Your Thoughts Exactly

Ever heard of the Doomsday Clock? It’s this big clock made by the Bulletin of Atomic Scientists, made to symbolize how close the world is to nuclear destruction. Right now it's set to 11:53 (seven minutes to midnight). I like it. It’s a bit melodramatic, over-the-top, and almost totally useless, but hey, can’t you just visualize the end of the world so much better with it?
I think these Atomic Scientists are a little too full of themselves to think that Doomsday will be the product of their little creation, so I’ve decided to compile a ranked list of the top reasons to lock yourself in a bomb shelter for eternity. Fun, huh? I’ve taken into account how likely the scenario is, how destructive it could be, and of course, my personal je ne sais pas. I give you the Doomsday List:

6.) Asteroids!
Basically, this would need to be a really large one; bigger than the one that killed the dinosaurs. And it would need to happen soon, because with every passing century, we put better and better telescopes out there and develop better and better weapons, so our chances of dealing with this threat go up as time goes on. In fact, if we found out an asteroid were going to hit the planet in a few weeks, couldn’t we just nuke it a bunch of times, to at least minimize the damage?
Likelihood Factor: Minuscule
Destruction Factor: High

5.) Aliens!
My personal favorite. We have no real good basis on which to judge the hostility of a potential alien race. Would they be like humans of the past, wiping out new cultures when they saw them, because of their valuable land? Or would they be more like humans of the present, sort of pretending to value new cultures while assimilating them and trying to turn them into their own? Or would they be much more advanced than us? History shows us that in warfare, technology makes a huge difference. Even a difference of a few dozen years can spell doom for the inferior-equipped side. In that light, if an alien race came to invade us, there’d be no stopping them. Not with computer viruses, not with good old American know-how, not with water (water, for the love of god), and certainly not with our weapons. I will give H.G. Wells credit in the sense that if there were one chance, it would be our germs. But it’d be unlikely even then, because I would assume an alien race capable of space travel would canvas a planet before invading. So the destruction would be total.
What if we’re lucky and they’re friendly aliens? Well, then perhaps all they would do is take over our planet and force us to do their bidding. If they’re REALLY friendly, then maybe they’d leave us alone, and not even make themselves known. Maybe the really friendly aliens are out there now! Still, even if they simply take over the planet, there’d be no reason for them to let us keep it. So I think that spells the end of human civilization. And the beginning of theirs.
Likelihood Factor: A notch above minuscule
Destruction Factor: High

4.) The machines!
Nanotechnology is the study of machines that can work with matter and energy on the molecular level. While we are nowhere near the level of sophistication require to destroy the planet, I have confidence that we can do it! One of the prime goals of nanotechnology would be to change molecules at the atomic level- being able to turn lead into gold, so to speak, to create any kind of matter from any other kind of matter. And, assuming this is possible, then it would be possible to create self-replicating machines. You can see the problems with this, I’m sure. The famous “grey-goo scenario” has these machines consuming the entire earth while turning it into more machines. Unlikely, but given that it is possible to create this by accident, I’ll give our accident-prone species a boost. Also, this scenario would take an enormous amount of energy, but the machines have time, right?
Secondly, artificial intelligence: if we ever do get to the point where we can create sentient life, it is only a matter of time before they/it is competing with humans, whether it be directly, for resources, or indirectly, for things like jobs and rights. In this scenario, it seems inevitable that the machines would win. While a scenario a la Terminator or the Matrix is unlikely, the machines have advantages that can’t be denied. While humans are left to the slow process of evolution, machines can be upgraded, tweaked, and enhanced. The human body is indeed an incredible machine, but if we’re at the point of creating artificial sentience, then I’d guess we can create some other impressive technology too. There is also the idea that humanity might choose to let the robots take over, in the case of Unabomber Luddism, or the case that we might merge our consciousness with a machine to achieve immortality. Either way, I consider that the fall of humanity.
Likelihood factor: High, but delayed
Destruction factor: Low to Extreme

