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“We will look back on diesel cars in the same way we view cigarettes and asbestos insulation”

I am sure that that within a few decades we will look back on diesel cars in the same way we view cigarettes and asbestos insulation. Future generations will ask how something so toxic to public health and to the environment could have been allowed to be pumped into our air, our streets, our homes, our schools.

Air pollution in cities causes more than 3m premature deaths globally each year. The evidence of a causal link between diesel emissions and asthma is becoming overwhelming: I am one of the many people who has developed asthma in adulthood because of air pollution. And research released just last week by the mayor of London, Sadiq Khan, found that more than 800 schools, nurseries and colleges are in areas where levels of nitrogen dioxide breach EU legal limits.

Mayors of many of the world’s great cities are taking bold action to tackle the scourge of air pollution. Paris, Mexico City and Madrid announced at the 2016 C40 Mayors Summit their commitment to ban diesel vehicles by 2025. Oslo will pedestrianise the centre of the city by 2019. San Francisco has just announced requirements that every parking space in new buildings must be equipped with electric vehicle charging capability. And Chinese cities such as Shenzhen and Nanjing converting entire fleets of buses and taxis to electric.

Yet it is important to acknowledge past mistakes. Many European governments incentivised consumers to purchase diesel cars over recent years, because their lower CO2 emissions contribute less to global warming.

Now the evidence is clear that diesel cars release more nitrogen oxide and nitrogen dioxide (NOx), emissions which contribute significantly to air pollution in cities and are more damaging to human health than emissions from petrol vehicles. Tests designed to identify cleaner vehicles have been shown to be largely useless, and the actual on-road emissions of most cars exceed health-based limits. Some have used this as evidence that politicians and campaigners concerned about climate change are naïve.

In fact, all this proves is the need for more radical and urgent action. If we are serious about tackling climate change, we can’t substitute bad with less bad: we need our cars to be zero emissions. The urgency of the climate crisis means that window of opportunity for incremental changes has passed.


To deliver on the ambition of the Paris Agreement, and limit global temperature rise to within 1.5 degrees Celsius, now requires fundamental shifts in how our cities operate. The debate around the relative climate and public health benefits of petrol versus diesel is a perfect example. The reality is that all combustion engine vehicles release greenhouse gasses, which contribute to a greater or lesser degree to global warming and air pollution.

Whilst we waste time arguing over the relative benefits of each, we get closer to the point of no return for catastrophic climate change. C40’s research Deadline 2020, which examines exactly what the great cities of the world must do to deliver on the ambition of the Paris Agreement, shows that we must  move as quickly as possible to zero emission vehicles, such as electric and hydrogen-fuelled cars, on the streets of our cities.

Politicians, scientists and campaigners must acknowledge when policies we believed to be effective, prove not to have worked. Pursuing well meaning, but ineffective policies will reduce public trust in climate action, whilst also wasting resources and effort that could be channelled into policies that do work.

Tokyo has a tiny number of diesel cars on its roads, because national and city governments have spent decades working together to disincentivise them. It is not surprising that Japanese car manufacturers are leading the way in developing the next generation of hybrid and electric cars. In just the same way, using policies such as road tax rates, scrappage schemes for high polluting vehicles and low emission zones based on the NOx emission of cars, mayors in every city around the world could accelerate the shift to zero emission vehicles.  

A key feature of the C40 network is that cities can share their experiences of what has worked to reduce their emissions, but also crucially what hasn’t worked. This allows mayors to implement policies faster, learn from the mistakes of others and reduce the cost of action compared to if they were acting alone.

Mayors of our cities deserve praise for their efforts to tackle climate change and air pollution. They are providing unique global leadership, through C40, the Global Covenant of Mayors and within their own cities.

Yet now is the moment to seize the initiative. Public concern about air pollution has never been more acute. Now is the moment for mayors be even more radical.

Mark Watts is executive director C40 Cities.

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