A mathematical concept that describes a complex situation in which inputs and outputs do not function proportionally. For example, as we have all been made aware in recent times, a small change in the temperature of the planet as a whole can cause massive changes in a great number of the earth’s systems, both artificial and natural. More simply put, a non-linear system is one in which causation appears to be indirect. Climate change is the indirect, unintended result of a similarly non-linear process known as modernization. But even that does not go far enough because not all the peoples on the planet have shown an interest in modernity, so if we are to search for the true cause of climate change we have to ask why one group of people pursued the path of industrialization and others did not. See also complexity theory.