I'd bet that the scientist who admit that they never even expected this event with the tuna even know what they are talking about now and I'd bet that the scientist stopped eating tuna along time ago.
As I understand it the tuna is 3% more radioactive than it was before.
It's just that the small
increase in radioactivity is due to a large
increase in the relatively uncommon radioactive cesium. There's a big "cesium signal" in the fish that came from Fukushima, which is really cool for tracking the spread of the radioactive release, but there are other radioactive elements in the tuna that stick around longer (potassium I think) that make it so that the large increase in radioactive cesium is only a small increase in the total radioactivity of the fish, which is already quite small.
It's cool that we can detect this kind of stuff, and it's helpful to understand fish migration patterns and so on, but there's just no health risk from this fish. Probably good for the tuna if everyone is scared of dying of cancer from them though... we're overfishing 'em. Could be Fukushima and overblown news reports will let them bounce back a bit
As far as a further Fukushima disaster depopulating the Northern Hemisphere? Nonsense. If you follow the links in that article you will find http://akiomatsumura.com/2012/04/682.html
where there's a quote from Robert Alvarez saying:
"About 134 million curies is Cesium-137 — roughly 85 times the amount of Cs-137 released at the Chernobyl accident"
The author at akiomatsumura.com then writes:
"Many of our readers might find it difficult to appreciate the actual meaning of the figure, yet we can grasp what 85 times more Cesium-137 than the Chernobyl would mean. It would destroy the world environment and our civilization."
I doubt that's supportable. The radioactivity released at Chernobyl barely destroyed the environment and civilization in TOWN, and had fairly small and unclear effects on surrounding countries (to the point where there's some question if thyroid cancers went up in neighboring countries simply because people started bothering getting CHECKED for thyroid cancer) and no dangerous effect to speak of around the world. The average dose of radiation that humans on this planet got from Chernobyl was equivalent to less than a day of exposure to the average natural background radiation.
85 times worse than that would be a lot worse but it wouldn't wipe us out. Not even close. Probably still isn't worse for someone in the U.S. than having radon in your basement. I wouldn't be surprised if we found some statistically significant increased cancer rates in the dense nearby plume if the plume hit land instead of going out to the Pacific first. Maybe even further afield. But we need to remember that to wipe out civilization from radiation
would require significant modification of life expectancy. So many of us die of cancer anyway ...
Now, I'm not trying to say there's no danger. That would be silly. I'm also not trying to say that everyone involved would be forthright and honest. It's already clear that people were trying to cover up the problems in nuclear plants in Japan and they won't stop now. And it would be a real disaster for Japan if there was a further massive release. We need to watch out for it. But I suspect the real
danger to the rest of the world is the massive fear and near-term economic impact of a "super-Chernobyl" coupled with the fact that Fukushima has already nearly completely destroyed the chance of new, safer nuclear fission plants as a clean plentiful domestic alternative to fossil fuels, and a further disaster would be the last nail in the coffin.
I am quite certain that the main consequences to the life, health and prosperity of most of our planet of further radioactive release from Fukushima have really nothing to do with radiation. Japan is a different story.
And extinction from a further radioactive release at Fukushima is even sillier. To make the Northern Hemisphere really uninhabitable (as opposed to just wreaking destruction on our modern way of life) there would have to be so much radiation that it killed people before breeding age and made it impossible to grow food and so forth. Look at what is actually going on very close to Chernobyl these days! Some people still live inside the highly irradiated zone. It's not a desirable place to live but if you just uniformly dumped that concentration of radiation on the whole Northern hemisphere such that no one had a choice but to live with the new radioactivity of their surroundings, we'd get used to it.
I read an article recently that was suggesting that the biggest real consequence of Chernobyl was that it eliminated a huge expanse of incredibly fertile land from food production for Europe, and that this has deeply serious economic consequences. If we weren't so spooked by radiation, this wouldn't be an issue, because the scare is significantly worse than the stuff.