John Tjostem is emeritus professor of biology at Luther College in Iowa. This article on the relationship of energy to sustainability is very easy reading with powerful thinking.
Stewart Brand, 2005 -Over the next ten years, I predict, the mainstream of the environmental movement will reverse its opinion and activism in four major areas: population growth, urbanization, genetically engineered organisms, and nuclear power. Reversals of this sort have occurred before.
Stewart Brand, the man who helped usher in the environmental movement in the 1960s and '70s has been rethinking his positions on cities, nuclear power, genetic modification and geo-engineering. See this video recorded talk at the U.S. State Department in 2009 for amazing information about people in urban environments around the world.