Yes. I've flown with my dogs on UA, AA and DL and they all have temperature policies and will refuse to transport your pet if the temperature at origin or destination is too hot or to cold or is forecast to be too hot or too cold. The really crappy part is the decision to transport or not to transport your animal may not be made until you get to the airport and check-in (or attempt to). If the wx is obviously hot (or cold) you can make a decision before you go to the airport... but, if it's close to the margin, in my experience, you wind up taking your chances at the airport.

MVFlyer is correct DL and, in my experience, UA decline to transport pets during the summer. No guess work.

One other note -- if you are not flying with your pet, i.e. Fido is flying as an unaccompanied minor (as it were), it travels as cargo and may, or may not, get on the flight you wish.

We no longer fly with our dogs...