Certain actions have relatively direct impacts, so that it's easy to see the link between the cause and the effect. For example, GM's fault ignition switch scandal is said to have caused the deaths of at least 124 people because we can look at specific accidents and see what happened, and decide if the faulty switch that could inadvertently turn off the engine, disabling the power steering and air bags, was responsible.
But the VW environmental fraud scandal is a bit different. Rather than directly impact a few hundred people in a clear cut way, it is having an impact on tens and tens of millions of people (if not hundreds of millions), but in a much more diffuse way. This makes causality a lot harder to tease out, so the best that we can do is look at statistics over a large number of people. This can't prove anything over any single case, but it should nonetheless give us a pretty good idea of the harm that was done.
The New York Times has calculated an estimate of the number of U.S. deaths caused by the extra air pollution. They took two different approaches, one looking at the impact of power plant emission cuts that were done in some counties but not in others, which allows one an estimate of the benefits of the cuts on premature deaths caused by air pollution:
The estimated Volkswagen pollution, about 46,000 tons since late 2008, is the equivalent of about 4 percent of the power plant pollution reduction they measured, meaning it could be expected to cause an estimated 106 deaths if it had similar effects.
They also used 'mortality effects' numbers used by the Environmental Protection Agency to calculate the impact of the particulate pollution produced by nitrogen oxides. Using those they found:
Her method brought the effects to about 40 additional deaths over the period, in addition to some other nonfatal health consequences. That probably undercounts the impact, though, since it does not consider the effects of direct nitrogen oxide pollution or smog.
Of course, these are only rough estimates, and these numbers will probably be refined over time as researchers look deeper into it. But it does show that air pollution is not just an abstract crime against 'the planet', but has a real impact on many people, especially the most vulnerable of us (the sick, the elderly, the very young). And while death is obviously the worst thing that can happen, there's no doubt plenty of other health and quality of life issues that we should hold VW responsible for.
But here's the kicker: The estimates above are just for the United States. The 500,000 VW diesels that will be recalled there only represent a tiny, tiny fraction of the vehicles on the road. In Europe, where most of the 11 million cheating VWs were sold, diesel represent around 50% of vehicles on the road and air quality is in much worse shape. The impact could be multiples of what it is in the U.S., meaning potentially thousands of extra premature deaths due to this air pollution.
While I'm not an air pollution specialist, I think it's likely that the impacts are not linear. By that I mean that vulnerable populations (e.g., an old man with emphysema) probably face thresholds above which they simply can't go. For example, let's say that a 20% increase in pollutant levels leads to some problems, but ultimately it's not too serious, but a 40% increase might lead to serious health issues and probably death. In such a scenario, 40% is not twice as bad as 20%, it's much, much worse...