It takes 10 minutes to go up 10 degrees in a parked car on asphalt. If windows are closed temps can reach 130 degrees and melt plastic. Dogs and cats handle heat inefficiently - unable to sweat, they can only pant to lose heat. Recent changes in the law allow good Samaritans to break windows in locked cars if they believe an animal is in jeopardy due to a hot car. Also dogs should be exercised during the cooler parts of the day, before 10 am and after 4 pm.