Waters that flow across national borders are often the connecting resource for food and energy, while international food trade and regional markets for electricity and energy carriers traverse state borders. In 2002, the World Summit on Sustainable Development in Johannesburg implicitly recognized the nexus by listing water and sanitation, agricultural productivity and energy among its priority areas. Shortly afterwards, the concept of "virtual water" and the assertion that increasing scarcity of water, food and energy would result in "the perfect storm" by 2030 catalysed further thought and discussion on the nexus. The 2008 launch of the World Economic Forum's report "Water Security: The Water-Energy-Food-Climate Nexus" and Hoff's background document for the Bonn Nexus Conference marked the emergence of the nexus as we know it today.