Related is the danger of smoke from ordinary wood fire, see: http://www.samharris.org/blog/item/the-fireplace-delusion
I don't think you can say that at all. Of course burning plant matter produces carcinogens, but studies of marijuana smokers haven't found any conclusive evidence of greatly increased cancer risk. There have been some studies that show that smoking tobacco and marijuana together increases cancer risk beyond that of tobacco alone.
Smokeless tobacco causes mouth and throat cancers, so something is going on with tobacco itself (or something else common to cigarettes and smokeless tobacco).
There is some evidence that radioactive carcinogens found in tobacco play a part in cancer risk.
There is epidemiological evidence that marijuana smoking is associated with lung cancer. "Greatly" is subjective so I can't really comment on that.
"findings from a limited number of well-designed epidemiological studies do not suggest an increased risk for the development of either lung or upper airway cancer from light or moderate use, although evidence is mixed concerning possible carcinogenic risks of heavy, long-term use,"
"In summary, the accumulated weight of evidence implies far lower risks for pulmonary complications of even regular heavy use of marijuana compared to the grave pulmonary consequences of tobacco."
By greatly, I meant as bad as tobacco which dramatically increases the risk of lung cancer.
The previous poster was commenting on the health risks of tobacco being caused entirely by burning plant matter. However, the evidence suggests this isn't true.
> "In summary, the accumulated weight of evidence implies far lower risks for pulmonary complications of even regular heavy use of marijuana compared to the grave pulmonary consequences of tobacco."
Yeah, I think mostly this comes down to the above discussion of "greatly" -- marijuana seems to have some correlation with lung disease and cancer, but it seems to be less than tobacco.