Theaters are also shockingly lax about ventilation. When you have a big box full of sweaty people munching on all manner of stinky snacks, you have to blow out stale air to keep the room comfortable. But because buying and running ventilation equipment is expensive, many theaters don't bother. They simply run the air conditioner a little longer than usual to cut the humidity, typically with disappointing results. That's why movie theaters are cold, clammy, and smell like a monkey cage. It does, however, save on energy costs.
Up to this point, the cinema seems the clear winner. But there's a twist ending to this story—a real deus ex machina. If you drive to the theater, it will probably tip the scales dramatically back in favor of home viewing. Driving just five miles to a theater emits 4.6 pounds of carbon dioxide. That's more than nine times as much CO2 as your home theater system would be responsible for, and more than one-third of the emissions that electricity for the cinema's sound and light technology would create.