Hello, and welcome to part two of my global warming Coursera class. Part two is considered to be an optional add-on to part one, which is where all the sort of climate science content is. Part two is designed to give you a chance to learn how to do some simple climate modeling in a language called Python. So, the Python background you'll need to get in some sort of a Python class or tutorial. And the climate background you can get in this other class. But we will be showing how to use both Python scripting and also spreadsheets to create simple models of things that go on in the earth system science, such as the first problem we'll be solving is an energy balance problem where you have the solar energy coming into a planet and the infrared light leaving, and the temperature is determined by the energy balance. So in the other class we calculate the equilibrium temperature, the temperature that it would reach after a long amount of time, but in this class we'll be developing a model to take time steps so that we can resolve a transient change in temperature such as this. We have to be careful when doing time steps not to take a time step that's too far that would extrapolate us into numerical error kind of land. So this is what a spreadsheet version of that first problem might look like, with some parameter values up at the top that you can change interactively, and some time steps down below, sort of down through here. And this is a plot of planetary temperature as a function of time, and the different symbols there are the time steps. If we look at that as a Python script, you can see it's just a short little thing there. We can run that Python script, and it does the same thing as the Excel spreadsheet does. Other Python tricks that we will do in this class include an ice sheet. So, here, we're taking time steps and plotting the elevation of an ice sheet as a function of lateral distance. So there's snow falling everywhere throughout the domain, and the values at the edges are held at 0 as a boundary condition. And eventually it reaches a steady state, where the inflow and the outflow of ice at any grid cell reaches balance. And that's when the elevation of the thing stops changing. The red dot in the middle here, box was sort of a tower of water at the initial condition. And so the water started flowing out and it made waves that went all over the place. But now, after a few rotational periods, the flow has found this equilibrium where it's going around and around the tower of water instead of just flowing out from it. You can see these sorts of rings, so these are the basic equations of motion that govern fluid flow. Anyway, welcome to the class, and I hope you find it of use.