As countries and regions around the world began to develop, it slowly became evident that industrialization and economic growth come hand in hand with environmental degradation. Eco-efficiency has been proposed as one of the main tools to promote a transformation from unsustainable development to one of sustainable development. It is based on the concept of creating more goods and services while using fewer resources and creating less waste and pollution. "It is measured as the ratio between the (added) value of what has been produced (e.g. GDP) and the (added) environment impacts of the product or service (e.g. SO2 emissions)." The term was coined by the World Business Council for Sustainable Development (WBCSD) in its 1992 publication "Changing Course," and at the 1992 Earth Summit, eco-efficiency was endorsed as a new business concept and means for companies to implement Agenda 21 in the private sector. Ergo the term has become synonymous with a management philosophy geared towards sustainability, combining ecological and economic efficiency. History Although eco-efficiency is a rather new method, the idea is not. In the early 1970s Paul R. Ehrlich and John Holdren developed the lettering formula I = PAT to describe the impact of human activity on the environment. Furthermore, the concept of eco-efficiency was first described by McIntyre and Thornton in 1978, but it wasn't until 1992, when the term was formally coined and widely publicized by Stephan Schmidheiny in Changing Course. Schmidheiny set out "to change the perception of industry as being part of the problem of environmental degradation to the reality of its becoming part—a key part—of the solution for sustainability and global development." The major drivers in the early phase of eco-efficiency's development were the "forward-looking managers and thinkers in 3M and Dow." It was their involvement which catapulted eco-efficiency into development. The results of the WBCSD's work creating the "linkage between environmental performance and the bottom line was published in 1997 in its report Environmental Performance and Shareholder Value." Methods According to the WBCSD definition, eco-efficiency is achieved through the delivery of "competitively priced goods and services that satisfy human needs and bring quality of life while progressively reducing environmental impacts of goods and resource intensity throughout the entire life-cycle to a level at least in line with the Earth's estimated carrying capacity." It works by implementing 4 main types of ratios. "The first two are environmental productivity and its inverse, environmental