ABSTRACT
There are seven billion human beings on the planet Earth. This fact is simultaneously about sustainability and mathematics. First, sustainability: how can our planet support seven billion people? How much do seven billion people consume? What effect does this consumption have on the planet, on its forests, deserts, oceans and air? What will happen when the population reaches eight or nine or ten billion? What will happen if consumption continues to increase? These are primarily questions of sustainability: they are questions about the changing nature of the planetary ecosystem. A planet with seven billion people seems to be different from a planet with many fewer people. If you are reading this book, you may think some of these differences, including pollution, species loss and climate change, are cause for concern.