3.) Nukes!
Ah, that which inspired this list. It does seem inevitable that a nuke is going to go off in the future. But are we really 7 minutes from the proverbial midnight? In terms of a nuke going off, perhaps. In terms of the destruction of humanity? Probably not. The specter of a nuclear holocaust is diminishing, with the cold war over and the other nuclear powers no longer really willing to risk a war that would destroy their nation. Sure, there’s North Korea, almost assuredly getting a hold of nuclear missiles. And there’s the China part of the equation. But we didn’t nuke the USSR, so I think we’re safe from nuclear missile attack in the near future. However, the chances of a nuke going off are increasing, because Russia can’t account for all its own, and the US is not guaranteed to keep a hold of its own hundreds of years down the line, if the US crumbles. That increases the chance that John Q. Public will get his hands on one of his own, and pissed off that some city won the World Series again, blows it up in a fit of rage. And there’s the terrorists, for whom the nuke is the ultimate bargaining chip. Get one, and they’ll be taken seriously. I think, for the nuclear doomsday to happen, there’s going to have to be at least a few hundred, if not thousand, individuals to have their own. Of course, the political climate could change in the coming ages, and with thousands of nukes out there, the optimist in me thinks it’s always possible!
Likelihood factor: Medium-Low
Destruction factor: Medium-Low

2.) The germs!
AIDS! SARS! Ebola! Anthrax! Influenza! Diseases are big news these days, they generate fear and everyone loves a good scare. That’s why you’re reading this, isn’t it? AIDS showed us that some diseases are beyond our technology, and that long lasting diseases can trigger epidemics, regardless of their virulence or preventability. SARS showed us that diseases can become global in a matter of days. Ebola’s kills the victim too quickly to spread, Anthrax isn’t contagious, and the flu has been kind to us so far. With viruses and bacteria mutating more and more, livestock being pumped full of antibiotics to create super-resistant germs, it’s almost inevitable that something awful is being brewed in the blood of our friendly critters. The antibiotic problem is becoming so bad that pharmaceutical experts believe that in 50 years, we’ll be back to where we were before penicillin, when infections were the norm, and when all we had to combat bacteria were sulfa drugs. Still, viruses pose a greater threat than bacteria do, if only because they tend to be more contagious. There have been strides made in the fight against HIV and the flu, leading to antiviral agents being constructed, but HIV is remarkably resistant and remarkably clever. The flu has largely been a nuisance rather than a serious threat to humanity, but this could easily change with a couple key mutations. Couple this with the theory that there might be incredibly small disease causing proteins called prions, and we’re fighting a losing battle against the germs. The germs get bonus points for the inevitability factor, but don’t count out the humans yet either. We have genes as well, and given that some people have genetic resistance to HIV and that there are 6 billion of us running around, and the chances are high that we can survive them too.
Likelihood factor: Medium-High
Destruction factor: High

1.) George W. Bush.
Ok, ok. That was my political throwaway joke for the day. Moving on...

1.) Environmental destruction!
The environment is a sort of misunderstood subject. Much of humanity treats the earth as its slave, as if it were given to us by god and that we are free to do whatever we want with it. Then you have the environmentalists, who think that humanity is destroying the earth and that we are its keepers. We must save the earth, they cry! Interestingly, both of these groups are guilty of the same thing: hubris. The first group thinks humanity can do no wrong to the earth, the second thinks only humanity can save earth.
Well, environmentalists, the earth is going to be around long after humanity dies off, and so will bacteria, insects, and algae. It’s survived asteroid impacts, I think it can survive us. What they should be saying is, “save ourselves!” We need the earth for our own selfish purposes, and in that regard, maybe the industrialists have it right. We just need to take better care of it.
Ok, that’s my rant. Environmental destruction is number one on my list because humanity just doesn’t understand what it’s doing at all. Destruction of the rainforest, global warming, ozone depletion, etc. True, we MAY not be doing any harm, but that’s the whole point. We have no idea, and there are too many people on the planet to change it anytime in the near future. Even if the US passes the strictest environmental laws ever, we’re still only a part of the equation. And in fact, the damage may already be done, and most of it is irreversible. You can’t freeze back part of Antarctica, or replant millions of acres of rainforest, or bring back extinct species. The point is that as a species, we are a lumbering giant, and it’s going to take time for us to change. We also have a tendency to not do things until they smack us in the face. So if we wait until there is a problem with the environment, it will almost definitely be too late. Actual destruction gets a few minus points because even with the worst-case scenarios, it’s almost impossible to destroy civilization as we know it. Though in this case, overpopulation exacerbates the problem, not improves it, like I said for germs. In fact, I’d say overpopulation itself is a subset of this problem. What better way for humanity to kill itself off than through other humans?
Likelihood factor: High
Destruction factor: Medium

If you've got any others, I'd love to hear them. In fact, I feel like I forgot something. So comment away!