So this leads to the possibility that if it starts to melt back a little bit,
the grounding line gets deeper and deeper as you melt it back, and so
that makes it easier and easier for the ice to float up off of the ground.
And once it floats up, it can flow in one of these things,
which is called an ice shelf.
So ice shelves can be hundreds of meters thick,
they're not like sea ice which is just a few meters thick.
They're like giant cliffs of ice that you can see,
and they are actually floating in the water.
So an ice shelf itself when it melts doesn't cause the sea level to rise,
because it was floating already.
But the ice shelf can act to sort of pen in
the outward flow of ice from the ice sheet itself.
And so, when these ice shelves crumble and
collapse as they you have seen them doing in the last few years,
they can allow the ice behind it to flow more quickly into the ocean.
The Greenland ice sheet in contrast is not grounded below sea level,
but it is extra vulnerable because it's warmer at the surface.
In Antarctica, the surface of the ice is always pretty much below freezing.
And so, the only way to melt the Antarctic ice sheet
is to flow it off into the water and melt it in the water.
Maybe let it drift away up into warmer climates.
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