1. School of Geographical Sciences and Urban Planning; Arizona State University; Tempe Arizona 85287-5302 USA
2. School of Mathematical and Statistical Sciences, Global Institute of Sustainability; Arizona State University; Tempe Arizona 85287-1804 USA
3. Department of Environmental Earth System Science and Center on Food Security and the Environment; Stanford University; Stanford California 94305 USA
4. Department of Global Ecology; Carnegie Institution for Science; Stanford California 94305 USA