Could you describe IPAT?
IPAT is an acronym for the equation of model that links sustainability outputs to three causal factors. The letters represent the basic form of the model, which is: Impact = Population * Affluence * Technology.
How is this big idea applied to sustainability?
The most common form of the model is related to ecological footprint analysis. The Impact factor is demand for the hectares of arable land (weighted by productivity), and demand is driven by Population, Affluence (global GDP per person in dollars) and Technology (hectares of land needed for each dollar of output.
Chertow, Marian R. (2001). The IPAT equation and its variants; Changing view of technology and environmental impact.” Journal of Industrial Ecology 4:4, pp.13-29. Chertow provides an excellent overview of the history and application of IPAT models.
Theis, Tom and Jonathan Tomkin, eds. (2012). Sustainability: A comprehensive foundation. "Sustainability: A Comprehensive Foundation" pp. 8-12.