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My friend is a smoker. His dad is a doctor. Both claim there is no firm proof that cigarettes cause lung cancer. This article makes a similar claim -- in particular that smoking cigarettes is not proven to cause cancer, but that it is linked to an increased risk of dying from lung cancer:

Yes, a US white male (USWM) cigarette smoker has an 8% lifetime chance of dying from lung cancer but the USWM nonsmoker also has a 1% chance of dying from lung cancer.

Is there any firm science behind the argument that smoking does or does not cause lung cancer?

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    Here it is again! Someone insisting that the word "causes" only means 100% every time, ignoring how everyone else uses the word. Worse: this is being used to justify smoking? – Oddthinking Feb 6 '12 at 0:16
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    Ugh. I couldn't read a single sentence of that article without some kind of "skeptic alarm" going off in my head. That thing could be the coursework for an entire class on critical thinking. – John Rhoades Feb 6 '12 at 14:37
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    let alone about whether the smoking itself causes something or the chemicals deposited in the lungs as a side effect of that smoking :) Falling out of a 100m crane doesn't cause you to break your neck after all, it's the falling on the ground afterwards that does that :) – jwenting Feb 10 '12 at 7:35
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    The article seems to argue for a distinction between smoking makes lung cancer about 10 times more likely and smoking causes lung cancer. That's not really a big distinction. – matt_black Feb 10 '12 at 13:53
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    @Abdul: Most people use the term "A causes B" to mean that the intervention of A greatly increases the chance of B. HIV causes AIDS. Smoking causes lung cancer. I have noticed some people seem to define it differently (at least when having arguments) to be something like "implies" - the intervention of A means B must necessarily proceed from it. Under this definition, a single counter-example is sufficient to disprove the claim: Smoking does not cause cancer if there is at least one smoker who doesn't get it. Being shot in the head doesn't cause death. It is a perverse definition. – Oddthinking Jul 18 '16 at 17:17
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I don't have much to say here, because Cancer Research UK have already written a winning answer. (Sometimes the giants are tall enough that there's no need to stand on their shoulders.)

If you visit Tobacco, smoking and cancer: the evidence you will find explanations of all these facts:

  • Smoking is the single biggest cause of cancer in the world
  • Smoking greatly increases the risk of lung cancer
  • The people with the highest lung cancer risks are those who:
    • smoke the most cigarettes per day
    • smoke over long periods of time, and
    • start smoking young
  • Smoking is a major cause of several types of cancer
  • Stopping smoking can reduce your risk
  • Tobacco smoke contains many dangerous chemicals
  • Tobacco smoke contains significant amounts of dangerous chemicals
  • Chemicals in tobacco smoke can build up to harmful amounts
  • The chemicals in smoke are more dangerous in combination than individually
  • The poisons in cigarettes can affect almost every organ in the body
  • Nicotine is a very addictive drug
  • Smokers are still exposed to dangerous chemicals if they smoke filtered or ‘low-tar’ cigarettes
  • Alcohol and other substances worsen the effect of smoking
  • Second-hand smoking also causes cancer and kills thousands of people every year
  • Children are especially at risk from second-hand smoking.
  • Smoking while pregnant can harm your baby
  • Smokeless tobacco can also cause cancer

They explain it all clearer than I could hope to, and include references to 93 different journal articles. You've got to admit they've certainly done their research on cancer, those guys at err.. Cancer Research UK.

Oh look, a donate button. Maybe you can persuade your mistaken friend and his father to donate to make up for all the people they have misled with their ignorance and semantic word games?

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We know that smoking causes cancer due to research carried out a long time ago. In the original, and famous, paper Smoking and Carcinoma of the Lung by Doll and Hill, the authors attempt to answer the question of why there has been such a large increase in lung cancer. They consider different possibilities, but the data shows that smokers are more likely to get lung cancer than non-smokers (the paper contains figures by age and sex) and that heavy smokers are more likely to get lung cancer than light smokers. Other cancers are considered, to ensure that it is specifically lung cancer that is being caused. Overall, this paper is quite good evidence by itself (especially as it comes from a time when smoking was not seen as dangerous, so patients had no incentive to conceal the extent of their smoking), but of course there have been many more published since then.

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