With the seven billionth living human being imminent, it is important to consider that numbers of people alone do not explain the environmental impact Homo sapiens have on the earth. Developed by Stanford biologist Paul Ehrlich, Assistant to the President for Science and Technology John Holdren, and others back in the 1970s, the IPAT formula provides a useful lens through which to view Mr. or Ms. Seven Billion ("Giga Septem").
The I=PAT formula is an identity. I represents environmental impact, P population, A affluence, and T technology. While human population (that is, number of people) and affluence (that is, wealth per person) have tended to push I upwards over the last few thousand years, the technology factor (impact per wealth) has tended to decrease I by providing increasingly efficient means for accomplishing tasks. Because I is calculated as the product of P, A, and T, each factor is equally important.
Thus, while population growth certainly contributes to environmental impact, so do affluence growth and technological improvement. Welcome, G. Septem. Now that you have joined us, we will watch with fascination how wealthy you become, and how quickly technology improves during your lifetime.