A shopper at a supermarket asks for a plastic bag, only to have his head slammed into the checkout counter by the “green police” (“You picked the wrong day to mess with the ecosystem, plastic boy”). Another man attracts a spotlight from a green police helicopter for a “compost infraction” as he’s about to bin an orange rind. The green police bust down doors after finding batteries in the trash. They haul people from their homes for installing incandescent lightbulbs.

But to the driver who approaches a road checkpoint in his Audi, the green police react very differently. “Clean diesel? You’re good to go, sir.” And they wave him through.

It’s hard to believe, as diesel vehicles find themselves thrust into the spotlight of a global urban environment crisis, that Audi’s Superbowl advert was made just seven years ago. Air pollution now kills 3.3 million people prematurely every year – more than HIV, malaria and influenza combined – with emissions from diesel engines among the worst culprits; a joint investigation by the Guardian and Greenpeace showed hundreds of thousands of schoolchildren across England and Wales are being exposed to illegal air toxicity levels from diesel vehicles. And yet such was the more or less widely accepted thinking as recently as Superbowl XLIV in 2010 – namely, that cars running on diesel fuel could be driven with a pure, unclouded conscience.

Diesel was touted at inception as a wonder fuel. It was a way of driving cost-efficiently while doing your bit to save the planet. Government, industry and science united to sell us the dream: cars running on diesel would help us cut our CO2 emissions as we eased smoothly into a new eco-friendly age.

Audi’s Green Police Superbowl advert from 2010

It was particularly owing to advances in engine technology that the diesel passenger car market was able to blossom in the 1990s, particularly in Europe. Drivers liked the fuel efficiency of diesel engines, which made running costs cheaper than petrol over the long term. Governments, meanwhile, alarmed by rising carbon emissions, began advising citizens to switch to diesels, which were thought to emit less CO2 than their petrol counterparts. Diesel’s biggest moment in the UK was probably in 2001, when Gordon Brown, then chancellor of the Labour government, cut fuel duty on diesel vehicles as a deliberate effort to encourage people to switch.

It turns out we were wrong Former chief scientific adviser David King on backing diesel

The cracks took a long time to appear, but when they did they splintered rapidly. In 2012 came the first major evidence of some truly dreadful health impacts. Nitrogen oxides and dioxides (NOx) and particulate matter (PM) pumped out by diesel exhausts were fingered as silent killers. The studies multiplied. The European Environment Agency found that nitrogen dioxide (NO2) from diesel fumes had caused around 71,000 premature deaths across the continent in a single year. It said the UK experienced 11,940 annual premature deaths from NO2, the second highest in Europe behind Italy. The World Health Organisation declared diesel exhaust a carcinogenic, a cause of lung cancer in the same category as asbestos and mustard gas.

Then in 2015 came Dieselgate. In September of that year, Volkswagen, which vies with Toyota for top spot in the list of world’s biggest car companies and a firm that had for years been running its own marketing campaign in favour of “clean diesel”, rocked the industry by admitting that it had cheated on its emission tests. As recently as last week, David King, the UK government’s former chief scientific adviser on climate change, admitted ministers had made a huge mistake by promoting diesel. They had trusted the car industry when it said the fuel was clean. “It turns out we were wrong,” he said.

Cities worldwide have scrambled. The mayors of Paris, Madrid, Athens and Mexico City have agreed to completely outlaw diesel vehicles from the centre of their cities by 2025. The political leaders that make up the C40 group of global megacities are all taking steps to crack down on diesel vehicles and reduce smog. But other cities, including British ones, are tinkering around the edges; London is proposing low-emission zones and toll charges, but has stopped short of a ban.

So is this simply a period of bad PR, or has the backlash against diesel reached a tipping point? Has the one-time wonder fuel become the new asbestos – not to say mustard gas? And if this is really the beginning of the end for diesel, how much longer before the pariah is banished from the city for good?

London Bridge on a smoggy morning. Diesel cars produce 10 times the NOx of heavy trucks and buses. Photograph: Alamy

Banning diesel is trickier than it seems. The scale of the problem remains enormous. Diesel never made huge inroads into the US, where gasoline remained cheap, and where American automakers focused their innovation efforts on hybrid and electric vehicles. But in Europe, diesel passenger cars remain a major part of the auto industry: astonishingly, they still account for nearly 50% of all new cars sold across the continent.



Meanwhile, a study of the latest diesel cars by the International Council for Clean Transportation (ICCT) says real-world emissions of nitrogen oxides (NOx) are, on average, seven times higher than safety limits allow. A separate ICCT study showed that latest diesel cars produce 10 times the NOx of heavy trucks or buses, which are more strictly regulated than cars.

