Courts are considering banning the formerly "green" fuel diesel to reduce air pollution. But experts warn that diesel vehicle bans may not be effective - not even for environmental protection.
Stuttgart is an "Autostadt" - a city dominated by Germany's powerful auto industry. So it came as something of a surprise last week when a court issued an order that will likely force the city - home to Porsche and Daimler - to ban diesel-fueled cars within months.
The city now has to decide whether to ban just the most polluting vehicles, or all diesel cars.
The ruling is the result of a lawsuit by the nongovernmental organization Environmental Action Germany (Deutsche Umwelthilfe, or DUH), and is part of a broader strategy by environmental groups to use the courts to force action on air pollution.
Another court has also recently ordered Munich to ready a diesel ban.
The push comes amid ongoing findings that German automakers have been manipulating vehicle design and emissions tests in order to make diesel cars seem less polluting than they are.
Developments in this "Dieselgate" saga are spiraling out to the extent that the German government has called for an emergency summit of automakers in Berlin this Wednesday (August 2).
The problem in perspective
Based on recent revelations, there are 35 million diesel vehicles now on the road in Europe - sold from 2011 to 2016 - that could be exceeding nitrogen oxide (NOx) limits by at least three times, according to the Brussels-based nongovernmental organization Transport & Environment.
According to the European Environmental Agency, nitrogen dioxide emissions caused 75,000 premature deaths in Europe in 2012. A recent study estimated "excess" NOx emissions - that is, emissions beyond what is legally allowed - to account for 11,400 deaths in Europe.
Benjamin Stephan, a mobility campaigner with Greenpeace, says that judges are now stepping in because lawmakers have failed to respond to the unfolding Dieselgate scandal.
"Judges, when they look into it, ask: What would be the best measure to deal with air pollution?" he told DW.
"Diesel bans are the fastest, strongest measure if the cars are exceeding their limits."
But the German government - and the European Commission - disagree.
German Transport Minister Alexander Dobrindt said after the Stuttgart ruling last week that "blanket driving bans are the wrong political path."
European Industry Commissioner Elżbieta Bieńkowska wrote to national transport ministers in July expressing concern about the impending bans, saying "policymakers and the industry cannot have an interest in a rapid collapse of the diesel market in Europe as a result of local driving bans."
Such a collapse, Bieńkowska told European capitals, would deprive automakers of funds to invest in clean vehicles. A coordinated European response is needed, she said.
Many experts agree, and are questioning the effectiveness of diesel ban proposals from both a policy and environmental perspective.
Piecemeal ban: environmentally effective, logistical nightmare
Graham Parkhurst, director of the Center for Transport and Society in the United Kingdom, says that in order for the bans to have a meaningful impact, they would need to only apply to vehicles that have been sold very recently - a logistical nightmare.
"If you were to say only Euro 6 [the latest vehicle standard] were allowed, there would be a big effect on lowering pollution," he told DW.
But that means only the last one or two years of models. "I think there would be a great difficulty with consumers who bought modern diesel cars expecting them to be usable in an urban context."
He suspects cities will only ban cars earlier than the Euro 4 standard, which are around 10 years old. This, however, would not have much impact in reducing air pollution - mainly because not many of these cars are left on the road.
Results of bans and fees for polluting vehicles have so far been mixed, says Martin Williams, an air quality scientist at Kings College London.
He told DW that banning is most effective when implemented in the long-term - like the 2040 targets announced in London and Paris. "Manufacturers and the public need to have some time to adjust to this kind of thing."
Both Parkhurst and Williams say that the bans would need to be implemented nationally in order to go smoothly - but this, too, could be a challenge.
In the UK government's plan for reducing air pollution nationally, local authorities are given a choice of four different levels of vehicle they could institute fees for. "It would be very difficult and confusing if cities had completely different schemes," says Williams.
The evolution of diesel
So why is all of this happening now? Air pollution in cities, which is caused by a number of factors other than vehicles (see graphic below), has been decreasing in most EU countries.
Although the national average may be down, presence of the poisonous gas has increased in some city centers - due to more diesel vehicles.
Over the past 20 years, carmakers and governments in Europe have promoted diesel as a low-carbon fuel, because it burns 20 percent more efficiently than petrol.
Governments in countries like Germany and the UK offered tax incentives for people buying diesel cars. Today, half of the 2 million new cars bought in the UK each year are diesel, compared to 18 percent in 2001.
But although the cars may have been better in terms of carbon dioxide emissions, they are worse for air pollution - particularly with regard to NOx.
"In diesel cars, the engine burns at a higher temperature and is more efficient - but because of these higher temperatures, more NOx is being created," Stephan explained. Yet car companies claimed that through treatment of exhaust, this was under control.
Any climate advantage of diesel cars has since been discredited, he points out - because diesel cars have grown due to the space effective exhaust treatment systems need. "Diesel cars became bigger - and an average diesel car on the road now emits more CO2 than a petrol car."
Another pollutant being emitted from diesel tailpipes are tiny particles of soot - or "black carbon" - which not only negatively affect human health, but also constitute a greenhouse gas.
Automakers say the latest generation of diesel cars - Euro 6 - is the cleanest yet.
"The latest generation of diesel vehicles will deliver very low pollutant emissions on the road under the new real driving emissions test ... and emit significantly less CO2 emissions per kilometer than equivalent petrol-powered vehicles," a spokesman for ACEA, the European automobile manufacturers association, told DW.
Governments want the auto industry to address the pollution issue without harming consumers - this is the main commitment sought from automakers at the Berlin summit.
"The car industry now has a damned responsibility to rebuild trust and fix mistakes it made," Dobrindt told Germany's "Bild am Sonntag," the Sunday edition of the daily "Bild" tabloid.
He added that he will demand an "acceptable offer from the car industry" on how to reduce emissions at the expense of the producers, rather than the consumers.
The German government is hoping that this will prevent diesel bans in cities before any are finalized.
Environmentalists continue to push for the summit to bring a national ban. "Our demands are clear: We are saying that cars not meeting the current standards shouldn't be allowed to go into cities - and we need a refinement of the rules so cities can easily do this," said Stephan.
However, he added that despite demonstration of political action at the summit, he's not expecting any concrete results.