Every day I park my car in the same spot, which has not had any alterations done in years, nor has the surrounding area changed. No new trees, building, etc. I park my car in the same fashion each time, facing the same direction, and don't use a windscreen sunshield nor car cover. The windows are always closed. Nobody touches the vehicle or the surroundings during the day. I live in Beersheba, Israel, about 33 degrees north of the equator. The only changes to the situation in summer and winter are naturally-occurring.
In summer, when I get to the car at the end of the day the car is cool and comfortable. In winter, when I get to the car it is hot and needs to be aired. WHY?