Why hasn't all of humanity died out. Seems like everything bad is only powerful to a relative degree where there will always be some people that survive.
Why is it that the plague only wiped out millions of people and why hasn't an epidemic like aids killed us all.
AIDs? Of all possible diseases, you pick AIDs? (which, by the way, is not an epidemic). Either way, in the case where you were arguing something more immediately dangerous, such as Bubonic Plague or Anthrax this is because of genetic diversity among human beings given to us via natural selection through evolution. Basically, because if it could, we would have been dead long before we would've been humans. Even after that, we have the most developed medicinal system of all species, and can thus devise cures to said diseases.
Why do nuclear weapons only emit radiation to a close proximity instead of the whole earth.
Why shouldn't it? Why does gravity exist, why don't I just float off the world? It's inherent to it's nature by the laws of the universe. Unless of course your asking the direct scientific reasons why, to which I suggest you research on your own. It's mostly logical, as the explosion can only send ionizing particles so far, and they are subject to the inertia of the world around them.
Why haven't we got into a super war where everyone is destroyed?
Why would we? I have no desire to be destroyed, nor do most people in power to cause such a war. Said war did almost happen, I suggest you research the Cold War, but in the end the fear of Nuclear Holocaust proved to overrun the superpower's struggle for dominance. This is known as Nuclear Deterrence. Basically, because we have an evolutionary inherent wish for our species and ourselves to survive, and causing such a war would be counter-productive.
Why do hurricaines and earthquakes only kill people in a small area.
Again, you're questioning fundamental forces of nature. In the earthquakes example, the friction between tectonic plates that releases the energy to create and earthquake only happens where the tectonic plates are actually grinding against each other, and the energy is only so much as to cause the effect we know as an earthquake in a specific area.
Why haven't these new man made chemicals and what not given us all cancer?
Again with the forces of nature. We're not stupid enough to give ourselves cancer (at least not immediately stupid enough), and why should they have? Man made chemicals are not inherently different to any other chemicals.
So basically I just feel like humanity will always survive, even if people talk about global warming as a current example, but it's like I know well have a solution.
I agree that global warming will not kill humanity, but I do believe that humanity will inevitably end. Whether it be in the big crunch, or the idea that all atoms will inevitably decay to hydrogen, or if the universe reaches equilibrium of heat as thermodynamics state it inevitably will if it's a closed system, humanity will end one day.
So do you think this humanity saving might be caused by a supernatural force, or does the scientific reasoning behind all this that proves nothing amazing really happened satisfy you?
Scientific reasoning is not even needed, basic logic would suffice.