Not only does the temperature rarely get as high as 90, very few houses over here in the UK have air conditioning, so as the temperature change isn't so marked. When it hits the 80's I only walk the dogs in the forests where it is cooler and shadey and where there are ponds for the dogs to run into to cool off.
I thought of it because I know that on those hot days, bag carry out workers at stores and things are warned to be careful because the constant in and out at vastly different temps can make them ill. I just thought about it the other day when it was super hot out but very cool in and I wondered if it could affect the dogs, who seemed to want to go in and out a lot that day.
As Stephanie said we don't need air conditioning here, on hot summer days I am careful about choosing shady walks and I always have water for the dog with me (in one of those doggy water bottles) but it is rarely too hot here.