 In step four of this project, you're going to calculate the energy costs associated with your scenario for the future of the planet. And we're going to end up doing this, changing this renewable unit cost up here, this slider. And so initially you will have, by this point, you will have chosen a carbon emission scenario. You will have chosen a per capita energy scenario. You will have chosen a population limit, the fossil fuel energy intensity, to figure out how much carbon-based energy you can get. And you do all those things. If you look on page two, you'll see here's a graph with your, in blue, the global energy demand. And then in red, the carbon-based energy that you can squeeze out of this carbon emission history. And then the difference is going to be the renewable energy. So this is what we've got to work on now. And if you look at the very end of time here, 2,200, we see we've got something like 2,100 and about 50 exajoules of energy that we've got to supply. And our task now is to figure out how we're going to do that. What kind of energy source are we going to use to make up that demand? And so we make a choice, and here are some of the choices, wind, onshore, offshore, geothermal, hydro, solar, nuclear here. And they each have an associated cost with them. So you have to figure out what percentage of this energy is going to come from which of these sources. Then you'll average these prices, these unit prices for these renewable or non-fossil fuel-based energies. And then you're going to enter that into here. So let's say I do that. I make a decision that let's say I'm going to do the whole thing with onshore wind. Then what I would do is to take this little slider and move it down to 11.1. And then I run the model like this, and then I'll look on the next page. And I see here the costs. So here in blue are the renewable energy costs. In red are the carbon energy costs. And then in pink or purple here are the total energy costs.