The Impact Equation – Helps make sense of most things

I love equations, especially when the help make sense of everyday things. To me the impact equation is equivalent in understanding our world as the Golden Ratio is in understanding natural beauty. If you don’t like equations please bear with me, you will find it useful in understanding our current environmental issues.

I first came across the impact equation in a Bill Gates TED talk, Bill (or should I say Mr Gates) had used the Kaya Identity version to simplify the calculation of the amount of CO2 being emitted globally every year. But before I talk about the Mr Gates TED talk or Kaya Identity I should explain the original impact equation.

The original impact equation I = PAT, or I = P x A x T was developed in the 1970’s to describe our human impact on the environment. It is quite simply:

Impact (I) = Population (P) x Affluence (A) x Technology (T)

Basically the Impact (I) on the environment can be determined by the number of people we have on the planet, the more stuff we consume (affluence) and the efficiency of the resources used in producing the stuff (Technology). A very simple equation that can be used to calculate the environmental impact of all sorts of things, not just global environmental impact of the population.

The Kaya Identity used by Mr Gates, adapts the equation to simplistically demonstrate how global CO2 emissions can be calculated. The Kaya Identity was used by Mr Gates in the following way:

bill gates screen grabScreen grab from TED talk by Bill Gates

The great thing about the equation is that it can be adapted for almost anything. So if we think about an office building the equation could be:

CO2 Emissions from the energy use within the building


Number of Tenants in the Building


No of Services per Tenant (air conditioning, lifts, amount of tenant power,


Energy per Service (the energy used by the services provided – determined primarily by the efficiency of the systems)


Carbon Emissions per Energy Unit (determined primarily by the grid unless there is power generation within the building)

All the elements of the equation are quite easy to calculate or obtain, putting them all together helps us to understand the real impact of our built environment whether thats an office building, a household, a library or a masterplanned community. It’s not all about the last two elements of the equation.

This particular post is getting a bit long so I will post more next week about I=PAT for buildings but in the interest of food for thought, the equation does bring up some interesting issues

  • buildings energy performance should be rated on a per person basis and not a per meter squared basis
  • just improving the carbon emissions per energy unit can’t reduce carbon emissions enough to tackle global warming
  • the number of services being used per tenant is increasing at the same rate as energy efficiency improvements – cancelling out energy efficiency improvements
  • demand side management is way more important than supply side management.

6 Comments on “The Impact Equation – Helps make sense of most things”

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