Fig. 9. Metals intensity with changes in gross domestic product (GDP) per capita expressed as purchasing power parity (PPP) for 13 world regions. Source: Nakicenovic et al. (2003). Metals include refined steel and MedAlloy, which represents the sum of copper, lead, zinc, tin, and nickel. The dashed curves are isolines that represent a constant per capita consumption of metals. The thick line indicates the inverse U-shaped curve that best describes the trends in the different regions as part of a global metal model (Van Vuuren et al. 1999). From "Ecosystems and Human Well-being: Scenarios, Volume 2" by Steve R. Carpenter, et al., eds. Copyright (c) 2005 Millennium Ecosystem Assessment. Reproduced by permission of Island Press, Washington, D.C.