The Vine

The Oddities Of Sea-Level Rise


The way we're warming the planet, we can probably expect sea levels to rise at least a meter, on average, by the end of the century. That's what most scientific projections suggest, anyway. One kink, though, is that that's just an average—the seas won't go up uniformly by one meter all across the globe. Some places will see much higher rises than that, some places much lower. Michael Lemonick has a great Environment360 piece delving into some of the factors that make sea-level rise so odd and unpredictable. Wind patterns, for instance:

The trade winds that blow west across the tropical Pacific, for example, move water in the same direction, boosting average sea levels by as much as 24 inches on the western side of the ocean—in places such as the Philippines—compared with those in northern South America. If those winds shift with climate change, so would local sea levels.

Meanwhile, if the Gulf Stream in the Atlantic starts slowing down at all due to a combination of warmer temperatures and Greenland's melting ice sheet, that could force ocean water to pile up and raise sea levels along the eastern United States as much as 8 inches higher than the global average. Even more bizarrely, as the polar ice sheets shrink, that could affect the Earth's gravitational field in unexpected ways, sloshing the water around the planet unevenly:

About a year ago, Jerry Mitrovica, a geophysicist who teaches an entire course on sea level at Harvard, co-authored a paper in Science that laid out what would likely happen if the West Antarctic ice sheet, the smaller of the two sheets that cover the Antarctic continent, were to melt. (Like a complete shutdown of the Gulf Stream, this is not considered likely anytime soon. But recent satellite measurements have shown that glaciers that drain the ice sheet have begun moving faster toward the sea).

If you simply spread the resulting increase in sea level evenly around the world, it would amount to about 5 meters’ worth. But the ice sheet’s gravity is currently keeping sea level artificially low in the Northern Hemisphere, so if it disappeared, the actual increase along the U.S. mid-Atlantic coast would be more like 6.3 meters. In other words, as the West Antarctic Ice Sheet melts and loses mass, its pull on the surrounding ocean will lessen. Seas will drop around Antarctica and parts of the Southern Hemisphere, and that water will be displaced to more northerly areas, such as the east coast of the U.S.

Now that the gorilla has made its presence known, Stouffer is working with Mitrovica to understand its effects in greater detail. A joint paper, due out in a few months, will look into the gravitationally driven sea-level changes a melting Greenland could trigger. “The signal is so large,” says Stouffer, “that if you own beachfront property in Iceland, and all of the ice on Greenland melts and adds seven meters to average sea level, you end up with more beach. But in Hawaii, you get your seven meters of sea-level rise plus an extra two or three on top of that. It’s phenomenal to me that it matters that much.”

Agreed, that's... really odd.

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