Thereby penalising existing vehicle owners who can’t switch to a more efficient vehicle overnight.

We have to come up with a rigorous alternative that doesn’t disproportionately affect lower income folk, because people tend not to be overly concerned about nebulous concepts like the climate impacts on unborn future generations, especially when my carbon impact at the margin is negligible when taken in context of global population.

If it is an issue - then option is to have less driving. Take a bus once in a while. Or bike.

Or switch to another old vehicle. Take old Golf instead of RAM, etc.