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Why Sea Level Rise Varies Across The World


The Earth is getting hotter. Ice is melting. The oceans are getting higher. And over the last century, the average sea level around the globe has risen about five to nine inches. But that's just the average sea level rise. Depending on where you live, you could be experiencing a lot more or a lot less. NPR's Rebecca Hersher reports on why.

REBECCA HERSHER, BYLINE: When you imagine the ocean, you might imagine it like a bathtub and that all the ice that's melting is like turning on a faucet. Unfortunately, you'd be wrong.

CHRISTOPHER PIECUCH: The old bathtub analogy - so this is the analogy that in oceanography 101, the professor is very quick to dispel.

HERSHER: Christopher Piecuch is a climate scientist at Woods Hole Oceanographic Institute. The ocean, he says, is way more complicated than a simple tub of water. For example, currents and winds change how high the water is in different places.

ANDREA DUTTON: You could think about the East Coast of the U.S.

HERSHER: Andrea Dutton is a geology professor at the University of Florida. Off the East Coast, there's a huge conveyor belt of water called the Gulf Stream. And because of climate change, it's slowing down.

DUTTON: As that current slows down, it spreads out to the sides. And there's no place for it to go.

HERSHER: It pushes the water up at the coastline. That's helping to drive faster-than-average sea level rise along much of the East Coast; almost twice as fast as the global average in some places. It's happening especially fast from New Jersey south, not only because the ocean is rising but because the land itself is sinking. And to understand why, you have to go back to the last Ice Age, when there were ice sheets a mile thick all the way down to Long Island.

PIECUCH: You have this massive weight sitting on the continents. You could think of - when you go to bed at night and you sort of sit down on your mattress, what happens? The mattress sinks beneath you because of your weight.

HERSHER: But the area right at the edges of where you're sitting, it actually bulges up slightly. During the Ice Age, that happened to the land, too.

PIECUCH: Kind of like a seesaw - anywhere that was sort of around the edge of that ice sheet kind of got levered up.

HERSHER: In the thousands of years since, the bulgy area has been relaxing. That means the Mid-Atlantic coast from New Jersey down to North Carolina is slowly sinking. And lower land is effectively the same as higher water.

DUTTON: The Mid-Atlantic coast is one place that you hear about having more pronounced rates of sea level rise. And that's one of the reasons - because the land is sinking due to the fact that this ice sheet has melted and gone away.

HERSHER: Land can also sink if humans pump out too much water or oil from underground. That's happened along parts of the Gulf of Mexico and in cities like Bangkok and Jakarta. Earthquakes can also cause land to rise or sink. That's happening along the west coast of the U.S. All of these factors contribute to how the extra water from melting ice affects the sea levels in specific places. And there's one more big thing happening that's pushing water onto the land. The oceans are heating up.

DUTTON: So as you heat up water, it expands.

HERSHER: Warmer water takes up more space than cooler water. And the average surface temperature of the oceans has increased about a degree in the last century, which may not sound like a lot. but...

DUTTON: Water expands a lot, even with a very small temperature change.

HERSHER: That exacerbates sea level rise everywhere. It all adds up to wildly different experiences of sea level rise for people who live on different coastlines, which means local communities are leaning heavily on scientists to help them understand what's coming and to prepare for it.

Rebecca Hersher, NPR News.


Rebecca Hersher (she/her) is a reporter on NPR's Science Desk, where she reports on outbreaks, natural disasters, and environmental and health research. Since coming to NPR in 2011, she has covered the Ebola outbreak in West Africa, embedded with the Afghan army after the American combat mission ended, and reported on floods and hurricanes in the U.S. She's also reported on research about puppies. Before her work on the Science Desk, she was a producer for NPR's Weekend All Things Considered in Los Angeles.
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