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Why is sea level rising?

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NASA.

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We Asked a NASA Scientist.

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So on global scales, sea level is rising really because of our warming climate.

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There's two main factors causing sea level to change.

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The first is what we call thermal expansion.

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So as more heat gets trapped by the atmosphere,

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a lot of that heat gets absorbed by the ocean.

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When water warms, it actually expands
and that causes sea level to go up.

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The other reason that sea level is rising
is because of melting ice.

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So we have a lot of ice
contained in the ice sheets,

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the Antarctic, Greenland ice sheets
and different mountain regions.

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As the Earth warms, these regions are also warming.

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So what happens is this ice melts, and when it melts, that meltwater flows into the ocean.

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So again, this causes sea level to go up.

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On regional scales, the rates of sea level rise can actually be quite different.

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The ocean doesn't fill like a bathtub.

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Different parts of the ocean see more of an effect than others, depending on two main factors.

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The first of these is something
we call ocean dynamics.

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So as the climate changes,
there can be changes

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in our ocean circulation, the currents,
and this actually changes

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how water is distributed
and moved about the Earth, causing

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sea level to be different in 
some locations than others.

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The other reason that we see differences
in the rates from one region to the next

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is something
we call the ice sheet fingerprints.

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So there's so much ice being lost

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from these different locations,
from the ice sheets

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that it actually affects the gravity
and rotation of the Earth.

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And we have these distinct,
what we call fingerprints,

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that really dictate
where the water goes when it melts.

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So some parts of the world will see more of an effect from some locations than others

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and that can really cause changes in
the amount of sea level rise that we see.

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In sum, why is sea level rising?

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Sea level is rising really because of our warming climate.