The argument that increased urban density has very significant climate benefits has been well made by Edward Glaeser, David Owen and others. The US writer Alex Steffen has joined the ranks of those with books out arguing for promoting density, with the view that we simply cannot reduce emissions enough through low carbon energy alone. Urban density will do the trick. He appears to believe that cities can reduce energy use by 90%, but only seems to provide hand waving explanations of how this is possible.
However, a statement he made in a recent interview to The Atlantic is reflective of a common problem with solutions to climate change: the unwillingness to do basic arithmetic. He says:
For example if you have a more distributed energy system, you can have the energy system in one neighborhood go down, and energy systems in other neighborhoods remain unaffected. By distributing things, you make it possible for disaster to strike, and not have everything go down if something fails.
Now, presumably Steffen doesn’t have neighborhoods being powered by small modular reactors or gas plants with CCS in mind. So, he must somehow believe that neighborhoods can be powered entirely by local renewables, with perhaps some yet to be invented storage technology providing back up. A fundamental problem is that his vision of high urban density and localized energy production are in conflict.
Consider New York City. This city certainly fits the category of high urban density. However, think about what would happen if New York tried to power itself entirely from renewables within city limits: constant blackouts. This is a simple consequence of its high population density and the laws of physics. An author such as Steffen who claims to have thought deeply about climate change, urbanization and energy really ought to be aware of this. So, why can New York not power itself from local renewables?