There's an old saying I've heard many times from friends and family in Wyoming that pertains to wild bear sightings that goes: "you don't have to run faster than the bear to get away, you just have to run faster than the guy next to you".
How do you deal with the heat? Hopefully air conditioning is an option for you. For a grizzly in Yellowstone, there's one option readily available in many parts of the park. Head to the river and play hard.