The car manufacturers, too, have a hugely powerful lobby still at their disposal. According to Greg Archer, who once managed the UK government’s air pollution research, automakers used their influence to ensure a “regulatory holiday” after the financial crash. They claimed that the Euro 5 and Euro 6 emissions standards, aimed at limiting pollutants from exhausts, led to significant reduction in pollutants. But a recent study of real-world performance shows those claims were bogus: Emissions Analytics found that 97% of the diesel cars made since 2011 exceed NOx safety limits.

Governments were complicit, too. In one particularly egregious case, Germany agreed in 2013 to halt a proposed EU cap on bankers’ bonuses – dreaded by the City of London – in return for British support to protect the German car industry and thwart a stricter emissions regime.

Nor is it easy to persuade drivers to switch. Many motorists are understandably angry that they were encouraged to invest in diesel engines but are now expected to face clean air zones, pollution charges and other restrictions. Many feel that they are, in effect, being punished for what they were told was the smart, responsible choice. Mazyar Keshvari, an MP from Norway’s right-wing Progress Party, calls Europe’s anti-diesel pivot “the biggest swindle”, since many drivers there were teased into buying diesels with tax incentives.

The UK government is keenly aware of the hypocrisy. The government must publish updated clean air plans by 24 April, but the prime minister, Theresa May, has indicated she does not want to punish existing diesel drivers. She says she is “very conscious of the fact that past governments have encouraged people to buy diesel cars, and we need to take that into account”.

Honda’s Hate Something, Change Something clean diesel advert

While national governments wring their hands, it is cities that are taking the lead. In Germany, Berlin has already banned the oldest, highest-polluting diesel cars from its centre, while Munich is developing a clean air ban that will bring in some form of diesel ban in 2018. The Spanish capital, Madrid, has now introduced a system to halve the number of cars on the roads during smog outbreaks, based on odd or even number plates on alternate days; various other cities have experimented with similar trials.



In January, Oslo city council introduced a ban on diesel cars for the first time, halting their use completely for one day (during a high pollution alert). The city also plans to raise the road toll for diesel cars entering the city centre from 33 Krone (£3) to 58 Krone (£5.50) in rush hour.

The cities that have moved boldest have been the ones least likely to get too concerned about the fact that motorists, having been told one thing, are now being told another. Some have worried this could lead to a damaging kind of cynicism – a more skeptical attitude toward the latest environmental research. But councillor Lan Marie Nguyen Berg of Oslo’s Green party doesn’t think that will happen.

“It’s a long time ago now,” she says of the old pro-diesel incentives. “Since 2012 we’ve been talking about how bad (diesel) is for people’s health, and people are adjusting to the science. In the past year we’ve seen quite a big change in attitudes. People are well aware of the health implications now. They don’t think children and elderly people should have to stay in their homes to avoid pollution.”

Paris has been typically one of the more aggressive cities. Under mayor Anne Hidalgo, it introduced a system of coloured stickers to classify cars types and emission levels. Any diesel-run car made before 2000 will not be allowed on the roads inside the French capital. Diesel cars built between 2000 and 2010 could soon be subject to tighter restrictions, as the mayor tries to phase out diesel entirely by 2025.

The mayor of Paris, Anne Hidalgo, has unveiled a new car-free zone along the Seine river. Photograph: Michel Euler/AP

Some French drivers are unhappy. A national campaign group, 40 Million Motorists, says the new system is unfair to poorer diesel drivers who cannot afford to buy a new cleaner car.



Romain Lacombe, founder of Plume Labs, a Paris-based organisation that monitors air quality around the world, is not persuaded by their argument. He backs the new system because “it means the oldest cars will be the first off the road, which makes a lot of sense”.

“The stock of [diesel] vehicles will take time to be phased out, but I only see momentum building to move away from diesel,” says Lacombe. “There is a rising understanding of how damaging to health diesel emissions are. People are beginning to realise they are the first victim of their own vehicle. It’s a personal health issue, a life or death issue.”

When it is essential, you just have to do it Miguel Ángel Mancera

Sadiq Khan, the mayor of London, has stopped short of an outright ban on diesel, but he has ordered the replacement of the capital’s current diesel bus fleet with clean alternatives. The mayor’s office will also enforce a £10 toxicity charge, or T-charge, on the highest-polluting cars entering the city centre as of October. The measures are part of a wider plan to create an ultra-low-emission zone (ULEZ) in central London from April 2019.

Khan has expressly urged drivers to “ditch dirty diesel”, and has backed it up by urging the UK government to come up with a “national diesel scrappage fund” to fairly compensate diesel drivers, suggesting a sum of up to £3,500 offered for each car or van taken off the road.

