1 BILLION TOBACCO DEATHS IN 20TH CENTURY. “1.3 billion smokers worldwide in 2003, and that number is expected to increase to 1.7 billion by 2020.” Of 7.1 billion population in 2020, this is one in five humans smoking. (Peto R, Lopez AD. Future worldwide health effects of current smoking patterns.”
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2040350/