I=PAT: Incompletely Calculating Human Impact on the Environment

Humanity is using resources necessary to civilization’s existence at a faster rate than they can be replenished by the environment.  Though the majority of people now live in cities, our existence still depends on food grown in soil,  trees cut from forests, and water taken from streams, lakes, and aquifers.  We will forever be dependent on the environment surrounding us.  Thus, it is important to be conscious of how human activity affects the environment.

I=PAT: Trying to Measure Impact

In the 1970’s, a debate about these issues between Barry Commoner, Paul R. Ehrlich and John Holdren resulted in an equation to express how much impact humans have on the earth:

I = P*A*T

I = Human impact on the environment
P = Population
A = Consumption per person
T = Environmental impact per unit of consumption

This equation neatly summarizes some of the issues involved in environmental degradation.  If there is an increase in population, a greater amount of consumption per person, or more resource intense production, the impact is greater.  Using this equation, we can identify several different places where environmental impact can be reduced.

While I=PAT is a good starting point, I think it is too incomplete for rigorous use.  First, not all types of environmental impacts are equal.  Using a gallon of water in Phoenix to water your grass has a much greater effect on the local environment (or the environment of wherever they pumped the water from) than using the same amount of water in the rainy northwest.  I=PAT treats this consumption as the same.

The Possibility for Positive Impact

The most important issue I have with I=PAT, the problem that renders the equation fairly useless as presented, is that it does not take into account positive impact human activity can have on the environment.  Consider a mature pecan tree.  This single tree can consume upwards of 250 gallons of water each day.  Every year, it pours pounds of organic waste into the surrounding environment as it extracts precious nutrients out of the soil.

Yet we don’t consider the pecan tree to be a polluter and a water consumer.  Its just part of nature.  Lost leaves decompose into rich soil, seeds feed animals, and its branches provide a safe haven for birds.  

The thing is that humans are part of nature too.  No matter how separate we feel, we can never separate ourselves.  Just as the pecan tree, our effect on the environment is not completely negetive. 

This doesn’t mean that we shouldn’t consider excess use of water, burning coal, or dumping chemicals as negitive things.  We just need to maintain context, and to remember that humans can have a positive impact as well.  Select logging and burning, for instance, can promote the health of a forest.  Stocking fish can help reestablish lost fish communities.

I=PAT reflects thinking that says humans are innately separate and alien from nature, that we can only have a negative impact.  Its just not true.  The more we remember that we can have a positive impact, we are more likely to be proactive.