Just to prove you don't need a research lab and a high budget to start changing the world, two high-school kids in Utah invented what may be more efficient air-conditioning for cars. The Salt Lake Tribune describes them as being two kids doing a project for a science fair, who decided they were actually on to something and stuck with the project for two years afterwards. One was quoted as saying, "We aren't planning our lives around making air conditioners... We wanted to do something to help the environment and the economy."
Their concept is to use Peltier chips instead of compressed Freon to do the cooling. I have to say I'm a bit skeptical of this, because thermoelectric devices are notoriously inefficient--we're talking ~5%, as opposed to ~45% for most compressors. There are some people working on changing this, but for now that's how it is.
Another possibility is that these devices are good for vehicles because they are electricity-based, thus eliminating the need for a fluid-mechanical system that can have weight, size, and reliability problems. And a Peltier device can act as both air-conditioning and heating, you just reverse the direction of the current. But I think the revolutionary thing about small solid-state cooling chips in cars is that they can be distributed. People are more sensitive to the temperature of the things they touch than to the temperature of the air, so if you can directly cool surfaces in the car (like the steering wheel), you don't need to cool as much. It's like baseboard heating in a home. It doesn't appear that the inventors have thought of this, but in any case, it's good to see that two kids in a garage can come up with worldchanging inventions, and have big companies like Ricoh show interest (Ricoh awarded them winners of its first sustainable development contest), possibly even make the idea into a real product. We'll have to wait and see.
Frankly, I think the most effective thing for automotive AC would probably be Amory Lovins' idea of installing low-emissivity coatings in all the windows as part of the glass-lamination, to avoid the greenhouse effect in cars. This could reduce your cooling load by perhaps 75% (conservatively say 50%), with no electricity, compressors, or moving parts.
Note: It's hard to measure air-conditioning efficiency in percent, because it's not apples-to-apples, but the standard measurement is the "coefficient of performance" (COP), which measures the amount of heat pumped divided by the amount of energy input to the device. A typical building's air-conditioner (using a compressor like your car does) has a COP of 3, a really well designed one has a COP of 6; most Peltier devices have a COP of 0.4 to 0.7 . Perhaps the systems in cars perform much worse than buildings, due to constraints of size / ruggedness / etc.; I don't know. In any case, the teen inventors think it will be more efficient, and Ricoh thinks they're right.
