[Hupriene]

Not true. Many of the problems described by gp wouldn't affect the fuel efficiency of the truck, but still vastly increase the pollutants the truck puts out. Replacing your catalytic converter with a steel pipe is the obvious way to game a carbon tax.

[SilasX]

That would be an argument for taxing the pollutants too.

(Yes, it's not a perfect policy, but please don't criticize it with an argument equivalent to saying that a unit of pollution is infinitely bad. It's not.)

[thinkcontext]

Good point. There's a role for both.