1. “The National Environmental Policy Act of 1969,” signed into law by the U.S. Congress on January 1, 1970; available on the Internet at www.nepa.gov/nepa/regs/nepa/nepaeqia.htm (2008).
2. “The World at Six Billion,” ESA/P/WP.154, United Nations (1999).
3. World Population Prospects: The 2004 Revision, United Nations (2005).
4. “World Population Prospects: The 2006 Revision Population Database,” United Nations (2006); available on the Internet at http://esa.un.org/unpp.