How many nuclear bombs would have to be detonated to render our planet uninhabitable?
Would it have to encompass several targets or is any one place better than others?
I don´t know the answer, but I know that different nuclear devices produce different amounts of radiation falloff; so as well as raw explosive yield you´d have to take into account what kind of bombs are we talking about.
However many it would take to shatter the Earth completely, I suspect. Considering that there are deep ocean ecosystems totally independant of the sun living off the energy from seabed vents , and also that there have been foudn bacteria living in the bedrock several hundreds of feet and more below the surface, I think it would be extraordinarily difficult to eradicate all like on Earth.
…and all life, too.
ok - using the best and biggest - how many?
Uninhabitable meaning as to us?
I’m not considering splitting the earth into fragments, just wiping out human-kind and of course other mammals would follow suit.
I’m not a scientist, but I’d think even sea creatures would suffer some type of castrophe from this event.
Well, if you just want to wipe out humankind, I suspect yuou’d need an energy release on the order of the Chixulub K-T impact that wiped out the dinosaurs and ~90% of all life. This impact was estimated to have a yield of about 10[sup]8[/sup] megatons. Considering the larges warheads so far devloped are purported to yield 100 megatons, we’re looking at about a million of them.
ok - we don’t have quite that many, but i expect we’re all jointly working on it. Would one physical location be more advantageous than another to do this dirty work?
The best location would be one where large quantities of smoke/dust would be released; perhaps the Amazon would do the trick. Set the whole darn think ablaze at once and get ready for a long cold winter.
In 1982, Carl Sagan and four other scientists estimated that the release of 5,000 megatons of nuclear weapons could result in a “nuclear winter” that might wipe out all life on earth not killed directly by the weapons.
A brief Web search suggests that this theory may no longer be widely accepted. See here and this scary site that wants us to believe that nuclear war wouldn’t be all that bad.
Yeah, I really hate those nutjobs who have persuaded the ignorant masses that a nuclear war would be a Bad Thing.
But to get back on point, I think it would take far less than Q.E.D.'s million 100Mt bombs to so seriously disrupt the world’s ecosystems as to kill all humans and most other mammalian life. Don’t forget, that unlike the dinosaurs, the vast majority of humans are dependent for survival on a complex chain of mass production and transportation of food. Likewise, most of us no longer have the knowledge needed to raise food crops ourselves, or survive in the wild.
[nitpick]Q.E.D.: Although the Soviet’s biggest bomb was reputed to be 100Mt, the largest they ever tested was “only” 64 Mt. But you probably knew that.[/nitpick]
Yes, I did. Hence the use of the word “purported” in my post. But then, you knew that.
I was aiming for a figure guaranteed to wipe out all humans, and the K-T impact would certainly have done that. Perhaps an order of magnitude less would do the job too, but why take chances? 
Well, are you sure an event like the K-T impact would finish off ALL humans? We are a very adaptable bunch, widely dispursed over the world, and lots of creatures did survive the asteroid that the dinosaurs.
That isn’t what the quote said.
I would surmise much less than previously speculated.
Perhaps enough nuclear weapons to release extensive radioactive fallout to cause not just immediate death, but cause enough terminal illnesses to overwhelm remaining medical personnel and supplies. Ad to it a massive distruption of energy and food supply lines, comunication networks and transportation links. The destruction of major food growing areas by fallout and radiation should ensure crop failures for years. Yadda, yadda.
In short, use enough weapons to break the interdependent energy, food, communication and transportation links. The inability of most peoples to recover from that will do the rest along with contamination, diseases, etc.
I’d give it good odds. most of the creatures that survived the K-T impact were small in size and didn’t need large amounts of resources. It’s estimated that the resulting dust cloud blocked out the sun for several years, more than long enough for all photosynthetic plant life to die off, save for seeds which can keep for decades or even centuries until germination conditions are right. When the plants die off, the larger herbivores die off, and soon the larger canivores follow. I think it’s doubtful any humans could survive such an event.
Well, that being the case a COBALT BOMB or two should do the trick.
I read that this theory is being questioned lately (not sure if the question is “did it really happen” or “did it wipe out the dinosaurs”, just that it’s under fire).
Hmm… We have the benefits of not needing to get all our energy from the sun directly (nuclear power, hydroelectric power, and so on). Ought we not to have the capacity, at least in principal, to keep enough plant life alive that we could in turn sustain some (vanishingly small, admittedly) fraction of the human race for a goodish bit of time?
This gives me an idea - ok hear me out…it involves using people as batteries in the event of a global catastrophe. Now we’d have to keep their brains alive so we’d plug them into something I call “the Matrix”. Now this “Matrix” links people in pods together to generate energy to power my army of robots. Of course due to inherent instabilities in the system we’ll need a spillover city called Zion. Every hundred or so years…oh wait nevermind that will never work.
Maybe you should make that into a movie Bob. Better yet, make it into a trilogy!
I think humans could survive a KT level event. We are far more adaptable and more intelligent than anything that has come before us. Like that site linked by commasense shows, there are people who spend a large amount of time thinking about how to survive major disasters. If it comes down to it, at least those people would still be around when the dust settled. 
Well, hydroelectric plants are indirectly solar powered (sun cause water to evaporate, rise, then fall into the rivers. No sun = no evaporation.) but using nuclear and geothermal plants I imagine some very well prepared site - like Cheyenne mountain, could grow plants till the dust settles.