I-PAT is an equation that is used to illustrate the effects of human society on the environment.
Impact, the first term, is equal to Population multiplied by Affluence, multiplied by Technology. In this case, impact is defined as the effect on the environment. Given that you multiply these terms together, increasing or decreasing any one of them will have wider effects on the impact in the environment.
If you contrast hunter-gatherer societies and industrial production societies, their impact on the environment is markedly different. Hunter-gatherer societies had smaller populations, so ‘Population’ value is much lower. They were also less affluent (the ‘A’ in the equation)--they had fewer material possessions, meaning those possessions that required materials from the environment in order produce them. They were more technologically simple (the ‘T’ in the equation), so the overall impact was cumulatively less.
As the values change in the equation, the impact of the environment will change. The world has been running an environmental deficit, which is the idea that humans cause damage to the environment in a negative fashion. This means that people are taking more from the environment than they’re giving--they are destroying the environment more than they're protecting it. This can be very harmful for humans down the road because they are privileging short-term gains over long-term sustainability.
IN CONTEXT
In the short term, perhaps, people can argue that it’s favorable to wrest all those materials from the environment, to produce things and expel pollution into the air, because in return, they have nicer material things in the here and now. There's a short-term gain, but it could have long-term negative effects on the natural environment.
The natural environment consists of the material reality of the natural world--anything found on the Earth's surface or in the atmosphere can be considered part of the natural environment. Plants, animals, rocks, clouds, oceans, and even storms like hurricanes are considered a part of the natural environment, and these are damaged when humans run an environmental deficit.
Ecology is the study of how organisms interact with each other and the natural environment. Sociologists are particularly interested in human ecology, or the study of humans interacting with their environment, like the fact of producing an environmental deficit.
An ecosystem is a more specific look at organisms in a particular space, interacting with each other and with the natural environment to create a system in a particular locality.
EXAMPLE
Lake Superior is an ecosystem. The rainforest is an ecosystem. Even your neighbor's pond can be a micro-ecosystem.Because these things are systemic, ecology forces us to think about things in a systemic fashion--nature is a system that people are continually coming to understand in a more nuanced fashion. Nature is affected by human environmental impact in ways that can't necessarily be predicted. Running an environmental deficit can cause serious problems down the road, because nobody accurately understands the extent to which nature is systemic. It could potentially be intimately systemic in broader ways than is recognized and understood.
Source: This work is adapted from Sophia author Zach Lamb.