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When you fill a sink, the water rises at the same rate to the same height in every corner. That’s not the way it works with our rising seas.
According to the 23-year record of satellite data from NASA and its partners, the sea level is rising a few millimeters a year — a fraction of an inch. If you live on the U.S. East Coast, though, your sea level is rising two or three times faster than average. If you live in Scandinavia, it’s falling. Residents of China’s Yellow River delta are swamped by sea level rise of more than nine inches (25 centimeters) a year.
These regional differences in sea level change will become even more apparent in the future, as ice sheets melt. For instance, when the Amundsen Sea sector of the West Antarctic Ice Sheet is totally gone, the average global sea level will rise four feet. But the East Coast of the United States will see an additional 14 to 15 inches above that average.
Tides, winds and ocean currents play a role in these regional differences, but an increasingly important mover and shaker is the solid Earth itself. Global warming is not just affecting the surface of our world; it’s making the Earth move under our feet.
Unless a volcano or earthquake is in the news, we tend to think of our home planet as solid rock. But 50 miles (80 kilometers) below our feet, there’s a layer thousands of miles thick that can flow like a liquid over thousands of years. The tectonic plates of Earth’s crust float on this viscous layer, called the mantle, like a vanilla wafer on a very thick pudding.
If you were to put a strawberry on top of that vanilla wafer, the added weight would make the cookie sink into the pudding. In the same way, heavy weights on Earth’s crust push it down into the mantle, which flows away and bulges out elsewhere. The miles-thick ice sheets of Greenland and Antarctica have been depressing the crust beneath them for millennia. That weight has a second effect that you won’t see in your dessert: its gravitational pull on the surrounding ocean makes seawater pile up around the coastlines.
Continue reading at NASA’s Jet Propulsion Laboratory.
Ocean image via Shutterstock.
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