The "conceptual equation" I=PAT was developed by Paul Ehrlich and John Holdren in the 1970s to illustrate the idea that the impact (I) that humanity has on the planet is the result of multiplying our population (P) times our affluence (A) times our level of technology (T).
As any of the three values increases, whether we become more numerous, richer or more technologically capable, our overall impact goes up. The formula is a convenient way of organizing our thinking about the effect we have on our planet its natural systems as our numbers, wealth and technology increase over time.
The evidence of this impact is all around us, in the air (CO2 and global warming) in the oceans (acidification and the precipitous decline of fish species) and on land (loss of biodiversity, deforestation, habitat destruction, loss of soil fertility).
Here is an attempt to illustrate the increase in our impact over the last 12,000 years:
How can we be a little more precise about the overall level of impact we're having on the planet? To do that we need to assign measurable numbers to each of the three terms: P, A and T.
Determining population growth (the "P" term) is easy – we can simply count the number of people in the world. For the other terms "A" and "T" we need to use what are known as proxies – measurable items that stand in for the quality we are addressing.
There are a number of reliable proxies that could be used for the A and T terms that would make them countable.
My preference for the affluence proxy is per capita primary energy consumption that is turned into work. The premise is that the more energy you have at your disposal, the wealthier you are. As a hunter-gatherer I might have burned 2 tonnes of wood per year for heat, light and manufacturing, but of which only 1% of the energy was actually used. That would equate to 0.5 GJ of useful energy per person per year. Today the average primary energy consumption is around 50 GJ per person each year, or about 100 times as much.
A proxy for technology could be the number of distinctly different manufactured items that we use in our lives. In H-G times, this would probably not have exceeded 10,000 objects. Today it numbers in the billions. Let's say it's a billion. So we use a hundred thousand times as much technology today as we did then.
So using these proxies today we have 1000 times as many people, each of whom is 100 times as wealthy, using 100,000 times as much technology. When we combine them, we discover that human impact on the planet is 1,000x100x100,000 = 1,000,000,000 times greater today than in hunter-gatherer times 12,000 years ago. This is necessarily imprecise, but it serves to give an idea of the sheer scale of our increasing impact.
If one rejects the validity of the IPAT formula then there is of course plenty of wiggle room. Since I accept it as a conceptual signpost, I'm left, as I always am when I step back to look at the big picture, with the realization that we need to reduce all three of those factors - our population, our affluence and the level of our technology. And reductions like those are not what the human story has been about so far.
As far as I can tell, there has been no noticeable slowdown in our increasing impact in recent decades. Advances in one area like the slowdown of our population growth have been overtaken by increases in CO2 output and the accelerating loss of biodiversity. This trend makes small-scale interventions like adjusting the source of our electrical energy or improving our farming techniques tantamount to a simple rearrangement of the deck chairs.
Some people point to the increases in efficiency in energy use, manufacturing and farming as evidence that we may someday be able to "to do everything with nothing", resulting in a very low impact from human activity.
Unfortunately, increasing efficiency doesn't necessarily decrease the impact, as it allows us to "afford" more of the impacting activity. Consider the case of house construction. House construction is vastly more efficient today than it was three hundred years ago. Has this reduced the impact of house construction on the natural world? Or has it enabled more houses to be built, using more complex technologies and materials? The same goes for human activities such as transportation and food production – every time an activity becomes more efficient, we seem to just do more of it.
Is there anything we can do about this situation?
How can we change our story, our belief system, so that reductions in our population numbers, affluence level and technology level are seen as positive events rather than negative ones, as something to be worked toward rather than resisted?
If such a deep shift can be accomplished, it can only begin with individuals making individual choices. What stories have you been telling yourself about these issues? Will those beliefs help you to reduce your impact? If not, can you imagine a shift that would allow you to reduce your personal impact on your corner of the planet?