Florida used to be a land infested with yellow fever, ring worm
and various tropical diseases.
It was an unpleasant place, especially in the summer. With air conditioning
(and the coal fired power plants necessary to run the air conditioning), Florida
became habitable year round, making for permanent residents, not just socialites
from New York in Miami in the winter.

We've been here at Quest Air in Groveland in central Florida since the first
week of December, and outside working conditions (you go outside a lot when you
live in a trailer) have been excellent. In that time we've turned a chunk of
forest (over grown orange grove) into park land and camping area.

NY Times article
here:

The rise of the US sunbelt can be understood largely as a response
to the emergence of widespread air conditioning, which made places that are warm
in the winter attractive despite humid, muggy summers. It’s a gradual,
long-drawn-out response, because location decisions have a lot of inertia; few
people would choose de novo to live in the old industrial towns of upstate New
York, but the existing housing stock and the fact that people have family and
social networks prevent quick abandonment. So to this day temperature is a good
predictor of state population growth.