The IPAT Equation

IPAT Equation

If you want to understand what's causing the environmental sustainability problem, the place to start is the IPAT equation. At least that's how I felt in August 2001 when first reading about the equation. Night became day. I was electrified as all of a sudden I felt I was at last starting to grasp the true nature of the sustainability problem.

What opened my eyes was the beginning of a chapter about The Theory of Population-Environment Links in the AAAS Atlas of Population and Environment, by the American Association for the Advancement of Science, 2000. The chapter introduced the equation this way:

A Systems Approach

Cover of AAAS Atlas of Population and EnvirnmentIn every human interaction with the environment—even in the simplest societies—[there are] three major elements at play. They can be linked in the famous formula introduced by [Paul] Ehrlich and [John] Holden:

I = P x A x T, or

Impact = Population x Affluence x Technology

More explicitly, environmental impact is the product of population, multiplied by consumption per person, multiplied by the amount of resources needed, or wastes created, while producing each unit of consumption.

Ehrlich used the formula to show that population growth was the dominant factor in environmental damage. In reality, at various historical times, different elements have been uppermost. The increase in arable area in many parts of Africa up to around 1980, and the deforestation that went with it, was mainly driven by population growth. There was little rise in consumption of agriculture products per person, and little improvement in yields. By contrast, the dramatic rise in human output of chlorofluorocarbons from the 1940s onwards was due overwhelmingly to the introduction of a new technology.

... This complexity is best viewed using a systems approach, which helps top overcome the polarization found in the most prominent views of population-environment linkages.

The systems approach has two key differences from conventional approaches. It does not focus on a single factor, but instead builds in as many potential factors as possible, and it does not see human impact on the environment simply as a one-way street. There is feedback. Changes in the environment have an impact on human welfare.

Causal loop diagram of World3 modelThe IPAT equation is the foundation for initial analysis of the cause of environmental unsustainability. It's the basic question behind the entire World3 simulation model, the one used in the blockbuster best seller The Limits to Growth in 1972. The high level diagram of the World3 model is shown.

The IPAT equation has three factors: P, A, and T. P is population. This is the top node in the diagram. A is consumption per person. This demand increases industrial output. T is technology in terms of impact per unit of consumption. This is incorporated into the pollution and nonrenewable resources nodes. Thus the World3 model, the most influential model of all time for the sustainability problem, is basically an IPAT equation model. That's what you need for identifying the problem.

But it's not what you need for solving it.

As the above passage emphasized, solving the problem requires "A Systems Approach." That's why at the box at the top of this page we cautioned that:

It's crucial to remember that the three factors are intermediate causes, not root causes.

That's the muse we must follow as we proceed forward. Efforts like The Limits to Growth have found only the intermediate causes of the problem. The universal implied assumption is these or factors close to them are the root causes. These so called "causes" are deceptively useless for solving the problem because they lead you astray. You think a solution will work but it doesn't. Neither does the next one. Why? Popular solutions don't resolve the root causes, because the root causes have not been found in popular analyses like later editions of The Limits to Growth and thousands of other works.

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