As pointed out by many authors, sustainability is often vague and amorphous (See, for example, Dovers, 1989; Faber, et al, 2005; Glavič, et al. 2007). There is a clear need to make analytical and data-driven analyses of established and or proposed plans. MARKAL (MARKet ALlocation model) is an analytical tool that can be used characterize the impacts of sustainability plans at multiple spatial scales: global, national, regional, and local. In this study we apply the Long Island MARKAL model to answer three interrelated issues: 1, the development and incremental improvement of local and regional sustainability plans; 2, the impact of a national carbon tax, as a response to climate change, on sustainability planning conducted at the local level; and 3, the environmental justice implications of sustainability planning when energy sources are altered.