We're just four days into the Volkswagen diesel-emission cheating scandal, but it's not too early to ask about its ultimate ramifications.
The 482,000 VW and Audi cars being investigated by the EPA are a majority of all the diesel passenger cars sold in the U.S. since 2008, when new and tougher emission limits took effect.
If VW Group's engineers had to cheat to get those cars to perform acceptably once they passed the tests, then what does that say about the future of diesel passenger vehicles?
It's important to note that not every so-called "clean diesel" car sold in the U.S. since 2009 violates the regulations.
On the same test in which a Volkswagen Jetta TDI and Passat TDI that showed their real-world emissions to be grossly higher than the rules, those of a BMW X5 xDrive 35d remained legal under all conditions.
But the four-cylinder VW and Audi diesels had the largest sales volumes by far, while other diesel cars were either low-volume or sold by pricey brands like BMW and Mercedes-Benz.
If affordable diesel cars have to cheat to pass, can diesel have any future at all?
2015 Volkswagen Golf TDI SE
Thus far, U.S. media have posed the fate of diesel vehicles as an open question. But much commentary in Europe seems more decisive than that in U.S. media outlets.
Many German, British, and other European news stories and opinions suggest that the scandal will put an end to the use of diesel engines in light-duty passenger cars and SUVs.
British newspaper The Telegraph, for example, published an article openly suggesting that the "Volkswagen scandal could kill off diesel cars." And many more echoed the theme.
While diesels represent only a few percent of the gasoline-dominated U.S. market, they power about half of all cars sold in the European Union (though percentages vary greatly by country).
But the EU lagged far behind the U.S. in instituting stronger emission standards for diesels. Only this year did new and tougher Euro 6 emission standards take effect that largely duplicate the U.S. "Tier 2, Bin 5" limits in effect since 2008.
Meanwhile, the union is now starting to fine major European cities--including Paris and Rome--for persistent air-quality violations, which has led those cities to look for the quickest and easiest ways to cut emissions.
Paris, by Flickr user Alexandre Dulaunoy (Used under CC License)
Paris has periodically banned half of all cars from its roads due to smog, while exempting zero-emission electric cars.
Rotterdam has suggested that it will stop allowing parking for diesel vehicles built before 2005, those that were subject only to the minimal Euro 4 standards and which often emit visible soot and can be smelled at a distance.
France, meanwhile, has set a long-term goal of phasing out diesel fuel for light-duty transportation use in the country.
But the distinction between different sets of diesel-emissions rules often isn't accurately reported, leading to headlines that suggest all diesels will be permanently banned.
A number of commentators, meanwhile, echo the suggestion that the VW scandal represents a tipping point for diesels.
Former Wired editor and noted prognosticator Chris Anderson tweeted yesterday, "Someday history will record the VW diesel scandal as the global tipping point for electric cars."
2016 Nissan Leaf
2016 Nissan Leaf
Auto-industry analyst LMC Automotive echoed the thought in more measured words, suggesting that if diesel is crippled in the U.S. market, increasing volumes of plug-in electric cars become an obvious cleaner technology of choice.
Still, the view that the VW emission scandal marks the death knell for diesels is far from universally held.
Allen Schaefer, executive director of the Diesel Technology Forum advocacy group, told The Detroit News that the organization is "pretty confident" the "trajectory for clean diesel in the U.S." will continue in "an upward direction."
Time will tell.