 What is a smartphone really? It's a little bit of oil for the plastic, a little bit of sand for the glass, and a little bit of the right rocks, some red ones and some blue ones to make the various metals in here, and a huge amount of science and engineering wrapped up with some networking and some marketing and what have you. I've had people use their smartphones to send me messages saying that we scientists don't know what we're talking about with climate change. I've even had people use their smartphones to send messages saying that scientists have no more insight to how the world works than any other group. I suspect those people were trying to make a point and they might not fully have believed that. If you can imagine taking the sand and the oil and the red and blue rocks and giving them to various groups, the U.S. House of Representatives, the Church Women's Knitting Society, the football team, and asking them to turn them into a smart phone. I think you'd wait a long time, but scientists and engineers really have done that. In this phone, there's a GPS. It started as a U.S. Air Force project. It knows where I am in part because it has relativistic calculations that date all the way back to Einstein. And without relativity, it would get lost in less than a day. It wouldn't work. In here, there's a computer. It connects to the internet, which started also as a U.S. military project to get researchers to talk to each other. And the computer is designed with the principles of quantum mechanics that date back to Plonkin, to Einstein, and Bohr, and others. And the quantum mechanics also underlies our understanding of how radiation interacts with gases in the atmosphere that gives us such very high confidence that our CO2 is changing the Earth's radiation balance and that affects the climate. The physics of the quantum in the computer, the physics of the quantum in the air overlap. They're done sometimes by similar overlapping communities. They're done by people studying in the same schools using many of the same techniques. This works. And so does the physics of the atmosphere. And we can validate that, and it really does. There's another important point here. The fact that this works doesn't tell you who to call or what websites to visit. It gives you options that you must choose from. Science, the atmosphere and energy and climate doesn't tell you what laws to pass. It doesn't tell you who you have to vote for. It gives you options that you can choose from. So in this third section of the class, we're going to visit some of these options and decisions. We'll start with economics. Can we really afford to address climate and energy? Can we really afford not to address climate and energy? Then we'll look at some of the policies we might adopt and we'll tiptoe our way into ethics. What's the right thing to do? But I suspect you already sort of have a clear picture. The science doesn't tell you what to do. It tells you what you can do. And from that you can make wise decisions.