What does the fact that your car has four cylinders have to do with the environment? The most significant effect on fuel mileage is WEIGHT. Why are you not asking what is the lightest weight Mercedes ever made?
We are ALL concerned about the environment. Extremism that leads to driving cars with only four cylinders has an insignificant effect, even if everyone drove one.
The world is about BALANCE. What about folks who drive an SUV so they can haul several people rather than having three smaller cars on the road? Do the math on that.
In case you haven't noticed, this is America. I don't choose to drive an SUV, but if I did, and I were willing to spend the extra fuel money, it is my right to do so, just as it is your right to ride a bicycle if you wish. That's an idea, if you are so concerned about the environment, why don't you ride a bicycle?
Have a great day,