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The difference in life expectancy between smokers and non-smokers appears to be at least 10 years on average, in a survey of American adults between 1997 and 2004. The same paper lists causes of death (higher among smokers than non-smokers, as measured by hazard ratio), although this is not exhaustive: lung cancer, other cancers, ischemic heart disease, ...

This page is pretty complete with examples and references. In summary a lot of the evidence is empirical - you look at smokers and the quality of their skin and compare to non-smokers and the differences are statistically significant and reproducible. It seems as if this is old work, dating from the 1970s. So in many cases these are only observed ...