John Horgan in Scientific American:
The 70th anniversary of the bombings of Hiroshima and Nagasaki has reminded me of an extraordinary incident that occurred during the Manhattan Project, when Edward Teller and other physicists feared the fission bomb they were building might incinerate the planet. I heard about the incident in 1991 while preparing for an interview with Hans Bethe, who headed the Manhattan Project’s theoretical division. Teller reportedly did calculations suggesting that a fission explosion might generate heat so intense that it would trigger runaway fusion in the atmosphere. (Ironically, Teller later helped create thermonuclear bombs, in which fission catalyzes a vastly more powerful fusion explosion.) Teller brought his concerns to other physicists, including Bethe, an authority on fusion (and pretty much everything else in nuclear physics). After considering Teller’s concerns, Bethe and others concluded… Well, I’ll let Bethe tell the story in his own words. Here is an exact transcript of my interview with him, which took place at his home in Ithaca, New York.
Horgan: I wonder if you could tell me a little bit about the story of Teller's suggestion that the atomic bomb might ignite the atmosphere around the Earth.
Bethe: It is such absolute nonsense [laughter], and the public has been interested in it… And possibly it would be good to kill it once more. So one day at Berkeley — we were a very small group, maybe eight physicists or so — one day Teller came to the office and said, “Well, what would happen to the air if an atomic bomb were exploded in the air?” The original idea about the hydrogen bomb was that one would explode an atomic bomb and then simply the heat from the atomic bomb would ignite a large vessel of deuterium… and make it react. So Teller said, “Well, how about the air? There's nitrogen in the air, and you can have a nuclear reaction in which two nitrogen nuclei collide and become oxygen plus carbon, and in this process you set free a lot of energy. Couldn't that happen?” And that caused great excitement.