You have to feel for the Europeans out there who own small diesel-engined cars. For years, car companies and governments have extolled the breed, discounting the fuel and promoting it as the way to achieve economical vehicles with acceptable carbon emissions. Then it turns out that diesel emissions—which include a lot more than just CO 2 —are actually really bad for us. Plus, cheating appeared to be rampant within the industry.

After pushing diesel cars for so long, a volte-face is now underway, including measures to ban diesel engines from Paris, Athens, and Madrid (as well as Mexico City, which we do realize is not in Europe).

The plan, announced in Mexico City during the C40 Mayors Summit which took place this week, follows restrictions recently enacted by the Parisian mayor to clean up that city's air quality. Over in Japan, Tokyo actually banned diesel engines at the turn of the century, although advances in engine technology and emissions controls have seen that relaxed in recent years.

"Our ambition is clear and we have started to roll it out: we want to ban diesel from our city, following the model of Tokyo, which has already done the same," said Anne Hidalgo, Paris' mayor. The plan is to eliminate use of the fuel—and the mess it makes—by 2025.

Here in the US, that's the date by which automakers have to get their fleet averages up to 54.5mpg; a target that diesel is unlikely to help them meet given the terrible publicity that's followed the ongoing scandal of Volkswagen Group's emissions shenanigans.