Sustainability is a social goal for people to co-exist on Earth over a long period of time. Definitions of this term are disputed and have varied with literature, context, and time. Sustainability usually has three dimensions (or pillars): environmental, economic, and social. Many definitions emphasize the environmental dimension. This can include addressing key environmental problems, including climate change and biodiversity loss. The idea of sustainability can guide decisions at the global, national, organizational, and individual levels. A related concept is that of sustainable development, and the terms are often used to mean the same thing. UNESCO distinguishes the two like this: "Sustainability is often thought of as a long-term goal (i.e. a more sustainable world), while sustainable development refers to the many processes and pathways to achieve it."