The black cabs are, in some ways, a litmus test of whether diesel is on its way out. Many of the cabs use diesel, and drivers had initially complained about clean-air restrictions. But the Licensed Taxi Drivers’ Association (LTDA) now backs Khan’s idea of a scrappage fund. And last month the government and City Hall both announced a plug-in taxi grant scheme giving cabbies £7,500 to buy new electric models built in Coventry. Steve McNamara, general secretary of the LTDA, predicts diesel cabs will be “a thing of the past” within six years.

Mexico City is pushing to reduce air pollution. Photograph: Bloomberg via Getty Images

‘The most unpopular measure’

Although nearly three-quarters of all the world’s diesel cars are driven on European roads, bold moves are being made elsewhere, too. Hong Kong has introduced subsidies to help phase out older diesel vehicles. Later this year Seoul will ban all diesels made before 2006 from a city-centre low emission zone.

But it is in Mexico City, where mountains surrounding the metropolis help trap a semi-permanent blanket of smog over the city, that mayor Miguel Ángel Mancera has decided to ban diesel completely by 2025.

“I know it is a good thing for the city,” Mancera said on a recent visit to London to meet Khan’s team. “It’s something that is absolutely essential to protect the environment. We’re changing: our taxis have to be electric or hybrid, and our buses are being changed from diesel to new technologies.”

The mayor has also pledged to invest more in the public transport system and cycling lanes, and persuaded delivery companies to use their diesel trucks at night to reduce daytime emissions.



Will this work in a city where drivers are famously unruly? Mancera points to the 1992 scheme called Hoy No Circula (No Driving Today), which forbade the worst-polluting vehicles from being on the roads one day a week; the rules have since been tightened to include a Saturday daytime ban for the worst polluters. “It’s totally unpopular,” Mancera says. “It’s the most unpopular measure you can make – to stop people moving. Some people support it, but another part of the population get really irritated by it.”

But nevertheless, he says drivers will get used to the diesel ban the way they did to Hoy No Circula. “When it is essential, you just have to do it.”

Worldwide, polls suggest citizens of some big cities are beginning to put clean air before convenience. A YouGov poll last year showed 52% of Londoners would support a ban on diesel cars in London’s city centre; a similar poll in France on a ban on diesel in the centre by 2020 was backed by 54% of Parisians.

Analysis of diesel exhaust fumes. Volkswagen’s admission that it faked tests rocked the industry. Photograph: Patrick Pleul/EPA

This is probably how the death of diesel will come about – not through regulation, but through consumer disgust. Many auto experts expect the global sales dip that followed Dieselgate to continue, as consumers turn up their nose and manufacturers correspondingly invest less in new models. “The regulations will deter people, at least people in big cities, from buying diesel cars at their next purchase if they think they are going to be restricted,” says professor David Bailey of Aston University.



Are car buyers entitled to have any confidence at all in buying diesel, or do we need to get rid of it altogether? Unfortunately it is difficult to determine precisely how the latest breed of diesel cars compare with petrol ones, pollution-wise. Since the Volkswagen scandal, no one has a great deal of faith in emission testing done in the laboratory.

A tougher on-the-road testing regime, the “real driving emissions” (RDE) tests, is set to begin across the EU in September. “There is a going to be a tightening up on testing and it will make diesels cars more expensive to make,” says Bailey. “It will mean a lot of diesels cars disappearing, because it won’t be worth it for the manufacturers.

“I think a substantial reorientation will take place away from diesel, part of a larger shift away from the combustion engine toward electric cars in the 2020s.”

According to Steve Gooding, director of the RAC Foundation, a UK motoring research group, “the mere talk of action might already be altering buying behaviour”. He points to a recent dip in diesel car sales in the UK. But Gooding also argues that schemes to remove the highest-polluting diesel cars from the roads are impractical, mainly because working out exactly how “dirty” a car is remains difficult. “The issue is not just the age of a car, but where it’s driven, how far it’s driven and under what conditions,” he says. “Unfortunately, the data needed to target the most polluting vehicles accurately is not easily available.”

If smog-choked cities want the shift away from diesels to happen as quickly as possible, they will need the help of regulators – and also overcome the indifference of national governments. Oslo still has to convince the Norwegian transport ministry to approve its road toll hikes. Mancera will have to persuade the national government to replace the fleet of federally controlled diesel buses that chunter into Mexico City each day.

Yet the prize for hastening the decline of diesel could be huge – not least because, with so many big climate battles ahead of us, it would demonstrate that we and our political leaders can fix crises when science identifies them.

“I’m optimistic we can see the end of diesel vehicles,” says Berg. “The end of diesel would be a pretty big change in a relatively short period of time.”

Follow Guardian Cities on Twitter and Facebook to join the discussion, and explore our archive here