The Kaya identity was developed by Japanese energy economist Yoichi Kaya.[1]. It is the subject of his book Environment, Energy, and Economy: strategies for sustainability co-authored with Keiichi Yokobori as the output of the Conference on Global Environment, Energy, and Economic Development (1993 : Tokyo, Japan). It is a mathematically more consistent variation of Paul R. Ehrlich & John Holdren's I=PAT formula that describes the factors of environmental impact.