Imagine, if you will, that the Japanese military is more disheartened in the closing days of World War II. Deciding that they’d rather be live cowards than dead heroes, they accept the terms of Potsdam Conference and surrender; thus the Enola Gay is never launched on its dread mission. The atom bomb is still invented and tested as it was in reality, but it’s never demonstrated to the world in the theatre of war.
How would the Cold War have proceeded differently?
It’s possible that there would not be that much difference in the long run; the other nuclear tests would go ahead and the Soviets would eventually twig, whether by espionage or U.S. demonstrations to the world, just what destructive power the device has.
On the other hand, the fact that it wasn’t used on a city, with the shocking aftermath and obvious message it sends (f with us, we turn your cities into burning rubble and melt your citizens) may lead to both the governments and civilians of the U.S. and Soviet Union underestimating the consequences of nukes and pushing the bar further than they otherwise would have.
So either nothing changes or everything changes, not much help there, sorry.
Given that the effects of radiation on victims were such a surprise to the authorities, and given that after that, enough atmospheric testing was conducted to contaminate the bones of most children in America, I’d predict that without the horrific example of the city bombings, a lot more open-air testing would have been conducted, a lot more sloppily, seriously contaminating much of the earth.
Widespread contamination from the atmospheric testing is well known, even if scientists differ on their assessment of the resulting health effects. My original contention was that testing unrestrained by fears of Hiroshima and Nagasaki would have resulted in worse contamination before we had a chance to become aware of the potential damage.
I was going to mention this. Perhaps there would have been more support for the use of atomic bombs in the Korean War if they had not been used previously.