Local Sea Level

The numbers that come out of climate models are global. They represent the average change in sea level around the world. Most people care more about the change in the sea level where they live, because that is what will impact them — and that can vary a lot, depending on all sorts of factors. In some coastal areas, land is literally rising, still rebounding from the enormous weight of the glaciers that melted 10,000 years ago. While the land right under the glaciers was pushed down, land nearby was squeezed upward in compensation; those places are now falling slowly back. In still other areas, the land is falling because large amounts of oil and gas have been pumped from underground. The land is essentially deflating. Whatever the reason, if the land is falling, then local sea level rises faster than average; if the land is rising (the rarer case), the seas may barely keep pace, or even fall behind.

That’s not all. If the water right offshore warms faster than the ocean as a whole (due to local currents, for example), the water will expand faster, and sea level rise will outpace the global average. If a current that normally draws water away from a stretch of shoreline slows as the climate warms — which may well happen — the water can pile up behind it, like traffic on a partially blocked highway, driving up sea level.

In the United States, most coastal land is slowly sinking, not rising — especially so in the Chesapeake Bay area, Louisiana and the western Gulf of Mexico. And projections suggest that the Northeast Corridor could see an extra few inches of sea level rise over the next few decades, due to a slowing Gulf Stream current.

Next section: Impacts