There is a large range of possible sea level rises for this century, and different places will experience different local rates. How much the increase affects people and property, however, depends on yet further factors.
Most obviously, what does the shoreline itself look like? If the land rises sharply out of the sea, like it does along parts of the California coast, even several feet of sea-level rise might not be a big deal. If your house or a road is 100 feet up, you might not even notice. But in other places, such as Miami, the land is almost flat, with millions of people living there. In still others, such as New Orleans, large areas actually lie below the current sea level — and will lie further below as sea level goes up.
The ground itself can also have a big impact. In places with porous bedrock, like much of Florida, the rising sea can intrude on underground aquifers of fresh water that lie near the coast. In places where rivers and canals flow into the ocean, they’ll have more trouble draining, especially after major rainstorms, as the sea rises higher. Local flooding could become more common.
And finally — from the other side — sea level rise is raising the launch pad for coastal storms and high tides. In many places, only a few vertical inches separate what would be today called a once-in-a-century flood, from what would be called a once-in-a-decade flood. Rising seas will thus be experienced through ever-more frequent occurrence of extreme high coastal water levels and floods, long before anyone notices the average change. And it’s these floods that can hurt the most. For example, when the Mississippi and Louisiana coasts were devastated by Hurricane Katrina in 2005, by far the greatest damage came from the storm surge, not the wind or rain.
In considering the dangers from sea level rise, it’s crucial to take all of these factors — global rise, local rise, terrain, development, geology, drainage, storm surges, high tides, and more — into account.
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