In order to simulate the climate we have to simulate the
processes by which this heat gets carried from the equator to the pole.
We have to simulate the weather.
And this is hard because of a phenomenon known as the turbulent cascade.
We're stirring this or
we're driving this with a planetary sized forcing.
The difference between the energy coming in and out at the
equator versus the pull, that's a difference that's as big as
the planet, but the flow that results from that is not
as simple as these nice planet size arrows that I drew.
The flow tends to break up large large eddies,
large motions, and make smaller motions.
It's called the turbulent cascade.
A planetary sized forcing leads to large scale motions which then break up
and break up until, finally, they are the size of the
storm systems that affect us from hour to hour in the weather.
And so this is where climate science starts to get hard.
We simulate the climate of the earth and all of these motions, all of this
weather, on a grid like a checkerboard
in a computer program called a Climate Model.
The surface of the earth is represented by this grid and maybe
you have values for the pressure and the temperature in
the centers of these grid points and maybe you calculate what the winds
should be, the flows in the cells, the, the cell walls between these grid points.
The problem is that we would like to have as much detail as we
can have in our simulations of the weather so we can get things right.
We want to have enough grid points
so that we can adequately see, so that the model
can adequately express the smallest scales of the turbulent cascade.
And the problem is that if we decide to double the
amount of detail in a model, for example, that would mean having
twice as many grid points in the horizontal and twice as many
grid points in latitude, longitude and then also
in the vertical having twice as many grid points.
And so and then, the model steps forward in time and if we
make these boxes smaller it turns out that we have to take smaller steps in time.
A normal climate model might take a time step of 20 minutes, for example.
And if we made it twice as many grid points
maybe we could only take ten minutes per time step.
We'd have to take twice as many steps
to do a day or a year or something like that.
It turns out it's a very steep computational curve.
If we want to double the amount of detail we have to do 16 times more math.
And so it gets much, much harder and much, much slower.
Computers are getting faster but climate scientists are going to leave
the computer room wanting faster computers for a very, very long time.