Originally Posted by Nerys
as for evidence to support me only anecdotal evidence sadly.
Yeah, that's what this thread is about, really.
As for why you don't see as much of a swing in MPG vs. temperature, Pale's chart suggests a good reason: Note the temps where his fuel economy curve plateaus from roughly 65-70F and on up. Pretty darn close to the range of daily high temps in New Orleans.
(*edit* Correction on my part: I mistook "NO" in his user info to mean that Nerys lived in New Orleans.)
If you had air in your Metro, you'd notice a significant fuel economy hit.