Terribly off topic, but let's begin attacking this one step at a time.
1) Overpopulation: Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012? In fact, can you show me how this is as big as a problem as some people seem to make it out to be? Yes, some countries are 'getting crowded', but I'd like to blame individuals who can't keep their legs crossed on this one.
Final Result: This is not a Doomsday Scenario, unless you can prove otherwise.
2) Food Shortages: This ties into your Overpopulation tag, pretty much involving the same thing. Major News Flash: This only affects underdeveloped countries, and ultimately individuals who cannot get off their lazy * long enough to stop blowing all their questionably gained currency on drugs and alcohol, thus leading into a spiral of starvation. Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012?
Final Result: This is not a Doomsday Scenario, unless you can prove otherwise.
3) General Waste of the Earth's Resources: Funny, I'm pretty sure we USE those resources. There is no 'waste' involved when it comes to the Earth's resources. And ugh, this is 'Peak Oil' all over again, which is such a heavy stroke of debate that discussing it again is pretty much pointless, but I'll touch on it briefly. As it stands, we are in no IMMEDIATE (Note: This is NOT happening by 12/21/2012, let alone within that general time frame) of suddenly finding ourselves with out any natural resources.
As it has been stated before, these resources are not going to magically disappear one day. What WILL happen is that extraction will not be able to keep up with demand, and crap will get bad for a while. The renewable resources will be then in demand, and the use of natural resources will diminish to the point that only what is needed for the renewable resources to be produced at a fast pace is needed.
Regardless to all of that… Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012?
Final Result: This is not a Doomsday Scenario, unless you can prove otherwise.
4) War: We've been there, we've done that, this is probably the only one you've listed so far that I've gotten to that could actually kill off the majority of the population. The 'big problem' with this one is that every country that is not named North Korea is REALLY trying their best to avoid another World War. Surprising as this may sound, the world HAS learned it's lesson. Countries are figuring out it's much better to make your opposing faction look stupid in political debate, then trying to launch a warhead at them. Why? Because every other country will promptly dogpile you to obliteration, while the country you fired at shrugs it off.
Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012?
Final Result: This is a Doomsday Scenario (in the EXTREME circumstances), but has no connection to the given date, unless you can prove otherwise.
5) Terrorism: Read above, except this is childish in comparison. Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012?
Final Result: This is not a Doomsday Scenario, unless you can prove otherwise.
6) Climate Change: And now this is the one that's REALLY fun to talk about, because it's probably the only one that has any likelihood to actually be a big deal! The BIGGEST problem with me even wanting to touch this is because it's so off topic, I'm pretty sure you posted here with out caring to read the forum rules.
Sigh. Here we go.
Yes, this is a problem. Yes, there are efforts to fix and/or prevent it. Yes, people are taking it seriously. No, not enough people are taking it seriously. No, this won't kill us all anyway, ignoring the EXTREME CIRCUMSTANCES, but I do NOT acknowledge those. Yes, this should be a priority on the world's efforts on making sure it does not spiral out of control.
Ultimately, global warming/climate change is a two-pronged subject. While it is something we need to seriously keep aware of, it is also blown WAY out of the scope of realism by the right-winged individuals who want something done about it. It is much like 2012 in that regard that people take words and suddenly keep capslock on.
Can you show me evidence this will cause the death of nearly the entire population on 12/21/2012?
Final Result: This is potentially a Doomsday Scenario, but only in the most extreme of circumstances.
I look forward to your answers.