My idea is basically that cars should be combined with plants. I don't mean anything stupid like cars made of wood than run on leaves, but due to my lack of knowledge of the subject I'm sure it's probably just as absurd. But let me specify: plants produce oxygen when they take in carbon dioxide; in fact, plants being destroyed along with the rainforests is making the whole global warming thing worse. Now I don't know how quickly/powerfully plants are able to produce oxygen, but what if every car, for example, on its roof, had an area where plants grew (obviously the owner of the car would have to maintain them. So basically the exhaust pipe wouldn't just spew all of the emissions out into the atmosphere, it would go up to the roof, where plants would be kept in a greenhouse like attachment. Then they would be, at least partially, reduced.
I'm sure there are many problems with my idea, but I hope it's at least made for interesting reading.