Welcome to the new Environment Matters forum. I'm Steph Carter, LDWA Environment Officer and will be moderator of this forum. To get us started here's something to ponder...
Assuming we might get a few hot days in a British summer you may well be using your car aircon to keep cool while driving.
Did you know that having your car aircon on reduces your fuel efficiency? ( in other words you burn more fuel per mile, and emit more carbon dioxide per mile)
The alternative is to open the windows... but this also reduces your fuel efficiency as it causes more drag (resistance to movement) on your car
So which is best? Well first and foremost it's your comfort! The extra fuel used by the aircon is less than that used by opening the windows at high speed, while the extra fuel used by opening the windows is less than that used by the aircon at low speed. While it varies by model and make. Typically, for 40mph + the aircon is most efficient, less than 30mph, opening the windows is most efficient.
One other thing- when you get into a hot car and use the aircon, set it to take air from the outside for the first couple of minutes, but once the inside temperature is starting to get cool switch to recirculate. This means your aircon can keep the cool air inside the car cool, and use less energy than than having to cool down warmer air from outside.