The formula, which is a rephrased version of Barry Commoner's can be used in many different situations. It can be applied by, or to, high-consuming individuals, to give them some idea of the environmental cost of their lifestyles. It helps to concretize what so often is invisible, and I have tried to do this with the idea of the personal waste mausoleum and the carbon balloon. It can also be applied at a particular moment in time to countries or regions. The formula makes it clear that, for any given level of consumption per person or technology, higher population means higher environmental impact.
Fewer people mean lower total consumption and waste.
What we need is some measure of the share of each of our three elements in overall impact. If all three are pushing upwards, we can simply express the change in each one in turn as a percentage of the total change. Sometimes one or more of the three factors may be tending to reduce environmental impact. It might help at this point to look at some concrete examples. Take the case of the expansion of agricultural land.