Post Carbon Fellow Richard Heinberg was one of the experts quoted in this article on the energy future of cities.

 
From the article:

What could changes in energy supply mean for cities?

Heinberg: Ongoing urbanization means that societies need to keep providing more goods to growing ranks of city dwellers. Urban provisions require energy. But our current fossil fuel-based energy regime faces two serious challenges: depletion of the “low-hanging fruit” of global petroleum supplies, and the need to reduce carbon emissions to avert catastrophic climate change.

Energy challenges may result in systems that are more expensive to operate than current ones or that simply fail to deliver all the services that we currently expect. Such challenges could cause the current trend toward urbanization to taper off or even reverse itself. It is impossible to know how close we may be to that tipping point, but it could well occur during this century, and a decline in available energy is likely to be the key driving factor.