Why did 1954's Castle Bravo fallout cloud, rather than 1918's Spanish Flu or 1883's Krakatoa, finally convince humans of our interconnected biosphere?
Perhaps natural things don't really matter to us hubris-driven humans.
Because even huge natural catastrophes like Spanish Flu (and earlier global pandemics) and the volcano Krakatoa's volcanic winter didn't seem to count as much in the human mind as did a relatively small disaster that humans themselves were causing.
The unexpectedly large yield from the American thermonuclear test Castle Bravo in 1954 led to a strong plume of radioactive dust to fall on a Japanese fishing boat thousands of miles away, quickly killing one crewman.
It also added a relatively small amount of a much longer term radiation killer, strontium 90, to go high up into the atmosphere and then slowly fall all over the world, onto grass and then into cow's milk and eventually into the growing bones of babies.
There its high energy level of radiation output, plus its long life, would slightly increase a young child's chances of getting fatal childhood leukemia and bone cancer.
But recall, this fallout hit every child in the world - and now spread over hundreds of millions of kids per decade that relatively small increase in the individual death rate was poised to kill many thousands of them.
And the number of deaths per million of children was only going to go up with each new thermonuclear test adding more and more strontium 90 into the biosphere.
Traditionally the South Seas of the Pacific ocean was where people fled to get away from the rest of us ---- now nuclear tests there were bringing death to children in every other part of the world.
We could no longer run , we could no longer hide.
Just as we couldn't with Krakatoa or the Spanish Flu.
So I really don't have a good idea why we felt so different in 1954.
And don't give me the old chestnut about the new TV media of the 1950s --- for we had an equally good global media in 1883 and 1918 and it was called the wire services' telegraph.
Still, for whatever reason it did so, the Manhattan atomic Project probably did as much as the Manhattan penicillin Project to usher in our present environmental, small is beautiful, movement.