Your quick stop at the store turned into a 20 minute shopping trip, all while Hunter waits patiently in the car. You may think it's okay -- it's not too warm out, and you left a couple of windows cracked -- but Hunter could be seriously affected.
Oven on Wheels
It takes no time for a car to heat up, even when the outside temperature is mild. According to the SPCA, ten minutes is all that's needed for the inside of a car to reach 102 degrees on an 85 degree day. In thirty minutes, the car will be around 120 degrees. Even if it's a pretty spring day, your ride can still get pretty hot; according to a 2005 Stanford University study, a car parked in 70 degree weather took only 60 minutes to reach 116 degrees. At 74 degrees, it takes only 30 minutes for the car's interior temperature to climb above 110.
Cracking the Windows
A cracked window won't help Hunter when he gets a little hot under the collar. The same study found opening the windows a bit for extra air didn't help; the cars heated up at a similar rate. If you sat in a 100 degree car, you'd likely work up a good sweat fairly quickly. When you sweat, it dries and takes away excess heat. Hunter doesn't sweat like you; he perspires around his paws, which isn't enough to cool his body. He pants to get rid of excess heat, which is helpful when he's outdoors or in a ventilated area. However, in close quarters or high humidity, panting doesn't do much good for him.
Prone to Heatstroke
If Hunter is overweight, his extra fat adds insulation, trapping more heat. If he's pug-nosed, his smaller nasal passages add an additional challenge because it's more difficult for them to circulate air for cooling. Older dogs may have compromised organs, making them vulnerable to heat illness and puppies may not be fully developed enough to regulate their temperature. If you find Hunter can't stop panting, doesn't obey normal commands, has warm, dry skin and a rapid heart beat, he may be suffering from heatstroke. Other signs include vomiting, anxiety and high fever. Try to cool him off with cool water, cold packs and a cooler environment; of course he should see a vet as soon as possible.
Just as a car can heat up like an oven, it can also chill like a freezer. The ASPCA notes that cold cars can retain cold and cause animals to freeze to death. If Hunter wouldn't normally be lounging in the cold weather, then it's too cold to keep him in the car for an extended period and he should stay home.
Leave Him Home
When the conditions are right for your car to warm up or chill out, Hunter is best left behind in the comfort of home. If you insist on taking him with you on a warm day, bring a buddy that can wait outside the car with him so Hunter doesn't end up spending time in a sauna. Although you intend for your ten minute errand to be quick, it could turn into something a little longer, having disastrous consequences for your pup.