What were the effects of the heavy atmospheric nuclear testing done in the 40s, 50s and 60s on life on earth? The Tsar Bomba alone had to create some seriously irreversible fallout damage for most of the planet, right?
In: 1
Two things are useful to know about fallout, for making sense of its environmental impact.
The first is that the amount of fallout is pretty much related to the amount of fissioning that takes place in the weapon. So the 50 Mt Tsar Bomba, for example, was only 3% fission (1.5 Mt) — the rest of its energy came from fusion. So it was much less inherently contaminating than, say, the first two US H-bomb tests (10 Mt and 15 Mt respectively) that had much higher fission fractions (80% and 68%, or 8 Mt and 10 Mt, respectively).
The second is that the height of burst changes where the fallout goes. If the fallout is low-enough to the ground (or on the ground), so that its fireball mixes up dirt and debris inside of it, then the fallout comes down pretty quickly, within a few hours. This is called “local fallout” and is responsible for those [really nasty fallout plumes](https://commons.wikimedia.org/wiki/File:Bravo_fallout2.png) that deposit a lot of fallout in a large — but still limited — area.
For bursts that are higher up, you only end up with what is called “global fallout.” The fallout stays in the cloud a lot longer and radioactivity comes out only after a much longer time has passed, and over a large area. So this distributes material further, but it is less intense (because it has time for the really nasty stuff to decay), and it is diluted (less material per square mile or kilometer). You get global fallout from surface bursts as well. For a big-enough bomb, [you can track its movement over the entire planet](https://pbs.twimg.com/media/DuKeeRbWoAEF7dQ?format=jpg&name=4096×4096). But this is much less intense: it is a measurable but small up-tick in global radioactivity, essentially.
So the Tsar Bomba was mostly fusion and detonated in a way where it did not produce local fallout. It did produce global fallout, which circulated in the upper atmosphere for several years before it all came down. But the fact that it stayed up so long meant that the contribution of that detonation to the radioactivity to life on Earth was negligible.
But there certainly were other big tests that were surface bursts, and some of them did create significantly radioactive areas that are still places where people shouldn’t live today. But that is all from local fallout, so it is much more limited to the test sites. So, for example, the Trinity test site in New Mexico, where the first atomic bomb was tested, is still somewhat radioactive today. You can visit it safely, and even work there safely, but if you had large-enough groups of people living there full-time, especially people who are in stages of life that are more sensitive to mutation damage (children, pregnant women), then you would expect to see some measurable up-tick in the cancer rate. It is similar to what the Chernobyl area is like; it’s not actually a radioactive wasteland, but it is a chronic public health risk to have large groups of people living there. (With small groups, you probably would not be able to tell if there were an y additional or “excess” cancers that were higher than the baseline expectations.)
Atmospheric nuclear testing certainly left _measurable_ effects — you can see isotopic signatures (like the so-called [bomb pulse](https://en.wikipedia.org/wiki/Bomb_pulse) of C-14) in things like wood and bone and other organic structures from this period, and it is a tell-tale sign that nuclear testing happened in the past. But measurable does not mean harmful. For people who were not directly downwind of the tests when they happened, the increase to their cancer risks is small enough that we can’t measure it (that doesn’t mean it doesn’t exist, just that it is a small “signal” compared to the cancers caused by other reasons, like smoking and pollution and diet).
As for the broader environment, the effects are even more elusive.
Latest Answers