An important message this time of year.
And just in case you're ever arguing with someone who thinks it's okay on a "cool" day: http://caninecollegemi.com/1758/pets-in-vehicles/temperature-inside-car-chart-2/
It only takes 20 minutes to reach 100 degrees in a parked car with the windows cracked on a 70 degree day. That's easily an, "I'm just going to run in and pick up a few things." amount of time.