Paul Erlich (The Population Bomb) was interviewed on the Nature Podcast this week, and in response to a question of whether population or consumption was more responsible for the threats to the planet, he answered that that was like asking if the width or the length of a rectangle was more important to creating the area.
I take issue with this analogy, because it is easy to say which part of the edge of the rectangle is more important.
Given that a) we define the length as the longer of the two dimensions and b) that we define the most important contribution as the one that causes a larger change in the area for a given amount of increase in perimeter, we can easily see that the width is more important – if we increase the width of a rectangle by a given amount, the area increases more than if we increase the length by the same amount.
The same sort of calculus (and it really is calculus) applies to the population versus consumption questions. It’s much more complicated but it is, in principle, possible.