- I'm going to show you a picture of a rock
in the Baltic Sea.
This is the Baltic Sea between Sweden and Finland.
And up here is a rock, rather scruffy looking rock,
here it is, and it's actually a rather famous rock.
This rock we know in 1583 was a favorite place
for catching seals in the sea.
Seals used to sit on top of this rock,
which was just below the sea surface.
They used to bask there in the sunshine, having a nice time
and people would come along and hunt them.
Now in 1731, a famous man went to visit this rock
and his name was Anders Celsius.
He was a Swedish mathematician and he's the person
after whom the Celsius temperature scale is named.
And he went to visit this rock because he had heard tales
of how it was rising out of the sea.
And when he went to see it,
he drew the sea level on this little line, just here,
and he marked at 1731, which is when he went to visit it.
Now a hundred years later,
another famous person came to look at this rock,
a man called Charles Lyle,
one of the great geologists of the 19th century,
and he went to visit it because he had heard stories
that Celsius' rock was coming out of the sea.
And when he went to see it in 1835,
they drew another line on down here saying 1835
because Celsius' sea level had been lifted out of the sea
by about a meter by that time.
You can ignore all this scruffy writing here
which is something else.
And in 1931, they made another mark on this rock
which is now down here.
That's where sea level was in 1931.
And this rock is rising out of the sea
at about a meter every century.
And all around that part of the Baltic Sea,
the shoreline is rising out of the sea.
There a Viking harbors 1,000 years old
which are 10 meters out of the sea,
completely useless as harbors.
So the whole of that shoreline is coming out of the sea
and we can draw a map of just what it looks like.
And so these are contours
of how fast the shoreline is coming out of the sea.
And our rock was in the middle here
of this bullseye pattern.
That's where it's coming out fastest and it's coming out
less quickly as we go away from the middle there.
Now, what is this bullseye pattern about?
What it is about is shown in this little model here.
If you put an ice sheet on the earth,
the earth sinks a little bit because of the weight
of the ice sheet.
The ice sheet presses down on the surface of the earth
and down underneath those hot rocks flowing
like Potty Putty, they creep out of the way.
And here is our ice sheet resting on the earth.
What happens if we remove the ice sheet?
'Cause the ice sheet can melt really quite quickly.
So let's remove our ice sheet
with the polar bears, take it away.
And what actually happens then is the land
bounces out of the sea.
Here's where the shoreline used to be, this line in red,
and here it is bouncing slowly out of the sea
and the shoreline is retreating.
And that's happening because those rocks
which we pushed out of the way underneath
because we put the ice sheet on top,
are now slowly flowing back into where they were before.
And as they flow back in, they pushed the land back up.
And that is what is happening back here in Scandinavia.
This bullseye pattern in Scandinavia
is actually exactly the same shape
as the Scandinavian ice sheet.
It was pushed down, most in the middle here,
and it's now bouncing up most in the middle,
and it's bouncing up because the rocks deep down
which have been pushed out of the way,
are now flowing back towards the middle
of where that ice sheet was and lifting the land up.
And in fact, they're flowing back towards Scandinavia
from under us.
So we're actually going down slightly at the moment here
as all that rock is flowing gently towards Scandinavia.
So although the ice actually finished melting
6,000 years ago, those rocks are still gently flowing
back underneath where the ice was, and the ice is giving us
our best estimate of just how quickly those rocks
are flowing back 'cause the Baltic
is coming up about a centimeter a year,
that kind of rate.
And without the help from the ice,
it would be very hard for us to make an estimate
of just how runny it is down there.