Green Cats?

It occurs to me that my cats aren't very earth-friendly. The little bastards eat a ton of kibble, and poop an enormous amount. While they can move very quickly (to what end?) and rest often, they still seem to be incredibly wasteful. That is, for the amount of fuel they take in, they produce much waste. I know some of it is coming off of them in heat, but they're insulated! It's been entirely too long since college, so I can't recall the equations exactly, nor do I wish to really even contemplate the horrifying prospect of separating poo from litter in order to weigh it (luckily for myself and Science, kibble comes in handy pre-weighed bags). There will be no empirical evidence. Suffice it to say, my cats are doing their part to destroy the earth, their adorable little cat feet are leaving enormous carbon footprints, and I apologize heartily for this waste of resources. Sorry, earth.