I have been trying a couple of methods to deal with this problem - winding down the windows and driving off; turning the air-con to full blast and driving off; or waiting with the doors open.
Well, none of them have worked particularly well for me so far. But guess what? A little application of science has come to my (our) rescue!
The youtube video is in Japanese with Chinese subtitles so I will do a (rough) translation into English for the benefit of all readers.
Basically, the way to cool down a car that has been parked in the sun is to:
1) Wind down the windows on door of one side
2) Close it
3) Open and close the door on the other side 5x
Voila~ The car should be cooler by a significant amount!
And to clarify; this method doesn't use the force of the door opening and closing to expel air. So don't bother slamming or yanking the door. Rather, the act of opening aids in drawing in cool air into the car!
Well, the next time you find yourself in this situation, why not give this method a try? And let me know how it goes!