 Sustainability denotes some of the largest challenges that we will face as local communities and in the global sphere. They include a variety of areas such as global climate change, loss of biodiversity and their energy security. Rather than trying to deal with each of those subjects as part of this course, which require much more attention than what we can provide in the 12 modules, we will rather focus on how we can solve complex problems and how multiple dimensions of those problems may be overlapping as we try to solve them. So we're going to be touching on the natural sphere, on the social sphere, on the political sphere, on the economic sphere and also in terms of technological development. Types of land ownership. There's public lands and there's private lands. We're very familiar with the concept of private lands. It's based on the idea of ownership. We're familiar with property taxes, property rights, property lines, property titles. It's in our best interest to make sure that we utilize those lands thinking about the future. So if we have, for example, lands that have resources that can be mined, we may wait until the presence of the particular resource to go up. We can wait for better technologies. And for example, if you are producing certain kinds of pollutants, you're making sure that you're constantly removing them and mitigating their effects. Now when we move to public lands, you can imagine a philosophy by which we apply the best of our methodology with private lands into the public land regime. However, that happens to be mostly the exception. As a general rule, what we're going to see in the public lands is the worst kind of resource management. You're going to see very rapid extraction of resources. You're going to see extensive pollution and waste disposal. And private lands and public lands only constitute one small fraction of the resources that are available to us. So if we look at the public land regime and we group it with the other kinds of resources that don't necessarily belong to an individual or even to a particular country, we get what we call collectively the commons. And the commons include the atmosphere, include the hydrosphere and include a number of different types of public lands. Our management of the commons has been as poor for the lands as it has been for the waters as it has been for the atmosphere. And what we're trying to do as part of this class is we're going to try to use sustainability systems to move away from the philosophy that has taken us to dispose and to extract the kind of rates that we see in public lands. So in order to move away from that philosophy, we move from the single bottom line, which is the economic bottom line into a triple bottom line. You see the city of Pittsburgh. It's where you can get the needs of those three. Perhaps affected by assigning different values to it.