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Sea Level Rise is on the Rise

Sea Level Rise is on the Rise

As our planet warms, sea levels are rising around the world
– and are doing so at an accelerating rate. Currently, global sea level is
rising about an eighth of an inch every year.

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That may seem insignificant, but it’s 30% more than when
NASA launched its first satellite mission to measure ocean heights in 1992 –
less than 30 years ago. And people already feel the impacts, as seemingly small
increments of sea level rise become big problems along coastlines worldwide.

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Higher global temperatures cause our seas to rise, but how? And why are
seas rising at a faster and faster rate? There are two main reasons: melting
ice and warming waters.

 The Ice We See Is Getting Pretty Thin

About two-thirds of global sea level rise comes from melting
glaciers and ice sheets, the vast expanses of ice that cover Antarctica and
Greenland. In Greenland, most of that ice melt is caused by warmer air
temperatures that melt the upper surface of ice sheets, and when giant chunks
of ice crack off of the ends of glaciers, adding to the ocean.

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In Antarctica – where temperatures stay low year-round – most of the ice loss happens at the edges
of glaciers. Warmer ocean water and warmer air meet at the glaciers’ edges, eating
away at the floating ice sheets there.

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NASA can measure these changes from space. With data from
the Ice, Cloud and land Elevation Satellite-2, or ICESat-2, scientists can
measure the height of ice sheets to within a fraction of an inch. Since 2006,
an average of 318 gigatons of ice per year has melted from Greenland and
Antarctica’s ice sheets. To get a sense of how big that is: just one gigaton is
enough to cover New York City’s Central Park in ice 1,000 feet deep – almost as tall as the Chrysler Building.

With the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission – a partnership with
the German Research Centre for Geosciences – scientists can calculate the mass
of ice lost from these vast expanses across Greenland and Antarctica.

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It’s not just glaciers in Antarctica and Greenland that are
melting, though. Nearly all glaciers have been melting in the last decade,
including those in Alaska, High Mountain Asia, South America, and the Canadian
Arctic. Because these smaller glaciers are melting quickly, they contribute
about the same amount to sea level rise as meltwater from massive ice sheets.

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The Water’s Getting Warm

As seawater warms, it takes up more space. When water molecules get warmer, the atoms in those molecules vibrate faster, expanding the volume they take up. This phenomenon is called thermal expansion. It’s an incredibly tiny change in the size of a single water molecule, but added across all the water molecules in all of Earth’s oceans – a single drop contains well over a billion billion molecules – it accounts for about a third of global sea level rise.

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So Much to See

While sea level is rising globally, it’s not the same across
the planet. Sea levels are rising about an eighth of an inch per year on average worldwide. But
some areas may see triple that rate, some may not observe any changes, and some
may even experience a drop in sea level. These differences are due to ocean
currents, mixing, upwelling of cold water from the deep ocean, winds, movements
of heat and freshwater, and Earth’s gravitational pull moving water around. When ice melts from Greenland, for example, the drop in mass decreases the
gravitational pull from the ice sheet, causing water to slosh to the shores of
South America.

That’s where our view from space comes in. We’re launching
Sentinel-6 Michael Freilich, an international partnership satellite, to
continue our decades-long record of global sea level rise.

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