea level rise projection data used by Climate Central and others are based on three factors:
1. Expansion of the oceans as they warm.
2. Melting of glaciers.
3. Decay of the Greenland and Antarctic ice sheets.

At this rate, scientists are confident that we are locked into at least 3 feet of sea level rise, but the question is whether that will be in 100 or 200 years. One of the biggest uncertainties today is how quickly the Greenland and Antarctica’s East and West Ice Sheets will melt. The West Antarctic Ice Sheet (smaller than the more stable Eastern one, but whose collapse is already underway) will add up to 12 feet of sea level rise between 200 and 1,000 years from now. And a brand new study’s worst-case scenario predicts the seas could rise 6 feet by 2100.

Understanding the risk of sea level rise on hundreds of millions of people and trillions of dollars of property that are within a few feet of current sea levels is imperative to making more resilient decisions today. Maps are a critical way to visualize this threat.