Germany's powerful auto industry has come under increasing scrutiny in recent years as the country tries to lower its carbon emissions. 

A series of alleged cheating scandals have rocked its reputation. And over the course of the past year, one of its prized technologies, the diesel engine, has been partially banned in some European cities. The first ban of its kind in the world.

The environmental movement that had long been pushing for the sector to transform is riding high and broadening its focus. This autumn, tens of thousands of protesters hit the streets in Stuttgart, one of the centers of the German auto industry, to call for all combustion engines to be next.

Nisha Toussaint, a Stuttgart-based member of climate action group Fridays for Future, said: "I think we can't just say no more diesel right away – e-transport's not perfect. But we have to move away very fast. We need to take action now. It's not just some cars – it's all cars."

There was a time when diesel engines were more widely seen as part of the solution to improving air quality. That was before the Volkswagen emissions scandal, in which the company was found to have sold cars with faulty emissions controls to trick regulators into believing the car fitted their emissions standards.

And now, with increasingly strong warnings from scientists of a climate emergency, even European consumers – where most of the diesel market's prime customers come from – are changing their habits.

But it's not dead yet. Diesel sales may have plummeted, but they still accounted for more than a third of new cars sold in Europe last year. And one study conducted earlier this year claimed that more than three-quarters of those vehicles fitted with cheating devices were still on the road.

This year, a pro-diesel camp has emerged in Stuttgart, led by a man named Ioannis Sakkaros. Among Sakkaros's gripes is that those on lower incomes – often owning older cars – are being unfairly penalized by what is the world's first partial ban on diesel vehicles.

Sakkaros agrees urgent action on the climate is needed, "but it will be a big problem for us to cut down the cars which exist now. If they [the German government] knew [about] this problem, they could have handled it earlier. Why did they start now?"

The answer, in part, is because the German auto industry was still heavily invested in the future of the combustion engine – specifically cleaner diesel technology. Experts say the sector has been slow to adapt to an international market rapidly moving towards electrification, even as the big names of the German auto industry now advance hugely expensive and ambitious plans to reinvent themselves for the age of electrification.

In fact, according to leading auto industry expert Ferdinand Dudenhöffer, diesel engines can be very clean. But it may be too late for that. "They are more expensive so they don't meet customer budgets," Dudenhöffer said. "Second, it's not possible to sell diesel engines outside Europe because the world is saying: 'We don't want that technology.'"

Diesel's decline in Germany is just a snapshot of a much larger question in the climate debate: How to manage all these changes as fairly as possible in the rush to save the planet?