Which person had the greater impact in the 20th Century? Hitler, Gandhi, Einstein, etc. According to Nature , it is the duo Haber-Brosch because of their invention. Their Haber-Bosch process has often been called the most important invention of the 20th century as it “detonated the population explosion,” driving the world’s population from 1.6 billion in 1900 to 6 billion in 2000.
The German chemists Fritz Haber (Nobel in 1918) and Carl Bosch (Nobel in 1931) revolutionized world food production. The process uses high temperatures and high pressures to combine hydrogen and nitrogen from the air in order to produce ammonia, which is a main ingredient in fertilizer.
Nearly one century after its invention, the process is still applied all over the world to produce 500 million tons of artificial fertilizer per year. 1% of the world’s energy supply is used for it ; it still sustains roughly 40% of the population . Billions of people would not even exist without it.
On the flip-side, much of the nitrogen used in the process ends up back in the environment as a major source of pollution. Another bad effect is the Zyklon B poisson which was used in WW II’s Holocaust, was originally developed as a pesticide by Fritz Haber (jew) who was forced to emigrate in 1933.
So it’s remarkable to note that Haber’s almost paradoxical biography affected more lives and deaths than anybody else’s!
-  V. Smil, Nature, July 1999, p 415
-  Science 297, Sep 2002
-  M. D. Fryzuk, Nature 427, Feb 2004, p 498
-  Haber-Bosch process -wikipedia