Who would have GUESSED this?

Sometimes you need the A/C on:














But:
Turning Off the Air Conditioning Helps Save Fuel, Swiss Study Finds

!!!!!

I'm inverting two paragraphs. First,

The study, the results of which have just been published in the scientific journal "Environmental Science and Technology," shows that the fuel consumption of the test vehicles with air conditioning systems in operation increases with rising ambient air temperature and humidity, reaching a value of some 18 per cent on a typical Swiss summer day with an air temperature of 27 degrees and relative humidity of 60 per cent.

Sounds reasonable. Here's part of the opening paragraph now:

Even in Switzerland, with its temperate climate, the use of air conditioning systems is responsible for about five per cent of total fuel usage, rising to around ten per cent in urban traffic, as shown by a new study undertaken by Empa on behalf of the Swiss Federal Office for the Environment (FOEN). Furthermore, two thirds of the additional fuel usage could be saved if air conditioning systems were simply turned off when the air temperature falls below 18 degrees Celsius.

Is the latter reasonable? 18 degrees Celsius is 65 degrees Fahrenheit or so. That's not too bad. The problem is, fuel-efficient cars are designed to be driven with the windows up. On a sunny 65 degree day, the car interior will get considerably warmer than 65 degrees if the A/C isn't running, even if the fan IS running. So there needs to be a way to vent the excess heat on sunny days. Then this might help.