Lets just get real. The old, the young, the obese, the sick, the mentally challenged, and the idiots will all die off rather quickly. Very few, percentage wise of the populace will survive a true scenario. Most will be dead in three months or less... Quoting: Anonymous Coward 1003364
It is certainly true in that certain scenarios would could see a dramatic and scary decline in Humanity. That said, historically it hasn't happened, other than the last Ice Age. As such, it's not a persuasive way to convince people to prep. It is plausible, but not probable. I'd expect American to fare less well than poorer countries, strictly because a lack of prepping and skill sets needed. Also survival is based upon mental outlook, and given the preponderance of folks on medication for this, I'd expect a lot of people to not cope well, give up, or lose it. That couple seriously impact the survivability of anyone choosing to try to make it.
Some people count on a die off, and think they'll gather up supplies. In reality, I think that those supplies will be used up, then a die off. Depending upon season and supply houses and livestock, we could have fields of grain and vegetables, but no people to harvest them. The same could happen with livestock, but an inability to feed them. The same with food warehouses, but an inability to transport it minus gasoline.
Barring a major catastrophe, most of the time what happens is a slow decline, deaths from various causes, and then a readjustment period with deaths during that period. Either way, it's not a bright future, and having six months of food as a reservoir and skills and defensive capabilities will all help.