In their reply Baumgärtner and Quaas (2010b) argue against monetary valuation. They call for more meaningful sustainability accounting and indicators. More elaborate green accounting mechanisms, the authors continue, can only be developed when the aim of “sustainable
economic development” is defined. Baumgärtner and Quaas (2010b) reject externalities and propose refering to the concept of joint production and stocks. The definition given, however, does not reveal how these differ from externalities: “joint production means that along with the intended outcome of some action, (…) there are necessarily other effects which one may be aware of or not” that can be “material byproducts” or “immaterial changes” (p. 2058).