Dependent means it would not be physically possible to live in an area if it did not have air conditioning. For example, you would die very quickly in Phoenix, Arizona if you did not have air conditioning. It is not physically possible to live in 50°C heat for any extended period. Most of the southern portion of the USA was only sparsely settled until the invention and deployment of air conditioning. Krugman is on it.
The reason the city is called Phoenix in the first place is that it’s built on top of a much older community. People have lived (and kept cool!) in that area for thousands of years, although never with the current level of population density, of course.
https://archive.nytimes.com/krugman.blogs.nytimes.com/2015/0...
https://archive.nytimes.com/krugman.blogs.nytimes.com/2015/0...