I think the largest real "global level" danger over the next year or two is the upcoming highly active solar cycle. Periods of high sunspot and solar flare activity are normal and cyclical, but the one the Sun is moving into now looks to be especially strong, basically a season of especially bad "solar weather".
This would not have been much of an issue in the past, but our modern electronic communications and power networks are vulnerable to the blasts of charged particles that shower the Earth when large solar flares point in our direction. Living beings and the natural environment are protected from most of the effects of this radiation by the Earth's magnetic field, but electronic components in satellites are more sensitive to the effects.
Modern, highly-networked "smart" power grids are also more vulnerable than older grids; because these grids are larger and more interconnected to allow for easy transmission and routing of power over large distances, they are more affected by inductance and a huge magnetic field spike from a large solar storm could cause a huge voltage spike in the grid that could destroy transformers. Since the transformers would all need to be replaced, it could mean power grids being down for months over very large areas, even as power plants are functioning perfectly. This is a case where newer is not better, as older, less efficient/versatile power grid are also less vulnerable to the effects of inductance (i.e. smaller grids won't generate as high a level of DC voltage spike).
There was a solar "superstorm" in 1859 that temporarily disrupted telegraph service worldwide.
2012 or 2013 could very well see a period of large-scale power outages in the most technologically developed areas around the world lasting months on end. This may not be the "end of the world", but it would be a huge catastrophe with great loss of life and terrible economic effects.
Would humanity survive? Of course. Would YOU survive? If you live in a rural area with access to clean water, food, shelter (with heat if needed), and a means to defend your property, then yes, you'll be fine. If you live in downtown New York, London, or Shanghai, you would be faced with much greater challenges.
Last edited by JSB; 11-15-2011 at 05:18 PM.